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Old Oct 25, 2014, 05:28 PM
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Godless Commie's Avatar
Turkey, İstanbul
Joined Oct 2014
22 Posts
Question
Engine selection for a 3 meter twin boom plane

Hi there,

I am currently planning on scratch building a 3 meter wingspan, twin boom, twin rudder cargo plane.
The overall length will be about 2.17 meters, with the main fuse about 1.10.

Main fuse will have four wheels, and the 2 front wheels will be steerable.
Booms, together with the tail feathers shall be detachable just at the aft of the engine nacelles. I will use telescoping aluminum tubing for that section.

The plane will have twin engines, mounted on the wings.

Construction will be plywood, balsa, CF tubing, aluminum tubing, an aluminum skeleton for the wing center section + engine mounts and depron.

Rudders will be pull-pull on a single servo, elevator will be operated with a pushrod.
All servos will be in the main fuse for CG considerations.

The wing will be three pieces, center section will be permanently attached on the fuse, with outer sections (just outside the engine mounts - nacelles) mounted via CF tubing and plastic screws. (Wing center section will have a removable cover do do the joining)

Wing chord will be 46 Cm, tapering after the engine mounts, down to 34 Cm at the wingtips. Leading edge will be straight, all taper shall be at the trailing edge.

There will be ailerons and flaps.

The wing, elevator and rudder will be plywood sandwiched in foam, and the wing will be reinforced with CF tubing and spruce spars. I will use wing struts, as well.
Also, wing leading edge will be CF tubing, to minimize damage.

Do you guys see any problems with the idea please?

What sort of a target weight should I be aiming at?

Also, the big question is, I am planning on using 2 ASP .52 engines for this plane.
Do you think I will have enough to get it going?

(Or, should I resort to a JATO setup for take offs )
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Old Oct 27, 2014, 07:08 AM
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mosquitowings's Avatar
USA, OK, Warr Acres
Joined Feb 2004
537 Posts
Hmmmm, sounds to me like you need more engine, say two 50cc gassers! Depending on what you are trying to accomplish with the airframe.
Jim
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Old Oct 28, 2014, 03:41 AM
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United States, OR, The Dalles
Joined Apr 2011
1,370 Posts
That was what I was thinking too from the size, unless this plane is going to be glider-like in weight.
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Old Oct 28, 2014, 06:37 PM
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Godless Commie's Avatar
Turkey, İstanbul
Joined Oct 2014
22 Posts
Thank you for your responses..

This plan is getting more and more complicated every day.
I just want to try things I have never done from scratch before on this one.

I am now designing a custom retract system where I will pull the wheel trucks on the fuselage straight in, and the wheel bulges will open, and close once the wheels are tucked in for a clean look.

I just did a quick inventory, and came up with 15 servos total. (Servos and retracts will have their respective dedicated batteries)

Airfoil will be the classic Clark Y, flat bottom, with about a 2 degree angle of attack.

Wings will have 2.5 degree dihedral, midwing setup.

Looks like I will need "more engine", after all.

How about going with four engines then?

Also, can I mix and match the engines? (2 inboard ASP .61 engines on the wings, and 2 ASP .51s further out.)
That SHOULD get the plane up in the air, but do I have to have all four engines identical?
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Old Oct 28, 2014, 07:43 PM
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United States, OR, The Dalles
Joined Apr 2011
1,370 Posts
I think you'd best think four 1.80ish size engines, and with the price of glow around here I'd suggest gasoline. You really need to come up with an approximate weight.
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Old Oct 28, 2014, 08:13 PM
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Godless Commie's Avatar
Turkey, İstanbul
Joined Oct 2014
22 Posts
You have a point about gas engines, but I live in Istanbul, Turkey.

Gas is about $10/gal over here..
Plus, I can get nitro engines form Hobbyking for about 50-70 bucks, gas engines are about a grand a piece.
Also, I am very much used to glow stuff, andI actually like them.
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Old Oct 28, 2014, 08:14 PM
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ahrma_581's Avatar
United States, AZ, Ajo
Joined Jun 2012
228 Posts
I think having the tail booms detachable and a pull-pull rudder servo in the main fuselage will create problems with assembly and rigging at the field. Unless I'm missing something, which does happen quite often...
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Old Oct 28, 2014, 08:43 PM
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Godless Commie's Avatar
Turkey, İstanbul
Joined Oct 2014
22 Posts
You're right.
It's just a risk I will have to take. I really don't like exposed servos.
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Old Oct 28, 2014, 09:44 PM
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United States, OR, The Dalles
Joined Apr 2011
1,370 Posts
Super Tigre 3250 maybe, then?

Nothing wrong with glow, but here glow fuel can run $20 a gallon, where gas around $3, plus gas engines burn less.

If glow is cheaper there, or if you just prefer glow, go for it. I just think you need to be looking at bigger engines.
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