Performance of the Fw 190A on the Deck?

[Harri Pihl]

Originally Posted by Crumpp

You are about to be ignored. I know very well what the formula's are for as I am degreed in Aeronautical Science.

I see that your knowledge has improved somewhat since the days you were posting to the AH board. However, you seem to still have serious problems to deal with basic performance calculations, this case being a good example.

Originally Posted by Crumpp

Now go back and find where I said anything about there not being a relatively small top level speed reduction due to weight affects. No one has ever claimed anything but that. Graham is the only one who has tried to narrow the issue to that one subject.

The thread is about the performance on deck and Graham (and I) have pointed out that the effect of the fuel state to the top speed at deck is small. And we did that by using the correct method which accounts the change of the Cl/AoA.

However, you posted a formula:

V2/V1 = SQRT(W2/W1)

Which is valid only for the constant Cl/AoA and therefore wrong for this particular case. And this is exactly what Graham responded to you in the first page of this thread.

Note that the polar approach used by Graham and me works for any given flying condition while your approach works at one exact Cl/AoA.

All considered it’s a healthy concept to keep in mind: the flying weight of your aircraft directly affects its performance. Each time. Every time. No exceptions.

That is true and no one denies that. However, Graham was correct when he noted that at these particular conditions the effect of the fuel state is not that important, just few km/h.

[Crumpp]

The thread is about the performance on deck and Graham (and I) have pointed out that the effect of the fuel state to the top speed at deck is small. And we did that by using the correct method which accounts the change of the Cl/AoA.

No that is what YOU think it is about and have tried really hard to make it that subject irregardless of what is actually posted.

Which is valid only for the constant Cl/AoA and therefore wrong for this particular case.

You keep repeating that as if parametric study is not valid.

I see that your knowledge has improved somewhat since the days you were posting to the AH board

That speaks volumes. You are a gamer with a bone to chew.

All the best,

Crumpp

[Harri Pihl]

Well, the polar method is the correct method as pointed out several times due to simple fact that it handles the changing Cl/AoA correctly for this kind of analysis. In otherwords the exact change of the speed due to weight can be easily and exactly calculated given that the parameters are correct.

However, the constant Cl/AoA approach which you presented can't be really used for analysis because it does not actually answer the question in hand; it just demonstrates that at different weight, different speed (or power) is needed to maintain constant Cl/AoA.

As a friendly advice I suggest that you should change your attitude and try to actually listen and understand the other people instead keeping lectures on the subjects which the other people might understand better than you. The problem is that you tend to post on number of boards and you continously keep involved on heated discussions where you rarely admit that the problem might be on your side. This thread being a good example.

Perhaps you should actually thank people who help you instead attack; I teached you how to use the polar for turning performance analysis but for one reason or another I tend to receive a lot of harsh words from you.

[Crumpp]

Well, the polar method is the correct method

Once again, an argument of your own determination. The specific performance determination for an individual aircraft has not ever been disputed with the exception of pointing out that you do not couple the affects and take the calculation to it's conclusion.

You simply fail to see the forest for the trees. Your informal education is telling when you fail to recognize the value and mechanics of a simple parametric study.

Credit to James E. Lewis, "Modern Jet Transport Performance":

I teached you how to use the polar

What? Stop with the creepy weirdness.

I am sorry but Embry Riddle taught me to performance calculations in courses like ASCI 310 and ASCI 510.

From my online unofficial transcript in my undergrad days. That is my GPA in bold at the time I completed ASCI 310:

ASCI 310 01D4 Aircraft Performance 3.00 3.00I/A 12.00

Term 4.000 3.00 3.00 12.00
Cum 4.000 6.00 81.00 24.00

Some gamer with an internet education had nothing to do with my aeronautical science education. In fact most internet educated individuals suffer from exactly the same problem with an inability to put it all together.

Good Luck. Find someone else to stalk please.

Crumpp

[Franek Grabowski]

I am afraid you fail to note that Graham is aerodynamicist, who worked just on the issue. Weight affects horizontal speed, but it is MARIGINAL, just as is a smashed fly on a windscreen!

[Crumpp]

Weight affects horizontal speed, but it is MARIGINAL

Wow! Have I stepped on someone's corner of the internet?

Once again. Forest for the trees.

Nobody has disputed the direct effect is a marginal loss in speed. However a marginal loss in speed does not classify the affects of weight as marginal in totality.

Simply put, that is just basics when it comes to aerodynamics.

It’s like a doctor trying to prove that the tiny spot of lung cancer on the x-ray is marginal because it only affects a small portion of the lungs.


All the best,

Crumpp

[Crumpp]

Gentleman,

Find ONE scholarly published reference that states, "Because at high speed, the level speed reduction is marginal, the affects of weight are marginal.

Just one.

[Franek Grabowski]

To make it clear, we talk about weight change influencing speed change. Unless you are not reading, it was clearly stated that changes of weight due to use of fuel do not affect speed in measurable manner. Understood?

[Graham Boak]

No-one is attempting to claim that weight has no effect on overall performance. There are very good reasons why the discussion is very specifically about maximum speed at sea-level.

The thread began with the statement that Fw 190s could always outrun any Allied fighter. There is no doubt that this does not apply at high altitudes: above the full throttle height, any contemporary turbocharged or two-geared two-stage supercharged fighter will outclass the Fw 190. Whichever fighter is faster at sea-level will also be faster up to the full throttle height (with different relative full throttle height, things do get tangled) so it is reasonable to restrict the study to sea-level.

In which case it is certainly convenient to study the one campaign where a significant amount of low-level "racing" took place, namely the cross-Channel Jabo campaign. As part of the resulting discussion, it was suggested that weight might play a part. Not in stall, climb, cruise or ceiling conditions, but specifically at maximum speed at low-level. As I have shown, and anyone educated in subsonic aircraft drag and performance will recognise, the effect of weight is insignificant AT THIS EDGE of the envelope.

I don't have a collection of "scholarly published references" to check, having left most of such behind on retirement, but am totally unconcerned. I suspect few will make such a blatant statement, for it follows automatically from an understanding of the relationship between speed, weight and drag. But for reasons of military classifications, I could have produced a large number of flight manuals that present the maximum speeds at different weights: although in all fairness many would have a Mach Number limit rather than being limited by conventional subsonic aerodynamics. Presumably you would wish to exclude the ones I calculated myself, despite having passed the scrutiny of my peers, my seniors and critical authorities such as those at Boscombe Down: not to mention the ultimate test of service use. There are also the ones I have updated, where my numbers agree with those of my more illustrious predecessors.

As for parametric studies, these are dangerous. They can only hold within limits that are rarely stated. They have their uses in early design studies, or for simplifying matters for those who do not need to know more: sorry, that may often include general aviation pilots. How often do GA pilots need to fly at the maximum speeds of their aircraft? Often, such aircraft are limited to speeds below their true maximum.

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.

V2/V1 = SQRT(Dt1/Dt2), where Dt stands for total drag.
Di1/Di2 = L1/L2 where L is the lift. For WW2 aircraft, and for more modern types at low Lift coefficient, this linear relationship holds. The greater the lift, the greater the induced drag.
L1/L2 = W1/W2, I think that is fairly clear. The greater the weight, the greater the lift required. A one for one relationship.

so we have
V2/V1 = SQRT(Dt1/Dt2); SQRT(Di1/Di2) = SQRT(L1/L2) = SQRT(W1/W2)

Expressed this way, the error stands out. Dt1/Dt2 does not equal Di1/Di2.
Dt = Di + Do - where Do is the zero lift drag. Any increase in Di only leads to a lesser increase in Di+Do. In parts of the envelope where Di is greater than Do, the increase due to weight is a large proportion of the total drag, and the overall increase hence close to that in Di (but never equal). At the cruise, Di = Do, so a 10% increase in Weight gives a 5% increase in drag. In parts of the envelope where Do is greater then Di, then any increase due to weight is only a lesser proportion of the total. Near the maximum speed, Di is much less than Do, and so any effect of weight is only a small proportion.

If you want to check this, and your flight manual permits it, take your light aircraft, weigh it (and you) then fly it at its maximum speed. Any convenient low altitude will do. Hold this until stable - for ten minutes, I suggest. Note the pressure altitude, temperature and fuel consumption (to calculate the weight at the test point). I assume here that you can measure these things to a high quality, but suspect that normal aircraft instruments may be too coarse.
Repeat the exercise with three (weighted) passengers. Corrections for different heights, temperatures, and fuel states can be obtained. You might need to carry out the exercise several times to rule out random factors.

Alternatively, contact your professor and ask him what difference fuel weight would make to the top speed of a WW2 fighter.

My apologies to those who switch off whenever equations appear.

[Harri Pihl]

Originally Posted by Crumpp

Once again, an argument of your own determination. The specific performance determination for an individual aircraft has not ever been disputed with the exception of pointing out that you do not couple the affects and take the calculation to it's conclusion.

I think that I have said several times that the polar method handles all the variables correctly and works for any given flight condition while the your approach is limited to one given Cl/AoA. Therefore for this particular case, speed change due to weight change, the polar method is the correct one.

And if want to disagree, please prove that with calculation.

Originally Posted by Crumpp

What? Stop with the creepy weirdness.

I am sorry but Embry Riddle taught me to performance calculations in courses like ASCI 310 and ASCI 510.

I quess that you have missed some lectures then or why I had to show the correct method and point out your errors here:

http://forums.ubi.com/eve/forums/a/t...6131040055/p/1