Performance of the Fw 190A on the Deck?

[Crumpp]

Now we are getting somewhere!

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

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:

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

Is really exactly the same as this result:

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

delta V = +17,3 km/h

As demonstrated by your first set of calculations:

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

[Harri Pihl]

Originally Posted by Crumpp

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

The difference has been noted tens of time above; I calculate the new balance point of drag, thrust, Cl and speed at constant power; all affecting parameters are adjusted to reach new balance and in the end these are in perfect balance. This is the same as real world situation at constant power.

You calculate how much speed had to be increased to keep constant Cl and therefore can't reach the new balance at constant power. This is not the same as real world situation at constant power because there is no more power available and Cl can be adjusted .

Shortly:

Iteration method => all the parameters are adjusted => constant power problem can be solved.

Parametric analyses => at least one fixed key parameter => constant power problem can't be solved.

[Crumpp]

Parametric analyses => at least one fixed key parameter => constant power problem can't be solved.

We are not looking for specific aircraft performance at a constant power. We are looking for the significance of weight affects on the aircraft. We want to view the relationship of weight to the performance of the aircraft.

The math tells us that although:

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

In addition, the math also tell us that:

We can only conclude that weight has very significant affects upon an aircraft, even at high speeds.

Your inability to see past your simple specific performance calculations and understand the principles behind them is where it is easy to tell you have only an internet education, Pihl.

You do quite a bit of parametric study in aerodynamics. It is one way we learn about the relationships of forces in complex systems.

When we do a parametric study, we are not looking for specific aircraft performance but rather we are looking at the relationships of the forces involved.

This is why I said you, "cannot see the forest for the trees".

You very nicely proved that through your own calculations.

All the best,

Crumpp

[Juha]

Dear Crumpp
the tread began with a question on the speeds of certain aircraft at deck, not how weight affects on the aircraft.

You claimed we this and that, who are "we"? Or are you maybe a Royal person?

Just asking
Juha

[drgondog]

Originally Posted by Juha

Dear Crumpp
the tread began with a question on the speeds of certain aircraft at deck, not how weight affects on the aircraft.

You claimed we this and that, who are "we"? Or are you maybe a Royal person?

Just asking
Juha

That might be me, although 'we' are not royal.

I jumped in earlier to bring up two or three points as Harri moved into precision calculations to 'calculate' the differences.

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

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.

I never got an idea that he fully understands that calculating propeller thrust in context of force must take into account propeller drag as the velocity changes.

The approach used is a good ballpark. The reason I started nitpicking is that the 'true' equation for the solution sets are

Tp+Te = Dprop + Di + Dparasite at V1
and
Tp+Te = Drpop + Di + Dparasite at V2

or

Tp1/q1S + Te1/q1S= Dprop1/q1S + CL1**2/(pi*AR*e) + Cd0

and

Tp1 + Te1 = Dprop2/q2S + CL2**2/(pi*AR*e) + Cd0

Where q1S = 1/2*rho*V1**2 and q2S=1/2*rho*V2**2

Cd0 = Cd0 for both states, but 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

Last but not least, both of these aircraft are pushing Mach numbers in .55 range where profile drag based on activity factors and compressibility become increasingly important and in my GUESS different, for both of these ships, as the propeller designs are both different in diameter, activity and tip speed.

My own experience (many years ago) was to use the Crumpp's parametric approach as a guesstimate in preliminary design was the better way to figure out impact to performance profiles due to weight alone.

It has also been the 'easy way out' to convert Bhp from charts to THp for Sea Level parametric studies on such things as Turn or climb performance and fall back on Thp equation for thrust and Velocity when calculating Thrust available versus thrust required. Both approaches are flawed if precision is what you want.

But it is not adequate, by and of itself, at M> .55, or at increasing altitudes bwhere density changes are increasingly important.

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

Nuff said - I am bowing out of this conversation

[Crumpp]

Just asking

No, you are not just asking.

You are trying to infer something that simply is not present in my post.

Parametric study is the commonly accepted practice when we want to determine the affect of one parameter on a system. "We" refers to those who are formally trained in applied physics.

Like I said, you will do quite a bit of parametric study when you deal with aerodynamics whether that is in the classroom or as a member of a design team.

Simply put, there is no way one can have any amount of formal training in applied physics and not understand the value of parametric study.

You will fail the classes if you cannot answer questions about the cause, affect, and significance. On a design team, you will cost money, time, and possibly lives.

Mr Hari Pihl would earn a big fat "F" for the semester in any class on this subject I ever took or a trip to the unemployment line.

All the best,

Crumpp

[Ruy Horta]

Lets keep the discussion constructive and friendly, no need to turn disagreement into personal attack however "harmless" it might seem.

I don't understand any of it, but having such mathematical skills and models at hand to calculate and check historical aircraft performance is very impressive.

[Juha]

Crumpp
now this is not a class of applied physics, is it? The tread is on speeds of certain a/c at deck level. And Harri's calculation seemed to be very close to the values shown in the Kurfürst's table on the effects of weight to 109G's max speed at deck. I'm practical man even if I have university degree and to me the most important thing in calculations is that its result is as exact as possible and that it answered as exactly as possible to the question asked and we a not designing a/c here.

And I have trained to understand cause, effect and significance, don't worry on that.

That said I apprisiate the graph on Mid-43 speed comparision in your message #8, thanks for that.

Juha

[Crumpp]

And Harri's calculation seemed to be very close to the values shown in the Kurfürst's table on the effects of weight to 109G's max speed at deck.

Harri's mathmatical mechanics is correct. He has been taught by someone to work the formulas. I suspect as a hobby, perhaps through Radio Controlled Models.

All the best,

Crumpp

[Harri Pihl]

Originally Posted by Crumpp

We are not looking for specific aircraft performance at a constant power.

Hm... Graham's original statement was:

"Actually, fuel state is not that important with regard to maximum speed."

And my approach is simply to calculate how large the effect is with very basic methods. And given the problem, a constant power approach is clearly the right one.

Originally Posted by Crumpp

Is really exactly the same as this result:

Nope;

Delta V = -1,48km/h is the answer to the question in hand and is directly related to Graham's original argument ie how much speed would change at constant power if weight increase.

Delta V = +17,3km/h is the answer to completely different question ie how much the speed should change to keep Cl constant if weight increase.

Regarding my education, despite I have university degrees, I have never got or been taught aerodynamics lessons. All I know comes from some 25 years of designing, building, flying, flying again, crashing, repairing and crashing again, giving up and redesigning RC-planes and that includes computer analysis etc. And in AH board I've even posted pictures of my planes, I quess you saw them there before you were banned for very similar argumentation style you are showing here.

However, all the calculations needed for the analysis above, are indeed very basic stuff and anyone with basic knowledge on physics can do them. The problem here is that some people who claim degree on aerodynamics, seem to lack basic knowledge on physics.