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15_20cc gas power Telemaster

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15_20cc gas power Telemaster

Old 09-19-2015, 09:42 AM
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overbuild
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Default 15_20cc gas power Telemaster

I am looking for opinions on building a Telemaster the old design 95 inch wing span version. I think I would make the bulkheads wider to allow for a wider body area to fit in the ignition module and second battery .Also I think the wider bulkheads would make the engine mounting area larger.

I plan on fully sheeting the sides also. Any advise or input on how much to increase the bulkhead size is welcome.
Old 09-22-2015, 07:39 AM
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BMatthews
 
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That version flew with a common two stroke .60 like a homesick angel. So there's no doubt that it WILL fly with a bigger gasser that you want to use.

Look at the weight of a model use .60 and compare it to your gas engine. Plan on shortening the nose by a little to avoid nose heavy issues. You'll want to beef up the wood sizes in the nose as well to aid in absorbing and spreading out the added vibration.

I like your idea of fattening up the fuselage so the engine fits within the fuselage size. How much bigger to make it? You've got the engine and the plans for the model, right? So you're in the best position to figure that out.

Me? I'd take this opportunity to make the fuselage look a bit semi scale and give it a "DeHavilland Beaver" sort of look with a suitable lightweight aluminium pot as a cowling over the engine. Or since the fuselage is rectangular maybe give it an engine cowl that looks a bit like the OX5 powered version of the Curtiss Robin.

With the weight increase you'll likely want to look at using some carbon fiber and full on proper webbing on the wing spar. As in use the wood spar as per the original but cut the spar notches about .025 deeper and cap off the wood with .025 carbon fiber strip glued to the wood on the top of the upper spar and the bottom of the lower spar. And if the plans called for balsa vertical grain webbing between the upper and lower spars I'd change that to 1/32 plywood for the first 1/3 of each panel. That is because the plywood is less likely to shear away under any punishing loads from that nasty death dive full up recovery...

If the plans you're working with don't include flaps I think I'd add them. This is a great model to play with flaps. And with the added weight you're going to have with the gas engine and gear the flaps will make lifting off earlier and making slower approaches that don't over shoot that much easier.
Old 09-23-2015, 04:44 PM
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B Matthews thank you for your reply. The Telemaster I am flying now has 5/16 sheeted sides and weighs about twelve pounds a seventy magnum glow gets it airborn at half throttle . I am thinking to increase the bulk heads by one inch in width. The original fuse is not large enough to fit in ignition battery and module. I have used hard wood spars but I like your carbon fiber laminate idea.

Any and all suggestion are welcome.
Old 09-27-2015, 06:44 PM
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If it were me making a gas powered version with an engine of that size I think I'd scale up the plans to make the size suit the engine more. A 15 to 20cc gas engine will easily fly a 120" version of the Telemaster and the bigger model will support the added weight of the engine that much better.

The likely issue if you look at the various power plants is that the 15 to 20cc gas engines don't really make any more power than that .70 two stroke glow engine. But they do weigh a lot more. Plus it seems like you're intent on adding more structure to deal with the often higher vibration levels. And that's going to add that much more weight. Your present Telemaster is already over the suggested target weight of 9lbs and you're looking at adding even more with this current plan. So instead why not scale it up to 120" and then it'll be more suitable for a 20cc gas engine. Being larger in every way also means the airframe is automatically stronger so you don't need to beef up as many areas as you are thinking. And the beefing up you still need will be a lot more minor.

At least that's how I'd approach it.

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