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Telemaster Twin Project

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Old 01-30-2019, 06:16 PM
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mirion
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Default Telemaster Twin Project

I have been thinking about a twin for a while now. I think this is a pretty simple build compared to some of the others I have seen here but I would appreciate any input because even though I have been reading everything I can find for the past couple weeks there are still some questions. I want to use Saito 65's because I have them already and it is my favorite 4 stroke. I do plan to have an onboard glow system. I also already have a Senior Telemaster kit that I would like to use. I plan on turning it into a FPV platform eventually for the fun of virtually flying from the cockpit.Some of the things that I have read that others say:
  • A twin taildragger is difficult for ground handling and should be avoided
  • Each engine should have 4 degrees out thrust (one left thrust and one right thrust)
  • Vertical stab and rudder should be enlarged
  • Tail moment (length) should be increased
All of these thing can be achieved with some alteration but how necessary would these changes be with this plane that has a very light wing loading?

The standard Telemaster is set up as follows:
Wing Incidence-4.5 degrees positive
Stab Incidence-2 degrees positive
Engine-3 degrees down and 0 degrees right
Should I maintain all of these specifications?

Below are some drawings that I have been working on to visualize the proportions and design change requirements. Thanks for any input........Mike in Michigan



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Old 01-31-2019, 05:11 AM
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R8893
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Mike, You are probably going to get as many different opinions as there are responses to your post. I have bashed three sport/pattern planes to twins: Midwest Strikemaster, Kaos, and Direct Connection Sea Fury. All but the Strikemaster were tail draggers. Only aerodynamic change I made was to add about 20% of wing area to the middle of the wing to deal with the extra weight. I have never done out thrust on the engines. I did not increase the area of the tail group on the SM or Kaos. I went to a twin tail on the Sea Fury bash. (photos may still be here in a thread called obscure Russian bomber) Area probably increased.

I have a Handley Page O-400 twin WWI bomber that is a big, slow model somewhat akin to your Telemaster. 120" span, two ST 90's, Clark Y airfoil. Flat bottom of airfoil, stab, and engines all at zero degrees. It flies like a big trainer.

Based on what I have done I would suggest you place your engine nacelles under the wing to get the thrust line closer to the original design. That should maintain the original flight characteristics. I have found that a twin tail, like the Sea Fury bash, O-400, and an Me-110 I had helps with rudder control by having the rudders in the prop wash. Only other "words of wisdom" I have are to make sure you do not compromise the wing spars.

Chuck
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Old 01-31-2019, 05:38 PM
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My original Lazy Ace has gone through 3 recovering jobs and some major cosmetic changes. Its now cub yellow with a Texan canopy. The engine is an inverted YS 1.20 old SC that has been rebuilt. Made a cowl, increased the vertical stab 30% and the rudder is twice as big. elevator is twice as big this was done for glider towing and float flying.

I decided to make it a trimotor and used 3 OS .61 engines. The photos show the layout. The two on the wings were mounted as close to the fuse as I could in case of an engine out there would be less yaw induced by the other engine. No side thrust all three were straight forward with only 2 degrees of down.

How did it fly? Unlimited vertical but no faster than the single YS probably due to drag. Was heavier than the single and though it handled well even with one engine out it was not an improvement over the single. It was an interesting project but I returned it to the single engine air frame and still fly it to this day. Don't be afraid to experiment its a lot of fun and very little to loose. The only thing I would recommend is to place the engines as close together as the props will allow.

Dennis

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Old 02-02-2019, 10:20 PM
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I’ve built two Senior Twins over the last 10 years. The first was a trike gear with OS55’s. I did do outboard and down thrust. It flew great and engine outs were no issue. It was kind of boring like a Senior Telemaster is suppose to be. Fast forward to this past Fall and I was bored and decided I’d build another one, this time electric and a tail dragged. Figured I could lighten it up and provide more reliability with electric. I also set the nacelles for 0 down and 0 out thrust.

I got the chance to maiden it this week. Couple of things popped up. As you know the lifting stab of the Tele quickly leaves the runway making the tailwheel a mere ornament. The left torque could not be corrected using the rudder. The only way I was able to takeoff was to use full power a little elevator and it was airborne in about 10 feet.

I have changed my thrust angles to give one degree down two degrees of outboard thrust along with changing one of my motors to a pusher. I have not yet had a chance to test fly it again.



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Old 02-03-2019, 01:19 PM
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Thanks for the input everyone. It is noted and much appreciated.
jbarnes, I will be waiting to hear about the revisions you made to your electric Telemaster. When you say you put on a pusher motor I guess you mean that the propellers are rotating opposite directions? That is an interesting concept. I read where there are some glow motors that can be changed to rotate opposite for purposes of using them in a twin. The two piece wing that you have, is that your own creation or does one of the newer kits provide that option? The kit I have is a "vintage" Hobby Lobby kit and does not provide that option although I think I will try to figure out a way to incorporate it.
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Old 02-04-2019, 06:39 AM
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Hey Mirion, I had plans for the Senior laying around but then I caught wind that Hobby Express had just designed a new Twin Tele so I bought the kit from them. They told me I was one of the first to buy the kit so I suspect there are very few actually flying at this point. They really improved the kit from the old Hobby Lobby days. Everything fits together nicely and its easier to build than the old kit. I'm not much of an electric guy but I did get advice to switch to a pusher prop and reverse the rotation on one side to remove the torque. I've got several twins and I've not had too much trouble with left torque unless I have a engine out.

I also built this twin with DLE55's, no issues with torque and the tail dragger works good but the tailwheel stays down much longer than it does with the Tele.

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Old 02-11-2019, 12:06 PM
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I built a SR Telemaster kit back in the day and added a ply box and 35mm film camera, looking our under the left wing.

This plane in a tail dragger config should be no concern regarding ground handling. Tail comes up quickly (as does the whole aircraft), giving you rudder authority. Gentle application of throttle.
I left the vertical fin stock, and added @ an inch to the TE of the rudder.
Tail moment on the SR Telemaster is plenty generous - I would recommend no changes there.

other changes I made:
Bolt-on wing use 4 - 1/4-20 nylon bolts, spruce and ply mounts in the fuse, with brass threaded inserts. spruce hard points in the wing for the bolts to run against.

I installed, but never used, hard points in the wing and fuse for functional wing struts. You may want to consider those, and using spruce wherever possible for wing spars.
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