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Okay, think I get NACA's idea now
An issue of how would anyone succeed to mount intercooler there, is a new ball game.
While 2 cannons 4 HMGs as a SE fighter armament do sound like a good idea, the proposal has some shortcomings IMO. Ammo count, for example - we can stick to, say 100-120 shells or 250-300 HMG rounds per barrel. That way our SE fighter lugs around about same armament ammo weight as P-38, P-47, Typhoon, Tempest. Nice if one has at least 2000 HP on board, not that nice if there is only 1200 HP. Or, we can reduce the ammo count to save weight - US pilots would've hated us, and the weight of armament is still there.
We can delete a pair of HMGs, and the armament ammo weight is like at P-51D, Hellcat, Corsair - but our plane still lacks 300-400 HP if we want it to be competitive.
There are other minor things to consider, like need to purchase another 10000 cannons from UK, 3 guns (= cannon + 2 guns) are easier to install maintain than 6, less drag (3 openings less), single gun heater can heat all armament, almost no impact to accuracy if one gun jams, central battery is not susceptible to wing flex, less inertia - better roll...
My proposal cuts weight (P-39 was able to out-climb any contemporary US single-engined fighter anyway), while enabling all 3 guns to be fired simultaneously (similar bullet paths).
Sufficient indeed.
The minor issue would've been the change of CoG.
5 HMGs with at least 200 rpg yields 300 lbs to be expanded some 2-3 ft away from CoG, vs. 180 lbs that real P-39s had for 37mm 2 HMGs. It's 210 lbs for belt fed Hisso (120 rds) + HMGs.
I had to laugh when I thought of the aerodynamics of the the late 60s early 70s cars. While I love those cars and I still think they are some of the best looking cars ever (I had a 71 Cutlass S), I suspect there is turbulent airflow all over the place. All aerodynamic theories go out the door, Olds with the inlet closer to clean, laminar flow would be best. Chevy had all the turbulent airflow pile up at where the hood meets the windshield, which is also where cars took air in for the air vents since the mid 50s. The hood definitely had low pressure, and also boundary layer issues (low). If they had stuck up like a supercharged engine, it would probably had worked.Air flow can be a funny thing. back in the late 60s General Motors had a number of divisions competing with various "super" cars. Mid sized cars (for the time) with big engines and every one had a "ram" air option of some sort. Pontiac and Buick has two small 'scoops' about half way out the hood. Chevrolet had a rear facing trap door inlet at the base of the windshield. Oldsmobile had two BIG scoops (14 in X 2in If memory serves) under the front bumper. The Oldsmobile set up worked best (biggest scoops and in a high pressure area) the Chevrolet worked next best, the base of the wind shield being a high pressure area. Pontiac setup worked hardly at all while the Buick 'scoops" being very low and in the middle of the hood were actually in a low pressure area and sucked air out from under the hood/intake area. granted these are at much less than aircraft speeds but the air flow along a fuselage is not constant.
If the airflow is laminar, there should be no problem. However, the airflow could be perturbed by gaps and protrusions and possibly by stall caused by the cockpit, all causing turbulent airflow. I suspect stall would not be problem at the low speed it would occur. I am sure Bell understood this and tested the inlet for the conditions needed. They did appear to have a raised the inlet out of the boundary layer conditions, surprisingly, something Lockheed failed to do on the XP-80. The P-63, which updated issues with the P-39, appears to have a similar inlet, so apparently they uncovered no problems with this particular design.I would think that putting the intake behind the canopy has got to affect the airflow into it somewhat.
Not exactly, metallurgy for impellers that can cope with more than 30,000rpm inside a hot exhaust pipe are still experimental in 1940, the issue is technological and/or industrial limitations and not a failure to come up with ideas to solve problems, no shortage of ideas ever because everybody wants to be king of the world.We want a Army fighter aircraft that works right now. (i.e. around 1940)
1. Turborchargers are still experimental for fighter aircraft during 1940.
The Allison is a better engine than the Merlin from the F-series. The blower sizing was a doctrinal influence and not a technological one, and Allison performance under 11,000 feet is exactly the same as a low alt Merlin right down to the +15lbs two-minute WER. At this particular point the two engines are pretty much identical but the Allison is better built and tolerates lower fuel grades better. The medium alt Merlin is an interceptor engine and pursuit engines aren't interceptor engines, a Merlin 60-series should be compared with the P-38 turbocharged allisons and in this case the multiple stage blower is more reliable, but doesn't have the same development potential. When Packard started making Merlins a RR engineer toured the factory and decided to implement new bearing compositions and machining that Packard was doing with their Merlin 25, it was introduced into all British RR Merlin production because they improved the engine.2. The Allison engine is a dog at all but low altitude.
State of the art in 1936 mate. In 1941 state of the art is complicated multistage, multiple speed blowers, including your turbos.3. The RR Merlin engine is state of the art and arrangements are already being made for mass production in the USA. Britain is investing heavily into further performance improvments for this engine.
It might be interesting to put turbo Allisons in a Lanc but why would you put Merlin-25s in the P-39? You'd be better off putting a contemporary two-stage F7R or E9 motor, either will handle plenty of overboost easily and I see no problem with these motors.Seems like a no brainer to me. Pay Packard to expand production capacity so they can produce RR Merlins for the P-39 as well as for the Lancaster bomber.
I think the P-39 made the best of a bad situation. Stick the air intake up behind the canopy and take what you can get or try sticking it out to the side and then looping it up and over in the down draft carburetor (which might have more drag than the behind the canopy intake) or get really tricky and try to duct the intake air from the wing roots or nose past the pilot and engine.
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I think the P-39 made the best of a bad situation. Stick the air intake up behind the canopy and take what you can get or try sticking it out to the side and then looping it up and over in the down draft carburetor (which might have more drag than the behind the canopy intake) or get really tricky and try to duct the intake air from the wing roots or nose past the pilot and engine.
If the difference here is in the ram air design, I suspect the difference is in the ducting. The P-40 duct appears quite straight and long before it enters the turn to the carburetor. While this may increase friction loss, the divergent compression may be more efficient. The P-39 duct is short with a quick turn to the carburetor. This may cause losses. Also, duct design is complex and sophisticated aerodynamics which may have been in its infancy at this time, which could caused losses. It is really complex for supersonic airflow. The advent of stealth and the need for hidden engines and heat suppressed exhaust has driven ducting to an entirely new level of design.If essentially the same engine installed in a P-39 gives a different (lower) FTH than the when installed in a P-40 under ram conditions there has to be an explanation somewhere. If both planes are going roughly the same speed (with in a few %) then one is doing a better job of managing the intake air (RAM) than the other.