From: ntaib@silver.ucs.indiana.edu (Iskandar Taib)
Subject: Re: Rubber power
Organization: Indiana University
Date: Mon, 27 Jul 1992 16:57:56 GMT

In article <3140024@hpsad.sad.hp.com> rexm@hpsad.sad.hp.com (Rex Musgrave) writes:
>I have built a rubber powered plane for my son (age 7). It was an
>interesting building experience. We built the Flyline Models Monocoupe.
>I thought he could help with the building but it turns out that this
>stick and tissue design is the most difficult building experience that
>I have encountered so far. I did get some 7 year old help in coating the
>tissue with dope and we have an airworthy ship. She flies or rather goes
>through a powered glide. She is pretty stout having endured several 
>bumpy landings.

Rubber powered free flight can be the most challenging part of the
hobby you've ever tried, and can be the most rewarding. Sick and 
tissue might not be the best place to start out, though. Some of the
stick-and-sheet models would be a better way to start out learning 
about how to trim and fly these things. There is something called 
(I think!) the Blue Ridge Dart that would be nice to try. The impor-
tant thing is to find somethign with an undercambered wing... a plane
with a flat wing (eg. AMA Cub or Delta Dart) can be harder to trim.

My advice is to put the stick-and-tissue model aside for now until
you learn rubber winding skills on a stick model. A broken loop on 
a stick model means a whack on the fingers, on the stick-and-rubber 
job it means knocked-out crossmembers, holes in the tissue, a wrecked
fuselage (unless you use a winding tube or similar).

>My question is about rubber power. The plans say use a loop of 1/4 inch
>rubber and that's about all. What do you all know about rubber power?
>What about rubber types? How many turns can you wind up on it? Should
>we consider lubrication of the rubber? What other questions should I
>ask?

You need a winder. If you really want to get into it look in Model Avi-
ation and look for the FAI Model Supply ads for FAI Tan rubber. They
will sell you a 1/4 pound of rubber for $4-5 or so.. I usually buy the
pound packages at $13 or $14.. it doesn't last as long as you think it 
will. Get a bottle of their rubber lube too - its good stuff. 

The big idea is to stretch the rubber as you wind. First make up your 
loop (a little longer than the distance between the prop and rear peg)
of the right size rubber. For a stick model I have a helper hold the 
prop firmly (or stick the prop in a chain link fence) and wind from 
the other end. First lube the rubber. Use a foam brush or a piece of 
paper towel-the stuff is evil smelling and the fingers might not appre-
ciate it. Don't get any on the knot, although FAI Tan seems to be more 
tolerant of this than the old FAI dark. Hook your winder up to the 
loop, and while your helper holds on to prop, stretch the rubber to 
about 3 times its length. Start winding. I use a SIG 6:1 winder (the
16:1 is unsuitable for this... its more suited to skinny indoor rubber).
Count as you wind. At about 70% winds you'll feel the torque on the 
rubber suddenly go up. Start walking slowly towards the plane as you
put in the other 30% winds. After the motor is fully wound I usually 
pinch it an eighth of an inch away from the winder's hook then let the 
winder unwind. This lets me slip the loop off the winder and slip it 
over the rear peg. On a 16-17" loop of 3/16" rubber I can get a good 
650-700 turns. On my airplanes (similar to a North Pacific Star Flyer 
but bigger - 15" span, 7 inch Peck Polymers prop) I can consistently 
do 60-70 seconds, often longer (I lost one in a huge thermal at Law-
renceville one year).

Trimming is another matter. The initial burst of power from a rubber 
motor is difficult to control. I usually rely on a combination of 
right thrust and left rudder to get a good climb-glide combination. 
I trim the plane so it stalls going straight, then dial in enough 
left rudder so it glides properly. I then give it enough right thrust 
so that it doesn't hang on the prop (or loop) during the climb. Using 
this method I get the explosive vertical climb I enjoy so much on my 
stick models. 

Hope this helps....



-- 
-------------------------------------------------------------------------------
Iskandar Taib                          | The only thing worse than Peach ala
Internet: NTAIB@SILVER.UCS.INDIANA.EDU |    Frog is Frog ala Peach
Bitnet:   NTAIB@IUBACS                 !
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