Seeking information on the Flettner Fl 201 project in 1954

[Dave_Jackson]

Dual Rotor Powered Autogyro


"Anton Flettner again reappears, now the founder of his own company in New York after the war. The Fl 201 Heligyro, evolving out of his earlier work on the Fl 185, was a 30 - 40 passenger twin-rotor helicopter designed to takeoff and land as a helicopter but fly as an autogyro. Under United States Navy sponsorship the Fl 201 Heligyro was tested at New York Naval Air Station, Floyd Bennett Field. The model never advanced beyond the testing phase."


"After the war, Mr Flettner approached US Army with a new helicopter idea. Helicopters need no airfields and are theoretically ideal for short-haul transport of troops, but a big trouble with them has been that the life of the central nerve, the gear box for the rotor, is not nearly so long as military leaders would like. Rotor gears require major overhauls every few hundred flying hours.

In 1954, Mr. Flettner thought that he had the answer. He decided that if the gear life was the main problem, the rotor gears should be used less. He designed a helicopter with a forty troops capacity in which two conventional propellers would assume the burden of forward flight, with the intermeshing overhead rotors , drawing 20 per cent or less of the engine power and simply providing lift. The result, he said, would be gear life 10 times what it is when the rotor does the whole job. The Army financed the design with the idea that it might eventually invest in production."


Thanks for any additional information on this early rotorcraft project.

Dave

[riff_raff]

Dave_Jackson,

Saw your post on the electric helo thread. I don't know anything about the Flettner FI 201, but regarding the quotes about MRGB life, they are no longer valid. A modern MRGB typically would have an overall L10 design life of something like 5000 hours. In fact, the gears themselves are typically designed for unlimited fatigue life in tooth bending based on a composite load case. The component that typically limits MRGB life now are bearings.

As for the comment about the FI 201 MRGB operating at 20% MRP for 90% of life permitting "gear life 10 times what it is when the rotor does the whole job", that may not be entirely true.The main design drivers for gears/bearings in any MRGB are the loading experienced during hover in hot/high conditions at heavy gross weight, and operation in OEI conditions. In this respect, the FI 201 wouldn't be much different from a conventional helo.

Lastly, one would also need to consider the architecture of the FI 201 drivetrain. With these types of compound propulsion systems that divide power between the main rotor and propeller drives, the input sections of the MRGB would need to be designed to accommodate 100% of the engine output even though only 20% of that power goes to the main rotor.

Sorry for being a bit OT, but as you're likely aware I love discussing the subject of gearboxes! http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/thumbs.gif

Best regards,
riff_raff

[Dave_Jackson]

riff_raff

Thanks for the info.
Have sent you a private message.

Dave

[extrarotorwash]

Hi

Flettner founded the Company Flettner Aircraft Corporation in 1949 hes partner in the company was Admiral C.E. Rosendahl in Kew Gardens New York.

regards

[Dave_Jackson]

extrarotorwash

Thank you for the lead. There is information about him on the internet that may be interesting.

Dave

[riff_raff]

Dave_Jackson,

While you already likely know of it, the DTIC (http://www.dtic.mil/dtic/) is an excellent source for technical reports, especially legacy aero research dating back to the 1920's. I ran a quick search using Flettner Aircraft Corporation and got a couple of papers on tandem rotor research. I didn't take time to read thru them. But even if there is no specific discussion of the subject in the text of the paper, you can usually find links to other possible sources in the appendix.

NASA's Technical Reports Server (http://ntrs.nasa.gov) is also quite good. You can find extensive legacy research reports from both NASA and NACA. Unfortunately, the server NTRS operates thru often seems to be unavailable.

Hope that helps.
riff_raff

[Dave_Jackson]

riff_raff

Thanks for he leads. The DTIC is totally new to me. It will be looked into.


Dave

[cockney steve]

Don't forget the Fairey Rotodyne.....flew successfuly but killed by the Government of the day...(now where have Iheard that before?)

[Savoia]

David

Have been hunting high and low for further details on the FL201 'Heligiro' (as it was called) and, as you are doubtless well aware, there is precious little information out there.

The blurb I have reads:

"The FL201 'Heligiro' was an enlarged development of the FL185 with twin rotors, power to be applied to the rotors only in vertical and hovering flight. During forward flight, twin turboprop engines would provide propulsion. The aircraft did not progress beyond the design stage.

This was to have been a large aircraft capable of carrying some 30-40 passengers. Twin three-bladed rotors, approximately 80-90 ft. in diameter were to have been fitted."

I do have two PDF files which I would be more than happy to send you; one is a copy of a report dated 1948 entitled: British Intelligence Objectives, Sub-Committee Overall Report No.8, "Rotating Wing Activities in Germany during the period 1939-1945" (this includes among other things, diagrams of the rotorhead and transmission for the FL282) .. and another document (untitled) with a similar appraisal of German rotorcraft designs during the 1940's.

Both documents are courtesy of Cliff Gunsallus, Vice President of Engineering at Kaman Aerospace.

If you would like them, please contact me at: [email protected] and I shall email them by return.

Rgds

Sav

[Dave_Jackson]

cockney steve,....flew successfully but killed by the Government of the day...(now where have I heard that before?) Yes that does sound familiar.


Sav,

Thanks for the additional information.

The mention of "three-bladed rotors" on an Intermeshing helicopter means that Flettner was considering very rigid rotors. This, combined with "During forward flight, twin turboprop engines would provide propulsion.", represents the Advancing Blade Concept that was later built by Sikorsky as a Coaxial (http://www.unicopter.com/0891.html).

Thank you for your offer of two documents covering the rotorcraft in Germany during 1939 to 1945. There is a Flettner - FL-282 Kolibri frame in England and a transmission at the Smithsonian in the US. A number of years ago an American gentleman had gone to a lot of work to reverse engineer the craft. His intention was to build an exact replicate, fly it once, then return the motor to its owner and put the craft in an air museum.

Also, Prewitt Aircraft Company tested a FL-282 in 1947 and prepared a 146 page report. They recommend that interested Americans come and test fly the craft. A later report was written, which might have mentioned if anyone outside of Prewitt ever tested the craft, but I was never able to find a copy of this second report.

Your two .pdf files may provide additional information and will be very much appreciated. An email will be sent to you with the email address.

Thank you.


Dave