RSRA (Rotor Systems Research Aircraft) projects



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Looks like to me it's more of a high-speed testbed rather than an attack helo, along the lines ofthe Sikorsky S-72.
the caption on the picture 'a.jpg' says it all;

it's Bell's submission to the RSRA requirement, which was fulfilled by the Sikorsky S-72. see here:-

OK my friends,

and the helicopter was Bell Model-646,and not D-646,that is because the
D-600 was appeared in 1996;,1222.msg24790/highlight,d-600.html#msg24790
Ah, the Bell RSRA. I was in charge of that proposal while waiting for NASA and Bell to agree on the XV-15 contract. My unwritten orders were to provide a credible stalking horse for NASA Langley to use with Sikorsky so that they got a good price. The proposal had to be technically competent even though it was done on a shoestring budget so we didn't besmirch our reputation. The only good part of the deal was that I was expected, nay required, to lose. Bell management didn't want any part of that particular program. Losing wasn't hard, except for the engineers who poured their hearts into the effort - if I remember correctly, Sikorsky bid $24 million and Bell, $42 million. The latter was a little hard to explain since we had bid only $28 million to beat Boeing for the TRRA (Tilt Rotor Research Aircraft) program. Our glib explanation was that we had already developed the transmission and rotor for the Bell tiltrotor.

Personally, I thought the RSRA was a huge waste of time and money. One of my fantasies was that NASA would put the X-wing variant in the NASA 40x80 tunnel and it would come apart and destroy three dumb ideas, the RSRA, the X-Wing, and the 40x80. Actually the 40x80 was not really as dumb as the first two, but NASA forced the XV-15 to undergo an expensive and dangerous (and again, in my opinion not only unnecessary but useless) test program in the 40x80 before flight test. We managed to convince them to allow us to make a first flight and fly out to 40 knots (whoopee) in helicopter mode before the 40x80 entry. In addition to the risk (there's no inertia relief in a wind tunnel test, so it's relatively easy to overload the aircraft, particularly a helicopter, inadvertently), by the time we were done in the 40x80, we were out of money (the $28 million was really, really optimistic as it turned out; we knew it was optimistic but not really, really optimistic). What's worse, the tunnel could only put 200 knots or so on the aircraft and the real worry was at much faster speeds. Fortunately, the Navy came to the rescue with more funding (I was and always will be grateful to the late Hal Andrews) so we were able to get aircraft number 2 into the air, get to 300 knots (rounded up a tinsy bit, another story), and take it to the Paris Air Show, thereby demonstrating that the tiltrotor concept was worthy of even more money, some of which Bell management provided. However, the 40x80 effort delayed the program by at least a year, maybe two, and could well have resulted in its cancellation.

Bell Design vs. Model numbers can be confusing. The former were issued by engineering and fairly easy to get. The latter were recommended by marketing and authorized by executive management; getting one was a significant milestone for a program internally. Design numbers, if I remember correctly, were sequential. Thought was put into a model number, e.g. 209 Cobra (well, maybe not that one), 309 King Cobra, and 409 for the AH-63 program. As a result, a design and model number could be the same but refer to two completely different projects. In this case it was in fact the Model 646, since model numbers were almost assigned to formal proposals.
Interesting story Tommy - thanks for that insight. What did Boeing's TRRA look like - any idea or info?

Enjoy the Day! Mark
Mark Nankivil said:
Interesting story Tommy - thanks for that insight. What did Boeing's TRRA look like - any idea or info?

Enjoy the Day! Mark

Unfortunately, some of my files have disappeared along the way. This is the best I could come up with on short notice. Boeing Helicopter differentiated their proposal from Bell's in several ways. The rotor turned the other way ("down and out" versus "up and in"), the rotor was soft-in-plane vs. stiff-in-plane, the engines were fixed instead of tilting, and they had leading edge devices to reduce rotor download on the wing in helicopter mode. If the fuselage looks familiar, it's because it was an MU-2 airframe.


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Greetings All -

Interesting model of the S-72:

[eBay item no longer on sale]

Enjoy the Day! Mark
Some pics:


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hesham said:
Because no one noticed that design,Sikorsky DS-509.

In that case, just put a link directly to the one post:,6151.msg50730.html#msg50730

OR link the existing photo (instead of attaching it once again), like this:

hesham said:

anther drawings to this helicopter,type A and B,and they called it 646,
may be the Bell Model.

The proof for that report 646-099-001 & 003 was the Bell Model-646;

This document is submitted in accordance with the requirements of
NASA Contract NASL-1L251, Predesign Study for a Rotor Systems
Research Aircraft (RSRA). The RSRA is a compound helicopter with
a speed ability of 300 KTAS. It incorporates data systems which
make possible the in-flight measurement of values normally obtained
in wind tunnels.
Bell Helicopter Company (BHC) has conducted a 30-week conceptual
predesign of the RSRA. The analysis which led to the definition
of the RSRA configuration is described in BHC Report 646-099-001
(A Conceptual Study of the Rotor Systems Research Aircraft). The
proposed Development Plan for the RSRA is presented in BHC Report
646-099-003 (A Development Plan for the Rotor Systems Research
This Predesign Report describes the RSRA, including the major
subsystems. Detail Specifications and drawings are included.


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Large versions of the images of the Bell Model 646A (larger variant) and Model 646B (smaller variant) proposals for the RSRA program, still from the same report:


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This query might be taking things a little off-topic, but other than the OH-6A "Quiet One" programme, the Higher Harmonic Control programme and the Wallops Island quiet helicopter testing in 1986, did NASA carry out any other significant test programme utilizing the OH-6A/H500 helicopter, be they for rotor research or or otherwise? Thanks.

500 Fan.
Of course it was early concept,

please note it had a S-67 rotor and differs from the helicopter actually built.


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From Sikorskyarchives,

here is the RSRA.


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