I've been working on a new helicopter platform the last few months. Based on an MSH Protos heli which I chose because it's an extremely light weight platform, weighing in at only ~1200g without battery. It has a full belt drive which I much prefer to gears as it's quieter, lower vibration and more reliable. I've had a few problems with it because the belt drive makes a really awesome Van deGraaf generator... not a good thing on a UAV. But I solved that, and am conducting test flights now.
The flight controller is a modified PX4v1. I replaced the switching regulator with a MIC29300, so that I can run it on 2S direct with the servos. Main motor power is 4S 5000, typically this heli would run on 6S 3300. Using the MSH stretch kit and 465mm Spinblade Asymmetric blades. In otherwise standard form, this heli flew for 17 minutes on an old crusty battery, in -10C temperatures.
I have now added a subframe to hold an extra battery, FPV gear with a camera in the nose, and a vibration damped NADIR camera mount to be used for aerial mapping. The idea is to develop a mapping UAV that is superior to a multirotor, offering a valid alternative to a fixed wing for short to medium range missions. The VTOL capabilities would eliminate all the nastiness of catapults, and controlled-crash landings with onboard cameras in rugged areas. Even the price is attractive at about $400 for the basic kit with motor and ESC (no servos).
Specifications show the advantage of a heli platform. This machine has an AUW including the batteries and camera of only ~3kg. It is 80m long, and about 15cm wide not including the extended legs, and 30cm high. The blades fold for easy transport, without requiring any lose wires or vibration-prone electrical connectors as a folding multirotor does. It actually looks much bigger on the table than it really is. This seems to be very good compared to multirotors I've seen with the same performance. (payload and duration)
Vibrations are always a problem with helis, but manageable with the right design and construction techniques.
Arducopter really makes helis worthwhile. You could buy two entire heli systems including a Tx for the price of a single DJI Ace One non-waypoint controller. Or 7 for the cost of a single Ace One waypoint enabled controller. I strongly prefer the PX4 controller over the APM and Pixhawk, because it offers 32-bit performance in a small package that is easier to mount in a heli frame.
So does it work? I took it up for it's first photo tests yesterday, and it worked beautifully. Better than 80% photos are usable. It flies for 20 minutes in a hover with old, cold batteries (-5C). I'm hoping for closer to 30 minutes while actually moving (helis are more efficient moving than hovering), in warmer weather with new batteries. It should have an easy cruising speed of 15 m/s with little or no reduction in flight time. At 20 minutes, this would offer an 18km range, and 27 if it can do 30 minutes. If you wanted to do FPV and not mapping, you could configure it with a 3rd battery in place of the SX260 and fly for... 30-45 minutes, and a range of up to 36km. Top airspeed is still TBD, but probably 20-25 m/s.
Wind penetration and stability is excellent compared to both multirotors and fixed-wing. You could do a mapping mission in winds up to 40 km/h with little effect on stability or duration.
If the success continues, I'm going to consider building a large gasser heli. This would allow flight times up to 2 hours, or payloads on the order of 10 lbs for 30 minutes. So you could map large areas, or even perform light duty spraying operations. I'm thinking about local application of a herbicide for things like Giant Hogweed elimination, that sort of thing. Such a large heli does pose significant danger and should only be used in industrial, agricultural or remote areas.
Comments
Auto-Autorotation may be coming to Arducopter at some point in the future. A university group has already coded it:
Still there's no easy cure for servo failure... ;)
I worked on a drone with a ducted fan and vanes for anti torque. The execution was not elegant and the control was marginal. Actually had an uncontained failure of the fan on this project. Read ugly.
To FroJoBMX - I'm not certain if pitch loads are the driver on chord length. Practically, I think not. Pitch center migration with angle of attack will drive pitch change loads. So...you end up with the symmetrical blades because they have manageable loads due to a fairly limited pitch force. Go to a large lifting low aspect airfoil and the pitch change link would have to be quite large.
There was a thread here on autorotation being the holy grail. Should be fairly simple - just weight up the tips and be sure the low pitch angle on the blades is low enough to allow the free stream through the rotor to keep it windmilling. Using an ultrasonic proximity sensor and you could probably automate the flare and execute a reasonable (controlled crash without damage) landing. I think it would be a very worthwhile competition....Imagine intentionally running out of gas and having the helicopter autoland instead of freefall into broken parts.
Fackler, you are the man. It is very clear that you have alot to teach. Please carry on.
The argument from anti-complexity... A DFC rotor vs Arducopter; you decide what is truly complex. It is a huge compliment to the developers that it is just assumed that the Ardupilot system is white box simple. I do find it amusing though. The anti-pitch-change mechanics argument is like swallowing a camel and straining at a gnat.
But that is ok. Helicopters are not for everyone. :)
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Can you think of a reason why we could not see dramatic increases in chord length? I know for full scale helis, the swashplate forces are a limiting factor on chord. But judging by modern 3d flight, this is not a problem for us. I do alot of 3d printing. It is possible to print a nylon mold, for composites, and ABS blade cores. Foam cores could be molded too. Not my design but this is along the lines that I'm thinking of. http://www.thingiverse.com/thing:128964
Also, Rc Tiger Motor has some very sexy blades and motors.
Tiger Motors
Tiger Blades 28in (450 size)
Joby Motor
Ide like to try the Tiger blades on my 450. But it flew off of the side of a mountain( different topic).
Seems to me that a direct drive pancake motor and the Tiger blades would be a great place to start for increasing flight times. Hmm a multi blade head and direct drive main. We would need new frame side plates and a main shaft coupler.
If the tail rotor drive mechanisms where beefed up a bit, two helis could be joined. Now we are really talking about redundancy. tandem or side by side. OR if the there were a second tail rotor port( turned by 90* under the rotor plane) A collective/cyclic quad would result.
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Lots of blade twist. While examining the Sikorsky X2 the chord tapers in both directions from a central point on the blades. Im guessing that they are attempting to minimize flow reversal effects. If that is true, then would it mean that they would have a similar, if any, application of twist? For that aircraft, I could see retreating blade pitch to being set at zero.
Twist in a hover seems like a great idea, but aren't the aerodynamic trade offs really felt during auto rotation and at high speed? How could this be optimized? Where you alluding to an higher harmonic control system that has oscillators in the pitch control links? I have my own higher harmonic design. But what is the status of the Hughes design? Didnt they do some testing at AMES?
Yo.
Cold jet rotors, tip jets, powered maple seeds, ducted turbines, thrust vectoring, 3d airplanes...
BTW, it is possible to have less than 2 rotors. You can have a single rotor. Use vanes for controlling attitude. It's been done.
Depends on the airspeed. As retreating blade stall is approached the N-per rev increases exponentially before a full blown stall/ rollover pitch up and play dead.
Active control was experimented by Hughes aircraft as HHC (Higher Harmonic Control). They implemented active trim tab on the blades. There were some significant increases in performance and reductions in N per rev.
Servo tabs accomplish one thing, they obviate the need for hydraulics. The swashplate of the Kaman is tiny compared to say a Bell UH-1. - a similar gross weight aircraft. The servo has an actuator which can be trimmed in the cockpit allowing lift of the blades to be equalized in flight. It is aft of the blade. Because of the span position of the tab there are large drag losses with this system. The Bell 2154ST also had a linear actuator on a pitch change link. Obviously, there were artificial limits to this adjustment for safety reasons on both aircraft (run away actuator).
Coaxials are the most efficient hovering aircraft today. Tail rotors are power robbers.There are modes of flight that are not friendly to coaxials.
IMHO complex is not necessarily bad. C'mon people, they all said the helicopter was too complex...
Some important thoughts - It takes energy to produce vibration. Any reduction in vibration will result in freeing up power for useful work. We are now in a stage of flying that finds microprocessor controlled flight acceptable. Materials are close to miraculous. We are in the Golden Age of flying!
Fackler,
How much of the vibration on the retreating blade is caused by increased pitch and flow reversal at cruise? How much pitch is wasted on countering flow reversal negative lift?
Have you seen any systems with active twist?
Do Kaman servo flap blades pivot on the feathering axis? How much twist do the servo flaps cause?
Here is a book about hardcore Rotor Dynamics. Brilliant read.
Helicopter Flight Dynamics - The Theory and Application of Flying Q...
My key interests are top speed, drag reduction, hover efficiency, then anti-vibration.
The Unicopter webmaster has a lot of really cool ideas. Too bad he does not post here. We should invite him.
My key gripe is: people do a cursory trade-off analysis and then decide that they have found an ultimate airframe. I believe that this falsely dichotomous attitude hinders UAV development. You need to use the right tool for the job. All rotorcraft are multirotors. The minimum number of rotors is two The minimum number of independent controls is 4.
Most UAVs are blatant copies of some thing else. It is ok to copy, but we are not innovating when we do. The fact that a DraganFly costs $40k and cant out class an airframe that costs 10% as much is a problem. There are many airframe types that can outperform Sikorsky helicopters and multirotors in every catagory. But the community at large does not consider them. Perhaps because they are unaware.
An argument from an anti-complexity view point is fallacious. If you cant fly well, and crash alot, then get a easy to fix airframe, obviously. But, if you're are flying 100km, you clearly want range and are more likely to land than to crash. In the ideal world, airframes need only be designed to fly well. That should be our goal.
Collective pitch mutirotors, like the Stingray break the mold. What the Youngbloods are doing should be commended and accelerated. Collective pitch is the key enabling technology in multirotor endurance, safety, and size. However prejudicially deciding that it is too complex is a bad idea. Especially when you consider that an internal combustion power source is 45x more energy dense vs. Lipos. Auto rotation should be the holy grail for multis.
Coaxial Helicopters and Side-by-Sides, both compounded with wings and pushers, are the way of the future. The Sikorsky X2 and Mil V-12 have eluded to this. Compound helis, like the Cheyenne, are clearly better machines than what we fly today. Perhaps the Air Force deciding that the Army's Cheyenne was stepping on its toes is the reason that Align helicopters are missing a pusher and wings. It is too bad that current arducopter code does not support these options. *cough *cough
I would love to see a new kind of attitude emerge in the community. One that considers parts as parts, and then innovates, remixing as necessary. Even using COTS parts, we can already move beyond what is possible today.
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Moving beyond a COTS model is the second required phase.
We need to design a new rotorblade/head system. It doesnt need to be expensive, just designed with reynolds number in mind.
A new airfame structure that makes use of these blades in a new layout is also key.
Perhaps the Stingray could use a few upgrades.
As a dynamics engineer, and working for a company that designs, builds and tests rotor blades, I can assure you there are only a handful of engineers - literally - that have a grasp of what rotor dynamics are all about. I see what some people write and just shake my head.
My primary concern, to get the discussion back on track, is helping in an understanding of the things that screw up video performance since that seems to be part and parcel of the drone community.
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