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RCM Piper Twin Comanche - .049TD

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Old 04-18-2008, 11:46 PM
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jetpack
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Default RCM Piper Twin Comanche - .049TD

Here's a set of plans from RC Modeler that I thought would be a great twin .049 plane with micro gear, but where to I start with figuring its wingspan?

I would like to just scale down the RCM plans, which originally are designed as a 70" wingspan and .40's
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Old 04-20-2008, 04:04 PM
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Default RE: RCM Piper Twin Comanche - .049TD

Jetpack:

I would not build any TD.049 twin unless there is throttle control.

Built a scale Aerocommander with twin TD.049s back in 1983 - still have my hand drawn plans.
The plane was completely balsa sheeted and epoxy painted - heavy, but that was the way models were built back then. Both engines had their own 1 oz tank, and because there was no throttle control, I felt that the engines would run out of gas about the same time. Not so!
The maiden flight was beautiful - with both engines screaming at 18000rpm, had power galore and excellent flight handling. Then one engine ran out of gas and quit, and the airplane immediately went into an uncontrollable flat spin - one engine still screaming at 18000rpm.

Last I heard, the TD.049s have a throttle, but idle speed is still around 300rpm.
Anyway, my message is to be aware of .049 twins without throttle.

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Old 04-20-2008, 04:38 PM
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Default RE: RCM Piper Twin Comanche - .049TD

Got that covered with a couple of Tarno carbs.

I got to thinking about what wingspan and what method the build-up should be (non-sheeted wing) and thought it should compare to the size of maybe a Herr Beechcraft, and built somewhat like one?

The Herr I have read it was slightly underpowered with a Cox 049 and did better with Norvel 061 power or better, so I figure if a twin comanche was built along those lines it might be a fun plane, and one I've always wanted in RC.
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Old 04-20-2008, 07:45 PM
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Default RE: RCM Piper Twin Comanche - .049TD

Jetpack:

Last I heard, the idle speed was 3000rpm, not 300 as I had posted earlier. What idle speed do you get w/ 6x4 or 6x4 props?

Don't know the Herr Beechcraft or its structure. The Beech in my avitar is the Baron B55 w/ a pair os OS.15s.

If I were to build a PA-30 for 2 TD.049s today, I would use a brushless eqiuvalent to eliminate the single engine flying. I would use a balsa frame construction, 1/16 and 3/32 ply at hard points, and monokote covered. Wing would have D tube LE constr and fuse would have steerable nosewheel. Span would be about 40" or a wing area of about 2 sq ft. Weight could come out as as high as 25 oz for a wing loading of 12.5 oz/sq ft. and it would be a bomb!

And yes, it could be a fun plane.

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Old 04-20-2008, 08:28 PM
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Default RE: RCM Piper Twin Comanche - .049TD

This project is to use the couple of TD's I've built so electric is going to be confined to just radio and nav lights

I made a mistake about calling the Herr a Beechcraft, it is actually their Piper Cherokee kit.

A D-tube wing is a great idea. The Herr kit of the Piper doesn't have one, just a strip type leading edge, all open bay.

Going with a sheeted wing would be fantastic but can't see how it could be done due to weight issues, but a smooth wing would really top it off if possible.

Most of the cabin on the Herr kit is clear vacuum formed plastic, which saves lots of weight I think and would be a good way to go with this also.
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Old 04-20-2008, 09:48 PM
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Default RE: RCM Piper Twin Comanche - .049TD

Why I am thinking of building this is because I have the Herr kit already and looking at its size and weight and reports of it, and me originally wanting to use a TD isnt really going to be an option. Then I thought of making it a twin.

With the Cherokee and the Comanche are pretty close to the same outlines, converting the Herr could be a possiblility, even if not totally accurate.

Rounding the nose of the kit wouldnt be that hard for me to accomplish, and even a plug made to shrink a nose is even a possiblility to save weight just like the top of the cabin.

With the extra power a nicer wing could be made or even stretched.

The engine pods are really no big deal to make. A simple maple twin beam mount going to the wing rib at all the doublers (profile fuselage style) and then just a set of engine nachelle covers made from heat formed that could be slipped on and fastened. I dont think I would go through the trouble of building up and carving two engine pods out of balsa. The large clear canopy in the kit really got me thinking of how nice large vacuum formed parts can be where strength isnt needed.

You think I should try the airfoil section thats slated on the big plans or stay with a flat bottom? I dont think that wing cross section would work very well in 1/2A size?
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Old 04-21-2008, 02:41 PM
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Default RE: RCM Piper Twin Comanche - .049TD

Jetpack:
Looks like you have the potential of a fun twin with the Herr kit that you can modify.
Seems like you have a good handle on the mods to be made, so I would say - go for it!
I think I would take the easiest route to the end - that is modifying the Cherokee wing rather than design and build a completely new double tapered wing.
If I were to scratch build the Commanche, then I would stick as close to the airplane wing planform and airfoil as possible. The difference in airfoil will manifest itself in the pilot's handling qualities of the airplane which could be negligable in some cases. So I say, it's no big deal whether you use a symetrical or flat bottom airfoil.
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Old 02-27-2011, 03:11 PM
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Default RE: RCM Piper Twin Comanche - .049TD

Many apologies for dragging up such an old thread but I just stumbled on it while doing a Goggle search. I just found a Herr Cherokee kit in my pile that I've had for years but forgot I had. I remember at one time wanting to build it as an electric twin Comanche. Just wondering if anything came of the ideas in this thread or if anyone knows of any conversions done on other sites. I haven't been able to find any. Surprising just how little is out there on this kit....

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