RobT

My Feedback: (17)

I am finishing a 40% carden extra and was wondering what methods people use to keep the leading edges on both wings to be exactly the same.

Also how sharp should the leading edge be at the tips? for good 3d and good snaps / spins

Thanks

Rob

3DFanatic

My Feedback: (5)

I've read about taking a length of PVC pipe, cutting it in half down the middle, and using it for a contour sander. haven't actually tried it though.

CAPtain232

My Feedback: (40)

I do it all with a watchful eye and a steady hand..... I typically make the root sharp and the tips blunt (rounded)..... The helps the root stall before the tips and therefore the plane is less likely to drop a tip.

RickP

My Feedback: (2)

Rob,
You may want to try the aerodynamics or building forum for a technical explanation. I was listening to that conversation about leading edge sharpness too and to be honest I never realised that before. If you are wondering how to get both sides the same the only way I know would be to make a template at equal intervals along the LE, say every 5" and just make sure both sides are the same. I'm sure glad I'm flying from ARF's right now
RickP

rmh

As long as both wing panels are the same - don't fret over the sharp/round thing.
On that model- you have to add wood to make any real change- just blend the existing setup to a smooth transition.
We had two sets of em here this winter - they are just fine as is.
I use a straight 80 grit block- made from formica covered composition board.
The paper is from the Automotive Paint shops -in self stick.
After you make three distinct "faces" along the LE-- blend with new 100 grit.
The business of special curved blocks is -to me a waste of time/money- A long block and sharp paper will do exactly what's needed.
On our models - accuracy is of far greater importance than any " trick" LE setup.
You may find that your LE is bowed or has a slight dip along the LE to sheeting joint, at center panel.
This is due to the hot wire cutting process and simply is a ***** to get perfect.
Just try to make each wing panel as close to being the same, as the other panel.
After doing about a thousand of these - I have it down to a science now ------

F4u5

My Feedback: (81)

I just contour the top and bottom of the leading edge to the adjacent sheeting. I then give it a "shoe shine" running a piece of 100 grit back and forth across the squared edge. I just take my time and watch as I go. Much like Mr. Hanson above speaks of. Been doing it for 19 years now.

MarkNovack

My Feedback: (3)

Ditto the last two comments. Sand, look, sand look. For more surety, scribe a center line down the LE after paring it level with the wing. Try and never cut into the line until your final rounding.

One thing that I do that really seems to help is to count my sanding strokes. You will quickly develope a feel for consistent pressure on the sanding board and as long as the balsa is even in consistency (Carden quality ensures that it will be), counting your strokes between top and bottom can really help with symmetry. Five top half, flip, five bottom half.

Tapered or shaped sanding blocks have been a disaster whenever I tried them. The long block (40"x4" aluminum is nice) is the only way for me. Do not stroke straight down the LE, rather pushing at an angle of about 20 degrees across the LE.

Our current shaping methodology for F3A is to sharpen the leading edge gradually going towards the tip (it happens naturally because of the taper). I think it is the right way, but I cannot really say as to the effectiveness or even if it really makes a difference beyond psychological. Airfoil thickness and evenly cut wing cores have huge amounts more effect on stability and evenness of flight than LE shape for our small airplanes (as opposed to full sized).

Oh, how I wish I had the time and resources to spend half of my time researching these ideas and theories in practical applications with really scientific controls and enough consistency to make it trully valid. What fun it would be to try fifty different LE shapes over a few weeks period on the same airplane under ideal conditions and see the difference between theory and application. Just a few flights, cut off LE, try again, until a marked difference was noted with 100% surety.

Regards,
Mark

RobT

My Feedback: (17)

Thanks for the info Boyz

Rob

RickP

My Feedback: (2)

Rob,
Were you talking about making it blunt at the root and sharp at the tip to aid in breaking for snaps?
RickP

jongurley

My Feedback: (29)

sharp and blunt that is a interesting idea as far as stalling goes, I wonder how big of a difference it makes..

RobT

My Feedback: (17)

Yes Sharp at the Tips and Blunt at the root. It might give a tip stall, but it will aid in snaps and spins. All depends on what your looking for. Whyat I decided to do to get both sides close was use model clay as a pattern to match the two sides.

As far as how much of a diffrence it makes, huge. In copetition soaring kits they always included templetes for the L.E. in instructions. I guess I miss having those aids in the kit.


Thanks for all your input.

Rob

whs485

The split PVC tube works for me. I select what I feel is the best radii for the particular wing I'm building and split (on the table saw) a 24" length of PVC tubing of that radii. I feel that anything over 24"in length is too unsteady insofar as applied pressure is concerned, and really requires a two handed approach to get even pressure. I then apply a self stick sanding strip to the inside of the tubing, scribe a pencil line down the center of the LE and go to work.

dicknadine

the name of the game is to have it all fair in together, your idea of LE shape may be different than mine, BUT how does each fly in relation to each other? we do NOT have wind tunnels to design and build our models-- we leave it to the $$$$$$ guys, working for the US govt. just try to keep each half the same and you won't know the difference between a sharp and a blunt LE (figuretivly speaking) dick.

jongurley

My Feedback: (29)

Which would be optimal, for all around flying, alittle 3D, aerobatics, but still semi stable.... sharp or blunt.

RobT

My Feedback: (17)

A cross between the two.