[Crumpp]

No one has twisted your words, Harri.

Harri Pihl says:

"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."

You lose the forest for the trees as all you can see is your one specific solution you have been taught to parrot. You don't seem to understand that the force of weight continues to have the same affect on the aircraft whether it is at high velocity or low velocity.

If we increase the weight, our aircraft needs to overcome it to maintain performance.

I don't know how else to tell you that much clearer. Any lower level aerodynamics course will tell you exactly the same thing and to prove that you can easily perform a parametric study on your own.

Try thinking really hard on this part, Harri:

Certainly! Why is that change so small? What the differences?

Because the aircraft does not have the Power available to meet the new power required! The Angle of attack must increase and the velocity slow down.

Of course in a propeller aircraft as our velocity decreases we know our thrust increases!

The affect of weight is very much present and the aircraft's entire envelope is still reduced

There is change in the aircraft's ability to compensate for that affect but the affect of weight is exactly the same.

No change in the significance of weight.

That is evidenced by your own calculations:

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.

So when we isolate the affects of weights in a parametric study to see the true affect, we can only conclude that weight has very significant affects upon an aircraft, even at high speeds.


All the best,

Crumpp