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Tail Rotor vs Twin Rotor (ie Chinook)

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Tail Rotor vs Twin Rotor (ie Chinook)

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Old 9th Nov 2018, 03:45
  #41 (permalink)  
 
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To be fair....two people survived.

Airbus aircraft that shuck Rotorheads take everyone with them.
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Old 9th Nov 2018, 05:23
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I think all helicopters are evil. I believe aircraft should land and then stop not vice versa
Bob, there is a firm belief in sections of the helo world that anything that needs to accelerate down a runway to reach XXX knots in order to fly is inherently unsafe, despite what the following has to say.



Just to round off, most helo pilots learn to fly on fixed wing then graduate to helos.
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Old 9th Nov 2018, 05:27
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That is brilliant.
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Old 9th Nov 2018, 06:06
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vs No Extra Rotor at all

The rotor is driven only by tip jets. Air from a gas turbine is piped to the rotor tips where it is burned with fuel. Much whizzing round, no torque reaction. Oh, and NO GEARBOX in the rotor system. It seems that there will be far fewer plumet-out-the-sky-right-now single points of failure when compared to a helicopter with mechanically driven rotors.

A commercial failure in the 1950's apparently due to very high noise levels from the tip-jets.

https://en.wikipedia.org/wiki/Tip_jet

The Rotodyne was "A helicopter at take-off and an autogyro during forward flight".

A singe rotor variant was developed first. The best known model confusingly had three rotors (as per this thread's terminology) however only one of them was used for vertical takeoff, hovering and landing, the two conventional propellers being just that and used for high speed forward flight only. True single rotor variants were built.

Single rotor variants





Fairey UL Helicopter




Hiller Hornet




Fairey Rotodyne


https://en.wikipedia.org/wiki/Fairey_Rotodyne

https://www.theengineer.co.uk/issues...e-of-aviation/


https://www.britishpathe.com/video/r...ry/US+AIRLINER
8mins, no sound

https://www.bbc.co.uk/news/magazine-35521040
Why did the half-plane, half-helicopter not work?

Last edited by jimjim1; 9th Nov 2018 at 06:25.
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Old 9th Nov 2018, 06:15
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Originally Posted by Octane View Post
Hi Bob,

How would you like to go for a ride in one of these machines?
It has 2 rotors but is sort of in between a Chinook and a conventional helicopter. The design doesn't seem to have caught on...
https://www.youtube.com/watch?v=Xy0GMyfGu6s
I was impressed - right up until the pilot didn't flip it over and mow the grass where it had been standing all year:-)



Please don't forget the grass ...

Last edited by jimjim1; 9th Nov 2018 at 06:27.
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Old 9th Nov 2018, 07:35
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You mustn't forget that with the popular setup of having a little ant-torque rotor at the back, Mr Sikorsky had originally planted it facing up much like a tandem setup but spinning a little faster. Theoretically it should have worked but flying it in that configuration proved to be more exciting than is necessary so they bolted it back to point to one side.

Another concept for Bob's fancy is the intermeshing rotors of the K-Max. It'll knock your head off if you don't approach it from the front.
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Old 9th Nov 2018, 07:53
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Funny that the soundtrack for the Rotodyne sounded more like a B47 2-blader than a 4-blader plus 2 propjets.
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Old 9th Nov 2018, 09:47
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AC,

You have a point there but in real life, it actually sounded like a steam locomotive.

I lived in Maidenhead, about three miles from White Waltham in the early 60s. This was the last days for the Rotodyne and the last days of steam. The Western Region mainline ran right by the airfield. It was nearly impossible to distinguish the noise of the Rotodyne from that of a King or Castle at speed.
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Old 9th Nov 2018, 10:37
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If you want something REALLY complicated; try this.

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Old 9th Nov 2018, 12:13
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... and by way of comparison, here's a minimalist approach - the Hiller YROE-1:

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Old 9th Nov 2018, 14:07
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Care to tell me what this is then. Your starter for 10!
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Old 9th Nov 2018, 14:23
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It's an autogyro used as a towed aerial platform to provide longer-range surveillance to sufraced U-boats.

In the UK we tried the "Hafner rotabuggy" as a strap-on rotor system to turn a jeep into and autogyro for air-deploying the jeep. The tail and rotor system were to be removed after landing:



The same guy came up with the "Rotochute" as a system for getting a soldier plus full kit (more kit than a contemprary paratrooper) and ammo into hostile territory:



You name it, it's been tried...
PDR
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Old 9th Nov 2018, 15:47
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PDR - you spotter!Focke Achgelis Fa 330

It was flown as a kite towed by the submarine on a 150 metre cable, and could be quickly assembled or dismantled and stowed through a U-boat hatch. It could be deployed on the deck by two people. The rotor blades were set in motion by a pull cord, or by hand if there was enough wind. The kite would then be deployed behind the U-boat with its observor pilot aboard, raising him 120 metres above the surface where he could see much further. To bring it back in the towing cable was pulled by a winch. When the aircraft landed the rotor was stopped with a brake. Two to three members of the crew were trained to use the Fa 330...................

except when there was an emergency "dive" required......
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Old 9th Nov 2018, 15:50
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What that doesn't mention is the occasions when they saw an threatening Allied vessel or ship and the submarine cut off the 330 and dived without him.
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Old 9th Nov 2018, 15:55
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Originally Posted by JohnDixson View Post
CG Range: Single vs Tandem Rotor

A popular myth which has survived for years in spite of facts to the contrary. One example I was able to access online just now:

CH-47D Manual.
Max Weight: 50,000 lbs
CG Range at 50,000 lbs: 322-331 inches= 9 inches

MH-53E Natops
Max Weight: 70,000 lbs
CG Range at 70,000 lbs: 343.9-365.0 inches= 21.1 inches
Very interesting, John, and counter intuitive. All that from the canted tail rotor? Some from the height of the rotor head above the cg? Some peculiarity of the CH-47 control mixing? I've toyed with writing a paper on the Piasecki HRP development and want to be sure I don't believe something silly.
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Old 9th Nov 2018, 16:16
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Another difference between tandem and single-rotor helicopters is the relative indifference of the former to the wind direction in a hover/departure versus the need to be aware of it when flying the latter (less so in a Sikorsky than a Bell due to respective tail rotor control power provided). Of course, a tandem is equally inclined to be indifferent to heading the same way it's going in forward flight, to the point of preferring to be sideways. A tandem design also requires some thoughtfulness and caution with respect to the interaction of the cyclic and collective systems for pitch and height control. For example, a tandem lesson learned early on is that showing off with an aggressive pedal turn in a low hover might result in the rear rotor going into translation lift while the forward rotor has not, introducing a sudden nose-down pitch that the cyclic may not be able to counter fast enough with differential collective.
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Old 9th Nov 2018, 17:56
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TT: nothing to do with the canted tail. If you check the 53D for instance, you get similar results.

Re your post 56, the point is quite true, but somewhat mitigated by the fact that the two tandems in the US military inventory history, the CH-21 and CH-47, were/are both cargo helicopters, thus not expected to have a mission agility capability such as the OH-6 or ( wistfully ) the RAH-66 Comanche.Flew both the 21 and 47 at the test board at FT Rucker 1963-65, and both had more than adequate directional control. Before someone jumps me, I was addressing flight, and leaving the taxiing techniques discussion to another day, but even there a bit of finesse went a long way.

Last edited by JohnDixson; 10th Nov 2018 at 13:23. Reason: typo
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Old 9th Nov 2018, 19:17
  #58 (permalink)  
 
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Bob,

If you look out of your crew room window you will see a big new building on the other side of the airfield blocking your view of the beach. Within you will find any number of rotary pilots who would gladly offer you a coffee and then bore you rigid with helicopter principles of flight and tech. However, having re read your posts, best bring a tin hat and a humble pie to go with the coffee!!

I think next week is quiet all round for the station so PM me if you want to come and have a look round.
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Old 9th Nov 2018, 19:43
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Originally Posted by JohnDixson View Post
TT: nothing to do with the canted tail. If you check the 53D for instance, you get similar results.

Re your post 56, the point is quite true, but somewhat mitigated by the fact that the two tandems in the US military inventory history, the CH-21 and CH-47, were/are both cargo helicopters, thus not expected to have a mission agility capability such as the OH-58 or ( wistfully ) the RAH-66 Comanche.Flew both the 21 and 47 at the test board at FT Rucker 1963-65, and both had more than adequate directional control. Before someone jumps me, I was addressing flight, and leaving the taxiing techniques discussion to another day, but even there a bit of finesse went a long way.
John - thanks for the referral to 53D cig range. Iím beginning to suspect a tandem pitch-control limitation on cg. Note that I wasnít dinging tandem directional control but its directional stability. Another interesting facet of tandem performance was that confined areas were best departed sideways to get the most out of both rotors in the process.
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Old 9th Nov 2018, 21:00
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There cannot be much wrong with twin rotor helicopters. Bristow is buying a load.

Bristow buying Columbia
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