Fw-190 Dora-9 vs P-51D Mustang

[plan_D]

They stopped painting B-17s because of the increased weight, didn't they?

[FLYBOYJ]

Originally Posted by plan_D

They stopped painting B-17s because of the increased weight, didn't they?

Yep - like other aircraft late in the war...

It also eliminated another process during assembly.

[Jabberwocky]

Painting an aircraft makes quite a large difference in speed. Not only from its weight, but also from its drag. British testing of the Mustang I showed that when standard British camoflage and markings were painted on speeds dropped by around 8 mph.

The matte black paint originally used on Mosquito night fighters was abandoned because it had significantly more drag than the RAF standard semi gloss finish. Apparently the speed loss was on the order of some 22 mph.

Speed trials on an underperforming Spitfire Mk V (EN946) showed that rubbing down, repainting and polishing just the wing leading edge increased speed by ~6 mph. With some other fairly simple modifications, they later got the same Spitfire Mk V up to 385 1/2 mph, or about 15 mph faster than a standard Mk V.

The official speed and range for a Mk XI PR Spitfire was suppose to be around 420 mph and around 2,300 miles with a 170 gallon overload tank. However, ground crews and even pilots would regularly strip, fill, wax and polish all the aircraft leading edges, which reportedly gave another 10-15 mph speed and add up to 200 miles range over the by the book numbers. When speed is your only defence, you do everything you can to maximise the advantage.

[KraziKanuK]

Have heard that German paint was finer a 'grain' when applied than Allied paint, and thus smoother. True/false?

[Soren]

Something that might be of interest: http://www.anycities.com/user/j22/j22/aero.htm

[alejandro_]

An interesting note:

- Cooling drag: 16%

- Fuselaje: 30%

- Wings: 31%

- Various: 4%

- Horizontal tail: 6%

- Interference drag: 9%

- Induced drag: 1%

- Vertical tail: 9%

What are the usual values for these parameters? I had come accross some information in a book but it was on jet aircraft. Somebody mentioned the cooling drag being up to 50% of the total drag...

Regards.

[FLYBOYJ]

Very cool info!

[Soren]

The comparisons are very well explained and precisely calculated, using NACA's own aerodynamics program, thats what I like about it.

[wmaxt]

Originally Posted by alejandro_

An interesting note:

- Cooling drag: 16%

- Fuselaje: 30%

- Wings: 31%

- Various: 4%

- Horizontal tail: 6%

- Interference drag: 9%

- Induced drag: 1%

- Vertical tail: 9%

What are the usual values for these parameters? I had come accross some information in a book but it was on jet aircraft. Somebody mentioned the cooling drag being up to 50% of the total drag...

Regards.

Interesting, it would be great if we had the same info for the rest of the planes.

Here are a few overall drag coefficents (C/D) and Lift over Drag (L/D) numbers to compare (by NACA/NASA

Plane -- C/D -- L/D
B-17G - .0302 - 12.7
B-24J - .0406 - 12.9
B-29A - .0241 - 16.8
B-26F - .0314 - 12.0
P-51D - .0163 - 14.6 the article above puts the C/D of the P-51D at .019957 which fits better with its relative performance.
P-38L - .0268 - 13.5
F6F-3 - .0211 - 12.2
PBY-5A .0309 - 7.73

wmaxt

[Lunatic]

Originally Posted by wmaxt

Lunatic,

The site I referenced is what I belive after seeing a large number of descriptions of both systems including post war AAF and NAA descriptions which stated, True laminar flow was not achievable due to manufacturing tolerances available at that time. To keep the surface smooth on a B-47 required slippers, How many times have I seen people riding the wing or walking in boots on a P-51 wing? I viewed these several years ago but will try to find them again.

How much speed added, are we talking here
P-51D 9,000lbs/1650hp = 5.4 lbs/hp and 437
P-47N 16,000lbs/2800hp = 5.7lbs/hp and 460mph
F4U-4 12,000lbs/2200hp = 5.3lbs/hp and 446mph
P-38L 18,000lbs/2850hp = 6.3lbs/hp and 414mph
Bf-109K 7348lbs/2,000hp = 3.7lbs/hp

The P-51 doesn't show anything special here, infact the F4U-4 is doing as good with higher drag cloth wings and a radial engine. The P-38 is giving up a full pound per hp for 23mph. AND the N is not only 23mph faster but is carrying more weight for each horse and that terrible radial engine.

But the problem is you are referencing info based upon old released data. For instance, top seed on the F4U-4 was not 4446 mph, it was 464 mph TAS at ~20,700 feet! That number is right out of the F4U-4 pilot handbook. For most US planes, immeadiately following WWII, the top speed figures given reflect Military Power, not WEP.

Also, in your figures for the P-51 power where is the radiator thrust? Yes, it does not overcome the drag of the plane, but it does cancel out 90-100% of the cooling system induced drag, which does not occure for any of the other fighters you've listed (actually the F4U-4 cooling system does generate some thrust, but much less than that of the P-51).

Originally Posted by wmaxt

I'm not sure where your numbers come from but that level of extra thrust isn't showing up in the performance of the P-51. The Placement of the cooling scoop/plenum in a high drag area and the resultant smoothing of the airflow provides most of the effect your seeing.

I took the numbers given from various sources, and the fact that, at any speed over ~180 mph IAS the P-51 cooling system cancels out at least 90% of the cooling system induced drag. Cooling systems accounted for between 10 and 20% of the drag on WWII prop fighters, I used 12% which I am confident is low for the P-51 since it was a slick design, and extrapolated the numbers from there - somewhere there is a figure for how much equivalent HP the radiator thrust system is making at a given speed (I'll try to find it when I have time - IIRC it's 340 hp @ ~ 400 mph at 20 or 25K). The key point is that drag increases with the square of the velocity, and so does the radiator generated thrust. So at higher speeds the effective power provided by the system becomes quite large.[/quote]

Originally Posted by wmaxt

The Merideth Effect is a minor jet engine just without the open flame, the same rules of thermodynamics apply. The only thrust is that provided by the expansion of the air caused by the radiator heat. If that wasn't true every aircraft we fly today would have a big scoop under the wing to get free horse power. The P-51s system slowed the air more than any other giving a. better cooling system performance and b. a little thrust many of the estimates I've seen were from 50lbs to 150lbs

And just how much thrust do you think was being generated by the prop? Cruising at 400 mph, 150 lbs of thrust is probably more than 10% of the prop thrust. Another thing is the fact that as the reaches increasingly higher speeds the prop thrust becomes limited because the tips cannot exceeding mach, thus prop efficiency is dropping off, where the radiator thrust is not effected by such concerns. As for the cooling system effectiveness, sheer size of the radiator core (which is why I believe my figures are low - on the P-51 the cooling system was huge so the drag was probably closer to 20%, not 10%) ensures exceptional cooling which was one reason the P-51 didn't benefit much from water injection.

As for every plane today having such a system... they would if they used conventional engines and flew at high speeds. However, any modern plane that is going to stustain these kinds of speeds is going to be using a jet or a turbo-jet engine. It's a solution to a problem that is no longer really relevant. At the speeds of modern civilian piston powered prop's the expense of routing the cooling system in a manner similar to that of the P-51 is not justified for the meager gains achieved at the speeds these planes fly.

Originally Posted by wmaxt

I have also seen the speed of the P-51 creditted to either the laminar flow or to the cooling system without mention of the other, which is it?. The P-51 was a very good aircraft but it wasn't perfect nor was it as good as its press.

wmaxt

Some of both. Personally, I think the laminar flow wing was more about providing room for fuel than anything else. Having the maximum thickness at the center rather than 25% back from the front of the wing makes for a lot larger tanks. Some advantage when cruising was achieved vs. a conventional wing of the same thickness, but there were conventional wings that were thinner, provided the same lift, and induced less drag - they just had no room for fuel. So I'd say the radiator thrust system not the laminar flow wings was the bigger contributer to its speed.

=S=

Lunatic

[Jabberwocky]

Lunatic:

My October 1944 and April 1945 charts for F4U-4 both have 446 mph as max speed for military power and 452 mph as max speed for War Emergency Power at 70" HG and 20, 300 and 20,800 feet respectively.

Configuration was clean and T/O weight was ~12,500 lbs

This is the first time I have run into the 464 mph figure. Are you sure it isn't just a typographic error?

[Lunatic]

Originally Posted by Jabberwocky

Lunatic:

My October 1944 and April 1945 charts for F4U-4 both have 446 mph as max speed for military power and 452 mph as max speed for War Emergency Power at 70" HG and 20, 300 and 20,800 feet respectively.

Configuration was clean and T/O weight was ~12,500 lbs

This is the first time I have run into the 464 mph figure. Are you sure it isn't just a typographic error?

Check for yourself...

http://www.history.navy.mil/branches/hist-ac/

Notice the "clean configuration" figures in the notes and convert KNOTS to mph.

=S=

Lunatic

[Jabberwocky]

Originally Posted by Lunatic

Check for yourself...

http://www.history.navy.mil/branches/hist-ac/

Notice the "clean configuration" figures in the notes and convert KNOTS to mph.

=S=

Lunatic

Thanks for the link. Great stuff. My Broadband is going to be worked overtime tonight!

Looking at the F4U-4 link, I think it possible that one of us has made a mistake in our calculations.

Max speed is given as 393 knots @ 20,500 feet.

1 knot = 1.1508 miles

393 kph = 452.25 mph

So, by my calculation, the max speed of the F4u-4 is 452 mph.

Also, check the knots to mph conversion chart on the side of the 1.6mb F4u-4. 393 knots is pretty much bang on 452 mph.

[DerAdlerIstGelandet]

Originally Posted by syscom3

So youre saying the FW190 can handle 9G turns? Wouldnt the pilot black out before then?

Yeap but that does not mean that the aircraft can not handle the 9Gs.

[syscom3]

If the pilot is unconscience, then it doesnt matter if the plane can handle 9 gee's or 20 gee's. Its going to be shotdown.