Circular Proposal X-609 (February 1937): Mid-engine response
- Thread starter gjs238
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swampyankee
Chief Master Sergeant
- 3,954
- Jun 25, 2013
The layout is clearly feasible -- witness, among other aircraft, the P-39. It's just that there's no particular advantage to it.
Shortround6
Major General
It may depend on what you are willing to give up to get it.
The Circular Proposal X-609 may have been a bit unrealistic to begin with. One web site (which could be wrong) says one of the requirements was 1000lbs of armament. Now this may include gun mounts, local reinforcing, ammo boxes/chutes, heaters and gun charging systems in addition to the weight of the guns and ammo. A MK IX Spitfire (or MK Vc) carried about 650lbs worth of guns and ammo leaving 350lbs for "extras" before it hit the 1000lb mark and both had a lot more than 1150 hp available.
Bell figured the drive-shaft was worth about 50lbs and the extra stiffing of the fuselage to keep the prop in line was worth about 50lbs so the P-39 arrangement was about 100lbs heavier than a regular airplane with a nose mounted engine.
The 100lbs may not be much of a penalty IF everything else goes right. But it didn't for the P-39.
The Circular Proposal X-609 may have been a bit unrealistic to begin with. One web site (which could be wrong) says one of the requirements was 1000lbs of armament. Now this may include gun mounts, local reinforcing, ammo boxes/chutes, heaters and gun charging systems in addition to the weight of the guns and ammo. A MK IX Spitfire (or MK Vc) carried about 650lbs worth of guns and ammo leaving 350lbs for "extras" before it hit the 1000lb mark and both had a lot more than 1150 hp available.
Bell figured the drive-shaft was worth about 50lbs and the extra stiffing of the fuselage to keep the prop in line was worth about 50lbs so the P-39 arrangement was about 100lbs heavier than a regular airplane with a nose mounted engine.
The 100lbs may not be much of a penalty IF everything else goes right. But it didn't for the P-39.
GregP
Major
Once they removed the turbocharger, the P-39 was consigned to middle and low altitudes, where it did just fine, performance-wise.
I have always liked the P-63, especially the one with the auxiliary supercharger ... we just never did get very many. Since the life of piston fighters was winding down anyway as we rushed into jets, maybe it's just as well.
The Arsenal VB-19 looks interesting but was a 1947 aircraft. The Bolkhovitinov Sparka looks interesting but isn't really mid-engine ... it is a tandem engine unit. The General Motors XP-75, the last one, looks good but was not selected for production. I like the Heinkel He-119, but they didn't elect to produce that one either. The Sud Ouest SO.8000 LOOKS like a mid engine with a driveshaft, but I think it is just a mid engine with the engine turned around and the prop in the middle of the plane, using booms for the tail, just like the Vultee P-54. Not a true driveshaft. The Vought XF5U-1 WAS a true driveshaft, but they never FLEW it even though it was finished and ready for flight! A truly idiotic decision, if ever I saw one. The Yokosuka R2Y is a true driveshaft but they only built and flew one before the war ended.
Of all of these, only the Bell P-39 and P-63 were anything like "mass-produced," and I wonder how it would have fared if the development of the turbo version had been allowed to continue. Surely it could not have done worse than the non-turbo version.
I have always liked the P-63, especially the one with the auxiliary supercharger ... we just never did get very many. Since the life of piston fighters was winding down anyway as we rushed into jets, maybe it's just as well.
The Arsenal VB-19 looks interesting but was a 1947 aircraft. The Bolkhovitinov Sparka looks interesting but isn't really mid-engine ... it is a tandem engine unit. The General Motors XP-75, the last one, looks good but was not selected for production. I like the Heinkel He-119, but they didn't elect to produce that one either. The Sud Ouest SO.8000 LOOKS like a mid engine with a driveshaft, but I think it is just a mid engine with the engine turned around and the prop in the middle of the plane, using booms for the tail, just like the Vultee P-54. Not a true driveshaft. The Vought XF5U-1 WAS a true driveshaft, but they never FLEW it even though it was finished and ready for flight! A truly idiotic decision, if ever I saw one. The Yokosuka R2Y is a true driveshaft but they only built and flew one before the war ended.
Of all of these, only the Bell P-39 and P-63 were anything like "mass-produced," and I wonder how it would have fared if the development of the turbo version had been allowed to continue. Surely it could not have done worse than the non-turbo version.
You could have easily gotten that 100 lbs back by doing away with the tricycle undercarriage configuration.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Or omit the nose-cannon
Shortround6
Major General
The P-39 had a number of problems that interrelate. Problems that might be shared with other mid-engine designs.
With the engine close to the center of gravity for and aft loading got a little dicey. Plane was not supposed to flown with out ammo for nose guns unless ballast was carried. It may not have been the only plane with such a restriction but running light in the nose aggravated it's tendency to stall and spin. Pulling the 37mm and putting in another .50 cal would have saved a lot of weight but not if you had to pack in a good part of the difference in ballast.
With the engine and pilot taking up the majority of the room in the fuselage you need some were to stick the fuel that is near the CG. The P-39 picked the wing rather than the fuselage belly. It might have worked except that the requirement to go to self sealing fuel cells screwed things up. Long thin fuel tanks loose a bigger percentage of their volume to the self sealing set up the US used than short fat tanks. P-39 fuel capacity dropped to 120 US gal from the Prototypes 200 gal and YP-39/P-39Cs 170 gallons. The Fuselage belly was full of radiators and oil cooler. Originally they had been in the wing roots but the air ducts were too restricted by the wheel wells leading to poor cooling. The Airabonita stuck the radiators in under wing ducts a bit like the Spitfire only flatter and wider. Airabonita was also slow.
P-63 got around some of this by A, using a two foot longer fuselage and changing the location of the engine and center of gravity, getting rid of the spin/stall problem ( or at least reducing it to less than most other fighters) B. Using a new wing with a different airfoil (thicker over a larger portion of the cord), different wing construction, 4 more feet of wing span and and 35 sq ft more wing area, but even this only added a few gallons to the fuel capacity.
Any mid engine fighter is going to face some of the same problems. Engine sitting near the center of gravity taking up volume wanted for consumables. It depends on what you want the plane to do. Short range interceptor and you can fit the fuel needed.
With the engine close to the center of gravity for and aft loading got a little dicey. Plane was not supposed to flown with out ammo for nose guns unless ballast was carried. It may not have been the only plane with such a restriction but running light in the nose aggravated it's tendency to stall and spin. Pulling the 37mm and putting in another .50 cal would have saved a lot of weight but not if you had to pack in a good part of the difference in ballast.
With the engine and pilot taking up the majority of the room in the fuselage you need some were to stick the fuel that is near the CG. The P-39 picked the wing rather than the fuselage belly. It might have worked except that the requirement to go to self sealing fuel cells screwed things up. Long thin fuel tanks loose a bigger percentage of their volume to the self sealing set up the US used than short fat tanks. P-39 fuel capacity dropped to 120 US gal from the Prototypes 200 gal and YP-39/P-39Cs 170 gallons. The Fuselage belly was full of radiators and oil cooler. Originally they had been in the wing roots but the air ducts were too restricted by the wheel wells leading to poor cooling. The Airabonita stuck the radiators in under wing ducts a bit like the Spitfire only flatter and wider. Airabonita was also slow.
P-63 got around some of this by A, using a two foot longer fuselage and changing the location of the engine and center of gravity, getting rid of the spin/stall problem ( or at least reducing it to less than most other fighters) B. Using a new wing with a different airfoil (thicker over a larger portion of the cord), different wing construction, 4 more feet of wing span and and 35 sq ft more wing area, but even this only added a few gallons to the fuel capacity.
Any mid engine fighter is going to face some of the same problems. Engine sitting near the center of gravity taking up volume wanted for consumables. It depends on what you want the plane to do. Short range interceptor and you can fit the fuel needed.
wuzak
Captain
Wasn't part of the problem the cannon firing through the hub?
If that wasn't a requirement (or was it a design feature) the pilot's compartment could have been moved further forward, as could the engine (if so desired) freeing up space for a fuel tank in the fuselage on or near the centre of gravity.
If that wasn't a requirement (or was it a design feature) the pilot's compartment could have been moved further forward, as could the engine (if so desired) freeing up space for a fuel tank in the fuselage on or near the centre of gravity.
wuzak
Captain
I'm thinking like the Rolls-Royce Flying Test Bed, based on the Mustang airframe.
GregP
Major
Don't think it was a problem except for the cannon chosen. It was a feature that was very desirable. Perhaps if they's chosen a shorter cannon, the same could have been done.
Perhaps not.
If they HAD deleted the cannon, they certainly could have moved everything forward in the design stage. Once in production, the chances were remote indeed for a complete retooling of the line.
The drawing above shows the engine being inside the cockpit. Think of where the exhaust stacks are on a Merlin and go from there. Glad they never tried to really build and fly it. It would have been horrendously loud in the cockpit only inches from the Griffon!
Perhaps not.
If they HAD deleted the cannon, they certainly could have moved everything forward in the design stage. Once in production, the chances were remote indeed for a complete retooling of the line.
The drawing above shows the engine being inside the cockpit. Think of where the exhaust stacks are on a Merlin and go from there. Glad they never tried to really build and fly it. It would have been horrendously loud in the cockpit only inches from the Griffon!
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wuzak
Captain
The P-75 is also an example with the cockpit pushed forwards
The Rolls-Royce Flying Test Bed mockup
I can't find a better angle, unfortunately.
The Rolls-Royce Flying Test Bed mockup
I can't find a better angle, unfortunately.
GregP
Major
It's a good enough angle and I've seen the models. The P-75 is a big beast and the exhaust location shows enough room for a real cockpit, which is good since they made it and flew it. I'm glad they didn't buy it!
I've seen a video of a flight demonstration ina Bell P-63 and I must say the noise from the driveshaft bearings and U-joints is considerable. After hearing that I'm not sure I'd want to be in one for a couple of hours. Maybe when I was much younger ... and if I had some Bose noise-canceling headsets.
I've seen a video of a flight demonstration ina Bell P-63 and I must say the noise from the driveshaft bearings and U-joints is considerable. After hearing that I'm not sure I'd want to be in one for a couple of hours. Maybe when I was much younger ... and if I had some Bose noise-canceling headsets.
wuzak
Captain
The Rolls-Royce FTB used a torque tube between the engine and reduction gear. I wonder if that would have made much difference to the noise?
GregP
Major
Sounded to me like bearing noise in the video of the P-63. I could be wrong ...
Not sure what ELSE it could be, shafts don't make any noise when they spin. Could have been gear noise but I competed on off-road motorcycles, track bikes, and boats, and I know what gear noise sounds like, particularly square-cut gears.
Didn't sound like V-drive gears, sounded like bearings. Maybe that's all they needed ... new bearings.
Can't say for sure as I don't fly warbirds. If you think boats are expensive, try warbirds!
Not sure what ELSE it could be, shafts don't make any noise when they spin. Could have been gear noise but I competed on off-road motorcycles, track bikes, and boats, and I know what gear noise sounds like, particularly square-cut gears.
Didn't sound like V-drive gears, sounded like bearings. Maybe that's all they needed ... new bearings.
Can't say for sure as I don't fly warbirds. If you think boats are expensive, try warbirds!
- Thread starter
- #15
This seems to be the biggest issue with the layout.
Seems best to reserve that CG space for fuel, ammo, oil, etc.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
A mid-engined plane certainly was considered by many aircraft designers at one time or another, but the design presented more problems than benefits.
One of the problems with having the engine set back in the fuselage, was over-heating issues. While some designs were able to overcome that situation, others were plagued by it (including the Yokosuka R2Y). Even the Do335's rear engine cooling was problematic.
Another problem was accessibility. Performing maintenance on a mid-engined aircraft was reported to be a complex chore compared to traditional, nose-mounted powerplant.
Here's a proposed mid-engined aircraft by Messerschmitt. It was intended to use parts from the Me309 project, such as tail components, landing gear, etc. However, if they had pursued the development, I imagine there would have been alot of bugs to be worked out and in the end, the effort wouldn't have given much in the way of advantage over more conventional types already in service.
One of the problems with having the engine set back in the fuselage, was over-heating issues. While some designs were able to overcome that situation, others were plagued by it (including the Yokosuka R2Y). Even the Do335's rear engine cooling was problematic.
Another problem was accessibility. Performing maintenance on a mid-engined aircraft was reported to be a complex chore compared to traditional, nose-mounted powerplant.
Here's a proposed mid-engined aircraft by Messerschmitt. It was intended to use parts from the Me309 project, such as tail components, landing gear, etc. However, if they had pursued the development, I imagine there would have been alot of bugs to be worked out and in the end, the effort wouldn't have given much in the way of advantage over more conventional types already in service.
Aside from those mentioned by Dave, another problem with the likes of the Fisher P-75 was that it's a monster of an aeroplane; I've stood next to the one at the USAF Museum; it's huge. The Rolls Royce FTB would have been a respectable size, but it was powered by a Griffon. The P-39 compares with other fighters of its generation in terms of size and engine power output. It was designed pre-war, after all. For a pre-war specification, you can't go too far wrong with a conventional tail dragger layout. There's no need to over complicate things if there is no obvious benefits to the aircraft's performance with the incorporation of such things.
- Thread starter
- #18
Two thoughts:
1) Could the cockpit and engine be located forward aft of CoG to leave all or most of the CoG space available for consumables?
2) A far forward cockpit would provide excellent visibility for carrier operations and less obstructed view for air to air gunnery.
1) Could the cockpit and engine be located forward aft of CoG to leave all or most of the CoG space available for consumables?
2) A far forward cockpit would provide excellent visibility for carrier operations and less obstructed view for air to air gunnery.
