Hot wire cutting tips?
 

Not exactly a beginner topic, but,

We are starting to play around with cutting foam wings out of whatever foam I find at home depot/lowes.
We have the wire cutter and now I'm working on making the airfoil template and cutting jig.

Going to try a straight wing and a delta wing (delta wing might be pushing it a bit, we'll see how the 1st one comes out)

Any tips greatly appreciated.

whats the best foam?
Lowes has Dow Blue styrofoam insulation 2" x 2' x 8' and Polyshield expanded polystyrene 2" x 4' x 8' ( this has a layer of plastic on it)

The blue feels heavier, denser, stronger? looks good. ( I've also seen pink insulation somewhere )

what wing dimensions? I'm thinking 9" x 20" - 24" on the straight wing and the delta, 22" long, 9" at the root and 5" at the tip??

what airfoil shape to use? I've found a few online or I'll just copy one off the plans from one of my kit planes I built.

I'll use these wings with an OS .15LA or TTPro .36 ???

if lucky, I'll get something usable

Steve

RE: Hot wire cutting tips?
 

There are definitely a few tricks to cutting a foam wing.

Give me a few minutes and I'll work up a few diagrams

RE: Hot wire cutting tips?
 

There is always this: http://www.rcuniverse.com/magazine/n...roduct_id=3815

RE: Hot wire cutting tips?
 

Thanks Mike!

pop

RE: Hot wire cutting tips?
 

Fomica makes the best templates IMHO. Scraps can be gotten for free from most cabinet shops. Takes a little more time to make a template with Formica but then you have it forever.
Stainless steel fishing leader from Cabela's or Bass Pro makes great cutting wire. $10.00 will get you a lifetime supply and it includes shipping!
The smoother the templates edges the less ripple you get on the wing.

RE: Hot wire cutting tips?
 

What gauge of stainless steel wire are you using? The Cabela's in Winnipeg doesn't know what I am talking about?

Jim

RE: Hot wire cutting tips?
 

Bass Pro on line has it. I tried the store in Springfield and they don't carry it.
.016 is the size described in this great article
http://www.rcsoaringdigest.com/pdfs/...SD-2008-11.pdf

RE: Hot wire cutting tips?
 

I was fortunate to be taught to fly by David McDonald in Eldon, Mo. MANY moons ago. He taught me foam cutting also. I still have one of the Joy Stick (049 low wing stick, no throttle) wings we cut back then. I mud face planted that plane over and over the balsa sheet over white foam was very tough and yet light. It was really WAY to fast for my skill level...I knew it and didn't care, I just flew it when no one else was around. Learned to glue that fuse back together really well[>:]
I don't see any problem with this in the beginners section. A new flyer may NEED to be able to do this stuff on his own to be able to afford it. Besides ITS FUN!:)

RE: Hot wire cutting tips?
 

My brother in law is working on the hot wire setup and has a good handle on that.
I have to come up with the Foam, an airfoil template and the setup for holding the foam...

I'm thinking of cutting the template out of oak and coating it with epoxy..
This ones a test so longevity of the template shouldnt be an issue?
Should I go with a flat bottom or symmetrical airfoil?
initial use will be for sscombat using .15 engines ( I've built a gnat with coroplast wings now I want to test the foam wings )
Down the road I want to make glider wings...

Looks like choice of foam is:
HD's pink Owens corning foamular - 2" x 2' x 8'
or
Lowes Blue Polyshield Styrofoam - 2" x 2' 8'

I plan on cutting a 2" x 2' x 1' block off the end of the 8 footer and use that as my wing blank. to cut a roughly 9" x 22" wing half ????

HAs anyone used these materials and is one better than the other?

thanks
steve

RE: Hot wire cutting tips?
 

the SSC guys use the 25lb strength foam and 40 for the open B wings, although you could use whatever you can get. for the SSC airfoil, they are usually using the E-203. use a program like compufoil or profili to generate the templates. This is an awesome video on foam cutting, he makes t look so easy, but it is so easy to mess up a panel, have fun!
http://www.rcgroups.com/forums/showthread.php?t=462759

there is also a combat sub thread on this site, RCU. check it out

RE: Hot wire cutting tips?
 

I think, but not sure, that some of the fumes can be toxic from some types of foam. At the very least have good ventilation.

RE: Hot wire cutting tips?
 

Urethane foam, the blue/pink/green stuff produces toxic fumes make sure you have good ventilation. It is also stronger and sands well - wear a mask!

If you are looking for cheap and cheerful try covering with brown paper and PVA. Strong and easy to repair. Excellent for models up to about 25 and some larger deltas.

I like to cut with color markings on the templates to be sure that I am getting an even cut. I sit down with the foam lightly clamped down and against an end stop. I pull the cutter towards myself. with a small amount of downward pressure. Do not pull hard, let the hot wire cut but do not stop either that gives a ripple.

These are all built with blue urethane foam and brown paper. The Lanc has 4 x 15s and is a veteran of many airshows. It was built By Barry Beech of Mainly Models.

RE: Hot wire cutting tips?
 

Sorry, I was unavoidably detained last night, so I never got to finish this. But I'm all done now.

For starters, I like to have a wooden dowel with a hole through it on each end so that you can "Hold" the wire for better control. Something else worth noting is that cutting a wing by hand is really a two-man job, so call a buddy over.

Now, make your templates. Plywood works, but something smooth like formica will cause less snagging of the wire. More importantly, leave tabs on each end for "Landing" spots.

Once you have the templates cut out, draw a centerline through them, then draw a vertical line at the start, end, and through the widest part (Lines 1,2 and 3). Line "3" is going to become our "Reference Line". (Note, the "reference line will vary with each wing. For this example. I am considering a standard wing

Now, draw another line centered between 1 and 3, and 2 and 3 (They don't have to be exactly centered, eyeballing it is good enough)

Keep splitting the lines in two until your lines are about 3/8" apart (Note, obviously, there will be more lines to the rear of line 3)

Do the same to your second template, but be sure to make the exact same amount of lines.

-

Number the lines top and bottom on both templates (Both sides, because you'll be cutting a right and left wing) And drill two holes that a nail wil fit snuggly into. (Note that in my example, the reference line is now numbered "9", but your numbers may be different)

Take the measurements for "A", "B", "C" and "D"

-

Now, cut your blocks to length and draw a reference line across the top and down both sides. Draw a centerline on each side.

Mark the measurements for "A", "B", "C" and "D" on their respective sides

Place a piece of straight plywood on each of the ABCD lines and hold each one in place with two nails (Drill snug holes in the wood for the nails first)

-

Heat up your Bow and trim off the front and rear of the block

-

Remove the plywood guides and put the templates in place. Be sure they are centered front-to-back and on the centerlines

Lay the block on a flat surface with some books or other weights on top so it won't move. Now, with one man on each side, lay the cutting wire on the landing tabs. Enter the block and start counting the line number (out loud) to each other as you cut so that you are both on the same number at the same time.

When you get to the landing tab at the end stay there for a few seconds! Do not move the wire because the center of the wire will be lagging behind slightly, so you want to both wait until the wire has completely cleared the foam before you move the wire away.

Now you can flip the block over (Leave it in the shuck that you just cut off as a cradle) and cut the other side.

Repeat for wing two, but don't forget to make it for the opposite side!

RE: Hot wire cutting tips?
 

Great thread!

Well the link has already been provided to "A Beginner's Guide to Cutting and Bagging Foam Wings" but you may also be interested in the article I wrote called "Building and Using
an Automatic Foam Core Cutter".

You can find the article on the "Articles/Files" page at www.TailwindGliders.com

Curtis
Montana

RE: Hot wire cutting tips?
 

I was wondering how to cover the for for CHEAP!
Sounds like this may be the answer?
Brown paper, like a brown paper bag? we have sheets at work for wrapping packages. that may work?
What is PVA?

This will be for ssc combat planes running .15 engines.. Trying to get a working plane then try and get some club members inerested in a little combat this year...

Thanks
All

steve

RE: Hot wire cutting tips?
 

For combat planes you don't even need to cover them.

Lay a strip of nylon-reinforced packing tape on top and bottom where the spar would be and go crash it into someone else's Combat plane.

RE: Hot wire cutting tips?
 

we use the colored packaging tape for covering, applied right and it keeps the fuel from getting to the foam

RE: Hot wire cutting tips?
 

Brown wraping paper from a roll. Carpenters wood glue thinned down about 40% with water. This produces a better finish, a stronger wing or fuz and is much easier to repair than parcel tape. However it is more work to apply and needs a fuel proofer to finish off. If you are interested dig around there is a fuller explanation some where on RCU of how to do it.

Or look here [link=http://findarticles.com/p/articles/mi_qa3819/is_199908/ai_n8871174/]CLICKY[/link]

This pile of junk flew again 1/2 an hours work on each airframe.

RE: Hot wire cutting tips?
 

All kinds of good info, thanks guys.

How about the size?

Using an OS .15LA

I'm thinking 2 - 9" X 21" wings joined for a 42" wing With a little dehidral..????? or just make 1 - 42" straight wing???


cut to this shape.

RE: Hot wire cutting tips?
 

for the SSC class, there is a minimum spec on the wings, its 400 sq in minimum. with my coro birds, its about 9" x 54" and a little taper mixed in there most guys use anywhere from 54" to 60" wings for SSC

RE: Hot wire cutting tips?
 

Do you have a part number for the item from Bass Pro?

RE: Hot wire cutting tips?
 

do a search at basspro.com for stainless steal leader
Click on the pics and scroll down

or try this number 38-481-672-02

RE: Hot wire cutting tips?
 

this is probably the best stuff
http://www.skykingrcproducts.com/acc.../renewire.html

RE: Hot wire cutting tips?
 

Would that size be for .15 engines? I'm currently flying a gnat with a 16" x 36" coroplast wing.
I know they also use .25 but we wanted to go slow for our first attempt at combat.
Thanks, I should check the specs for ssc was only thinking of how the plane flys... i want the planes to be ssc legal..

steve

RE: Hot wire cutting tips?
 

hey Steve. the SSC class is the best class to start in, slower pace, cheap engines etc. the SSC planes are about 65 mph ad the open B gets up to close to 100 mph.

the rules for SSC states
.15 or smaller engine with a retail max of $85.00
400 sq in min on the wing area
2 1/2 lb minimum weight
17500 rpm max with a 8-3 prop

with a plane close to the min weight, they can be pretty fast, getting over 3 lbs and they start getting alot slower
the pilots also have to use some energy management, ie not to may loops or climbs. wind will also have an effect on the planes

if you look at the battle axe or avenger type planes, you will see the very long w.s. tall rudder and not muh else, that has become the standard combat design
The group here in CA likes to use semiscale coro warbirds and have had really good luck with them also, but then again, the long wing comes into play
Gnats are fun but they really are not that great of a comat plane, unless everybody has a gnat, then its fair game

its best to start ou and use what is used in that area. that way you can got to other areas and fly the normal stuff. check on the RCCA site for guys that in your area and talk to them, go see an event and have a great time!

RE: Hot wire cutting tips?
 

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/

RE: Hot wire cutting tips?
 

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

RE: Hot wire cutting tips?
 

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

RE: Hot wire cutting tips?
 

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

thus plan B!

RE: Hot wire cutting tips?
 

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.

RE: Hot wire cutting tips?
 

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....:D
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......;)

RE: Hot wire cutting tips?
 

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

RE: Hot wire cutting tips?
 

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!

RE: Hot wire cutting tips?
 

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

RE: Hot wire cutting tips?
 

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....;)

RE: Hot wire cutting tips?
 

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

RE: Hot wire cutting tips?
 

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.

RE: Hot wire cutting tips?
 

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.

RE: Hot wire cutting tips?
 

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" ;):D[>:]

RE: Hot wire cutting tips?
 

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