Coaxial Vs Flat

[Av8Chuck]

On RCGroups there's a bit of a debate about the efficiency of and X8 verses a Hex. The claim is that with the same motors, props, and payload the Hex is 5.61Kg and the X8 is 5.77Kg. The Hex hovers at 45A and the X8 at 62A plus the motors are 10 degrees hotter. So the claim is that the Hex has approximately 25% more lifting power than the X8.

I had a Y6 and Hex, both had the same Avrotto 2814 motors with 12" props, the Y6 was more stable, more responsive and seemed to lift off much easier with the same payload. However, I never thought about it in terms of efficiency and would be the first to admit my impressions were a result of just flying around, not very scientific.

[FONT=arial, helvetica, sans-serif]Its hard to imagine that a Hex can lift 25% more payload than an X8. I would love to hear Kloner, SleepyC and anyone else for that matter opinions about this. I realize that a lot of this is subjective and there are a lot of variables but if the difference is as great as suggested I'd imagine that it would be pretty obvious. [/FONT]

 

[SleepyC]

I haven't really test max payload with my X8 VS Hex, but my Big Hex with 330KV T-Motors gets around 2 min more flight time than my X8 fitted with U5's (clones for a review for my old gig)

BUT, I have noticed that X8's or Y6's do seem to handle wind better. But on calm days the flat rigs are WAY more stable...

I think each format has it's + and -.

But I am going to try 15/5 on top and 16/6 on the bottom of my X8... I'll see if anything feels different.

 

[FerdinandK]

X8 pros:
smaller
lightweight frame
shorter wires (less wires)
one motor can fail

Hex pros:
can be flown without landing legs (and save weight therefore)

I have done hex and X8 with the same motor/esc/propeller combo:
Hex:

lateron flown without landing legs

X8 you can see in this video with the same payload:

Hex with Landing legs 2kg payload and 1kg battery:
AUW 4900gr, flighttime 15min
This is also the lift-limit for this copter, I cannot fly with more weight.

X8 with landing legs 2kg payload and 1kg battery:
AUW 5000gr, flighttime 16min
This copter can be loaded up to 6,5kg
Here a video of the same motor/prop combo with at least 5750gr:

I would say it strongly depends on the motor prop combo

Another point is, that if I think of my 28" copter, there is no choice then to build an X8 if you want to use a car for transport.

Not everything posted in the inet is a dogma.

best regards
Ferdinand

 

[Quinton]

Is it just me or can anyone else not see videos in Firefox?

I just read that thread, it "sort of" makes sense, but it fails that 8 motors will have more lift every time.

It won't have more lifting capacity, as it depends on how hard your motors can go, it may be more efficient hovering though.
My own example o 3515-15 T motors with 16" props..
thrust is 1060g @ 50% 4.8A

6 motors that is 6360g thrust @ 28.8A
8 motors that is 8480g thrust @ 38.4A (figures will not be exact as its bench tests)

It could be 25% less efficient but it still has more oooomph

So of course the x8 will be using more power, but it also has more lift capacity as long as you don't run out of power which you may well do with the hex.
Is it not like a big car/small car scenario, the big car will use up a lot more petrol, but it will be able to carry a much heavier weight, the small car will be great until it tries to lift a the same weight as the bigger car.

So in reality it just depends what you want to carry and how hard you want to fly.
Ill stop talking s*it now, as I am still trying to figure all this out

 

[Droider]

What about me. THE biggest user of Coaxial rigs from Y6 to x8. Its a no brainer if you want bomb proof usable system for commercial work. IF like Kloner you live in the perfect world then I am sure the big flats are king. BUT when you have to get the job done Coax is king, I just don't buy 25% more efficiency on a flat over Coax. There again I could not give a toss over them that like playing with ecalc and the likes. Horses for courses the coax rules every time here in the UK.

On RCGroups there's a bit of a debate about the efficiency of and X8 verses a Hex. The claim is that with the same motors, props, and payload the Hex is 5.61Kg and the X8 is 5.77Kg. The Hex hovers at 45A and the X8 at 62A plus the motors are 10 degrees hotter. So the claim is that the Hex has approximately 25% more lifting power than the X8.

I had a Y6 and Hex, both had the same Avrotto 2814 motors with 12" props, the Y6 was more stable, more responsive and seemed to lift off much easier with the same payload. However, I never thought about it in terms of efficiency and would be the first to admit my impressions were a result of just flying around, not very scientific.

[FONT=arial, helvetica, sans-serif]Its hard to imagine that a Hex can lift 25% more payload than an X8. I would love to hear Kloner, SleepyC and anyone else for that matter opinions about this. I realize that a lot of this is subjective and there are a lot of variables but if the difference is as great as suggested I'd imagine that it would be pretty obvious. [/FONT]

 

[Av8Chuck]

Thanks Dave, didn't mean to leave you off the list

 

[kloner]

I enjoyed running the xy8 of barts, but i didn't like the motors on the bottom. made it weird to handle/transport, for an octo was always seen as a quad by my clients. we fly in up to 24mph winds with a flats, fly up to 40 mph sustained speeds, never really seen a reason to change anything till recently with all the low kv big prop motors coming out and the sizes flats take to provide service to swing such big props.

when i flew an x8, it would kick butt through the worse turbulence but it'd give little bucks and jerks when it'd hit hvac air movement..... it didn't have a very good field of view with the motors hanging down.... and it was hoverfly so it was a lot of stress to fly. smooth but stressful

 

[Old Man]

It gets more complicated. An X8 is 5% to 6% more efficient than a flat 8 all else being equal. A very innovative aerospace company just ran a series of tests on that theory after it was presented to them and it proved factual. Doesn't sound like much but on a tethered 150lb MR it mattered quite a lot.