Hi,
Almost 1 year ago I started a topic on the diydrons forum in wich I asked on how much efficiency loss I will have on converting my quad to an X8. Almost no reaction to my question. Nobody could give some figures wich I could use for my calculations. The only helpfull answer I got was from somebody who said that the efficiency loss depends on prop size and distance between the props.
Time has past, other projects are closed so I'm starting with the build of a Y6 multirotor. And the first thing before building the frame is a thrust test of 2 motors in sequence. Result is a 10% efficiency loss. See full graph and info on my blog at http://wipo-y6copter.blogspot.be/
This figurs can by handy for everyone who is building Y6/X8 copters. Currently I'm building the frame, but I will try to post more efficiency loss tests for other prop sizes asap.
Comments
Brad and others
Here is data from another practical test: https://docs.google.com/spreadsheet/ccc?key=0AsH8A-9COlqudFlkUmx3X3...
This represents test data for bigger propels and for only one thrust area; about 2000-2100 grams per pair of propels. I got as efficiency loss between about 18-23% and 29-35%. Lower values are for 1455 and higher are for 1655. Efficiency was between 6.5 - 9.5 grams/watt.
But overall better flight time would give 1655 although it had greater efficiency loss.
Few words about method:
Values I took using camera. I took few images from each test run and wrote values down from image. I used few images because my instruments has too poor refresh rate and this way average might be closer to real. Test bench is ground effect free.
If we compare these results with yours, we are too far from each other. From these tests we could only say that efficiency loss is something between 10-40% depending on, who knows what?
@Henri
Thanks for the offering: I would be grateful if you share those tests with 14 inch propellers. I'm planning to convert my quad into an X8, and that information would be useful. I'm not using APC propellers, but Turnigy. Mainly because I was looking for 4.5 pitch propellers, and could not find them from APC. Anyway, I think your results will give me a starting point to look at.
David
@Brad Hughey: thx for adding this info, but these kind of papers are to difficult for me and a lot of other poeple.
For those poeple like me I'm trying to provide figures from practical tests.
If the sumary of this paper is a theoretical efficiency loss between 20% and 40% then it is indeed very strange that I got only 10% efficiency loss in my practical test. I only know that I use the same prop on both motors, the same motor, CCW an CW prop, the same ESC and they are connected to the same power source.
Maybe you could find some time to make a simular pratical test and post your figures, so we can compare.
Sorry to have missed the original post, but my participation has been sporadic lately.
Guys, thrust from propellers has been studied extensively since, well, before the Wright Brothers flew. There is an extensive body of work from which to draw.
My favorite paper on the subject is Dr. Gordon Leishman's seminal work on rotor overlap, to be found here:
http://terpconnect.umd.edu/~leishman/Aero/AHS2002_Griffiths.pdf
In essence, there is ALWAYS an efficiency penalty to be paid for overlapping rotor disks, depending on the distance between the disk centers and the thrust line vertical separation. For a completely coaxial configuration, this penalty is somewhere between 20% and 40%, depending on the separation distance. To only measure a 10% impact means all other things are not equal, or there's something else amiss. That said, efficiency isn't always the most important thing compared with packaging and agility.
@Wim
Thanks for the info on the landing gear etc. I'll keep taps on your posts. I was considering upgrading to bigger hardware, mainly a Y6 but I'll see what gives after some more testing. Thanks for the great work.
Interesting topic. I did some testing this spring, not on efficiency, but just trying to equalize current draw between motors. I have the Hextronic DT700 motors on my Y6. Running APC 11x4.7 on both there is a 10% difference in amps. The best result I got is With 11x4.7 on top , and 12x3.8 on bottom. This was somewhat unexpected, as most have indicated that higher pitch would be Natural on the lower propeller.
Lars
Im ok with the thrust loss, how about runtime? thats all that matters right?, X8/Y6 use less hardware=less weight....so it should all come out in the wash(excuse the pun)?
Few weeks ago I did similar tests with 14 inch APC multirotor props but and asked in one other forum if someone is interested. No big interested there.
If someone needs data for larger props APC 1455MR/MRP and 1655MR/MRP I would write data to excel.
My tests focused to find best possible X8 prop configuration to lift 8-10kg in to air. I also did tests for searching efficiency differences between single and co axial setup. Image of my test bench is here: http://www.flickr.com/photos/93810780@N08/9411188074/
Does someone need such larger copter data here? I create new thread if does. Once testbench is now built I could also run other tests with this bench if needed. I leave two motors installed for future tests ( APC will do more sizes and pitches in near future).
Some more Y-6 Prop discussionsHERE, Please feel free to contribute
I have installed 10% smaller props on top motors versus bottom motors. I used 11x4.7 on top and 12x3.8 on bottom. I also tested a configuration with all props at 12x3.8
Result:
-hybrid size prop config reduce total current comsumption at hover by 10 amps on a total of 60 amps
-the single size prop config with all 12x3.8 requires 4% lower throttle to hover
The x8 config allows me to carry at ease 2 kg of payload including battery while the quad version allowed me only about 400gr
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