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Old May 04, 2016, 02:15 AM
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Question
I want to use a vertical tail prop instead of an elevator

I want to use a vertical tail prop instead of an elevator ( please see this thread for a detailed description http://www.rcgroups.com/forums/showthread.php?t=2555678 )
Is it possible to use a pitch stabilizer to control the tail prop as it would control an elevator?
My tail prop would have a nominal thrust to balance the aircraft, and I would like to be able to use the tail rotor as an elevator with stabilizer.
Any ideas?
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Old May 04, 2016, 04:24 AM
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I would try a heli tail rotor assembly + gyro connected to the elevator channel instead of the rudder.
Ronaldo
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Old May 04, 2016, 06:04 AM
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This would be a good starting place.


Scale Flying model of XC-142 VTOL (16 min 27 sec)
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Old May 04, 2016, 12:34 PM
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Quote:
Originally Posted by ronaldopn View Post
I would try a heli tail rotor assembly + gyro connected to the elevator channel instead of the rudder.
Ronaldo
Could I use a gyro to control the tail prop instead of the elevator? Can ch2 (elevator channel) be connected to an ESC and motor?
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Old May 04, 2016, 02:08 PM
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You may consider a constant speed motor and control blade pitch with elevator channel. The gyro could be in head mode so it would keep the tail locked until you add up or down elevator.
Take a look at how 6ch RC helis are setup, should give you some ideas. RC helis have tail rotors which are driven by the main motor through geared shafts or belts. In your case you would need a constant speed motor to drive the rotor.
Ronaldo
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Old May 04, 2016, 02:37 PM
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Couldn't the gyro correct for variations in motor speed? I wouldn't want to spend on a variable pitch prop (cheapy!).
I have the stabilizer shown in the pic, could I use that to "stabilize" the motor with pitch variations?
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Old May 04, 2016, 04:16 PM
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Quote:
Originally Posted by djacob7 View Post
Couldn't the gyro correct for variations in motor speed? I wouldn't want to spend on a variable pitch prop (cheapy!).
Probably yes but I assumed you wanted to have good up and down control. With a fixed prop you would only be able to increase or decrease thrust in the same direction. Some fixed pitch helis (4ch) use this system (tail motor+ fixed pitch blades) but it only works because you have a constant torque in one direction due to the main rotor. The tail motor speed varies to add more or less counter torque and keep the nose in one direction. When tail motor reduces the speed the main rotor torque wins and tail rotates.

With a variable pitch tail rotor and a head lock gyro I believe you would be able to have a very fast and controlled up/ down movement as the blades can reverse pitch. The gyro would keep the tail locked level if used in HEAD/ LOCK mode or it can just smooth the oscillations if used in RATE mode.

Iím not familiar with your gyro so I canít comment. I have a little experience with CP helis and for me it looks like a viable option. You may post your questions on the Electric Heli forum and see if they suggest a specific setup.
Ronaldo
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Old May 04, 2016, 04:18 PM
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Quote:
Originally Posted by ronaldopn View Post
I would try a heli tail rotor assembly + gyro connected to the elevator channel instead of the rudder.
Ronaldo
I connected a motor/esc to the elevator channel and some weird results showed up. With the elevator in neutral the motor didn't turn, but as soon as I pulled the stick down the motor went to full throttle.
Up elevator didn't do anything.
Does anyone understand what's going on?
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Old May 04, 2016, 04:58 PM
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Did you hear the initializing beeps of the ESC?
The ESC needs to be initialized with 0% signal (like it does with throttle stick at lowest position on channel 3). It should work if you hold elevator stick down before plugging the battery (if channel 2 is not reversed)
Please don't do any of these tests with a prop installed.
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Old May 04, 2016, 05:28 PM
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[QUOTE=ronaldopn;34690328]
The ESC needs to be initialized with 0% signal (like it does with throttle stick at lowest position on channel 3). QUOTE]

It works! Did exactly what you said.
But I still have a problem. I want the neutral position of the elevator stick (including the trim) to have just enough thrust for balancing the plane (equivalent to the elevator being horizontal).
How can I achieve that?
Maybe the only way is to select the right prop, and maybe trim the prop length until the plane balances where it should?
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Old May 04, 2016, 05:56 PM
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[QUOTE=djacob7;34690515]
Quote:
Originally Posted by ronaldopn View Post
The ESC needs to be initialized with 0% signal (like it does with throttle stick at lowest position on channel 3). QUOTE]

It works! Did exactly what you said.
But I still have a problem. I want the neutral position of the elevator stick (including the trim) to have just enough thrust for balancing the plane (equivalent to the elevator being horizontal).
How can I achieve that?
Maybe the only way is to select the right prop, and maybe trim the prop length until the plane balances where it should?
This is why you want a RC heli tail rotor rather than a prop, then you can adjust the pitch control links to get the neutral position right (and a heading lock gyro will compensate to a large extent, it is how they are designed to work).
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Old May 04, 2016, 06:05 PM
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"This is why you want a RC heli tail rotor rather than a prop..."
Great idea! I will surely look into using a variable pitch heli prop.
Could I use a pitch stabilizer on either the prop rpm or its pitch as one would do with an elevator?
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Old May 04, 2016, 06:35 PM
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Quote:
Originally Posted by djacob7 View Post
"It works! Did exactly what you said.
But I still have a problem. I want the neutral position of the elevator stick (including the trim) to have just enough thrust for balancing the plane (equivalent to the elevator being horizontal).
How can I achieve that?
Maybe the only way is to select the right prop, and maybe trim the prop length until the plane balances where it should?
If you have a computer radio you can use curves to achieve the speed you want at any desired position. For an instance:
stick at neutral (50%) = 20% (servo signal).
Your setup is far from being practical and I doubt it will work

Quote:
"This is why you want a RC heli tail rotor rather than a prop..."
Great idea! I will surely look into using a variable pitch heli prop.
That's what I've been suggesting since my first post

Quote:
Could I use a pitch stabilizer on either the prop rpm or its pitch as one would do with an elevator?
The gyro will act only on the servo that controls pitch. The gyro senses attitude variation and it doesn't know (or care about) the prop speed and will act on blade pitch to counter act that movement.
When setting up you need to make sure the gyro is making the corrections in the correct direction otherwise the tail will rotate uncontrollably. You can test this with the motor turned off by moving the tail up and down and watching if the tail blades change pitch in the direction that counteracts the tail movement.
When setting up the trickiest part will be setting up gains which are basically how fast the gyro makes the compensation. It will be a trial and error thing though.

Ronaldo
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Old May 04, 2016, 07:40 PM
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I'll be trying several solutions one at a time. It looks like I might have several options.
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Old May 05, 2016, 12:05 PM
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Thanks to Ronaldo's tips, I'm able to control two motors with one radio. The tail motor is controlled with the elevator stick. The elevator itself will be fixed with a slight reflex. The only problem left is the elevator stick is too sensitive - a little movement changes motor rpm too much. I'm learning how to add expo to smooth out the sensitivity.
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