Continuous flaps running under fuselage?

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WK95

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Say we have an aircraft that has a dihedral outboard on the wing. The inboard section thus has no dihedral and the outboard sections on both the left and right wings are parallel to each other. Say there is a full length flap connecting these two inboard sections runs under the fuselage.

Here's a picture of a lift profile.
wing22.gif

The part of the continuous flap under the wing would increase lift while also increasing drag. But how does the part of the continuous flap that runs udner the fuselage affect the lift profile and drag? How would it affect the lift profile and the drag?
 

JamesG

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Unless its a delta and the continuous flap is at the trailing edge of the entire aircraft. Then you would probably see some worthwhile benefit, esp. if the "fuselage" is blended or streamlined to take advantage of it.
 

WBNH

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Kolb Laser used flaps extending under the fuse...as a speed brake I have to believe...can't imagine it affected lift under the fuse. Wasn't a lifting body and the flap was mid fuse, not trailing. Project was cancelled, though, with only one or two examples built IIRC.

See at 0:20

 
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Aesquire

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Under fuselage flaps/brakes are also a popular thing on Q-series and Long-EZ's.

Very little pitch change, usually, but lots of drag which is a good thing on a slippery aircraft. Much easier to construct than sailplane type spoilers.

My thinking is because the belly flap doesn't materially change the airfoil of the wing, and has no air coming together from top & bottom, like a wing flap, it's lift numbers are pretty poor, with only the air flowing down the sides of the fuselage to alter the "flow field". Mostly turbulent and random vortex stuff, so I think it best not to count it on the lift side of any equation.

better for many purposes than fuselage side mounted air brakes, since there is usually much less affect on flow over the horizontal stabilizer.

Ideally you want it flush with the belly when retracted.
 

SVSUSteve

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better for many purposes than fuselage side mounted air brakes, since there is usually much less affect on flow over the horizontal stabilizer.
Actually kicking that idea around on my design since it is potentially more feasible than side-mounted or tail cone mounted air brakes. Although I am not sure how much effect side mounts would have on the horizontal stabilizer because the plan is for a cruciform tail which should put them clear of any disrupted airflow.
 

WK95

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With all those perforations, I imagine they also work as airbrakes. I wonder how those perforationsaffect the coefficient of lift for the section of the flap that is under the wings.

On airliners.net, I read that supposedly, those perforations in spoilers work to reduce the intensity of the wake or turbulence behind those spoilers though.
 

rhbelter

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Ahoy, All,
Years ago, I was designing a quite conventional side by side low wing airplane -w a 160hp Lycoming . AND -- I had access to a excellent ~~ 3' x 4' wind tunnel.

The wing fuselage intersection of my design, at the trailing edge was a flat fuselage -w- vertical sides - smooth curved fuselage (wind tunnel model).
I fastened on split flaps of different configurations. My best behavior and CLmax was with the flaps stopping about 10" (full scale) from the side of the fuselage. (Handy for wing walk).
I don't have any of the numbers ---after more than fifty years.
Never built it.
Enjoy /s/ Bob

 

bmcj

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Hi Bob,

First of all, welcome to HBA.

Do you have any design sketches to share? Have you been able to satisfy your aviation passion in other ways in the meantime?
 

rhbelter

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Ahoy, All (again),

Sorry 'bout that. My CLmax was with the split flaps being NOT under the (flat bottom) fuselage, but out on the wing, and ending about ten inches (full scale) outboard of the side of the fuselage. The flap under the fuselage really raised the drag, but dropped the CLmax a lot.

Nah, no design sketches. Back then, AutoCAD did NOT exist --- Sheeesh!!! --- Electricity was barely invented.

I was a TailHook Naval Aviator. And ---The Navy Design Officer of the A6-E Intruder.

Enjoy /s/ Bob
 
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