Performance of the Fw 190A on the Deck?

[Harri Pihl]

Originally Posted by Graham Boak

Your basic equation. V2/V1 = SQRT(W2/W1) is actually inverted. the greater the weight, the greater the drag, the lower the speed. I assume this is a simple typo. The equation is a concatenation of three relationships.

There seems to be a typo but the relation itself just shows that at given Cl (or AoA) the weight and speed relation stays constant. That also means that the formula can't be used to determine speed change in the case where the Cl changes.

The way I calculate the speed change is very basic stuff. I assume that at any steady flying condition drag equals thrust ie:

D = T

Drag being:

D = Cd * p * V^2 * 0,5 * A

Where Cd is drag coefficient, p is density, V is speed and A is reference area (wing area).

And Cd being:

Cd = Cd0 + Cdi

ie total drag coefficient is zero lift coefficient plus induced drag coefficient the later being:

Cdi = Cl^2 / (pii * AR * e)

where Cl is lift coefficient, AR aspect ratio and e efficiency factor. The lift coefficient is:

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

where L is lift force (9,81 * weight in this case using SI).

And the thrust is:

T = (n*W) / V

Where n is efficiency and W is engine power.

I use spreadsheets for iterations, in the Typhoon example I used Cd0 value 0,019, wing area 25,83m2, AR 6,2, 80% prop efficiency, e value 0,8, density 1,225 kg/m3 and weights 4800kg and 5300kg.

[Crumpp]

Your basic equation. V2/V1 = SQRT(W2/W1) is actually inverted. the greater the weight, the greater the drag, the lower the speed. I assume this is a simple typo. The equation is a concatenation of three relationships.

That is completely wrong, Not even close to the fundamentals of aerodynamics completely wrong.

Graham you have been away for a while. If we hold AoA constant and increase weight, speed MUST increase.

Lift has to increase to meet the amount required. If our weight goes up then our lift required also increases. Our lifting pressure has increased.

Remember our fixed relationship of Coefficients of Lift, Drag, and angle of attack. Holding angle of attack constant, we know the ratio is constant. The only way to increase the forces and maintain the same ratio of lifting pressure to dynamic pressure is raise the dynamic pressure to meet the higher lifting pressure.

Look, I can produce multiple references what I am saying. You guys have, "please believe me" and you compadre's....well, whatever the heck that is

All the best,

Crumpp

[Crumpp]

There seems to be a typo but the relation itself just shows that at given Cl (or AoA) the weight and speed relation stays constant. That also means that the formula can't be used to determine speed change in the case where the Cl changes.

Riding coat-tails right down the drain....LMAO.

[Nick Beale]

Originally Posted by Crumpp

Riding coat-tails right down the drain....LMAO.

On the other hand you might like try being polite, even when you disagree with what others have said.

[Harri Pihl]

Originally Posted by Crumpp

Riding coat-tails right down the drain....LMAO.

Perhaps you should try to prove your point with calculation instead.

[Graham Boak]

[If we hold AoA constant and increase weight, speed MUST increase.

Lift has to increase to meet the amount required. Crumpp[/quote]

AoA is Angle of Attack, the angle an aircraft makes with the airflow, for anyone still with us who doesn't know the term.

Ah. I begin to understand. However, there is no need to hold AoA constant. Why should you want to? Yes, lift has to increase to allow for the extra weight. This is done by flying at a slightly higher AoA giving a slightly higher CL, and hence a higher drag. Higher drag = lower speed. QED. However, this increase in drag is insignificant, for the reasons explained.

If, for some reason, you wanted to fly at the same AoA (bearing in mind that no machines of the period had the instruments to do this) then yes, an increase in weight would have to be balanced by a higher q, or speed. But you are already flying at maximum power, so you can't do this.

This flying at constant AoA would, I think, be relevant to cruise, where a heavier aircraft does indeed require a higher speed. This is because the optimum cruise point is where the induced dag (which reduces with the square of the speed) equals the zero-lift drag (which increases with the square of the speed). An increase in weight needs an increase in lift, which creates an increase in induced drag. A new optimum, induced drag = zero lift drag, requires a higher zero-lift drag which is found at a higher speed. The resulting AoA will be close to, if not identical to, that of the previous weight.

Your equation may hold at cruise conditions, if AoA is held constant. It does not apply to flying at maximum power, where additional lift can only be found by increasing AoA.

[Crumpp]

This flying at constant AoA would, I think, be relevant to cruise, where a heavier aircraft does indeed require a higher speed.

Graham I think it certainly has been quite a while since you worked with aerodynamics. From what I understand, it is like riding a bike and it comes back.

You missed the point on the parametric study. The only way to judge the affects of weight is to hold a constant, adjust weight, and measure the results. Otherwise we miss the forest for the trees.

That is the basic scientific method and is generally accepted for aerodynamics and applied physics.

Not doing it leads to false conclusions on the relationships. We wind up with statements like the affect of weight is insignificant because we only see a small reduction in speed.

Here is another reference on this subject:




Now I understand you only wanted to make the point that "in regards to top level speed" in a very narrow definition, the affect of weight is insignificant.

I guess you could make that statement. I certainly would not make it. Once again it sounds to me like a Doctor claiming the small size of a cancer tumor means it is insignificant to the body.

On the other hand you might like try being polite, even when you disagree with what others have said.

Hi Nick,

Point taken. And you are correct. Thanks.

All the best,

Crumpp

[mayfair35]

Gentlemen:
I thought this thread was about whether or not the FW-190A was faster on the deck than any allied fighter? Well, why not ask those who were there? Forget trying to prove it by calculations as they completely ignore pilot ability and experience.

In my encounters, no FW-190 ever outran me on the deck or at 30,000 feet. Although I did not have the opportunity to dance with a FW-190D on the deck, I did a good jitter bug with at least 20 FW-190Ds and another 15 or so FW-190As at 30,000 feet. I was faster and could easily outturn them. On the deck, I had no problem staying with them. I chased one when my guns were jammed and was able to check his RPM at 2700 so I presume he was at full throttle. I had to keep retarding my throttle to prevent overrunning him. My P-51D indicated about 372mph at 100 feet. We changed the engine when it would not indicate more than 360/365 on the deck. We had one P-51D said to indicate 390 mph at zero altitude, but I have to wonder if there was a problem with the airspeed indicator, as none of the other pilots reported that speed.

I recall reading a report from an 8th AF pilot who stated that a FW-190 ran away from him on the deck but do not recall what model it was.

Surely there must be other P-51 or FW-190 pilots on this board who could add some actual experiences to this discussion and whose end results differ from mine?

Cordially, Art Fiedler

[Crumpp]

Hi Art,

We had some Vets from the 9th AF in the museum a while back. I will get more details from Mark as he related their story to me.

Anyway, it went something like this:

In the last few days of the war their flight came across an FW-190A down low. Wanting to take a good peek at this lone aircraft, the flight moved up on the 190's rear unnoticed. As the lead P51 moved off to the side to get a better look, the German pilot realized he had 4 P51's on his tail.

In an obvious panic, he rolled, split-S, and dove away. They followed him. After leveling off at treetop height, black smoke poured from the 190 and he left the P51's behind.

Oskar Bösch also outturned and outran a P51 flight over the Ardennes in December 1944. He told me that the first Mustang overshot him as he banked hard right. He then entered a turn fight with that Mustang which went for several circles before gaining gun solution. When he looked back, he saw a several Mustangs in the same circle. That is when he broke hard, opened up his "Ribbennol", and dove for the trees. He counted 5 Mustangs in pursuit that eventually gave up the chase.

http://baileyprints.com/prints/war-wolf.html

Oskar credits the low level speed of the FW190 as the reason he survived the war. In his words, "In my Focke, I feared no fighter I could see."

Thank you Art for your service to mankind. It is the reason why we can openly discuss these events today.

All the best,

Crumpp

[Crumpp]

Mr Feilder I have sent you a PM.