Air scoops

[taglialavore]

If I´m asked why some Unlimited P-51´s use the belly air scoop (dog house?) like factory ones, separated from fuselage because of boundary layer driving reasons, (even Tsunami did it), ...and others are without such separation, because of less drag due to smaller frontal area (Strega, Dago Red), what should I respond?
Which is the explanation to this?. Some people prefers one design, and others the other way?...is it a compromise?
Yesss, you got it, I´m lost and confused about it, please someone explain me. Thank you.

[MLenoch]

Re: Air scoops

The theory for the P-51D style scoop is that the lip located away from the belly skin captures air that has no energy loss due to the boundary layer airflow along the wing-fuselage skin ahead of it. Thus the air has higher energy (faster, etc.) and thus produces higher cooling efficiencies inside the scoop for the radiator. Many aircraft have such scoops where the need for higher energy air is important (DC-7, A-1E, F-16 to name a few). NACA (NASA) ducts are flush in profile, yet in theory obtain re-energized air flow due to their configuration. (Now look at the F-35 which uses a tailored inlet profile without a separated scoop to maintain high energy airflow and secondarily provide a low observable shape. Boundary layer research evolution!)
I do not know why the scoop without the separation are used on some of the racers. I do not know if their frontal area is the same as stock P-51D scoops. Early A-36/P-51A aircraft had similar scoops that were against the belly skin. In the P-51B/C/D/F/G/H series, the boundary layer separated designs were produced.
Many engineer type will say the same things above when walking down the ramp at Reno and noting these against the skin coolant scoops.
(Would be great to hear other explanations/opinions)
Thx,
VL

[Vessbot]

Re: Air scoops

Since the racers have water spraybars on the radiator faces to aid in cooling, I imagine they might not have as high a need for clean air going in there and it's more worth it to get rid of the drag....

[Mluvara]

Re: Air scoops

It's also prudent to look at the difference in the location of the leading edge of the scoop on various mustangs, along with the exit door theory. There has been a lot of science, lessons, trial and error in scoops. Some mustangs have different radiators entirely, including their geometric location in the fuselage and how the air is directed to them.

Michael

[JET1]

very good basic explaination and the scoop actually produces thrust

The theory for the P-51D style scoop is that the lip located away from the belly skin captures air that has no energy loss due to the boundary layer airflow along the wing-fuselage skin ahead of it. Thus the air has higher energy (faster, etc.) and thus produces higher cooling efficiencies inside the scoop for the radiator. Many aircraft have such scoops where the need for higher energy air is important (DC-7, A-1E, F-16 to name a few). NACA (NASA) ducts are flush in profile, yet in theory obtain re-energized air flow due to their configuration. (Now look at the F-35 which uses a tailored inlet profile without a separated scoop to maintain high energy airflow and secondarily provide a low observable shape. Boundary layer research evolution!)
I do not know why the scoop without the separation are used on some of the racers. I do not know if their frontal area is the same as stock P-51D scoops. Early A-36/P-51A aircraft had similar scoops that were against the belly skin. In the P-51B/C/D/F/G/H series, the boundary layer separated designs were produced.
Many engineer type will say the same things above when walking down the ramp at Reno and noting these against the skin coolant scoops.
(Would be great to hear other explanations/opinions)
Thx,
VL

of course the thrust in lbs is minimal but an elongated scoop will produce 15 or so lbs of thrust depending on the configuration and weather conditions.

[BellCobraIV]

Re: Air scoops

My favorite scoop was the one Stilletto used when Matt J. raced it. My second favorite was the one Stilletto designed with but not flown with, where it went straight out the trailing edge of the flaps. The drawings looked really cool!

[Peashooter]

Re: Air scoops

My favorite scoop was the one Stilletto used when Matt J. raced it. My second favorite was the one Stilletto designed with but not flown with, where it went straight out the trailing edge of the flaps. The drawings looked really cool!

But, but Stiletto didn't...nevermind...

[taglialavore]

Re: Air scoops

Since the racers have water spraybars on the radiator faces to aid in cooling, I imagine they might not have as high a need for clean air going in there and it's more worth it to get rid of the drag....

This is a good one, I can think that those racers with spraybars may not use the air scoop separated from the belly (of course may be some exceptions), but as a rule of thumb, it is a good explanation.
You get "the necesary cooling" with water spray so you can reduce a little the frontal area eliminating the gap.
By the way, I thought Stilletto had no air scoop in the belly at all, but surely I´m wrong.

[Leo]

Re: Air scoops

I thought Stilletto had no air scoop in the belly at all

It was made of Invisiblinium...
I tink I have read that the system on Stilletto actually worked very well, at least once the plane was moving. Still remember how they used to tow it out to the runway, start it up and take off before it had a chance to overheat!
I sure like the way it looked.
My favorite was MAII's last scoop, the bulge with the NACA in it. THAT was cool.

[taglialavore]

Re: Air scoops

[QUOTE=BellCobraIV]My favorite scoop was the one Stilletto used when Matt J. raced it.
Was it placed in the wing leading edge or in the fuselage belly?

[t-dub]

Re: Air scoops

[QUOTE=taglialavore]

My favorite scoop was the one Stilletto used when Matt J. raced it.
Was it placed in the wing leading edge or in the fuselage belly?

Neither.....

[AirDOGGe]

Re: Air scoops

I would imagine that Dago has a smaller, closer-to-the fuselage belly-scoop because she does all her "business" at low (racing) altitudes, where the thicker air and higher top speeds mean a smaller scoop mounted closer to the fuselage can provide for sufficent airflow while reducing drag over a stock model.

The stock scoop has to work at high altitudes in thin air, so they have much larger inlets than racing 'Stangs require.

As far as HOW and WHERE it's mounted, if a smaller scoop is providing enough cooling air while used at racing speeds and heights, then mounting it father out into the airstream to avoid the boundary layer (and possibly increasing drag) isn't necessary.

Looks like they did their homework...

[t-dub]

Re: Air scoops

It was made of Invisiblinium...
I tink I have read that the system on Stilletto actually worked very well, at least once the plane was moving. Still remember how they used to tow it out to the runway, start it up and take off before it had a chance to overheat!
I sure like the way it looked.
My favorite was MAII's last scoop, the bulge with the NACA in it. THAT was cool.

These shots are for you Leo. It was kinda COOL lookin'.........

[t-dub]

Re: Air scoops

[QUOTE=taglialavore]

My favorite scoop was the one Stilletto used when Matt J. raced it.
Was it placed in the wing leading edge or in the fuselage belly?

Maybe this will help. The first shot is Stiletto w/ Scott Sherman in 1988. The second is Matt in 1992. (look closely.......) Sorry for the poor pix quality.

[Mluvara]

Re: Air scoops

[QUOTE=t-dub]

Maybe this will help. The first shot is Stiletto w/ Scott Sherman in 1988. The second is Matt in 1992. (look closely.......) Sorry for the poor pix quality.

I don't know what analysis/research/testing was done on the wing scoops and exits for Stiletto, but I would think that it was pretty dirty for the wing since once something is disturbed, the rest behind it doesn't matter too much...

Who knows what the air looked like coming out of the exits too... Airfoils were generally meant to be continuous without disruption. Still, a pretty cool idea.

Michael