tail buffeting and leading edge fillets, strakes

I've recently bought a little rag and tube homebuilt. It's a Stits SA6b
"Flut-R-Bug". It's a tailwheel version and had some cosmetic mods so
that it is a fairly attractive little bird (relative to the butt ugly
original configuration). This is a midwing, strut braced design.

There is some buffeting on the horizontal tail when the plane is banked
30 degrees or more. I've been told that it is turbulence from the
wing/fuselage junction. The published fix is to make leading edge
fillets (strakes). I've seen similar tail buffeting in other similar
size and configuration airplanes. In the Schweizer 1-26 glider for
instance, this buffeting is greatly reduced by sealing the gap between
horizontal and elevator.

I will be sealing the control gaps as a matter of course and will be
(attempting) to make some leading edge fillets. The fillets don't have
to be large. Something like 12 inches long at the root and extending 9
or 10 inches out on the wing. The current plan is to hotwire some foam
forms using airfoil templates and fiberglass them.

I have two questions:

How much of the buffeting is due to the horizontal/elevator gap?

Do the fillets need to match the airfoil or would a generally
streamlined shape do just as well, or is there a third option for
determining how the fillets should be shaped? (simplifies construction
if I can just bend them out of aluminum).

Thanks for the advice,

Wallace
Glasflugel H301 N301BW
Stits SA6b N5423M

Do some tuft testing. Unfortunately, it will probably show so much
turbulence that you may give up before you find what the fix is.
There are all kinds of possibilities. Wing root. Strut intersections.
Gear intersections. Tail intersections. Wing separation properties.
The list goes on ad infinitum.

It should be noted that some planes put stall strips on the
wing leading edge just to generate vortices that will impact the tail
and create buffeting. By moving the strips up, down, or spanwise,
you can tailor when the buffeting comes in. Highly desireable as a
stall warning method. Maybe you already have a good feature.

Temporary fairings can be made of almost anything and taped in
place. Look at some of the work done by Dick Johnson on investigating
the PIK 20.



In article , Wallace
Berry wrote:


I've recently bought a little rag and tube homebuilt. It's a Stits SA6b
"Flut-R-Bug". It's a tailwheel version and had some cosmetic mods so
that it is a fairly attractive little bird (relative to the butt ugly
original configuration). This is a midwing, strut braced design.

There is some buffeting on the horizontal tail when the plane is banked
30 degrees or more. I've been told that it is turbulence from the
wing/fuselage junction. The published fix is to make leading edge
fillets (strakes). I've seen similar tail buffeting in other similar
size and configuration airplanes. In the Schweizer 1-26 glider for
instance, this buffeting is greatly reduced by sealing the gap between
horizontal and elevator.

I will be sealing the control gaps as a matter of course and will be
(attempting) to make some leading edge fillets. The fillets don't have
to be large. Something like 12 inches long at the root and extending 9
or 10 inches out on the wing. The current plan is to hotwire some foam
forms using airfoil templates and fiberglass them.

I have two questions:

How much of the buffeting is due to the horizontal/elevator gap?

Do the fillets need to match the airfoil or would a generally
streamlined shape do just as well, or is there a third option for
determining how the fillets should be shaped? (simplifies construction
if I can just bend them out of aluminum).

Thanks for the advice,

Wallace
Glasflugel H301 N301BW
Stits SA6b N5423M