Chevrons on flaps and elevators?

[John Carrodus]

I see some Stunthangar debate on Charles's show and here about the use of full span trim tabs on elevators.
I have some questions please?
 (1) How or why do they work?
 (2) There appears to be several types- is the 'T' section or air dam - I call it, more effective.
 (3) Do they make a worthwhile/useful difference ? ( I know the usual reply, if they did everyone would own one!)
 (3) Has anyone Chevroned their elevators?
 (4) It seems to be only and elevator thing. Why not flaps as well?

Cheers in advance
John

[Chris Cox]

Hi John, I’ll try to answer your questions.

(1) How or why do they work?

Great question, and I’m not sure we have an accurate aerodynamic answer to this just yet.  Some people call these Gurney Flaps, but I do not agree with this as Gurney Flaps we’re designed to create downforce on race cars.   We place our strips/wedges on both side of the elevator trailing edge creating equal turbulence/drag in both up and down elevator deflection.  My very simple theory is that drag is created, causing the elevator to more effectively find neutral, explaining why level flight is improved and the return to level/straight flight when exiting a corner.  People much smarter than me think this explanation is rather simplistic and feel other forces are at work.

(2) There appears to be several types- is the 'T' section or air dam - I call it, more effective.

I think over the past year or so, people have got a little carried away with what is needed.  My initial experiments was with several layers of 1/8” Fine Line tape, which showed immediate improvement.  From here we/I went to 3/8” ramped wedges, 3”, 4”, 6”, and finally full span along the elevator trailing edge.  All worked well, but in some instances, the full length strips caused excessive drag and in electric setups, drained batteries before completing the pattern.  Interesting enough, after all this, I found the thin tape strips, about .020 - .025” in height worked about as well as anything, and negligible drain in the batteries.  Rather than building fancy strips or “T’” plates, I would try this first. Simple and easily installed and removed if you do not like the results.

(3) Do they make a worthwhile/useful difference ? ( I know the usual reply, if they did everyone would own one!

I think they do and most (not all) people who tried them think so as well.  Three of the Top 5 at the Nat’s used them, and the two who did not had not tried them as yet.

(3) Has anyone Chevroned their elevators?

Not sure what you mean?

(4) It seems to be only and elevator thing. Why not flaps as well?

A buddy of mine tried them on only the outboard flap, thinking it might result in better line tension.  It didn’t, and the airplane was not happy, but my friends was when he finally landed, as he was certain he was going to crash.  Feel free to try them on both flaps and get back to us. 

Cheers,

Chris Cox

[Perry Rose]

I call them drag strips. They can be used as a trimming tool also. I have a plane that turns down much better than up. I put a partial strip on one elevator half to even the turn rates.
I compare the strips to the feathers on an arrow.

[Dan McEntee]

   The first place I had ever seen these was on the ailerons of some indoor R/C aerobatic models, but never read any explanation about them. Ailerons deflect both directions, so I would think the effect is similar for ailerons. When deflected they help roll rate and lock on to straight flight better.
  Type at you later,
  Dan McEntee

[Chris Cox]

   The Ailerons deflect both directions, so I would think the effect is similar for ailerons. When deflected they help roll rate and lock on to straight flight better.
  Type at you later,
  Dan McEntee

Yes, this is true.  Tim Just, our full size aerobatic expert tells me it only takes about a 6” strip on the ailerons to feel a change in handling characteristics.  Just speculating, but if we added strips to both the elevator and flaps on our models, I wonder how that might affect handle pressure when maneuvering?  My guess is that it would greatly increase, maybe  more than we would want?

[John Carrodus]

Thanks Dan , Perry and Chris. I'm now keener than ever yo give this stuff a go. If the control forces increase , perhaps stepped elevators (on the tips like the Spitfire - and at the top of many rudders,
might be the way to gain mechanical leverage? 

Chevrons.
Boing are using these on the outside of their engines to smooth flow and quieten the engines.
I wonder what a similar rippled pattern might do to flaps and rudders for eg?
Fascinating stuff.
John

[Paul Walker]

Can you provide a picture of what you are calling a Chevron?

[GERALD WIMMER]

Hello This got me curious as Chevrons are those V shapes used on military uniforms??
In aircraft terms they are just scallops that add turbulence.
 Found a good video of why chevrons that add drag are added to new jet engines to reduce noise here:



Regards Gerald

[John Carrodus]

Thanks Gerald.
CORRECTION on my part.
Chevrons increase turbulance.....
Therefore one would wonder if they would serve the purpose of the TE elevator tape/ trim tabs for slotting the plane back on track and improving corners?
I will give it a go.

[Jim Benzinger]

Hello This got me curious as Chevrons are those V shapes used on military uniforms??
In aircraft terms they are just scallops that add turbulence.
 Found a good video of why chevrons that add drag are added to new jet engines to reduce noise here:



Regards Gerald

Those increase the mixing of air from the free stream and fan exhaust. Thus reducing the shearing of the air--reducing noise. Not for aerodynamics, for noise and reduced drag.

[John Carrodus]

Guy Markham is onto it.
See his story further down this page
             Vortex Generators
They look a hell of a lot like Chevrons to me and seem to do the job.

Just as an aside a couple of things have just come to mind. Shark skin is rough and some swimmers use suits copying this characteristic for more speed ( I guess even a fraction of a percent could be the difference between first and second place.) I believe Team NZ had a similar micro finish on one of their successful America's Cup boats. Many years ago I asked a crewman at an air display why his RNZAF P3 Orion had a dimpled finish on the spherical chin infrared camera. By creating controlled turbulent airflow it creates less buffeting like on a golf ball was the logic apparently.