Rear-Engine Pusher Fighter?
- Thread starter gjs238
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wuzak
Captain
The McDonnell Model 1 was designed around the R-40C competition that gave us the XP-54, XP-55 and XP-56 (as well as the Bell XP-52/59). It had a fuselage mounted engine (P&W X-1800, Wright R-2160 or Allison V-3420) driving a pair of wing mounted pusher props via right angle drives and extension safts. It wasn't selected for further development, but got the USAAF interested enough to get McDonnell to design Model 2, which became the XP-67.
P-39 Expert
Non-Expert
Always thought that a single engined pusher was the ultimate WWII fighter.
I would have used a radial like the P-56 with a cooling fan. These were already used in tanks powered by radial engines so they weren't new. Simplicity of the radial with the aerodynamics and reduced frontal area of an inline. Tricycle gear, heavy nose armament, pilot out front for better visibility, big fuel tank in fuselage over the CG. No propwash to fly through. Flying wing, canard or twin boom tail, it could have been done and would have been very efficient.
I would have used a radial like the P-56 with a cooling fan. These were already used in tanks powered by radial engines so they weren't new. Simplicity of the radial with the aerodynamics and reduced frontal area of an inline. Tricycle gear, heavy nose armament, pilot out front for better visibility, big fuel tank in fuselage over the CG. No propwash to fly through. Flying wing, canard or twin boom tail, it could have been done and would have been very efficient.
Shortround6
Major General
Tanks don't fly at 20,000ft.
The mass airflow of a tank doesn't change much with speed and the mass airflow stays pretty constant as tanks don't often operated at high altitudes (number of tank battles in the Alps?)
I would also note that even the radial tank engines used 80 octane fuel and used either very little or no supercharging so they were making much less power per cylinder. Which reduces the cooling load.
Fan cooling could be done but tank engine installations were hardly a good pattern to follow.
The mass airflow of a tank doesn't change much with speed and the mass airflow stays pretty constant as tanks don't often operated at high altitudes (number of tank battles in the Alps?)
I would also note that even the radial tank engines used 80 octane fuel and used either very little or no supercharging so they were making much less power per cylinder. Which reduces the cooling load.
Fan cooling could be done but tank engine installations were hardly a good pattern to follow.
wuzak
Captain
The frontal area will not be reduced to that of a in-line powered fighter.
The XP-56 was a fat turd that was about 80-100mph slower than a similarly powered F4U, and 30-50mph slower than an F6F, itself no slim beauty.
Sticking a large diameter radial in the middle of an aircraft is probably not the cleverest thing to do....
wuzak
Captain
Of the three XP projects that flew, the XP-55 was closest to its "guaranteed" performance, being around 30-40mph slower than estimated. It was, in fact, about the same speed as a similarly powered contemporary P-40. Climb rate was not as good, IIRC.
The XP-54 was the only one of the three to crack the 400mph barrier, albeit with special paint, filled gaps and hand polished finish. STill, that was 100mph slower than the original estimate, and some 70-80mph slower than later estimates.
It suffered from being bigger than a P-38, with less power from an experimental engine that was going nowhere, and was 2,500lb more than the P-38 for empty weight. Climb rate was found to be similar to a laden bomber....
The XP-54's weight nearly doubled from the original proposal.
The XP-56's top speed was estimated by NACA as 340mph after extrapolating test data.
The XP-54 was the only one of the three to crack the 400mph barrier, albeit with special paint, filled gaps and hand polished finish. STill, that was 100mph slower than the original estimate, and some 70-80mph slower than later estimates.
It suffered from being bigger than a P-38, with less power from an experimental engine that was going nowhere, and was 2,500lb more than the P-38 for empty weight. Climb rate was found to be similar to a laden bomber....
The XP-54's weight nearly doubled from the original proposal.
The XP-56's top speed was estimated by NACA as 340mph after extrapolating test data.
P-39 Expert
Non-Expert
Just an example showing that cooling fans were in use. The P-55 and P-56 used cooling fans.
P-39 Expert
Non-Expert
Depending on the inline fighter the frontal area could have been very close.
My example uses a radial in the rear, not the middle.
wuzak
Captain
swampyankee
Chief Master Sergeant
- 4,031
- Jun 25, 2013
Frontal area, per se, is not that important; wetted area and avoidance of separation are. Rear-engine pushers have a number of disadvantages, which have combined to keep it a rare configuration for prop aircraft.
- If the prop is at the extreme rear, the possibility prop strikes on takeoff and landing has to be designed for. This means either longer landing gear or restrictions on rotation angle. The former increases weight, while the latter increases runway.
- The engine is a big, heavy lump, the position of which dictates the location of the wing. This, in turn dictates the area of the tail surfaces.
- Tailless aircraft, like the XP-56, run into the problem of limited pitch authority, which largely precludes flaps, and the elevators' decambering the wing, which reduces lift at a given angle pf attack. These drive up runway requirements. Flying wings also tend to have poor pitch damping, which is one of the issues that killed the B-49.
- It's nice to be able to see behind, but if the engine is behind the pilot, the largest fuselage section will be, too.
P-39 Expert
Non-Expert
Not really, eliminates the driveshaft and frees up the middle area for a large fuel tank.
wuzak
Captain
I was speaking aerodynamically.
Testing by NACA showed some loss of propeller efficiency when fitted to a big radial than for an inline, due to the greater blockage.
I imagine that having a blockage directly in front of a prop would not be great for its efficiency.
wuzak
Captain
The XP-54 did not have the prop at the extreme tail, but used the lower tails on the ends of the booms to prevent prop strikes, which obviously limited rotation.
Looking at the side view:
It seems possible that the Vultee deigners could have placed the main landing gear in the booms, near to or level with the prop, folding forward into the front of the boom/wing.
That would have eliminated the need for the lower fins and allowed for greater rotation.
And hopefully have reduced the very long take-off run.
The XP-55 didn't have any sort of protection from over-rotation and prop strike.
The placement of the wing precluded having the main gear any further back.
With its lower fin, the XP-56 didn't allow much rotation at all.
buffnut453
Captain
One of the last original designs by Brewster Aero Corp before it went under was for a twin-boom naval fighter:
Not sure how those booms would have stood up to arrestor landings, but it's an interesting concept.
Not sure how those booms would have stood up to arrestor landings, but it's an interesting concept.
