Built-up airfoiled stab and elevator

I want to buid a built-up airfoiled stab and elevator for the first time. The thing I don't quite understand is the construction method for a thick 1/2" stab and elevator on large stunt ships.

It this done on a flat surface using square balsa stock, then carve the airfoil and taper in later? But, what about the elevator. Isn't it easier first the taper the rib, then glue them in on a flat surface. But this method create a offset angle in the LE and TE of the stab. What is your method, please show pics if possible?

Why don't you use a miniaturized version of the Tom Morris jig blocks, with laminated LE & TE? Cut the ribs out, with a notch front & back for the alignment strip. Cut your own stripwood from sheets, otherwise it will be deathly heavy. Light stripwood is not bought a the LHS, it's made at home. Ted says to bandsaw it, which seems logical. Steve

Build up your stab and elevators out of square stock LE and TE and rectangular ribs in between. You can slot the spars if you so desire with an embedded hacksaw blade or jigsaw blade in balsa for about a 1/16th deep sawcut.

How to taper? Get a set of 3 or four foot steel rods, 1/2, 7/16, 3/8 etc. down to 3/32.

If the LE is to be 1/2 in then use the 1/2 inch rod for one side. Pin it in place on your board with a couple T straight pins. Place the assembled elevator part against it with the LE against the 1/2 inch bar, place another 7/16 rod on the TE of the part. I find it best to set up the first bar so the part and sanding block are near the edge of the table; that way the sanding block is not interfering with the table top on the low edge of the part. Holding the smaller rod against the part to capture the part between the two rods; sand the part with a flat true sanding block. When you have removed 1/16 at the trailing edge; flip the part over and take the next smaller rod and repeat the process. Continue flipping and sanding till you get about an 1/8in TE or 3/32 TE and you are done. Now finish the LE to suit your fancy ie radius or angle etc.

It is much easier to assemble square parts then sand to shape afterwards.

I cannot take the credit for this idea. Learned it recently and it does work great. Thank you, whoever you are.

I do not know how to sand an airfoil on a stab. Does anyone out there know how to do that trick short of templates?

Bob Smiley
A Lancair 360 builder/pilot trying to be a modeler.

LAST EDITED ON Feb-14-04 AT 01:59 AM (CDT)
 
Thanks for the tip. I started working on the 1/2" stab. I decided to use 3/8 square for the LE and shim the LE 1/16" with a scrap piece of balsa to center it on the board.

Nice job of building there, looks dead straight
Uh what is the model please?
vincent

The model is a Ted Fancher "Imitation". Its basically a profile with a radial R/C engine mount. The kit was kitted by AJ Freeflight and the wood is not very good. The only stock wood I am using is the fuselage. Most of the balsa stick are very heavy and there is NO INSTRUCTIONS on contruction, just the full size plan.

Are you planning on sheeting the Stab when you are through? It looks like the grain in the center section is running the wrong direction - cord wise instead of span wise, and there is a splice in the Trailing edge at the center.

LAST EDITED ON Feb-16-04 AT 03:01 AM (CDT)
 
Curt,
I did not realize that it should be span wise in the center. I thought it like another rib but thicker. There is no spice on the TE, that is just a center ink line.
Maybe I should sheet it with 1/32" balsa, that shouldn't be too heavy.

LAST EDITED ON Feb-14-04 AT 06:20 AM (CDT)
 
You could order a foam core from one of the foam cutters..

Here's a thread on one method that works well: http://www.clstunt.com/htdocs/dcforum/DCForumID1/6504.html

LAST EDITED ON Feb-16-04 AT 11:30 PM (CDT)
 
First, I don't think you can easily sand an airfoil into a built up surface as shown in the photo. It makes no sense to begin with a perfectly flat stabilizer which is too thick. It will be an exercise in frustration to attempt to airfoil the pictured stab. It works better to build with airfoiled parts. There are two ways. the first way would be to use a Tom Morris type construction with oversize leading and trailing edges forming the jig. It is my opinion that all built up stabilizers need to be sheeted with 1/16" for rigidity. If you use the Morris method, sheet both sides before shaping the stab. Personally, I don't like the butt joints between the sheeting and the leading and trailing edges, but it can build decently shaped surfaces.

I build mine "up in the air". I start with a laminated spar using thin spruce strips for the top and bottom spar caps. To this, I add ribs and the leading edge soft 1/4" square which I've tapered a bit. Next, I glue on the bottom sheeting with CA. Finally, I apply Tightbond to the top of the ribs, spars and leading edge. Then position the top sheet. The trick here is to use a lot of making tape strips to attach the top sheet. I use about forty or fifty. First apply about ten strips more or less equally spaced, then straighten the stab visually. It will be flexible enough to twist and bend quite a bit. It will tend to stay where you put it. Continue to add strips and visually straighten. The stab will tend to warp in the direction you are adding strips but this tendency can be used to selectively remove warps and bends. The masking tape easily distorts and permits twisting. The stab stiffens as you add tape but remains somewhat flexible even when the complete perimeter is covered with tape. When you like what you see, let it dry and sand to its final shape.

I build control surfaces basically the same way. I add ribs to spars, CA the bottom sheet and apply the top sheet with Tightbond and masking tape as described above. My elevators are a bit thinner than my stab trailing edge.

I build thicker surfaces than you plan. My stab ribs are about 1/2" tapering to 1/4" at the tips. My laminated spars are 3/8" thick, leading edges are 1/4" square. Elevator and rudder spars are 1/4" with all ribs 1/4". All sheeting is 1/16". Maximum thickness of my stabs at the root is usually 5/8" to 3/4". Also I add short stub aux spruce spars at the thickest point of the stab.

Normally, I jig everything. There is no satisfactory way to jig an airfoiled stab, particularly one which tapers at the tips. It is surprisingly easy to build an accurate,visually aligned stab. The complete set of tail surfces, as shown in the last photo, with hinges and elevator horn weighs 60 grams. This is a fairly rugged set for a .65 sirplane. For a 46 airplane, I'd build a half ounce lighter or 46 grams.

LAST EDITED ON Feb-17-04 AT 08:55 AM (CDT)
 
>Most of the balsa
>stick are very heavy and there is NO INSTRUCTIONS on
>contruction, just the full size plan.

Have you read Ted's 2-part Imitation article? Talk about instructions!! If not, I would be happy to U.S. mail it to you. Just send me your address either on the forum or by email.

Also, I recall some interesting stuff about the Imitation on the forum a while ago. You might want to search all including archives if you haven't already.