Voodoo in pieces...

[GRNDP51]

Re: Voodoo in pieces...

They are not doing the change with the goal of a better bomber escort.

Jarrod

Now this was funny, I would love to see the look on the B-17 pilot's faces when Voodoo pulls up next to them

[taglialavore]

Re: Voodoo in pieces...

They are not doing the change with the goal of a better bomber escort.

Jarrod

Of course they don´t. May be my english is not good.
I can think the thrust and so the speed are bigger and the induced drag also, so the angle of incidence of the flow is also bigger?. Surely must be more complicated because the bigger thrust tends to pitch down the nose and the tail have to play a different game. There are more moments actuating in this complex equilibrium.
Sorry, I´m only asking.

[L.E.D.]

Re: Voodoo in pieces...

Actually at race speeds, induced drag (drag caused by lift) is kind of the least of your worries. The amount of lift the plane needs is the same as its weight at all speeds. (In turns, of course, more lift is generated, and induced drag becomes a bigger factor.) At high speeds lots of the drag is parasite drag - which is why wings are clipped (less airplane), bondo is applied and everything is polished (lower drag coefficients). Another big drag contributor at high speed is trim drag. The wing has a pitching moment that wants to point the nose down and the tail has to counter it. That tail load can be thousands of pounds! (Think of the fuselage oil-canning you see in some pics.) The tail is making its own induced drag making lift *downwards* that the wing has to make up for to hold the plane up - and make more induced drag.

Lots of things can be done for this- move the CG back, and live with reduced stability and handling qualities, - reflex the flaps and ailerons (rig them to ride trailing edge up a little) making the wing have a smaller pitching moment coefficient, and tweak the relative angle between the wing and the tail so that you need minimum elevator deflection to be in trim at speed, because deflection is draggier than streamlined elevator. Changing the thrust line helps, and you can also *not* clip the horizontal tail - if it has to lift down, more span will let it do so more efficiently.

Anyway, what I'm getting at is that incidence changes are more about trim drag than induced drag. =)

[taglialavore]

Re: Voodoo in pieces...

Actually at race speeds, induced drag (drag caused by lift) is kind of the least of your worries. The amount of lift the plane needs is the same as its weight at all speeds. (In turns, of course, more lift is generated, and induced drag becomes a bigger factor.) At high speeds lots of the drag is parasite drag - which is why wings are clipped (less airplane), bondo is applied and everything is polished (lower drag coefficients). Another big drag contributor at high speed is trim drag. The wing has a pitching moment that wants to point the nose down and the tail has to counter it. That tail load can be thousands of pounds! (Think of the fuselage oil-canning you see in some pics.) The tail is making its own induced drag making lift *downwards* that the wing has to make up for to hold the plane up - and make more induced drag.

Lots of things can be done for this- move the CG back, and live with reduced stability and handling qualities, - reflex the flaps and ailerons (rig them to ride trailing edge up a little) making the wing have a smaller pitching moment coefficient, and tweak the relative angle between the wing and the tail so that you need minimum elevator deflection to be in trim at speed, because deflection is draggier than streamlined elevator. Changing the thrust line helps, and you can also *not* clip the horizontal tail - if it has to lift down, more span will let it do so more efficiently.

Anyway, what I'm getting at is that incidence changes are more about trim drag than induced drag. =)

Thank you very much L.E.D.

[John]

Re: Voodoo in pieces...

Hello TAG,
just to add to the excellent explanation by L.E.D.: The stock P-51D has positive incidence at the root of the wing, and we know that even a mildly cambered airfoil will produce lift when traveling through the air at zero angle of attack. Since the race P-51's are lighter than a stock Mustang, the extra positive incidence is likely not required; especially at high speed as L.E.D. has mentioned.

That being said, I would like to know Strega's main wing incidence setting(?). I'm guessing that it is near zero degrees. Someone somewhere said it was 10 degrees different(thus the "X" on Strega's Fin), but I cannot fathom that.

...so what was the 007 back in the day?

[Gibbs]

Re: Voodoo in pieces...

Hello John, from what I understand 10 degrees is impossible.
Stock P-51 (all models?) wing incidence is variable to max. +1 degree.

Gibbs

[Mluvara]

Re: Voodoo in pieces...

Why the boil off people. Dago, still the fastest Mustang around the sticks flew just fine with that scoop hanging into the breeze.

One thing that is lost in a lot of this discussion is the course changes since Dago flew its record run. Year after year, we have seen a tightening of the course, along with new calculations. Most of these have increased sustained g, slowed the airplanes down on the course.

Michael

[taglialavore]

Re: Voodoo in pieces...

Hello TAG,
just to add to the excellent explanation by L.E.D.: The stock P-51D has positive incidence at the root of the wing, and we know that even a mildly cambered airfoil will produce lift when traveling through the air at zero angle of attack. Since the race P-51's are lighter than a stock Mustang, the extra positive incidence is likely not required; especially at high speed as L.E.D. has mentioned.

That being said, I would like to know Strega's main wing incidence setting(?). I'm guessing that it is near zero degrees. Someone somewhere said it was 10 degrees different(thus the "X" on Strega's Fin), but I cannot fathom that.

...so what was the 007 back in the day?

John,
What you say has a lot of sense also and helps me to round the idea about changing the AOI.
May be it means faster landing speed normally, but as the weight is lower, it possibly has less landing speed.
I don´t know which is the landing speed in this case, compared with a stock P-51.
Thank you!

[Race5]

Re: Voodoo in pieces...

Hello TAG,
just to add to the excellent explanation by L.E.D.: The stock P-51D has positive incidence at the root of the wing, and we know that even a mildly cambered airfoil will produce lift when traveling through the air at zero angle of attack. Since the race P-51's are lighter than a stock Mustang, the extra positive incidence is likely not required; especially at high speed as L.E.D. has mentioned.

That being said, I would like to know Strega's main wing incidence setting(?). I'm guessing that it is near zero degrees. Someone somewhere said it was 10 degrees different(thus the "X" on Strega's Fin), but I cannot fathom that.

...so what was the 007 back in the day?

No way it is a 10 degree change. That would be a change of 15" per 10 feet. I have never heard the exact number but I would guess it is less than 2 deg.

[AAFO_WSagar]

Re: Voodoo in pieces...

I don't know if this adds to the discussion but, years ago, either Tiger or Kerch, probably Kerch, told me that stock Mustangs were set up with wing and tail incidence that were, essentially, a compromise. The airplane was tasked for many jobs and had to be as good as possible at each of them. Also, bear in mind, in some cases, the guys flying them were relatively low time pilots. The airplane needed to be a sweet flyer and from everything we've all heard over the years, they do, indeed, fly well in stock configuration.

Fast forward to the needs for a race plane. They are quite specific in that the airplane can now compromise everyday handling traits and the ability to do many things very well, for a set up that aims to gain one thing at the sacrifice of others. It's now best at going fast and turning left. Still flies well, just not AS well...

Again, hope I'm recollecting correctly, not repeating a previous message and adding something to the discussion.

[Curt_B]

Re: Voodoo in pieces...

The wing incidence change on the Mustang has the effect of increasing the fuselage angle of attack. For symmetrical fuselage shapes, this would be negligible since the fuselage drag vs aoa curve is pretty flat for small angles. In the case of the Mustang, increasing the fuselage angle slightly reduces drag due to the upswept radiator afterbody, effectively making it more streamlined. Of course once this is done, it points the engine in a different direction, so that would have to be checked. The tail incidence is a fall out and would need to be reset for streamlined elevator deflection. All of this is fine tuning of course to get the most speed. The original Mustang is fine as built.

[John]

Re: Voodoo in pieces...

The wing incidence change on the Mustang has the effect of increasing the fuselage angle of attack. For symmetrical fuselage shapes, this would be negligible since the fuselage drag vs aoa curve is pretty flat for small angles. In the case of the Mustang, increasing the fuselage angle slightly reduces drag due to the upswept radiator afterbody, effectively making it more streamlined. Of course once this is done, it points the engine in a different direction, so that would have to be checked. The tail incidence is a fall out and would need to be reset for streamlined elevator deflection. All of this is fine tuning of course to get the most speed. The original Mustang is fine as built.

Curt, I've often pondered the effects of changing the fuselage angle through the air on Strega(mostly thought that the wing incidence change was mainly an attempt to line up the prop thrust line with the relative wind), but I didn't figure out that it was also about the radiator after-body. Perhaps it is the reason for the long after-body on the P-51H Mustang(to reduce drag without decreasing main wing incidence too much). Thanks for your input, it is always very educational.

Could we maybe see extended aft wing fillets(forgot the technical term) on Voodoo again?

[Wild Bill Kelso]

Re: Voodoo in pieces...

007x!!!

[Curt_B]

Re: Voodoo in pieces...

John, Directing the engine might have been the original reason they did the wing incidence change. Whatever the original reason. the reduction in after body drag is why it works. Trim and induced drag would be unaffected once the tail incidence is adjusted too, other than the engine would have an uplifting component reducing tail trim drag, but decreasing forward thrust. It'd be easier to change the thrust line than do a wing incidence change. The extended 'H afterbody was to decrease drag, they wouldn't have cared about connecting that with wing incidence since it had to fly long ranges at heavy and light weights. and maneuver at max CL at low and high speeds. After all, they spent more than 120 days on the 'H. Would it really surprise anyone if the Strega strakes showed up during this mod.

[SkyvanDelta]

Re: Voodoo in pieces...

Great paint job on Voodoo as it goes from a black and white checkered flag on the side of the fuselage to sharks teeth on the bottom air scoop. Who did the graphics layout on Voodoo?

I made a picture collage of the top mustangs so it would make for an easier comparison. The outwardly differences are obvious - but the real magic for the Dago scoop is on inside guys. Personally I thinks it's pretty unrealistic to think Dago will ever be rebuilt as a racer, and her secrets should not be lost just because she is. I like the idea of the scoop mod for Voodoo.

I'm kinda torn on the wing incidence mod though. Someone once told me that is why Tiger/Strega slip in the corners (hard to keep the ball centered) - and the Dago went fast enough without it. Regardless... I'm sure someone will correct me if I was misinformed and it doesn't really matter one way or the other. I just think it's great to see a committed owner & crew working on making Voodoo all she can be. That don't come cheap OR easy.

Anyway - enough of my ramblings... pics are better.

Dago Red - Strega - Voodoo