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Hawk 75 with Grumman F6F style engine


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#31 bearoutwest

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Posted 11 February 2018 - 05:03 AM

So following Shadow-Greg's PW R-2000 suggestion, and Shadow-Jeff's encouragement, I have cobbled together some Hawk 87A-R2000 sketches and calculations.
(See linked sketch for reference: https://www.flickr.c...posted-public/ )

Engine dry weight comparison:
Allison V-1710-81,  1,352-lb
Packard V-1650,     1,640-lb
PW R-2800,          2,340-lb
PW R-2000,          1,585-lb

So dry weight of R-2000 is about 55-lb lighter than the Packard-Merlin, and about 230-lb heavier than the Allison.

In the attached sketch, I have used the DHC-4 Caribou engine cowl, but turned upside down, with the air inlet on the chin side.  This keeps the pilot eye-line clear over the top of the cowl.... and I quite like the looks of the chin-mounted intake scoop.  I have moved the R-2000 closer to the firewall than the R-2800 location, but left some extra room to accommodate a - possibly - larger supercharger.  This results in the approximate engine CG at 4-ft 9.2-in forward of the assumed 40% chord Centre of Lift.  Remember that the assumed CG for both the Allison and Packard-Merlin was at 5-ft forward of 40% chord; compared with the R-2800 CG at 5-ft 8-in forward of 40% chord.

This roughly equates to the R-2000 being able to be used on the P-40M airframe with very little ballast weight near the tail.

I have very little detail as to what the cooling air requirements were for the Caribou, so have kept the engine nacelle as-is for now.  The red-lines are my interpretation of streamline possibilities from nacelle back to fuselage aft of the firewall.  Thrust line of the R-2000 (as drawn) is about 6.5-in below that of the V-1710, but about the same higher than assumed for the R-2800.  We know the Hawk 75 had been tested with 4-bladed props, so that was a possible get-out-of-jail-card for ground clearance issues.

R-2000 prototyped circa 1940.  Development of R-2000 was delayed as R-2800 seemed more useful and thus higher priority.  I guess, had there been a real requirement, R-2000 could have been developed faster at a shadow factory with minimal delay to the R-2800.

So what do you think of the Hawk 87A-R2000?

...geoff

 

 

....more fun later:
I found some cool drawings of the Hawk 81A-P&W Sp on the internet.
(Ref: http://www.wunderwaf.../52/Draw/18.jpg )
Taking the drawing on the front cover of the Pratt & Whitney R-2000-24 Maintenance Manual, I have approximated the scale based on the R-2000 diameter of 1.247m.

Cobbled together comparison sketch is also in the flikr-page linked above.  It's the Hawk 81A-R2000_a2 sketch with plan and elevation.

The R-2000 seems to fit vertically into the allocated space for the R-1830, though internally, some modification to the air intake ducting may be required.  Engine thrust line seems to be maintained as per the R-1830 without problem.

In the plan view, I don't have an equivalent plan sketch of the R-2000, so I have taken the engine diameter from the side-elevation and replicated it in the vertical view.  It seems to fit - just - into the relative location, though it's a tight fit on the drawing.  If the scaling of the various components is correct, then the sides of the Hawk 81A-PW-Sp may need widening or perhaps local cylinder "bumps" as per the Macchi C.200.

Still, seems a reasonable fit of engine into airframe.  Probably stay with the Hawk 81 unlengthened fuselage (as seen here) for a more balanced look.
 


Edited by bearoutwest, 11 February 2018 - 07:50 AM.


#32 Rick65

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Posted 11 February 2018 - 07:52 AM

Given the R-2000 is basically a bored out R-1830 with some design changes fitting it to a P-36/40 air frame should be easy as the Y1P-36 (Model 75E) first flew with a R-1830 in 1937. Wiki quotes an over 300lb weight difference between a R-1830 and a R-2000 but it may be that they were not measuring comparable configurations/ancillaries etc. Maybe we need to consider a P&W R-2000-SSC7-G ie a R-2000 with a two stage supercharger in a similar cowl to NX28990. Should look the same and be slightly faster than NX28990.

#33 Ricky

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Posted 11 February 2018 - 10:52 AM

In your sketch it almost looks like the rear fuselage needs shortening!

#34 bearoutwest

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Posted 11 February 2018 - 11:25 AM

In the 1st sketch with the P-40M as a base, and the Caribou engine nacelle....yes, looks too long a tail.

 

The second sketch, based on the Hawk 81A-PW-Special drawing (plan and elevation), the tail is the short P-40B/C (Tomahawk, Hawk 81A) type, and looks much more balanced.  (By eye anyhow.)  See my comments edited above.


Edited by bearoutwest, 11 February 2018 - 11:26 AM.





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