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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ash Small wrote ...
... Now, when the props are arranged in the hex configuration here, they effectively approximate to one large prop, producing a column of moving air much larger than each of the props, and roughly equivalent to the total area under all six props....
this may very well be, ive always wondered what the flow pattern looks like since the velocity is faster after the prop, the pressure should be lower, therefore a curve cone exhausting toward the ground. but i cant find pics to validtate this.
i think it would look like a liquid rockets exhaust under-expended. (But, we have intake, a rocket doesnt deal with.) one mole of air before the prop, at low velcity high pressure, one mole at low pressure high velocity after the prop.
EDIT:
single propeller velocity/pressure change diagram, i think the pressure drops since the velocity is so increased, cuasing the inward curve. As a sereis circuit the number of particles moving must be the same everywhere in the fluid flow. i think, tired must sleep...
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
It would be complex to represent, I think, but the losses are associated with turbulence/eddy currents at the periphery of the jet.
Several smaller jets will have much greater losses than one larger jet, due to the cross section/surface area thing, but if the jets are close enough together they 'approximate' to one large jet, I think.
I've tried to represent some eddy currents by sketching freehand in paint, not brilliant, but you get the idea
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Dr. Spark wrote ...
My next mini drone will be one of these @
I guess the closer together the props are, the more efficient it will be, but it's a trade-off against manouverability. I'll post a sketch of a concept heptacopter in the 'Novel flying machines' thread later.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
That Hilter video is great! (These are the kind of problems that really harm a company.) i have my local small, and my local large hobby stores bth telling me DJI are a bunch of "flaming jerks" to deal with. (with regards to purchase agreements and sales)
I had no idea they were having problems, I use the multiWii pro boards, and open source is surprisingly reliable. I had know idea DJI had a widespread "fly away" issue. I set many of these up back in 2011-2012, for others. The DJI / NAZA stuff was always to much in the way of "expensive garbage", so I got turned on to MW by a fellow expert flyer, never looked back. That must have been about 2011 or so.
300-400$ (DJI) versus 22-70$ is big, and so far, all problems and crashes with MultiiWii were my fault.
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