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
I have a new Pixhawk sitting around which was going to replace my APM2.6 in a motor glider. But I am reluctant to change anything that is working well. So the thought occurred to me that I may try it in one of my TDR's. Arduplane has had a lot of work done on it by some very clever people so I am wondering if Arducopter has that same level of development to be as reliable? The TDR is a lethal weapon so I need to be sure it's safe and will work with a ppm Dragon link Rx. LRS. Anyone out there having problems? Or anyone NOT having problems.
Hi Rob,
yes, I twisted them a little bit by hand, you know - they are small and I am tall :-) (couldn't do it on the SAB). On the SAB blades you could see the top carbon layer in 45° layout, they know why. Look at a polar diagram with lift vs. alpha and you see how sensitive it is.
You mean you tried to twist the red-tips by hand, and found them flexible? I never even through to test that, but it's another valid consideration. As is the comment about trailing edge thickness.
Hi Rob,
I saw today a Thundertiger E360 with Spinblades symmetrical Red Tips, they look quite o.k., but don't have much torsional stability. Maybe they twist and this would ruin the lift distribution, creating excessive drag.
The SAB blades for this E360 are very good, with the sharpest trailing edge by far.
The Spinblades 105H (asym.) tail rotor blades on a Logo 600 SE seemed to have the same problem as your blades and they had an almost 2mm thick trailing edge too. I can't imagine that they perform as advertised.
Maybe you can get your Spinblades replaced.
The Spinblades are nice, and perfectly balanced. However, they have a nasty leading edge. There's a sharp ridge that I presume remains from the manufacturing process. Some other blades have this too.
Hi,
@Rob: the very short answer Cm = moment
@Carles: try a standard plane without a tail (yes, Cm is very important for flying wings)
I try to give a very simple answer with my limited English. The flow around a 3D body (let's call it wing in our case) depends on many things. To be able to understand what is going on we try to break it down as much as possible. First simplification is to use 2D and use a windtunnel or a software to measure/calculate the loads on a section. Basically its all about the pressure distribution along the surface. By definition pressure vectors vertical to the Angle Of Attack are summed and called lift and those in the flow direction are called drag. Forces around a certain point create moment. So the big three are lift, drag and moment. Depending on the Reynolds number, the airfoil section, the AoA, the roughness of the surface, etc. you will see different pressure distributions and the center_of_pressure will change its position unless Cm=0. If Cm is not equal 0, your forces twist the wing, which leads to different forces, which in turn change the twist and so on. Vibrating blades i.e. create more drag. All of this is more or less only of academic interest unless you want to design your own stuff.
I would decide how much maximum thrust I need on my AP-heli and find the efficiency range on the ESC. Set the blades for maximum lift and the ESC on the high end and adjust the pinion to get the needed headspeed for the maximum thrust. If you are lucky you are still in the efficiency range of the ESC for hovering/normal flying. If not adjust for your best compromise. Do this for each of the different blades you want to compare. Now you can compare and report 'best compromise in this application'.
p.s.: Spinblades is usually a quality product and they have asymmetrical tail blades as well.
I dont know why would you need to know anything else apart of the lift and drag coefficients with the given angle of the attack.
Cm?
Hi,
@Rob: I apologize, ultrafuge = Armin.
Black and white answers are only good for advertising. I recommend to listen to Jim Fackler or others who offer answers in shades of grey, the usual keywords are ... it depends... :-)))
'There's an important thing to look at when comparing airfoils, that is Cl/Cd/Alpha.' ...and don't forget Cm.
I work on full size production and prototype blades. In dynamics we always seem to get funny looks because we have to hedge answers. At least we know we have to hedge answers... There are only a couple absolutes with helicopters - 1. You cannot descend below ground level. 2 Air gaps in control / rigging will result in a proof for rule #1.
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