Multicopters versus the Wind ?

[matwelli]

Interesting discussion.

Definately think the keeping it all compact is the way forward, current quad design has the cameras up close to the centre line, and i am playing with a body design thats about 50mm thick, and 800mm overall diameter, with radius edges it should not be two bad in the wind, and the long "chord" (its a flat plate in the air, acts like a simple wing) "should" help resist pitching moments.

My question for those that are knoweldgeable is this.

Efficiency goes up when prop diameter/area is increased and RPM's drop. Current trends seem to be going from 10" to 12" and KV's down from 900's to 600's.
If the T580 hype is anything to believe (and there are some crediable testers) the lower kv/bigger prop certainly seems to give a 20% efficiency gain.

Now...if the wind is primarily acting on the bits that stick out, and we can tidy up our designs, and largely on the swept area of the props...... would a higher RPM, less efficient, smaller prop diameter/area actually be better in the wind ?

The anology to me is the big prop/low kv setup are "treading air" to stay up, the small diameter/high kv, and doing it by standing on colums of fast moving air

Thoughts ?

Second thought, would a ducted prop setup be less affected by the wind ? as the wind would have no direct access to the prop surface ? the consideration would be the intake side to make sure if the multirotor pitches back, the prop dosent starve as the intake will be in a wind shaddow.

 

[Droider]

I just love the thought process open discussion creates.. thats why this site is really going places.. keep it coming and thanks to everyone for pitching in.

Dave

 

[jes1111]

I wouldn't choose prop size based on wind drag - the priorities for their choice lie elsewhere. In general, I assume that full-scale helicopters have the right idea: big blades, turning slowly is the way to produce maximum lift for minimum power.

If I understand correctly, you're contemplating an enclosed fuselage? You'd need to be very careful that you don't inadvertanty create a crude airfoil that would itself produce upward or downward thrust as a reaction to wind passing over it. And given that a multirotor moves laterally by tipping itself then you need to consider any flat surface as a potential source of wind drag even if it is "normally" in line with the wind. Ergo, any design wih an enclsed fuseage, rotor ducts, etc. may well exhibit other desirable characteristics but wind stability is probably not going to be one of them!

I believe that compactness is the key - keep the fuselage small, the arms thin, etc.

Re: camera mounting. If you were toa design an idel aircraft for carrying a camera it would certainly not be a multirotor. A multirotor moves itself by tipping, so the craft is actually going to magnify andy effect the wind has on it. Imagine the wind moves the craft 10cm parallel to the ground. To get back to where it thinks it should be, it must "tip and slip". Therefore the camera mount has to work overtime to compensate. It has to be very quick, very smooth and very "tight" (i.e. no play in the mechanism). To achieve this, it needs to be sturdy, well engineered, with very fast, hi-resolution servos. The mechanism needs to be suitable for, and tuned to, the weight of the camera, i.e. a mount that performs well for one camera may not do so for another.

Naturally, the greatest problems are when shooting video. For still shots, it can be argued that the chances of a sharp image are actually diminished by attempting to stabilise the camera. On a fully compensating mount (inevitably of less than 100% effectiveness), the chances are that the camera will be moving quite "violently" at all times, increasing the probability of image blur. A partial solution to this dilemma is possible by tuning the aircraft's controller to favour attitude stability over position, i.e. to allow a certain amount of wind-induced translation in preference to tipping the aircraft in order to maintain position. It's possible that the forthcoming OpenPilot system will incorporate a "still photography mode" based on this idea.

Another approach for still photography would be to "switch off" the compensation altogether, i.e. just use the mount's servos to aim the camera. Then fire off multiple shots and rely on chance that one of them will be sharp

 

[matwelli]

More like this http://www.cybertechuav.com.au/-Overview,85-.html

i hear you on the flat surface, possibly being undesireable, i guess thats what experimentation is all about, so a nice bubble shaped center, that exhibits no lift in any direction enclosing all the gear, and the motors/rotors out on the thinest booms possible is probably the way forward

Dont know if I agree on the helicopter principle , pound for pound i am sure any multi out lifts a std RC heli
if we all stuck to agreed convention - there would be no MR's

 

[jes1111]

More like this http://www.cybertechuav.com.au/-Overview,85-.html

i hear you on the flat surface, possibly being undesireable, i guess thats what experimentation is all about, so a nice bubble shaped center, that exhibits no lift in any direction enclosing all the gear, and the motors/rotors out on the thinest booms possible is probably the way forward

Dont know if I agree on the helicopter principle , pound for pound i am sure any multi out lifts a std RC heli
if we all stuck to agreed convention - there would be no MR's

Yeah - that Cyberquad is probably VERY efficient but I somehow doubt it will be a good performer in wind.

And, yes... we need to try out all these ideas