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Help! Need To Hot Cut Large Foam Installation For 12 Feet Wings!

#1
Okay, here is my build

Making 12 feet First Main wing and my dad found 2/4 thick 4 feet long by 2 feet wide foam board installation; and it is the stuff used for heat cutting, so I just watched the video:


Not finding in the search on creating super major large wings, first main wing will be 12 feet long total; 2 6 feet wings combined making 12 feet, then secondary main wing will just be 6 feet.

I've found the Brushed ESC

We live on a cow farm and wondering if electric fence wire is the same wire used to cut the foam and we have a Ace Hardware Store in town to get the PVC pipe, and what battery do I need to work the ESC to cut the foam, also got the servo tester as well.
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#2
Firstly it would be better to make the wings in smaller sections that you later glue together. The bow drag on such a large bow would give poor results unless you can do it extremely slowly and with a very steady hand.

As for a wire for the bow I would use a very thin music wire though in the past I have used the wire from an old toaster which I unwound from the heating elements. It worked well at 12V over around a metre but with such a large bow you might require higher voltage, (24+).

Just my thoughts!

Have fun!
 

willsonman

Builder Extraordinare
Mentor
#5
The number one factor in hot wire cutting is the sag that is induced on the wire from heating it. Metal expands as it is heated so this is natural. A spring on one end can help but if there is too much tension the wire will constantly snap due to weakening of the wire as it heats up. For large wings, I never do sections more than 18". This allows for segmented customization of servo placement without having to figure out how to manipulate an entire wing panel for spar and wire channel placement. For my Bugatti, I did single cuts for each wing and it was a big challenge with the taper from the root to the tip. The single cut ensured that I had better transition from the differing root and tip airfoils without having to extrapolate a mid-rib former for cutting. 18" is a good size for handling and the larger panels get complicated as the edges of the wire will cut faster than the middle. The amount of foam the wire is melting is called the "kerf" and it will be greater at the edges of the cut than the center... requiring more sanding to eliminate humps in your panels. There is a lot more to hot wire cut wings than just cutting them with a bow. ;)
 
#6
The number one factor in hot wire cutting is the sag that is induced on the wire from heating it. Metal expands as it is heated so this is natural. A spring on one end can help but if there is too much tension the wire will constantly snap due to weakening of the wire as it heats up. For large wings, I never do sections more than 18". This allows for segmented customization of servo placement without having to figure out how to manipulate an entire wing panel for spar and wire channel placement. For my Bugatti, I did single cuts for each wing and it was a big challenge with the taper from the root to the tip. The single cut ensured that I had better transition from the differing root and tip airfoils without having to extrapolate a mid-rib former for cutting. 18" is a good size for handling and the larger panels get complicated as the edges of the wire will cut faster than the middle. The amount of foam the wire is melting is called the "kerf" and it will be greater at the edges of the cut than the center... requiring more sanding to eliminate humps in your panels. There is a lot more to hot wire cut wings than just cutting them with a bow. ;)
thanks, was hoping those who know about this would find the post, excellent, just what I was wondering about.
 

PsyBorg

Fly Angry
Mentor
#7
I believe @Rockboy also documented his setup and process for hotvwire cutting wings in the Monster FW 42 build thread if you wanna look thru that for more visually helpful information.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#8
for tapered wings i use a pivot point cutting setup and some 90lb fishing steel. Theoratically with a pivot point setup you can just keep pulling out the line and do as big of a wing as the space you have to backup. But in practice, as willsonman says, there can be a lot sag. The biggest thing i have cut yet is my 90" wing, that was about 2x 40" wing halves. If you look at the picture of my friend cutting out a different wing you can see the big wood dowel i have for a handle. That combined with the 90 lb test line means i can PULL on that wire. And you need to. Like really lean into it. The more foam the more friction/slow down/drag its going to cause as it melts thru the wire. So doing a 72" cut...man i dont know if thats even possible, at least to get a nice consistent airfoil. Maybe if you oversized your templates with the expectation that you are going to sand it down close to the real shape....

Not saying you shouldnt try it, but like has been mentioned, maybe save yourself some work and break up the shape.

Me cutting my 90" cores:
http://instagr.am/p/BSfIlUzhZso/ http://instagr.am/p/BShmNPkhj5g/
1537217665319.png
 
#9
for tapered wings i use a pivot point cutting setup and some 90lb fishing steel. Theoratically with a pivot point setup you can just keep pulling out the line and do as big of a wing as the space you have to backup. But in practice, as willsonman says, there can be a lot sag. The biggest thing i have cut yet is my 90" wing, that was about 2x 40" wing halves. If you look at the picture of my friend cutting out a different wing you can see the big wood dowel i have for a handle. That combined with the 90 lb test line means i can PULL on that wire. And you need to. Like really lean into it. The more foam the more friction/slow down/drag its going to cause as it melts thru the wire. So doing a 72" cut...man i dont know if thats even possible, at least to get a nice consistent airfoil. Maybe if you oversized your templates with the expectation that you are going to sand it down close to the real shape....

Not saying you shouldnt try it, but like has been mentioned, maybe save yourself some work and break up the shape.

Me cutting my 90" cores:
http://instagr.am/p/BSfIlUzhZso/ http://instagr.am/p/BShmNPkhj5g/
View attachment 114953
awesome, oh for your image on your profile, need to add some hair and shades.