Cutting a 40+ inch foam combat wing

Cutting a 40+ inch foam combat wing
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Cutting a 40+ inch foam combat wing - 6/7/2006 3:35:24 AM

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I've got everything I need to make a 48" bow, but I got a few questions you more experienced guys may be able to answer. First off, my setup is going to be simple. I'm using a car charger and a leviton dimmer for the power source. Since the distance is 48", will I be looking at potential problem heating the center or should it heat evenly? Any suggestion for wire diameter? Any stumbling blocks I should look out for?

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RE: Cutting a 40+ inch foam combat wing - 6/7/2006 3:51:23 AM

vicman

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Get an old train transformer you will have better luck. Also I got some real good wire if you need some.

Shoot if you need to borry my power supply I could swing a shipping arrangement.

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RE: Cutting a 40+ inch foam combat wing - 6/7/2006 4:30:53 AM

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The wire gets the same temp over it's whole length. 48 inches is really a long cut, you might want to cut it in two parts, it will make no difference in the strength of the wing. I use fishing leader 80~120 pound test, it's .031 diameter. I use about 20volts on a 30 inch cut. Formica make good cheap templates, make them as smooth as you can.

< Message edited by soarrich -- 6/7/2006 4:31:34 AM >

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RE: Cutting a 40+ inch foam combat wing - 6/7/2006 4:52:00 AM

Andrew

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quote:

ORIGINAL: soarrich

The wire gets the same temp over it's whole length. 48 inches is really a long cut, you might want to cut it in two parts, it will make no difference in the strength of the wing. <snip> Formica make good cheap templates, make them as smooth as you can.

I agree with Rich -- wire temp is constant across the length, but 40+ inches can be a long cut and the foam will suck the heat out of the wire. Cutting two shorter panels would probably be better and you don't have to worry as much about the wire bowing in the middle.

I use .018" 502 stainless steel wire from McMaster-Carr. I also use formica for templates. I glue the rib outline to the formica with a glue stick, rough cut with a fine tooth bandsaw, finish shaping with a file, then polish with fine sandpaper. Like Rich noted, you want them to be absolutely smooth so the wire does not catch or drag.

The airfoil plotting program, Profili, has an option to print cutting templates with station numbers -- or you can just number by hand.

I use a PC power supply with a homemade PWM circuit for heat control.

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RE: Cutting a 40+ inch foam combat wing - 6/7/2006 7:07:51 AM

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I'll take you through the downest and dirtiest set up for cutting from a pivot point, I just don't have the time now. I'll put together a photo essay, HOT WIRE 101. The longest cut I ever try to make is 24", ditto on formica templates, and I use sheetrock screws to hold the template to the end of the foam blank. The other key ingredient is the $7 dimmer, but I use good old 115 VAC to feed the dimmer, been doin' it this way for 20 years, never felt a tingle. Cutting voltage is about half of "E" applied. I use .020 stainless single strand aircraft safety nut wire, and a low heat to not melt out the foam as the cut is in progress. Heat control is key. Also get a fan to blow the fumes out the garage.

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RE: Cutting a 40+ inch foam combat wing - 6/7/2006 1:38:26 PM

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Whoa, I have to chip in. I can't go along with using house current!!! Some people work in their garage or basement on concrete - bad, bad combination.

As for the rest, I've cut a lot of foam since the mid 70s. Nichrome wire, fishing leaders, .018 CL lines - they all work if the temperature is OK. Slow is good for me. The biggest span I could cut with regular success was 36-inches. Any more than that you need center bracing anyway. Formica templates have worked out well.

I used to get horrible headaches cutting white foam in my basement. Was told that the gas used to form the "bubbles" was toxic. Moved to the garage with a fan blowing across the work surface. Problem solved.

Lately we've been using blue or pink foam for combat wings and fuselages. Like, way better dude! Also more expensive but the denser/firmer foam requires less bracing and is easier to finish/tape and keep straight. Good luck. Its hard to beat foam for any combat application - IMHO.

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RE: Cutting a 40+ inch foam combat wing - 6/7/2006 2:19:59 PM

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You know, I jumped on this idea without even locating any foam! Raymond, where do you find the blue/pink stuff?

Well, if you keep the insulation on the wire all the way up to the bow, 110 should be safe enough. I don't plan on touching the wire anyway! BUT, anytime I see a wide span bow, it always seems to be low voltage, high current. I want the wide bow for other purposes too. The bow design I'm using is an H. I'm putting a turnbuckle and spring on the top of the H and cutting wire on the bottom. That should solve the droop problem, right? I've got a pretty heavy spring (26.5lb max) and am a little concerned with stretching the wire.

< Message edited by ptulmer -- 6/7/2006 2:20:41 PM >

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RE: Cutting a 40+ inch foam combat wing - 6/7/2006 3:59:22 PM

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We found our blue foam in the yellow pages under insulation.

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RE: Cutting a 40+ inch foam combat wing - 6/7/2006 4:51:36 PM

Andrew

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quote:

ORIGINAL: combatpigg

<snip>.........but I use good old 115 VAC to feed the dimmer, been doin' it this way for 20 years, never felt a tingle.

Hey, I've seen you electrician guys working -- unless it's a 4KV line, you all act like it's not even hot!!!

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RE: Cutting a 40+ inch foam combat wing - 6/7/2006 5:15:47 PM

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funny how there are plenty of warnings against 120ac, but so few folks mention there is a 3' smokin hot length of wire that can blister ya right up. Comes right to it, I've been hit with 120 & 277 plenty of times (retrofited flourecent balasts while lights on in hi-rises), I hate a blistered burn more than a 120 jolt... but I went thu 3-4 lineman pliers a year from 277 arc divots.

I dont see how AC using a heavyguage, insulated wire right up to the filiment would be any more dangerous than having 48 of hot wire in the garage anyway. If you are the kind of guy that can swap out a lightswitch or outlet while hot, go for it.

Warning: The part that will burn you, is hazardous to touch because of electrical concerns

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RE: Cutting a 40+ inch foam combat wing - 6/7/2006 6:15:32 PM

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quote:

ORIGINAL: ptulmer
where do you find the blue/pink stuff?

The blue is Dow, the pink is Corning, HomeDepot and Lowes have it, but it's really not what you want. The pink is called Formula 150 or 250, the numbers mean 15 pound and 25 pound per square inch crush strength, the Dow is similar, the are used on vertical walls for insulation. What you want is Dow HiLoad 60 it's 60 pounds per square inch crush strength, it's used under concrete floors in contruction, or get surfboard foam.

quote:

ORIGINAL: ptulmer
The bow design I'm using is an H. I'm putting a turnbuckle and spring on the top of the H and cutting wire on the bottom. That should solve the droop problem, right? I've got a pretty heavy spring (26.5lb max) and am a little concerned with stretching the wire.

You'll still get bow in the wire, it's not a droop problem, it's a drag problem. The way you'll be cutting the hot wire touches the foam melting it, but it does touch, you'll pulling it through the semi-solid foam, the wire will drag. The way it's done to get really good cores is melting the foam with radiate heat from the wire, no drag, the wire never touches the foam, but you need a couple thousand dollars worth of equipment to do it this way.

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RE: Cutting a 40+ inch foam combat wing - 6/8/2006 2:31:55 AM

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Patrick, for 1/2A combat, I think you want to use white foam, it is lighter than the colored foams. It is also less toxic to work with. If you can find a manufacturer who deals with virgin polystyrene, that's going to be the lightest, otherwise, just go to Home Depot. Remember that weight works against you in the air, and also in a crash.

If you cut with your shoes on, and promise not to handle the neutral and dimmed hot [60 volts, maybe] line at the same time, then you have my permission to use line voltage.

Plus if you get hungry while you're working, just slide a hot dog onto the line.

< Message edited by combatpigg -- 6/8/2006 2:34:07 AM >

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RE: Cutting a 40+ inch foam combat wing - 6/8/2006 3:05:25 AM

vicman

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Offer Stands and I have a bow. I even have a nifty little plumb line cutter for FFF.

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RE: Cutting a 40+ inch foam combat wing - 6/8/2006 3:55:06 AM

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Ok, I just whipped out a wing panel, I measured the cutting voltage and it was 7.8 VAC. The voltage in the barn is 120 VAC. These photos show how to cut a tapered panel from an adjustable pivot point. The pivot is a # 10 screw, a fender washer and a couple of nuts mounted to a plate. The C clamp allows me to move the pivot point back and forth on the table, depending on how much taper the wing panel is going to have. The pivot gizmo allows me to adjust the height of the wire. tonight, I cut a symetric airfoil and the C/L of the foam blank was 15/16" from the table top, so that is where I set the pivot, 15/16". First I had to cut out a foam "blank". My blank jig is made for doing both LE and TE cuts without moving the sheet. For mass production, send 2 sheets through at a time, but for 1/2A, it doesn't have to be fancy. The more jigged up you are, the more precise your end results, though. The heat should be set so it takes about 5 seconds or more just to do a cross cut through the 1 7/8" thick [they call it 2"] foam. The heat for tracing the template to do the airfoil work was low, but not so low that you have to saw your way through. Ideally there should be wispy hairs on the finished product if the heat was right. This method only needs 1 template, but some guys use an outboard template too. There needs to be 4 feet of wire or more in the circuit for the dimmer to work right with this voltage, so the cutting bow has heat going around in a loop, with a hunk of maple as an insulator between the extreme ends of the wire, and some kind of springy spring to take up the slack

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RE: Cutting a 40+ inch foam combat wing - 6/8/2006 3:57:01 AM

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So far I've seen bows up to 72" run on DC, simplicity will probably win out and I'll try line voltage first. It'll be easy enough to keep it safe on a permanant structure. After you get hit with 360 volts at 20 hertz, not much else hurts anyway.

An electrician like CP would have a field day on my frame. Stick your arm through it verrry carefully on a good, hot, sweaty summer day! Ringing current is ~100 volts at 20 hertz. Cross a couple of them and you bounce around a little and look something like this.---->

Vic, let's see how this works. If I want DC, it might be worth the shipping $ to take a look at yours. PM'd ya!

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RE: Cutting a 40+ inch foam combat wing - 6/8/2006 4:18:53 AM