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Rubber power

Increasing flight time

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aquila15/01/2019 17:10:43
18 forum posts

Hi,

How do I increase flight time on indoor rubber, is it longer motor? larger rubber? just want longer motor run,

thanks,

Peter

Tony Bennett15/01/2019 17:19:39
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5016 forum posts
129 photos

fit a longer motor.

when winding pull it right out and as it tightens up let it slowly go back into the model.

Tony B

Denis Watkins15/01/2019 17:28:31
3388 forum posts
151 photos

Props too Aquila

As always, the prop, can turn more slowly and last longer in the air

Rubber power is a science

Rubber strands start point is one and a half times the length of the fuz

Give us some measurements, the span, chord etc etc

 

Edited By Denis Watkins on 15/01/2019 17:29:14

Jonathan M15/01/2019 19:32:09
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601 forum posts
267 photos

Duration determined by rubber length, whereas torque (power) is a function of rubber thickness.

But be aware that increasing the length will add extra weight, which could mean you also need very slightly thicker rubber to overcome the extra weight and get to the same height as previously, which could also impact on your hoped-for duration - so there are diminishing returns. Taken to the extreme, you can end up with a model which becomes so heavy it has to fly unrealistically fast to get and remain airborne, becomes ever harder to trim with no real improvement in flight times, and which possesses a lot more kinetic energy ready to be expended in airframe damage if it hits something solid.

Also be aware that, unless your CG is exactly at the mid-point of the rubber motor, increasing either length or thickness will upset the balance - usually making the model more tail-heavy. (This is why modern practice is to have the rear-peg much further forward than historically, so that small adjustments in motor dimensions don't upset things too much or require nose-weight changes.)

Is this all for free-flight or are you using rubber as the motive power for in indoor RC model?

PatMc15/01/2019 20:05:27
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4003 forum posts
501 photos

Don't forget to lubricate the rubber. I used a silicone grease, bought as a tube from (IIRC) Maplins, that doesn't cause the rubber to perish. It may be available from other electronic supply retailers or you can get it along with many more FF goodies from here.

Another point is to adjust the power to suit the venue. The model should not climb too fast & not quite touch the ceiling before starting to descend with the prop still turning but just giving enough power to slow the descent.

Edited By PatMc on 15/01/2019 20:11:05

Tom Sharp 215/01/2019 23:04:23
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3303 forum posts
17 photos

Never did the big rubber powered models myself, but I seem to remember that the experts used to wind the rubber in a reverse direction, then fold the wound rubber to give two lengths, then wound the resultant twin strands in the normal direction. This was believed to give a smoother power output.

John Tee16/01/2019 14:19:47
713 forum posts
65 photos

Not a regular free flighter but I use washing up liquid to lubricate my very basic motors. Lets the rubber slide over itself more easily for slightly longer runs.

John

John Duncker16/01/2019 18:29:51
64 forum posts
7 photos

One of the key things is to get better rubber. It is quite a while since I played with this but rubber varies a LOT.

I believe the competition guys speak with reverence of a batch made in 1999 and carefully hoard their supplies.

Pirelli was rated much higher than Dunlop.

Martin Dilly 116/01/2019 19:22:19
27 forum posts

Aquila, where are you located? Your best bet is to talk to a local free-flight club and get advice from the people who compete in a free-flight rubber duration class. As people have implied, simply getting a longer motor run can depend on prop pitch and diameter, rubber weight, cross section and length, all, of course, constrained by model weight or, in some cases, contest rules. Pirelli and Dunlop rubber ceased production many years ago; try here: http://www.flitehook.net/ for Tan Super Sport, which is the rubber of choice today.

Do you want to fly indoor or out? People who fly F1D, the World Championship indoor class, routinely get a power run of around 30 minutes from 0.4 grams of rubber in an aircraft with an airframe weight of 1.4 grams, flying at about half walking speed and with the prop turning at around 40 r.p.m.

onetenor16/01/2019 21:03:05
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1881 forum posts

I used to use castor oil and soft green soap mixed to lubricate rubber motors. Worked wel A couple of years ago I found an old tin box not seen since t thishe 50 s. Aha I thought is this a treasure or rubbish. I thought on first opening it was the former. Some lovely round section Pirelli rubber brought over from Italy by a cousin of my dad who worked in the Pirelli factory and knew I was an aeromodeller. Sadly though as I went to pick it up my fingers encountered a squidgy sticky mess of perished rubber. Weight for weight I found the round section gave a longer run in general. I would like to try some again but although there is some round section on the market I don't know the quality. Has anyone used any and can tell me what it's like. It seems to be available in arts and crafts and fabric suppliers. Not shirring elastic which is covered (great for rigging wires) in fine cotton thread I'd send for some myself but am not in a position to make a model to try it out.

Tom Sharp 216/01/2019 22:33:18
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3303 forum posts
17 photos

In the 1940's 1950's Pirelli produced a yearly batch of rubber strip for the wine growing industry. This had variations in quality each year, which was irrelevant to grape growers, but important to modellers that used the said rubber for model propulsion.

Therefore each year Aeromodeller magazine used to publish an analysis of the rubber on offer.

By the way, grape growers used the rubber to tie the vines to the support fences, rubber causing no damage to the vines.

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