Performance of the Fw 190A on the Deck?

[Kurfürst]

Effect of take off weight at greater flying weights - Me 410:

[Harri Pihl]

Originally Posted by drgondog

Harri - you have been very evasive about zero Velocity Thrust as well as explaining why the 'practical' approach to calculating high Hp/low velocity thrust equation doesn't work... or more to the point what is missing from the Trust discussion.

Could you please answer the questions?

I have pointed out the relevant relations between the power and thrust regarding subject of this thread. Which were also completely wrong in your argument.

Regarding the zero speed thrust calculation, which is not the topic of this thread, I suggest that you get for example that mentioned Hamilton Standard Red book. It gives you all the information and relations needed to calculate entire speed region of an airplane. Note that there is no a single mention about the THP in entire book at least in my copy.

My demonstaration should be clear enough; thrust part is simply:

T = (n*W)/V + et

Where et is exhaust thrust. Overall similar approach can be found from Hoerner's "Fluid Dynamic Drag", chapter 14, if you are interested to learn more. The demonstration calculation is solved so that D=T at the new balance point and affecting factors are adjusted accordingly.

Given the large number of questions you have, and mostly off topic, my impression is that you try to derail the discussion out of topic after you have been pointed out to be wrong in the case of the power and thrust relation.

[Harri Pihl]

Originally Posted by Crumpp

So your claim is the affect of weight is different at top level speed than the affect of weight at L/Dmax?

Nope, I claim that calculating the speeds and power required for constant Cl at varying weight is different problem than calculating effect of weight to top speed of the plane at constant power.

Basicly your calculation does not answer to the same question than mine and your calculation does not answer the question in hand while my does.

Originally Posted by Crumpp

Can you explain, in words, what happens at top level speed with a change in weight one step at time for us?

Can you explain in words as well what happens to an aircraft trimmed for level flight at best range cruise that suddenly increases in weight? Sort of a reverse of the albatross effect.

We have been calculating the steady flying conditions so far while your questions are about unsteady conditions.

Basicly you are using the same tactics here as drgondog; if argument fails, derail the discussion to somewhere else.

[Harri Pihl]

Originally Posted by Juha

Most seemed to have but not all, at least DN-54 and one other, was that DN-64, anyway one Z-5, ex Z-3 a/c, seemed to have older system, ie 2 exhaust pipes which came through upper part of NACA ring.

Ah, I just looked Pentti's three views and saw the ejectors... Finnish DNs are indeed strange bunch of planes

[Juha]

Thanks again, Kurfürst!
That I have seen earlier but had forgot altogether!

Thanks
Juha

[Juha]

Hello Harri.
Quote: "Ah, I just looked Pentti's three views and saw the ejectors... Finnish DNs are indeed strange bunch of planes"

Yes, they are. I checked a couple Do 17 sources but best pictures I found from Hämäläinen's Pommituslentolaivue 46, for ex on page 169 there is a good photo on the right engine of DN-58 without NACA ring and ejector exhausts are clearly seen. Of course there is nothing wrong in the photo of DN-60 on page 11 in SIHL 3/2006.

Juha

[Pawel Burchard]

Originally Posted by Juha

Yes, they are. I checked a couple Do 17 sources but best pictures I found from Hämäläinen's Pommituslentolaivue 46, for ex on page 169 there is a good photo on the right engine of DN-58 without NACA ring and ejector exhausts are clearly seen. Of course there is nothing wrong in the photo of DN-60 on page 11 in SIHL 3/2006.

This type of 'individual' exhaust is also to be seen on late Do 17 Z in German service (and seem to be pretty common), not certain if this could be some sort of flame dampers rather.

regards,
Pawel

[Juha]

Hello Pawel
Yes I looked also into the old Do 17 Profil and noticed that the two Croatian Do 17Zs shown seemed to have the new system with ejector exhausts as also some of LW's Do 17Zs some other LW Do17Z had the old 2 exhaust pipe system. To me the new system looked like normal fishtail ejectors. You probably have seen the clearly more substantial flame dampers at the end of the ejector pipes of Do 217 night bombers.

Juha

Ps in FAF most seems to have the new exhaust system but also DN-53 had the old one.

[Crumpp]

Nope, I claim that calculating the speeds and power required for constant Cl at varying weight is different problem than calculating effect of weight to top speed of the plane at constant power.

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

Is the acceleration of gravity different from cruise to maximum level speed? Does mass change?

The facts are there is no change in the affect of weight.

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

Basicly your calculation does not answer to the same question than mine and your calculation does not answer the question in hand while my does.

The parametric study I showed you answers the question, "What is the affect of weight on an aircraft".

Yours answers the question, "What is the specific performance of this aircraft under one specific condition of flight".

They are not the same thing. You don’t seem to have enough of grasp of aerodynamics to understand that.

We have been calculating the steady flying conditions so far while your questions are about unsteady conditions.

Do you know the significance if you have been describing two different aircraft at two different weights mathematically in steady flight while I have been describing one that suddenly increases in weight and moves to equilibrium?

It makes absolutely not one single tiny shred of difference. The affect is still the same.

My question is asking for you to explain in detail what happens when the weight of an aircraft is increased at best range cruise and to explain in detail what happens at maximum level speed.

If you are not capable of explaining it just say so and I will do it for you.

All the best,

Crumpp

[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.