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Old Dec 02, 2010, 09:42 PM
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simplest

There is a saying that necessity is the mother of invention. I couldn't find any machinist around and so, after supper, I started thinking and I came up with the simplest arrangements yet; made from common materials, only a drill press needed for fabrication.

I went to Lowes and found some aluminum C-channels that fit nicely inside each other. They are intended to be edgeing on plywood. They have 3 sizes. I chose the nominal 3/8" and 1/2". One little piece of each size channel is required with three holes in each piece.

In the sketch below the light blue piece is the ordinary prop adapter which is mounted to the motor shaft and holds the lower channel in place with an o-ring.

The upper channel pivots on the lower channel through the red pin.

The purple-ish bit is aluminum flat bar to make the flybar.

The green bolt secures the flybar and the prop (no shown but on top of and perpendicular to the flybar) in place with a nut on top.

Still thinking about the best way to keep the flybar and the prop in the correct position rotationally.

I should have the first prototype done in the next day or two.
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Old Dec 03, 2010, 04:09 AM
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Quote:
Originally Posted by v22chap View Post
Ask the engineers on the V-22 and that is why I did it on my V and I just did swash plate tilt not the whole nacelle like they do and I could tell a difference . Might be different for your bird ... but like I said I never tried in though ... it might work too !!!! That is what makes this R/C VTOL so fun as there are no set aerodynamic principals set out for us to follow and everyone can just test it out and have the fun of seeing something new come to life !!!!
Translational lift will tend to dampen sideslip if the rotors are tilted inward. But don't expect it to make the ship self-straightening. The dihedral effect only applies to fixed wing planes, and is not always correctly explained
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Old Dec 03, 2010, 05:57 AM
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Originally Posted by Brandano View Post
Translational lift will tend to dampen sideslip if the rotors are tilted inward. But don't expect it to make the ship self-straightening. The dihedral effect only applies to fixed wing planes, and is not always correctly explained
On my prototype, I made the tilt angle ground adjustable so I can test the effect of tilt-in. Now that I'm going to stabilized rotors, this may be a moot point.
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Old Dec 04, 2010, 04:37 PM
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1st prototype flybar/prop adapter

Here are some photos of the first try at making one of these.

I spun it up and I noticed that at low RPM it does the "flybar correcting wobble" thing, but as RPM increased it did this less and less. This makes me think the flybar is too heavy and I need to shorten it. Need to read up so more on flybar design.

Now for the testing and refining.
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Old Dec 04, 2010, 08:26 PM
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testing results

I did some testing with the flybar/prop this evening.

As originally built I think the flybar was too long. When spun up to hovering speed, the centrifugal forces were too strong and the prop behaves as if it isn't free to pivot at all.

I then started cutting the flybar back little by little. After several trimmings,it seemed that it was starting to get a little better but I then ran in to a new problem. Because the feather hinge line does not line up with the prop's cg; when rotating; the prop tilts off to one side and stays there. The weight of the prop leaning over cannot be overcome by the smaller flybar anymore and it just stays to one side or the other. I tried holding the plane upside down to see if this would help, with gravity assisting the prop to stay on center but no go.Even upside down, the prop would go off to one side when the motor was started and stay there.

Now I think I know why (at least in part) helicopters have the feather hinge/feather shaft lined up with the blades.

I can't see any practical way to line up the feather hinge line with the cg using any ordinary prop, so the only feasible solution may be to use a helicopter rotor. Not the results I was hoping for.
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Old Dec 04, 2010, 08:47 PM
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Before you give up on this .. I would say .. try a wire flybar / weight / or paddle arrangement the diameter you had the first setup that worked . This would make it more like the smaller helis that use this type of non collective head setup .. and see if this would maybe work ... and you can keep the same length that seemed to control ... but add weight or remove it from the end .. And maybe try using heli flybar paddles also .
Just a couple ideas to try
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Old Dec 05, 2010, 07:48 AM
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Thinking about this some more over my first cup of coffee this AM, maybe I can bend the flybars down to lower the cg of the prop/flybar assembly so the the cg is closer to the feather hinge line??

If the upper c-channel were replace by square tubing which would nest inside the lower C-channel, prop mounted above the square tube, flybar mounted below the square tube, the balance about the feather hinge may come out better.
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Old Dec 05, 2010, 07:06 PM
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I came up with this design this afternoon.I substituted a prop saver for the upper c-channel. I cross drilled the prop saver for the feather hinge pin. The prop saver bolts act as the fly bar.

I don't know if I'm there yet, but it is much better than the previous prototype. The feather hinge line is much close to the prop. It only takes very short flybar bolts to make it work. The machining is off a little so it vibrates a lot when I increase the rpm, but it is starting to look hopeful.
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Old Dec 06, 2010, 04:41 AM
Vacuum Tubes Forever BCT2/BCR3
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Just found this link. Some links that might be of interest.

http://en.wikipedia.org/wiki/Boeing-Vertol_VZ-2
http://en.wikipedia.org/wiki/LTV_XC-142

Have you considered using puffers to control yaw and pitch and motor mixing to control roll? A small ducted fan could be used to provide air for the puffers.

Interesting project!!!

JohnB
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Old Dec 06, 2010, 05:57 AM
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here is one with a ducted fan in the tail for pitch control.

I like F&T's approach better myself.

VTOL R/C Tilt Wing Hover (1 min 30 sec)
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Old Dec 06, 2010, 09:44 AM
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These home-made hubs have the flybar at 90 degrees to the prop (like a normal heli) but all the coaxial helis (and the mSR and piccoZ) have the flybar at 45 degrees to the blades.

I don't pretend to understand why it works, but it looks significant.
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Old Dec 06, 2010, 08:41 PM
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Originally Posted by RobinBennett View Post
These home-made hubs have the flybar at 90 degrees to the prop (like a normal heli) but all the coaxial helis (and the mSR and piccoZ) have the flybar at 45 degrees to the blades.

I don't pretend to understand why it works, but it looks significant.
I'm with you. I don't understand why they work or why the smaller lead angle is more stable but they are. The little PicooZ helicopter have an even smaller angle between the flybar and the blade and I think they are more stable still.

It may even be the case that for the VTOL application, the extra stability of a 45 degree flybar is needed??
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Old Dec 08, 2010, 11:52 PM
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Tilt Rotor coaxial helicopter transitions in a second

The transition has a lot of G's
Tilt Wing Coaxial Helicopter VTOL RC (0 min 42 sec)

Tilt Wing RC (0 min 18 sec)


Please follow my youtube channel i will be coming out with new videos of different hybrid aircrafts from my lab each month like heli-chutes, tilt rotor free wings , stol jet gliders etc.
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Old Apr 23, 2011, 01:59 PM
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hey F&T could you post up some close up's and details on your control vanes on this rig?
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Old May 10, 2011, 01:15 PM
We Do It With FRQZ
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i cant believe u did it again...
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