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Vstall, Vcruise, Vne
Similar but different, anyone figure out what the actual stall speed is empty/loaded/bubble top off/bubble top on?
Anyone figure out what the pitch speed of the HiMax 3516-1350 with the APC 9x6E prop combo (RMRC deluxe combo) is? I'm playing with numbers on motor & prop combinations for max efficiency and required speed range. So many factors to consider.... Thx in advance. C eg a Scoprpion SII3014-830 swinging an APC 10x5E prop gives a thrust/PowerIn ratio of over 6.0g/W, but a pitch speed of 41.5mph |
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This Scorpion on 3S is not really a good fit. On 4S it will give you a pitch speed over 60mph with a 9x6e but the thrust will still be low which will make take-offs and steep, climbs difficult. With a 10x5 (4S) the pitch speed will be closer to 50mph and the thrust will go up but it will still be below the weight of the plane. Take-off and climbing will be better but you won't have a lot of acceleration because of the low Kv. |
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Vstall, Vcruise, Vne - and target power train combosQuote:
That brings to the good question what power train parameters should one be using/targeting? I was doing some reading and guys were talking about targeting prop max pitch speed at about 2.5x stall speed (as a good start), >=50W/pound weight for ground take offs, 75-100W per pound weight as a good "spirited" power, and prop pitch to dia ratio of about 0.6:1 to 0.8:1 for cruisers (vs 0.5:1 for 3D, 1:1 for speed racers). With a stall speed during reviews quoted somewhere of about 18mph (I hope to find what others have found) that gives a prop pitch speed of ~45mph, much lower than the HiMax combo on 3S. With a loaded weight of about 2.2kg/5#, the HiMax at 350W gives about 70W/# which is nice. Your 9x6 prop tests are showing thrust of about 1350-1425g on 3S, or about 2/3 of the all up weight, so I guess that is a reasonable target (ie <=1200g might be too light)? I was looking at the Scorpion motor charts and starting to think I could boost efficiency at the expense of top speed by swinging a slightly larger prop with a lower kV motor, while maintaining take off and cruise thrusts around targets Q on your tables - the second table showing comparison of props at fixed RPM and speed of 28.1MPH - is that latter the "ambient air speed" ie a simulation of the aircraft under cruise, with the resultant unloading etc? How did you do that? I can only think of a room fan blowing at the test setup. Ideally this weekend I'd like to maiden my Penguin and get some watt vs airspeed results with my Eagle Tree, weather permitting. |
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The power train questions are good ones but keep in mind these are simple "rule of thumb" ideas which have been around since before efficient outrunners existed. While 50w/lb might be OK on a high wing trainer with proper landing gear and a smooth runway, for the Penguin I would put this number closer to 75-100w/lb as it doesn't track straight, it has the motor thrust acting as an overturning moment forcing the nose down and very often we are taking off from grass or hand launching. As far as "spirited" power, I would put this as high as 150w/lb because with the high angle of incidence it takes more power to accellerate straight and level. So, IMHO, 450 - 600watts is a decent place to be. I have flown mine quite a lot on the SK3530 with a 9x6 which loaded in flight will max out at about 380 watts. With this set-up it takes quite a bit of runway (grass) to get off the ground and the in-flight acceleration and climb authority is pretty mild. With the NTM3536 and the same prop which maxes out near 530 watts the take offs are much shorter and the climb autority is significantly better. Both of these power set-ups use about the same amount of power in cruise so air time doesn't change significantly. As far as pitch speed goes, I think anything over 50mph static is enough. In flight I generally average 26 - 28mph and really only see speeds above 50 in a dive. As far as stall speed, I would put mine closer to 15mph, maybe lower, but my Penguin weighs ~69oz(~1965gr). Keep in mind here that using a low pitch prop, while you do increase the thrust it is at the expense of not just top speed but the ability to accelerate as well. On the chart, there is no calculation magic, it is simply an RPM match. What I should have done is add a third chart showing the props matched at a given thrust which is how I show multirotor props: Multirotor 10 inch prop test results This gives a much better idea of prop efficiency. Good luck on your maiden and let us know what your data logger tells you. I'm always looking for more data points! Cheers! Mark |
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About the ICE50 and temp
Mike,
wide open with a 9X4.5 and a Cobra 2820/8 I draw 45amps (3S). nakelp86, I have my ICE50 right behind the downwards facing camera port with the port open. I also have no canopy so air comes in through the front under the camera mount. Finally, I leave the elevator servo cover off, so I do have some flow in there. The last ICE50 I had ran hot, too, relative to other ESCs. It is a relatively low RF noise ESC, though, so I keep using it. But I don`t think it will ever run in the temp range of the stock 60A esc. |
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Last edited by s_linste; Jun 27, 2013 at 04:46 PM.
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Servos and Linkages
I'm waffling here - I know many have moved the elevator servo to the back and many have upgraded the linkages... but... do we have to? ie has anyone had any real problems with the stock linkages and stock setup, other than snapping the elevator bit off in a hard landing? Do they work loose or does their total "slop" really make that much of a difference on this aircraft, assuming easy and relaxing flying (vs 3d)?
Reason: I had already glued the fuse halves together and cut the servo hole before I read about moving the elevator servo to the back and I'm worried I'll end up doing a hack job trying to remount it. Plus I have the V1 fuse and fittings which I gather are a little different. |
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hokey... the least that describes it haha
Im too cheap to do anything about it... paid a ton for my plane ya know... |
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From the EagleTree forum
I'm posting this here, too:
I was flying in 30km/h gusts tonight and decided to do a RTH test to see how it would fair. On my Penguin, I set full throttle for climb, 20A draw for cruise (which cuts nicely into head wind) and, as recommended during the Servo Wizard, zero throttle for descent. I am wondering if this might be the wrong approach since when the plane tried to lose altitude from 650' down to my RTH alt of 500' it got into a self-amplifying resonance as it tried to keep the nose on the heading. In other words, without the forward vector of the motor, the head wind would blow it left, it would compensate right, get blown too far right, compensate harder back to the left, etc.. leading to a pretty strong oscillation. I guess it could've kept that up till 500' and things might've turned out ok, but I intervened before things got out of hand. I figure it could have an easier time losing altitude into a head wind if it had a bit of throttle. Thoughts? |
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Last edited by SFBC; Aug 19, 2013 at 06:31 PM.
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A picture from my penguin and 100% rmrc gear over the Missouri river in Montana.
just thought I would share with the people who have never been here |
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As far as the stock linkage parts, I think they are really sloppy and very low quality and I replaced them with Dubro and GP gear. I've seen the metal control horns fail (fatigue) and don't believe there should ever be loose metal on metal linkage connections. |
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