Hi All, Just pulled this image in from SUAS News (Thank you Gary) to illustrate a few really good concepts that it incorporates and talk about better Multicopter design a bit.
This copter has a lot of things right and is really a study in design excellence.
1. Most obvious is a sliding ball full enclosure camera Gimbal, very pro and really something we should be striving for.
2. The motors are on the bottom under the arms: More aerodynamically efficient with no prop wash interference and very little intake interference. Noticeably increased flight times and greater lift capability and much quieter.
3. Large slow high efficiency props and pancake motors: These are way more efficient than faster motors with smaller diameter more conventional props.
4. Carbon fiber aerodynamic frame arms: Again more aerodynamically efficient, light and strong.
5. Fully enclosed framework and a simple spring loaded landing gear that provides as little interference with the prop wash as possible.
Basically this quad incorporates the best design features I have seen so far and definitely provides food for thought.
I thought it might be worth soliciting comments and other thoughts about optimal multicopter design techniques.
Best Regards,
Gary
Comments
Camera Ball Turret
Vid.: https://www.youtube.com/watch?v=NT9qEMnf6Xc
Citation from: http://www.unicopter.com/A084.html:
Meanwhile, putting the pusher prop at the back, so the airplane does not have to fly through that prop's slipstream, means that the prop now has to fly through all the disturbed airflow coming off the airframe. The efficiency losses from that are typically at least 2-5%, and can be well in excess of 15% in some cases, not to mention the increase in vibrational stresses and noise, the added FOD ("Foreign Object Damage") of stuff coming off the airframe, rocks kicked up by the wheels on takeoff, etc.. Keep in mind that on a propeller driven aircraft, only a very small percentage of the airframe is actually immersed in the propeller slipstream, and therefore only a small percentage of the total airframe drag is affected by the slipstream. Meanwhile, essentially all of the thrust comes from the propeller, so anything you do that hurts the propeller's ability to do its job will have big effects on thrust and efficiency.
Did not find a more scientific article on my short search. But thats in general what I thought: having a disturbed airflow into a propeller is worse than having some disturbance behind it...
No Stephen, that is not the case, 2 NSK bearings, on on top and on the bottom.
These are the new MK motors.
I also run motors upside down and connect the prop to the shaft.
No rubbing, its the way it is. It's less effeicent.
I can troll through a Rcgroups thread from 5 years ago, Rusty. OMM and Jim, we did these tests i remember well :-)
Simon
Maybe the motor is rubbing. I'd imagine some motors are made with thrust bearings in one direction, but not the other? That is, the motor spins freely then the prop is pulling the motor apart. But perhaps when the prop is squishing the motor together, you get more friction.
I know what i am doing, i live and breath copters. It's what i do for a living. Full time:-) 6+ years
Of course they are on the right way.
Now let's get back to the question, WHY is it less efficient?
It shouldn't be, it's simply pulling air over the boom instead of blasting air over the boom, right?
Simon
He already indicated that he didn't flip the props over, I think, when he wrote:
"I simple rotated the motor, the prop is the correct way:-) Opened MKtool and reversed the direction in the software.."
Apparently he reversed rotation, which is not the issue here. These props are asymmetrical. They have a front face and a rear face that are different. Flipping motors also flips the prop faces. There is only one fix for that, physically removing the prop and turning it over. It is unkind to suggest this is an "unbelievable" mistake. It happens all the time, as a matter of fact, in the real world. As I already stated, I've done it myself.
Can you please take a close up picture of your setup the way it was in the latter half of that video? I want to see which way the prop is facing.
Hang on, hang on hang on.
Simon, did you serious run the propellers backwards in your test, and claim that that shows putting props facing down is less efficient?
It can't be. I can't believe somebody would do that, so there must be some misunderstanding here. I can't make anything out from that video.
Thanks for taking the time and effort to do this experiment. Confirming that you did not flip the props over after inverting the motors? That would account for a significant loss of efficiency. On a marginally-powered plane (and most multicopter props are all more or less still airplane designs) reversing a prop can make the plane unflyable. On overpowered aircraft, such as most larger multis, it results in a noticeable performance hit, as seen here. Just last week I put a pusher prop on backwards on a low-power flying wing (HK Phantom) and was lucky to not crash it, it would barely fly above stall speed. Flipped it over and away we went. How about repeating the experiment with flipped props, we would really like to see the numbers.
I wouldn't invert the props, obviously :-)
Here is the Video, It's on Vimeo.
hovertest from Simon Jardine on Vimeo.
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