Aeronavics / Droidworx Skyjib Ti 8 or x4
- Thread starter jjon667
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here's a test not by me........ coaxial vs not. there is another test i can't remember where showed similar data 25-30% loss vs flat... the data was on another forum though i think.it's been a while since i seen it. https://www.youtube.com/watch?v=tFJyE3Uns3o&list=UUq2rNse2XX4Rjzmldv9GqrQ it doesn't seem too difficult to test like this and see if changing up prop pitch or different prop size would negate any loss. you would just need to build a similar jig. science project anyone? not sure how scientific it is but maybe could add to the discussion
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I have converted my flat CS8 with MK electronics and 2814 motors to X8 setup in the past. What I got was around %20-25 less flight time. I converted it back to flat octo for better flight time since this setup was already an inefficient 4S setup. With up-to-date motors and 6S setup, loosing %20 efficiency over flat setup is not that important since the flight times are already good.
Why I can't really understand is, am I the only one who is having the "props getting into the camera view" problem with X8 setup? With a 360 gimbal, they get into the view of 5D Mark III and 24 mm lens. But, with frame designs like DJI S1000 or Mantis, the arms are not parallel to the ground, they are pointing upwards with an angle, so they would help to get rid off this problem.
For me, with Cinestar style frame, it has been almost impossible to get fast and straight shots with X8 setup and a 360 gimbal.
Why I can't really understand is, am I the only one who is having the "props getting into the camera view" problem with X8 setup? With a 360 gimbal, they get into the view of 5D Mark III and 24 mm lens. But, with frame designs like DJI S1000 or Mantis, the arms are not parallel to the ground, they are pointing upwards with an angle, so they would help to get rid off this problem.
For me, with Cinestar style frame, it has been almost impossible to get fast and straight shots with X8 setup and a 360 gimbal.
yes certainly an issue for some setups. i believe some go with the xy version instead of the normal x so the booms y out more. other then the mantis arms i don't know of a solution but have seen what your talking about. with big props i really don't know how it would be possible not to get them in view un-less the cam is slightly pointed down or using longer lens.
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MombasaFlash
Heli's & Tele's bloke
Lowering the camera plate will help a lot but that is not so straight forward with the CS design whereby u/c legs are incorporated into the camera mount. Personally I prefer to keep the camera mount and under carriage separate. I tried the AV200 360, which is similar in concept, and did not like it at all. The pilot is at the mercy of the camera operator, who must deactivate the Pan axis on the ground if the whole thing is not going to spin on the ground. I use red and green pool noodles on the skids for simple orientation and this is lost if the legs can rotate.
It is high time Freefly came up with new MR and Mount designs.
SoCal Blur
Member
What...and remove all room for debate? I think not! LOL
You obviously have difficulties understanding the term efficiency and unfortunately allege things I did not claim.
Again, If you say:
Then your following statement is contradictory:
Explanation: If two contra rotating propellers are more efficient than a single propeller then they must generate more thrust than a single propeller if each propeller (of the two contra-rotating propellers) just receives 50% of the amount of power of the single propeller.
Also, if the above holds true then following is also true: If two contra rotating propellers are more efficient than a single propeller then they must generate more than double the thrust, if each propeller (of the two contra-rotating propellers) receives the same amount of power as the single propeller.
This is just simple logic and analogy of sentences which explain the term 'efficiency'.
Nowhere do I claim that two contra-rotating propellers do generate double the thrust per se.
And if you are interested in efficiency of contra-rotating propellers then you should look at following links and not ignore them:
Here's a contra-rotating propeller analysis:
http://cafefoundation.org/v2/pdf_tech/Noise.Technologies/AIAA.1986.Prop.Noise.CRot.pdf
http://www.dynamic-positioning.com/dp2006/thrusters_jukola.pdf
Here are commercial examples:
http://www.scana.no/sites/all/files/Contra Rotating Propulsion_0.pdf
http://www.wartsila.com/file/Wartsila/1278512476073a1267106724867-Wartsila-O-P-IHIMU-CRP.pdf
http://www.rolls-royce.com/Images/gasturbines_tcm92-4977.pdf
http://www.volvopenta.com/volvopent...ps_duoprop/pages/the_benefits_of_duoprop.aspx
http://www.kaman.com/aerospace/aerosystems/air-vehicles-mro/products-services/k-max/
SoCal Blur
Member
Clearly there is no point in continuing this discussion so lets just agree to disagree and move on.
ovdt said:
(Just to make sure: In order for a co-axial propeller to be more efficient it definitely needs to be contra rotating.)
Contra-rotating propellers are supposed to more efficient because the rear propeller can recover the rotational energy of the wake of the front propeller.
However, the second propeller may need to be adapted in order to benefit from that wake (e.g. different angle of attack).
Once should also keep in mind: As 4 contra rotating propellers can be larger than 8 flat propellers, a coax set-up could still reach a higher efficiency (even if the second propeller is not properly designed to benefit from the first propellers wake). (In a hovering not moving application a large slow propeller is more efficient than a small fast propeller, because the small propeller has to bring a smaller mass of air up to a higher velocity in order to generate the same amount of thrust and this requires disproportionally more energy, as thrust is v * m and energy is 1/2 * m * v^2.)
MombasaFlash
Heli's & Tele's bloke
Huh? Do you really want to have to keep on arguing with globi?
I was trying to do you a favour me ol' mucker!
SoCal Blur
Member
Huh? Do you really want to have to keep on arguing with globi?
I was trying to do you a favour me ol' mucker!
Roger that - thanks!
Droider
Drone Enthusiast
Ok chaps calm down.. just go COAX and let everyone who wants to argue over efficiencies do it soemwhere else.. I hate tittle tattle and nit picking.
You just CAN NOT calculate for everything in this debate.
COAX every time for me for majority world flying.
Dave
@MF I do it for £19,999.00 ;-) Quality!
You just CAN NOT calculate for everything in this debate.
COAX every time for me for majority world flying.
Dave
@MF I do it for £19,999.00 ;-) Quality!
MombasaFlash
Heli's & Tele's bloke
OK, I'll accept a donation of $19,998 - but purely in the interests of science and community service.