Performance of the Fw 190A on the Deck?

[drgondog]

Originally Posted by Franek Grabowski

Bill, it is obvious that P-51B/C was aerodynamically slightly different than D/K. I cannot say for sure, but I suppose there might have been some other slight differrencies, eg. in props. That said, drop of maximum speed was the result of several minor changes, and not only one factor. Still, 10 mph is within marigin for error and may purely depend on quality of factory fresh aircraft, not to mention worn out airframes.

Gene lednicer did a very nice study and published reports based on VSAERO for both the B and D in comparison with Spit IX and Fw 190A and D-9. The reason I mention this is that in his modelling the 51D was actually slightly cleaner, and the difference was that the bubble canopy had complete lift distribution w/o separation from the top of the windscreen, aft. In addition the sloped windscreen of the D (more than B) suggested less stagnation at the windscreen. The B quickly separated above the cockpit. No Malcolm Hood version was modelled for the B.

The reason I bring this up is to suggest that when you add the same extra internal weight for the B as the airframe increases for the D, the report implies that the same P-51B, loaded an extra 600 pounds, or conversely take out the guns and ammo, and re-test..

would show an even greater Vmax difference than 10+ mph as the 51B was slightly 'draggier' in parasite drag than a D.

All you say is true generally speaking..but having said that, the delta Weight causes the airspeed to vary as V2/V1 = SQRT(W2/W1)
using the same exact airfame and power conditions.

Overall, the point that Graham tries to make is not that the weight is unimportant. He just merely points out, that differencies of weight caused by fuel consumption are mariginal for aircraft performance in horizontal flight. It does matter in vertical manouvers, though. This is obvious for anyone, who ever attempted to calculate such things, just as it is obvious, that adding a few pounds of putty and lacquer will increase the horizontal speed!

Franek - Respectfully, I made a living for several years "calculating such things" following a Masters Degree in Aero. Having said this, my real expertise was Structures, Aeroelasticity and finite element modelling.

It is not so obvious to me that Weight delta does not affect top speed - because it does. You may not agree my math or logic, but respectfully, bring your own if you have a different POV.

Marginal seems to be what you are debating and I'm ok with you and Graham dismissing the value to Max speed available to say a P-51B after getting rid of its Fuselage tank 85 gallons. The math says it's about 10-12 mph.

If that is insignificant to you we can agree your terminology, but the delta is not due to plugging gun ports, or polishing the airframe, or switching engines...

Hari - two things about your comments.

First- at Vmax the Thrust Hp is maximum for that altitude and weight.

When weight increases, for the same airframe, the Thrust Hp remains the same, but Vmax decreases alightly as the AoA must increase to maintain level flight for that Thp and weight condition.

In other words the Thrust available is the same for both weight conditions, but the velocity Attainable is Less for the heavier weight conditions.

In other words, Thrust HP may not increase beyond the max Thrust Hp available in level flight.

If you want to demonstrate the math that proves a slight increase in AoA from freestream impingement on the propeller plane increases the change in momentum of the mass flow through that plane (positively) - give it your best shot.

By your anology , as the ship climbs at a steeper angle relative to freestream, the thrust would increase?

By using the Propeller/Engine thrust equation as you used it (which is appropriate for level flight) then as the angle of Attack increases you would quicly reach a point where sustainable velocity is much lower than it was in level flight... and your thrust increases dramatically above it's max rated Hp Thrust in level flight. Do you believe this?