boom weight ??

[Double Pappa]

What do you folks feel is the maximum ecceptable weight for the boom on a 3m ship with over 1k square inches of wing?

[lincoln]

Needs more data. Design weight? Configuration? One clue is to look at the drawings at charlesriverrc.org. If I'm not mistaken, you'll find weights of components on some of them. But if the nose isn't too short you can probably get away with more than the weight in say, a Supra boom. Those are probably very much optimized. As I recall, when I attempted to make booms for Supras, my efforts were all over the place, from 70 too 100 grams! Polecataero claims 38 and 58 for Bubble Dancer and Supra respectively. For a v-tail you might want a bit more torsional stiffness than even the Supra. And if you're not in control of the layup you might need to find one even heavier.

[Andy W]

Nah, too complicated. I say 27g.
..a

[Double Pappa]

Okay 27 it is !!!! LOL

Not on this planet. Not when it's 1.125 x .625 x 42".

The lay-up I likw so far gives me a 68g boom. I may stiffen her up a bit and if it jumps to 75g I can live with that.

[Andy W]

3oz for a 42" boom is pretty good. A friend of mine makes his from kevlar, with carbon tow for stiffness. They're coming out low, can't say exactly how low though..
..a

[Charged]

I just recieved a Supra boom from kennedykomposites . It weighs 46 grams ,its lenght is 90 cm diameter 3cm to 1,6 cm . Seems a good layup very stiff and good quality .Kevlar windings are inside .

[atmosteve]

This is a timely thread for me too. Today i was given a wound CF golf shaft, 42" long, 5/8" wide at handle end, 5/16" at the bottom. Its 70 grams. I suspect there may be a little too much flex in the tail end of this boom for my liking, I can perhaps imagine some flutter when winching the 136" of Oly III wing on a pod and boom fuse with this golf shaft boom.
Anyone else tried a shaft of this kind? I spose I could always CF re-inforce the rear part of the shaft at the expense of weight, or find a heavier club shaft.
Anyway, the DIY pod and boom concept sure is an interesting one to pursue.

[jirvin_4505]

In the yahoo allegrolite forums is discussion on rolling booms for bubble dance style models. Richard hallet posted some layups and weights.

IIRC on charles river Mark D gives the layup for the Supra boom (although never quite understood his notes on carbon orientation)

VHO posted some weights in his notes when he did a build log for the bubble dancer. Boom rolled on a pool cue.

@atmosteve.. I worry about the small diameter of a golf club. I use these as a mandrel to make DLG booms. With you being a committed woody builder wouldn't a rolled ply boom be more appropriate? I can help you with rolling your own carbon boom on a pool cue if required :)

cheers jeff

[roydor]

My tail booms are 30 mm to 28 mm in dia. 800 mm in length 50 grams.
Very strong. I made one 36 grams but seems a bit flexible.
http://www.rcgroups.com/forums/showpost.php?p=10172522&postcount=21

[RicVaughn]

I'm Andy's friend and I make a kevlar/carbon boom for electric sailplanes that's 1 1/2" X 1"X 40" that weighs 44 gm.

Ric

[Double Pappa]

Ric, Thanks for posting. What fsbrics are you using. In my case I am building an open class glider and a little weight isn't always a bad thing. I am coming in at 68 using all glass. It is still pretty stiff and we all know how durable glass is. I may take out some of the glass and add some carbon or I may just add the carbon to what I have already.

[RicVaughn]

Hi,

I use 1.7 oz. kevlar and 12K carbon tow. I have not had any issues with electric sailplanes, but I don't think it would hold up to a full pedal launch. For that, I would use all carbon.

Ric

[atmosteve]

I would love to learn to lay up a boom, however with the way things are it would probably take too long to do.
What I do have that looks promising is a 2.15m wound CF light game fishing rod called a Penn powerstick, line rated at 15Kg. It seems to have the right attributes as to size, weight and stiffness. Will have to strip it of the grip and guides and see how it weighs up.

[Double Pappa]

The skills to roll a boom are not difficult to develop. The difficult part as you can see from this thread is getting the mix right and the tapers right to give you what you want.

Ric- the only concern I have with going all carbon is it coming out brittle. I would rather have it flex a little than snap. I think I will stay with my glass and add a layer of unicarbon to add some stiffness.

[Andy W]

A well made carbon boom will still flex a little. Carbon isn't brittle unless it's impacted - i.e. if you hit it with a hammer (or another model!) :)

Glad Ric chimed in..
..a

[Double Pappa]

Thanks Andy for remiding me. I should know this from fly fishing and shooting carbon arrows.

[lincoln]

The skills to roll a boom are not difficult to develop. The difficult part as you can see from this thread is getting the mix right and the tapers right to give you what you want.

Ric- the only concern I have with going all carbon is it coming out brittle. I would rather have it flex a little than snap. I think I will stay with my glass and add a layer of unicarbon to add some stiffness.
I can tell you that an Ava boom, which I think is all carbon, can survive a plunge which puts the nose about 8 or 10 inches into the dirt. Plowed dirt, I admit, but enough to pulverize the fuse just in front of the wing.

[Double Pappa]

Lincoln, There has to be a story behind that !!!! I am really happy with my glass booms but I will try one with a bit of carbon in place of some of the glass. Given the size of the plane a boom weight under 75g should work very well.