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Old May 10, 2013, 03:43 AM
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Quote:
Originally Posted by kevin matthews View Post
If it has a chance with rubber power I'd like to know what sized rubber motor would be required.
Kev, I really think you shouldn't give up on rubber yet! That's not a bad weight for all that wing area.

Give me a moment and I'll look at the figures for you, but first one more question: what diameter and type prop are you planning to use? Bigger is better obviously.

One thing you could do that would really make a difference is move the motor peg forward to the rear cockpit former (around the second 6 on the decal) This shortens the motor space but would cut down on the nose weight a lot.

Jon
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Old May 10, 2013, 11:19 AM
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carbondale il
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Jon, I'm thinking an 11" blue plastic propeller.

Kev
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Old May 10, 2013, 12:03 PM
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Kev,

First off I'm assuming you have about 360 inches square of wing area?
Could you just confirm the chord of each wing?

The weight looks very good even with nose weight and a chunk of rubber. If my area assumption is right you will be ok up to about 200g all up.

Based on a few guesses about your prop I would say you will need about 12strands of 1/8th rubber and a total motor weight of 18-22g, this would give a motor 18-22" long and run times of 30-40 seconds. This is a prediction based on a rubber power calculator (not experience!) but this should be good enough for a modest climb without overpowering it. The actual motor required will depend on the dragginess of the model and the climb rate you want but that's where I would start if it was me.

What is the current distance from the prop hook to the rear peg? If you able to stretch wind you may be able to go for longer motors.
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Old May 10, 2013, 02:32 PM
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Kevin,
the ONLY time I've weighed a model, is to confirm it meets a specfic event category rules. Like an A-1 twline glider, etc. I never weighed my FF gas or Unlimited Rubber models, unless i got curious. Seldom was.

FF scale may have certain weight rules for FAC events but those restrict rubber wt only, IIRC. But then, IMHO, those events are more flight performance competition oriented, than the old AMA rubber scale rules, which had more emphasis on scale fidelity.

I like FF scale for the flight realism THAT IS POSSIBLE with that mode of power. FF gas (which includes electric) comes in a sclose second, though this grenre seems near extinct these days.

I tend to balance my models emperically. Adding nose weight until it glides well. If everything looks good at that point, I start power timming, If you think you are using too much clay for visual reasons, get the balance close with lead shot or strips inside the cowl. Fine tune with clay or remove some of the lead. A moderatelly weighted model that flies well may not be the best/lightest performer but will find its share of thermals.
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Old May 10, 2013, 11:01 PM
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Kev and others...

Attached is photo's of my Gippsland GA-8. 40" wing span, as you see it, not quite 4 oz.

George
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Old May 11, 2013, 12:28 AM
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Yak, Thanks for the good news! The upper wing chord is 6 3/4". The bottom wing chord is 5 3/8". The distance from the rear motor mount to the propeller shaft hook is 13 1/2".

PP, I'm thinking of using thin brass strips for the ballast, and yeah, I'll leave some room for clay ballast fine tuning.

Kev
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Old May 15, 2013, 10:23 AM
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lead is best because its important to get it as far forward as possible - in your case in the cowl somehow.

And lead takes up least space.

I too think that will fly with the weight. All WWI models need massive front weight, especially rubber ones with no actual 'engine' at the front.

A heavy undercart helps a bit but really you never were going to get away without nose weight.

Accept it as part of the design. As others have said there's a lot of wing area as well. If you wanted a duration model you wouldn't have built this model would you?

The ideal for rubber scale is a longish gentle climb to not very high and a cruise and gentle glide. Biplanes don't glide well so even it it lands on et last vestiges of the rubber motor, that's OK too.
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Old May 16, 2013, 01:51 PM
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vintage, Thanks for the opinion. It's good to hear the TMS is within weight requirements. I think I'm going with brass sheets cut with a jeweler's saw into circles with a hole in the middle and put the sheets into the nose depression where the engine indication is. I'm shying away from cutting on the fuselage to get inside to place the ballast there. I had a talk with my doctor yesterday and he said I should give it a try to fly. He said if I'm worried about it crashing during a hand launch I can try ROG for trimming. I'm going to have to add some support to the undercarriage, it seems a little light to hold up during landings. Here's the thing - I knew it wouldn't fly like a duration model. I built a 24" TMS from the Guillow's kit awhile back. I cut down the formers, ribs, stab and rudder structures, etc. and replaced the kit wood with contest stringers, and left a few out. With the plastic cowling and propeller, it is really close to needing no ballast at all. I gave that model to a friend but I thought I could replicate it. The weight is in the stab and rudder. I built them both not to warp and the vinyl colors added considerable tail weight.

Kev
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