VTOL Tailsitters without the quad attached!(Look, ma! No multicopter!) - RC Groups
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Oct 26, 2017, 02:13 PM
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wazoo22's Avatar
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VTOL Tailsitters without the quad attached!(Look, ma! No multicopter!)


Most of the VTOLs you see are hybrids, particularly the tailsitters. Airplane with multicopter attached. But there's another way, and it's not easy, but it's really fun!
All these airplanes flew, but the little bug is the best so far.. It's a hot number for old eyes and reflexes.

Concept:
A fixed wing airplane needs only about 40% of it's wing area in cruise. It's only at landing and takeoff that all that area (lift and drag) are needed. So, transfer the job of takeoff and landing lift to two motors, coaxial so one can be shut down in flight and for yaw control in vertical(hovering) flight.
Front motor does about 60% of the work on takeoff or hover, and swings a big prop, which folds neatly. Yaw control comes from varying the torque developed by each motor inversely, Once you get it tuned, it works very well.
Both motors together need to produce about 1.8 to 2 times the gross weight, so you can operate at less than 70% power in hover and you will have extra throttle travel to yaw the plane till it's in level flight, where the regular elevons take over.
Control comes from a MicroVector and a KK2.1.5.
MicroVector operates with zero stabilization in hover (essentially a pass-through state) while the little KK2.1.5( with the marvelous aid of Happy Sunday's OpenAero VTOL software) drives. The transition to level flight is the hardest part, and you better have two mistakes of altitude when you first try it. Then the KK is p[ass-through, and the MicrVector does the work.
I'll continue with video if there's a lot--OK, some--interest.
Thanks, and keep flying!
.
Last edited by wazoo22; Oct 26, 2017 at 02:43 PM.
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Oct 26, 2017, 04:26 PM
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I like the idea of using two motors stacked axially since the cruise prop can be optimized, but I would think you would have major yaw control issues in hover especially while descending unless you can "blow" a good percentage of the elevons with high velocity prop wash. I've built quite a few single rotor "blown surface" VTOLs and they all have had control issues in hover and descent. But it sounds like you have already flown this bird so show us video !

All of the control can be done with KK/OpenAeroVTOL. Unless you are using the Micro Vector for some specific reason (GPS ?) OpenAeroVTOL can provide a smooth transition from hover to FFF.

Here's a video of one of our 2 rotor vectored thrust (no control surfaces) tailsitters showing smooth transitions.

Two Rotor VTOL with 2 Position Autolevel (1 min 53 sec)
Last edited by OwlCity; Oct 26, 2017 at 04:39 PM.
Oct 26, 2017, 05:53 PM
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Those are amazingly large motor mounts!
Oct 27, 2017, 06:49 AM
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wazoo22's Avatar
Quote:
Originally Posted by OwlCity
I like the idea of using two motors stacked axially since the cruise prop can be optimized, but I would think you would have major yaw control issues in hover especially while descending unless you can "blow" a good percentage of the elevons with high velocity prop wash. I've built quite a few single rotor "blown surface" VTOLs and they all have had control issues in hover and descent. But it sounds like you have already flown this bird so show us video !

All of the control can be done with KK/OpenAeroVTOL. Unless you are using the Micro Vector for some specific reason (GPS ?) OpenAeroVTOL can provide a smooth transition from hover to FFF.

Here's a video of one of our 2 rotor vectored thrust (no control surfaces) tailsitters showing smooth transitions.

https://youtu.be/fxYCPhQqK8U
I saw this a while ago. Very nice, smooth transitions indeed. But I need to be able to shut down the lift motor and cruise efficiently.
What I'm trying to do is go one or two steps beyond what the KK2.1.5 board can do, like GPS, RTL and autonomous flight. The Vector offers all of this except fully autonomous flight, and active, competent development. I'd much prefer to stick with only one FC, and I've grown to like Happy Sunday's very versatile concept so well that I just can't bear to go back to a system where I have to live within the limits of someone elses' concept. OAVTOL allows me to "roll my own" without being a coder, or particularly adept with arcane languages and symbols, like the Pixhawk.
As for yaw control, that problem is solved. I Program 30% yaw volume, opposite polarity, into the lift motor mixers. Then I turn on the P1 yaw gyro for those motor mixers, use a lot of "P", moderate "I" and I limit, and she stabilizes pretty well in yaw, as the video will show you.There is also plenty of yaw stick authority, provided you have sufficient power available beyond hover to allow the motors to have some lift headroom. Those motors were SS2208, and worked well with a full battery, but once the juice got low, hover was not safe for landing.I've gone to SS2212-980s. Lots of power now.
My one transition to date was filmed by my wife---with the camera in "photo" mode-- so I only have a lot of video of hover testing, with both models shown. I'll try to include video here. I'm a total novice with video- be warned!
This is the very first hover test- being very cautious. I have zero experience with multicopters, and need to get up to speed there. Ignore date on video- is wrong.

hover testing 2 2017 10 08 (2 min 47 sec)


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