A little helicopter history

[Dave_Jackson]

Mart,

The remarks in my previous post are not speculation! The number in front of each remark is the Sikorsky document that it came from.

You obviously have an interest in Sikorsky's ABC craft. Perhaps your technical speculation, and the rebuttals, will be reduced, plus your knowledge be enhanced, if you first read this, and the linked, web pages; or buy the Sikorsky documents.

[IFMU]

Not sure if S-69 was FBW or not

Look at the era they flew the S-69 during. Did your car back then have a carb or electronic fuel injection? I think that may lead you to an answer.

did it preceed Shadow version of S-76?.

It seems like in the past several decades the designation number has been close to the year of conception. I think the S-92 was announced in 1992, though it was longer before it was certified. In either case, the model number is a sequence designator, so the S69 would have preceeded the S70, 71, 72, 73, 74, 75, and 76. The S70 was the blackhawk, some of the ones in between were probably research aircraft, or the designation never went anywhere. Maybe they were top secret intermeshers.

-- IFMU

[NickLappos]

IFMU,
The S-1 was Igor's first machine, and it didn't make it over the trees. The S-2 did, and so on!

The S numbers were used for big proposal efforts as well, so not every S number flew.

The only Sikorsky machine without an S number was Comanche, which was a Boeing collaboration.

I flew the ABC, it had regular controls, lots of them! 225 knots was a scream, frankly!

[Graviman]

Dave, old chap, not rebuttals just observations. I just misread your last post as being a comparison between lateral machines and coaxial. Thanks for additional info though.

From your site i would say altering the phase angle just redirected the forward cyclic required to compensate flapback to load up advancing sides, otherwise compensating for flapback would transfer load back to retreating sides nullifying ABC advantage. I am suprised that opposed lateral cyclic wasn't preferred over lead angle trimming though. This may have just been easier to control in flight. For automated system opposed lateral cyclic would make more sense to my mind.

IFMU, thanks for clarification. I wasn't sure whether numbers were in order. Then again i'm here to learn this sort of stuff!

Nick, that project sound's like my definition of fun! How did you find lateral control at speed? I'm curious in context of altering phase angle to load up advancing blades.

Mart

[Dave_Jackson]

Mart,

In post #38 you mentioned

In coaxial you can design the machine with sufficient clearance .........

Premonition? This latest Sikorsky patent may bring a smile to your face.

http://patft.uspto.gov/netacgi/nph-P...S=PN/7,210,651

or if the above does not work try;
http://www.uspto.gov/patft/index.html,
go to 'Patent Number Search' and enter the patent number 7,210,651

Dave


Edited to add the following United States Patent Applications by Sikorsky for coaxial transmissions;

20060269414, Variable speed transmission for a rotary wing aircraft.
20060269413, Rotor drive and control system for a high speed rotary wing aircraft.
20060266883, Split torque gearbox for rotary wing aircraft with translational thrust system.

[Graviman]

Skimmed patent, Dave (pics don't always work for this site). Intermeshing may well offer a simpler solution for forward flight (equal flapback both rotors). For sideward flight the risky area is the crossover azimuths fore and aft of the intermeshing hubs. So active servo technology would benefit any counterrotating machine.

The main arguement to my mind has to be the compactness of the main gearbox with intermeshing. Being able to keep the rotorshafts short is a benefit for resonance control. The increased package space also allows independant root & tip control. In practice active tip servo helps on both counts - assuming multiple redundancy...

Mart

[IFMU]

First, apologies for dragging up an old thread. But I read this article in the November Sport Aviation today about a former Luftwaffe pilot, Gunter Voltz. Like many of his fellow Germans he came to the states after the war. He had 1800 combat hours in the Fieseler Storch. He said in the article "one reason the Germans were slow to develop helicopters was they didn't need them - they had the Storch."

-- IFMU

[Dave_Jackson]

You're going to get slowrotor excited,

Slepcev Storch ~ Vertical take off in a 16-mph wind.


Heck. You're going to get the Navy excited.
The only boats that they have, which can't go fast enough for vertical take-offs and landings, are their rowboats.

Dave

[slowrotor]

The Slepcev claims of 15mph flight are exaggerated.
Quote from website: "The aircraft will fly at 22mph at full flap and 30% of power. Take off run into a 16mph wind is vertical with no forward roll".

So what is the stall speed, 22mph or 15mph?
They can make any claim they want using indicated airspeed. I had an airplane that would indicate 0 mph in a steep climb.

The engine can provide lift for takeoff, but using full power to reduce the landing speed is not practical. That's why the landing distance is longer.
slowrotor