Performance of the Fw 190A on the Deck?

[Crumpp]

You are most welcome Boomerang. I personally am most thankful to Col Feidler for joining us too.

Clearly, it is impossible to assess the reliabity of the cause and effect relationship set out in this statement. What is striking, however, is the statement that one aircraft was significantly faster than the others in the squadron. This is entirely consistent with the idea that there were considerable variations between the performances of aircraft of the same type.

Absolutely.

It's funny too the bond that forms between a pilot and his aircraft. Even my little GA family mover has an emotional attachment.

I mentioned to my wife last flight that I was thinking about getting a Mooney. It's faster and more economical than what we have now. The wife wouldn't have a thing to do with that idea. Completely out of character for her, she snapped at me to quit being disloyal to "Bravo Fox" as the plane had always carried us safely through every encounter. I though it was funny as she is not a pilot. Women huh? God bless em.



Of course, I will admit that the last thing I do before shutting out the lights in the hanger is get pat her on the cowl and thank her for being such a good airplane.

Oskar told me he was extremely upset when he lost one particular FW190 after being shot down. He was really upset when they hauled the plane off to the scrap yard an still remembers little details about that one aircraft. It was definitely his favorite.

You might also wish to consider his Fig 16, where the 1g and 4g flight envelopes for the F-5E can be seen to be very close together, at max speed at sea level. That's very little change for a 300% increase in weight. You can see why the change in level speed due to a 5% increase in weight is regarded as insignificant.

I think we are still just looking at maximum speed and nothing has changed in my opinion:

Crumpp says:

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.

From Perkins and Hage, "Airplane Performance Stability and Control"










Additionally it is very hard to compare aircraft like the F-16 to WWII designs. The entire design emphasis has evolved over time as to what is important in the fight due to the abundance of thrust available.

From Andrew M Skow paper "Agility as a Design contributor" AIAA library:




Mr Skow's paper is a worthwhile read and I meant to share it but unfortunately it exceeds the boards allotted attachment size for pdf files.


All the best,

Crumpp

[Nick Beale]

Obviously, I enjoy a bunch of equations as much as anybody but then I glanced up, saw the title of this thread and got distracted...

Something else I picked up from AIR40/152 was some numbers for the Fw 190 F-9. I've posted it as an attachment to preserve the layout, superscripted letters etc.

I get the words and the gist but if anyone can explain some of the other terms used, I'd be interested.

[Crumpp]

That looks like Vmax for Kampfleistung, Notleistung, and Dauerleistung speeds for the FW-190F9 in the 1st and 2nd Gear supercharger for the aircraft with and without a load both indicated and true.

The time to climb, climb rate, and service ceiling at 4100kg is included as well.

That is from the Kennblatt and is used for flight planning purposes.

All the best,

Crumpp

[Franek Grabowski]

Bill, it is obvious that P-51B/C was aerodynamically slightly different than D/K. I cannot say for sure, but I suppose there might have been some other slight differrencies, eg. in props. That said, drop of maximum speed was the result of several minor changes, and not only one factor. Still, 10 mph is within marigin for error and may purely depend on quality of factory fresh aircraft, not to mention worn out airframes.
Overall, the point that Graham tries to make is not that the weight is unimportant. He just merely points out, that differencies of weight caused by fuel consumption are mariginal for aircraft performance in horizontal flight. It does matter in vertical manouvers, though. This is obvious for anyone, who ever attempted to calculate such things, just as it is obvious, that adding a few pounds of putty and lacquer will increase the horizontal speed!

[drgondog]

Originally Posted by Franek Grabowski

Bill, it is obvious that P-51B/C was aerodynamically slightly different than D/K. I cannot say for sure, but I suppose there might have been some other slight differrencies, eg. in props. That said, drop of maximum speed was the result of several minor changes, and not only one factor. Still, 10 mph is within marigin for error and may purely depend on quality of factory fresh aircraft, not to mention worn out airframes.

Gene lednicer did a very nice study and published reports based on VSAERO for both the B and D in comparison with Spit IX and Fw 190A and D-9. The reason I mention this is that in his modelling the 51D was actually slightly cleaner, and the difference was that the bubble canopy had complete lift distribution w/o separation from the top of the windscreen, aft. In addition the sloped windscreen of the D (more than B) suggested less stagnation at the windscreen. The B quickly separated above the cockpit. No Malcolm Hood version was modelled for the B.

The reason I bring this up is to suggest that when you add the same extra internal weight for the B as the airframe increases for the D, the report implies that the same P-51B, loaded an extra 600 pounds, or conversely take out the guns and ammo, and re-test..

would show an even greater Vmax difference than 10+ mph as the 51B was slightly 'draggier' in parasite drag than a D.

All you say is true generally speaking..but having said that, the delta Weight causes the airspeed to vary as V2/V1 = SQRT(W2/W1)
using the same exact airfame and power conditions.

Overall, the point that Graham tries to make is not that the weight is unimportant. He just merely points out, that differencies of weight caused by fuel consumption are mariginal for aircraft performance in horizontal flight. It does matter in vertical manouvers, though. This is obvious for anyone, who ever attempted to calculate such things, just as it is obvious, that adding a few pounds of putty and lacquer will increase the horizontal speed!

Franek - Respectfully, I made a living for several years "calculating such things" following a Masters Degree in Aero. Having said this, my real expertise was Structures, Aeroelasticity and finite element modelling.

It is not so obvious to me that Weight delta does not affect top speed - because it does. You may not agree my math or logic, but respectfully, bring your own if you have a different POV.

Marginal seems to be what you are debating and I'm ok with you and Graham dismissing the value to Max speed available to say a P-51B after getting rid of its Fuselage tank 85 gallons. The math says it's about 10-12 mph.

If that is insignificant to you we can agree your terminology, but the delta is not due to plugging gun ports, or polishing the airframe, or switching engines...

Hari - two things about your comments.

First- at Vmax the Thrust Hp is maximum for that altitude and weight.

When weight increases, for the same airframe, the Thrust Hp remains the same, but Vmax decreases alightly as the AoA must increase to maintain level flight for that Thp and weight condition.

In other words the Thrust available is the same for both weight conditions, but the velocity Attainable is Less for the heavier weight conditions.

In other words, Thrust HP may not increase beyond the max Thrust Hp available in level flight.

If you want to demonstrate the math that proves a slight increase in AoA from freestream impingement on the propeller plane increases the change in momentum of the mass flow through that plane (positively) - give it your best shot.

By your anology , as the ship climbs at a steeper angle relative to freestream, the thrust would increase?

By using the Propeller/Engine thrust equation as you used it (which is appropriate for level flight) then as the angle of Attack increases you would quicly reach a point where sustainable velocity is much lower than it was in level flight... and your thrust increases dramatically above it's max rated Hp Thrust in level flight. Do you believe this?

[drgondog]

Originally Posted by Franek Grabowski

Bill, it is obvious that P-51B/C was aerodynamically slightly different than D/K. I cannot say for sure, but I suppose there might have been some other slight differrencies, eg. in props.

Forgot to answer this in detail. The external differences were to remove turtledeck, change the slope of the windscreen, add the bubble canopy, increase the Root chord to five a steeper angle of the inboard wing to fuselage.

Internal differences, Uplocks for wheels, increased thickness of ammo doors and add 2x .50's plus 660 rounds of ammo, and beef up the vertical stabilzer spar/fuse attach structure..slight change in horizontal stabilizer incidence

Props same except K had a slightly different prop, only to extent of removing sleeve at propeller hub. Same wing except as noted above

Later the D got metal elevators, tail strake.

Net - 51D cleaner, heavier, slower than P-51B-15 with same prop and engine in both airframes - about 10-12 mph on a statistical average via flight tests at Wright Pat and Eglin and NAA facilities.

[Harri Pihl]

Originally Posted by drgondog

First- at Vmax the Thrust Hp is maximum for that altitude and weight.

I don't actually calculate the thrust hp but directly the thrust from the brake hp; the hp chart I used just gives the bhp.

Originally Posted by drgondog

When weight increases, for the same airframe, the Thrust Hp remains the same, but Vmax decreases alightly as the AoA must increase to maintain level flight for that Thp and weight condition.

The thrust remains same at original velocity but at the new balance point at lower speed the thrust will be higher.

Originally Posted by drgondog

If you want to demonstrate the math that proves a slight increase in AoA from freestream impingement on the propeller plane increases the change in momentum of the mass flow through that plane (positively) - give it your best shot.

Ok, I'll demonstrate using the calculation I did for the P-51B:

First thrust at original 9680lbs (4390,85kg) and 352mph (566,368km/h=157,3244 m/s):

1580hp = 1178014 W
exhaust thrust = 120kp = 1176,798N
Propeller Thrust = (0,8*W)/V = 5991,216N
Combined thrust = 7168,014 N

Then thrust at 10280lbs (4663,008kg) and 351mph (564,887km/h=156,913m/s)

1580hp = 1178014 W
exhaust thrust = 120kp = 1176,798N
Propeller Thrust = (0,8*W)/V = 6006,923N
Combined thrust = 7183,721N

Now we know that at the supposed new balance point there is 15,7N more thrust available so lets check if the D = T at these points:

First at 9680lbs

Speed =157,324m/s
density = 1,225kg/m3
wing area = 21,83m2
Aspect ratio = 5,83
Lift = 4390,85*9,81 = 43059,51 N
Calculated Cd0 = 0,020504
e = 0,8

Cl = L / (A * 0,5 * r * V^2) = 0,130111
Cdi = Cl^2 / (pii * AR * e) = 0,001156
Cd = Cd0 + Cdi = 0,021659

D = Cd * r * V^2 * 0,5 * A = 7168,014N = T Check!

Then at 10280lbs

Speed =156,913m/s
density = 1,225kg/m3
wing area = 21,83m2
Aspect ratio = 5,83
Lift = 4663,008*9,81 = 45728,487 N
Calculated Cd0 = 0,020504
e = 0,8

Cl = L / (A * 0,5 * r * V^2) = 0,1389007
Cdi = Cl^2 / (pii * AR * e) = 0,0013171
Cd = Cd0 + Cdi = 0,0218206

D = Cd * r * V^2 * 0,5 * A = 7183,721N = T Check!

Q.E.D.

Originally Posted by drgondog

Your specific references for each claim you just made for the P-51B?

It's calculated backwards from the linked chart:

http://www.wwiiaircraftperformance.o...level-blue.jpg

And using something else does not make a big difference, ballpark should be correct. The point here is to show the principles.

Originally Posted by drgondog

For example "e" is derived empirically, because the effect of spanwise lift distribution, increase in trim drag and the increases in all forms of drag on the airframe. .8 is a good rule of thumb for conservative preliminary design purposes - but only that unless you have test results?

It's just an estimate. I can calculate e from various data but 0,8 should be a good enough estimate.

Originally Posted by drgondog

Ditto prop efficiency. .8 to .85 are good Prelim Design numers. So where would point me to .8 as being correct for the P-51B?..

Same here, just an estimate. I have the Hamilton standard red book so I can make a better estimate but again 80% should be good enough for the purpose.

Originally Posted by drgondog

Having said that, how do you arrive at approximately 1mph delta for a 6% weight increase? What math are you using?

I have listed the formulas on the page 5 of this thread and Chapter 14 of Hoerner's "Fluid Dynamic Drag" shows an example.

Basicly we don't know the Cl, drag, thrust nor speed at new balance point. However, we know how each of these behaves so we can solve the problem with iteration process. If you look the above calculation, you can see that it really works.

I can put together a small spreadsheet to demonstrate the calculation if you are interested; you can change the parameters and see the results instantly. My stuff is written in Finnish so translating might take some time.

[Harri Pihl]

For 600lbs increase from 9680lbs to 10280lbs in the case of the P-51B causes 1,48km/h speed reduction for max speed at sea level. The parameters being 352mph at sealevel and, 1580hp (67") and 120kp exhaust thrust, prop efficiency 80% and value of the e being 0,8. Calculated Cd0 being 0,02054.

[drgondog]

Originally Posted by Harri Pihl

For 600lbs increase from 9680lbs to 10280lbs in the case of the P-51B causes 1,48km/h speed reduction for max speed at sea level. The parameters being 352mph at sealevel and, 1580hp (67") and 120kp exhaust thrust, prop efficiency 80% and value of the e being 0,8. Calculated Cd0 being 0,02054.

Your specific references for each claim you just made for the P-51B?

For example "e" is derived empirically, because the effect of spanwise lift distribution, increase in trim drag and the increases in all forms of drag on the airframe. .8 is a good rule of thumb for conservative preliminary design purposes - but only that unless you have test results?

Ditto prop efficiency. .8 to .85 are good Prelim Design numers. So where would point me to .8 as being correct for the P-51B?..

Cd0 = .02054? and your source is? That is higher than the Ames wind tunnel model with real airframe.

Having said that, how do you arrive at approximately 1mph delta for a 6% weight increase? What math are you using?

[Franek Grabowski]

Bill
There must have been some differrencies in aerodynamics, because P-51D turned highly unstable at high speeds and had to be modified. That is one thing.
Another is accuracy of such calculations. As we know, engineering theories are based on approximates and simplified theories, and quite often we do not know what is actually going on. This is very important in understanding calculations of performance.
If methods widely used give us 10% accuracy (~40 mph!), and the result must be verified in tests of actual aircraft, which then has some not insignificant margin for quality of production, then we find that those few miles are just unmeasurable. On the other hand, we know that horizontal speed is just resulting from several factors. The most important is the airfoil used, then wing, then airframe, then engine and prop. Given each factor's share, it was concluded that small changes of weight are just unimportant in overall picture. That is what Graham is trying to show all the time.
BTW
Spitfire IX and Mustang III/IV/IVA were powered by the same Merlin engine. Which one was heavier and which one was faster?