lower mounted motors

[learn2fly]

I am planning on building a tricopter this summer and when researching i saw someone mounted (not a Y6) the front 2 motors on the bottom. This got me wondering why some one would do that? After much searching, somethings I found, read that
Pros: noticeably (roughly 5%) longer flight times
quieter
greater lift capability
more aerodynamically efficient (descends better)
Cons: props more vulnerable
less stable due to lower thrust point
props are more likely to be in the video when recording and for FPV
I am wondering if there are anymore things I should know about when deciding?

 

[trigger]

I guess it has to do with "thrust column efficiency" : if you mount your motor/props facing downward, there's no boom or plate in the way interfering with the air, so it's more efficient overall.

You should check Cyberdactyl's thread (http://forum.flitetest.com/showthread.php?8290-The-CyberHex), he seems to have a lot of knowledge on the subject

 

[Cyberdactyl]

Doesn't matter above or below...

http://forum.flitetest.com/showthread.php?8290-The-CyberHex&p=93629&viewfull=1#post93629

 

[cranialrectosis]

In short, if you have copter parts directly under the rotors, the rotors provide less thrust and more vibration on the copter.

You also want the CG level with the FCB to the extent that you can. Ultimately if you can put the motors, battery and FCB on the same plane (Z axis) you will get better performance. This is NOT as important as getting the CG correct on the X and Y axes.

Ours is a hobby of compromises and you WILL crash and break parts. Most beginners do not fly well enough to notice little differences like a 5% flight time. I recommend you build as per the original recipie and work on getting a basic copter in the air. Altering the build on a complex project like a multirotor makes it more challenging to build, troubleshoot and maintain all of which tends to add expense.

IMO, leave the tweaks to a future build and for this one use the KISS principle and get your foot in the door.

 

[Cyberdactyl]

I suppose me saying, "doesn't matter either above or below" is a bit vague and misleading.

And, to be clear, "TCE" is my nomenclature. In regular aviation it's more or less called the Slow Down Efficiency Factor or SDEF

In addition, there are so many variables that be tweaked for improvement either pushing or pulling. A small planform obstruction either above or below is a relatively average variable in the 'efficiency pie chart' IF the obstruction is not ridiculous.

 

[Balu]

While we are at it. If you mount two motors coaxial to each other (one on top, one on the bottom), does it provide more lift?

My feeling tells me that the second motor mainly pushes the air from the first one?

 

[FinalGlideAus]

They do provide more lift but it is far less efficient than mounting the second motor next two it. It is the same reason why a three blade prop is not as efficient as a two blade. In other words, a hex is far more efficient than a Y6

 

[Cyberdactyl]

You can get a small increase in efficiency in a stacked prop config by having a slightly more aggressive advance ratio on the lower prop.

 

[learn2fly]

Thanks! I think I am going to start out with what is known to work well and when I have more skills, will tinker-around to see what is best for me.