Sikorsky Raider X - FARA contender

[JohnDixson]

Yes, SD and wasn’t that beyond ironic, at least to those of us who vividly recall the oft repeated rule at SA in 1972-3 as we put together the design: “there will be zero exceptions”.*
But to my post: can you point me to the FARA Material Need Doc or whatever the Army called the specific requirements document? I’d like to read it.
* Actually, we found it necessary to take, as I recall the number was 10 exceptions to the spec requirements as stated in the RFP, and that resulted in details where one part of the quoted underlying requirement document was at odds with another requirement and you couldn’t do both. Met with the Army and got that stuff straightened out. Boeing would have had the same difficulty in those areas.
There was one handling requirement that we were unable to perform, and probably flew 20+ hours before giving up.
If you can get a look at the picture of the first flight of the UH-60A first prototype, 650,and direct your attention to the vertical tail fin, you’ll notice it was huge, and also very highly cambered. Those features went back toward the no exceptions rule at SA.
The reason for that tail was that there was a requirement ( at design gross weight ) that at zero tail rotor thrust, the aircraft had to be capable of level flight at best endurance speed with a sideslip angle not to exceed 30 degrees. Our problem was finding a way to prove to ourselves, much less anyone else, that our flight condition was zero thrust. NOW, the old timers among our readers may recall that at one point during the original S-58 development, this very test was accomplished and a report was made public about it. But that group had a tail rotor with a flapping hinge and we did not. Thus we tried all sorts of different tail rotor and structural data to get to a condition of zero tail rotor thrust with that very stiff and strong XBR4 crossbeam tail rotor, but never convinced ourselves that we had it for real. We had an Army Test Pilot assigned to our team by Army Flight Standards in St. Louis and he was in on all the testing, flight reports etc and all that information went to St. Louis, so they knew what was going on in detail. Finally, neither we nor they had any ideas that we hadn’t tried, and at the same time, that huge vertical tail with all that camber was creating problems of its own which resulted in conflict with some other handling requirements, the most obvious one was that the aircraft had to be able to fly from hover speed to either the 145 kt cruise point or 150KIAS-can’t recall, with the directional trim not changing more than 1/2 inch of pedal position. With that cambered tail, you can imagine that speed changes were accompanied by chasing the ball around ad infinitum. In fact, keeping the aircraft in trim doing almost anything was a continual task, and finally the requirement went away and after a few iterations we came up with the vertical tail you’ve seen since.
I have to say that the attempts to find zero TR thrust resulted in some very interesting and ingenious ideas being flown. There were any number of times when we finished a flight and thought we had it, only to look at the data and find the opposite.