Hopefully we can get back to the original topic of the Airacobra versus German (or other contemporary) fighters.
Here is how I would characterize the Airacobra:
It was a very slick aircraft aerodynamically at least for profile drag.
There were no protruding radiators though it did have a small belly bump.
Its choice of airfoil probably hurt its maneuverability to some extent.
(Root: NACA 0015, Tip: NACA 23009)
The symmetrical airfoil tends to have a lower than typical Coefficient of Lift (about 1.3) but the NACA 23000 series airfoil at the tip is a bit higher lift and one of the more common airfoils used in fighters of this era.
NACA Report L-602 - Flying Qualities of P-39D-1 states that max CL is about 1.4.
This is in contrast to the stall speeds listed in Operating Manual for P-39Q-1:
(105 MPH Clean, 90 MPH Flaps Down)
With a stall speed of 105 MPH, even at a weight of 7800 pounds which is about what it would weigh with full fuel and ammunition but no external stores, the calculated CL is only about 1.30.
Perhaps there are a couple MPH in rounding errors?
As Shortround6 pointed out in another thread, the Mid-engine arrangement cost some extra weight in the Airacobra because of additional strength needed between the engine and propeller. There was probably a bit more than that for the separate oil reservoir and pumps needed for the remote reduction gear behind the propeller.
The Tricycle gear made for great ground handling and visibility and easy take-offs and landings, but also cost some extra weight about what a smaller tail wheel might have cost.
The hidden radiators and oil coolers were good from a drag standpoint but not so good from a cooling standpoint.
The Airacobra would tend to overheat in prolonged ground running or in hot climates.
In flight tests, it also had a tendency to overheat.
In the air, there was the CoG movement issue which actually seemed to be more a result of firing off the ammunition for the .50 Cal Cowl Guns than the Cannon ammunition. This has already been discussed at length.
Apparently it was possible to make the Airacobra "Tumble" by flying vertically until airspeed dropped to zero and with proper control inputs, but it was a fairly violent maneuver even if it was planned (from Pilot accounts found in Crowood book about P-39).
Other handling characteristics were a very sensitive Elevator (from NACA L-602) and a rather mediocre roll rate which was about 85 degrees / second max. Perhaps the Russians were able to increase this a bit by deleting the wing guns.
Stall characteristics were very good with a tendency to mush at the stall and the wing tips stalled last for good lateral control.
Speed of a late model Airacobra (P-39Q) was quite good. With the Wing Gun Pods removed, it was probably very close to a 400 MPH aircraft.
Thoughts?
- Ivan.