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cutting wing tube socket in foam - 6/19/2004 1:13 AM   
Buzzard Dave



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From: Tampa, FL, USA
Status: offline 		Hi all, i've done a lot of built up wings (over many years) and are just trying to begin doing foam cores.

what are the tricks, gotcha's, etc when cutting cores especially when it comes to the wing tube sockets?

seems like, after cutting the core, you make a small slit pocket in the wing perpendicular to the socket where it ends. then you put a guide down in that slit and a guide on the root and cut with one end of the bow sticking down in that pocket just outside of the guide.

what's the easiest way to make that pocket? after cutting the socket for the wingtube, what is the best way to brace (with webs) the wing tube in the foam?

(i'm talking about 80 inch WS symetrical airfoil wing BTW).

thanks much.....David S. - Tampa, FL

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RE: cutting wing tube socket in foam - 6/19/2004 2:48 AM   
davidfee



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Status: offline 		I think it's simpler than that. I've never done it personally, but I understand you can just make a loop-shaped hotwire and use a straight edge as a guide. I guess you could also slice the wing core chordwise at the point where the tube would end and then use two templates and a normal hotwire bow. I dunno... never needed to do it so far.

good luck,
-David

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RE: cutting wing tube socket in foam - 6/21/2004 8:48 AM   
iskandar taib


 

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From: Kuala Lumpur| Malaysia, MALAYSIA
Status: offline 		The way CL hollowed out wings are cut is to drop a stiff wire through the core (or more often, the core blank - before you cut the outside shape) after heating the end of the wire with a propane torch. The cutting wire on your bow is fed through the resulting hole, and appropriate "inside hole" templates are used to cut out the middle of the core. Labor intensive. I suppose you could do likewise to cut out foam for the joining tube.

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RE: cutting wing tube socket in foam - 6/24/2004 1:50 AM   
dbarrym



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From: Carlsbad, CA, USA
Status: offline 		There are many ways to do this. Melting out the hole with a heated piece of thick music wire is OK for servo cable channels but too inaccurate for wing tubes.

The "u-shaped" hotwire trick works well on medium sized wings. I use .040 or .062 music wire bent to shape and mounted to a ply plate (through some bakelite insulation blocks) that maintains the wire in proper alignment. I tape/pin a piece of spruce stock to the wing core or top shuck to use as a guide fence to ensure a straight cut. Determining the proper cutting speed and amps (i.e. heat) is crucial, practice on scraps first.

Another method is to make templates, like Iskander mentioned, and cut out just like you would a full core. The only trick here is that you need to make a decent size cutout (2" square or so) at the outboard end for bow clearance. This is how most production cures are cut. This is easiest with large or thick wings.

For thin wings (sailplanes) I use a piece of brass tubing, sharpened on one end (grind/sand to a sharp edge and then file some small triangular "teeth") and carfully align and twist/push through the core. It helps to glue in the root and sub-rib(s) that carry the tubing loads to the skin first, you can usually see the tube as it moves through the core, check every 1/4" or so, from above and in front, to make sure the tube is aligned properly.

As to webs, for a lightly loaded IMAC type model a 1/8" ply full chord width ply root and 1/3 chord sub rib at the end of the wing tube is usually adequate. Make sure that the tube extends 1/4'1/2" past the sub rub - and the aluminum or carbon joiner tube extend at least that far past the sub rib as well.

I have made many wings using these methods, all work great. Practice first.

barry

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RE: cutting wing tube socket in foam - 6/29/2004 8:30 AM   
Mike James



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From: Anchorage, AK, USA
Status: offline 		... And don't forget to account for the dihedral and/or wing taper.


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RC Design and Building - www.nextcraft.com

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RE: cutting wing tube socket in foam - 6/30/2004 6:37 AM   
Camel65



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From: Iuka, MS, USA
Status: offline 		Cut your cores with the dihedral set in reference to the bottom of the shuck. Then make a fixture to hold a shaft about 1/2 dia shaft parallel to your work surface and be able to spin the shaft and slide it at least the distance your tube carrier will be inset into the core. At the end of the rod bore it so you can attach a forstner bit the same dia. of the carrier. A stop to push the root end of the core up aginst helps a lot. Then slide your roatating shaft in the core the proper depth. Go slow and use a vac to pull the foam bits out and make a few in and outs as you travel further in the core to keep from enlarging the hole with cutting fouling the bore. Hope this made sense. If not I'll try to explain any questions that come up.

Regards
Bill

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Bill

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RE: cutting wing tube socket in foam - 6/30/2004 6:26 PM   
Ed Smith


 

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Status: offline 		A simple method. I use a similar procedure for spar slots that do not go all the way to the tip.

80" span, 40" each panel. Lets say a 10" tube in each wing.

So after the cores are cut, cut the panel chordwise 10" from the root

Position templates with the size of hole you want and a saw cut into the hole from the top, on each end of this short piece.

Wirecut down the sawcut into the hole, cut out the hole.

Slip the tube into place. Align the two pieces of panel in the bottom blocks and glue back together.

Job's done, fast, accurate, nice smooth hole.

Ed S

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