Rubber band

[rayd]

Say Phugoid:
By chance, would you or other members have a rule of thumb guide you're aware of re nominal specs for bands in rubber powered planes? I'm limited to rubber power or static display now but would like to fly 'em a couple times. Kit builders seem to feel band supplied is NG. I have kits... waiting in the wings for assembly (mostly Guillows, 2 old Comets) and many plans for scratchbuilding. There must be something around to provide guidelines. Perhaps not, so builders experience would suffice. And there's always trial and error.

Example, I lean toward 25" span with approx 12" path of rubber thru fuselage. Not sure what such a plane would weigh, but unpainted, regular balsa. But I see things like....use this brand rubber, but what thickness? how many strands? (2 which I gather is 1 loop, more?) should it be 12" long? and how chunky ...1mm? more) Lots of variables. Details....many, more than I ever imagined. Most of my past flying model experience w/gas engines.

As kids, we'd used loop that came in kit, maybe plane flew, maybe not so good. We could care less about...variables?? I'm likely making a mountain out of a molehill here, but come the holidays, I don't want to give local neighbors airplanes with wimpy bands or overpowering ones that bust quickly, especially if prop winder makes double knots galore. If there's some info out there, on-line, please let me know, or your experiences will do just fine. Thanks Ray

[Phugoid]

That's a big question Ray!

Rubber comes in pretty well much the same thickness, but in various widths running from 1/16" up to 1/4"

There are the common widths, then you can but it stripped into intermidiate sizes for indoor use where the amount of power is critical -too little and then no take off (rise off ground or ROG) and too much and you hit the ceiling!

The length of the rubber can be anythig you like, the longer rubber will give you a long more gentle run, shorter rubber will give you a shorter more powerful run. I normally settle with 1.5 to twice the prop hook to peg length, to wind it you'll need a winder, and stretch wind, that is pulling the rubber our of the nose whilst winding, you can pack in more winds that way and keep the knots nice and neat.

For a 25" span model you'd be looking at least at a 7" prop and start with 3/16" rubber. If there is not enough power then go to a loop of 1/4" the if still not enough two loops of the 3/16". It is as you say a real trial and error thing, but best to start out low and build up. Obvioulsy the choice of prop, the weight of the model etc all have their part to play. As a stab in the dark, given a high winger type (a cub or some such design) at 25" span you'd be talking about a weight of around 30-35g AUW for a decent flyer.

I can't really do this justice in a single post. On the Guillows site they sell a super book by Don Ross. There is a whole chapter in there about rubber selection, winding, lube and max winds and more. As well as that the book is very good for the hobby as a general reference.....

Andrew

[rayd]

Phugoid:
Yes it was a big, somewhat loaded question. You seem to know much about this subject, and gave a lot of info that I was unaware of.... it will be helpful come build time, and beyond. Many thanks for your helpful advice. Ray

[DenisCullinan]

[quote="Phugoid"]Don't bother with the band with the kit it is useless. Buy some tan rubber which you can buy cheap on line. It's all the same thickness only the strip width changes. 3/16" is about the right width for 500 series birds, and don't forget to lube it with castor oil or castor oil mixed with green soap, otherwise it will snap in no time.[/quote]

The best lubricant for rubber is silicone grease or spray (in a spray can), which is easy to get. It's completely inert towards rubber and it won't throw off droplets as the rubber unwinds.