woodie
Posts: 301
Joined: 6/10/2002
From: Placerville,
CA, USA
Status: offline
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quote:
ORIGINAL: RC_Pattern_Flyer
Just out of curiousity, what RPM's are the E props running. Are they more efficient so we run slower rpms.
For instance... while i wait for props, i can swing my 17X12 glow apc at 6800 RPM. This is slower than on the os 160 at say 7900 rpm. When i put th E prop on the motor, equivalent size, 17X12... what rpm should i expect? more or less or the same, if it is the same, am i not down on power? confused ...
Chuck
The efficiency increases as the daimeter increases. That is why we can get away with slower turning props. However, having said that, at some point the pitch speed (rpm x pitch) will come into play. If you want to turn glow props, you just about have to turn them roughly the same speed as the glow motor will which usually means you need a higher kv motor (or more volts) to get to that rpm.
A lot of us have gone to 13, 14 and 15" pitch electric props to have the speed available when we need it. Given the wind demands, some change props (pitch) depending on the wind, others may run the higher pitched props all the time and just throttle up when they need the speed. With our computer radios, it is easy to have various 'settings' whether they be conditions or dual rates to control how high the motor will turn.
I have been running a 20x13 APCe on my Dualsky 6360 and have flown in winds in the 25mph range with no performance problems. Yes, I was pulling slightly more from my packs but still no capacity problem. Have tried the 20x15 which some have good success with and the plane will definitely 'move out'. Throttle response is different, I think you have to fly the 20x15 more like a 2 cycle motor to get consistent speeds, others may have better ideas how to use it.
Recently, I have tried a 20.5x14 APCe (not a wide blade) and it looks like it may be a good combination for controllable speed and thrust. Only have a few flights on it but it 'feels good', just faster than my 20x13.
Steve has described his efforts to reduce weight and maintain performance and I think it is great we are pushing the envelope to find out what the limits are for batteries, motors, weight, etc. And I would add, if you haven't flown an electric plane back to back flights with the first at 8+ oz heavier then drop the weight, it is VERY noticable. Uplines are much easier to maintain a constant speed, downlines are noticeably slower.
A few of us here in NorCal have been experimenting with mid range settings and have been able to reduce the overall mah usage per flight a considerable amount without sacrificing any vertical performance. Flights are in my 10.75lb Genesis. This is a combination of lowering the midrange cruise speed and increasing the prop pitch. I can now fly a full P07 flight with med to large maneuvers at what I consider a nice speed (not slow) and still handle the wind and use under 3000mah from a TP5300 10S pack. This has been proven in competition in the last 2 contests around here with both in pretty substantial wind. We have done this with both outrunner and inrunner type motors. I have not tried lighter batteries in my Genesis , but could comfortably drop to 3700s with capacity to spare at this point and it would drop the weight about 6 oz further dropping the mah required.
The trick is to not force the plane to accelerate quickly just to get to cruise speed. Any throttle setting higher than what you need is just burning amps in acceleration just to get to the cruise speed. This has made a surprising difference in the total mah used.
Don
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RE: want to loss 17 oz?? diffferent e-pattern approach - 
