Gap Seals

[skippydiesel]

First a confession  - I sometimes can't leave well alone especially when something is preventing aviating ( weather, head cold etc)

 

Some considerable time ago (5 years or so), I installed mylar gap seals (strips) on my ailerons (supplied by a Sydney printing company) - work just fine. Not sure if there has been a significant improvement ( handling response or air speed) but they give me a warm inner  glow and no down side.

 

Contemplating gap seal on my flaps now (Bunnings Aerospace stick on furry draft excluder 3-5mm gaps ) - not sure if I can expect any performance gains - what think you?

 

Could extend project to include elevator and rudder.

 

I should mention that flap & elevator gaps are already pretty good. Flap gaps 3mm along lower surface when fully deployed, probably near 5 mm when in cruise config. Elevator consistent 3 mm in all config. Rudder a bit odd - symmetrical clearance both sides - running from about 2mm top out to 10 mm mid way and back to 5 mm near bottom (can't see any advantage in shape).

 

This would be a minimal cost project but may be hard to justify if no advantage likely (even a knot or two would be great) other than the fun of doing it.

 

 

[Old Koreelah]

Skip I too have sealed my elevator gaps. Can't be sure of the effect, but like you, it makes my feel like I've done what I can. If I could find the right material I would also seal the ailerons, which are a bit wider than most. 

 

Not looking for speed improvement, just maximum control surface efficiency at low speed.

 

Regarding your flaps, depending on their design, a gap could be beneficial. Being so far back from the leading edge, the upper boundary layer is quite thick and might need a well-designed gap to re-energise the airflow.

 

 

[skippydiesel]

Hmmm - like all knowledge a little can be "dangerous" - (with the exception of fowler type flaps and other systems that actively seek to encourage air flow from high to low pressure) I understood that the movement of high pressure air from under the wing/control surface, through gaps, may cause premature boundary layer separation/turbulence on the upper surfaces and in doing so reduce efficiency/lift ?????

 

Further this "bleeding" of air from high to low is most likely at low speed with large deflections of control surfaces. It may be that any benefit is most likely at take off/landing phase but in my case I am hoping for improved cruise.

 

Don't know if my memory of this is correct however if true it seems to me that reducing that air flow should give some performance benefit - I guess cost/benefit comes into this somewhere.

 

 

[facthunter]

 I'd go for the elevators as a pretty sure thing to help but get advice on most other applications.. I'd like to see some wind tunnel tests first. Nev

 

 

[Yenn]

Elevators can benefit from adding VGs They can increase the elevator control at very high angles of attack. Probably more effective than gap seals.

 

 

[jetjr]

I installed gap seals - glider mylar strip- on elevator on Jab in replacement of the adhesive tape used, looking for longer lasting gap seal.

 

On first flight couldn't work out what howling noise was, a bit disturbing, then it went away

 

Upon landing the mylar seals had flogged themselves to pieces 

 

Since went to clear outdoor tape with good results but adhesive is so good that paint will come off with it unless warmed up

 

VG work well especially on underside of elevator

 

 

[mkennard]

On my Jab I used the sail repair tape on the elevator. Lasting ages.

 

 

[Kyle Communications]

There is a video on youtube with a kitfox. He fitted gap seals and did the testing before and after. The result was........basically no difference at all

 

 

 

 

[facthunter]

 Not surprising. It has a pretty basic set up. No real attempt at an airfoil shape.  A full flying stab is efficient but challenging design wise to eliminate flutter. Elevator gap sealing can't do any harm.. Simple flap is only an air dam and mostly more drag and just a little extra lift. It's never efficient or needing to be. Aileron, well you only use them when deliberately rolling ( Or trying to) .  Nev

 

 

[Bruce Tuncks]

I've read that in the Reno races, lots of tape is used and lots of gaps are sealed. Now we don't notice a knot or 2 but you would when racing.   As far as fowler flaps are concerned, it was good advice to be cautious there because there might need to be some airflow from below to the top surface.

 

There was a guy at Reno who had his canopy taped! He cared more about winning than being able to get out.

 

 

[Downunder]

I've read that in the Reno races, lots of tape is used and lots of gaps are sealed. Now we don't notice a knot or 2 but you would when racing.   As far as fowler flaps are concerned, it was good advice to be cautious there because there might need to be some airflow from below to the top surface.

 

There was a guy at Reno who had his canopy taped! He cared more about winning than being able to get out.

 

The faster you go, the more the smaller improvements matter.

 

I would suggest 80 to 100 kts, extremely minimal improvements, if any at all.

 

100 to 140 kts, slight improvement. Maybe a knot or two.

 

140 to 180 kts, now we're getting somewhere. 5 to 10 improvement, maybe more.

 

200 kts plus. Any small improvement in aerodynamics will see results.  

 

 

[spacesailor]

The HummelBird cleaned up & gap sealed gains 10 MPH.

 

BUT 

 

More HP does exactly the same.

 

spacesailor

 

 

[skippydiesel]

Thank you all for your input/advice.

 

I think Downunder makes some very good points but am surprised at Spacesailor - you fly a HBird, that almost defines you as a person passionately interested (as I am) in getting the most from a litre of fuel. Mor HP means more fuel burnt - a cleaner/more aerodynamic airframe means more speed for the same buck.

 

I went out to my hanger today, with all the necessary stuff,  to start gap sealing. As is so often the case it turns out not to be as simple as first thought. After doing a very comprehensive in/out referbe about 3 years ago, one would think I would have remembered that to remove the elevator,  the whole tail must be removed, similar story for the flaps (wing off). I think I could do the rudder without much bother. I think I will put all my gap seal stuff in a nice dust proof draw and wait for a long wet/bad weather spell, to re start this "make work" rush of blood to the head..

 

 

[Bruce Tuncks]

My Jabiru experience supports what downunder said. I have used plastic and tape to sharpen the rear of the quite rounded Jabiru original struts. I had read that this would be worth 3 knots. ( 90 to 95 knot cruise )

 

Trouble is, I can't tell if it has achieved this or anything at all.  A cruise is not at full throttle, it may be that the plane needs a mm less throttle than before , if so I can't tell.

 

Maybe I could stop the engine at altitude and measure the sink-rate at different speeds?  I also guess that formation flying with another similar plane could be done, but this would be hard to do too. 

 

 

[turboplanner]

If you put a vacuum gauge on the manifold you’ll get a good before and after for a series of cruise speeds.

 

 

[spacesailor]

"surprised at Spacesailor - you fly a HBird, that almost defines you as a person passionately interested (as I am) in getting the most from a litre of fuel."

 

Last one to be Registered. But not flying due to"Wingload factor" (95-10 ) Had to be Flying to get "Grandfather" exemption.

 

How about this one !.  3.9 litres per 100 K

 

spacesailor

 

 

[Keith W]

Stop worrying about how fast your going and just enjoy the flying

 

 

[Bruce Tuncks]

congratulations space

 

 

[spacesailor]

"Stop worrying about how fast your going and just enjoy the flying"

 

Not Just the speed.

 

Been building for years, & never knew there would be a time limit on what you had to do for the Bureaucracy.

 

Could have had it flying four years before that cutoff date.

 

Dam good looking, efficient. fairly safe  to boot, with the number of walk-aways from crashing.

 

After all a Nice New plane with a Nice New pilot flying an aircraft with a joystick that only needs finger caressing, 

 

No like GA's, hands on large movement controls.

 

OH, Did I mention cheap to build, fly & maintain. 1/2 a litre of engine oil. 20 litres of fuel, gives a days flying. (6 litres.P.hour, gives 3 hours plus two litres for reserve)

 

spacesailor

 

 

[Old Koreelah]

...Trouble is, I can't tell if it has achieved this or anything at all.  A cruise is not at full throttle, it may be that the plane needs a mm less throttle than before , if so I can't tell...

 

How to test?

 

When I built my spats I flew four big square tracks at exactly 2600 and 2800 rpm, with and without spats. 

 

I recorded average ground speed and indicated fuel burn. Not super scientific, but easy to do.

 

 

[skippydiesel]

Stop worrying about how fast your going and just enjoy the flying

 

Not after speed per say but aerodynamic efficiency  - which may give more speed for the same energy expenditure, which reduces fuel consumed per trip OR reduce energy consumptions for the same speed which gives lower fuel consumption per hour.

 

 

[facthunter]

 As said, it's a bit academic unless you are doing about 150 + Knots and it's something else to look after/get in the way of inspections etc. Give it a good clean  (and polish) all over. Not as much fun as fiddling though but it will look loved and fly a bit faster (or seem to). Nev

 

 

[Raytol]

I have done gap seals for a Lancair 360 and a Lancair 4. The 360 got an extra 12- 15 knots and the 4 it reduced the overall drag by 17%.

 

It is worth it on heavy slippery aircraft.  On the gliders you can actually hear the drag reduction! Not so much on lightly loaded slower aircraft.

 

 

[Bruce Tuncks]

Great stuff Raytol.  I have a Lancair 360 handy here and would like any gap-sealing tips you have. The Lancair belongs to my son, but I like to help with the  maintenance etc.

 

 

[Raytol]

Sure Bruce Tuncks it is easy.

 

Go to Bunnings and look for "Norton Outdoor tape" it is a clearish tape with water resistant glue. It is about 50mm wide.

 

The tape is put where the aluminium hinge is ( ailerons on the top and flaps on the bottom of the surfaces, etc).

 

You can do all the hinged surfaces including the u/c doors!

 

The tape spans the gap, try to get it roughly even on both sides of the hinge.

 

There is some tricks....(1) deflect the surface fully away from the hinge. This allows the surface to keep full deflection and the tape does

 

bunch up a bit but it is better to be sealed than worry about a small bump in the tape ( which seems to flatten in the air).

 

                                .....(2) If possible extend the tape slightly past the end of the surface and round off the ends ( stops it peeling off).

 

I've probably forgotten something... let me know how you go.