Trim Tabs?

[Shawn Kuntz]

What's the best way to add a trim tab to the outboard wing?

[Ward Van Duzer]

I've done this about 4 different ways... I guess it depends on the "LOOK" you want, or don't care about! The ugliest (for beat up old profiles you don't care about) is to cut a piece of tin or brass sheet, similar to fuel tank material into an approx 1 1/2" X 3" rectangle and put a crease in it lengthwise down the center. Glue this under the OB trailing edge near the tip with GE Silicone. The metal can be bent up or down to adjust for the needed amount of trim required. Quick and Dirty!

Second (and third) method involves cutting the tab into the trailing edge (on a no flap airplane) and either gluing it in position (and hope you get it right) or using a sheet metal hinge to make it adjustable. Or you can put a little horn on it (small horney hinge points work fine) and set up a little R/C threaded push rod and clevis for your adjustment.

On flapped airplanes I love the Randy Smith technique. Design the flap to end about 2-3 inches before the end of the wing tip. Then hinge the outboard tab with a horney hinge point and another small hinge and use the R/C routine (above) to adjust. The inboard tab gets glued (Built-in) to the inboard tip.

Other folks have done this with clear plastic so that the tab is "invisable", but it doesn't seem real practical to adjust those. OK for "warts" though.

W.

[Jim Thomerson]

I just put a clear plastic trim tab on an airplane.  Cut it out of a package some files came in.  I bent it like I thought It should be and glued it on the bottom of the trailing edge with canopy glue.  Got it about right.  I suppose you could use canopy glue to glue a couple of pieces of bendable wire to the plastic for more positive adjustment still fairly invisible. 

[Kim Mortimore]

A lot of people have the idea that a trim tab must extend behind the TE to be effective, forming a highly visible "This wing is warped" announcement to everyone who sees the plane (still talking flapless wings).  I've had much success with an idea borrowed/stolen from combat megastar Phil Cartier.  (I wouldn't have thought of anything this simple and easy myself in 10 to the 10th years!) 

Start with a length of preformed, tapered trailing edge stock.  There are several sizes.  I like the stuff that is 3/4" wide and 3/16" deep.  1/4" deep x 1" may be useful for larger planes or more severe warps.   Take a wild guess what length of tab to start with, somewhere between 2 inches and 2 feet long.   

Using double-stick tape, attach the tab under the TE near the tip of whichever wing requires it, choosing which wing wisely so as to correct for the warp, not make it worse!     Position it so the thin edge of the tab is pointing forward, and the 3/16" deep edge is either flush with the TE or a bit forward of flush, to make it even less visible from above. 

Test fly your plane.  If it returns to earth in one piece and is not smashed to smithereens--a lifetime toothpick supply      pull the tab off if necessary and adjust the length of the tab as need for more or less corrective action.  The stuff is cheap, so if you need a longer tab, no big.   Toss the shorter one and cut a new, longer one.

Once you have found the ideal length, if you want the tab to be permanent, rather than just a temporary band-aid until you can dewarpialize your wing, you can paint it the same color as the wing, funnycote it, or if you are not vain about the straightness of your wings, you can print TRIM TAB in Margic Marker on it. 

I am not big on tweaking flaps, so I have used this same technique on the trailing edge of flaps with equal success.

Back to the first sentence about what people expect a trim tab to look like, a few people have looked at my funny tabs and said "What is that thing?"  "What does it look like?"  "It looks like a piece of wood taped to the bottom of your wing."  "Yes, you're right." 

Thanks Phil.     

Kim Mortimore

[phil c]

The best trim tab  is NO trim tab.  Regardless of flaps or no flaps, if the plane has a roll to it, twist the wing and re-iron or otherwise dewarp it until it flies straight.

thanks for the kudos Kim, but even the wedge trim tab can be over done.  It does work better than any adjustable tab because it can be bigger, with less angle.  But if you need a tab more than 3 in. long to trim the plane, fix the wing and get rid of the tab.  Same for twisting the flaps.  Trim tabs and twisty flaps work best at only one speed and one angle of attack.  A straight wing will work anywhere.