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Ash Small

Tue Jul 01 2014, 11:14PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Personally, I'm of the opinion that what's required is custom made props and no ducts, as this should help to keep overall mass down, but I do think it's worth pursuing the existing assymetrical tri-copter format, though. All the software has already been done, for example.

Patrick

Tue Jul 01 2014, 11:17PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Ash Small wrote ...

Personally, I'm of the opinion that what's required is custom made props and no ducts, as this should help to keep overall mass down, but I do think it's worth pursuing the existing assymetrical tri-copter format, though. All the software has already been done, for example.

Im intrigued, what propeller shape would you propose?

Ash Small

Wed Jul 02 2014, 12:02AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Probably something more close to a conventional heli blade.

Patrick

Wed Jul 02 2014, 12:04AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

not my machine, not my work or child...

link to this machine:

how can we increase air mass in-flow, while accelerating it to a lower velocity over all, without such a great diameter?

Dr. Slack

Wed Jul 02 2014, 07:49AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Patrick wrote ...

how can we increase air mass in-flow, while accelerating it to a lower velocity over all, without such a great diameter?

Not entirely sure what you're suggesting here, but
a) it's much the same total area as a rotor with fewer blades, so similar mass of air, similar velocities, so similar lift and lift-induced losses to a more conventional rotor
b) it's heavier
c) it has waaaaay more surface area in contact with the air, so will suffer higher viscous/friction losses, regardless of disc loading

Ash Small

Wed Jul 02 2014, 12:24PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I think turbines are generally used where very high disc loadings are called for, eg high pressure applications.

Completely the opposite of what we're after here.

EDIT: The assymetric tri-copter layout was arrived at in order to obtain the necessary control and manouverability required without resorting to swashplates. If anything, the current design lacks stability.

Building a lightweight 'Y' frame, and mounting long thin props at the extremities should increase stability, in an already 'inherently manouverable' design. If we lose the ducting, but retain the existing motors, batteries and control circuitry, etc, any increase in 'all up weight' can be minimized. We can improve efficiency and stability in an inherently manouverable design.

BigBad

Wed Jul 02 2014, 01:44PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

Yes, I think theoretically a single double length blade would be more efficient than the normal double ended blade. (Single blades are used on some powered gliders, it's not completely dumb, but you'd probably need a counterweight, although that could perhaps be the motor or something.)

Using more blades only reduces the aerodynamic efficiency; but going from 1 to 2 doesn't make that much difference so far as I know, I haven't seen the numbers on it. But certainly going 3,4,5,6.. efficiency goes down because the blades interfere.

Turbines are used where you want to pump the air into a volume at positive pressure, if you don't fill the disk with blades most of the air will push past the blades in between.

Still, it might be worth trying (3 or) 4 blades, it won't be as good as two sets of double blades/motors, but it might not be that much worse, and you can spin the blades slower, and you don't need extra motors and structure and power circuitry.

Ash Small

Wed Jul 02 2014, 06:37PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I think the point that BB is making here is that you don't want lots of blades or lots of blade area.

While a 'one bladed helicopter' is quite novel, I imagine that by the time you've added conter-weights and whatnot, it would be simpler to have two, thinner blades. Some helicopters have four thin blades (I was reading somewhere about balancers, etc, which apparently are sometimes required with two blades).

Most helicopter blades droop somewhat at rest, and 'tilt up' (for want of a better expression) under load.

Mass is obviously a consideration here, but adding counterweights is counter-productive, in my opinion.

If the blades are thin enough and the pitch shallow enough, gearing down may not be required, but the simplest form of gearing down is probably a reduction belt drive, which might allow the motors to be placed at, or close to, the intersection of a 'Y' frame, should you choose to go that route.

Patrick

Wed Jul 02 2014, 07:22PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

ok lets go back to 3 props, with 2 blades each, 14 inches in diameter, 5.5 pitch.
and ill make up endurace by adding a piston electric generator.

Ash Small

Wed Jul 02 2014, 07:39PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Patrick wrote ...

ok lets go back to 3 props, with 2 blades each, 14 inches in diameter, 5.5 pitch.
and ill make up endurace by adding a piston electric generator.

There does come a point where switching to 'diesel-electric' makes sense, but ideally I'd like to see some graphs first.

I still think 14" is too small to make a sgnificant improvement in efficiency, but if that's all that's available and you don't want to make your own it's a step in the right direction.

EDIT: I still think you need to reduce disc loading tenfold although I'm still hoping to get my head round the relevant maths. I'm not sure how detrimental this would be to manouverability, etc. though.

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