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Black hawk down -

Old 14th Sep 2022, 09:42
  #21 (permalink)  
fdr
 
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Interesting kit-setting of the MRB, not in the same league as the T-72 turret but not a bad effort. Quick maths, the drivers have about 0.6g longitudinal acceleration from the waltz, with that, how easy is it to get to the PCL's on the UH-60?

Pretty amazing that the machine takes that long to get out of sorts with loss of T/R, guess the hinge offset is helping the driver maintain a semblance of control, most other machines will be out of control completely early on with the feedback of the cg-hub offset. U guys did a fine job on the UTTAS, J.D.
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Old 14th Sep 2022, 13:42
  #22 (permalink)  
 
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FDR, thanks…..but we both and all owe thanks to a Colonel Bud Patnode and the group he headed up circa 1970 and came up with the handling requirements for the UTTAS. The hinge offset increase and matching cyclic control range resulted from a couple of things, but among them was the requirement to land on a slope of 12 degrees at any angle to the slope, and to land on a slope of 15 degrees at 90 degrees to the slope, both left and right. BTW the 12 degrees up and down slope capability existed for both most forward and most aft center of gravity loading at design weight.
( the Army built appropriate slopes at Shell Field, Ft Rucker and we checked out our 10 young operational pilot evaluators on those slopes-those pilots had some fun with that, but basically, except for the wheels and brakes, the same principles they had been taught for the UH-1 held true. )

There was some interesting initial fallout from the hinge offset increase, within SA engineering and flight test:

Folks might recall the first Skycrane, the S-60, which was basically an S-56 power train and control system on a new crane-type fuselage. There was some internal concern about the higher control power ( hub moment ) with such a machine, which had a much lower inherent fuselage roll inertia. The concern was whether with very heavy loads the resultant control sensitivity would lead to a serious over control tendency. No worries….we will do a flight test to examine same. ( this all happened before I signed on but the folks involved were still around to tell about it ). So they fabricated some sets of controls to incrementally increase the sensitivity and started testing. Initial results weren’t showing much of an issue so a decision was made to go to a 50% increase in sensitivity. Pilot Ed Mullins put it this way when telling me about it: “ John, the moment I picked it up into a hover, I knew we were screwed “
( Now the S-60 had a pair of R-2800 P&W engines running on 115/145 fuel ). The ensuing crash on the flight field at Stratford would have been fatal for both pilots, but the cockpit broke off and rolled away from the fireball. Both pilots were Ok and soon back on flight status.

With that background, and the increased hub moment vs roll inertia of the UTTAS, we used the flight simulator at UTC Research CTR to evaluate this area. Now mathematically the numbers did not look like there was a problem…but I crashed every time in that sim…..and so did the Ch Engr Pilot and the Ch. Pilot., so we cut down the roll control sensitivity for the first hover of the UTTAS ( UH-60A )-it was not even close to being an issue-and put the control range back to where it should have been and is today, for the second flight.
Explains my skepticism re sim based decisions in future years. ( and yes-that was a “ Gen-Hel “ based sim program ).

Last edited by JohnDixson; 14th Sep 2022 at 19:24.
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