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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...
i just think were heading towards a conventional helicopter, with all the cost and complexity i wanted to avoid.
Well, the vane idea might work, but a belt driven tail prop only needs one servo. (and we know it works)
Also, this Enstrom design, with the conrods inside the propshaft will be pretty much indestructible if the blades are designed to shear off in a crash. All the swashplate assembly is well hidden away inside the craft. This also considerably reduces drag, and lowers the C of G.
Also, there are some very good reasons why helicopters are almost all the same..........
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ash Small wrote ...
EDIT: How many servo's will vanes require?
4 probly, but theyed be micro servos and all moving in the same direction for yaw. so simple and cheap.
fast forward to 1:35, youll see a machine i may have to compete against again. Georgia Tech is always a competent group though, they really knew what they were doing on every occasion i saw them fly in North Dakota.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Patrick wrote ...
i just think were heading towards a conventional helicopter, with all the cost and complexity i wanted to avoid.
So how about going for an unconventional helicopter? I'm thinking twin counter rotating blades 'Chinook' stylee, , with no swash-plates, just fixed blades. Without swash plates, you need twin counter-rotators, as flying at any speed will result in the leasing blades generating more lift while the reverse ones can stall (which is what cyclic pitch fixes in a single rotor helicopter). With counter-rotators, forward flight will twist the machine, but you still end up with overall balanced lift.
If we are going for duration here, then each rotor is driven by its own 4 stroke gas engine, mounted on the same shaft as a small 3 phase motor used as a generator, to do the two jobs of a) generate the small amount of power needed for the control fan array and b) load or unload the motor quickly to servo the rotor speeds quickly for pitch control. A fast control servo shifts the load from one generator to the other to pitch the machine, and a slow control servo throttles the two gas engines to equalise the loading on the generators.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Dr. Slack wrote ...
Patrick wrote ...
i just think were heading towards a conventional helicopter, with all the cost and complexity i wanted to avoid.
So how about going for an unconventional helicopter? I'm thinking twin counter rotating blades 'Chinook' stylee, , with no swash-plates, just fixed blades. Without swash plates, you need twin counter-rotators, as flying at any speed will result in the leasing blades generating more lift while the reverse ones can stall (which is what cyclic pitch fixes in a single rotor helicopter). With counter-rotators, forward flight will twist the machine, but you still end up with overall balanced lift.
If we are going for duration here, then each rotor is driven by its own 4 stroke gas engine, mounted on the same shaft as a small 3 phase motor used as a generator, to do the two jobs of a) generate the small amount of power needed for the control fan array and b) load or unload the motor quickly to servo the rotor speeds quickly for pitch control. A fast control servo shifts the load from one generator to the other to pitch the machine, and a slow control servo throttles the two gas engines to equalise the loading on the generators.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
One larger internal combustion engine is ALWAYS more efficient and lighter than two small ones.
While the Chinook does have two gas turbines, they are both linked, and either can 'fly' the chinook (this is a safety feature in case one engine fails)
I still think you'll have torque related problems using an IC engine without a swashplate, as IC engines don't develop sufficient torque at low RPM to spin the prop up to speed.
The weight and efficiency gained by using a swashplate (and single rotor?) far outweigh any advantage gained by using two IC engines.
I think if you're after efficiency with an IC engine, you always end up at the 'conventional 'copter'.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
There's no reason why contra-rotating props can't be the same diameter as a single prop would be. They can also be of thinner section if you have twice as many blades, so it needn't work out much heavier..
It would require some sort of gearbox, though.
EDIT: I think the Chinook design could be more efficient than concentric props of the same diameter, as the area under the props is greater, resulting in less velocity, and therefore less peripheral losses. (larger slower turning props are always more efficient, although one large prop is always more efficient than two, all other factors being equal. Concentric props 'may' be more efficient if they are larger than two 'chinook style' props. We're going into 'grey' areas here.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
no more guessing!!!!!!!!!!!!!!!!!
ive got a totally re-engineered thrust stand, this will allow me to generate lists of data on motor props and ESCs... all in 1,000 RPM increments. i may put a anemometer somewhere too.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Yay for measurement.
Now for Mk2, if you mounted the motor on a bearing, and resisted the rotation with some means of measuring torque (spring, weight on a stick, another set of small scales, whatever) you could measure true torque/power at the prop, and you'd have a motor dynamometer as well.
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Novel flying machines
