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Old Sep 01, 2012, 05:25 PM
Keep it Simple Stupid
razortoe's Avatar
United States, NC, Raleigh
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Quote:
Originally Posted by AvB View Post
Pdawg, Troy would be the guy to advise, but from watching his video I think you'd pour then stand the mould with the tip down, and let it fill to the root.
With such a short span, this might work. If i understand correctly though, unless you smear it around all inside surfaces, it won't adhear well to the wing skins. I also remember reading earlier in this thread that, letting it expand out from a puddle doesnt work so well. But please feel free to give it a try and proove me wrong.
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Old Sep 01, 2012, 05:36 PM
AvB
Wind, hill, ... I'm keen ...
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Actually I think that's probably correct. With small panels you shouldn't have any problem doing it within the working time. Smearing it quickly while it's runny means you get good bonding to the surface all over, and the greatest amount of expansion. If you can do that and join them quickly as I did you should get a great result.
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Old Sep 01, 2012, 08:27 PM
I hate propellors
emufingers's Avatar
Australia, SA, Normanville
Joined May 2009
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Good to see the foam experiments.
There are plastic self mixing applicators available, but I haven’t been able to get a price. If they were reasonably cheap it would be possible to inject the mix into the closed mould and let it free rise against gravity to the open end of the mould.
There are lots of different foams. Here are some interesting ones. They are all about $25-35 per litre. If the RF100 is not too dense to produce a lightweight wing its hard skin properties would make it very interesting.
Ecofoam MF710 (free rise density of 71 kg/m3) is a two part polyurethane system that comprises of a polyol and isocyanate component. When mixed in their correct proportions produce fine-celled foam . This product is water and HFC blown. The system is designed for use in moulding applications where good skin is required. The foam can be used for moulding components such as imitation wood, computer cabinets, shoe heels as well as for moulding fishing lures. The product can be manually drill mixed (@ a minimum speed 2000 rpm) or processed through a polyurethane foam dispensing equipment.
RFOAM35 is a rigid foam used in applications requiring either thermal insulation or good boyancy properties. Commonly used as void fill in boats, surf skis and moulded fibreglass building panels. Available in 2kg, 10kg & 50kg. Rise density of 35kg/m³
RFOAM100 Rigid Foam 2kg
96kg/m³ - Rigid foam designed for self skinned or structural components. Apart from the hard skin, the final mouldings have high softening temperature combined with high compressive and flexural strengths. Available in 2kg, 10kg & 50kg.
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Old Sep 01, 2012, 09:28 PM
AvB
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Need to check out the other foams. Working time is important .. the guy I spoke to said that the higher density foams have shorter working times than the GP330. The GP330 was also available in small quantities ... I think it was $22 for 2 x 500mL tins of polyol and iso. But I hope we can find something with a longer working time.
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Old Sep 01, 2012, 10:02 PM
I hate propellors
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The technical sheets on these foams are availabkle on the AMC supplies site.
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Old Sep 02, 2012, 05:04 AM
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Slovenia, Kamnik
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Hi guys!
I also make PU filled wings and tails for stormchaser...
I use 200kg/m foam its realy hard!,i joining the molds with wet seam and layups,i think thats importat you have a realy good wettet layups with epoxy that you want a joint it provide good PU and layup bond.I also make LE edge close with carbon stips so the LE edge is no delaminating and makes LE edge bullet proof
The PU foam cost me 35€ for 2kg-for a wing i use 340g so its cheap..


Simon
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Old Sep 02, 2012, 05:57 AM
AvB
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Simon, it was you describing the use of the PU in your Stormchaser that motivated me to try PU!
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Old Sep 02, 2012, 07:59 AM
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Cleveland Cuyahoga, Ohio, United States
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Good foam info here;

http://www.shopmaninc.com/foam.html
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Old Sep 02, 2012, 09:26 AM
I hate propellors
emufingers's Avatar
Australia, SA, Normanville
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If the foam is suitable this system is ideal. Two part foam with a mixer dispenser gun. A small kit that would do about 5 two meter wings for under $40 inlcuding the gun.

Check out the videos to see the control that the gun gives.

http://www.abbuildingproducts.com.au...os-pa-2819.php

and its in Australia
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Old Sep 02, 2012, 11:26 AM
Current project: Electrolyte
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Emufinger,
The idea of being able to spray the foam in the mold is amazing! Correct me if I'm wrong but from what I've read so far, based on AvB's initial experience and Troy's post and BjB video, the insulation type foams may not be ideal?
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Old Sep 02, 2012, 01:10 PM
working to the closest cm
jirvin_4505's Avatar
brisbane australia
Joined Nov 2002
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Very nice foam application!

Quote:
Originally Posted by emufingers View Post
If the foam is suitable this system is ideal. Two part foam with a mixer dispenser gun. A small kit that would do about 5 two meter wings for under $40 inlcuding the gun.

Check out the videos to see the control that the gun gives.

http://www.abbuildingproducts.com.au...os-pa-2819.php

and its in Australia
Hey that is some very cool videos - the controll of the foam application looks amazing.

Thanks to Avb reference to two stroke's posts I had an enjoyable time going through the crunchy planks thread. Some very cool PU stuff going on!

Reading there I was reminded of a technique of soaking ordinary sponge in epoxy and wringing it dry to use as a space filling method. I used it many years ago to stiffen up the rearend of power plane fuselages.

Not sure of the mechanical properties? I do recall that it was susceptible to delaminating but it was a very limited application. In the crunchier plank thread there is reference to using it as a filler in vertical tails.

(to do... Add links)

Cheers Jeff
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Old Sep 02, 2012, 01:23 PM
Dean
A10FLYR's Avatar
USA, CO, Littleton
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I think that foam lacks rigidity. Seems to me you can prchase it in a rattle can from Home Depot.
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Old Sep 02, 2012, 03:25 PM
Keep it Simple Stupid
razortoe's Avatar
United States, NC, Raleigh
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Quote:
Originally Posted by A10FLYR View Post
I think that foam lacks rigidity. Seems to me you can prchase it in a rattle can from Home Depot.
My spray-foam insulation guy explained there are several different kinds they use. There's a slower kicking door-and-window foam, which when cured reminded me of slightly rigid cotton-balls. i.e. no good for us.

He says the kind they typically spray in between open-wall studs (sheeted on one-side only), is 1lb/ft³ but it kicks in 2-seconds. Again, no good for our purposes.

The spray insulation available here is called 'Great Stuff'. Whatever it's density is, it kicks almost instantly, so no good.

---

That spray gun looks useful, though from the vids, the foam seems to kick really quickly. There's no mention of the mix ratio used in the kits not whether it's adjustable. If you wanted to use your own foam, you'd have to feed it from a pressure pot of sorts. Seems it would be a good setup if you were doing this for production. I'm not sure how useful it would be for hobby use.

---

From my reading, the higher-density foams seem to have a longer pot-life. Since 4 or 6 lb density was already suggested, the longer time may be just the ticket. Though it'll certainly be a heavier wing.
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Old Sep 02, 2012, 08:51 PM
I hate propellors
emufingers's Avatar
Australia, SA, Normanville
Joined May 2009
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From what I can see, the gun does a fixed 50:50 mix, which woukld suit most of the foams on the market. It is a low pressure gun so this is what I am thinking.

Get hold of a gun.
Get two small old lpg cylinders
Place the ingredients of you selected foam in each of them
Drill extra holes in the walls of the tanks and fit a compressed air fitting to be supplied from compressor. They are easy to drill btw)
Hang the tank upside down, or modify the tap assesmbly to draw from the botton of the tank ( an extension tube)
Connect the gun to the usual threaded outlets. Use standard gas fiittings to convert
Start on a low pressure say 10 psi and work up until desired spray pattern is achieved.
The gun bleeding technique in the videos should still work
There is also a solvent for PU foam advertised if things go hard.

Voila a mixer gun for fifty bucks and 15 litres iof handi foam to insultate you hot box.
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Old Sep 02, 2012, 08:59 PM
AvB
Wind, hill, ... I'm keen ...
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I am happy with the technique I used, and I think the benefits of full-area-spreading the mixed liquid and closing the wing mould are 1) best possible adhesion of foam to skin; and 2) you can use a light foam but get some compression of the expanded foam in the mould (back pressure) which increases the density against the skin, which is where you need it most. The only issue with the technique was the need to work fast and have extra hands, but that's doable. I'm planning to do more with the technique and the only thing I'd like to change is to source a foam with a longer working time. The RFOAM35 seems to have a slightly longer foaming time - 30 secs longer if their figures are accurate, which could help. But for me, at this point there's no problem to solve ... the technique has produced a good result and I'm sure that with more refinement I can get it even better.
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