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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Dennis Toth on January 05, 2019, 03:09:08 PM
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Guys,
I have been working with the APC EP props on my electric Stuka and found a couple simple mods that increase thrust and decrease amps. The Stuka with 4S2500 Zippy compact pack is a bit over 41 oz. I have been flying with a 10x5.8 APC EP props running at 9700 rpm. This pulls the ship at a normal lap time (around 4.9, 59 1/2' C to C). The ship flies fine but in higher winds has a tendency to slow a bit on the verticals. Seems it needs more drive off. I took one of the props and sanded in about 0.010" (guess) undercamber in the last 1 inch of the blade tips, I also clean up the back of the blades near the hub about 1 inch off the hub (the APC's have a bit of an extreme twist here), cleaning off the sharpness gives a smooth flow off the hub.
I tested the standard prop on my thrust test stand (from Hobby King) and got a reading of 39.6 oz of thrust at 18.35 amps @ 9500 rpm. I next tested the modified prop and got a thrust of 51.1 oz @ 18.12 amps. I did a second test just to confirm it was that high and got 50.96 oz @ 18.15 amps. The mods take about 15 mins to sand it (I used a piece of scrap shaped leading edge for the undercamber and a flat sanding block to do the hub area). I hope to fly the ship next weekend if the weather is good. Will post results.
Best, DennisT
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Pictures?
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50% more thrust for almost the same amps (slightly) less at the same rpm is outstanding.
I can't wait to hear the results of the flight test.
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I finally figured out how to transfer and resize my photos to meet the size for posting. I did a retest today(it is about 20 deg cooler) and found the original out of the package prop was 45.6 oz @ 19.5 amp, the mod prop was 48.6 oz @ 19.03 (all done with the same full charged battery pack today). This is more in line with what I expected. Sorry about the difference in data, when I did the first test and saw the 39 oz thrust number I thought it was fine as it matched up with some earlier test on a APC 10x6 I did over the summer, I was wrong for not doing a second test on the base prop.
Ok, the photo shows the back of the blade hub smoothing, the prop on the bottom is the tip under camber sanded in. Second photo is the Hobby King thrust test stand with amp wire loop (the thrust tester I have only does thrust, I check the amps with a Craftsman clamp meter 82369).
I guess the only true way to see if there is an improvement if to fly it and see how much is pulled from the pack and if the UC tips add some extra pull out of the exits. Hope to get to this next weekend (work getting in the way again).
Best, DennisT
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Still looking forward to the flying results. I'll bet the extra thrust is noticeable.
R,
Target
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Very interesting. One point that was not clear. Was the rpm setting the same for both test? Or did it change
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Guys,
I have been working with the APC EP props on my electric Stuka and found a couple simple mods that increase thrust and decrease amps. The Stuka with 4S2500 Zippy compact pack is a bit over 41 oz. I have been flying with a 10x5.8 APC EP props running at 9700 rpm. This pulls the ship at a normal lap time (around 4.9, 59 1/2' C to C). The ship flies fine but in higher winds has a tendency to slow a bit on the verticals. Seems it needs more drive off. I took one of the props and sanded in about 0.010" (guess) undercamber in the last 1 inch of the blade tips, I also clean up the back of the blades near the hub about 1 inch off the hub (the APC's have a bit of an extreme twist here), cleaning off the sharpness gives a smooth flow off the hub.
I tested the standard prop on my thrust test stand (from Hobby King) and got a reading of 39.6 oz of thrust at 18.35 amps @ 9500 rpm. I next tested the modified prop and got a thrust of 51.1 oz @ 18.12 amps. I did a second test just to confirm it was that high and got 50.96 oz @ 18.15 amps. The mods take about 15 mins to sand it (I used a piece of scrap shaped leading edge for the undercamber and a flat sanding block to do the hub area). I hope to fly the ship next weekend if the weather is good. Will post results.
Best, DennisT
This is worth trying.
Unless I am mistaken, it is the RPM's and the prop alone that determines thrust. If you have a battery that can supply the required amps to keep the RPM's constant regardless of the load than it should not matter what the "S" value is which is the brass ring for my Nobler. I can barely squeeze an 4S 2200 into the nose. I can get a 3S 2800 or maybe even a 3000 in there just fine. So if this holds up, I can get the same thrust at a lower RMP and go to a smaller and lighter battery, drop 4oz of weight (2 Nose, 2 Tail) and obtain world peace. Then I woke up..............