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Sep 08, 2014, 08:25 AM
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elkski's Avatar
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why trilerons?

I admit I first heard of this word in the last few months.

What is the purpose? To reduce flutter?

About the mechanics? If you cut the flap perpendicular to its hinge line then the ends of the adjacent flap and trileron tips will be different distances from their respective pivot points. That means some shear on the elastic tape? Is this desired? Or would it be best to make the cut so that the angles are equal and tips travel the same dia arc? So movement of the tips is more closely related?
What tape is best? Blenderm?
How do you use a spring?
If your cut is only 0.02" wide how does this small amount of non attached blenderm stretch enough?
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Sep 08, 2014, 09:03 AM
Will fly for food
davidjensen's Avatar
Mr. Reynolds likes them and yes blenderm will stretch enough
Sep 08, 2014, 09:34 AM
dnbarrie11's Avatar

Lots of benefits

Jerry Robertson of Flagstaff AZ was the first to use "trilerons" on sailplanes. He could go into extreme detail as to the benefits. The main benefit is that they smooth the airflow off the tip, (especially if the go all the way to the tip). This translates to improved roll rate, often requiring less deflection.

I had a Jerry designed Sisu two meter that utilized trilerons as option. I flew without and later added them. I couldn't believe the difference. It made it fly like an open class plane with improved roll rate.

I contacted Jerry and he will respond later. He's having computer issues right now.

Darwin N. Barrie
Chandler, AZ
Team Futaba
Sep 08, 2014, 09:41 AM
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elkski's Avatar
Thread OP
Any input on how best to position cut line between the flap and tri would be appreciated.
Sep 08, 2014, 10:31 AM
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davidjensen's Avatar
Without pictures we don't understand what your referring to. With the tape it may reduce the throw at the tips but that is not a problem as DLG have huge ailerons. You will get plenty of aileron even without much movement at the tips.
Last edited by davidjensen; Sep 08, 2014 at 10:36 AM.
Sep 08, 2014, 10:48 AM
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elkski's Avatar
Thread OP
Thanks David, your view 3 pic looks like the cut bisects the angle?
It seems like the angle of the carbon rod would have to be perfect and even then it might bind things or wear out the hole and result in slop?

I will doing the tape and bisecting the cut. But one thought I have is to place a strip of wax paper on the cut so the width of in adhered blenderm that can stretch is wider ?
Last edited by elkski; Sep 08, 2014 at 11:09 AM.
Sep 08, 2014, 01:02 PM
kcaldwel's Avatar
From Mark Drela back in 2003 on the Yahoo SAL group:

"--- In [email protected], "Martin Kopplow"
<[email protected]> wrote:

> Trilerons - if designed carefully - can help to accomplish a better spanwise

> lift distribution with different flap deflection angles. Especially in

> thermaling configuration they can reduce drag.

Hmm, that's not what I get.
I've looked at full-span ailerons, trilerons, and fixed-tip ailerons
on the SuperGee wing with a vortex-lattice code. The trileron is over
the outer 5 inches of the tip, and in the fixed-tip configuration the
aileron ends 2.5 inches from the tip.

Results for three different flight cases:

1) Level flight at CL=0.75 (min sink), +4 degree camber from
full-reflex position.
Full-span: e = 0.998
Trilerons: e = 0.999
Fixed-tip: e = 0.999

2) Steady roll rate at 40 deg/s (fast thermal turn entry), CL=0.6,
+2 camber
Full-span: e = 0.908 aileron = 5.42 deg
Trilerons: e = 0.895 aileron = 5.61 deg
Fixed-tip: e = 0.874 aileron = 5.84 deg

3) Steady 30 deg. bank turn at CL = 0.7 , coordinated (with opposite
aileron). +2 camber
Full-span: e = 0.986 aileron = -1.95 deg
Trilerons: e = 0.986 aileron = -2.01 deg
Fixed-tip: e = 0.985 aileron = -2.08 deg

Case 1) is even.
Case 2) clearly favors the full-span aileron. This is the maneuver
Case 3) slightly favors the full-span aileron.

The span efficiencies are pretty close, so induced drag is not a big
factor. But larger aileron throws increase profile drag pretty
rapidly. Note that the fixed-tip requires about 10% more throw than
the full-span to get the same effect. The trileron is somewhere in
Sep 08, 2014, 10:09 PM
Registered User


I have used trilerons only on my 2 meter planes that have winglets. My reasoning was to nullify the drag producing vortex that comes off the end of a chopped off deflected aileron . It should reduce tip stalling also. The winglets improve aileron effectiveness so any roll authority loss due to the trileron would be recovered. Without winglets I would have the normal hinge line continue straight out to the tip.
Jerry Robertson
Sep 08, 2014, 11:24 PM
Registered User
In the case of a deflected aileron, the plane is doing a roll. With the trileron, the entire tip has an average alpha that is different than the freestream, to the same degree as stopping the aileron short of the tip. Inboard of course it is better. But when the aileron goes entirely to the tip, then the average alpha of the tip is closer to that of the freestream.

To correctly match the propeller-ish profile of zero lift line shift from root to tip that would be ideal for a roll maneuver, one needs no aileron deflection at the root and maximal at the tip. Even having constant chord ailerons going full span is a considerable compromise. Separate inboard and outboard ailerons with appropriate deflection rates is less of a compromise but still a compromise.

Trilerons are not all that good, but certainly beat stopping the ailerons short of the tip. Stopping short of the tip is just plane aerodynamically ugly.

IMHO, trilerons as a technique is a partial solution to a problem that was independently solved by better structural techniques and materials some time ago. Trilerons are no longer needed.

Sep 09, 2014, 09:04 AM
F3B and F3K
RetoF3X's Avatar
Hey Gt

While I agree with your post, there were certain wing planforms being used in F3B that could benefit from trilerons. They used wing tips that were locally swept back (Estrella, Shooter, Radical), similar to David's second picture. Essentially trilerons allowed a close to constant chord aileron to extend further out. Some of them where actually not triangular, but trapezoidal, to better approximate a constant % of the local chord. With a straight aileron, you would get chords above 50% at the very tip on such a particular wing planform, which would not work well.

I actually had a beater Estrella that had a left wing with a conventional aileron and a right wing with trileron. The conventional aileron had at the very tip a large chord (over 30%), whereas on the other wing, the trapezoidal trileron kept it close to constant. You did not notice anything in normal flight, but on winch launch at CL max, it would preferably stall to the conventional aileron, which kind of made sense. This was not a prove of an advantage of trileron, rather a badly designed aileron/wing planform.

Now that most F3B, J and DLGs have converged towards elliptical wing planforms, constant chord can be maintained all the way to the tip with a straight aileron or flaperon. Hence there is no need for a trileron anymore IMHO.

Last edited by RetoF3X; Sep 09, 2014 at 09:15 AM.
Sep 09, 2014, 10:23 AM
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elkski's Avatar
Thread OP
I hope I am soaking up a fraction of this great info. So much info in RC, DLG for this over 50 brain to soak up in one year.
Great posts guys. Gt, reto, otbers who must be allstars also in one post! Priceless.

OK so let me ask one more time. My Stella has the trilerons like it or not. Maybe to help with flutter? The designer will have to answer.
So my question is about the mechanism. Micro level. I worked where i could call out tolerances of .0005" and no machinist dared to mumble. They knew i used such callout judisously
Where is best to cut the separating line?
Its not so simple to me.
If I cut perpendicular to flap hinge the point on the flap tip will have a longer rotation radius than the adjacent point on the trileron tip. If I cut at bisecting angle the tip points are at same rotation radia and points will just separate along one axis.

If I cut perpendicular the tip points move in two axis. Putting more shear movement on blenderm tape.
So my concern is this shear movement a good thing for flutter or not? Is it going to wear out tape faster? Pull it up sooner?
Sep 09, 2014, 04:40 PM
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davidjensen's Avatar
Don't worry about the stress on the blenderm tape. You will have to replace it once in a while and it may limit the throw out at the tip but it does not matter. You can widen the gap and let the blenderm tape take up the space giving more tape to stretch. Your micro managing things that don't really make a difference. Get her done and go fly. Fluttering a small DLG like the Stella is not an issue unless your a gorilla.

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