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.
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Oh, and Jim, that reminds me... the answer to even the most pointed question related to helicopter aerodynamics is "it depends". There is no black and white answer on anything.
Jim, yes, I could simply look at slope of depletion, or... simply time flown. But I'd really like to put real numbers to it, and also be able to change the RPM in-flight to find the peak efficiency point for each blade.
Carles, asymmetric blades are not necessarily more efficient in general, on a helicopter. There are too many things going on. There's an important thing to look at when comparing airfoils, that is Cl/Cd/Alpha. That is to say, the Coefficient of Lift vs. Coefficient of Drag across various Angle of Attack. Asym blades would typically have a higher peak Cl/Cd, but the peak can often be very sharp, and falls off quickly at Alpha that is not optimum.
And with helis, the Alpha is almost never optimum. There are too many things going on. One key point is that we have the blades spinning in a disk. Every "section" of blade has a different velocity. And the induced velocity of the inflow is not uniform. Nor does it match properly with the velocity profile of the blade. So while one bit of the blade may be operating in the ideal Cl/Alpha zone, the rest of it is not.
There's little argument against the idea that the asym blades produce more lift. But it's not clear that they are more efficient in practice, on a helicopter.
Rob- Very astute observation re efficiency. To the critical engineer, the data often raises as many questions about how to parse data than where to go forward. If you look at the slope of battery depletion maybe you will resolve the power used issue?
The asymmetric blades are more efficient in general, there is not discussion on that. The point is if the spinblades are more efficient.
I haven't been able to find any other provider of asymmetric blades, do you know if there are other ones?
Hmmm.... is Ultrafuge = Rob? Just so I know. (everyone else, I've been talking off-line with another Rob who really knows his stuff).
I only got a chance to do one flight with the symmetric 475mm blades. It flew about 16 minutes, and had 3.75 V/cell when I was done. I've flown the asymmetric blades for 20 minutes, but that was taking them down all the way to 3.3V/cell. I really need to get power instrumentation on this thing to know for sure. And then put it in Alt-Hold, and vary the headspeed to find the peak efficiency.
In theory, we know the peak efficiency is likely to occur just before stall, which would mean that there is absolutely no reserve lifting capacity. We don't actually want to operate in this regime. So the best blade will actually be the one with the best compromise between efficiency at the actual rpm we want to run.
One great thing, if the symmetric blades actually aren't more efficient, the idea of a tandem heli is back on the table!
Is there any news of the performance of the asymmetric blades?
Hi,
the answer for the question 'asym blades vs. standard blades' is easy, but only in theory ! If you look at the polar diagram of i.e. NACA0012 vs. NACA2412 you see, that the 0012 is optimized for 0° angles and the 2412 for more AoA than the 0012 and a 4412 for more AoA than a 2412 and so on. So in simple theory the blades for an AP-heli should have an asym airfoil optimized for constant lifting conditions.
Practical test however CAN show different results, because airfoil sections are only part of a wing and there are factors like accuracy of production, weight, twist under load and induced drag, etc., etc.
A test with two different blades needs to be done by adjusting the optimum headspeed for each blade, which leads to efficiency issues of common ESCs. High headspeeds will tend to show, that thin symmetrical blades are best, low headspeeds with high alpha will show the advantage of asymmetrical blades. Quality issues in manufacturing will easily ruin every theory.
In short, if you find out what theory predicts be happy and keep on researching, if not, buy the next set of blades and keep on testing :-)))
Rob, I bet if you start up a hobbyking live chat, you can get them to send you a new side frame to replace the funky one. You can argue that for your special application you need 2 that are exactly the same.
congrsts for the 500..
any one care to post a list of what to get ?
motor / servos / esc ?.. i realy have no idea ..
thansk
Oh, and I got the HK500 whatever-whatever TT FBL yesterday. The one with the black metal. I'm a bit disappointed. Well, so far, I think the metal parts are OK. Some of the plastic parts are a bit crappy. One CF frame is fine, the other was cut out very strangely. It's usable, but it's not right. Hard to describe... Say there is supposed to be a square cut out. Well the sides on the squares are pinched in, so it's almost like a big fat cartoon "x". Not quite but... you get the idea. More noticeable on smaller features.
So far, I think I can do a really nice clean build. Much more room in the frame than the Protos. I should be able to put the PX4 tilted sideways, right in the frame. And the the ESC, BEC, etc, all internal. Should be nice. Again, 500 is a much nicer size than 450.
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