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Old Mar 10, 2016, 07:16 AM
olivdudu is offline
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olivier
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Help!
drawing of a VTOL based upon a tricopter

Hello

I would seek a piece of advice . I am drawing on turbocad, the 3 views plan of my future plane. I whish I would build a twin boom "chimera like" vtol. I will use the engines and props of my former tricopter. The prop diameter is 9 inches. When I draw a Y shape tricopter, upon which I place a 55inch long wing, matching their balance points, I end up with booms so far from each other, thus giving a huge, much too long stabilizer... and too small ailerons... I made the drawings so that the propellers do not turn upon any part of the wing. So, I have two questions:

- can I shorten the "tricopter", even if a part of the radius of the prop, turns upon a part of the wing??? I guess this will create some unexpected vortex...

- can I draw the "tricopter" on another shape, no longer observing the 120 angle??? In that case, will the KK2 board compensate the differences between the lenghts of the "arms"??? and will I have to match a common balance point? I noticed on some VTOL that the "tilting" motors, set on the leading edge, are not at the same distance than the rear engine, sometimes, we can notice that the rear engine has not the same propeller size too...

Would some one help me cure all this questions please?

thanks by advance

Olivier
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Old Mar 10, 2016, 10:02 AM
Ran D. St. Clair is offline
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Quote:
Originally Posted by olivdudu View Post
Hello

I would seek a piece of advice . I am drawing on turbocad, the 3 views plan of my future plane. I whish I would build a twin boom "chimera like" vtol. I will use the engines and props of my former tricopter. The prop diameter is 9 inches. When I draw a Y shape tricopter, upon which I place a 55inch long wing, matching their balance points, I end up with booms so far from each other, thus giving a huge, much too long stabilizer... and too small ailerons... I made the drawings so that the propellers do not turn upon any part of the wing. So, I have two questions:

- can I shorten the "tricopter", even if a part of the radius of the prop, turns upon a part of the wing??? I guess this will create some unexpected vortex...

- can I draw the "tricopter" on another shape, no longer observing the 120 angle??? In that case, will the KK2 board compensate the differences between the lenghts of the "arms"??? and will I have to match a common balance point? I noticed on some VTOL that the "tilting" motors, set on the leading edge, are not at the same distance than the rear engine, sometimes, we can notice that the rear engine has not the same propeller size too...

Would some one help me cure all this questions please?

thanks by advance

Olivier
The balance point of a multicopter must match the balance point of the airplane but there are many ways to achieve that.

For your specific case, the rear motor needs to be 2 units of measure behind the CG, and the two front motors need to be 1 unit ahead of the CG. Overlapping props with wings is a bad idea and just throws away lift. You can move the front motors inward towards the center line of the aircraft, meaning that the tricopter will no longer be 120 degrees as you say. This will impact the symmetry of the PID parameters in pitch and roll, but they were not going to be perfectly symmetrical anyway. As soon as you added a wing, fuselage, tail, etc. and all the rotational inertia associated with them, the whole thing became non tri-symmetric anyway, but it is not a problem. Don't move the motors in too far. They still need to have a reasonable lever arm side to side for adequate roll control.

The more generic answer to your question is that things have to balance, but they don't have to be symmetrical in any sense. You can use larger/smaller motors, longer shorter lever arms, etc. to achieve balance. There is a detailed discussion on this topic in the user manual for the OpenAero-VTOL User Manual. I suggest you download it from the end of the first post in this thread.

http://www.rcgroups.com/forums/showthread.php?t=1972686

Also, everyone wants to build tri-copter based VTOL's lately. They certainly can work, but in some ways they are less than ideal. The down wash from the rear motor creates a general down wash field that pushes down on the horizontal stabalizer and makes it more difficult to do a smooth level outbound transition. Quad based designs tend to be better because all of the motors can be far enough out from the center line so the downwash field mostly misses the horizontal stabalizer. You can still tilt the front motors and shut off the back motors if you want.
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Old Mar 10, 2016, 03:08 PM
olivdudu is offline
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thank you so much Ran, for this quick answer . I will redo my drawings according to your advice. I keep on doing the project with a tri-concept, for it allows me a good weigh saving compared with a quad (or a quad plus propulsion engine with booms) , to airship a camera for Aping. I will post a build log on rc group ... In fact, the only use i want for this plane, is to hoover from for landing, in places where I cannot use my usual twin boom pusher ... I will not do any stunt or so, just landing gently in places where I usually can't land

Cheers!!!

Olivier
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Last edited by olivdudu; Mar 10, 2016 at 03:13 PM.
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Old Mar 14, 2016, 12:06 PM
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Ran do you think by having an inverted-vtail it could at least a bit reduce the downwash on the elevator i presume, since it would be higher (or maybe a A tail or how its called with the elevator on top of the rudders)?
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Old Mar 14, 2016, 12:32 PM
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Ran do you think by having an inverted-vtail it could at least a bit reduce the downwash on the elevator i presume, since it would be higher (or maybe a A tail or how its called with the elevator on top of the rudders)?
A "T" tail, or as it is sometimes called an "A Tail" offers a slight advantage but not much. In SFF (Slow Forward Flight) the overall flow field around the aircraft extends well above the top of the wing and well below as well. It would require a very tall tail to get up and out of the downward flow region entirely.
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Old Apr 14, 2016, 09:04 AM
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Quote:
Originally Posted by Ran D. St. Clair View Post
A "T" tail, or as it is sometimes called an "A Tail".
Aren't t tails and A tails completely different things?
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Old Apr 14, 2016, 10:20 AM
Ran D. St. Clair is offline
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Aren't t tails and A tails completely different things?
Sorry, my terminology is confusing, and mostly just wrong...

A T tail usually means a single vertical stabilizer with the horizontal stabilizer on top, or at least near the top.

An A tail is usually an inverted V tail which implies twin booms.

I don't know of a letter based description for a twin boom design with two vertical stabilizers and a horizontal stabilizer at or near the top. I should not have called it a T tail though.

At some point you need a picture, because short hand descriptions don't cut it.
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Old Apr 17, 2016, 11:52 AM
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It's a half H-tail!
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