FRISE ailerons & flaps selection

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Millor

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Nov 1, 2020
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Dear colleagues,

as some of you may know, I am currently building a RW19 Stork (STOL). Time has come to start with the wings and its ancillary components and because the construction plans offer two different alternative designs for the ailerons/flaps I would like to get your advice.

Both ailerons/flaps designs are of the Frise type. Leaving aside aesthetic preferences, in order to chose one or the other option I would rather concentrate in the one which gives better STOL performance.

Option A features:
  • cleaner hinge fitting
  • tighter gap between aileron/flap and the wing trailing edge (which may not be of advantage, though)
  • easier construction
ribs_frise_OPT_A.jpg

Option B features:
  • circa 18% lighter, meaning some 12oz saving for the set of 2 ailerons + 2 flaps
  • slightly greater area
  • a better airfoil?
ribs_frise_OPT_B.jpg

I will be grateful to hear your comments and suggestions on the way to proceed.
Thank you,

Oscar
 

TFF

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Apr 28, 2010
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15,404
Location
Memphis, TN
A
The point of the Frise is to help with adverse yaw by dragging some of the aileron in the airstream on the bottom surface. Makes the plane less of a chore to fly.

With B you end up with that big space so your ailerons and flaps are not part of the lifting or much reduced in effectiveness. You also have another point of drag all the time depending on how clean the air leaves the trailing edge of the main rib plus you have two trailing edges.

If you could have B’s as a flap for the extended geometry but tucked in in cruise it would be great. Essentially a Cessna flap.

Gap seals really help. Air that passes between the gap of a flight control is a loss in lift. Aerobatic planes use it for more control authority. A STOL plane would use it for more lifting margins.

Junkers ailerons/flaps have a full wing rib profile and then the flight controls as a separate entity.
 

Millor

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Nov 1, 2020
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Thank you TFF.
I do also think that A is a smarter solution. Your proposal for a ,,Cessna,, flap sounds good but would involve modifying the design beyond my capabilities, so I'd rather remain with the stock solution.
 
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