Tuft Testing & Fuselage Interference

[mike.smith]

I've always thought at the break in the fuselage and the intersection of the flaps with the fuselage, there must be a lot of turbulence and therefore drag. So I decided to do some tuft testing with and without a fairing. More tufts and more testing are needed, but initially it certainly appears that an intersection fairing improves things.

https://www.youtube.com/watch?v=-FxvUdQCZTg

I made the fairing of .025 aluminum, and attached it with duct tape. It's patterned after the fairing I've seen on a P-51 Mustang :-)

[DCASonex]

Mike,

Any photos of actual fairing ? Looks like it works on video, but cannot see what the fairing is.

David A.

[NWade]

I've always thought at the break in the fuselage and the intersection of the flaps with the fuselage, there must be a lot of turbulence and therefore drag.

Mike - You beat me to it! I've thought the same thing and have been looking forward to doing similar tests when I complete my Sonex.

My first sailplane had no fairings or shaping of the wing root at the fuselage junction, and that definitely affected performance. There was a fairing kit you could get, which consisted of some thin fiberglass "sleeves" you slipped over the wing and taped to the fuselage. It worked great, and definitely lowered stall speed and improved the glide-ratio by 2-3 points. (Its not the greatest photo, but you can make out the wing-root fairings in the center of this photo)

On a faster-moving aircraft a fairing will increase the wetted area and this add additional skin drag - so it will negate some of the benefits; but a proper-sized fairing might produce a detectable improvement in performance. I'll post photos and info once I'm flying and I can test similar mods.

Thanks for sharing!

--Noel
Sonex #1339

[airscribe]

Very nicely done, Mike...thanks from I'm sure many of us...

Still building my Waiex, but already had planned to make and test similar fairings -- after completing my Phase 1 flying, of course.

Installed aftermarket fairings around the leading edge and at the flap/fuselage intersection on a Comanche 180 we used to own....they worked....so planned to model similar fairings for my Waiex -- leading edge and at the same spot you did -- and tuft-test them once finished with Phase 1....believe they have the potential to reduce parasitic drag more than any penalty for the increased whetted area...

Thanks for confirming this idea...

Dave

[sonex892.]

Thats impressive Mike. There is definitely a big difference. Just wondering do you have the plans type flap gap seal angle attached to the fuselage? I cant tell from the video.

Steve

[WaiexN143NM]

Hi mike, all,
Keep us posted! When your done testing please post with dimensions, thickness of sheet, bend angles. Is it flat or curved? Hard to tell from pics. Neat!

WaiexN143NM
Michael

[mike.smith]

Mike,

Any photos of actual fairing ? Looks like it works on video, but cannot see what the fairing is.

David A.

It's the still image in the video, to the left of the "faired" video.

[mike.smith]

Thats impressive Mike. There is definitely a big difference. Just wondering do you have the plans type flap gap seal angle attached to the fuselage? I cant tell from the video.

Steve

Yes, I do. So it still acts as a stop for the flap. The fairing is just layerd on top.

[mike.smith]

(Its not the greatest photo, but you can make out the wing-root fairings in the center of this photo)

I can see them. They look very much like the one I made.

[mike.smith]

Hi mike, all,
Keep us posted! When your done testing please post with dimensions, thickness of sheet, bend angles. Is it flat or curved? Hard to tell from pics. Neat!

WaiexN143NM
Michael

I definitely will. And if anyone else wants to give it a go, it never hurts to have more than one test subject.