Building Light - Page 2 - RC Groups
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Jan 15, 2002, 10:11 AM
Registered User
If you really want to build light, you can probably get tips from

For light balsa, just take a postal scale to the hobby shop, and check the balsa every time you go. If you're real serious, you will also measure the stiffness, per article at above web site.

Use the right density in the right place. The tail should be light, but the area where the motor or landing gear is attached should be denser.

Foam is probably light for small planes if it's thin enough, but I'm sure I can make a lighter wing than the one that comes with a Light Stick. My balsa frame for the MOOsquito came out at about 28g for a 25" airframe that was not particularly optimized. This includes covering and wheels, but not motor, radio, etc.
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Jan 15, 2002, 11:06 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Nice link. Another source of info like the rubber power books.

From there there is another link to who sell true weight indoor balsa. It costs about double to triple what my balsa from National cost, but the densities are stated up front so you know what you get. And, they have some pretty low densities, in the 4 pound range.

Unfortunately, now I have some reasonably light balsa -- which is a problem easily solved with a credit card. Building lighter with less glue and perfect joints, now that will take time, practice, and effort.
Last edited by Gordon Johnson; Jan 15, 2002 at 09:36 PM.
Jan 15, 2002, 09:33 PM
Old Desert Rat
Arizona Chuck's Avatar
Maybe I'm off base but I have a scale, light balsa and all the stuff to build light. I can to the conclusion that to build light it is a state of mind. You have to think "LIGHT", if it does not need it, don't put it in. If you can use smaller, do it. If you find yourself saying "That is not much", even if isn't "much" the attitude seems to run the weight up 25%. You have to think "light" to build light. Even the sawdust that lands on the floor isn't in the plane to add weight.
Jan 16, 2002, 01:21 AM
rpage53's Avatar
I agree with Chuck that if you are able to design while you build, you can achieve real weight savings. The lightest wood is almost always the weakest wood. So a 3/32" stringer of 10 lb wood should be lighter and stronger than 1/8" of 6 lb wood.

At the real light weight of some indoor fliers, you may not have any choice but to go with very light wood to maintain some cross section (a 1/64" stringer isn't worth much). But at that point, wood is not the best building material.

As Michael pointed out, foam is structurally lighter and stronger than balsa. It is also more uniform in density and strength. As a composite with paper, carbon, aluminum or plastic it is hard to beat.

Wood is very easy to work and I think that explains its continuing popularity. I'd be using a lot more balsa myself, but I've developed allergies that make it impractical.

Jan 16, 2002, 09:41 AM
Registered User


We use alot of SIG contest grade balsa for our kits and for laser cutting. It is the key element in "LIGHTNESS". If you request contest grade balsa from SIG it is much lighter then their std. balsa but you must ask for the contest grade or 4-6 # balsa.

Jan 16, 2002, 10:27 AM
Sticky Shepherd
Graham Stabler's Avatar
10 build it light then it doesn't need to be strong
20 if it doesn't have to be strong it can be built light
30 goto 10

I applogise this isn't in C or Java but its been/being a long day.

I too read the books of Don Ross and Lew Gitlow, they really get you thinking!

I have found my key methodologyogylogy to be to build things as stong as they have to be and no stronger and then add a bit of convenient weight here and there, like a decent motor mount or battery mount. This gives you a light model that still has some reliability.

I also have to agree with epilot. Foam is great, blue/pink/depron whatever it is liight and of course building from it is a good way of making your whole plane light. I have had a lot of sucess with depron in very thin sheets. My latest model a 12" ir controlled two cell SE5a has a 1mm thin sheet fusulage, the edges where the sides meet are bevelled and the construction is like zipping a banana. There are no formers apart from the nose but its as strong as an ox. I think 0.5mm would have done. I did use that material for the curved parts as these were not structural just to give the correct shape. AUW 23.7g.

This thin depron can be purchased from Flighthook in the UK but I know its actually made in the US especially.

Jan 16, 2002, 01:28 PM
in persuit of low wing loading
Gordon Johnson's Avatar
In my quest for sheet foam I recently got some 1/2mm and 1mm sheet foam from Kenway Microflight. I don't think it's Depron. The 1/2mm is pretty floppy. Yet you have used 1/2mm Depron. This makes me think that because Depron tends to be stiffer than some of the other sheet foam (e.g., wallboard foam) that this is why you are able to use the 1/2mm. Which parts of a plane do you usually use 1/2mm? I may need to get some of the 1/2mm Depron from Flighthooks. They don't seem to have a web site, only an email. Do you happen to know if they ship overseas?

I'm toying with the idea of making a Depron or sheet foam version of Dave Robelen's Punkin (that I'm now building with balsa) as my first try at a cabin foam plane for actuators (alth thinking about a Piper Cub). I'll ask you Aeronutz guys questions as I go along -- probably start a thread for it. Don't hold your breath, my building schedule is very slow.
Last edited by Gordon Johnson; Jan 16, 2002 at 02:01 PM.
Jan 16, 2002, 04:24 PM
Sticky Shepherd
Graham Stabler's Avatar
The half mil depron is fairly stiff and certainly no problem if you are making peanut/pistatio sized models. In fact the main problem is that it doesn't bend it tends to crease. Genrally I use it for my rudders as a mylar film hinge can be trapped between two layers. On my se5 I took a peice of the 0.5mm and folded it in half and then rolled it between my fingers. The effect is to create loads of creases on the inside but a fairly smooth outer surface. I used this for the turtle decking etc and as this was just added to the top of the 1mm depron box it didn't need to be too strong. The kenway foam you mention sounds like it might be even more suitable for this.

I don't know if flighthook do overseas but you can but ask. If you get desperate perhaps I could forward some to you.

good luck with the models. My own building style is fast (i love foam) but very sporadic.

Jan 16, 2002, 06:08 PM
Registered User
Good thread!

There is a great virtuous circle as Graham's mini-program suggests.

We have to learn to fly any plane in the time it gets from shoulder level to the floor - if it is serouusly light we get longer to observe and react and it does less re-kitting on contact!

Also - fast is fun and there is no worry if the carved masterpiece gets dinged. There are plenty more lurking in blocks of foan just waiting to be liberated

is skinned in the making process - there is a (relatively) smooth skin on it - therefore the thinner sheet is relatively heavier and stiffer

Has a grain - ie there is a stiffer direction which should be aligned to resist the loads (i.e. along the wing). probably it is an extruded product which produces the "grain"

Cutting foam sheet

Can't get Depron? - slice up block or thicker sheet to any reasonable thickness. I keep a hot wire fixed parallel to a sheet of melamine faced board and push the block of foam past it sliding on the face of the board. hieght of the wire governs thickness.

No control of voltage used or really needed - if necessary extend the hot wire and use croc clip to vary length and hence temperature
power supply - battery charger, ordinary type - indicates about 3 amp
Hot wire - remove from any heating appliance (Or buy)
Tension - spring (or use weights) (or a section cut from inner tube)

Give it a try - its very easy
When marooned abroad I have made small 4 and 6 inch cutting bows using hair-dryer heating element and powered them with 2,3,or 4 1200 nicads to get cutting temperature

When I get home the weekend I could take pics of my slicing bench if this would be interesting to anyone?
Jan 16, 2002, 06:26 PM
Registered User

Hair drier wire

What does the hotel manager say when he finds out you dismantled his hair driers to make mini hot wire cutters for your foam toy planes? "You must be an Aeronutz man?"

I the past I have sent a box of different foams over seas to help get folks started, I might do that a couple more times ....
I just bought 67m2 of White Depron so the shortage is OVER!
I just look around for light things ... then find a use for them. If it is heavey or expensive we dont have a use for it!
As Graham says - with foams, make it too weak and add stiffness as required, cary the flight stresses in the surfaces like a real metal skin plane does
Jan 16, 2002, 06:46 PM
Registered User
Depron shortage over?

67 M2 of depron - is that enough for a quarter scale Catalina/PBY?
Jan 16, 2002, 09:33 PM
Crash Master
Gene Bond's Avatar
Finally tried a little one. Using .060" 'virgin' foam plate material.

GWS everything.
4.25oz w/ 7x120NiMh

Will it fly? Will the wind ever quit?!!!

Will have to be fast, as the loading is 6-6.5 oz/sqft, but who knows....

will be an actuator candidtate, when ready for the next step...
Jan 16, 2002, 09:37 PM
Crash Master
Gene Bond's Avatar
Finally tried a little one. Using .060" 'virgin' foam plate material.
My J-3:

GWS everything.
4.25oz w/ 7x120NiMh

Will it fly? Will the wind ever quit?!!!

Will have to be fast, as the loading is 6-6.5 oz/sqft, but who knows....

will be an actuator candidtate, when ready for the next step...
Jan 17, 2002, 10:25 AM
Sticky Shepherd
Graham Stabler's Avatar
I searched and searched for nichrome wire for my cutting and was given a bit. When I whent to the local model shop they had it too. Doh!!

Andrew's right about learning to trim on a power glide. I sort of coined the term TBD (trim before destruction). I think its worth phycing yourself up before a test flight, then your brain goes faster and you can record what happens. Too often I have seen my latest model fly into a wall and only remebered a blur. Not too helpful for trimming.

A light model tip is sellotape, its actually quite heavy but its really strong (remember christmas). It can be used sparingly as a reinforcement to prevent ripping of your foam. The nose of my old faithful two cell model is mainly tape now but still holds itself together.

oh and nice model

Jan 17, 2002, 10:47 AM
Registered User

Foam cutting wire

I use stainless steel fishing leader from the local sporting goods store.A good shop will carry it from .011 to .040.I usually use about .014 and cut cool/low temp with about one amp current. Works as good as all the other wire type I have tried and I have tried many.

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