Flap Gap Seal

[stede52]

John,
Now me understand

Steve

[alan]

Here is my first flight report of the flap gap seals as I saw them installed at Sun & Fun 2011. First, they are 77" long and 2-1/2" wide installed using 1/8" aluminum pop rivits with a 1" overlap of the rear wing bulkhead, leaving 1-1/2" overhanging the aft edge of the wing above the flap.

I built these seals from .020" aluminum. Paint cost far more than the parts.

I wanted to see if there was a real benefit beyond the abjective "feel" of a lower stall speed and increased lift with flaps. I installed just the starboard (that's the right side to you 'lubbers) seal and went flying. My logic (?) was that if the flap gap seals provided extra lift it would be manifested by a rise in the starboard wing.

What with the floor of Houston's Class "B" just 2000' over my home field I stayed around 1500' and convinced my buddy, Terry, to watch from the ground with a portable radio. I also requested he call my wife right after the 911 call. Flying into the wind at 45kts GPS GS and about 50mph IAS I pulled one notch of flaps.

One notch of flaps yielded no extra lift from the right wing. I pulled two notches of flaps.

Two notches of flaps yielded no extra lift from the right wing. The stick was centered with no tendency to turn. I pulled three (full) notches of flaps.

Three notches of flaps required me to add quite a bit of right aileron. I, of course, reported all the above to Terry. He requested I remove the right aileron input so he could see the result from the ground. The Highlander entered an immediate left bank and turn. The bank was easily held from becoming a death spiral but did take almost half of the available stick movement to correct.

After retracting all flap input, I returned to the ground with a no flap landing and installed the port wing gap seal.

Conclusion: This was a short test flight but it seemed to conclusively prove the advantages of these gap seals to be limited to full flaps only. Perhaps I should order some .025" aluminum and build another set. I used the thinner stock because it is what I had. If it is too flexible it might not correctly direct the air until there is a large flap deflection. I'm just guessing here because I have to way to see what the seals are doing in flight.

I didn't have time to fly again after installing the second, port, gap seal, so that report will have to wait for another day.

Alan

[Johnny C!]

Excellant test procedure &
I appreciate your thoroughness.

John

[Dave Krall CFII SEL SES]

Why not go to safe altitude and do actual repeated stall speed tests in all configurations?

[Gary H]

Heck, Just land!! feel it by the seat of your pants!! Mine DO make a difference. (My strip is 700') I like-em !

[Dave Krall CFII SEL SES]

Heck, Just land!! feel it by the seat of your pants!! Mine DO make a difference. (My strip is 700') I like-em !

How much difference do they make?

[alan]

The last time I posted a flight test on these gap seals I was not a big fan. I used the wrong material and thickness because that is what I had lying around. They were too thin and floppy to do the job. I even heard/felt them vibrating during a day trip. Not good. I removed them and ordered the correct material. After obtaining and painting them, I installed one seal on the starboard wing, just like last time. I again climbed to 1500 feet right over Dunham Field and pulled the first notch of flaps. I had to move the stick just slightly to the right. Nice. More lift. I then pulled two notches of flaps. The stick needed quite a bit more pressure. Quite a bit more lift. Yahoo. I then pulled, cautiously, the third notch of flaps, about 30 degrees. Now I needed almost full right aileron to keep the wings level. Yeehaa! Or maybe Aheeee! (Cajun for yeehaa). I'm not really a test pilot, so I retracted all flaps and made an uneventful flap-less landing. Big grin. I debriefed with Terry for awhile and then installed the port gap seal. By then the wind was picking up again so I was unable to do any more testing that day, or even that week. When I finally flew again it was still bumpy so even though there was a definite improvement from previous flights it was impossible to quantify.

Later flights told the tale. Apparently there is improvement even with the flaps up. The airplane flies slightly but noticeably nose down now, suggesting the center of lift has shifted aft slightly. I'm thinking that before there was higher pressure air bleeding up through the small gap even in level flight due to the angled shape of the trailing spar causing some drag and detached air over the top of the flaps.

The flaps give quite a bit more lift and quite a bit less drag now, both a good thing and a bad thing. Good because the glide is extended a large amount. Bad because picking a spot to land nearby and hitting that spot is now harder. Maybe I should just say it is different than it has been for the last 400 hours. It is also quite easy to stall the horizontal stabilizer in a slip. Very exciting! The nose pitches down sharply but recovers immediately. The horizontal stabilizer stalls before the wing when practicing stalls as well so I did not see any reduction in stall speed. I guess I need some more vgs. And some more practice. Hey, another excuse to go flying!

I had tried a couple of full flap take-offs in the last few years but there didn't seem to be any reason to them, beyond just the learning experience. I can't remember much about them except it didn't work too well. Now....wow! Pilot only, full fuel, hot day, cross wind, stick back, the airplane gets light, lifts off in about 1/2 the distance of a pre gap seal flapless takeoff, or slightly more, and climbs at 800 to 1000 fpm at 40 mph indicated. When crossing the fence at my 2900 foot grass homefield I'm at more than 300 feet.

A full flap landing has a much reduced sink rate. The extra lift is extremely noticable, the lack of drag is equally. Now I'm thinking it might be benifical to increase the number of flap settings to get to maybe 45 degrees.

Alan

[rmullins]

What was the type and thickness of the metal you used this time?

[alan]

.025" 6061-T6. 2" x 77". Nice and stiff, attached with 1/8" aluminum pop rivets. Overlaps rear spar 1".

Alan

[GDS]

Has anyone used fabric gap seals on their flaps and ailerons?

[stede52]

GDS
if you are talking about sealing the gap so air will not pass thru...you don't want to do that. They do that with gliders and high performance aircraft, but not with the highlander style of flaps and ailerons. You want to maintain attached airflow over these surfaces to increase their effectiveness.

Steve D

[Gil T]

I have a set of 77" x 2 1/2" gap seals (flat) 6061T6 that I don't need. If anyone coming to Arlington would like to buy them make me an offer and I will bring them with me. I'm trying to recoup some of the cost of that whole sheet I had to buy and have cut. I'll be driving and leaving Arizona and it's 115 degree weather this Sunday.

Thanks and I hope to see a bunch of Highlanders up there.

Gil

[Trilander Ted]

I just tried my new gap seals earley yesterday and today. So far, I'm very impresed with the gain in preformance. My ship is a tricycle gear type Highlander I converted in 2008, hense(TRILANDER). It sets heavy on the nosewheel beacause of the aft main gear,and so a fare amount of back pressure is required to rotate. Then it assends with little or no back pressure, or that is the way I usualy depart the last 850+ hours. I tried a full flap take off right out of the box and almost immediately levitated into the air and continued a rapid clime at 40 to 45 MPH, raised the flaps slowly and was above pattern altitude way before the end of the runway! It was 6:30 AM 85*, no wind ,half fuel, right seat empty and way to high on final and just parachuted in with full flaps. I seldom use full flaps and would slip in if needed, (makes passengers worm squrm). I went out at 6AM this AM and it seems the nose is lower at high cruse, but it was already 95* @3000ft, so I'll test some more later. PARKER AZ. Ted

[Johnny C!]

Ted,
I love your paint scheme. I have a
pic of your bird in my screensaver
slide show at work.
I appreciate the report on the gap
seals. I will add them to Lima Charlie
before I get her in the air, hopefully
this year.
My question is, what engine is in
your Trilander?

I call mine a Escalander, by the way.

Later!

John

[Trilander Ted]

Jonny C! Thanks for your kind word for my WWII primary trainer design wana-A-be tribute colors. I'm an older dude now, and it reminds me of the airplanes I liked as a child.
The engine is the usual 912S with a Kiev three blade prop,(72inch I think). I use the Enigma EFS and a Lorance 2000 and like them well.
I used some heavy black vinyl tape on the flap to stop possible chafe against the gap seal overhang. It's the same type I use to protect leading edges on the horizontal stabilizer, landing gear legs and it works great for gap seals on the elevator/horizontal stabilizer also. (easy trick) By the way, I had to buy a 4 X 8 sheet of .025---6061T6 from Aircraft Spruce as my usual sources didn't stock it. Be sure and use at least 6061 or stiffer. I had eight stirps cut 2 1/2" X 77" and gave four to GIL T. Gil will be back from vacation soon, and wants to install them on 28TU, so we each have an additional set for someone.
It's 117* at my house in Parker, AZ. (5:30PM) so I won't be testing soon!
CHEER'S Trilander Ted