Luftwaffe and Allied Air Forces Discussion Forum - Performance of the Fw 190A on the Deck?

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- - Performance of the Fw 190A on the Deck? (http://forum.12oclockhigh.net/showthread.php?t=13886)

Re: Performance of the Fw 190A on the Deck?

Quote:

Originally Posted by drgondog (Post 70873)

One is that he calculated a Cd0 for the Mustang rather than use one or more of the much lower referenced values.

Using different Cd0 does not make large difference on speed reduction. You can of course do the calculation with different Cd0 and see.

Quote:

Originally Posted by drgondog (Post 70873)

Two he used the Hp to Thrust conversion as if it was a law of physics and seemed to not fully understand the full context of all the forces acting on the Mustang, including Thrust of the airplane at rest.

The method I used is good enough for Hamilton Standard, Hoerner, NACA... should be good enough for internet discussions as well, particularly when the speed change is so small.

And it really is related to the laws of physics.

Quote:

Originally Posted by drgondog (Post 70873)

I wanted Harri to walk through this to show that the relationship between (Tprop1- Dprop1)=Thrustnet holds true for both velocites (and weights) in order to use the equation Thp=thrust x V/375 in mph or Thp=thrust x V/326 in kts and hold THp constant

You can take that mentioned Hamilton Standard Red Book and walk through it your self. However, the speed change is so small that there is no any practical difference. Same is true also for compressibility effects.

Quote:

Originally Posted by drgondog (Post 70873)

Harri - I respect your approach - but don't think it is adequate for precision for the reasons I have stated.

I don't claim that my calculation is a precision model, as example Holtzauge has far more sophisticated model; still, we got similar results for this particular problem. However, I do claim that it is good enough for testing the scale of the effect, to test Graham's statement in other words. Small errors in n, e, compressibility effects, Cd0 etc. do not cause large difference.

Re: Performance of the Fw 190A on the Deck?

Quote:

Harri Pihl says:
I have never got or been taught aerodynamics lessons.

We know this by now but it is nice to see that you can admit it when cornered.

That is a start.

My suggestion would be to go find someone you trust whom is actively teaching or working in the industry. You are obviously an older guy if you have been doing model toys for 25 years.

Perhaps taking an adult education class is another possibility.

Only observing direct results can get us into trouble in science and engineering. One must understand the cause and affect of the underlying forces not just looking at simple end results.

All the best,

Crumpp

Re: Performance of the Fw 190A on the Deck?

Quote:

Originally Posted by Crumpp (Post 70935)

One must understand the cause and affect of the underlying forces not just looking at simple end results.
Crumpp

I think the original topic of the thread was indeed "the simple end results" — could an Fw 190 pilot on the deck get away from the guy who was trying to kill him? Live or die? Simple end results.

Re: Performance of the Fw 190A on the Deck?

Quote:

I think the original topic of the thread was indeed "the simple end results" — could an Fw 190 pilot on the deck get away from the guy who was trying to kill him? Live or die? Simple end results.

A Focke Wulf running from a P51 is not really a complex system, Nick. It's a simple foot race which was pretty much answered in the first few posts.

Is this still a question in people’s minds?

That is a far cry from the science behind the statement fuel affects are insignificant because we only perceive a small drop in velocity. That was nicely demonstrated by Harri Pihl’s own math.

See his post #150

http://forum.12oclockhigh.net/showpost.php?p=70836&postcount=150

And my reply in # 151

http://forum.12oclockhigh.net/showpost.php?p=70846&postcount=151

Weight affects are a complex system and we know the affect of weight does not change at high velocity.

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

All the best,

Crumpp

Re: Performance of the Fw 190A on the Deck?

Quote:

Originally Posted by Crumpp (Post 70945)

It's a simple foot race which was pretty much answered in the first few posts.

My point exactly — but there seem to have been another 16 or 17 pages since then.

Re: Performance of the Fw 190A on the Deck?

Quote:

but there seem to have been another 16 or 17 pages since then.

Because a much more complex issue grew out of the first one.

All the best,

Crumpp

Re: Performance of the Fw 190A on the Deck?

Well, there are no outran Fw 190 pilots alive for obvious reason.
I am afraid, I am slightly lost as to what is the current problem with thrust. Just too many posts, almost at once.

Re: Performance of the Fw 190A on the Deck?

Quote:

Originally Posted by Crumpp (Post 70935)

We know this by now but it is nice to see that you can admit it when cornered.

So far in this thread only me and Holtzauge have been able to calculate the speed loss correctly regardless our education.

And without continous personal remarks and harsh language, you have presented.

Quote:

Originally Posted by Crumpp (Post 70935)

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

Well, you just calculated how much additional speed was needed to maintain the Cl. And that is impossible at constant power, the top speed situation ie aircraft has no such ability.

Re: Performance of the Fw 190A on the Deck?

Quote:

Originally Posted by Nick Beale (Post 70955)

My point exactly — but there seem to have been another 16 or 17 pages since then.

Well, I pointed out the differences between the methods at page 3, post #24 of this thread.

Edit: actually the post #21

Re: Performance of the Fw 190A on the Deck?

Quote:

And without continous personal remarks and harsh language, you have presented.

Not really. I think that is your personal perception.

I think you have been very rude.

Quote:

Well, you just calculated how much additional speed was needed to maintain the Cl. And that is impossible at constant power, the top speed situation ie aircraft has no such ability.

You are still confused on parametric study, huh?

Harri Pihil, I calculated the affect of weight on the aircraft. That affect does not change simply because the aircraft no longer has the ability to compensate for it.

This is not the Mulberry bush for us to go round and round.

You claimed:

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Quote:

Quote:

Originally Posted by Crumpp http://forum.12oclockhigh.net/images...s/viewpost.gif
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.

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I responded:

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Now we are getting somewhere!

Quote:

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

delta V = -1,48 km/h

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.

So this result:

Quote:

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

delta V = -1,48 km/h

Is really exactly the same as this result:

Quote:

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

delta V = +17,3 km/h

As demonstrated by your first set of calculations:

Quote:

Quote:
And we can check this with your formula as well:
Quote:

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