Hotwire Template Tips

by apnewton | January 16, 2016 | (13) Posted in Tips

Are you ready to advance beyond folded foamboard wings?

Hotwire cutting is the next step for many builders, and it's not as difficult as it may seem. I find it quicker and easier than folding foamboard. It's also much more accurate, and cheaper if you don't have access to Adams foamboard.

You don't need a fancy power supply, I use a 3S or 4S Lipo depending on how wide my wing is. You don't need fancy wire either, I use stainless steel fishing wire, 40kg breaking strain, and a simple pine wooden frame.

The trickiest part is making the cutting templates. This article explains a quick, cheap and easy method using metal window flashing. It's thin aluminium, readily available from hardware stores, and can be simply cut with scissors.

1. Choose an airfoil

Do an internet search for the airfoil you want and copy the image onto your computer. Good airfoils to look at are:

Clark Y - good all round airfoil for powered planes and slope soarers

RG15 - thin and semi symmetrical for gliders. The Clark Y of the glider world.

Sipkill - has some reflex in the rear section, specially designed for flying wings 

2. Print it at the right scale for your wing.

I use the scale option in my printer window and adjust the value until the print comes out at the right size.

3. Glue the airfoil print to the template material

Spray adhesive works well here

 4. Cut out the airfoil with scissors

Do Not use your partner's prized sewing scissors! Cheaper scissors will do the job just fine.

5. Poke holes for the holding pins

I use 5 large pins to hold the templates in place.

And there you have a cheap, accurate and durable temlpate, which will let you cut beautiful perfect airfoils out of any sort of foam. I use yellow XPS insulation foam. Blue or pink insulation foam is the same stuff.

 

Here are instructional videos covering template making, hotwire bow and power setup and an arty closeup video of the process.

 

 

 

Here are the maiden flights of two planes built using hotwire cut wings

Good luck and I encourage you to give hotwire cutting a try. It's very rewarding and easier than it looks.

More info here

anewton.net

Newton Airrlines blog

COMMENTS

circle&stripe on January 17, 2016
Thank you for your article, very nice. Lots of great ideas for the hotwire beginner as I hope to be soon. Living in Florida quickly kills all my DTFB planes. I especially liked the stainless wire & aluminum former suggestions. 5 Stars
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apnewton on January 17, 2016
I find using a Lipo for power makes it safe and portable too. I have a plan to take my rig to the flying field and do demos from my car boot. Good luck
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bird2jump on January 17, 2016
What do use for your fuselage, elevator and rudder? Also foam or DTFB? Or another material like Balsa? Great work on the foam wings. How is the weight comparable to DTFB and Balsa wood wings?
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apnewton on January 17, 2016
Depron mostly. But I have also used XPS foam and balsa for ele and rud. There is no DTFB equivalent in Australia so I cant compare the weight.
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apnewton on January 17, 2016
...actually compared to my tape-covered depron wings, the hot wire foam wings are a little lighter but stiffer.
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HilldaFlyer on January 18, 2016
As always - great article! 5S
This I'm going to try - the aluminum. So far I've been fixated on formica - since I have it and a scroll saw.
Also, a question if you don't mind. Have you tried to make a tapered wing? I've taken a stab at it and it is tricky getting the short tip chord not to melt while cutting the longer cord of the root. Any tips?
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apnewton on January 18, 2016
Thanks Hildaflyer. I have tried a little bit of taper and washout on a flying wing. It is more difficult and at this stage I cannot say I have mastered it. My solution was to avoid large tapers.
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Kytka on January 19, 2016
In principle, there are two hints for tapered wings:
1) use as low teperature of the wire as possible (this applies also to symetric wing, but it is even more important here) -- you still do not need a fancy power supply, just warry the distance between alligator clips (shorter the distance, higher the temperature).
2) cut in two people while using the markers (one is reporting the markers and the other one tries to follow the best he/she can). This did not work for me as well as I liked (it is rather hard to have the constant speed of cutting on both ends, which results in a bit wavy surface), so in the end, I made a gravity wire cutter, which really solved the problem.

Anyway, thanks apnewton for the aluminium tip, I will test it. So far, I always used a plywood, since it is not conducting well (and therefore not cooling the wire at the template contact), but a thin aluminium sheet seems reasonable, as its thermal capacity is low. And it would save a lot of hassle with sanding the plywood to have a really smooth wire movement.
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Kytka on January 19, 2016
Oh - one more thing - it works better to cut one side of the wing at a time (cut one side, flip the wing and cut the other side), at least for me. I even used to make two templates - one for the top and one for the bottom part of the airfoil. But this is not crucial.
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apnewton on January 19, 2016
Excellent information, thanks. I have tried upper and lower templates but prefer the single one.
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Flyingninja on January 18, 2016
Wow! Thanks so much for all this info! I was just thinking about hot wire foam cutting yesterday!


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apnewton on January 19, 2016
Glad you like it, worth a try.
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rick_harriss on January 19, 2016
Good ideas on how to cut foam for wing spars
https://www.youtube.com/watch?v=9y-qBoAzX3E

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efbe on January 19, 2016
Here a link to an "automated foam cutter"
http://www.rcsoaring.com/rcsd/RCSD-2008-11.pdf
I build it once an it worked wel, after some experimenting.
efbe
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flying panda on January 19, 2016
This is really helpful. Thanks
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WConway216 on January 20, 2016
Great article! I loved how easy it looked, but it's time to try it for myself. How do you line up the templates on either side of the foam? Is it just guess work, or is there a technique?

William
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apnewton on January 21, 2016
I just eyeball it mostly but you can place alignment marks on each end for the leading and trailing edges. Just measure up from the bottom of foam. This is how you can accurately design in some washout or twist.
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Neskair on January 21, 2016
Great Article! Nice timing on this. I was just about to try hot wire foam cutting. Thanks!

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apnewton on January 21, 2016
Go to it. Very rewarding.
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QuadReaktor on January 21, 2016
Build my own wing with the method ive seen in Davids YT-Video https://www.youtube.com/watch?v=R0ZCnR_g6ZU
Here are my Pictures:
http://www.kopterforum.de/gallery/album/1947-delta-wing-bau-schritt-f%C3%BCr-schritt/
http://www.kopterforum.de/gallery/album/1947-delta-wing-bau-schritt-f%C3%BCr-schritt/?st=50

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Jon L on January 21, 2016
I use a 12 volt battery charger with the stainless steel fishing wire.
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Hotwire Template Tips