foam wing honeycombing  
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All Forums >> RC Airplanes >> Scratch Building, Aircraft Design, 3D/CAD >> foam wing honeycombing
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foam wing honeycombing - 9/4/2002 11:31:46 AM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline 		Here are some pictures of how the honeycombing operation was done on my FAI pattern model. Overall weight reduction is important in these models for vertical performance but particularly keeping the outboard flying surfaces as light as possible strongly benefits snap recovery & roll dampening. The wings still have to be sufficiently strong to take the high G loads & countless hours of practice inflicted on them by pattern pilots. I recall the cell removal weight reduction was roughly 60% of the basic core weight & that seems to be a good strength compromise for this application. The wings are sheeted with contest (4-6 pcf 1/16” balsa). Note the continuous remaining foam ‘spar’ running from root to tip. It serves several purposes: it houses the plug-in aluminum spar/socket system, it acts as a base for the 0.014” x 0.25” vertically orientated carbon fiber spar which is also connected to the socket & it acts as a conduit for the servo lead trough. The criss-cross web pattern yields a good compromise in weight reduction & torsional rigidity. The honeycombing template jigs were made my exporting a dxf cad file to a local sign shop, they convert it to their own toolpath program & a 2d cnc router cut them from 1/16” aluminum. I made sure there was a nice radius on the cell corners & also incorporated the servo cutout position. The templates are permanently attached to a sacrificial set of outer foam shells with spray adhesive. The (mind-numbing) honeycombing operation consists of: insert & align a foam core in the jig assembly, secure it with masking tape here & there, burn a pilot hole into each cell with a soldering iron, set up the assembly vertically using a clamp on the workbench, then using a short section of wire, hot-wire remove each cell.

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foam wing honeycombing - 9/4/2002 11:33:57 AM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline 		the cnc aluminum jig from .dxf cad file

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foam wing honeycombing - 9/4/2002 11:35:07 AM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline 		a close up of the finished wing core with cells removed

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foam wing honeycombing - 9/4/2002 11:37:10 AM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline 		The bench clamp. It helps to keep the core & template assembly fixed & orientated so the cutting operation with the hot wire stays perpendicular to the jig.

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foam wing honeycombing - 9/4/2002 11:43:26 AM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline 		Retract version used at the World champs sometime during the Jurassic period. God, the jpegs are yellowing! I used a different spar system at that time made from 1/8" lite ply. The retract jig was a sub-assembly but it matched the cell layout of the main jig. Gotta love that cad stuff man.

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foam wing honeycombing - 9/4/2002 1:49:46 PM   
majortom-RCU


 

Posts: 1583
Joined: 12/11/2001
From: Merrimack, NH, USA
Status: offline 		I nominate ptxman for modeler of the month!

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       Post #: 6

Yep! - 9/4/2002 2:42:06 PM   
Mike James



Posts: 2465
Joined: 1/19/2002
From: Anchorage, AK, USA
Status: offline 		Excellent, as always, Peter!

Thank you for sharing all your work with us. The photos clearly show what would take a lot of words to describe otherwise.


_____________________________

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RC Design and Building - www.nextcraft.com

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foam wing honeycombing - 9/4/2002 9:48:50 PM   
AV8TOR


 

Posts: 427
Joined: 12/28/2001
From: Mount Vernon, OH, USA
Status: offline 		Ptxman a couple of comments, instead of CNC cutting the aluminum plate consider finding someone to laser cut it. It will be cheaper unless you are doing this yourself. What did you use for hot wire setup?
I have not used this product but take a look at this and let me know what you think.
http://www.centralhobbies.com/kiss/kiss.htm
I have yet to talk with anyone who uses this. The end result looks pretty clean.

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       Post #: 8

foam wing honeycombing - 9/4/2002 10:13:32 PM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline 		[QUOTE]Originally posted by AV8TOR
Ptxman a couple of comments, instead of CNC cutting the aluminum plate consider finding someone to laser cut it. It will be cheaper unless you are doing this yourself. What did you use for hot wire setup?
I have not used this product but take a look at this and let me know what you think.
http://www.centralhobbies.com/kiss/kiss.htm
I have yet to talk with anyone who uses this. The end result looks pretty clean. [/QUOTE]

Been there done that. My experience with laser cutting aluminum is: 1) a slightly inferior surface finish apparently due to the density or metallurgy of aluminum. Steel sheet of the same thickness for example has a better edge finish apparently. I could have used steel but the aluminum was handy. 2) higher costs with laser cutting. This might be a function of the particular laser/cnc shops where I live but my guess is any city has more more cnc router sign shops than laser cutters, maybe that keeps the prices in line, dunno. I know some of the 2d cnc router shops are commonly cutting 1/2" aluminum with carbide bits so they have the capability.

Im aware of the kiss system, seen it, havent used it. From what I can tell its basically some batteries in a box with the voltage optimized to short lengths of cutting wire. I have a lot finer heat control using my variac & need it for wing cutting anyway.

The hotwire 'setup' is basically a short section of foam cutting wire with shallow loops on the end which are attached to simple handles to hold it tension during cutting. I fiddled with mini bows but they arent worth the headache. Feeding the wire in & out of the pilot hole has to be quick in this case simpler=better.

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       Post #: 9

foam wing honeycombing - 9/5/2002 12:04:39 AM   
AV8TOR


 

Posts: 427
Joined: 12/28/2001
From: Mount Vernon, OH, USA
Status: offline 		[QUOTE]
The hotwire 'setup' is basically a short section of foam cutting wire with shallow loops on the end which are attached to simple handles to hold it tension during cutting. I fiddled with mini bows but they aren't worth the headache. Feeding the wire in & out of the pilot hole has to be quick in this case simpler=better. [/QUOTE]

I run a 5-axis router so I know what they are doing. Shops in our area will usually laser cut that cheaper than the cnc.
So you are basically holding it vertical and tracking the template by hand then?

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       Post #: 10

foam wing honeycombing - 9/5/2002 12:32:18 AM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline 		[QUOTE]Originally posted by AV8TOR


I run a 5-axis router so I know what they are doing. Shops in our area will usually laser cut that cheaper than the cnc.
So you are basically holding it vertical and tracking the template by hand then? [/QUOTE]

5-axis? Mmmm - nice. I think I need one of those in my shop . Your laser vs cnc price reference doesnt surpise me & likely is a function of the particular suite of manufacturing shops in your area vs mine. I recall having some wood parts quoted by 2 laser shops some time ago, they were 100% apart.

Yes, I am holding the hot wire section by hand horizontally & traversing around the inside of the honeycomb cells with the core/template assemby clamped in place as shown on the pic. Basically this orientation gives the best feel that the wire is in coincident positions on the templates around the cell periphery. It doesnt take much practice before you can feel the corners equally & the wire is never that far out of position. The handles are basically wood dowels with hooks to hold the wire & complete the electrical circuit. Wire tension is supplied by arms & controlled by brain. Put a football game on in the background, this is boring, tedious work.

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foam wing honeycombing - 9/5/2002 9:05:48 AM   
Giant Scale



Posts: 856
Joined: 6/8/2002
From: Baltimore, MD, USA
Status: offline 		ptxman,
The wings look awesome. I need to core a wing in a similar manner but was not going to make the pattern that intricate. Would a simple triangular pattern work as well? Take a look at the tail section on this plane, I was going to core the wing with a similar pattern. Was it expensive to get the templates made? The wing panel I need to core is about 6ft long, I was going to make the templates out of formica or tempered masonite.

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foam wing honeycombing - 9/5/2002 9:54:17 AM   
Cdallas2



Posts: 547
Joined: 2/7/2002
From: Kamloops, BC,
Status: offline 		Well thanks ptxman - I now finally know what you guys mean by honeycombing your wings.

I just don't see all this work and expense to justify saving a few ounces.

_____________________________

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       Post #: 13

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foam wing honeycombing - 9/5/2002 10:17:39 AM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline 		[QUOTE]Originally posted by Giant Scale
ptxman,
The wings look awesome. I need to core a wing in a similar manner but was not going to make the pattern that intricate. Would a simple triangular pattern work as well? Take a look at the tail section on this plane, I was going to core the wing with a similar pattern. Was it expensive to get the templates made? The wing panel I need to core is about 6ft long, I was going to make the templates out of formica or tempered masonite. [/QUOTE]

I think a triangular pattern would work equally well, lots of pattern planes had this including sharp corners. I played with a lot of different geometries in cad came up with this because it best suited the application from a weight & strength compromise. There is little weight saved by honeycombing accross the ailerons & I like firm flying surfaces so that portion was omitted. I dont fly your big scale stuff, but my instinct would be to make the cells a bit smaller & make more of them. You will get more rigidity & remove about as much material, however, there are more cells to remove. I really think the continous remaining foam spar is a good feature.

My templates cost roughly 200$C (125$U) for 2 wing, 2 stab, 1 rudder (all 1/16" 6061 aluminum) & and matching mdf panel templates used for blocking the foam (materials included). For reference this is a 2m span (78" 1100 in2 nominal area plug-in wing. I supplied the .dxf file. As mentioned before, prices seem to vary quite a bit so shop around.

A wood based template like masonite will be cheaper in terms of material cost but the hotwiring cut quality will not be nearly as good. Formica would be better, metal is the best. I actually tried some laser cut 1/4" ply templates. They worked not bad for about 10 sets of wings & then the wire started to slowly burn little ticks here & there & start the hanging up process. If its just a one-off job for yourself, you may not care, my circumstances were different.

You have to fillet all the cells in cad if you are exporting to a cnc router - the diameter of the bit will take care of that by default. The other thing I thought would work (but got talked out of) was first join both template materials together with spray adhesive, cnc cut both top/bot simultaneously to save some $ & then just carefully seperate them with acetone. The particular shop I used advised against it but I still think it would have worked.

I should also mention there is a big strength difference by not having continuous sheeting over honeycombed panels, but thats a whole other discussion. Good luck!

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       Post #: 14