To: Crab
Lu, I don't have to get in an R-22 to predict the outcome of your obscure test.
1. The R 22 naturally sits slightly nose up and left skid low in the hover due to C of G and the pilot compensating for tail rotor drift and roll (you call it translating tendency) - if you select a "wings level attitude ie do not correct for the above effects the helicopter will start to move right quite quickly.
IT IS MY UNDERSTANDING THAT THE ROBINSON MAST IS TILTED 2-DEGREES TO THE LEFT TO MINIMIZE IF NOT ELIMINATE TRANSLATION DUE TO THE PROPELLER EFFECT OF THE TAIL ROTOR .
2. If the cyclic is then moved forward along the centreline of the aircraft (almost impossible to do accurately without a stick-plotting setup) it will begin to transition into forward flight still moving right as well.
I AGREE THAT IT WOULD BE DIFFICULT TO MAINTAIN THE CYCLIC ON THE RIGGED NEUTRAL CENTERLINE BUT NOT IMPOSSIBLE. IF THE HELICOPTTER IS TRANSLATING TO THE RIGHT DESPITE THE MAST TILT THIS WILL DIMINISH WHEN YOU GET THROUGH TRANSLATIONAL LIFT WHEN THE TAIL ROTOR BECOMES MORE EFFECTIVE AND YOU REDUCE COLLECTIVE AND BRING THE TAIL ROTOR MORE TOWARDS NEUTRAL. EVEN IF THERE IS TRANSLATION, IS THIS A PROBLEM IF THERE ARE NO OBSTRUCTIONS?
3. Translational lift will make the disc flap back and to keep accelerating the cyclic must be moved forward to overcome it.
THIS IS NORMAL. AS A PART OF THE TEST THE PILOT WOULD MOVE THE STICK ON THE RIGGED NEUTRAL CENTER LINE
4. Inflow roll (transverse flow) will cause the aircraft to roll towards the advancing side of the disc - RIGHT side on R22.
THIS IS ALSO TRUE AND TO COUNTER THE RIGHT ROLL THE PILOT MOVES HIS CYCLIC TO THE LEFT. IF IT IS SAFE IN THE RECOMMENDED TEST THE PILOT IS ASKED TO TRANSITION THROUGH TRANSVERSE FLOW AND PASS THROUGH IT AS THE HELICOPTER WOULD I ASSUME RETURN TO ITS’ NORMAL POSITION. IF THIS IS NOT THE CASE, THEN THIS PART OF THE TEST IS INVALIDATED.
5. As the aircraft started out moving right with wings level and has now rolled to the right as well - how can it ever go left as you suggest.
THIS PARTICULAR PART OF MY ARGUMENT IS A BIT DIFFICULT TO EXPLAIN BECAUSE IN THE PROCESS OF REPLYING TO A LOT OF NEGATIVE POSTS I BEGAN TO LOOK DEEPER INTO THE ORIGINAL PREMISE THAT I HAD IN WRITING MY REPORT TO THE NTSB. IF I WERE CORRECT IN MY ASSUMPTIONS THE HELICOPTER WOULD FLY TO THE LEFT BECAUSE OF THE 18-DEGREE OFFSET. I STILL BELIEVE THAT AND, THAT IS WHY I SUGGESTED THE TEST. WHAT I BELIEVE IS THAT WHEN THE PILOT COMPENSATES FOR TRANSVERSE FLOW EFFECT BY INPUTTING LEFT CYCLIC AND WHEN HE PASSES THROUGH THAT HE RETURNS THE CYCLIC TO A POINT WHERE THE HELICOPTER IS FLYING STRAIGHT AHEAD AND IN THE PROCESS HE HAS COMPENSATED FOR THE 18-DEGREE OFFSET. THIS IS FOR ILLUSTRATION PURPOSES ONLY. A LONG TIME AGO A SIKORSKY TECH REP WAS VISITING AN AIRCRAFT CARRIER. WHILE ON BOARD HIS ADAM HAT BLEW OVER THE SIDE. HE PUT IN A $10.00 CHGARGE ON HIS EXPENSE REPORT AND IT WAS REJECTED. HE DID THAT TWO MORE TIMES AND EACH TIME IT WAS REJECTED. ON THE NEXT SUBMITTAL HE ADDED A NOTE SAYING THAT THE HAT WAS IN THERE, TRY AND FIND IT. THE 18-DEGREE OFFSET IS IN THERE JUST LIKE THE HAT. HOWEVER IF THE PILOT DOES NOT KNOW EXACTLY WHERE IT IS HE CAN GET KILLED IF HE EVER ENCOUNTERS A ZERO G SITUATION OR, IF HE EVER GETS INTO A POSITION WHERE THE FLAPPINGLOADS ARE STARTING TO INCREASE.
Becauase of the way you say the R22 is rigged there may be some cross coupling between pitch and roll but this is likely to be an acceleration cross couple and only manifest itself when the cyclic is moved sharply and with considerable displacement.
CROSS COUPLING OR PITCH COUPLING ARE ALLOWED IN THE CERTIFICATION OF A HELICOPTER BUT ONLY TO THE POINT THAT IT IS NOT UNCOMFORTABLE FOR THE PILOT TO MANAGE CONTROL. WOULD YOU FEEL COMFORTABLE TO FLY THE LYNX WITHOUT THE AID OF ELECTRONIC COMPENSATION FOR THE 15-DEGREE OFFSET?
BECAUSE OF THE IMPRECISENESS OF THE ROBINSON THE PILOT IS NOT EVEN AWARE OF THIS CONDITION BECAUSE HE HAS BEEN TRAINED TO PUT THE STICK WHERE IT WILL MAKE THE HELICOPTER FLY FORWARD OR ANY OTHER DIRECTION.
The paragraph has been removed to protect the innocent.
Because of the nature of a teetering head (yes I know it technically has flapping hinges but it behaves the same way) the fuselage attitude does not change immediately following a cyclic input - there is a delay while the disc flys in the appropriate direction before the fuselage is dragged along behind it. (See previous R22 post regarding control power).
I AGREE WITH THE ABOVE COMMENT.
There is a basic flying lesson for you for free - try to understand it.
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The Cat
[This message has been edited by Lu Zuckerman (edited 26 January 2001).]