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
http://www.humanpoweredhelicopters.org/articles/nasa-tp-3675.pdf
...
Andrew (ref. 45) presented work on theoretically
optimizing the hovering coaxial rotor configuration. He
found that vertical spacing gave the greatest gains in
performance up to H/D = 0.05, with no practical gains
thereafter. He also found that there was a “trade off
between increase in induced power on the upper rotor
with the reduction in upper rotor radius and the enhanced
performance of the lower rotor as proportionately more
disc is exposed to clean air. Most promising results were
obtained for a 8% reduction in upper rotor radius.”
...
great to see this kind of testing. so even with 9inch (about 20cm) you're seeing 10%. I guess you are measuring the thrust by putting the copter on a scale?
I've also heard (with no support) that using one larger prop and one smaller prop (possibly with different KV motors) can increase the thrust with a significantly reduced loss in efficiency. If you have different sized props, it might be worth messing with what prop goes where and seeing if it makes any noticeable difference. Nice work!
I have already two years, with one frame XAircraft 650v8, apm 2.5
10x4.5 XAircraft x8 original engines and battery 6000mah 3s Turnigy Plush 10 amp ecs
drive 20 minutes, 17 minutes are what really use weighing 2.2 kilograms, I think if I have losses EFFICIENCY security are offset by losing an engine.
I've flown with 7 engines.
Hi Wim
I've just bought a 3DR Y6 so I'm really interested in your findings, especially anything you find to increase efficiency.
Thank you very much!
Thank you very much for clearing up guesswork!
Thanks for posting this Wim. I am also working on a Y6 multi rotor for 3D Robotics. What we, and others on DIY DRONES have found is that it is best to use either larger props or use props with greater pitch on the bottom of the coaxial setup . This is to account for the reduction of clean laminar airflow to the bottom props. An example would be 10x4.7 on the top and 11x4.7 bottom or 10x4 top and 10x6 bottom.
Also, 9 inches seems like a lot of distance between the top rotor and the bottom. Have you run this test using shorter distances? I have heard that the sweet spot is between 4 and 8cm. Best of luck to you.
Very interesting. I just converted my hexa C to a Y6 last weekend. Standard setup for the 3DR Y6 is 10' props on top and 11" on the bottom but they are spaced about 3-4 inches apart.
I may need to do a bit more tuning but I've seen a slight difference in responsiveness between the two models and the battery life seems to be less as well. I've expected this though.
I'm sure we'd get various outputs based on motor and prop size differences but I'm not aware of anywhere that shows the results of the possible configurations. My main goal would be extended and stable flight time on the Y6. Do you know of anything online that could show how the different configurations might affect these goals?
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