Performance of the Fw 190A on the Deck?

[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.

[Harri Pihl]

Originally Posted by drgondog

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.

Originally Posted by drgondog

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.

Originally Posted by drgondog

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.

Originally Posted by drgondog

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.

[Crumpp]

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

[Nick Beale]

Originally Posted by Crumpp

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.

[Harri Pihl]

Originally Posted by Crumpp

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.

Originally Posted by Crumpp

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.

[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