Battle Axe: http://www.treneffrc.com/ and http://www.treneffrc.com/battle_axe_build_along.asp
Avenger: http://www.georgiacombat.com/OpenCombatDesigns.html and http://www.teamseaholm.com/

this weekend we will make our first attempt at cutting out a wing based on the battle axe wing ..
Based on photos I come up with 30" wing half. 9" at the root and 6" at the tip. gonna use the airfoil below.
We are going to try a couple of methods.
One plan - attach the wire to a pivot point roughly 100" from the root of the wing. cut along the 9" root template. the anchored pivot point will control the other end of the wire. Adjust the pivot point so I get a 6" wing tip at 30" out from the root template... Will that work? I question how tight we would have to pull on the wire to make it follow the airfoil shape all along the wire? will drag cause the far end of the wire to "lose" its shape?

2nd plan is to attach a 9" template on one side and a 6" template on the other side and with one person on each side, drag the wire over the template...

having never done this we are trying to be flexable and will go with what works...

I'll take pics..

Steve

I don't think your pivot ides is going to work for more reasons than I have time to list

I have my doubts also. BUT we did find a setup described that way with one end anchored..

thus plan B!

Hi Popriv

For the kind of wing you are cutting you need two templates. I have tried the pivot when cutting a delta wing and it sort of works but went back to two templates on that as well as I wanted a different aerofoil at the tip.

The tendency will be to melt out the area by the wing tip. Deltas are difficult, but they are doable. A low aspect delta needs the temp set as low as possible. The panel can come out bowed from leading the wire through the foam before the lagging wire middle of the wing panel catches up.
Some melt out is workable/usable, but bowed panels from sag in the wire are useless junk.
I've been cutting from a pivot point for 25 years, the guy who taught me had been doing it since foam was first introduced as THE WAY to build control line combat planes in bulk.
The quality of your work will only be as good as your templates and the accuracy of your set up....the hot wire does not lie....
I use a $7 light dimmer switch coming straight off of 115VAC and in 25 years I'm on my 2nd dimmer now. I'll bet I've cut 50 "finish grade" sets of wings by now.
I use .020" solid stainless wire, it takes about 6 to 8 feet of it between your alligator clip "electrodes" for the dimmer to control it....so for most set ups there is extra stainless cutting wire in the circuit that lays slack.
The pivot point is height adjustable and I Cclamp it to the work table where the imaginary "projected" lines of the wing's leading and trailing edges meet.
The "T"handle is a chunk of wood with a nail driven through the middle, then folded back to give the cutting wire something to tie to.
The formica templates are sheet rock screwed to the foam. A little 3M77 helps, too.
You won't get shocked with this power source, not even a tingle..just make sure you are controlling the "HOT" with the dimmer and not the nuetral. Always wear shoes, too......

Combatepig, we are going to try the pivot point. do you use just the one template at the root of the wing when cutting from the pivot point?

I could "see" a template at the small end of the wing. just as a guide for the wire??

If the delta wing doesnt work I'll go for a strait wing...

I'll get something to fly , if only on its way to the ground.

Steve

Steve, I've used just 1 template, but you really need to pull hard and be very steady. Getting into the right stance/posture/position is important.
I'm no expert at hot wiring low aspect deltas [done 2] but I would think a template at the tip will help. You are learning to hot wire the most difficult type of tapered wing.
Make sure your pivot point is perfectly adjusted height-wise. I use a 10-32 screw, nuts and fender washer to make that happen. All foam needs to be measured for the exact thickness/centerline.
Don't expect to hit a homerun your first time up...learn from your errors and keep trying. Always place a board or something flat to secure the foam blank before you start cutting.
I usually place my free hand on the foam blank. Have fun!

I have 6 blanks to try and cut and I'll be surprised if any of them are usable.
This first try is pretty much just to get the feel of it...
If it goes bad. we will switch to a simpler setup.
Unless we get lucky!


steve

Test the heat setting on scrap, the temp is perfect if you leave thousands of hairs on the cut....
bubbles and pits, big wide kerf, no good.
Wipe the wire before or after each cut with a paper towel.
"Dress the wire" with a smooth round tool to make sure it is perfectly smooth.

You aren't making a [low aspect/short span] delta for combat, are you?
The highly swept leading edge will keep scores down....

I'm trying to copy the wings I see on a number of SSC combat planes.

Battle axe, avenger...
measurements I made by scaling a web photo up to full size to estimate the wing sizes.

1/2 a wing will be 30" long. 10" at the root and 6" at the tip. for a total 60" wingspan.
seems big for an OS .15LA but thats what they are running on those planes..

from the look of those wings the tip is centered on the root so the LE sweeps back and the TE sweeps forward...

Would the low aspect/short span delta you describe be like a jet wing? ( highly swept back LE, short wing and a straight TE ???)

Kinda ignorant on the wing terms.... but learnin..

thanks for the tips..

Steve

This is a Delta http://www.btemodels.com/vortex.html
From http://www.grc.nasa.gov/WWW/K-12/airplane/geom.html :
Aspect ratio is a measure of how long and slender a wing is from tip to tip. The Aspect Ratio of a wing is defined to be the square of the span divided by the wing area and is given the symbol AR. For a rectangular wing, this reduces to the ratio of the span to the chord length as shown at the upper right of the figure.

AR = s^2 / A = s^2 / (s * c) = s / c

High aspect ratio wings have long spans (like high performance gliders), while low aspect ratio wings have either short spans (like the F-16 fighter) or thick chords (like the Space Shuttle). There is a component of the drag of an aircraft called induced drag which depends inversely on the aspect ratio. A higher aspect ratio wing has a lower drag and a slightly higher lift than a lower aspect ratio wing. Because the glide angle of a glider depends on the ratio of the lift to the drag, a glider is usually designed with a very high aspect ratio. The Space Shuttle has a low aspect ratio because of high speed effects, and therefore is a very poor glider. The F-14 and F-111 have the best of both worlds. They can change the aspect ratio in flight by pivoting the wingslarge span for low speed, small span for high speed.

The U-2 spy plane was an example of a high aspect ratio wing.

Steve, I see what you're up to now......piece of cake. The wing you are doing will have the pivot point pretty far back there. IIRC I had to clamp an extension to my work table to get the pivot point far enough back to cut 30 inch plus panels.

I have cut a few Avenger wings with this method. SMOOTH is the key word for the template.
another tip is be patient and don't lead the cut at all. That means move the handle slowly with little or no bend in the wire in the direction of movement. A slight (very slight) bend to keep contact with the template is ok. There is a tendancy to pull TO hard to allow faster cutting. Don't do it, just ease it along. Its a little like sawing, you have to let the tool do its job.

CP is spot on about coming out hairy, but then some of his balsa planes are a little "hairy" [>:]

Yes, I came up with a pivot point around 6.5 feet from the root template.

would you use the 2 piece template / where you cut the top then remove the airfoil shape and theres a bottom template ( which was supportig the top template) then cut along the bottom template.?


OR

just screw a template onto the foam and cut all around that 1 template?

is that clear???


Also I see some templates have the " nub" on the LE to rest the wire as you enter the cut.
How does this leave the LE?

Ahhh the details LOL..

Steve

IT leaves a flat LE which you then add a strip of balsa to and sand to shape

Two piece templates are much easier to use. For the wing you are going to cut as I said before forget the pivot method make two, two piece templates.

This assumes you are adding a balsa LE.

Make clean vertical cuts on your foam slab so you have a slab that is the correct size with tip and root angles set correctly. Align the templates so you have the flat of the back of the LE on the front edge of the slab.

Work from the front to the rear. I like to have colour coded points on the templates because I work on my own but numbers work too, esp. if you have a helper.

Cut the top first remove the top part of the template and cut the bottom front to rear. The stub on the front of the LE on the template makes sure you get a clean entry on the foam.

There is a good chance of ripples on your first attempts. They are caused by hesitations on the cut [ or bumps on the templates. ] Sand them fill with light weight spackle and they are good to go.

Most people I have shown how to cut get pretty good results after 3 to 4 attempts.

Wipe the stringy bits of the wire after every cut. Do not be tempted to go for a 'really hot' wire, one I found it much better with just hot enough to cut slowly is easier to manage.

HAVE SOME POSITIVE VENTILATION GOING AN EXTRACTOR FAN IS GOOD BUT OPEN WINDOWS AND ANY FAN BLOWING AWAY FROM THE WORK TOP IS OK.

Pic is not mine but I used something similar. JD

Steve, I just use templates like I show in the picture and hot wire the bottom with one pass and the top with the second pass. There is no single way that works for everyone, just be really detail oriented to get the set up as smooth an operation as you can. It's good to have examples of the production kits to get ideas from.....a lot of R&D has gone into those models, probably more than any other type of model!

What CP and JD said. This is the method sailplane builders use and those guys are fanatics when it comes to accurate air foils. Look up "feather cut system" There are free plans to make it as a home built and a calculator to use to get tapered wings hands off.

Hey, you're talking about me, no offense, I am a glider fanatic.

If you go to www.TailwindGliders.com on the "Articles/Files" page you'll find an article I wrote for RCSD on how to build an automated foam wing cutter like the Feather Cut. You'll also find an MS Excel file on how to determine the hookup points on the swing arm, it's a simple calculator if you will. And lastly, there is an instructional DVD called "A Beginner's Guide to Cutting and Bagging Foam Wings". Everything is free except for the DVD.

Curtis
Montana