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A few years back I took a trip to the Hiller Air Museum in San Carlos CA. http://www.hiller.org/index.shtml For this trip I decided to bring my sketchbook along and do some sketching on site which I find to be an enjoyable challenge. One exhibit they had there was the Hiller XH-44 coaxial helicopter http://www.hiller.org/hillerXH44.shtml . While studying the craft and talking to several of the museum staff I realized how if things had gone differently aviation could had gone down a different path.
If Sikorsky-style format of main rotor and tail rotor had not become the prominent layout for helicopters then maybe designs like the one I sketched in the bottom right might have become common sights. The only company up to now that has really pursued the coaxial design was the Russian firm Kamov because it filled certain specific operation requirements. I rather like idea using more of the engine thrust for lift instead of countering torque. Apparently even Sikorsky thinks there could be some advantages to it http://www.sikorsky.com/sik/about_s.....20080827_1.asp
If Sikorsky-style format of main rotor and tail rotor had not become the prominent layout for helicopters then maybe designs like the one I sketched in the bottom right might have become common sights. The only company up to now that has really pursued the coaxial design was the Russian firm Kamov because it filled certain specific operation requirements. I rather like idea using more of the engine thrust for lift instead of countering torque. Apparently even Sikorsky thinks there could be some advantages to it http://www.sikorsky.com/sik/about_s.....20080827_1.asp
Category All / All
Species Unspecified / Any
Size 1114 x 847px
File Size 267.4 kB
The US Navy ddeployed a neat A co-axial helicopter back in the 60's for drone anti-submarie work. http://en.wikipedia.org/wiki/Gyrodyne_QH-50 Some of them are still in use for other things.
This is pretty awesome and looks like it would actually work.
This tech is already in use tho. Check out the Ka-52 Alligator.
http://lh4.ggpht.com/TolipM/R0yTeM6...../s800/Ka50.jpg
This tech is already in use tho. Check out the Ka-52 Alligator.
http://lh4.ggpht.com/TolipM/R0yTeM6...../s800/Ka50.jpg
To my knowledge that is why Kamov established such strong relationship with the Soviet Navy. The coaxial design allowed for a much smaller rotor diameter while still possessing excellent lifting capability. This also meant they stowed easier in small ship hangers. It was only with the Ka50/52 that they got a foothold into the Army contracts in Russia.
Yes, the Kamov Ka-50 'Chernaya Akula', and the Ka-52 derivative.
Like any other aircraft, the contra-rotating rotor design is a compromise. One of the problems with the design is the requirement of having a long upper rotor shaft with a complicated set of linkages to ensure that the upper rotor adjusts the blade angle of attack for the opposite rotation. But, overall, it's still less vulnerable to damage from ground fire, because the vulnerable area is smaller than on a Sikorsky-style design.
One problem that won't be solved any time soon has resulted in the rotor shaft of these designs being very tall; the reason for this is tip lift. When a helicopter is moving forward, the rotor blade that is advancing has a higher velocity relative to the air, and generates more lift than the retreating blade, creating a torque that tries to tip the helicopter toward the retreating blade (as speeds get faster and faster, eventually the retreating blade stalls and the helicopter flips over). Counter-rotating rotors solve that problem -- there's an advancing and retreating blade on each side of the helicopter. However, you still have the problem of the lower rotor having that asymmetric lift; the common way to reduce the effect is to allow the rotor to hinge upward to spill some of its lift. But with a second rotor above it, that severely limits the amount of flap the lower rotor blades can have (and the shaft separating the two is still quite long), so the blade hubs must be extremely stiff. This bending of the advancing rotor blades creates a similar limitation to the helicopter's speed, although that limit is higher than a single larger-diameter rotor's would be, since the shorter rotor blades can more readily be made stiffer.
Like any other aircraft, the contra-rotating rotor design is a compromise. One of the problems with the design is the requirement of having a long upper rotor shaft with a complicated set of linkages to ensure that the upper rotor adjusts the blade angle of attack for the opposite rotation. But, overall, it's still less vulnerable to damage from ground fire, because the vulnerable area is smaller than on a Sikorsky-style design.
One problem that won't be solved any time soon has resulted in the rotor shaft of these designs being very tall; the reason for this is tip lift. When a helicopter is moving forward, the rotor blade that is advancing has a higher velocity relative to the air, and generates more lift than the retreating blade, creating a torque that tries to tip the helicopter toward the retreating blade (as speeds get faster and faster, eventually the retreating blade stalls and the helicopter flips over). Counter-rotating rotors solve that problem -- there's an advancing and retreating blade on each side of the helicopter. However, you still have the problem of the lower rotor having that asymmetric lift; the common way to reduce the effect is to allow the rotor to hinge upward to spill some of its lift. But with a second rotor above it, that severely limits the amount of flap the lower rotor blades can have (and the shaft separating the two is still quite long), so the blade hubs must be extremely stiff. This bending of the advancing rotor blades creates a similar limitation to the helicopter's speed, although that limit is higher than a single larger-diameter rotor's would be, since the shorter rotor blades can more readily be made stiffer.
*shi nods and rubs hir chin* i got some of that... sorry but not all ofit. and thank you for the heads up. i remembe rhearing the russians praise some twin roter chopper they had.. almost as much as there black eagle tank <.< scary things those are with 'upgrade hardpoints' anyway. :) *bows* thank you.
Then of course you had these.
http://www.jeffsheliphiles.com/heli.....ta/Kaman.shtml
Intermeshing rotors . . .
Great design, man, Very spiffy.
http://www.jeffsheliphiles.com/heli.....ta/Kaman.shtml
Intermeshing rotors . . .
Great design, man, Very spiffy.
On top of that...
The 'Main and antitorque' and even coaxial designs have some issues with spiralling downwash, so a stable hover means you have to keep in constant control. It's not as much a 'balance on a razor' as with a Harrier, but you still have to keep both fists in play.
With the Synchropter layout, though... Perhaps it's because there's no 'upper' or 'lower' rotor, so there's not so much spiral to the downwash around the body, or perhaps it's because the rotors are angled off to the sides, but a Synchropter has a tendancy to kind of... Fall into a stable hover, if you let go of the cyclic.
The only issue is control authority for yaw. But I think that's shared with the Coax designs, too... It's one of the few things the Sikorsky antitorque tail has going for it. S'also why the Kaman K-max has the big tail; There's a moving rudder on the center upright.
The 'Main and antitorque' and even coaxial designs have some issues with spiralling downwash, so a stable hover means you have to keep in constant control. It's not as much a 'balance on a razor' as with a Harrier, but you still have to keep both fists in play.
With the Synchropter layout, though... Perhaps it's because there's no 'upper' or 'lower' rotor, so there's not so much spiral to the downwash around the body, or perhaps it's because the rotors are angled off to the sides, but a Synchropter has a tendancy to kind of... Fall into a stable hover, if you let go of the cyclic.
The only issue is control authority for yaw. But I think that's shared with the Coax designs, too... It's one of the few things the Sikorsky antitorque tail has going for it. S'also why the Kaman K-max has the big tail; There's a moving rudder on the center upright.
The only issue is control authority for yaw. But I think that's shared with the Coax designs, too... It's one of the few things the Sikorsky antitorque tail has going for it.
I'd imagine mechanical simplicity is probably the biggest point in favor of the Sikorsky design, actually.
I'd imagine mechanical simplicity is probably the biggest point in favor of the Sikorsky design, actually.
Only by a razor-thin margin, really.
Even on a design where there's a straight run down the tail boom to the tail rotor, you've still got a long rotating propshaft down the boom (gyroscopic procession!) plus a gearbox to make the right-angle turn to face the tailprop sideways. On any design where the tail rotor's up atop a vertical stab, you've got another gearbox to maintain. On top of that, you've got to run control linkages, be they mechanical, hydraulic, or electrical, down to the mini-rotorhead on the tail prop. True, the tail prop only has collective control, but you still have a whole buncha spinning moving parts down there. And they're all stretched waaay out back.
On a Coax, you get rid of the whole tail boom assembly and the gearboxes and stuff therin, but now you've got to run two separate, independent sets of control linkages up to the rotors. In most designs I've seen, they use a clock-style 'cannon tube' assembly, where you're feeding your control lines for the upper rotor up through a hollow, oversized pipe which is the axle for the lower rotor. (And I've seen some gunship ideas where they stuck a stationary camera turret on top of THAT.)
On a Synchropter, you have the Coax's need for two complete and separate sets of rotorhead controls, but no need for running the drive and controls which spin one way through a tube which is spinning the other way. Synchronizing the two rotors together is dead-easy, and is slightly less complex than the gearbox that sends power down the tail because it's all the same gear ratio.
Even on a design where there's a straight run down the tail boom to the tail rotor, you've still got a long rotating propshaft down the boom (gyroscopic procession!) plus a gearbox to make the right-angle turn to face the tailprop sideways. On any design where the tail rotor's up atop a vertical stab, you've got another gearbox to maintain. On top of that, you've got to run control linkages, be they mechanical, hydraulic, or electrical, down to the mini-rotorhead on the tail prop. True, the tail prop only has collective control, but you still have a whole buncha spinning moving parts down there. And they're all stretched waaay out back.
On a Coax, you get rid of the whole tail boom assembly and the gearboxes and stuff therin, but now you've got to run two separate, independent sets of control linkages up to the rotors. In most designs I've seen, they use a clock-style 'cannon tube' assembly, where you're feeding your control lines for the upper rotor up through a hollow, oversized pipe which is the axle for the lower rotor. (And I've seen some gunship ideas where they stuck a stationary camera turret on top of THAT.)
On a Synchropter, you have the Coax's need for two complete and separate sets of rotorhead controls, but no need for running the drive and controls which spin one way through a tube which is spinning the other way. Synchronizing the two rotors together is dead-easy, and is slightly less complex than the gearbox that sends power down the tail because it's all the same gear ratio.
And, just to hammer out one last thing...
The Sikorsky design isn't prevalent because it's the BEST.
It's prevalent because... Well, no, it wasn't even the first.
It was the first to fly with the media watching, basically.
Germany was playing with helicopters near the end of the second world war, and they were all playing with the synchropter intermeshing-rotor design.
The only reason they couldn't get them into production was, by that time, they couldn't get ANYTHING into production.
The Sikorsky design isn't prevalent because it's the BEST.
It's prevalent because... Well, no, it wasn't even the first.
It was the first to fly with the media watching, basically.
Germany was playing with helicopters near the end of the second world war, and they were all playing with the synchropter intermeshing-rotor design.
The only reason they couldn't get them into production was, by that time, they couldn't get ANYTHING into production.
The Chinook can fly faster than the Apache because all engine power goes into lift and propulsion. I'd imagine a coaxial helicopter would be a bigger mechanical headache than the Chinook design of 2 separate rotors, hence why we don't have too many coaxial helicopters despite the advantage of not having to siphon off engine power to spin a tail rotor.
on the subject of aviation design and different roads, one idea that I have always had was taking the german volksfighter and putting a pontoon set underneath it. the original sea dart trials had the engine intakes too close to the water. I think putting the engine on the back might work better....
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