The upcoming 3.5.0 release of APM:Plane includes support for QuadPlane - a hybrid plane/multi-rotor that allows for high speed long distance flight with vertical takeoff and landing.
The above video shows a converted HobbyKing Firstar 2000 doing a fully autonomous mission, with VTOL takeoff, followed by automatic transition to fixed wing flight and then a VTOL landing. The planes builder, Jack Pittar from CanberraUAV, is shown with the plane below.
The plane itself was fairly easy to build, with the simple additional of rectangular section aluminium arms on the Firstar wings and 4 quad motors.
One issue we found is that the battery we are using (a 3S 4Ah 65C) doesn't handle the 65A needed for vertical takeoff well, with the voltage dropping to 10V on takeoff. After takeoff completes and it transitions to fixed wing flight it quickly recovers. We will be changing the battery setup for future flights.
A second issue is that the wings tend to twist a bit in flight, especially when yaw is commanded. That greatly reduces yaw authority when hovering. We are still thinking about the best ways to prevent wing twist.
The new QuadPlane support is documented at http://plane.ardupilot.com/wiki/quadplane-support and is included in the 3.5.0beta1 release (I will do a separate blog post on that release shortly).
In the near future we expect to add support for other hybrid frame types, including tilt-rotors and fixed wing aircraft with other types of multi-rotor frames attached.
This QuadPlane follows on from our earlier Senior Telemaster QuadPlane which used two Pixhawk flight controllers.
We built the Firstar QuadPlane to test the new code where a single flight controller board running APM:Plane is used, which makes for much simpler operation. We plan on now building a much larger version, with a 50cc petrol motor for fixed wing flight.
Comments
@JB and Iskess,
The QHOVER mode will actually weather vane now. With no stick input what it does is try to maintain zero yaw rate. It doesn't try really hard though, and in testing (both in simulators and a real quadplane) it does tend to weathervane. If you find this isn't sufficient in a real flight then please provide a log if you have one and I can have a look at how it could be improved.
Note that basing it on the estimated wind direction would only work if the plane had been doing sufficient forward flight beforehand to build up an estimate of the wind direction. The wind direction is not actually properly observable while holding in a hover. You could try to infer it from the way the plane is drifting, but that will tend to be quite inaccurate for a quadplane except at high wind speed because quadplane aerodynamics don't tend to be very symmetric. They naturally tend to drift a bit.
More interesting I think is the landing transition for NAV_CMD_VTOL_LAND. I originally made that try to hold the heading from the landing course, because I thought that is what users would want (if you plan a landing on an east-west course I thought it would be good to hold that heading so the plane lands the way the landing is setup). I found that as I upped the wind in the simulator that the quadplane became quite unstable in the landing if it was a cross-wind, so I changed it to use the same system as QHOVER, and it now weathervanes the tail around so it is pointing into the wind for the landing (if there is sufficient wind to overcome the yaw resistance). That works really nicely and landings in high wind are quite stable.
Cheers, Tridge
I second the weather vane mode and have mentioned it elsewhere before. I think Tridge is fairly busy though! ;-)
With a quadplane it consumes a fair bit of power to maintain position and heading out of the wind, unlike a standard quad without wings, the quadplane has to fight any lift the wings and rudder are producing whilst the quad motors tilt the aircraft. The issue is that tilting the quadplane in any direction like a normal quad, even forwards, results in negative lift being produced by the exposed wing surfaces, which in turn requires even more power from the quad motors to maintain altitude. The plane starts fighting the quad in a regressive loop.
The other advantage of pointing the aircraft into the wind is that the plane motor can be used to counter the wind to give lateral positional control in exchange for a small amount of power, requiring the quad motors only to provide enough lift to maintain altitude. In fact using the plane motor results in some extra lift generated by the wings which in turn reduces the load on the quad motors, depending on the wind.
Ideally, if the wind is significant enough to produce some lift from the wing surfaces (ie above a setpoint/level where the quad power consumption is consuming more to hold position out of the wind in hover), the weather vane mode would use the quad motors to point the nose into the wind and possibly even increase the angle of attack of the wings to produce more lift in a hybrid hover mode like a bird of prey. I think this will considerably improve quadplane hovering in windy conditions, but is unlikely to be that helpful at low wind speeds, say under 4-5m/s.
There are only limited reasons to maintain heading in hover, typically on a quad this is because one wishes to point a camera in a particular direction. On a quadplane using a camera on a turret would likely result in better quadplane hover performance, without impeding camera view angles..
I think in principle the quadplane should be operated as a airborne "hovercraft with unlimited altitude", rather than be flown like a quad.
That means that the quad never does anything more than maintain altitude at a level attitude, and every horizontal axis movement command is translated into the aircraft yawing to that heading and applying the forward plane motor to move laterally. The plane motor could even potentially be used in reverse thrust as well for example to counteract small gusts. Being able to calculate exact realtime wind vector would likely result in the most efficient use of available lift components to achieve the desired pathway. Maybe differential dual airspeed sensors could work? I'd like to see a single multidirectional ultrasonic airspeed sensor one day!
Originally I proposed that the plane and quad modes do not actually "transition" from one to another per se, rather that the user can "tune" what level of control is applied to whichever control mechanism, be that quad motors or plane surfaces and horizontal motor, which leaves the possibility for lifting body type hybrid quadplanes with minimal wing surface areas and resulting low drag. Imagine a lifting body design with tiny high stall "winglets" that can VTOL with minimal quad components. In a new breed of quad racing one could gain a very substantial amount of speed similar to a pylon racer, but still have the low speed high-G cornering ability of a quad! :-)
Overall I think a quadplane does not have to adhere to conventional flight "physics" in the sense that it has to fly as either a plane or a quad, rather that it can be designed to seamlessly fly using both, depending on the lift state of it's individual components.
Anyways that's my two cents.
Regards
JB
How do you feel about changing the QHOVER so it doesn't try to hold heading, and instead simply weather vanes into the wind so the quad isn't fighting the tail. Or even better, use the wind direction calculation to actively maintain a heading into the wind.
Hello Tridge
Thank you for your quick response.
if I understand correctly I replace the Flight Mode in the parameter list.
I use Mission Planner 1.3.34.2,
where can i da insert the commands?
greeting
Rainer
@Daniel, I don't think tiltrotor will be very difficult but I haven't had time to work on it yet. I'll certainly announce when it is done, or if you are interested in helping with the code then let me know and I can give you some pointers.
@Rainer, the extra flight modes are the same as existing flight modes. You just edit the FLTMODEn parameters. So if you want flightmode 3 to be QHOVER then you would set FLTMODE3 to 18.
I don't know which ground stations have added the names for these flight modes yet. If the new modes aren't listed then you will have to edit the flight modes manually in the advanced parameter list.
For the auto-mission commands, that also needs GCS support to add it to the editor.
Which GCS are you using?
Cheers, Tridge
WOW WOW WOW AND WOW!! Thank you so much andrew, I have been looking for something like this for quite a while now. I was almost starting to try and develop it myself! Amazing work, certainly a game changer!
When do you think you will have support for tiltrotors? I would love to have a talk with you to see if i can help in any development.
Thanks again!
Daniel
Hello Andrew Tridgell
Thank you for the wonderful work.
I have some questions about the Flightmods and navigation,
How do I get the Flightmods
17: QSTABILIZE
18: QHOVER
19: QLOITER
activated or where they must be inserted, a screenshot would help.
the next problem
how do I get the commands inserted
DO_VTOL_TRANSITION
NAV_VTOL_TAKEOFF
NAV_VTOL_LAND
a screenshot and a description would be helpful
best regards
Rainer
I have written and video'd a build log for a VTOL conversion of a Volantex Ranger Ex
http://px4.io/portfolio/quadranger-vtol/
Good work tridge!
Hi Tridge,
JB Aletky is correct that the yaw authority can be increased or decreased depending on the frame type use. In this case I understand that the flex is along the wing axis and therefore a standard quad X frame should provide additional yaw authority. So it doesn't make sense that the wing twist should reduce the yaw authority.
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