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Hot wiring wing cores


spitzy

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Dag blamit!

 

I had too much wire sag and or went too fast when turning the bottom aft corner of template "A" and "B". The wing core looked great right next to the template but I lost at least a 1/4" off the lower aft portion of the wing core moving towards the center.

 

I was afraid of that happening and it did.

 

Suggestions?

 

I wonder if I need to modify the hot wire saw some how using a spring to keep the wire tight...

 

Anyone else experience this?

 

All I can figure is to go REALLY slow around that bend.

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The usual suspects are:

(1) Wire is too thin. I used 0.041 Iconel.

(2) Wire is too loose. It's amazing how tight you can get it after the wire is hot. Especially with a screwdriver inserted into a hole at the base of the pipe.

(3) Wire's not hot enough. It should produce the angel hair. Most people set the wire heat by dragging a small piece of foam over the wire. Remember that a full length wing core will cool the wire alot more than the test piece. Cut hotter.

(4) Slow down the pace. You should only be moving an inch or so every 5 seconds.

(5) And yes, go slower around corners, fishtails, and pause points.

 

My hotwiring tips are here.

 

You can salvage the cores by cutting them in half chord-wise fore to aft. Insert a quarter inch sheet of blue wing foam (hotwired), gluing the upper and lower cores to the sheet with 3M spray adhesive, then hotwiring the cores again.

Wayne Hicks

Cozy IV Plans #678

http://www.ez.org/pages/waynehicks

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In regards to saving the wing core:

 

1) Is it OK to glue foam where it's missing even if it is a perfect match.

 

2) I thought the best way to get a very close fitting piece of foam to "micro" on the trailing bottom edge was to nail the bottom contour checking template to the bottom piece scrap foam from my initial cut (this bottom piece is "the negative" of the resulting wing core). When I cut along the bottom contour template, I will shave a chunc of foam out that should perfectly match the bottom of my faulty wing core...

 

3) Would microing this piece in there reduce the strength? Doesn't seem like a problem because we are glueing piece of the wing together in ways that would be more likely to reduce the strength of the wing. Also per the Rutan video, the micro bond is stronger than the foam anyway.

 

4) Would microing in this piece screw up the trim of the plane by adding weight? Probably there is more error when you lay up the wings than this little bit of micro. Probably the density of foam and micro is very nearly the same anyway.

 

5) Would this interfere with the hing points some how?

 

I'm using .032 SS safety wire per Rutan. Were can I get the iconal stuff?? I'm also going to experiment with a spring system. In case the wire stretches during the cutting process or incase the pipes rotate thus reducing wire tension.

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(1) In regards to saving the wing core, is it OK to glue foam where it's missing even if it is a perfect match.

 

-----> Yes, you can do that. If you micro on a new piece, then you'll have to shape it by hand. The hotwire won't go through the cured micro.

 

2) When I cut along the bottom contour template, I will shave a chunc of foam out that should perfectly match the bottom of my faulty wing core...

 

----> Yes, that's the general idea.

 

3) Would microing this piece in there reduce the strength?

 

----> No, it will not reduce the strength. The micro bond is always stronger than the foam itself.

 

4) Would microing in this piece screw up the trim of the plane by adding weight?

 

----> It does add weight, but so does eating a biggie burger instead of a junior burger. :) Your call, is it better to add a few ounces of micro and fix your cores, or do you prefer to pay $$ and wait a week or two for more foam?

 

5) Would this interfere with the hing points some how?

 

----> Nope. I forgot which wing we were discussing -- canard or mains. But if canard, you cut through the micro anyway when installing the clark foam for the elevator hinge attach points. If mains, the aileron hinge areas are glass to glass. No foam or micro will be left in those areas.

 

I'm using .032 SS safety wire per Rutan. Were can I get the iconal stuff??

 

----> The "Iconel" isn't as important and just having a strong wire that can be pulled alot. Your 0.032 should work fine. Just tighten it more after it gets hot. I chose Iconel because that's what the saw had on it when I borrowed it! :o

 

I'm also going to experiment with a spring system.

 

-----> I know people of high esteem have used the spring system. I had no problems with just tightening the pipe. The only times I broke wire were the time I forgot to detension the wire before turning off the power.

Wayne Hicks

Cozy IV Plans #678

http://www.ez.org/pages/waynehicks

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  • 9 months later...

I've had wire break failure where the wire rubbs on the template, a tip from another forum was to slide 2 sewing machine thimbles onto the wire, the thimbles ride on the template, I'm anxious to try that method next foam cut session.

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a tip from another forum was to slide 2 sewing machine thimbles onto the wire...

Great tip!

I'm just getting ready to cut cores and will give this a shot! I would think that would also prevent any hang-ups that may have occurred due to a rough spot on the template. Also, I believe you would have to touch up the cutouts for the spar caps and such due to a rounding effect (similar to a router.)

T Mann - Loooong-EZ/20B Infinity R/G Chpts 18

Velocity/RG N951TM

Mann's Airplane Factory

We add rocket's to everything!

4, 5, 6, 7, 8. 9, 10, 14, 19, 20 Done

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TMann, If the thimble trick works please post the tip in a more generally read category. This thread and category is very specific to a small segment of readers I think? It'll be a long while before I'm cutting foam again to acid test the method. Thanks.

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Yeah.....I'm going to give this a shot. I would point out that I think they meant 'bobbins' not thimbles. ( they are the tiny spools used in the machine.)

T Mann - Loooong-EZ/20B Infinity R/G Chpts 18

Velocity/RG N951TM

Mann's Airplane Factory

We add rocket's to everything!

4, 5, 6, 7, 8. 9, 10, 14, 19, 20 Done

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TMann, If the thimble trick works please post the tip in a more generally read category. This thread and category is very specific to a small segment of readers I think?

I moved the thread here because it is of broader interest than only Chapter 10 of the Cozy Mark IV.

 

However, realize that using the search engine here would have found the thread for anyone searching on the right keywords.

Jon Matcho :busy:
Builder & Canard Zone Admin
Now:  Rebuilding Quickie Tri-Q200 N479E
Next:  Resume building a Cozy Mark IV

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I ended up giving up hot wiring my wings. Mostly because I coundn't find a dedicated partner to do it. I purchased my cores from Feather Lite. They did a fantastic job. I also got a chance to visit thier shop up in Ukia. In case you didn't know, they used to work for Burt Rutan.

 

Anyway, their set up uses a very thick wire under a great deal of tension. If I was going to do it again I would purchase my cores from Feather Lite. If I didn't have the cash I would use a thick wire, and build a more agressive tool to tension the wire.

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It seems like we are making a wing out of a canardhill here.

 

While there is no problem purchasing the cores,(which I highly recommend), hot wiring is quite simple, and quite rewarding. The thimble (bobbin) thechnique seems great, however with that little chunk of metal there, it will be difficult to accurately tell the wire position on the template. Positional relationships are important, and critical on corners, such as spar cutouts. Additionally, the inner flange of the bobbin must ride between the template and the foam tending to either crush the foam there, inadvertently ride high or move the template away from the foam. Two objects cannot occupy the same space at the same time (yet).

 

It seems as if, with the exception of no-one being available to handle the other side of the saw (On my dragonfly, I used my 11 yr old son), the problem you(s) are having is with the selection of the template material, and the finish on the edges.

 

Whether it be masonite, metal or even formica, the edges must be smooth and polished with no nicks. If the edges are not smooth or benicked you will have problems.

 

If you are going into production, by all means use a thick wire as wear does have it's say, however with the relatively small amount of hot sawing you will do on your wings and canard, it is really unnecessary.

 

Get to know the process. It is not as daunting as it seems. Thousands upon thousands of wings, etc have been made successfully by it's technique.

 

For my dragonfly, I used thick safety wire. I made little handles (1"dowells center drilled), which I placed on the wire and orentated them just outboard of the templates during the cutting. I suspended the saw from a counterweighted pulley affair from the ceiling to make it almost weithtless and guided the cut using these little handles.

 

It's fun and when you see the shaped chunk of foam you produced, with so little effort, it gives you a real shot in the wing.

I Canardly contain myself!

Rich :D

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Use the INCONEL 600 HOT WIRE from ACS. When placed next to a hotwire tool that uses anything else, you'll see it sag a lot. That requires you to tighten the wire but if you forget to loosen it at the time of shutoff, it will break as it cools and shortens.

 

My hotwire tool uses a couple pieces of aluminum angle with a small section 1.5" of copper pipe with a bolt through all to wrap the wire around before terminating at an eye bolt.

 

The angle pivots on a single bolt axis where it joins the frame and extends a good 12 inches above the tool. Another bolt with a 1.5" copper pipe spacer is at the top. I then use a couple of bungee cords to maintain the tension.

post-2251-141090155889_thumb.jpg

T Mann - Loooong-EZ/20B Infinity R/G Chpts 18

Velocity/RG N951TM

Mann's Airplane Factory

We add rocket's to everything!

4, 5, 6, 7, 8. 9, 10, 14, 19, 20 Done

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Spitzy,

 

So, I'm curious, does Featherlite hand cut their cores? I suppose if you had hand cut as many as they have you would be pretty good at it.

 

I was having trouble finding a dedicated partner to cut my wings as well so I took the road less travelled. I just taught my computer to do it all:D That is, of course, a bit easier said than done but it works now:banana:

 

I've tried a number of different types of wire and tensioning systems. I've found that the .032" ss called for in the plans is very strong. You can tighten the heck out of it. I don't think I ever broke it. Still, it doesn't matter how tight the wire is, if you have the wire too cool and/or go too fast, the wire will lag. The only way to prevent this is to either have a wire under infinite tension or to precisely control both the speed and heat. Even then it can be challenging to get just the right speed/heat combination when when you have a large difference in wire speeds between the root and tip such as on the winglets. It can certainly be done adequately since there are so many of these airplanes flying but it takes some practice. Unfortunately, with the price of foam and shipping lately, practice is expensive, but it is even more expensive not to get enough of it.:irked:

 

BTW, the bow I use is very similar to the one pictured above but made of different materials. It works great! I haven't broken a wire due to overtension in a long time and it is fully automatic. It doesn't make much sense to have an automatic wing cutting machine if you still have to mess with wire tension and heat settings:)

EUREKA CNC

Eureka%20small.gif

Extreme Precision CNC Hotwire Cutting

Perfection To The Core!

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