de Havilland DH88 Comet as a fighter?

[PMN1]

Could the Comet racer have been turned into an effective fighter, change the Gypsey engines to something more powerful, bring the cockpit forward??

[GregP]

Not in any recognizable form. It was basically a twin-einge mail plane designed for two low-power engines. To put something like a pair of merlins in it, the entire airframe would have to be redesigned.

Don't get me wrong, it could have been "scaled up" but, if it had been done, the product would not resemble a Comet ... maybe something more like a Westand Whirlwind. You would certainly want the bubble canopy and addingheavier engines as well as armament would entail a LOT of airframe modifications.

I submit that the Whirlwind WAS essentially a fighter version of the Comet, and the engines they chose were not a success, so the Whirlwind wasn't, either.

[Wuzak]

I believe that de Havilland did propose a military version of the DH88 Comet, but I'm not sure that it was as a fighter.

[kool kitty89]

The version proposed to the RAF (and rejected) was to be a high-speed bomber.

This is an interesting topic, despite how impractical, the Comet certainly looked right for a fighter. (IMO a lot like the Me 262, particularly the 2-seat version)

I'm not sure the Comet's structure would be strong enough to endure the high stresses encountered by most fighters, however I don't know specifically what the Comet's limitations might be.

One note is that the construction of the Comet was not the same as that of the Albatross or Mosquito. The latter two used balsa core birch plywood with monocoque fuselage structures and birch plywood wings while the Comet used a more conventional wood skeliton with spruce plywood skin.

Assuming the fuselage and tail were strong enough (and assuming rearranging the cocpit and fuel tanks was possible), you'd probably need a new wing, better suited to a fighter and strong enough to mount the larger engines, somewhat shorter span (~38 ft seems reasonable) and a broader chord to allow an area of ~210-220 ft^2.
I rather like the idea of a twin Gipsy Twelve/King powered Comet derivative with the engines mounted in the same fassion as on the Albatross.

The comet was a good deal smaller and lighter than an aircraft such as the Whirlwind and I expect such a fighter would be in a similar weight range to the Spitfire, Bf 109 and similar. (5-6,000 lbs loaded)

[Wuzak]

Assuming the fuselage and tail were strong enough (and assuming rearranging the cocpit and fuel tanks was possible), you'd probably need a new wing, better suited to a fighter and strong enough to mount the larger engines, somewhat shorter span (~38 ft seems reasonable) and a broader chord to allow an area of ~210-220 ft^2.
I rather like the idea of a twin Gipsy Twelve/King powered Comet derivative with the engines mounted in the same fassion as on the Albatross.

The comet was a good deal smaller and lighter than an aircraft such as the Whirlwind and I expect such a fighter would be in a similar weight range to the Spitfire, Bf 109 and similar. (5-6,000 lbs loaded)


I can't recall any high powered twins having a span as small as you suggest. The proposed Supermarine Type 327 was to have a span of 40ft, with a wing area of 28.3m² (293ft²). Yes it was a heavier aircraft, but basically equivalent in size and weight to a Typhoon.

The Tairov Ta-1/Ta-3 http://warbirdsforum.com/showthread.php?t=1707&highlight=tairov had a span of 41.5ft, and again was much heavier.

I think the weights you are talking about would be for a plane with smaller, lighter and less powerful engines, so the performance of the plane might not be what was required.

[kool kitty89]

It wouldn't be "high powered" twin as such, but an aircraft arround the same size as the Spitfire, Hurricane, Bf 109, P-36/P-40 etc.

The advantage over the single engined planes is that it will use 2x smaller, less powerful, streamlined, air-cooled engines (Gipsy Twelve) with similar total power (more with further development as a combat engine) to the early Merlin, and the fuselage and nose free to carry the fuel and eamament. (carrying all the fuel in the fuselage will partially offset the loss in rool rate due to outboard engines)

This means the wings don't have to be able to carry fuel, weapons, or landing gear internally, but simly be able to carry the nacelles and cooling air ducts. (main gear retract into rear of nacelles) This means a relatively thin, low drag wing can be used. Alternadively the landing gear could retract into the wing center section under the fuselage. This twin engine layout also facilitates the installation of a tricycle undercarage.

The centerline armament arrangement means much more concentrated fire without the need for synchronisation, as well as the ability to mount weapons that have problems with wing mounting or cannot be synchronized.

THe wooden structure will mean less use of strategic materials, though it also means that the life expectancy of the aircraft will tend to be lower, the airframe less resistant to combat damage (particularly HE shells), and will tend to be more difficult to repare in the feild. (it may also not be suitable to tropical climates due to warping with changine humidity and seperation of glue)


Of course, to remain compeditve the Gipsy Twelve/King would have to be developed further as a combat engine. With more powerful supercharger, possibly with 2-speed gearing (possibly later 2-stage unit) and increased rpm up to ~3,000. Assuming the engine design allowed it this should get power up to ~700-750 hp per engine by the early war period with high-octane fuel and later possibly ~850-900 hp. (assuming cooling is sufficient -which may require improved cooling fin arrangement, though the cooling air arrangemtn was already much better than contemporary air-cooled inlines- the engine should top out at ~1,000 hp by the end of the war) These improvements seem reasonable comparing the contemporary US and German air-cooled inverted V-12's.

The Gipsy Twelve was historically equipped with a single-stage single-speed centrifugal supercharger, and was the first British engine to be used operationally with the De Havilland constant-speed propeller. It produced 525 hp at 2,600 rpm for Take-off. It was mounted with a very streamlined, tight fitting cowling with cooling air intakes in the wing on either side of the engine with the air then duced foreward from behind the engine then over the cylinders and exhaused through an retractible duct below the engine. (this resulted in a mucch more streamlined arrangement than other air cooled inlines and also distributed the cooling air evenly over the cylinders, avoiding the problems of hot rear cylinders often encountered with such engines)

http://upload.wikimedia.org/wikipedia/en/9/94/DH_91_Albatross_-_Fortuna_-_Croydon_Airport_1939.jpg

[Romantic Technofreak]

Kool Kitty tells us that something like the Mosquito would have been possible much earlier. And, in my eyes, the tapered nose of the DH 88 cries for a third engine...;)

Regards, RT

[kool kitty89]

Not necessarily, as I mentioned the structure of the DH.88 was of a conventional wooded skeleton with spruce plywood skin. (as well a a fair amount of fabric used, the final surface over the plywood skin, similar to what was used on the Mossie's wing)

The structure of the mosquito was that pioneered in the Albatross, birch sanwinched balsa-core plywood creating a frameless monocoque fueselage and a birch plywood wing. Extensive use of glue with minimum use of fasteners (the fueselage was constructed of two formed shells glued together and the wing was secured by glue, though some screwas and fasteners were used in the wing structure).

This advanced construction gave very high strength (not aganst bullets/shells mind you) at a significantly reduced weight. The frameless monocoque fuselage significantly increased internal space as well. (important for passengers and for bombload)

So this may not have allowed a Mosquito any sooner.


If you mean the DH.88 derivative as a fast bomber, I'm not entirely sure on what it would have been like, but assuming it was a direct development of the Comet, it would be far smaller than the Mossie, as I mentioned with the fighter concept, more comperable in size to a single engined fighter. (much like comparing series of interwar Hawker biplane bombers to contemporary fighters) Such a design would prabably have an internal bombload of around 500 lbs.


And on the fighter in question, it should be noted that the Gipsy Twelve was somewhat newer than the Merlin, not running until after the Hurricane had flown and was about to enter service.



It should also be noted that neither is such a fighter (compact twin with Gipsy King engines) or a successful fast-bomber like the Mossie limited to wooden construction, wood has particular strategic and economic benefits, but dural has its own, and tends to be better from a maintenance and durability standpoint.
There is no reason that aircraft like the A-20 or Ju 88 wouldn't have been as sucessful as the Mossie as fast-bombers -not to mention other roles- had they been similarly configured. (the Ju 88 in particular had a lot of unneccesary "techno garbage" resulting from RLM's insistance, in addition to the defensive armament and resulting increase in weight drag and crew)

[Ricky]

Interesting idea - a light fighter based on a pre-war racing plane. Mind you, all other attempts at this kind of thing were failures. Still, all the rest were single-engined (I think...)

[kool kitty89]

That's true, and there were also purpose built light weight fighters that failed as well. (also single engined) Many of those racing designs however, were for speed only, such as record breakers, or others that were speed and distance record breakers (like Hughes' planes) but not so much with a load. The Comet was a long range fast mail plane.

Of such high speed mail plane racers, several did see military service, but as fast bombers like the He 70.


Also, I found a nice cut-away drawing of the Comet: http://www.fine-art.com/members/36681/imagesBig/File7465161363.jpg

[GregP]

kool kitty89!

Thanks for the cutaway!

[kool kitty89]

Threre are a lot of nice aircraft cut-aways done by that artist: http://dart.fine-art.com/aqd-asp-intPage_1-F_Hubert-L_CANCE-buy-sQuery.htm

[GregP]

Thanks, Kool Kitty! Great link!

[Ricky]

After looking at that cutaway, they'd really have to do some internal moving-about to make it useful. Remove at least one of the fuel tanks to fit any guns, and ideally swap the remaining fuel tank and pilot around. But then you'd have to re-jig the centre of gravity, etc...