...Don't know ???

[Bootlegger]

     Mornin Guy's,  I have read two trains of thought about tapered trailing edges.
  One say's don't taper and the other say's do taper.
 What do you do and why do it this way
  Thanks for your help.....

[L0U CRANE]

Gil and Ty,

Somewhere, recently, there was a detailed discussion on the shape of the back edge of the surfaces.

Short and sweet of it, as I grasped the comments, was:

Rounded TE isn't as good as perfect sharp edge or sharp clean change to a vertical back edge (right angles to the chord line.)

Air 'attaches' to the surfaces it flows over, and a clean edge discourages air from flowing from higher pressure side to lower pressure side. ...Like a squared transom on a speedboat, the water finds its own way to rejoin, somewhere away from the back end.

The 'boundary layer' was mentioned in that discussion, and it gets thicker along the chord of the surface air flows over. The boundary layer is slower moving than the free air further off the surface - it is what could attach and mess things up. There are ways, apparently, to estimate the thickness of the boundary layer at the back edge of whatever surface.

So, a taper to about the thickness of the boundary layer at the end of the flap, or elevator, chord is at least as efficient as a true sharp edge. Estimated 'squared' back end height was around 3/32 to 1/8", if I recall, for a mid/large-size stunter wing chord.

It is also stronger, more warp resistant, and a lot less susceptible to hangar rash...

[Bootlegger]

    OOOOPS, I shuda said that I'm lookin' at the trailin edge of the stab.
  I hope that didn't cause some confusion...   This icon is what I was doin'...

[Bill Gruby]

Bootlegger;

   Sorry I've been busy, Ty is right,if you read the reply by Lou you will see the first sentance mentions rear surfaces, not just wing TE's. A trailing edge is a trailing edge, wing or stab, samo samo.  FWIW



              "Billy G"   

[Joe Messinger]

I don't know if this has any relevance to tapered trailing edges on aircraft but tapered bases on bullets affects flight in some areas of ballistic performance. 

"Boat Tail" bullets have a taper on their base and are more stable in flight as their velocity decreases.  As a bullet travels through the air it creates a cone shaped path in the surrounding air from the nose to base.  As velocity decreases, the width of the cone (at the base) narrows and eventually the air flows along the sides of the bullet.  As it reaches the low pressure area at the base of the bullet, it curls in behind the bullet creating turbulence which can cause oscillation affecting the flight path. The tapered base reduces this turbulence.  Again, this affect is only significant at relatively lower velocity which occurs at long distances. 

Of course our c/l planes aren't traveling at bullet velocities and their speed doesn't decrease steadily throughout their time of flight but perhaps some parallels can be applied to tapered bullet bases and tapered trailing edges?  Just a thought.

Joe

[Bootlegger]

   Thanks a lot guy's...

[john e. holliday]

I don't know why someone hasn't mentioned this, but, I was always told at the speed we fly models, the tapering of the moving surfaces cuts down the sensitivity around the neutral point.  I have tried with little success to keep the trailing edges as square as I could.  DOC Holliday