Aerodynamics, Power, Speed, and Drag

[GregP]

http://www.aa.washington.edu/faculty/eberhardt/Image22.gif


The figure above shows the "power curves" for induced power, parasitic power, and total power (the sum of induced power and parasitic power). Again, the induced power goes as 1/speed and the parasitic power goes as the speed cubed. At low speed the power requirements of flight are dominated by the induced power. The slower one flies the less air is diverted and thus the angle of attack must be increased to increase the vertical velocity of that air. Pilots practice flying on the "backside of the power curve" so that they recognize that the angle of attack and the power required to stay in the air at very low speeds are considerable.

At cruise, the power requirement is dominated by parasitic power. Since this goes as the speed3 an increase in engine size gives one a faster rate of climb but does little to improve the cruise speed of the plane. Doubling the size of the engine will only increase the cruise speed by about 25%.

Since we now know how the power requirements vary with speed, we can understand drag, which is a force. Drag is simply power divided by speed. The figure below shows the induced, parasitic, and total drag as a function of speed. Here the induced drag varies as 1/speed2 and parasitic drag varies as the speed2. Taking a look at these figures one can deduce a few things about how airplanes are designed. Slower airplanes, such as gliders, are designed to minimize induced power, which dominates at lower speeds. Faster propeller-driven airplanes are more concerned with parasite power, and jets are dominated by parasitic drag.

http://www.aa.washington.edu/faculty/eberhardt/Image23.gif


Not much to start with, but it is a start! :)

OK, we can continue as we have time. Feel free to join in and discuss aerodynamics. From the above, you can see that at full power, the power varies pretty much as the cube of the speed since induced drag starts out very high and decreases until it is not much of a factor at high speeds, particularly at the speed of high-powered piston fighters.

So, twice the speed will require eight times the power (2 * 2 * 2).

From this, wse can infer a few things.

if we have a 1450 hp plane that goes 437 mph (a P-51D comes to mind), and we want to go 480 mph, the calculations are easy. Without changing the airframe, we must do as follows.


Starting speed: 437 mph. Starting HP: 1450.

Ending speed: 480 mph. This equals 1.098398 times the original speed, or a 9.8398% increase. Cube 1.098398 to get 1.325194, or a 32.5194% increase in power. Therefore, we need 1,921 hp to go 480 mph assuming we do not change the airframe, thereby increasing or decreasing drag. This also assumes the propeller has enough blade angle movement to increase the pitch enough to actually GO 480 mph. If not, the speed will be limited by the propeller pitch limits.

In reality, if everything is OK with the prop, there is still a small contribution due to induced drag, so I'd say we'd fall short at about 478 mph or so.

OK, it's a start!


P.S. All of the above may seem completely wrong since a modern-day P-51D Reno air racer at the top of the game goes around the pylons at about 480 mph with 4500 hp or so. Please remember that the Reno air races are NOT at the best altitude for the P-51D (which is about 25,000 feet if I recall correctly ... I didn't check). At Reno altutude, a stock Mustang will probably run in the 360 mph range or so (check the Bronze results for accuracy). Real-world aerodynamics varies with altitude, temperature, and a host of other factors including airflow leakage inside the fuselage. Also, the Reno racers are moving around a circular course (not eXactly circular ... more or less egg-shaped).

In a straight line, if the Mustang had 1690 hp to start with (as some references suggest) and could go about 360 mph in stock condition at Reno in a straight line, the we'd expect about 498 mph with 4500 HP at Reno.

Coincidentally or not, that's about exactly how fast Dago Red goes when making 4500 hp or so in a straight line at Reno. Actually, it goes a might faster, but the airframe has been "cleaned up" with shorter wings, less drag, a new propeller, profiled wings, and a sealed airframe, so I'd EXPECT a slight improvement.

:)

[montanamotor]

Aaaah,

love it, GregP!

Err - could I persuade you into doing the very same computations about the Ambrosini 403 Dardo, too...???

PLEASE!!!!

With 750 hp, the 403 Dardo did a proven 378 mph / 640 km/h at 23000 ft / 7200 m. Outstanding supercharger-efficiency, as it seems. At levels with RR!

What, if I'd now double the power output of it's engine from 750 to 1500 HP - provided, the rated altitude remains the same?

Will it do 500 mph / 805 km/h - or not?

The wheight of the plane would remain about the same, too, as I have calculated already. The wheight penalty which the big continental-V12 would add to the Ambrosini's airframe, may quite accurately be deducted again by dispensing with the 403's armament and, armour.

Cheers!

Michael :D

[Mark J]

That sounds about right Greg. Take the Spitfire. It started the war with just over 1000hp and a top speed around 350mph. By wars end the power had doubled (Mk14) yet the top speed had only increased by 100mph.

cheers

[Wuzak]

The new power is twice original power.

Therefore top speed is the cube root of 2 x original top speed.

Cube root of 2 is 1.25992

New top speed is 476mph...

100% more power for 25% more speed.

[Dogwalker]

378mph=609kmh
About the maximum speed of the SAI 403 there are different figures.
To be sure, I'll assume the maximum speed reported by D'Amico of 630kmh/391mph, so, for 1500 hp the max speed will be of 794kmh/493mph.

[montanamotor]

Oops!

Again! Me and the Mile won't ever become close friends...

493 mph / 794 km/h don't really sound bad to me, at all. It seems like, if one was going to go REALLY fast, wood would be the optimum choice for the contruction material, rather than Aluminum? Ever noticed that, ANY "Wooden Wonder" was always on top of it's class, when it came to speed?

Well - in fact: Maybe a layer of wax applied to the S.A.I. 403's complete surface (like the Yak 9 got wax applied to her full surface prior to delivery) might assist the Dardo to finally slip through the 500 mph-barrier...?

Anyway: This is REALLY good news, friends.

One last question to our Italian friends: What is the difference between a "Dardo" and a "Frecchia" ? Both words mean "arrow", as far as I am informed. But why use two different words for one and the same item?

Shaken, but not stirred,

Montanamotor

Cheers! :D

[GregP]

Hi Montanamotor,

Sure, I can do these computations.

Let's see:

1) 750 HP and 378 mph at best height.

2) If I had 1500 HP, that would be twice the power.

3) The cube root of 2 is 1.259921.

4) 1.259921 times 378 mph would give about 476 mph, or close to 766 kph.

5) in the real world, I'd expect 755 - 760 kph.

6) If you wanted to go 500 mph (804 kph), you'd need 1,736 HP and a propeller that had enough pitch change to go that fast. Not inconsequentially, the airframe would also have to be capable of 500 mph. Most fighters of the WWII era did not have sufficient flutter margin to increase the speed by that much without changing the control surface balance to maintain flutter margins. In the case of the Ambrosini 403, I'm not sure if it was cleared for an 800 kph dive or not. If so, the power needed would be about 1,736 HP as stated above, and that WAS available from Rolls Royce, Daimler-Benz, and other makers, but not at a size and weight that would easily shoehorn into the 403 airframe.

After I posted this, I realized that Wuzak had already done the honors, and in MUCH less space! A good, concise post, Wuzak! I suppose I'm too wordy ...

[montanamotor]

Hi,

GregP, Wuzak and Dogwalker! Thanks for the crushing of figures. This really helps me a lot, i.e. motivates me even further.

The S.A.I. 403 Dardo, according to different sources, during test-flights had proven to sustain a Vne in a dive of 468 mph / 750 km/h indicated, and 593 mph / 950 km/h true airspeed.

That speed is - besides some readings of a FW 190 that was test-flown by it's creator Kurt Tank - the highest speedo-reading I know a fighter of WW II could go, and probably the highest speed a prop-fighter of WW II could survive, anyway (as far as I know).

So, an according-to-the-rules built airframe of an S.A.I. 403 in plain stock condition (!) should be able to live with a true airspeed Vmax of 475 mph / 760km/h to 490 mph / 790 km/h with ease. In doing so, there would still be a margin of 110 mph / 175 km/h to 125 mph / 200 km/h to the true Vne left for safety.

About flutter: I always now when I reach terminal speed on ANY vehicle, as soon as the bottoms of my trousers start to flutter...

Cheers!

Montanamotor [:o)]

[GregP]

Hi Montanamotor,

In addition to have a USA pilot's license, I fly radio control aircraft when I get around to it.

I have experienced flutter in those several times. It is usually fatal to the airframe except in the odd case where you can load the plane with "g" forces and reduce speed before the fluttering control surface departs the airframe.

About the highest speed piston fighters, the P51H could hit about 490mph and saw some service in WWII late in the war. There were several versions of the P-47 that were also about 480 mph or so. The Australian CAC-15 and Martin-Baker MB-5 also come to mind as fast, capable fighters that were not proceeded with due to the coming of the jet age.

Had they been built, they would have been 500 mph or better aircraft.

[Wuzak]

The Supermarine Spiteful was capable of 494mph, the prototype Hornet 491mph. There was a prototype P-47 reportedly capable of 505-507mph.

Greg, I have never really known what "flutter" is.

Is it to do with the airflow separating from the wing earlier than normal, leaving the control surfaces in turbulent air? Moving of the control surfaces would then be inconsistent, whilst the turbulence causes the controls to "kick back" through the stick.

Now, back to drag and power.

We have already established that drag is proportional to the square of velocity, and that the power required to drive the plane at v-max is proportional to both the drag and the velocity - ie power is proportional to the cube of the velocity, which can be written as:

P = k*V³

Or P = (k*V²)*V, where k*V² is the drag force.

The value k is a constant, though in the real world it is most likely not. This value is often also written as CdA (yo will see that occasionally in car reports).

The reason for this is that the drag force Fd is proportional to...

The square of the velocity V
The frontal area of the object A
and the coefficient of drag Cd

ie Fd = Cd*A*V²

The value Cd can be calculated. There are some formulas for simple shapes. And it can be estimated using an iterative calculation method. Today there are computer programs that do this (Computational Fluid Dynamics), but in WW2 it had to be done by hand. Without calculators.

Digressing slightly, the famous D-Type Jaguar won the Le Mans 24 hour race 3 times in a row, from 1955-57. The body shape was designed by Malcom Sayer, a mathemetician/aerodynamicist. He calculated the shape to minimise drag...


Anyway, often the best way to determine the value of Cd is by using a wind tunnel.

Back to the example of the SAI 403....

The original had a 750hp Isotta-Fraschini R.C.21/60 V-Engine. If we upgrade that to a Rolls Royce Merlin 61, with rated power of 1,390 hp (1,035 kW) at 23,500 ft* (7,170 m) [1,565 hp (1,170 kW) at 12,250 ft (3,740 m) - http://www.answers.com/topic/rolls-royce-merlin] the drag coefficient and frontal area will be increased due to the larger size of the motor and the increased cooling requirements.

But we can compensate for that in our calculations of top speed....


* This rated power is at an altitude very close to the maximum for the SAI 403, as posted earlier.

For the original:

P = k*V³ => 750hp = k * (391mph)³ [Using dogwalker's maximum speed]

=> k = 0.000012547

k has units, but we will ignore them for now. If we use consistent units the results will be in the same units as we started with.

Now, if we estimate that the increased radiator size and increased engine size has resulted in a 10% increase in the CdA, we estimate the new k as:

k = 1.1 * 0.000012547 = 0.000013801

To get the velocity we rearrange the terms so that:

V*³ = P/k

=> V = (P/k)^(1/3) [^(1/3) = cube root]

Thus V = 465.2mph (749.1km/h).

If we do assume that the Merlin has 1500hp @ 23,000ft, with 10% drag increase, the top speed becomes 477.2mph (768.3km/h).

Without the drag increase we have 480.3mph (773.3km/h) for the case of 1390hp and 492.6mph (793.1km/h) for the case of 1500hp.


If we can maintain a drag increase of now more than 10%, the power we need to get 500mph is:

P = 0.000013801 * 500³

=> P = 1725hp (1287kW)

If the drag increases by 20% over the original we will require 1882hp (1404kW).

[montanamotor]

Friends,

THIS is what I call an in-depth-answer. Great stuff. Sometimes I think that, if I had learned to realise the beauty of mathematics earlier in life, maybe I had become an engineer, too.

But now, being an editor, all I can do is, write about the facts that other people find... SOB!

Anyway: It's good to know you.

Back to piston engines: Over the last few years, there has been lot of interest in developing new piston-diesel-engines for aircraft. I am really keen on knowing where this will lead us.

Side-look: In Brazil, there is a manufacturer of agricultural aircraft (cropdusters), who only just came up with one of his new planes using ALCOHOL - Ethanole - as fuel. It's great fuel, too: Knock-resistance of Ethanole is as good as Avgas LL 100, it features super internal cooling ( 4 times better than gas), and the power increase of the engine without ANY performance-related alterations towards the identical Avgas-burning powerplant sums up to about 7 percent - caused by cooler induction temperature.

Only downside: alcohol-fuel-consumption of an engine is up 50 percent over the consumption of Avgas of identical rated power - due to lower caloric value of the alcohol.

But - best advantage of Ethanole for the pilot comes after a long day at work, dusting crops to the horizon and back: After a day's final touchdown, he always has his own reserve of Caipirinha readily at hands...

Cheers! :D

Montanamotor

[Red Admiral]

Temperature vs. Altitude

Temperature decreases with altitude according to the formula;

Temperature = Initial Temperature + Altitude*Temperature Lapse Rate

This relationship is derived from empirical evidence, not theoretical results. The Temperature Lapse Rate for air is -0.0065K/m

At sea level, the mean temperature is 288K (15°C).

The graph below shows the variation of temperature with altitude;

http://img.photobucket.com/albums/v12/red_admiral/temperatevsaltitude.jpg

As can be seen, the temperature decreases with altitude until about 17km at which point it stabilises to a value of c.180K (actually it increases slightly). This point is the boundary of the troposphere and stratosphere which varies in height between 6000 and 17000m at the poles and equator respectively. It is not a distinct boundary and varies with weather and other atmospheric affects.

next, Pressure and Density.

[Red Admiral]

Maximum dive of WWII planes I've seen is the 980kph of the Re 2005, probably an absolute max of 1000kph. There was little flutter at this speed and the dive remained controllable. The main reason for this are the thin wings of the Re 2005. I'll see if I can find some diagrams of airflow over wings close to the Mach as I don't want to draw them. Instead of flowing steadily over the wings a sharp barrier of air builds up, losing lift and increasing drag.

IIRC the Italian fighters were more strongly built than others, especially the German ones. Limiting g for german planes about 6g IIRC with failure being at 1.3*6g = 7.8g , For Italian aircraft the specs were higher with limiting g about 8g and failure being 1.5*8g = 12g

With regards to power available, if you want to go really fast its possible to tune the engines and get considerably more power from them. In 1943/44 Derby tuned a fairly standard Merlin 61 (IIRC) and got 2450hp sustained from it. A standard WWII engine will do 40hp/L , by the end of the war the Sabre was running at about 65hp/L and the Crecy at nearly 190hp/L. If you're using the Continental I'd expect 50-60hp/L without it going boom.

[Wuzak]

Pressure temperature and density are all related.

http://en.wikipedia.org/wiki/Atmospheric_pressure
http://en.wikipedia.org/wiki/Temperature
http://en.wikipedia.org/wiki/Barometric_formula

The density of the air has a big part to play in terms of the drag on the vehicle (plane), changing the coefficient of drag Cd.

That is why the approximation of a speed for an increased power needs to be at the same altitude as the original top speed.

[GregP]

I see above that there may be some confusion about flutter and I thought I'd address that.

A control surface (as an aileron) has static balance and a dynamic balance point.

By static balance, it is meant that the surface does not tend to move while at rest on the ground. That is, it is balanced around the pivot point so it has no "favorite position". Sometimes this is not necessary. On many designes, for instance, the elevator will tend to sag downward while on the ground at a standstill with the controls free (unlocked) and no one in the cockpit. This is not always a bad thing, though it CAN be.

Dynamic balance is harder to explain. Think of a flag on a flagpole. In a wind, it whips back and forth at the back end of the flag. If a control surface is shaped wrong at the trailing edge or if it is balanced wrong, it can tend to do the same thing. If the trailing edge tapers into a point, the surface will flutter at SOME speed no matter what you do. The correct trailing edge shape is a straight taper to a point or a straight taper to a chopped-off, thin trailing edge, without rounded edges. Also, I'm sure you have seen elevators that have a small section near the end of the surface sticking out ahead of the pivot line. Think of a rudder with a section that stick forward of the hinge line near the top. This is called an aerodynamic balance and is used to lessen the amount of force needed to move the surface. The force needed is the normally-required force minus the force from the balance area that tends to help deflect the surface. The trick is to size the balance area correctly. If the aerodynamic balance area is too large, the surface is said to be overbalanced.

An example of an overbalanced surface is the rudder on the Handley-Page Hampden. If the pilot applied too much rudder, the surface would snap over into full deflection and it would be difficult to get it back to center ... not a desirable situation, to say the least. Look up almost any account of the flying qualities of the Hampden and you'll see this characteristic noted.

Anyway, at some airspeed, most surfaces will tend to wobble up and down (or left and right) like the flag in a wind above. When this happens, it creates a huge increase in drag localized at the surface hinge points, and whips the stick (or wheel) back and forth in the pilots hands (probably broken hands), assuming the flight control system is strong enough to handle the flutter without breaking or stratching so as to make the flutter seem less sever than it is. Designers want to make this "flutter" airspeed a few knots or more above the maximum permitted diving speed so flutter is not a factor as long as the aircraft is kept within the approved flight envelope. That is why there are limits on the airspeed indicator and why you become a test pilot if you exceed the design limits. In some cases, you may get away with it. In some cases, you'd better have a parachute.

While fluttering, the sirface also transmits aerodynamic forces to the fixed part of the surface.

To make thuis easier, I'll assume we are dealing with an elevator that has a fixed horizontal stabilator in front of it. Think of the Spirfire (no, it didn't have a flutter problem) with the stab and elevator.

OK, the elevator starts to flutter. That is, it starts moving up and down, usually several times per second. In normal flight, the stab is stressed to withstand the sudden application of up or down elevator, but the stab was never intended to withstand rapid movement to the extremes of travel at high speed several times per second and starts to experience more back-and-forth stress at a faster rate than it was designed for. If that happens, one of two things usually ensues. Either the elevator departs the aircraft or the fixed stabilator AND the elevator depart the aircraft. The sound of flutter is unmistakeable and will not be misunderstood by anyone who hears it. It literally sounds like the aircraft is "fluttering". Wish I had a sound bite of thuis phenomenon, but I don't.

Hope that helps a bit.

May all your flights be flutter-free. :)

[GregP]

I appreciate the apparent interest in this topic and would have opened it long ago if I had thought there was interest.

Goes to show you that you can't tell what people might be interested in unless you try it.

Looks to me like we have at least 4 - 6 people in here who are interested enough to make good contributions. Maybe we'll see more in the future. Let's keep it up every once and awhile ... when we have time.

Cheers to all of you. [:p]

[montanamotor]

You're right,

GregP. This is a fabulous way to get first-hand-knowledge in digestable form. Very often, specific information is either transported too conveniently - "appetisers only" don't saturate... - or too elaborate: You don't go shoot a cow, if want one hamburger, only.

The different G-load-factors maximally to be applied to german and italian aircraft, are most interesting. I wouldn't know where else to fetch such highly valuable information.

To Red Admiral: Thanks for the hints you gave me. Every day, I can learn something new and valuable in this community. Your assumptions on the power potential of the Continental V 12 AVDS 1790 are very accurate. With 1500 hp at 3500 rpm, it will be a very strong and reliable powerplant. Don't mind the revs: The basic design with a bore x stroke of 146 x 146 mm, has enough reserves to achieve it. There's only some classic engine tuning required. No witchcraft neccessary, here.

Rather than going for a Merlin, I'd stick to the Continental for several reasons:

1. It's aircooled - so there's no need for a mayor plumbing effort in using it in a plane, especially when using it in the almost aircooling-purpose-built SAI 403 Dardo's nose.

2. It's invertable: As I pointed out elsewhere, installing the Continental in a plane upside-down-wise is possible and straightforward. On the other hand, I have never heard of any instance where even a trial was made to install a Merlin inverted. Did you?

3. Cheapness and abundance of parts: Used Continental V-12's are on sale at approx. 5000 Euros / 6000 Dollars, actually. A Merlin is to have at ten-fold this pricetag, only.

4. Additionally, the Continental's strong and reliable internals are still to be bought from stock - some are even manufactured under license over here in Germany, by MTU.

5. As the Dardo would be going to be an "experimental-class" plane, there's no need for using an FAA-approved engine, either.

6. Finally: A friend of mine being a certified aero-engine-rebuilder with his own company over here in Germany, I am quite confident that some day soon we will see the Continental V12 airborne - installed in a wooden, winged cargo-box called "Dardo"...

Cheers!

Montanamotor

[GregP]

Hi Montanamotor,

If you are really considering a Continental rebuild, you might consider the following:

1) Yes, you can get the Continental going. You apparently have local resources that are good ones.

2)You'll have a virtual one-of-a-kind engine.

3) It will be difficult or impossible to get it serviced away from your local engine source. So, as long as you don't have an engine problem away from home, you may be OK. If you do, you'll incurr the expense of removing the engine and shipping it to the local shop for repair, the repair itself, shipping it back to whre the airframe is located, reinstalling it, testing it, and aurframe storage while the engine work is being done.

4) When it comes time for annual inspection, you'd best have another, government-approved inspection agency willing to inspect the one-of-a-kind engine for a reasonable fee. One-of-a-kind engines often generate very high annual inspection costs.

Just a few real-world items to consider. There is NOTHING wrong with the Continental, but it may be an expensive one in the end ... amd may not be. Good luck!

[GregP]

Montanamotor,

One last thought about making an SAI 403 Dardo:

If you DO make one, follow the plans exactly, including all braces, all shear webbing, etc. The only departures I'd make would be the engine and cowling and to add carbon fiber reinforcement to the main spar on both the top and bottom of both the wing and stabilator. That way, you have some excess strength that is virtually no extra weight since you must use epoxy for the wood spars anyway. The weight is in the expoxy, not in the carbon fiber (is it fibre in Italy?)

Anyway, in making radio control models, I have tried both carbon fiber and non carbon fiber on the same type model, and I have dived with a hi-g pullout on both. The ariframe without the carbon fiber broke and the carbon fiber model did NOT break. They weighed virtually the same. In an aircraft the size of the SAI 403 Dardo, I'd expect a total weight penalty of about 5 pounds or less. That is about 2.5 kg or so ... well worth the strength it gives you.

[Wuzak]

quote:Originally posted by GregP

carbon fiber (is it fibre in Italy?)


I believe it is fibre everywhere except the US and where English is taught by Americans..... ;)[:p]

And it is metre, litre, etc...

btw there is a word meter - it is any device used for measuring a quanitity of some description.

[GregP]

Hi Wuzak,

Keep the timbre limbre ... and don't let a metre eatre ...

I think spelling is a national thing. We in the USA tend to go "the other way" and I hope you can forgive the colonial spelling tendencies.

Most of the time I post in metric units in deference to the the fact that most nations are metric. Sometimes I include both units, English and Metric ... maybe I should call them US and metric, but "English" is the traditional nomenclature.

I have not adopted the 11.234 instead of the 11,234 ... but that is personal preference.

Still, I think we all understand each other. Anyone with Microsoft Excel and a modicum of sense can convert. If anyone wants a good conversion spreadsheet, send me your email and I'll send YOU one. I will not spam you or send you a virus ... I use Trend Micro PC-Cillan and it works quite well (and is up-to-date) :)

Or, I can send a public application that does the same thing (mine is more accurate).

If anyone wants to post a spreadheet on this forum and knows how, let me know and I can send it to Taglia free (or anyone else). These things are public knowledge (or SHOULD be) and I see no reason why it should be for sale! :)

It took me some time to do, but not that much time ...

Too damned many copyrights on "public" knowledge ... the idiots are still copurighting WWII photos! These damned things are 60+years old! How can they be copyrighted?

Makes no sense to me ... laws or NO laws. 60 years old is PUBLIC knowledge and public publishing rights, at least to anyone with a grain of sense. I think 50 years is LONG ENOUGH. Period.

Damned legal system anyway ... [V]

[Wuzak]

Yes, Americans can be a contrary lot!

You all forget to put 'u's in words such as harbour, labour, neighbour, etc, for example.

As for units, I believe that the US was one of the first countries to sign up to the metric system - but have pretty much ignored it for the last 200 years or so...

Interesting that several imperial units changed size when they were made into US units. At one stage I believe that there was a US inch, ever so slightly different from the standard imperial inch!!! That has since been standardised.

There is one glaring example of this which persists to this day - the gallon. The US gallon comes in around 3.7l, whilst the imperial gallon is around 4.5l. Made for an interesting discussion of fuel consumption a little while back!

As for the decimal indicator, we in Australia, and in the UK too I believe, use the "dot" as the decimal point, whereas many European countries use the "comma".

The metric system is a very simple system, but unfortunately some countries/comapnies deem it necessary to use their own variations. Such as in torque - the standard unit is Nm, whilse some will use kgm. Also, we were taught that in engineering the units go up in thousands - kilo, mega, giga (10^3, 10^6, 10^9) etc but some use things like Deca (Da - = x 10). Centimetres, for example, was something that only tailors and dressmakers used!

[GregP]

When the metric system was defined in 1791 by the Paris Academy of Sciences, the meter was one ten-millionth of the distance from the equator to the North Pole. The second was the time for a pendulum one meter long to swing to the other side. These definitions were hard to deal with and were difficult to duplicate. When was the last time YOU tried to measure a very long distance, and then take one ten-millionth of it? Especially with technology from the 1700s or 1800s? Since 1889 the definitions of the basic units have been established by an international organization; the General Conference on Weights and Measures. The system of units defined by this organization is based on the metric system, and has been known as the International System (or SI for Systeme International in French) since 1960.

From 1889 to 1967, the second was defined as a certain fraction of the mean solar day. The second is presently defined using a Cesium atomic clock, and is the time required for 9,192,631,770 cycles of Cesium clock radiation. In 1960, the meter was redefined using the wavelength of orange-red light emitted by atoms of Krypton (86Kr).

In November 1983, it was changed again in a more radical way. The new definition of the meter is: ¡§the distance light travels in vacuum in 1 / 299,752,498 sec (or, more properly, s).¡¨

This has the effect of defining the speed of light to be exactly 299,792,458 m/s.

The standard of mass is the mass of a particular cylinder of Platinum-Iridium alloy kept at the International Bureau of Weights and Measures, called a kilogram. I wonder if Platinum-Iridium corrodes? We could go on with this stuff (is stuff an archaic term?) for many pages, but ...

Enough stories and history already! Let¡¦s get to it. There are many unit systems, but the four most common these days are: (1) the English System, (2) the MKS System, (3) the CGS System, and (4) the SI System. These basic systems are described below:

Metric
Item English MKS CGS SI
Length Yard (yd)
3 Feet (ft)
36 Inches (in)
(0.914 m) Meter (m)
(39.37 in)
(100 cm) Centimeter (cm)
(2.54 cm = 1 in) Meter (m)
Mass Slug (14.6 kg) Kilogram (kg)
(1000 g)
(0.06854 lb) Gram (g) Kilogram (kg)
Force Pound (lb)
(4.54 N) Newton (N)
(100,000 dynes) Dyne Newton (N)
Temperature Fahrenheit („aF)

Celsius/Centigrade („aC)

Centigrade („aC) Kelvin (K)
„aK = „aC + 273.15
Energy Foot-pound (ft-lb.)
(1 ft-lb = 1.356 J) Newton-meter (N-m) or Joule (J) Dyne-centimeter or Erg
(1 J = 107 ergs) Joule (J)
(1 J = 0.7378 ft-lb.)
Time Second (s) Second (s) Second (s) Second (s)
Table 2-1


There are many unit conversions, and these are but a few. If other units are needed, they aren¡¦t too hard to find. Next we turn to electrical units. These are essential for electronic communication. NEVER give anyone a reading without units. It WILL bite you eventually if you do! The essential electrical units are included in the following table. The abbreviations and the powers of 10 are covered later in this chapter.

Unit of: Description Comments
Charge Coulomb (C): A coulomb of charge is defined as the total charge associated with 6.242 x 1018 electrons. A single electron holds a charge of 1.6 x 10-19 C. Charge is closely associated with current and voltage.
Current Ampere (A): A current of 1 Ampere (sometimes abbreviated as 1 Amp or 1 A) is a flow of 1 coulomb per second. You have to be a small, quick technician to count 6.242 x 1018 electrons in 1 second! Useful derived units include Amps (A), milliamps (mA), microamps (ƒÝA), and nanoamps (nA). Current is always flowing through; never across a device.
Capacitance Farad (F): A capacitor has a capacitance if 1 Farad if 1 Coulomb of charge is deposited on the plates by a potential difference of 1 volt across the plates. Capacitor values are almost all in units of microfarads (ƒÝF), nanofarads (nF), or picofarads (pF). A few large caps are up in the farad (F) range.
Resistance Ohm (Ă): A resistor with 1 volt across it and 1 Amp of current through it has a resistance of 1 Ohm (1Ă). Resistors are usually expressed in Ă, kĂ, and MĂ. They are marked with color bands as described later.
Voltage Volt (V): A potential difference of 1 volt (1 V) exists between 2 points if 1 Joule of energy (1 J) is exchanged in moving 1 Coulomb (1 C) of charge between the two points. Voltage is usually expressed as either AC (VAC) or DC (VDC). Voltage is always across, never through a device.
Inductance Henry (H): Inductance is measured in Henries. The ability of a coil to oppose any change in current is called self-inductance; the "self" is usually omitted. Inductors are usually measured in mH, UH, or nH. Some RF circuits use nH and pH inductors. Coils are called "Chokes" in obsolete "electrospeak" since they tend to oppose (choke off) any change in current through them.

Sorry, seem to have lost the formatting ... darn computers anyway ... if you are intersted, I can send a Word document. :)

[GregP]

One more observation:

WWII fighters were made as rapidly as possible. They were NOT made to be world speed record holders. As such, there is considerable aerodynamic cleanup that is possible on the production line that could have yielded another 20 knots or so of airspeed (actually indicated airspeed or IAS) if it had been done.

I am given to understand that some airframe sealing WAS done, but it was not robust and deteriorated rapidly, thus causing many internal airframe air leaks, bleeding off top speed.

Can anyone confirm this?

If not for the air leaks, true airpseed, or TAS, could have made the piston fighters of the time VERY close to 500 mph (804 kph) units, assuming the airframes would have tolerated this speed without flutter or Mach effects.

The P-38 would not have tolerated 500 mph since it had about a 16% thickness to chord ratio. The Spitfire COULD since it was only about a 13% thickness to chord ratio. That made the difference between Mach 0.85 and a vertical dive into the ground.

Many P-38s dived vertically into the ground.

So ... given today's knowledge, we could probably design a 650 mph (1045 kph) piston fighter easily ... IF there were one or more 2500 HP piston engines available, and if there were sufficient money there to do it. Does anyone know of such an engine? (must be an aircraft engine, not something for a ship ...)

My take on it would be a sightly swept-wing fighter-type design with a 2500+ HP piston engine and a contour not unlike the CAC-15 or P-51H with some ectra streamlining. The propeller would, of course, have to be slightly supersonic (or supercritical, maybe Mach 1.05 at the extreme tip) and the airframe would have to have area rule and a positive cooling thrust, like the original P-51 did. I'd say 2,500 rpm at max power and an efficient supercharger or turbocharger ... or a geared engine to GET the correct propr RPM.

Today, I think the engine could be done by a V-6 of relatively small displacement (yielding a lighter aircraft), maybe a small V8, similar to the ill-fated Pond racer, but the power would have to be 2500 HP or more and reliable. That CAN be done.

The problem is simply one of two:

1) money, and

2) the desire to DO it

10% thick wings with area rule, swept or slightly swept (25° -35°)geometry, and a powerful, reliable eigine, COULD pass the 500 MPH mark easily. Geting to 650 mph is another thing, but is POSSIBLE ...

The former Soviet Union actually almost made such a plane in the form of the turboprop Bear (Tu-95 / 142). It can go 585 mph (941 kph) and can out-accelerate the turbine fighters of most nations, including the U.S.A., at least for a short time.

An operation such as an unlimited hydroplane boat, as campaigned in the U.S.A., if applied to aircraft could easily break all records.

C'mon, DO it, someone ... hell, I'll volunteer to help for free!

[Dogwalker]

The original SAI 403, like the Mosquito, had an integral fabric covering over the plywood skin.
Today, stronger and lighter fibres than that disposable in wartime in Italy can be used.
It's even possible to use a (costly) monolitic carbon fibre covering respecting the original plans.
On the other hand, the steel armour of the cockpit is no more necessary.

[montanamotor]

Hi, friends!

Aaaaah - this is getting better all the time! GregP, Wuzak, Dogwalker - I'll address all of you simultaneously now, because otherwise I would lose the thread myself...

About the abundance of information you give in this community: Give us more! I LOVE it! It's a joy for me to enter this community every day, only to find yet another piece of information to saturate my interests! Don't stop that, please! (I mean, as long as we don't have to pass examns at the end of each semester, to stay registered in TGPlanes...) :D

One kind of difference in metering units, that may have caused dozens of aircraft losses in history already, may be the difference between the "Imperial Land Mile" at 1609 metres (!) and the "Nautical Mile" at 1852 meters.

To complicate things even more, speed in aircraft nowadays is most commonly indicated in "Knots" (Nautical Miles per hour), whereas distances are still often described by using the Imperial Land Mile per hour. But why then are we - as many other english-speaking people commonly do - even now expressing the speeds of aircraft now and again usually in "IMPERIAL LAND MILES PER HOUR"????? Aaaaaah!

CLEAN THIS MESS UP, PLEASE! Meters and, Kilometers are so easy to use. A child can use them properly! Why the Hell keep using such a failiure-prone "mile-something"-metering system - even supplemented by metering the altitude in "Feet" at 30,3 cm (And why not use "Yard" and "Fathom", also...?) - in aeronautics? This is medieval! If not to say: Imperialistic...

Sometimes it looks to me like, hitting mountain tops or, running out of fuel due to miscalculated speeds and ranges is a thrill english-born pilots don't want to miss in the World?

New topic: Cleaning up a plane's surface gives it a REMARKABLE advantage in speed. I read elsewhere that, the application of dull camouflage-paint on it's otherwise slick and polished airframe ALONE did cost the P-51 Mustang 15 mph / 25 km/h of it's Vmax! Remove it again, and it will go this speed faster again.

Wonder, why all american Army Air Force-Planes from Mid-1944 where not painted anymore, but featured a polished Aluminium-surface, instead? That's why! The wheight and THE DRAG of DULL paint applied to an airframe are really substantial!

The Hawker Hurricane during WW II was notorious for losing an extreme amount of speed during an individual's plane's service life. Starting at 522 km/h fresh from the factory (don't know the mph-readings, so I'll leave those out here) after one year in service, due to extreme weathering of the paint (Cellulose-based paint back then, I presume), due to wear of the airframe and maybe also due to gaining drag and wheight by installing additional equipment - during the Battle of Britain the AVERAGE speed of ALL Hurricanes in service was reduced down to 480 km/h! This is a 44 km/h loss! This was determined by an official RAF-investigation.

Synthesis: Sealing seams as much as possible, using high-quality, high-gloss paint (if not: dispensing with paint at all) and monitoring the wheight and drag of an airframe very carefully during it's service life may give you easily a speed advantage of more than 5 percent over a neglected specimen's speed performance. Not bad, eh?

This leads me to the reinforcement of a Dardo's airframe-structure and overall surface with carbon-fiber. Yes! You are right! Good advice. Strong stuff. I highly recommend it myself. And it would look good, too. During my professional life, I personally had very much to do with high-performance cars and, motorcycles, yet. Therefore, I personally know first-hand that, a smooth vehicle-surface of meticulously applied woven carbon-fiber-fabric looks GORGEOUS! And it works fantastically, too.

About the Continental V12 - first: When I am going to rebuild it for my aeronautical purposes, it won't be only one, but several engines, that would be rebuilt simultaneously. Once you start such a project, it's SUBSTANTIALLY cheaper per engine, to do so with several engines at a time than one engine only or, one after another. By that, a replacement, if neccessary, would be no mayor issue at all. As well, there will potentially be other customers for accordingly rebuild engines, too. So maybe, It won't be costly, but even profitable in the end, to rebuild those Continentals. Who knows...?

Secondly: I am not going to do these rebuilds in my home garage. Instead, the overhaul, tuning and adaption of the engine(s) for inverted installation will be done in my friend's professional aircraft-engine-workshop. (Ya' know - I love life, too. I don't need a shabby, poorly assembled engine to quit during take-off, sitting behind a fueltank swashing with 600 liters of fuel...) This should alleviate any potential problems during the annual engine revisal, too.

Did I leave something out? Yes, the 800+ km/h prop-plane. Aaaahh - hmmm - I mean: SAI has proven already that, their airframes have the potential to fly well with swept wings. And the Continental V12 has proven already that, running on pure Methanole as fuel ONLY - it can put out up to 2500 hp without damage.

Well - hmmm: Would someone now please add 1 and 1...? :D

No - for my personal use and pleasure, I'd always prefer the "real", straight-winged Dardo.

But, Hell: Do I know what will be going to happen, after the Dardo once has taken off for her "second first-time"? No. Do you?

Cheers!

Montanamotor [8D]

[GregP]

Actually, the swept-wing thing I mentioned was a potential NEW aircraft. I was not intending to suggest a swept-wing Dardo ...

I know Aerfer made a swept-wing thing prior to turning the airframe into a jet (the Sagittario 2 and the Ariete), but the Dardo is an SAI classic that I wouldn't dare to suggest you ruin by changing the wing type. Sacrelige!

Best of luck to you!

Please keep us posted and post some pictures during the build up.

One last thing, I'd put the carbon Fibre inside the wing wrapped around the spar, not on the outside!

[Wuzak]

Some categories of drag racing use 500cid (around 8l) V8s, highly supercharged and running on methanol they pump out around 2500hp.

But as these are designed around racing for no more than 6 or 7 seconds we might want to back them off a bit adn run two of them in tandem. We can then gear them to drive contra rotating props.

These V8s are quite light too - much lighter than a normal aero engine.

They also run Rootes type blowers - probably not the most efficient type of supercharger. Change them to centrifugal type superchargers (which are available), and then possibly try for a turbo compound set-up.

That should give you a reliable 2500hp, in a reasonably compact package.

[GregP]

There is a company in the U.S.A. marketing an Aluminum V8 of the LS1 variety (same as the Chevrolet Corvette) for aircraft use. Supercharged and coupled to another one as suggested above would be very nice combination, I agree.

PLEASE someone DO it and achieve the world piston speed record!

[Wuzak]

quote:Originally posted by GregP

There is a company in the U.S.A. marketing an Aluminum V8 of the LS1 variety (same as the Chevrolet Corvette) for aircraft use. Supercharged and coupled to another one as suggested above would be very nice combination, I agree.

PLEASE someone DO it and achieve the world piston speed record!


It would seem that the target for the record is not as high as it might be.

The current record (as far as I can tell) is 528.33 mph (849.55 km/h), held by Rare Bear.

http://www.aerospaceweb.org/question/performance/q0023.shtml
http://www.aviation-history.com/garber/vg-bldg/grumman_F8F-1_c.html

Considering that Supermarine and Hawkers had Eagle 22 powered aircraft designs estimated to be capable of doing that in 1944/5, it might very well be possible....

[Red Admiral]

Dimensional Analysis

Why do we perform wind tunnel tests? The answer is that we have confidence that the behaviour of the fluid mechanics about a real aircraft or a real aircraft wing may be obtained accurately by a suitable small model once we know how to scale our results. This is because the model and the real thing are dynamically similar. The process of dimensional analysis is how to scale the results using dimensionless groups. There are 3 dimensions, Mass, Length and Time into which everything else can be attributed. The dimensionless groups remain the same regardless of the size and they can be used to predict the behaviour on the actual aircraft from results obtained on the model.

The number of dimensionless groups is given by Buckingham's Pi theorem;
Number of dimensionless groups = Number of Variables – Number of Dimensions

An example will probably be more helpful in order to illustrate this technique.

The lift force on a wing is thought to depend on the mean chord c, the mean thickness l, the air velocity V , the angle of attack %alpha, the viscosity and density of air.

We now determine the dimensions of the variables above,

[Lift Force] = M L / T^2
[c] = L
[l] = L
[ V ] = L / T
[%alpha] = dimensionless
[%mu] = M / LT
[%rho] = M / L^3

One dimensionless group can be seen immediately, the lift force depends on the angle of attack %alpha

Another dimensionless group is l / c which is [L] / [L] which is an aspect ratio

Defining the other dimensionless groups is more difficult. The sum of powers of the dimensions will result in zero for a dimensionless group, so;

[LF]^a + [c]^b + [l]^c + [ V ]^d + [%mu]^e + [%rho]^f = 0

Excluding %alpha because it has no dimensions

Now we substitute for the dimensions of the variables and obtain 3 simultaneous equations with 6 variables which is impossible to solve all at the same time.

Mass; a + e + f = 0
Length; b + c + d – e – 3f = 0
Time; -2a – d – e = 0

We now set a and b to zero and l to 1 in order to obtain a solution
The solution is c = d = f = 1 and e = -1
We now substitute back into the variables to obtain the dimensionless group, (%rho * V * l) / %mu which is the Reynold's number for the wing in question.

We then set the values differently in order to obtain another dimensionless group
Lift Force / (%rho * l^2 * V^2) which gives us an expression for the lift force on the wing

Say we now want to move between a scaled test model and the actual aircraft. The dimensionless groups remain the same so if we know the lift force on the scale model we can find the lift force on the actual aircraft. {s} scale {a} actual

Lift Force{a} = Lift Force{s} * (%rho{a} / %rho{s}) * (l^2{a} / l^2{s}) * (V^2{a} / V^2{s})

This also means that we can test the model aircraft in different fluids (e.g. Water instead of air) and at slower velocities.



I apologise for the Greek but the forum doesn't seem to like the characters.

[Oli]

I'd just like to say that although I don't post much I do read this forum regularly, and I'm enjoying your topic Greg. Keep it up.
(PS quote:Kilogram - it's kilogramME! :D, like programme)

[GregP]

Thanks Oli.

I will add as I get time, and the other posters are doing a pretty good job, too!

There may be more interest in this than I would have imagined.

[GregP]

OK, maybe another addition or two to Aerodynamics.

First, assume we are flying a level turn. That is, we are making a turn without gaining or losing any altitude. What is the g-loading?

The short answer is g = 1 / cosine (angle of bank).

So, if we are in a level, 30° banked turn, the g-load is 1 / cos(30°) = 1 / .866 = 1.155 g. At 60°, the g-load is 2.000.

The stall speed increases as the square root of the g-load. So if we have a level-flight stall speed of 85 knots, the stall speed in a level 60° bank will be 85 * square root (2) = 85 * 1.414 = 120.2 knots. The multiplier works for any speed unit ... use kph for the stall speed and you will still be correct.

Bank Angle-------g------Stall Speed Multiplier

0°-------------1.000------------1.000
10°------------1.015------------1.008
20°------------1.064------------1.032
30°------------1.155------------1.075
40°------------1.305------------1.143
50°------------1.556------------1.247
60°------------2.000------------1.414
70°------------2.924------------1.710
80°------------5.759------------2.400

Note that a level 60° bank will load you with 2 g and the stall speed goes up by 41.4%. 3 g is a 70.53° bank. That is, of course, true only in a level turn.

Do most people in Europe still use "degrees" or are you using grads?

The cosine of 90° is zero, and that means you can't maintain level flight in a 90° bank. But ... SOME aircraft CAN do that! The answer is, of course, that these aircraft generate lift from the fuselage when in a 90° bank. The old Pitts Special biplane comes to mind here ...

The formula assumes all the lift is coming from the wings.

Also, Military jets can seem to make 90° banked turns at airshows. The real answer is that they are NOT in a real 90° bank at all, but more like an 83° to 85° bank. It just LOOKS like a vertical bank from the ground.

Last in this installment, the stall speed varies with the weight of the aircraft. The actual formula involves the coefficient of lift, the density of the air at the temperature and altitude you are flying, and the square of the velocity.

The "Rule of Thumb" that works quite well is the the stall speed will increase or decrease by half the percent of weight change from a known stall condition.

By way of example, suppose we are flying a Cessna 172 with a normal flaps-sown, stall speed of 43 knots at a weight a 2300 pounds. Yes, I can can do it in metric units, too). What is the stall speed (1 g, straight and level) if we are flying at a weight a 2100 pounds?

This is easy.

2100 / 2300 = 0.913. This is a weight reduction of 0.087 or 8.7%. Take half of that to get 4.35%. The stall speed will decrease by 4.35% since the weight decreased, so the 1 g, level-flight, flaps-down stall speed will be 43 - 4.35%, or 41.13 knots.

Round to 41 knots and you won't be off by much. Most airspeed indicators are not readable to less than a knot anyway. By the way, these numbers are close, but not real. The normal "clean" stall speed is about 43 knots. Flaps down stall speed depends heavily on the year model and can be as low as 34 knots or so depending on year and gross weight.

This "rule of thumb" works for both modern lightplanes as well as WWII fighters, and will get you very near the actual stall speed for reasonable weight increases or decreases. By "reasonable" I mean you must stay within the normal accepted limits of flight. Don't go over maximum gross weight or lighter than the empty weight.

All for now ... :)

[GregP]

Maneuvering Speed

The concept of maneuvering speed is important in light aircraft design, less so in military aircraft. Simply speaking, the maneuvering speed (called VA) of an aircraft is the highest speed at which full and abrupt use of the controls will not result in damage to the aircraft. Above maneuvering speed, you can literally “pull the wings off” if you quickly yank back on the stick all the way to the limit, perhaps damage a wing with full and abrupt use of aileron, or maybe break the tail with full and abrupt use of rudder.

Simply stated, the wing (or other surface) will stall before reaching its g-limits at or below maneuvering speed.

When would we use maneuvering speed?

Usually, it is most important in rough air, such as when you wander into a storm or experience a day of heavy turbulence. Why is maneuvering speed less important in military aircraft? Well, they are usually built quite strongly, and are much less prone to breakup in flight. Most light aircraft (in the Normal category in the U.S.A.) are designed with a maximum load factor of about positive 3.8 g with a 50% safety factor. The “safety factor” is not intended to be used and if the 3.8 g is exceeded, the wings will be “bent” and you may well get home, but the aircraft cannot fly again without major repairs that amount to a rebuild of the airframe.

Maneuvering speed changes with weight. It is usually quoted at maximum normal operating weight, and gets faster if the aircraft is heavier and slower if the aircraft is lighter. To calculate the new maneuvering speed at a lighter weight, the formula is as follows: Va new = Va * square root (new weight / spec weight).

Let’s do an example. I choose a 1999 Cessna 172-R. With apologies to Montanamotor (I still think in English units!), the specifications are as follows:

Item---------------------------English---------------------Metric
Empty Weight------------------1600 lbs-------------------725.7 kg
Useful Load--------------------857 lbs-------------------388.7 kg
Gross Weight------------------2457 lbs------------------1114.5 kg
Stall Speed Clean---------------44 kts--------------------81.5 kph
Stall Speed Landing Config------33 kts -------------------61.1 kph
Maneuvering Speed---------------99 kts-------------------183.3 kph (at 2457 lbs or 1114.5 kg)
Fuel Capacity-------------------53 US gal----------------200.6 l
Oil Capacity---------------------8 qts---------------------7.6 l

OK, let’s plan a local “fun” flight as follows:

Item---------------------------English---------------------Metric
Empty Weight------------------1600 lbs--------------------725.7 kg
8 Quarts of Oil-----------------15 lbs----------------------6.8 kg
40 gallons of fuel-------------240 lbs--------------------108.9 kg
Pilot--------------------------210 lbs---------------------95.3 kg (suppose we fly alone)
Assorted charts and things------35 lbs---------------------15.9 kg
------------------------------------------------------------------
Total Weight------------------2100 lbs--------------------952.5 kg
OK, how does this affect the specifications?

1. Maneuvering Speed:
English: Va new = 99 * square root (2100 lbs / 2457 lbs) = 91.5 kts
Metric: Va new = 183.3 * square root (952.5 kg / 1114.5 kg) = 169.5 kph

2. Stall Speed: The new weight is a 14.5% decrease in weight. Take half of the to get 7.27%. The new stall
speed is 81.5 kph – 7.27% = 75.6 kph clean, and 56.7 kph in landing configuration.

These are not great changes from the published specs, but the pilot flying alone in a light aircraft should slow down to about 15 kph below the published maneuvering speed in rough air in order to be safe and the aircraft will stall at a slightly lower speeds than published.

In practical terms, the real-world pilot should make these calculations for a very light aircraft only once, and should adhere to them after that. When I was flying a C-172, I never left for anywhere without at least 30 gallons of fuel, full oil, me in the pilot’s seat, and about 20 pounds of charts, headsets, and assorted stuff. So, I calculated the maneuvering speed once for a light C-172 aircraft and used the published Va for a heavy aircraft. If I was light, I simply slowed down in rough air to the lower of the two maneuvering speeds. The lower stall speeds did not affect me at all since I flew from a long paved runway in Arizona (Scottsdale). I regularly practiced spot landings, and you quickly get to where you can hit your spot flying just from the feel of the controls.

All for now. Cheers.

[GregP]

Looks like we ran out of interest in this. I am surprised it went this far ... :) ... so, I suppose this thread has run its course.

I'll get back to WWII aircraft now ... wait, that's the SUBJECT of this forum!

Yeah ... I almost forgot ... [:I]

[Lightning]

Hi Greg P,

Quoting you:
quote:The P-38 would not have tolerated 500 mph since it had about a 16% thickness to chord ratio.

You knew I'd respond to this. :D

The P-38's critical Mach number has been given by various sources as being between 0.68 and 0.72. That is without regard to the dive flaps on the later variants. These flaps did not increase the critical number, but they added another 20 mph to the maximum speed at which control could be maintained.

Tony LeVier did dive tests from 30,000 ft with a P-38J equipped with dive flaps. He recorded Mach 0.71 and true airspeed values of around 550 mph. At no time did he start to lose control.


Under standard atmospheric conditions of temperature lapse-rate and pressure gradient (these almost never exist under actual conditions), Mach 0.71 is 540 mph at sea level. What conditions were at the time of LeVier's tests was never stated in the accounts I have read. Temperature, however, is an important factor. At any rate, he definitely exceeded 500 mph TAS by a wide margin.

Regards,
Lightning

[Lightning]

Hi Greg P,

Quoting you:
quote: . . . you can't maintain level flight in a 90° bank. But ... SOME aircraft CAN do that! The answer is, of course, that these aircraft generate lift from the fuselage when in a 90° bank.

When you see an airplane executing a "knife-edge" pass or a 90-degree-banked level turn, there is a little bit of "cheating" going on. You'll always see that the nose is held above the horizontal. This generates a vertical force equal and opposite to the plane's weight. It does this in two ways:

(1) It produces action-reaction lift by deflecting air downward from the lower side of the fuselage which is held at an angle of attack to the relative wind.

(2) It directs a significant portion of the engine's thrust upward to produce a vertical component of thrust.

These two forces combine to equal, and thereby offset, weight. The result is a 90 degree bank in which no altitude is lost. (But don't expect the "ball" to be centered.)

Regards,
Lightning

[GregP]

Hi Lightning,

You are correct (as I'm sure you know), but the P-38 was notorious for getting into a "compressability" situation in which it was difficult and sometimes inmpossible to pull out from, hence the "dive flaps" to aid in dive recovery.

Maybe Tony Levier DID dive to 540 mph, but you can rest assured that no combat pilots did this deliberately. If they did, it was either a terrifying or a fatal experience and they certainly didn't do it again.

Right about 500 mph was where the P-38 grew teeth and bit the unway pilot, so I pretty much stand by my statement, and it has been corroboratted by many wartime P-38 combat pilots, and THEY should know.

Tony Levier was a Lockheed test pilot and his job was to go to edge of the envelope. A combat pilot's job is a bit different. He is supposed to survive and destroy the enemy while keep his aircraft in the best condition possible under the circumstances.

As for the 90° banks, yes the nose can be pulled up to form an angle with the flight path. The result is both engine and fuselage lift, as I stated. Although I didn't specifically state engine lift, I DID say that some aircfraft can produce lift in the 90° position. I stand corrected partially as engine lift plays a part.

I chose the Pitts Special biplane because I once saw a full-size Pitts perform a knife edge loop. Now THAT is significant side lift!

As usual, your comments are incisive and, in general, correct. :)I welcome further discussion on this or other subjects.

[Lightning]

Hi GregP,

Quoting you:
quote:
Right about 500 mph was where the P-38 grew teeth and bit the unway pilot, so I pretty much stand by my statement, and it has been corroboratted by many wartime P-38 combat pilots, and THEY should know.

Your point is well taken (as most of your points are). My posting was in responce to the statement that the P-38 "would not tolerate" 500 mph. The plane itself could easily tolerate over 500 mph; it was the pilot that was the limiting factor. Even if you use a critical Mach number of 0.68, the Lightning could exceed 500 mph at any altitude below 10,000 feet.

The combination of weight, power, and clean design led to the Lightning's ability to accelerate very quickly upon entering a dive. Before pilots were trained to recognize and deal with the onset of compressibility, it was too easy for some of them to reach and exceed critical Mach number before they realized it, and then, it was too late.

This led to the Lightning's getting an undeserved bad reputation among the early inexperienced P-38 pilots--a reputation that followed it untill compressibility was understood and addressed by proper training. Many times a pilot could have dived after an enemy without difficulty but was afraid to try.

The advent of the dive-recovery flap, although it did not eliminate compressibility, delayed entry into the danger region and allowed better control of the airplane once there. At this point in the Lightning's career, compressibility was no longer a thing to be feared--only understood. The enemy fighters that had dived or split-essed away from earlier Lightnings and their inexperieced pilots were now routinely followed in these maneuvers by P-38s--to their great surprise.

Regards,
Lightning

[GregP]

Hi Lightning,

A well worded reply. I was never sure that the P-38's problems at transonic speeds were ever really solved because I was never sure they fitted it with a with a wing of a different thickness ratio.

My references are packed away, but I'm pretty sure the P-38's wing (and the wings of most American WWII fighters) were about 16% thick. That was the factor that made sonic behavior problematic to start with, and I was never interested enough to investigate whether or not it ever changed.

Maybe I shall do that just to find out ...

As a point of discussion, I believe the Spitfire had wings that were about 13% think, and that is why it had pretty good behavior at high speeds. Coincidentally, the elevator and horizontal stab airfoil must ALSO be considered when trying to "fix" high speed behavior.

OK, maybe 500 mph wasn't the limiting speed to the P-38, I bow to your knowledge there. However, it certainly was not much more than 540 mph where the P-38 got a bit "dicey" for the average combat pilot ... even after the dive flaps were fitted.

I've read too many first-hand reports of pilots having high-speed difficulty in the P-38 for me to really believe that the average combat pilot in WWII ever really trusted the plane at very high speeds. Maybe they DID though.

I am certainly no expert on the ragged edge high-speed behavior of the P-38 Lightning. [B)] Since that is your "handle" in this forum, I stand corrected by "Lightning." [:I]

[Lightning]

Hi Greg,

Quoting you:

quote:My references are packed away, but I'm pretty sure the P-38's wing (and the wings of most American WWII fighters) were about 16% thick. That was the factor that made sonic behavior problematic to start with, and I was never interested enough to investigate whether or not it ever changed.

The P-47 and P-51 had slightly thinner wings than the P-38, and thier critical Mach numbers were a little higher. The P-51 had Mach 0.76 while the P-47's was a bit lower.

The reason the Lightning's wing was as thick as it was goes back to the USAAF's original specification for a high speed/altitude interceptor. It was specified that all performance requirements be met with internal fuel only i.e. no drop tanks. The only place such a fuel load could be internally stored was in the wings. Designer Kelly Johnson would have preferred a thinner wing, but the restraints imposed by the USAAF made that an unavailable option.

Later in the war, Johnson and Lockheed proposed a thinner wing as a way to improve the high-speed characteristics of the P-38. This would have required a relatively short shutdown of the assembly line in order to incorporate the the change. The USAAF would not allow this as the need for the uninterupted delivery of Lightnings was considered of paramount importance.

The P-38 thus retained the thicker wing even into its final versions. This meant that the critical Mach number of around 0.70 (as I said earlier, various sources state between 0.68 and 0.72) remained unchanged. The dive flap did not increase this number; it allowed control to be maintained as it was approached, and it slowed acceleration down somewhat so that critical Mach number was not achieved so quickly. Dive angle,on the other hand, was drastically increased, and this, in many cases, was more important than diving speed.

Early problems with instability in the Lightning's tail surfaces had nothing to do with compressibility or Mach number. The USAAF incorrectly determined that it was due to "tail flutter." Their "cure" was a requirement for counter-balance weights to be added to the elevator.

Kelly Johnson said they were wrong and proved it. The real cause of the problem was turbulence generated at the junction of the wing's center section with the "pod" (not the boom). The fix was a fillet installed at thi location to smooth out the airflow. This solved the problem, but the USAAF still maintained their requirement for the counter balances. Kelly Johnson said that the only thing these weights did was to cause some pilots to be killed or injured during bailout. (Over all, the P-38 was no more dangerous to bail out of than the single-engine fighters, but that's another subject.)

Upon reading the P-38 Lightning's history, it appears that the USAAF was one of its biggest problems!

Regards,
Lightning

[GregP]

Good points, all. Interesting you should metion the USAAF as one of the problems because that is my take, too.

It was the USAAF and US Navy that:

1) Deleted the supercharger from the P-39, rendering it a low-altitude-only plane and greatly reducing its effectiveness.

2) Denied Grumman the time to reduce the dihedral on the F6F Hellcat to improve the roll rate.

3) Denied North American the time to fully test the P-51D, so many were made without the stub fin and were less than stable in yaw until retrofitted.

There are more, but the pointi s made; the US Government meddled in the design if aircraft during the war and did MUCH worse in the procurement of same.

When Jack Northrop refused to merge with Consolidated Aircraft, he was put on a black list and Northrop never fully recovered from that. Making enemies high up in government has never been particularly "wise," but Jack wanted to keep the company he founded. As it turns out, Northrop was finally "acquired" anyway.

These examples point out the built-in stupidity of allowing political figures to serve for a lifetime in our system as long as they keep getting re-elected. I think they should have term limits, as our President does. If they don't, they develop too much power.

Many-term Senators and Congressmen are one of the evils of our system. I'd love to change that, but have no power to do so.

[Lightning]

Hi Greg,

As we discuss this topic, the blunders of the USAAF just seem to keep multiplying. They also refused to try the Merlin engine on the P-38 even though Lockheed had already drawn up the plans for the installation. I don't know what the outcome would have been, but it was certainly worth a try.

Another example was the handling of the XP-58 "Chain Lightning." It started out as a long-range bomber escort, but the USAAF kept changing its mission and adding ever-more equipment requirements. In the end, it was a tremendously heavy airplane without a defined mission.

As for the polititions you mention, you are Sooo right! Don't get me started! [}:)]

Regards,
Lightning

[GregP]

Hi Lightning,

About the Chain Lightning. I am almost in disbelief of how much the specs and intended mission(s) changed AFTER Lockheed had already started the airframe!

Once a plane has commenced the manufacturing stage, it seems only prudent to change only those things which could improve the missions the airframe was designed for in the first place! Hello! McFly! Duhhh ...

The only exception I can think of is maybe to add radar in a WWII design where none was originally envisioned. Even THAT, however, would have detracted from the performance of other than a night fighter since WWII radar sets were pretty crude and heavy compared with more modern units and they usually had both very draggy antennas mounted and an extra crew member, so I question even that exception.

By the time the P-58 was finished, nobody involved in the whole project was anywhere near remotely satisfied with the result and they were proven right when flight testing revealed the ugly truth. I'm sure there were some interesting comments made in closed meetings during THAT project by all concerned. :D

All the P-58 really needed were turboprops that were 10 years in the future! Imagine if it had been fitted with Rolls Royce Darts like the Viscount! That could have been a really interesting aircraft, especially if it had also been fitted with leading edge slats and maneuvering flaps as well as the Darts.

Of course the Dart, while a very good turboprop, was not really an aerobatic engine, so maybe the technology was a a few years beyond even the extra 10 years I mentioned above. We'll never know, but even if such an opportunity had presented itself, the USAAF would probably have passed on it as they passed on P-38 Merlins ... for some inexplicable reason. Maybe the controlling person on the procurement board hated Packard for some reason, or maybe his brother worked at Allision ... who can say?

In any case, the USAAF had some seriously stupid people in positions of relative power. Of course, the USAAF had no corner on this as there were some seriously stupid people in almost every major air force with the possible exception of the Swedish air force. Their solutions to very complex problems of supply and autonomy of action were always fairly innovative and successful.

I rate the most inept air force in world history as the German Luftwaffe. Herman Goering couldn't lead a thirsty horse to water, despite some very technologically advanced designs and proposals that showed and proved their promise of performance. I do not fault teh german airfraft industry, just the Nazi leadership, especially the Luftwaffe leadership and procurement people. For soem reason, the RLM hated Prof. Heinkel despite some clearly superior design solutions.

Next were the Japanese who couldn't seems to ever get any cooperation between the Army and Navy designers, and who duplicated efforts between the two services when forced cooperation would have resulted in more aircraft of better capability. Idiotic leadership.

The USAAF was probably third among the stubborn, pig-headed air forces of WWII, but they at LEAST had the ability to make a lot of aircraft while being stupid about it at the exact same time, so they were ahead of everyone in distributing their stupidity around the world.

Look at how many P-39s were used in various theaters of war! And that's just ONE example. OK ,don't get ME started either ... I might ... continue ... [}:)]

[Kutscha]

Depending on which Merlin model. If it was pre 60 series Merlins then the tc Allisons were better. If it was 60 series Merlins then they would have been the pretty much equal until over 25,000' when the tc Allison would have been better. The only thing the Merlin would have done was get rid of the complexity of the turbocharger.

One other point is where these Merlins would come from.

The USAAF was not that totally pig-headed for the Merlin went into the P-51.;)

[GregP]

Hi Kutscha,

Thanks for toning down my tirade. Yes, they made a few good decisions. They also had their problems, as I stated above.

Anyway, the reasoning behind the decisons that were made may very well have looked different if WE had all the information THEY had at the time.

Things ALWAYS look different in hindsight, but when the decisions are made at time, sometimes in a partial vacuum that is only filled in years later, they may very well seem reasonable.

I suppose I need to keep that in mind when I speak of the decisions made in WWII or any OTHER time, for that matter. Case in point; I DO NOT know the data they had to examine in 1942 in order to make the decisions they made, so I suppose should SHUT UP and just accept history as the things that happened at the time. Let's keep in mind that in 1942, Pearl harbor had just been bombed, the U.S.A. was reeling under having lost numerous ships and over 4,000 men in one attack, we were definitely NOT ready for war, and I do NOT know the status of the engines that were available for use or the quantity of the metals needed for superchargers when the decision was made to delete the supercharger from the P-39.

So ... here I am making judgments in a partial vacuum with the benefit of 60 years of hindsight. OK, I'll rescend the stubborn, pig-headed part and say that all sides may well have had reasonably good reasons for the decisions they made AT THE TIME.

I still think that hindsight shows a LOT of these decision to be quite faulty when analyzed in the presence of the facts that may or may not have been known at the time.

So ... maybe they weren't quite as stupid as we may think with the benefit of 60 years worth of investigory effort to peruse.

Damn, I KNEW this would happen! [:I] Turned into a grumpy old man AGAIN! [}:)]

[Kutscha]

Greg, I didn't see it as a tirade. Remember they did not have the instant (well almost) data acquisition we have today with computers and the I-net.

Up north of you, we have our own. Two that jump out are the CF-105 and resently the new copters. Billions squadered on both. The Americans especially got a bonus with the Arrow when most joined the their aero-space programs.

On the P-51(Allison), it sat on a back burner at Wright-Patterson for awhile. It was by chance that it became the premier USAAF escort fighter.

On the P-39 and the tc, part of the reason it was dropped was because the B-17, B-24 and P-38 needed them.

It was not only the USAAf and USN but also the USArmy. The Sherman could have been replaced with a better tank. The Sherman could have been fitted with a better AT gun earlier than it was. The Russians offered the T-34 to the Americans but was turned down. Can you imagine a T-34 using American expertise, inginuity(improvements) and manufacturing?

Not picking on the Americans for the British and Germans had many promising a/c that went no where or were too late.

[GregP]

Kutscha,

Didn't know you were Canadian! I have a story for you that you, as a Canadian, can probably appreciate.

In 1984 I was at the Seattle Seafare exposition with m y ex-wife. She wasn't "ex" at the time. We took a tour of a Canadian Destroyer that was moored in Seattle for the event and she, having a bee-bee size bladder, needed to use the "head." A Canadian sailor was assigned to escort us to said "head." When we were returning to the tour group, we passed through the bridge area and he asked if I'd like to sit in the Captain's seat.

Me being me, I accepted. There was a small ledge at the top of the bridge room that was recessed and only the person sitting in the Captain's seat could see it since the Captain's seat was raised about three feet above the rest of the floor with a tall seat in addition to the rasied floor. I supposed it was for good visibility for the Captain since there WAS good visibility over the bow.

Anyway, stenciled across the small ledge were the words;

"In Order To Avoid Confusion From All The Various Senors, Occasionally Look Out The WINDOW!"

I laughed about that for YEARS ...

You Canucks have a GREAT sense of humor, at LEAST the Canadian Navy!


P.S. I have never known where the word "Canuck" came from. Does the word "Canuck" have a positive or negative connotation in Canada?

If negative, I apologize in advance since I have always liked the word for some odd reason or another and have never seen anything in print that would lead me to belive that it it other than something like a national nickname for a Canadian citizen. However, it COULD mean something entirely different since it sounds vaguely like an Indian name. I have often found that "Indian" sounding names (Indian as in Cowboys and Indians, not Indian as in the country of India), though they may SOUND good to me as a White American, sometimes have some really insulting translations.

As an example, the word "Squaw" means something less than complimentary about an Indian woman, though I always, in the past, sensed it to mean "married Indian Woman" as it is used in Hollywood Westerns and common language. In Arizona, U.S.A., near Phoenix, we used to have a small hill called "Squaw Peak." The local Indian population protested so vocally that the official name got changed to somethign else, even though EVERYONE in Phoenix knows which hill is "Squaw Peak."

Apparently being "Politically Correct" is more important than landmark identification. Hence, my question ...

Sorry, not aerodynamics-related or even aviation-related, but still of interest ... to me anyway, and I'll desist from asking other non-aviation-related questions. [:I]

[Kutscha]

Greg, no idea where Canuck came from or when it started to be used. If a Canadian gets upset from being called a Canuck, there is something wrong with that person. The Vancouver NHL hockey team is called the Canucks. A downhill skier was nicked the Crazy Canuck > he was a wild man on the slopes. So, afaik there is nothing negative.

Before we return to our regular programming, I have one for you Greg, though not humorous.

In 1978, while in New London for a boat race, got a tour of an nuclear Attack boat. The race had been rained out so we went back to the hotel. Naturally the weather cleared. We were all sitting outside having a few ;) 'cool ones', being Canucks and all ;), and a pick-up truck drives up. Two coloreds (is that PC?) get out and ask about the boats as they had never seen a tunnel boat before. Had a nice little conversation and then one asks if we would like to have a tour of a sub. Five of us say, sure, but ask how are we going to get onto the base (Cold War and all). One says we will say your are Canadain relatives [:0] > we are all white. Get in the back of the truck (has a cap) and sure enough we are let through the gate and get a nice tour from stem to stern, except for the 'bridge' and reactor area.

Canada is said to come from the native word for village. Tale goes that when Cartier landed in the New World, the cheif turned and pointed and said canada, inviting Cartier to the village. Cartier did not see a village and took canada to be the country.

Now back to our regualr aviation programming.

[GregP]

Actually, "colored" is really no longer used. Most perfer to be called "black" for some reason or another (probably has something to do with wanting a racial name that was not invented by White people, but I'm not really sure ... it comes from the 1960s, when nothing racial in the U.S.A. made much sense to anyone). However, everyone will know what you mean if you use "colored."

So ... back to aerodynamics.

One thing to keep in mind about aircraft that show a speed improvement over and above the formulas is that many aircraft showing such drammatic improvements may LOOK externally similar, but probably have extra aerodynamic improvements that account for speed increases beyond the formulas.

A case in point happens when an otherwise similar-looking aircraft is fitted with wing fillets. They have the effect (if properly designed) of reducing interference drag, thus removing a drag component. The wing is the same, the fuselage is the same, everything is the same, but the newly-filleted plane is faster as a result of less drag.

That happened when Roy Lopresti reworked the Globe Swift design a few years ago into a more modern aircraft. He found that relocating the stock wing, adding fillets, eliminating some major cooling drag with proper baffles and sealing of teh cooling airflow, and a host of other "unseen" improvements including eliminating the wing slots made the original design morph from a 150 mph airframe into a 200 mph airframe with only a 33% increase in power. The results were almost entirely due to elimination of form, interference, and cooling drag coupled with a modest power increase.

The same can be said of WWII fighters.

They made a Spitfire that was intended as a world record plane, but the Heinkel He-100 and Messerschmitt Bf-109R raised the world piston speed record beyond what was expected of the special Spitfire, so they turned it into a "Photoreconaissance model."

That particular airframe COULD have been improved a LOT more, but maybe the technology of the times wasn't up to it.

1) The special Spitfire was fitted with a fixed-pitch, wooden airscrew. A metal constant-speed would be been a LOT better

2) The interference drag from the wings was never really looked at and may have been a possible source of drag elimination.

3) The wing thickness ratio could have been changed for a less draggy unit and the wing could have been "profiled" for an exact match to the desired shape.

4) The exhaust stubs were pretty much stock and could alos have been cleaned up quite a bit if desired.

5) The control surfaces could have been gap-sealed.

6) The wing and tail surfaces could have been filleted with better shapes.

7) Fuselage airflow could have been sealed better.

There is more, but the net result could have been a Spitfire that would have taken the record. However there WAS a war on, so maybe they were correct to ignore the speed record at that time.

Just a few thoughts on aerodynamics after the breief departure from WWII aviation above. :)

[Red Admiral]

If i remember a pilot and his fitter went around their Hurricane filing the tops off the rivets. This improved maximum speed by about 20mph iirc. Sealing the planes better would also help quite a lot.

The exhaust stubs varied from mk to mk. The later marks had individual ejector stubs which provided considerable extra thrust, especially at high altitude - one reason not to use a turbocharger.

For speed record attempts, the Napier Heston racer with Sabre engine in late 30s. With a 4000hp Sabre VII its hard to imagine anything going much faster. I think montanaman might have some competition as well, I found a group that are trying to make a full size replica, using some modern materials for strength and light weight. It seems their goal is for 500mph+

http://www.jaapteeuwen.com/ww2aircraft/pictures/jpg/heston-napier%20racer.jpg

[GregP]

No doubt teh Napier Heston was beautiful and had an immense speed capability.

I doubt if the fin and rudder would handle 4,000 hp given the short-coupled design, but you can always throttle up in controlled amounts until you reach the rudder's limit of direction control.

An updated Heston that goes 500 mph would be neat but useless since the world piston speed record is just under 530 mph. They should do a "clean-up" until they can beat the existing record by enough of a margin to take the record back if tey are going to all the effort of building a Heston.

Of course, all that is irrelevant if the intention is to have an exact Heston replica. I was thinking of improving the Heston, but maybe the group in question is not thinking that way at all. If their intent is a replica, I wish them well and hope they install at LEAST some modern avionics. :)

I like the Heston, the Me-109R in both configurations, and the He-100. I think the P-51H, XP-4J, XP-72, the martin-Baker MB-5, and the Australian CAC-15 were faster than all of the above, but they came later when piston speed records were not very interesting to the crowd that was enthralled with new turbojets.

The Germans also had the Dornier Do-335. Even the Me-109K was pretty fast at altitude, but it was a non-starter at low altitudes.

The Tempest had potential, too.

I really believe that a concerted design effort could very well result in an airframe that would go 550 - 560 mph on available piston power, maybe a bit faster. Unfortunately, the last time a large-displacement piston engine was developed was with Government money and it was WWII, so the "new" design would probably have to use a Merlin of some sort, an R-3350, R-4360, or a significantly-developed Allison of sort sort ... unless someone spends a LOT of money to develo a new engine.

Since the economical viability of such a development is obviously not there, we are probably "stuck" with 65-year old engines. There is just no market for a 4,500 hp piston engine with a limited life span and very few sales on the horizon.

On the other hand, Geneal motors markets a very nice Aluminum block auto engine in the Chevrolet Corvette. Making one develop 1,500 hp is not too difficult, and couling three of them together is not an unsurmountable obstacle. The resulting 24-cylinder engine would have decent life span and could be designed so as to use clutches to let any eninges making power contribute to the drive, rendering failure of one engine a non-event.

Such a power train could be developed for a "reasonable" amount of money if there were an airframe available to take advantage of it. The only thing needed is the desire to do it, the funding, and the aerdoynamicists and engine people to get it done.

I'd estimate it could be done for several million dollars and that, while a lot of money, is not entirely out of line for the result.

I'd say the possibility is definitely there. As for the airframe, I'd hire Burt Rutan's Scaled Composites to do it, and maybe John Roncz for the wing. The engines could be developed by many small companies that ALREADY do high-powered Corvette engines.

A company called Ross can develop reduction gears and the clutch system, and there are several propeller possibilities. The avioncs can be normal commercial stuff, and I'd stress the airframe for ±10 g. The wing might well wind up swept, probably not more than 35° or so ... maybe less.

The all-up weight wouild probably not be more than 9000 pounds or so in a record-ready condition. The only real obstacle is the desire to own the world absolute speed record for piston-powered aircraft and the team to get it done.

Maybe speed has lost some of its allure over the years, but Lyle Shelton's Rare Bear, the current world speed record holder, is flying at more than 60 knots over the design speed of the wing! Beating his airplane would not be EASY, but it certainly possible since teh Bearcat was never the fastest thing around anyway.

Of course, Lyle's Bearcat ain't exactly "stock." :)

[Lightning]

Hi All,

I think that, speed-wise, the piston-engined fighter planes of WWII (and shortly thereafter) were at about the practical limit for aircraft used in their roles.

To have made them very much faster, speed would have been of such high priority of design that all other capabilities required of the fighters of that era would have been seriously compromised. In order to achieve level speeds in excess of 500 mph, airframes/wings, engines, and propellors would have had to have been specialized to the point where range, payload, ceiling, climb/dive ability, and maneuverability would have been seriously degraded.

There are always trade-offs when one specification takes priority over all others. The great fighters of WWII were, in my opinion, the pinnacle of compromise between the capabilities required of them.

Greg mentions "Rare Bear" as being the fastest piston-engined airplane but correctly cites the fact that it is not a stock F8F. Can anyone imagine "The Bear" maintaining that title if it were fitted out with the combat-required equipment of a WWII fighter?

A more practical example is the Goodyear F2G (Super) Corsair. In order to combat the growing threat of Japanese "Kamikaze" attacks, the Corsair was adapted as a high-speed, low-level interceptor. The resulting F2G was optimized for these performance characteristics at the expense of those which made the the standard Corsair such a great overall fighter. The F2G was beautifully suited to its specific role, but it was not the great fighter that the F4U/FG1 was.

Regards,
Lightning

[Red Admiral]

http://history.nasa.gov/SP-4219/4219-081.jpg

http://history.nasa.gov/SP-4219/Chapter3.html

[GregP]

An interesting chart since I know of no aircraft in WWII that had 2500 HP and weighed 5750 pounds or less.

Not the Spitfire, Hurricane, Mustang, or any OTHER fighters I know of.

Early Spitfires were 5800 pounds, but had only 1030 HP. An XIV weighed 8498 pounds and had 2050 HP.

A Hurricane Mk I was 6600 pounds with the same 1030 Hp as the early Spit. A MK IIB was 7300 pounds with 1280 HP.

A North American P-51D Mustang was 11600 pounds with 1490 HP.

A Messerschmitt Bf 109 E-# was 5520 pounds, but only had 1125 HP. The much later Me-109G-6 was 6950 pounds and had 1475 HP.

The Yakovlev Yak-3 was 5862 pounds and had 1650 HP, and so was closest to the chart figures. It fell short of 2.5 pounds per HP by a considerable ammount.

My take is that the chart is what they may have WANTED, but they coudn't GET there, and likely could NOT have gotten there, especially if the thing actually had armament.

Any comments?

[Red Admiral]

The chart is from one of the NACA researchers who wanted to build a high speed research plane. Predicted speed was about 566mph. It would have used a Rolls-Royce R engine and had 9% chord thickness wings. It was dropped for reasons unknown.

The article goes into more detail and has a diagram of the critcal mach for P-38 wings.

[GregP]

That makes sense. A research aircraft at 5750 pounds and 2500 HP was possible, but there WAS a war on and I doubt funds would have been allocated anywhere unless the aircraft was of such a design such that it might be made into a warplane.

In any case, a Rolls Royce R-engine had a lifespan of about an hour at full throtte, so let's just say the engine supply would have to have been large to get anything useful from thec raft.

[Groggy]

quote:Originally posted by GregP

That makes sense. A research aircraft at 5750 pounds and 2500 HP was possible, but there WAS a war on and I doubt funds would have been allocated anywhere unless the aircraft was of such a design such that it might be made into a warplane.

In any case, a Rolls Royce R-engine had a lifespan of about an hour at full throtte, so let's just say the engine supply would have to have been large to get anything useful from thec raft.


Hi Folks,
Last weekend there was an air display at RAF Waddington near Lincoln.
Several people said afterwards that the best display was put on by the Royal New Zealand Air Force with a very impressive display by a Lockheed Martin Orion doing well over 400+knots on the deck. This must represent just about the practical limit for a prop/airscrew aircraft (+ residual jet thrust). Any one know the out put of the Alison’s?
What 2ndWW aircraft engines could have given or approached such power?
What engines could have given 2000hp+ in 1945?
What is the top speed of the Orion?
On a different tak what was wrong with the NACA in the 2ndWW? They had some very good people but from their reports at the time no real ideas about jets? Why were they kept out of the loop?

[GregP]

The Orion engines are Allison T-56 units and have 4900 hp (3660 kW). I know of no production engines in WWII that had that type of power.

Lycoming made an experimental 36 cylinder radial engine called the XR-7755 that made 5000 HP (3728 kW) at 2600 RPM in 1943. One is in the Smithsonian Museum. But, it never reached production status and was enormous, so the cowling would not have been nearly as aerodynamic as the units on the Orion.

For those who do not know, American radial engines were designated by their displacement in cubic inches. Thus, the XR-7755 dispalced 7755 cubic inches, or 127 liters (litres?), and is the largest aviation piston engine ever made. It consisted of nine 4-cylinder engines mounted to a common crankcase, thus making up the 36 cylinders.

[Mark J]

Hi again Groggy

Thanks for the reminder. I was in the RNZAF for 5 years and was stationed at Whenuapai, the home of our Orions. I got to drive the crews, deliver rations and fuel our 5 planes (then painted white) during that time but sadly never got the chance to fly in one. I remember the occassional airfield 'beat-up' after a successful sub hunting exersice and the low level runs were impressive. The sound delay and four black exhaust trails I'll always have to remind me of my short time at that airbase.

cheers

[Groggy]

quote:Originally posted by Mark J

Hi again Groggy

Thanks for the reminder. I was in the RNZAF for 5 years and was stationed at Whenuapai, the home of our Orions. I got to drive the crews, deliver rations and fuel our 5 planes (then painted white) during that time but sadly never got the chance to fly in one. I remember the occassional airfield 'beat-up' after a successful sub hunting exersice and the low level runs were impressive. The sound delay and four black exhaust trails I'll always have to remind me of my short time at that airbase.

cheers


Hi Mark,

They are still Smoking !!! It seemed to be trade mark for American engines in the Fifties.

Hi GregP,
Many thnks, I am old enough to remember pre service Lockheed Electra talk of about 3,200hp to 3,500hp per Alison. This was lodged in my mind as the base figure for the power.
I should have remembered that the power out was a lot more even when the PV3 first entered service let alone now.
Last night started to dip in to a book on Fedden, There was a photograph of comparisons of the sleeve valve cylinder head for Hercules, Centaurus, and the Projected Orion engine that he was working on before he was Sacked by Bristols in 1942. The Orion would have been a wopper, but not as big as 127 litres.