Where's That Air Scoop?

[Halo]

For you aeronautical engineers out there, what are the relative merits of placing air scoops in nose, in wing, on top the fuselage or beneath the fuselage?  

I can see the value of the P-39 and P-63 air scroops behind the canopy for a rear engine, and certainly nose air scoops seem to make the most obvious sense for front-engined aircraft.  

But it seems counterproductive to put an air scoop on the bottom (or top) halfway back on the fuselage behind a front-engine aircraft like the P-51, and yet the Mustang is often called the best fighter of WWII.

What's the big secret here, and why didn't more aircraft have this configuration if it is so effective?

[GtoRA2]

The scoop under the mustang is the radiator and intercooler scoop.

If you look close it also has a scoop under the prop for the carb.

[Wolf14]

Not sure if this will give you an exact answer to your question, but hopefully it will provide an answer to some greater or lesser degree......


http://www.hitechcreations.com/forums/showthread.php?s=&threadid=126853&highlight=lee+atwood

[Halo]

Thanks, Wolf14 and GtoRA2.  I vaguely remember that thread, and Atwood's article and other comments shed a lot of light on this subject.  So, the Mustang's outstanding speed and range were mostly the Meredith effect (producing "thrust" from radiator), the laminar flow airfoil, and the Whitcomb area rule.

I can't recall any other WWII aircraft having a more pronounced zig to inside wing's leading edge and a larger belly scoop than the Mustang.  

So basically the big belly scoop allowed a sort of jet thrust that negated much of the drag.  

Yeah, I've noticed the smaller air scoop in the Mustang nose but didn't realize what it was for.  

Jets also have a similar variety of intake placement from nose to wing to top or bottom of fuselage (plus sides of fuselage).  But most intakes always seem closer to front of engine wherever it is placed.  

What provoked this thread was always wondering why the Mustang's big scoop was so far behind the engine.  Still can't recall any other aircraft, piston or jet, with scoop that far behind engine.  

And (sigh) ... still hard for me to fathom, e.g., can't really grasp why any air intake would most efficient behind any engine instead of in front of it, nor can I think of any more Mustang-like examples in air, on land or sea.

[bustr]

Is that why the LA7 got it's scoop moved under the pilot rather than the LA5 just back of the cowling?

[bozon]

the radiator can be placed in many ways and locations. In the spit/109 for example, it's under the wings.

making a drag efficient radiator / cooling system was one of the greatest mysteries back then (and  somewhat still is). Inline planes seem as if they should have much less drag than radials due to their nice shape and narrower front, but then they have to stick this radiator out to cool in the breeze...

I suspect the calculation of what happens to the airflow as it enter the scoop, transfer heat with the radiator and come out to the surrounding flow, was way beyond engineering capabilities back then (no computers, just pen and paper...).
So optimization must have been done by intuition and trial and error.

Bozon

[Guppy35]

Don't forget the Hurricane had the radiator scoop under the belly as well.

Dan/Slack

[Charge]

To me it seems that the P39 has the worst placing of the carb intake scoop. It probably loses a lot of its ramming effect if flying anything but straight.

It is also better to place the scoop some distance away from the fuselage as is seen improved in 109 F to E where it was too close the fuselage to begin with.

-C+

[J_A_B]

"Still can't recall any other aircraft, piston or jet, with scoop that far behind engine. "

Take a look at the Ki-61, Hurricane and MC-205, to name a few.



J_A_B

[HoHun]

Hi Halo,

>For you aeronautical engineers out there, what are the relative merits of placing air scoops in nose, in wing, on top the fuselage or beneath the fuselage?  

I'm not an aeronautical engineer, but in my amateur opinion, it's as follows:

- Nose: Close to the engine, easy to implement, few internal losses
- Wing leading edges: No additional frontal area, possibility to place it outside propeller arc
- Underwing: Possibility to place it outside propeller arc. If inside, airflow becomes less turbulent further back from the propeller, so aerodynamically more efficient.
- Belly: Airflow becomes less turbulent further back from the propeller, so aerodynamically more efficient.
- P-39/P-63-style: No additional frontal area, close to the engine in mid-engine configuration.
- On top of anything: Possibly poor operation at higher angles of attack.
- Below anything: Not very sensitive to angle of attack changes.
- Outside the propller arc: More laminar airflow
- Inside the propller arc: Better low-speed cooling, better cooling on ground (run-up, taxiing etc.)

So a designer had to set his priorities according to the requirements for the specific aircraft he was creating, and to decide which advantages outweighed which disadvantages :-)

Regards,

Henning (HoHun)

[Halo]

(QUOTE) Take a look at the Ki-61, Hurricane and MC-205, to name a few. (UNQUOTE)

Hmmm, you're right, J_A_B, more than I expected ... including the French D.520 and VG-33, the Yugoslav IK-3, the MiGs 1 and 3, La-7, Fiat G-55, Yak-3, 202 and 205, Defiant.

The P-51D's belly scoop still seems to be the most prominent, but it has more company than I remembered before checking further.

Your observations make sense to me, HoHun, et al.  Looks like most designers were glad to get past props into the more streamlined jets.  Which brings to mind turboprops, turbofans, ducted fans and various hybrids,  but that's another thread.