Performance of the Fw 190A on the Deck?
 

Gentlemen:

Are there comments about the report in Don Caldwell's excellent JG 26 War Diary Vol 2 that 'The survivors claim today that the Fw 190A could outrun any Allied fighter on the deck, regardless of the official performance figures'.

This statement occurs in the section of the book dealing with JG26's role in Normandy after D Day, so it would apply e.g. to performance of the 190 A versus the Spitfire IX, not the Spitfire XIV, and similarly for the other Allied fighters.

I was a bit surprised by this statement, but presumably getting this sort of this correct was literally a matter of life or death. This forum has also taught me that assessing aircraft performance is more complex than reading simplistic tables of numbers.

On a technical level, would excellent speed on the deck relate to the radial versus in-line engine issue?

Thanks

Don W (Boomerang)

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

The maximum speed at sea-level is linked to the maximum speed at full-throttle height, and has no connection to the inline/radial choice. For a first stab at understanding more, plot a graph of airspeed (x-axis) against altitude (y-axis). Many sources will quote speeds at different altitudes, usually sea level and at the full throttle height of each supercharger setting. You can draw a straight line linking the sea-level value and the first full-throttle height point. The slope of this line will be the same for all types of similar performance. (Not quite true, but good enough to make the point.) Thereafter, plotting any max. speed point will allow you to find an approximate sea level speed.

Beware aircraft with two-speed superchargers (eg Spitfire Mk.IX), use the point for the lower full throttle height not the absolute best.

The statement is clearly made by the survivors, as there certainly are Typhoon pilots who succeeded in catching and shooting down Fw 190 low-level raiders. Also the Spitfire Mk.XII, of course. In practice the types were so close that the difference between individual examples was more important: a "good" Fw would run away from a "poor" Typhoon, and vice versa. More generally, of course, successful pilots will always believe that their aircraft is better than the opposition, as long as the types are broadly similar. For them, it has been.

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

Excellent points.

Objectively, the P-51B-15 for example, had a 1650-7 engine with better low altitude capability than the -3 and was extremely fast on the deck.

Based on flight test data, and assuming both engines were operating correctly it is hard to expect a 190A7 for example, or even a D-9 to outrun this Mustang on the deck.. and the -15 was plentiful during the Normandy campaign

I forgot to mention one other fact about the 51 - namely the extremely low wetted drag of the airframe in comparison with the Spit and Fw 190A. The D-9 was closer to the 51.

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

I go along with Graham's comments: the more Allied pilots' accounts I see, the more confused I get. One day they'll say they could easily catch a given type of enemy aircraft, the next " these [whatever] were too fast" or "we were unable to close" etc. The performance figures we all use don't seem to apply!

I'm sure a lot had to do with the particular situation of a combat but I also wonder whether individual machines of the same type were much more variable in performance than we now realise? Certainly you read pilots saying that a particular aircraft they flew was aither a good or a bad one of the type.

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

Gentlemen:

Now that the forum is running again, I can thank you for your responses.

I must say (based I'm sure on a much smaller sample) that I share Nick's thoughts - there doesn't seem to be the simple correlation between reports of fighter versus fighter combat that you might expect from published performance data.

One final point - is there any possibility that the fuel status of an aircraft would have a noticeable effect on performance i.e. an aircraft low on fuel would have greater speed than one with near full tanks?

Regards

Don W

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

Yes, fuel status definitely is very important, especially on a P-51!

Apart from that some technical factors on the not exactly, maybe even misidentified Luftwaffe AC which influence these "races":
- subtypes of 109G-x; 109K; 190A-x; 190F-x 190D-x(MW-50 yes/no) with different engine-subtypes
- did the german use WEP-systems like MW-50 or GM-1 or "erhöhter Laderdruck" (if available&working on his plane).
- maybe the german had external loadouts like MG151/20-gondolas, a droptank, bomb(s) - bombracks themselves can cause ca. 15km/h difference in v_max!
- status of the german A/C's surface due to bad painting, dirt, bad repairs, removed covering etc. pp.
- trim status
...

We can see: A lot was possible.

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

Actually, fuel state is not that important with regard to maximum speed. Drag is made up of two components, the lift-induced drag and the rest, or zero-lift drag. Weight has no effect on zero-lift drag. At cruise, the two components are equal. The lift-induced drag increases with the lift coefficient, which is high at low speed and low at high speed. So at high speeds, and at sea-level, the lift-induced drag would only be a small proportion of the overall drag (of the order of 15%, perhaps). Lift-induced drag goes up with weight (because the aircraft needs greater lift to equal this weight) but you are only looking at the difference in weight of the fuel, compared with the overall weight of the aircraft. So you are only looking at a small proportion of the smaller part of the drag.

In most combats the opposing aircraft will be at similar fuel states, around half: after such a jabo attack the escaping aircraft might well be at a lighter state, the interceptor heavier. This sort of difference might show in a long steady chase, as did occur over the Channel after some Jabo attacks, but a few mph would not normally be noticed.

Weight is much more important in manoeuvre and climb, there the fuel state could be more important. Most of all near the ceiling.

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

Quote:

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

Hi Everyone,

Weight very much affects our aircrafts envelope. It has a direct relationship with velocity.

V2/V1 = SQRT(W2/W1)

There is no real mystery to the variation in pilot accounts. If you examine the aerodynamic properties, all of these designers very much knew what they were doing. Aircraft must be viewed as a system and not one or two isolated characteristics. Aircraft performance is always a percentage variation over a mean average as well. Fit, finish, and conditions of flight make all the differences. Pilot skill is another factor.

In the FW-190 vs P51 it very much depends on the particular aircraft set up and conditions. You can make no blanket statement at low altitudes without knowing this information.

Here is the 8th USAAF assessment made during the war. Credit goes the Smithsonian NASM archives:

http://img175.imageshack.us/img175/1...board06je6.jpg
http://img175.imageshack.us/img175/1...e266dd178e.jpg


http://img140.imageshack.us/img140/7...board05ud5.jpg
http://img140.imageshack.us/img140/7...877cebb286.jpg


Here is a comparison chart of a variety of flight tested data that overlays the altitude range of the bomber stream. It closely matches the 8th USAAF conclusions.

http://img413.imageshack.us/img413/1...mpareiirz4.gif
http://img413.imageshack.us/img413/1...db79a14ff6.jpg

What does this information tell us about specific aircraft performance? Nothing. What it does say is that given a 3% normal variation there is very little to choose between any of these aircraft with a few notable ranges. Generally speaking at low altitudes, the FW190 was the fastest aircraft in the theater. At high altitudes, the P47 reigned supreme. All of these aircraft were continually upgraded by their perspective design teams.

The most important factor in aircraft performance is going to be the pilot. It is not a cliché. The ability of the pilot to properly trim, smoothness of the control input, and operation of the aircraft make a huge difference in performance. Pilot inputs can vary measured stall speeds as much as 30 mph IAS in "level flight".

The Allies had an overwhelming superiority in both numbers and quality of pilots. A USAAF pilot received ~8 times the flight experience in operational type aircraft before being posted an operational unit. The majority of Luftwaffe pilots were poorly trained for the job they were asked to do. The ebb and flow of the entire air war exactly matches the amount of training given to the pilots comprising the force. Type of aircraft is simply irrelevant.

The importance of pilot experience can be easily verified by picking up the phone and calling any aviation insurance company.

All the best,

Crumpp

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

If we examine the shape of the L/D curve for each of these designs, then we can see some important differences in the combat qualities.

All the best,

Crumpp

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

[quote=Crumpp;70205]

Weight very much affects our aircrafts envelope. It has a direct relationship with velocity.

V2/V1 = SQRT(W2/W1)

[End quote]

No. Weight affects the envelope, indeed, but the direct relationship is wrong. For aircraft of this vintage, it is probably true that induced drag has a linear relationship with weight, but induced drag is only part of the story. The effect of weight on speed varies with altitude, because it varies with induced drag only, and induced drag increases with altitude (at any given speed). At low altitude and high speed, the drag term is dominated by the zero-lift drag. This is made up of skin friction drag, profile drag and excrescence drag, none of which vary with weight.

For high altitudes and low speeds, the effect is reversed, as the drag is dominated by the lift-induced drag, and the top left corner of the envelope is notably smaller at higher weight. The bottom right is hardly affected.

I made my living doing these sums. There's a lot about aircraft performance I never knew, but I think this is fairly basic.

The rest of the posting is sound, and a very useful addition.

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

There are so many variables in an actual combat situation that performance graphs, valuable as they may be, are only a factor.
Pilot skill comes first, initial attitude, i.e can acceleration be got by diving. mishandling controls can loose speed, firing guns, especially the cannon, soon knoks off a few knots, wrong setting of rad flaps. I could go on, but it comes back to the pilot in general unless the aircraft are seriously mismatched.

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

Hi Graham,

Let's not confuse our concepts. To avoid confusion and hurt feelings lets define our conditions. I am going to cover some basics again for everyone.

Let’s look at the entire curve and affect of weight. This avoids confusion when we get down in the weeds. When we get in the weeds it does seem like adding weight increases our speed and based on conditions the relationship is direct or inverse depending on what we hold constant. When we put it all together it requires more power to achieve the same performance. Increasing weight means we must travel faster to achieve the same performance and out limits of performance have been reduced.

Credit to Professor David F Rogers United State Naval Academy:

http://img373.imageshack.us/img373/7...effectscw6.jpg
http://img373.imageshack.us/img373/7...24f511e67c.jpg

What we notice is that at any point on the L/D curve, the corresponding lighter weight requires less power and our aircraft can achieve a faster velocity. The effect is clear; add weight and our aircraft's performance is reduced. Vmax occurs at a slower speed.

If we get into the weeds on the specific effect:

Where some confusion on this issue seems to lie is in the fact in coefficient form, lift, drag, both have a fixed and finite relationship with Angle of attack. A Coefficient of lift has only one corresponding coefficient of drag and these occur at a specific angle of attack. For the reader, coefficients of lift and drag simply represent the ratio between lifting or drag pressures and the dynamic pressure.

If we keep velocity constant adding weight means the coefficient of lift must increase to meet the new lift required. This means the angle of attack must increase and with it the coefficient of drag.

If we cannot increase our coefficient of lift to meet the new lift required, then we must increase the amount of dynamic pressure to meet the new lift force required. The ratio of lift and drag pressure must remain constant if we are to keep our angle of attack the same. However to meet the higher lift forces required, we must raise the specific values of lift force to dynamic pressure.

The only way to increase the forces and maintain the same ratio at the same angle of attack is to increase the speed.

The confusion lies in the fact we no longer have the power available to overcome the higher drag forces required at the new velocity. Our sustained aircraft performance envelope shrinks and the angle of attack increases as our performance is now thrust limited.

Here is a "big picture" on these relationships:

http://img390.imageshack.us/img390/2160/ldratioud4.jpg
http://img390.imageshack.us/img390/2...0da7e60c26.jpg

Does this mean that "heavy" aircraft are "bad"? Aircraft are not a single characteristic but are a system. The effects of weight are easily mitigated through proper design. I certainly would not be so presumptuous as to assume any of the design firms in WWII were incompetent.

Facts are they were all the best and the brightest of their perspective countries. The design contemporary aircraft they produced were the F22 raptors of their day.


All the best,

Crumpp

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

Your first graph makes the point very well indeed. At the point of maximum speed (top right) changing the weight has only a very small effect on the speed. Away from this point (bottom left) changing the weight has a more significant effect.

My apologies if my explanation was unclear, but that's what I thought I said.

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

Quote:

My apologies if my explanation was unclear, but that's what I thought I said.

No problem at all. Aerodynamic discussion can get very sticky especially if conditions are not well defined.

While weight effects are smaller at high velocity, they are far from insignificant. Weight certainly makes a difference not matter what portion of the envelope we examine.

The relationship with velocity is direct at a constant Angle of Attack. The reality is that the aircraft does not always have the power available to maintain the necessary angle of attack so it must increase the angle of attack to account for weight.

I have enjoyed this discussion with you, Graham.

All the best,

Crumpp

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

Thanks, but I think we can still differ on the term "significant".

Can we place some numbers into this discussion? Turning to "Putnam's Hawker Aircraft since 1920" - purely for convenience, I'm sure other sources will do - we find the Typhoon quoted at an empty weight of 8,840lb, and a loaded weight of 13,250lb with 2x1000lb bombs. So for the Typhoons chasing Fw 190 Jabos we have a maximum weight, full fuel, of around 11,000lb. The fuel capacity of the aircraft is 140 gallons (actually quoted for the Tornado, so if anyone knowns different?) which will give a fuel weight of some 1120lb, using the specific gravity of kerosene not gasolene, but near enough I think.

So the total fuel weight is close to 10% of the total aircraft weight. Given that no aircraft will continue fighting without reserves and fuel to get home, nor without expending fuel to reach the combat area, we have a realistic weight range of about 5% of the total aircraft weight. (Obviously slightly more for a P-51 that has just dropped its tanks)

The induced drag, the only part affected by weight, is some 15% of the total drag at maximum speed, sea level - and that may be slightly generous. You'll have to trust me on that, but given a set of aircraft characteristics you can calculate it, and it won't be far off. So we have a range of 5% of 15%, or a total of 0.75% of drag due to the variation in combat fuel weights. The speed change is proportional to the square root of the difference in drag - so we are looking at perhaps half a percent of speed - less than 2 mph top.

This is less than the effect of a poor coat of paint, or that snazzy non-standard rear-view mirror, or a badly-fitting engine cowling. Certainly less than aircraft-to-aircraft (or engine-to-engine) variation.

I know that every little helps, especially for a low-fuel Fw 190 running for home with a fuller Typhoon behind it, but I don't think that's significant.

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

Hi Graham,

There is no need to guess. We can simply use normal BGS formulation to make a sound prediction.

V2/V1 = SQRT(W2/W1)

V1 = 300KEAS

V2 = ?

W1 = 10000lbs
W2 = 10500lbs

V2 = {SQRT(W2/W1)}*V1

V2 = {SQRT(W10500lbs/10000lbs)}*300KEAS
V2= 307.4 KEAS

If we hold angle of attack constant, we must increase our speed 7.4KEAS or 8.5 mph if we add 500lbs weight. Well one just might think that is insignificant. It certainly isn't gong to make much difference in what we can we catch or run from.

Now lets look at it from the Power required relationship in our fictional aircraft. Using standard BGS formulation for a power producer:

Pr1 = 2000thp

Pr2/Pr1 = (W2/W1)^3/2
Pr2 = {(W2/W1)^3/2}*Pr1
Pr2 = {(10500/10000)^3/2}*2000thp

Pr2 = 2680thp

Or a 34% increase in the amount of power required! That 4-5 KEAS in reality represents a very significant reduction in the designs power available.

Not really. The induced drag is the only a direct affect of weight increase. The reduction in power available certainly does effect our ability to overcome the power of drag other than that due to lift. Remember the power of drag other than due to lift increases at the cube of velocity.

All the best,

Crumpp

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

For what it's worth, there's a data sheet on National Archives AIR40/152 that gives fuel loads, payloads, armament and performance for the Fw 190 F-3, F-8 and G-3.

Speeds, common to all three sub-types are given as:

a) 380/0

b) 430/0

v= a) 410/5,5

v= b) 470/5,5

I'm guessing that a = loaded (bombed-up?) and b = unloaded, while the figures are kilometres per hour/kilometres of altitude (remembering that in German a comma is used where English uses a decimal point).

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

The correct way to to calculate the effect of the weight to speed is to calculate the change of the induced drag due to changed Cl and find the new balance between thrust and the drag by iteration method.

As an example if we assume that the Typhoon does 580km/h at sea level with 2200hp and 80% propeller efficiency at 4800kg. With these parameters a 500kg weight increase will decrease speed by 1,92km/h.

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

You are correct Nick! The speeds wouldn't be labeled Va, Vack, Vw, Vwck would they?

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

Quote:

The correct way to to calculate the effect of the weight to speed is to calculate the change of the induced drag due to changed Cl and find the new balance between thrust and the drag by iteration method.

I assure, we are using the correct BGS Algebraic formulation to predict performance in the event of a weight change.

Credit to John E Lewis and Charles E Dole:

Quote:

A former Marine, the late CHARLES E. DOLE taught flight safety for 28 years to officers of the U.S. Air Force, Army, and Navy, as well as at the University of Southern California.

http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471370061,descCd-description.html

http://img155.imageshack.us/img155/2...changesou0.jpg
http://img155.imageshack.us/img155/2...534d84355f.jpg

http://img231.imageshack.us/img231/4...hanges2nx2.jpg
http://img231.imageshack.us/img231/4...eca138a59f.jpg

All the best,

Crumpp

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

No, I use very basic polar calculation to determine the speed change when the weight changes.

The difference between mine and your approach is that I calculate the changed induced drag due to weight change (which means that Cl/AoA change is accounted) while the formula you use, assumes constant Cl/AoA which is a wrong approach for this particular case.

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

Of course we are holding CL constant. We are demonstrating the affect of a weight change. If the aircraft does not have that quantum increase in power available, then it must reduce performance to the point Pr = Pa.

A 50% increase in weight represents an 83% increase in power required at the same CL. That is far from insignificant.

It is not a very large change in velocity but it represents a very significant reduction in the aircrafts envelope. For Gods sake, fly a plane with and without passengers to look at your performance or one with 1/2 fuel as opposed to full tanks.

All the best,

Crumpp

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

Crumpp: There is no point in doing calculations using this equation of simple ratios. It contains no effect of altitude, which is relevant to the effect of weight on speed. It would be true if all the drag was lift-induced, but it is not. It would be more appropriate for addressing the stall speed, if in the inverse sense. There it is induced drag which is the dominant term, and zero-lift drag that can be neglected. I assume that you are working to some derived system of equations, which do not hold true for this case. It is always better to go back to the basic principles of lift, drag and thrust (power).

Your comments on power drop is puzzling, as there would be no power drop. Maximum speed is when thrust = drag: over such small differences (yours or mine), inputs such a propellor efficiency and engine power will not change so thrust is constant. The only change is drag: I repeat that the only component of the drag that changes with weight is the lift-induced drag. The size of the change in the induced drag is of the order of that I quoted.

Drag is dependent upon the square of the speed. I think I see what you mean about "power of drag" being to the cube of speed, but it is not a concept I'm familiar with, nor necessary in this case. I think you are trying to say that to regain 8.5 mph (on a Typhoon sl top speed around 300 mph) would take an extra 34% of power - even on a cube law this is overstated as only some 9% would be required (1.03 cubed).

Harri: your calculation shows an even smaller change than mine, but given the respective assumptions we are clearly in the same ballpark. My estimate of 15% induced drag may be out by some percent, but equally I don't think that any Typhoon actually achieved 2200hp at its top speed, which I think you may be overstating. Perhaps some of the later Tempests did. Actual performance of the Sabre is not defined very well in the references I have.

Nick: the main effect of the loaded case is the additional drag of the bombs and carriers.

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

Well, I and Graham are demonstrating how much the increased weight reduces the top speed; increased weight naturally changes the Cl/AoA at top speeds. However, you are demonstrating how much the speed (or power) should be increased to keep Cl/AoA constant.

Basicly you are using the wrong approach for this particular case; we are interested about the speed change due weight change and that also means that the Cl/AoA changes.

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

I just used some quick and dirty values out of hat for the demonstration; the purpose was just to show the correct approach for this kind of calculation.

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

Quote:

Basicly you are using the wrong approach for this particular case;

Baloney. You are arguing that the speed reduction is insignificant but you fail to see the entire picture.

The small change in speed represents a very significant reduction in the aircrafts performance envelope. It's all tied together and you cannot separate the affect.

That aircraft's entire envelope is reduced.

No I am not "wrong". You wish to separate that which cannot be.

In fantasy land in a realm with no significance to the real world, weight affects are insignificant because top speed is only reduced a small portion.

In reality, weight affects are very significant and the number one concern of most designers.

Two wrongs do not make a right.

All the best,

Crumpp

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

Bottom line is the idea we can classify weight affects as insignificant because in a very short sighted manner we only percieve a small velocity change is fundamentally flawed.

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

Quote:

The difference between mine and your approach is that I calculate the changed induced drag due to weight change (which means that Cl/AoA change is accounted) while the formula you use, assumes constant Cl/AoA which is a wrong approach for this particular case.

Harry PHil,

I am very familiar with "your technique" btw. It's not new or original. In fact I use it in a spreadsheet I constructed to predict aircraft performance. I would be glad to share that spreadsheet with you.

However you still have to go back and couple the affects of the power reduction. Only this time we have to do it manually. The end results are exactly the same.

The standard BGS formulation presented in numerous aerodynamic and engineering text I posted in this thread works just fine at illustrating the affects of weight. The end results are exactly the same.

An increase in weight represents a significant reduction in performance.

All the best,

Crumpp

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

What I and Graham have pointed out is that for these kind of aircraft the speed reduction is small at high speed near sea level. And we both do that correctly by using the polar and iteration method which accounts needed higher Cl/Aoa.

Your approach assumes constant Cl/AoA which is not a correct approach for this particular case because with given available power the plane can't maintain constant AoA at higher weight.

It's not "my technique" but very basic use of the polar; Graham does the calculation with the very same principle and anyone with sound basic knowledge would use this technique. And I teached you to use it in Ubiforums some time ago:

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

You might remember that then you claimed this technique as "misuse of formulas" so I afraid that the sensible discussion is impossible in this case as well.

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

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

Once more I am pilot and aircraft owner so I see these affects first hand every time I fly my family on a trip. It's not some academic exercise.

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.

Instead of having a nice conversation, we are dealing with your lack of understanding on how a parametric study works to determine the affect of something. Parametric study is the most common and accepted way of determining the cause, effect, and magnitude.

My issue has always been that Graham's original post:



Is not true because one cannot separate the affect as Lift, drag, and Angle of attack all have a fixed by design finite relationship. If the only affect of adding weight was small reduction in top level speed, then we could say it was insignificant.

It is not insignificant. That small drop in level speed represents a very significant reduction in the aircrafts entire maneuvering envelope.

In no way, shape, or form can we say that weight does not matter and has little affect on the airplane.



http://www.principalair.ca/article-weight.htm

All the best,

Crumpp

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

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.

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.

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.

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

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.

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

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

All the best,

Crumpp

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

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.

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

Quote:

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":

http://img354.imageshack.us/img354/8...purposech3.jpg
http://img354.imageshack.us/img354/8...0f8e24f512.jpg

Quote:

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:

Quote:

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

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

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

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!

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

Quote:

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

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

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.

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

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?

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

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.

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

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.

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