Flightline: 66/TBD

"user314" (user314) 10/26/2020 at 11:00 • Filed to: flightline, Planelopnik, planelopnik history, Helicopterlopnik

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Overhead view of a coaxial helicopter in operation

One of the disadvantages of rotor-born flight is the torque produced by the rotor as it turns. This would, if not addressed, cause the fuselage of the helicopter to spin in the opposite direction of the rotor blades. Traditional helicopters counteract this force with a !!!error: Indecipherable SUB-paragraph formatting!!! , !!!error: Indecipherable SUB-paragraph formatting!!! or !!!error: Indecipherable SUB-paragraph formatting!!! , all of which are mounted perpendicular (or nearly so) to the main rotor’s plane of rotation, and act to not only prevent rotation but also to maneuver the helicopter. The disadvantage of these devices is that they rob the main rotor of power (in some cases up to 10% of the engine’s output is routed to the tail rotor), they present a hazard to ground crew when in operation, and they add weight and complexity to the chopper. Another method of stabilization are the !!!error: Indecipherable SUB-paragraph formatting!!! , which has two intermeshing rotor discs, the !!!error: Indecipherable SUB-paragraph formatting!!! , which have two rotors spinning in opposite directions one in front of the other or (rarely) the !!!error: Indecipherable SUB-paragraph formatting!!! , which has the rotors side-by-side. Coaxial helicopters also use two sets of rotors, but they are mounted one atop the other. In addition to increasing the amount of power available to the rotors, coaxial designs are also quieter than traditional helos, as it is the interaction of the main and tail rotor washes that create the “whumping” sound associated with choppers. They also tend to be more compact than other designs, as they lack the long boom needed for a tail rotor, though they are taller, having stacked rotors.

The concept of coaxial rotors came from Russian-born polymath and writer !!!error: Indecipherable SUB-paragraph formatting!!! , who demonstrated a scale model of a coax helicopter to the Russian Academy of Sciences in 1754. About a century later, Henry Bright was awarded a patent from the British Patent Office for a coaxial design, and in the 1930s the !!!error: Indecipherable SUB-paragraph formatting!!! -built D’AT3 and the !!!error: Indecipherable SUB-paragraph formatting!!! both demonstrated the concept in actual flight.

One of the primary designers of coaxial helicopters is !!!error: Indecipherable SUB-paragraph formatting!!! , which first incorporated the feature on the post-war !!!error: Indecipherable SUB-paragraph formatting!!! , which was powered by an alcohol-burning BMW motorcycle engine, and has featured prominently on its KA-25/27 ASW helis and the Ka-50/52 attack chopper.

A Ka-25PS “Hormone-C” of the Soviet Navy in 1987

Development of the !!!error: Indecipherable SUB-paragraph formatting!!! (NATO reporting name “Hormone”) began in the late 1950's, as the expanding Soviet Navy required an anti-submarine helicopter. The rotor system introduced aluminium alloy blades pressurized with nitrogen for crack detection, lubricated hinges, hydraulic powered controls, alcohol deicing and automatic blade folding. ASW equipment included radar, dipping sonar and a towed !!!error: Indecipherable SUB-paragraph formatting!!! unit. The main production Ka-25BSh could carry a little over 4,000lbs of torpedoes or depth charges (conventional or nuclear), as well as optional extras including fold up seats for 12 passengers, rescue hoist, external auxiliary fuel tanks or containers for cameras, flares, smoke floats or beacons. In addition to the ASW variant, Kamov also introduced the KA-25BshZ mine sweeper, the Ka-25K which designed to relay over-the-horizon radar data to cruise missiles, and the Ka-25TL which was to detect US/NATO cruise missiles.

Ka-27 helicopters on the deck of the Novorossiisk

Kamov began designing a replacement for the Ka-25 in 1969, with the prototype !!!error: Indecipherable SUB-paragraph formatting!!! (NATO reporting “Helix”) flying in 1973. Mission requirements and the need to fit in existing hangar space resulted in a broad resemblance to the Hormone, despite being a ‘clean sheet’ design. In addition to ASW and SAR variants, there is also the Ka-29 (“Helix-B”) armored assault heli, which can carry troops and/or rockets, gun pods, missiles or bombs, and the Ka-32 produced for the civilian market, with transport, fire fighting, SAR, police and aerial crane variants. The Ka-27 is in service with the Russian Navy, several client states of the former Soviet Union, and the South Korean Air Force and Coast Guard, and Ka-32s are operated by !!!error: Indecipherable SUB-paragraph formatting!!! around the world.

Ka-50 “Hokum-A” of the Russian Army

The !!!error: Indecipherable SUB-paragraph formatting!!!   - ‘Black Shark’ (NATO reporting name “Hokum A”) attack choppers was originally developed in the early 1980's in competition with the Mil Mi-28 to replace the Mi-24 “Hind” as the USSR’s attack helicopter, but have since been accepted into service with the Russian Army and several other client states. The Ka-50 is rather unique in that it is flown by a single pilot instead of a pilot and weapons officer as is typical with the AH-1 Cobra, AH-64 Apache and Mi-24 “Hind”. Operational testing showed that pilot workload was similar to that of a fighter-bomber pilot, such that the pilot could perform both flying and navigation duties. Also unique was the ejection seat, the first fitted to a helicopter. Prior to firing of the seat, charges would sever the rotor blades and the canopy would be jettisoned. With the Mi-28 “Havoc” seeing service in the regular army, the Ka-50 have been accepted by Russian special forces as their support chopper.

Russian Air Force Kamov Ka-52 “Hokum-B”

A modification of the Ka-50, the Ka-52  - ‘Alligator’ (NATO reporting Name “Hokum B”) was designed to act as dedicated scout, with the forward fuselage being redesigned to accommodate a pilot and systems operator side-by-side. With the end of the Cold War and Russia’s subsequent economic issues hampered acceptance and production of the Alligator, though beginning in 2008 the Russian Air Force began acquiring two dozen Ka-52s, with an additional 150 being ordered in 2011. In 2015, Egypt ordered four dozen Ka-52 ‘Nile Crocodiles’ for its army.

Kamov Ka-52K naval variant

A further development of the ‘Alligator’, the Ka-52K  - ‘Mud Shark’ is a navalized variant, featuring anti-corrosion construction, folding rotors and wings, and a new radar system. The Russian Navy had ordered the Ka-52K to fly from a force of four !!!error: Indecipherable SUB-paragraph formatting!!! amphibious assault ships purchased from France. Due to the Russian invasion of the Crimea, the purchase was canceled, and the ships were eventually sold to Egypt. Kamov won a tender to supply the ‘Mud Sharks’ to Egypt along with their ‘Nile Crocodiles’.

Front view of an XH-59A Advancing Blade Concept (ABC) rotor system aircraft in flight at the Marine Corps Development and Education Command Air Facility.

The Sikorsky X2 on display alongside the S-97 Raider

In addition to Kamov, Sikorsky has also developed coaxial designs, with their !!!error: Indecipherable SUB-paragraph formatting!!! and !!!error: Indecipherable SUB-paragraph formatting!!! experimentals leading into the S-97 Raider and SB-1 Defiant. The S-69 and X2 are compound helicopters, with the S-69 featuring two turbojet engines for additional thrust, while the X2 had a pusher prop. The S-69 reached a top speed in level flight of 238kts, but vibration and fuel use proved to be excessive. The X2 proved to be a more refined design, without the vibration that grounded its predecessor. On 15 September 2010, test pilot Kevin Bredenbeck achieved Sikorsky’s design goal for the X2 when he flew it at a speed of 250 knots in level flight, an unofficial speed record for a helicopter. The demonstrator then reached a new record speed of 260 knots in a shallow 2 to 3 dive. Interestingly, in level flight more power is being put to the pusher prop than to the rotors, with a lift-to-drag ratio roughly twice that of a conventional helicopter.

The Sikorsky/Boeing SB-1 Defiant during a flight demo

The Sikorsky/Boeing !!!error: Indecipherable SUB-paragraph formatting!!! is a joint entry into the Army’s !!!error: Indecipherable SUB-paragraph formatting!!! program, which is seeking to develop replacements for the Army’s !!!error: Indecipherable SUB-paragraph formatting!!! , !!!error: Indecipherable SUB-paragraph formatting!!! , !!!error: Indecipherable SUB-paragraph formatting!!! , and !!!error: Indecipherable SUB-paragraph formatting!!! helicopters.  

S-97 Raider prototype

Broadly similar to the Defiant, the S-97 was Sikorsky’s entry into the Army’s !!!error: Indecipherable SUB-paragraph formatting!!! program, which was canceled in 2013. The design was scaled up into the Raider X, which is in competition with the !!!error: Indecipherable SUB-paragraph formatting!!! for the Army’s !!!error: Indecipherable SUB-paragraph formatting!!! (FARA) program.

MrDakka > user314 10/26/2020 at 11:44

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Obligatory Fortunate Son

PyroHoltz f@h Oppo 261120 > user314 10/26/2020 at 11:51

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“ Prior to firing of the seat, charges would sever the rotor blades and the canopy would be jettisoned.”

I would love to see this in action, from a safe viewing distance.

Maxima Speed > user314 10/26/2020 at 11:51

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Ive always kinda wondered about the interaction of the air flow from the top to bottom rotor on those.

user314 > PyroHoltz f@h Oppo 261120 10/26/2020 at 12:29

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Adding this blind, hopefully it’s good:

MUSASHI66 > user314 10/26/2020 at 12:51

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Soviet attack choppers are fucking sexy. That’s all. 

user314 > MUSASHI66 10/26/2020 at 13:01

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Except for the Havoc:

The arrangement of the radome and sensors looks a little, well, Goofy

MUSASHI66 > user314 10/26/2020 at 13:06

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I’m a simple man - I see a front mounted gun and wing mounted rocket pods, I don’t care about the rest.

To be honest, American attack choppers are amazing too. 

kanadanmajava1 > user314 10/26/2020 at 13:31

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There was also a weird solution of intermeshing rotors. It’s kind of a combination between transverse and co-axial rotors. Only handful of such helicopters have been b uilt and H uskie is clearly the most successful (193 examples built).

Thomas Donohue > user314 10/26/2020 at 13:31

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Helicopter without rotors stayed unusually stable and aloft!

415s30 W123TSXWaggoIIIIIIo ( •_•))°) > user314 10/26/2020 at 13:44

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Huskies must be counter rotating but in two offset locations instead of in line.

user314 > 415s30 W123TSXWaggoIIIIIIo ( •_•))°) 10/26/2020 at 13:55

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Correct; the rotors on synchropters like the Huskie go through each other’s plane, coaxials are stacked, tandems like the CH-46 and -47 are front-to back, and transverse like the Mil V-12 and Fa-223 are side-by-side.

PyroHoltz f@h Oppo 261120 > user314 10/26/2020 at 14:40

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Would have loved a real life test and not a a but this was cool nonetheless.

ttyymmnn > user314 10/26/2020 at 14:46

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Kamov? Alcohol burning? An unlikely coincidence....

user314 > kanadanmajava1 10/26/2020 at 15:36

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It’s interesting how certain companies latch onto ideas and make them de facto signatures. Kaman loves them some synchropters , Kamov does coax, Blohm und Voss (or at least what Richard Vogt designed) went balls-deep on asymmetrical designs, Piasecki/ Vertol made a lot of tandem choppers .

Rock Bottom > user314 10/26/2020 at 16:30

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An interesting (and often overlooked) part of this story is how long Sikorsky has been working on their c oaxial birds. Most interestingly, t hey differed from the Kamovs in that they didn’t just stack 2 conventional articulated hubs , opting for a more radical rigid-in-plane hub. You can see how much closer the Sikorsky rotors are than the Russian blenders. That’s a move to limit shaft moments from the upper rotor and improve aero performance and response . It’s a harder dynamics problem to solve, but it lets you sneak the rotors much closer together than the Soviet way.

I know the first ABC flight vehicle was crashed and converted into a wind tunnel test article in the mid 70s . Last time I saw her , she had become a giant hornet colony that was abandoned on the North end of the NASA Ames Research Center, where it looks like she might still be. Seriously, this thing was PACKED with hornets. The nasty ones that sting you just because they’re curious what sound you’ll make.

Per usual, e njoy a few pics: First is the initial 1970 entry of an ABC rotor in the NASA 40x80 wind tunnel. This was only a rotating hardware test, before the rest of the vehicle was designed .   Second shows the converted ABC (former) flight vehicle in the 40x80, I think this was in 1980. Third is Google showing it still sitting pretty much where I remembered it, probably  still full of friggin’ hornets.

kanadanmajava1 > user314 10/26/2020 at 17:11

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I guess some designer just has a bright idea and falls in love with it. Then he just wants to make something usable out of it. Jack North r op really love the flying wing.