Performance of the Fw 190A on the Deck?

[Harri Pihl]

Originally Posted by Crumpp

Ok then. All I am asking you to do is just explain what is different.

Let's demonstrate the differences using the values of the P-51B I allready calculated for constant power above for 9680lbs and 10280lbs. We allready know that, for these given parameters, my calculation is correct. Because your calculation is made for calculating required speed for constant Cl, we can solve the very same problem with my calculation as well and see the principal differences:

The lift coefficient at 9680lbs (4390,85kg) and 352mph (566,37km/h=157,324 m/s) at sea level is, as allready demonstrated:

Speed V =157,324m/s
density r = 1,225kg/m3
wing area A = 21,83m2
Lift L = 4390,85*9,81 = 43059,51 N

Cl = L / (A * 0,5 * r * V^2) = 0,13011

At 10280lbs required lift is:

L = 4663,01*9,81 = 45728,487 N

So we can solve the required speed at constant Cl at higher weight using these:

V = SQRT( L / (A * 0,5 * r * Cl)) = 162,17m/s = 583,66 km/h

And we can check this with your formula as well:

V2/V1 = SQRT(W2/W1)

583,66km/h/566,37km/h = SQRT(4663,01kg/ 4390,85kg)

1,031 = 1,031

So we can see that both calculations methods give the same result for that specific problem.

However, the result for this specific problem, the speed change required for constant Cl at higher weight, is over ten times higher than the result for the problem in our hand. Note that we calculate steady conditions here ie D=T at level flight.

Speed change due to weight change if power is constant and the other parameters are adjusted accordingly as demonstrated earlier is:

delta V = -1,48 km/h

while the speed change to keep Cl constant when the weight change is:

delta V = +17,3 km/h

We can also calculate the power required using the similar drag and thrust calculations as demonstrated above and we find that this higher speed at constant Cl requires 1748,98hp ie 169hp more than with original values (assuming otherwise the same parameters, including exhaust thrust).

What we see here is:

1. Calculating speed change to keep Cl constant at varying weight is completely different problem than calculating speed change at constant power when the weight changes (ie our problem in hand)

2. The magnitude of the results is completely different, over ten times difference in this particular case.