Custom Cut Leading Edges - RC Groups
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Oct 24, 2017, 03:21 PM
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J Bergsmith's Avatar
Discussion

Custom Cut Leading Edges


Anyone cutting their own leading & trailing edge stock? If so, can you share your techniques? I posted this in the wrong forum and got a few responses, looking for some more ideas. This would be in 36" and 48" long stock.

I have a table saw and bandsaw. I've used my bandsaw to cut leading edges with good results, haven't tried trailing edges yet.
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Oct 24, 2017, 03:55 PM
An itch?. Scratch build.
eflightray's Avatar

Picture added.


Leading edge, I usually use a cut to width length of 1/2" balsa sheet, glued in position and cut to shape using a razor plane and then sand to finish.

Trailing edge, if there is no L.E. pre-profiled in stock, (usually the LHS has up to 1.1/4" wide), I do my own 'built up' version with 1/16" sheet top and bottom and triangular ribs. They turn out lighter and less prone to warping.

Ray.


I don't actually have a table or band saw.
Last edited by eflightray; Oct 25, 2017 at 09:09 AM. Reason: Addition
Oct 24, 2017, 04:54 PM
B for Bruce
BMatthews's Avatar
I've always just cut square or rectangular and shaved it then sanded.

The thing about "stock shapes" is that they generally don't fit anything really well. So really it would be on a case by case basis. But in preparation for the trailing edges at least I'd say buy a plank each of thicknesses you think you'll use fairly regularly. Then angle the saw blade suitably and slab off slices that correspond to the TE shape done in a vertical orientation. One cut at an angle then back to 90 and the second cut and you have your two lengths. You can do this regardless of airfoil shape. It just means that you might need to slightly alter the rear end of the ribs to meet the lower side of the TE stock at 90 to the lower curve tangent to match the shape of the stock.

Another option is to run off a rectangle from something like 3/8 or 1/2" sheet then run it through an angle cutting jig to end up cutting the rectangle diagonally to get two suitable size pieces with one cut. Or if two cuts then you just have a slip of waste after the second pass for the "thick" side.

For the leading edge I'd run off a big CAD drawing with three or four faceted angles. Then from a sheet of suitable thickness that is straight in all respects run it through the saw flipping it for each pass and each angle and finally slice off the "leading edges". The chines left by the facet cuts will easily and rapidly sand down to a pretty darn true shape with much care at all.

The trick would be in doing tapered edges. Then you would certainly need an angled carrier and work the cuts carefully to reach the shapes you're after. Even the carrier you use may need to be angled in thickness as well as in the plan view from above.
Oct 24, 2017, 11:04 PM
Registered User
I usually cut 45 degree notches in the ribs so I can use square stock leading edge. It is kind of hard to do accurately. Very little waste and much easier for a lazy guy.
Oct 25, 2017, 12:09 AM
B for Bruce
BMatthews's Avatar
I've done that on a good number of models too. It used to be a favorite method for lightly built control line stunt models with thick wings that naturally meet at roughly 90 just back from the leading edge roundness.
Oct 25, 2017, 11:58 AM
Registered User
For leading edges, I use an initial "false" leading edge, 1/8" thick, with the top and bottom edges roughly cut to the height and slope of the individual ribs that it is glued to. Then I add the top and bottom leading edge to main spar balsa sheeting, gluing this sheeting to the top and bottom of this false leading edge. Then I trim any overhang of the leading edge sheeting to create a flat vertical surface comprising of the false leading edge and the glued on sheeting. Then I glue on a square balsa stick to this vertical surface to build out the rest of the leading edge.
Then I carve away - hand plane, sand, etc., using a cardboard, "female" template of the desired finished LE to guide this carving.

The construction of a glued false leading edge to top and bottom LE sheeting provide a sturdy wing framework to withstand hacking away LE to form its final shape without risking racking/breaking the wing framework.

I believe that when formed LEs were available commercially, the LE sticks were made with industrial strength shaper woodworking machines, using custom made knives to make uniform, smooth leading edges.
In the last several decades, less expensive, portable woodworking routers have become available and frequent application is their installation in tables, such as the side table of table saw, and with a fence, use them to shape the edges of wood planks. With combination of correct off the shelve router cutters, one might come close to the final desired leading edge shape. There are outfits that will even make the exactly desired router cutter but I suspect the price would be steep.

And for a one time leading edge of a specific height and airfoil shape, hand work is quicker than all the set up time involved even if one had a 'full catastrophe woodworking machinery workshop' (smiley)

I agree with a previous poster in the use of top and bottom sheeting to form a trailing edge is generally both possible and definitely lighter than a solid trailing edge.

Michael in Ontario, Canada
Oct 25, 2017, 06:04 PM
B for Bruce
BMatthews's Avatar
There are just so many options for making a wing that it can sometimes be mind boggling.

If faced with both leading and trailing edges that are tapered I think I'd look strongly at the split "V" style trailing edge done with two sheet pieces and webbing to fill the open mouth. As Michael says it's lighter for starters. And in many a case just as fast or faster and it has the advantage of directly taking its shape from the ribs that hold the sheeting apart. In fact it's a method I've used many times on a variety of models with widely varied "tasks".
Oct 26, 2017, 12:25 AM
Scott
Pylonracr's Avatar
Another option for leading edges that I have used a few times is a carbon fiber tube. Cut the ribs with a half round front and glue the tube to them.

Scott
Oct 27, 2017, 12:41 AM
Registered User
ErcoupeEd's Avatar
If you have a bandsaw with a tilt table top, trailing edges are fairly easy.
Just make sure your bandsaw is adjusted carefully ( belt tension , etc, and a sharp blade.

There is a an add-on I bought at the EAA airshow several years ago from a vendor in the fly Market.
It can be purchased from "Stock Room Supply".
They are in Canada and it's called a "Little Ripper"
It makes possible very straight and very smooth cuts of larger balsa stock.
Let's say you have a balsa 4x4 x36 or 4x4 x48 inch block. You can cut a lot of very nice 1/16 thick sheets, 3/32 sheets, 1/4 inch sheets, etc

There is videos of it on You Tube.

How it works is the blade does not get pinched against a back guide and the blade does'nt flex giving you an uneven cut
Watch the videos to see what I am talking about.
It's a very useful attachment for scratch builders or anyone doing other wood work
In the videos they show sawing small logs .
But it also works great on other types of wood.

Put "Little Ripper" in the search on You Tube or Google Stock Room Supply
Oct 27, 2017, 12:54 AM
Registered User
ErcoupeEd's Avatar
I have a collection of Frank Zaic yearbooks and the one on Glider Design which has some really handy ways to cut wing ribs.
Oct 27, 2017, 07:26 AM
Registered User
AA5BY's Avatar
Quote:
Originally Posted by eflightray
Leading edge, I usually use a cut to width length of 1/2" balsa sheet, glued in position and cut to shape using a razor plane and then sand to finish.

Trailing edge, if there is no L.E. pre-profiled in stock, (usually the LHS has up to 1.1/4" wide), I do my own 'built up' version with 1/16" sheet top and bottom and triangular ribs. They turn out lighter and less prone to warping.

Ray.


I don't actually have a table or band saw.
Ray.... your pic illustrates the use of a sub LE and then a cap, which I've also been using on recent builds. It allows the use of a slightly softer and thus slightly easier to shape LE piece as shown. I've been using 1/4" sq fir for the sub piece.
Oct 27, 2017, 10:10 AM
An itch?. Scratch build.
eflightray's Avatar
I glue the smaller strip, (the key) to the larger one first, i.e. a one piece L.E., before the ribs get attached, perhaps not quite the same as capping if that is done after the ribs are attached.

The front piece is large enough to cover any sheeting that may go on, D-box, or full sheeting.

Then the best part. Out comes my trusty old razor plane, and the room slowly fills with balsa shavings.


Ray.


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