Anyone who has been involved in aeromodelling for a while dreams of having one of those days when everything works right. It doesn't happen often, but when it does it sure is nice!
CanberraUAV had one of those days yesterday. It was a wonderful sunny winters day at our local flying field and we were test flying our latest creations.
First up was the "Vampire Mark 2", a combined plane quadcopter built by Jack Pittar. It consists of a senior telemaster with a 15cc petrol engine, but with the addition of 4 quadcopter motors. It was the maiden flight yesterday, and it was setup with a Pixhawk controlling the quad engines and the rest controlled manually as a normal RC model. We flew with two pilots (Justin Galbraith and Jack Pittar). The takeoff was vertical as a quadcopter, and it then transitioned to fixed wing flight using the extremely simple method of advancing the throttle on the plane while lowering the throttle on the telemaster. Transition was very easy and the plane reached 31m/s in forward flight at full throttle. The landing transition was equally easy. Jack lowered the throttle on the plane while Justin raised the throttle on the quadcopter. No problems!
Given this was the first flight of a highly experimental aircraft we were pretty pleased with the result! Jack is thinking of building an even bigger version soon that will be able to complete the 2016 OBC mission with plenty of room for equipment.
Next up was our JS90 helicopter, originally built by Ryan Pope and adapted for autonomous flight.
This is the flybar version of the JS90-v2 heli from Hobbyking, with a OS GT15HZ petrol engine fitted, along with a Pixhawk2 and a new "Blue Label" Lidar from pulsedlight. We've been flying (and crashing!) this heli for a while now, but yesterday was finally the day when we got to try high speed autonomous flight.
apart from a small gap where we lost telemetry in the north west corner you can see the tracking in the auto mission was great. Once we learned how to tune a flybar heli (which turns out to be extremely simple!) it flies really well. We did have some issues getting it to fly as fast as we want. Above about 17m/s it occasionally pulled back and stopped for a second before continuing. We knew it could do more as it happily flew at over 27m/s in ALT_HOLD mode. With some help from Randy and a small code change to help with tuning we think we've tracked down the cause of that issue and expect to be doing 27m/s AUTO missions next weekend.
Next up was another quad plane, this one quite different from the big telemaster build!
We had been trying to track down a problem with loiter on the Parrot Bebop when running ArduPilot. We suspected there may have been a GPS lag issue, so we wanted to get some flight data that would allow us to compare the performance of a uBlox GPS with the GPS in the Bebop for dynamic flight. We thought a good way to do that would be to strap the Bebop to a plane and take it for a fly. The results were very interesting! For this flight we saw a lag on the Bebop GPS of over 5 seconds, which must be some sort of buffering issue. We'll chat to Julien from Parrot to see if we can track down the issue.
Next we thought it would be fun to see if something else could lift the tiny Bebop. Peter had his Solo there, so we strapped the Bebop to it and went for a fast fly in drift mode. Great fun!
Overall it was a fantastic day! Next week we're really looking forward to trying the Trex700 petrol conversion that Greg has built which you can see in the background in this photo of our build day on Saturday. The build looks really good and we expect it to perform even better than the JS90, as Greg has managed to fit a Pixhawk while still being able to install the canopy. That should reduce drag quite a lot.
The switch of focus for CanberraUAV to VTOL aircraft has been a lot of work, but the results are really paying off and we're having a lot of fun in the process. We hope that we'll have a lot more weekends like this one in the future.
Here are two videos of the telemaster in vertical flight. I thought I was taking videos of the transition between quadcopter and fixed wing flight but my phone ran out of memory and it was too bright to see that it wasn't filming.
Once I saw the photo of the X3 I remembered seeing it a while back, but I wasn't very interested n the concept at the time. Definitely has better scale-ability than the X2. From what I can tell yaw would be controlled by the side rotors until it reached enough speed for the rudder to take over? So essentially it has sideways tail rotors? Are they variable pitch or speed or both?
In the case of a RC version you'd probably want to use electric motors there with just speed control. One advantage is that if you using reversing ESC's you could potentially have high rates of yaw and a secondary "tail rotor", should one fail. The other question is if the main rotor remains powered in full forward flight or is only autorotating? Maybe if autorotating, a gyrocopter could nearly achieve the same level of performance? It would actually be fairly simple I think to have a electric motor to assist with main rotor startup or even hover. That might make for a low profile rotor head as well. What about a counter-rotating gyro using mono-props but with rotor stop to allow them to be used as wings? :-)
I managed to get to the Aero Freidrichshafen in Germany this year (one for the biggest GA shows in Europe) and one thing that struck me there was the proliferation of gyrocopters. They were everywhere, in fact I'd say there was more of them then conventional aircraft. They were also fairly cheap in comparison. The main reason for going there was to look at the full size electric aircraft and their hybrid petrol and even diesel hybrid drive systems. It's really starting to trickle through to aircraft now that hybrdisation can assist in efficiency, performance and safety.
I think a pusher heli is doable overall and I'm always for designs that remove the unnecessary bits! ;-)
I'm a bigger fan of the Eurocopter X3 design. I'm currently involved in a coaxial project, and honestly the mechanics are a nightmare. At this scale, it's hard to shrink down the linkage, so the head become very tall, and creates a LOT of drag. Hurts the high speed performance.
The X3 is very simple to do in scale.
I feel somewhat vindicated by your data points as it aligns with our results. :-) Your expertise is always welcome! I agree that a custom built heli UAV would be the best variation, and at that point we had to resign simply because we didn't have the expertise to develop such a craft in the time given. Maybe you need to put a pusher prop on the tail instead like the Sikorsky X2/S97? That would get it going! I know what it did to a standard off the shelf hex! The thing just doesn't look right somehow hacking around at that speed. Dunno why all the racers haven't done it yet. ;-)
Fixed wings and multi's on the other hand are more common to us and developing that , at least in our minds was more a matter of getting the plane part right and making sure the quad part didn't stuff up our efforts in trying to do so! The carrying capacity of helis is great but in this case we're now only picking up a 100g vial after searching a limited area, which just doesn't need the payload capacity anymore. Using fuel will nearly always get you there too with nearly anything that can fly, but as before I'm concerned about the safety case still. Some might argue that it will be half empty when it gets to the landing area...but I'd argue it's still half full.
We're only expecting to use the hover/VTOL component of our quadplane for less than 2 minutes overall by optimising our flight plan, which means it doesn't really need to have very much endurance. So it can be inefficient without impacting the rest of the flight. That means it can be optimised even further to reduce drag by using small, nearly under-dimensioned lift components. The original testbed only had 5inch props, the competition one will likely only have 8-10inch props for lift and about the same for the pusher. It might "scream" in hover but it won't do it for long before transitioning to the more important flight mode to get right. So no large props, or large inertia moments to contend with on impact, and no fuel either to get it that far.
I used to like the Osprey as an aircraft overall, but now I think of it as an over budget military project that needed to be completed because the generals pushing it where in a perpetual retiring vortex ring state. ;-p But seriously the design is just way to complicated and most definitely flawed at achieving the desired result of a fast VTOL, at least in my completely un-professional opinion. The Sikorsky S97 is closer I think. There's a NASA study on the web that promotes, in particular, electric VTOL aircraft as the next logical development, to the point they are saying it's scalable in design to full size aircraft. I'm holding out for that to come true and in the process try to get a configuration of that working for the challenge.
The weight of an imaging computer is trivial to a copter of this size. It would barely even notice 2kg of payload. And flying in a 25kt gusting wind, again, would be no problem at all. In fact, in the video above, I believe it is about 15-20kt, and it doesn't affect it at all. The only question really, is the limited airspeed of this particular machine, but then it would benefit on the return leg.
Here's a <2kg electric in a... well I don't know what the wind speed is but judge for yourself. It's just not an issue.
Shutting off the engine remotely is standard practice today. Restarting it would require a remote starter, which can be sourced off-the-shelf today.
JB, Couple data points:
I have a <2kg electric heli that flies at 35 m/s for 5 minutes. So no, it won't do the competition, but just as an example of what is possible. I have another running lower rotor speed that can do 25 m/s for 20 minutes with a S100 camera.
My gasser, I've had it flying circuits at 25 m/s in auto mode without issue. I've had it up to 30 m/s but that's about it. But note in this configuration, it's extremely un-aerodynamic. It's a flying brick with extra fuel tanks strapped on the sides, and basically a shovel on the nose intended to mount a camera but which will not likely happen. I was hoping I could get it to balance with a camera on the nose, but I'd have to add a lot of ballast to the tail. I'll probably try to convert it back to a clean configuration.
Previous to the addition of the camera support and fuel tanks, I hit 35 m/s while actually trying to fly slowly.
The trick really, is to design a UAV heli from the ground up, with the payload and fuel tanks properly integrated in an aerodynamic fashion, instead of the current situation where I'm taking an aerobatic design and mounting components externally.
Also, currently the speed is limited more by engine power than rotor aerodynamics. It's nowhere near the Retreating Blade Stall speed.
Heli's can perform quite well for endurance and speed, much better than quads, just look at robs G380, a very small heli, and how it performed compared to tons of other platforms for the figure 8 racing.
With that said, A plane is a very good solution as well, the challenge is the additional drag when adding the VTOL component. I think a tandem V-22 Osprey style solution would work well as the drag inducing VTOL component becomes part of the plane, although, to do it right I believe you would need collective pitch which adds in a lot of mechanical complexity.
Maybe a tricopter configuration with it integrated into the wings and the tail some how?
Maybe the Vtol component could be deployable and folded into the plane almost like landing gear after it is taken off?
I think there are many ways to skin the cat and I honestly think a heli or a VTOL plane could achieve the requirements you set.
As for safety, any aircraft at that size is a serious safety risk. A large plane with a 20+ in prop spinning, a Large quad with 28"+ props, or a heli with a 700mm blade or larger is all a very big safety concern. The nice thing with a plane or a heli is there is at least a chance of gliding down or auto rotating. A quad or multicopter is pretty much a falling heavy brick when something fails.
Re the Navio+ - got it working OK however I crashed it and tore off a connector - have not flown it again.
Was not happy with the compass errors I got.
I second the safety case with the heli, I don't think it will be easy. Getting through the deliverable will be harder now that it's limited to the top 20 only. I'm expecting a few teams to be caught out on the safety case this time around as it's likely to be scored heavily in that area this time, even though it appears their rules might be more accommodating. It's a numbers game, we went from 80 teams in D2 to 25 or so in D3. There will be more I think this time.
Until now I've been testing it with Arducopter code and I didn't interact with the autopilot and pitch for forward flight at all, instead I simply used a extra RC channel to control the forward thrust motor only using the finger dial on the Taranis, and arducopter controlled attitude using the props...it simply maintained level flight and I would roll/pitch to turn like normal fixed wing, but without using the wing control surfaces at all. Even without the wings the hex flies completely horizontal following the thrust angle of the pusher which in turn significantly reduces frontal area and drag. As a pusher hex it would hover at 8A and cruise at 60kmh at around 12A and nearly 100kmh at 23A. It's weird but works! It's also a pain to keep track of as it only a 250 size! ;-)
Once airborne a quick transition to forward flight (inside 10-20 seconds after launch) into the wind is similar to taking off into the wind with a wing. I don't see a requirement for extended periods in hover..the less time spent in hover the better, it needs to get off the ground, point in the right direction and cover the distance asap and then land. Rinse repeat. Only better yaw control is required in horizontal flight which I'm hoping to resolve with the new VTOL firmware which also has proper control surface actuation for forward flight and the custom airframe build with rudders!
BTW Even if it's a little off topic, how did you go with the Navio+ build? I finally dived into linux now and got it all working on my test quad, with wifi AP, live HD video, telemetry RF900/Wifi/3G using mavproxy etc. Even figured out FTP, webserver and OpenVPN/tor etc not just for on the quad of course! Have some Odroid C1's and XU4's on the way to test once they release those APM versions. Still chewing on getting the high power wifi AP working though.
@Rob_Lefebvre - I also think that a gas helicopter will have a difficult time. Sure you can carry the fuel however can you fly the same distance against a gusting 25kt wind with a camera and imaging computer? Can you hover and land and shut off the engine? The FAQ does say you can keep your motor running however you must have a clutch that will not in any circumstances connect the motor to the rotor in any failure mode. I am not sure there is any clutch on the market that satisfies the safety case.
@Sam - yes you are probably right however the rules say that the max wind is a 10 minute average of 25kts. I tried flying a quad in 20kt winds a couple of days ago and it was pretty pitched down. I would hate to be running another motor on the plane as well. How do you tell the quad autopilot that the other motor is running and not pitch down as it would want to do?