SuperStol XL Alaskan

[BDA]

Flap Cove VGs
I installed VGs at 30mm spacing the length of the flap IN the flap cove.

I started with the outboard end to straighten out the air around the strut end and then did the inboard end in the prop wash.

I tested after installing each set and saw dramatic performance gain with the sets at each end. Highly recomended.

Better flight deck angle when slow with flaps, better tail authority, shorter takeoff roll.

[Clark in AZ]

Can you post a pic or two of this? Interested.

Thanks,
Clark

[BDA]

Flap cove VGs
Just in front of the flaps when they are up/in.
30mm spacing

[mac]

I can certainly vouch for what Shawn is saying. I added VG's, starting at the inboard end of the flaps and have about 30% of the flap cove length covered, at the moment. Flew in calm wind last night and found more stability, much better visibility on approach and less rpm required to maintain the sink rate I like. Truly remarkable! I also have small flap fences on the outboard end of the flaps, which previously I found to be beneficial.

Will be flying in the Nevada high desert this weekend, so will be gathering more data. At this point, the thought is to slowly increase the length of the VG's along the flaps with further testing. Thanks Shawn for discovering this. I'm a huge fan. Love this airplane!!

[BDA]

That is AWESOME Mark!
Glad they worked for you!

I started at the other end and so I saw the biggest gain there - where there is alot of turbulence around the strut end - I am curious to see what your gains are as you get to that point?!

Document takeoff numbers and deck angle as you go if you can please.

[mac]

outside flap fence.jpg

flap cove VG's.jpg

After a little more testing, I decided to relocate my flap cove VG's a bit further away from the leading edge of the flap.............plus improved the alignment. Right now, I'd say the VG's are about 1-1/4" forward of the of flap leading edge but certainly outside the airstream during cruise flight. At the moment, I only have about 1/2 of each flap covered, starting at the inboard edge and will keep it that way for awhile.

While I don't have specific numbers, I can say, at least for my particular SS, the visibility over the nose on final is considerably better. For a given sink rate, with full flaps, I'm showing between 500-600 rpm less on final.......maybe even a little bit more. With little wind, I'm usually about 40 mph on final. I have a big bore 914. I'm essentially not so much "behind the power curve" as before. Additionally, the stability as I flare is much improved. Less rudder is required to keep things straight! Yes, this certainly could be that I'm ever increasingly getting more comfortable with last minute adjustments in the flare, but regardless, I like it!

One thing that I suspect contributes to the increase in stability is the outside flap fences. I made then removable, a bit smaller than what others have done and built them without removing the flaps. Used #6 rivnuts and stainless screws.

Finally, I've never sensed a "low tail feeling" in cruise flight with my SS. Who knows why? Might be that my SS is rigged a little different than most, with my horizontal's down incidence more like 2 degrees than the originally specified 1.6. That was due to a "communication" error early on with my build years ago. Additionally, I've covered my gear legs, have a slight forward sweep on my wings, built a closure between the turtle deck and flaps and the front cowl is totally different than "stock", with much more of a steamlined look. Fiberglass work was my thing for many years with composite airplanes. Couldn't help but change the cowl up a bunch!

Taping knitting string (tuft testing) to the underside of the wing shows I'm not getting any leakage through the fowler flap gap during cruise flight.............nor am I seeing any kind of fabric flutter on the underside of the wing during cruise flight, anywhere. Everything looks quite smooth and stable. When I pull the flaps, the strings take off through the gap!

The things I mention above are strictly my experiences and nothing more. No recommendations are made here. Your mileage can certainly vary. Everyone should remember these are experimental class airplanes with little oversight relating to changes. So, be cautious and work very slowly if any changes are contemplated!

That said, starting to really like the way this bird flies!!

[Clark in AZ]

Thanks for the continued feedback. I'm sure there are lots lurking that appreciate it too. Sounds like you're really getting it dialed in for you.

Clark

[BDA]

Thanks Mark!!

Specifically - what difference did you see moving them forward out of the gap?

[mac]

VG's in fowler cove 1-1.25 in. fwd.jpg

I really didn't move them "out of the gap", but rather just slightly more forward, with more consistency on alignment/straightness. Check the photo out. I suspect coming up with a method for applying the VG's in a straight line, with a consistent distance off the LE of the flap, is pretty important. For me, it was a little bit of an effort........and a sore neck! What I noticed, with the more attention to detail technique, was more "symmetry" with roll on approach.

Plan to fly a whole bunch more before making a final judgement here. But, at this point, they sure aren't coming off!!

[BDA]

I finally got around to putting the rest of the VGs full length (filled gap in the middle)
Test number 4
I did a few before and after landings to see if there was a difference
Before landings were all long - I am still misjudging the float.
After vgs were added to the middle, first landing was about 5’ past the line (I was really concentrating on not adding too much power - it was perfect!
Next 2 were short by 5’ - it feels so much better when slow.

The take off is what took me by suprise. I flew the tail w brakes on, then as soon as I let off brakes I jerked full flaps and took off instantly - that is so much fun!
All tests were 8knts wind

So - yes, VGs are incrementally better the more you put on (full length) of flap cove.
I cannot say takeoff was X amount of feet shorter because of different wind on dif days.
But I can say that the plane is 100% more controlable when slow. EVERYTHING slowed down. And I can see better.

I also added the VGs just behind the strut attachment (on wing) to try and straighten that air out again.

[BDA]

On the way back from Valdez I flew into severe turbulence and had to make an unplanned stop to wait it out.

Learned :
The wing extensions and struts are def strong enough for anything we are going to do.

Lots of lexan makes it easier to panic-search for nearby landing possibilities.

Visor on flight helmet will stop sheared rivets from headrack sheetmetal as wing stress transfers through fuselage and shears them off - they leave with velocity.

New seat cushions with stiffer foam resist pucker.

It is possible to be full power and show 1,000 fpm decent.

It is possible to land with 90* crab angle at 65 mph indicated into strip with 50’ trees and stomp rudder to stick the landing.

1 spectator on “field” - said “wow, that looked pretty windy up there, never seen anyone land like that before”, I took that as a compliment.

[mac]

Geez Shawn!!

I think you exceeded all the limitations as shown in the SS POH! Thanks for summarizing your trauma. Certainly comforting to know our airplanes are stronger than they appear. I'll still stick to mild, pleasant days and ground myself when winds pick up beyond my personal comfort level. Something about being an "old" pilot and dodging too many bullets to date!

Very grateful you eventually made it home safe!

[dkshow]

Glad you made it home, sounds like an exciting trip back. I've had to replace the rivets on both the head racks as well. I'm fairly certain when you get above 90mph the lift across the top of the lexan is stressing those rivets a bit much. I might find some stronger ones.

It's good to know you have a strong wing when you're in that stuff. Thanks for the report.

[BDA]

I have replaced the rivets with #6 stainless large head screws.

[CanadianSheepHunter]

Glad you made it home, sounds like an exciting trip back. I've had to replace the rivets on both the head racks as well. I'm fairly certain when you get above 90mph the lift across the top of the lexan is stressing those rivets a bit much. I might find some stronger ones.

It's good to know you have a strong wing when you're in that stuff. Thanks for the report.

The rivets you had to replace were they stainless or aluminum?