TO: HELO TEACHER
“My mistake, in reading your report I got the impression the 1-2 degree sense of direction allowance was yours”. What I would really like to read at this point is the report that established these limits. You wouldn't happen to have a link would you?
RESPONSE: YOU ARE CORRECT, THE DEGREES OF COUPLING WERE MINE. I WENT BACK TO THE CERTIFICATION DOCUMENT AND I FOUND THAT I MADE A COMMENT ON THE BOTTOM OF THE PAGE. THE SECTION OF THE DOCUMENT STATED THAT THERE SHOULD BE A STANDARDIZE MOTION IN THAT WHEN THE CONTROLS WERE MOVED THE HELICOPTER SHOULD RESPOND IN THE DIRECTION OF CONTROL MOVEMENT. THE DOCUMENT ALLOWED FOR A CERTAIN DEVIATION DUE TO CYCLIC/COLLECTIVE COUPLING BUT NOT ENOUGH THAT THE PILOTS WOULD FIND IT UNCOMFORTABLE. My COMMENT STATED THAT 1-3-DEGREES OF COLLECTIVE/CYCLIC COUPLE WOULD BE ACCEPTABLE BUT NOT 18-DEGREES. I PICJKED UP THE COMMENT AND ADDED TO MY REPORT AS A MEANS OF COMPARING COLLECTIVE/CYCLIC COUPLE AS DESCRIBED IN THE CERTIFICATION DOCUMENT AND MY PREMISE THAT STATED THAT THERE IS AN 18-DEGREE OFFSET REQUIRING THE PILOT TO COMPENSATE FOR THAT OFFSET. THE SECTION THAT DEALS WITH THE SENSE OF DIRECTION IS SECTION 27.779 OF THE FAA NORMAL CATEGORY ROTORCRAFT CERTIFICATION REQUIREMENTS. DOCUMENT NUMBER AC 27.1 CHANGE 2
“I still feel, from my experiences with the aircraft, is that the biggest threat in a sideslip in the R22 is overcontrolling by the pilot. The limit being there to prevent inexperienced pilots from getting into trouble”.
RESPONSE: THE LIMIT OR RESTRICTION AGAINST SIDESLIP AND OUT OF TRIM WAS PLACED IN THE POHs FOR REASONS PREVIOUSLY STATED AND THEY APPLY TO ALL PILOTS NO MATTER WHAT THEIR LEVEL OF EXPERIENCE MIGHT BE.
“Also, can you please explain how the coning hinges prevent a 90 degree lead but allow a 72-degree lead”?
RESPONSE: IF YOU HAVE ACCESS TO A BELL 206 YOU CAN CHECK THE ROTORHEAD AND YOU CAN SEE THAT THE PITCH HORN TERMINATES AT THE TEETER HINGE. IF WHEN THE DISC IS TILTED OR WHEN YOU ARE IN A HOVER THE BLADES ARE DISPLACED FROM THE TIP PATH SELECTED BY THE PILOT THE DISC WILL FLAP IN RELATION TO THE FIXED SWASHPLATE. THIS CAUSES A RELATIVE MOVEMENT BETWEEN THE FIXED PITCH LINK AND THE PITCH HORN. IF THE BLADE FLAPS DOWN IN RELATION TO THE FIXED PITCH LINK THE PITCH WILL INCREASE AND THE OPPOSITE IS TRUE FOR THE OTHER BLADE THAT FLAPS UP. THIS PROVIDES A RESTORING FORCE AND RETURNS THE DISC TO THE COMMANDED POSITION. WHEN THE SWASH PLATE AND ROTOR DISC ARE PARALLEL THE ACTION WILL STOP. IF THE PITCH HORN / PITCHLINK ATTACHMENT ARE COINCIDENT WITH THE TEETER HINGE THERE WILL BE NO PITCH CHANGE IF AN EXTERNAL FORCE DISPLACES THE BLADE. IN THIS CASE THERE MIGHT BE A DISC DISPLACEMENT DUE TO GYROSCOPIC PRECESSION (MAYBE)
NOW, LOOK AT THE ROBINSON HEAD. TRY TO VISUALIZE A 90-DEGREE PITCH HORN. NOW TRY TO VISUALIZE WHAT HAPPENS WHEN THE BLADES CONE UP. WHEN THEY CONE, THE PITCH COUPLING WOULD INCREASE THE PITCH SETTING APPLIED BY THE PILOT TO SUCH AN EXTENT THAT YOU COULD END UP STALLING THE BLADES. IF YOU COULD GET IT OFF THE GROUND, TRY TO VISUALIZE WHAT HAPPENS DUE TO PITCH COUPLING WHEN THE CYCLIC IS DISPLACED AND YOU ADD IN ADDITIONAL PITCH ON THE RETREATING BLADE.
IF YOU COULD GET IT OFF THE GROUND AND YOU HAD THE POWER AND THEN INTRODUCED CYCLIC PITCH YOU WOULD IMMEDIADTELY BE EATING A PLEXIGLAS SANDWICH. THE POSITION OF THE CONE HINGES DICTATES WHERE THE PITCH HORN / PITCHLINK CONNECT POINT MUST BE. UNDER IDEAL CONDITIONS THE PITCH HORN / PITCH LINK WOULD TERMINATE COINCIDENT WITH THE CONE HINGE. FLIGHT MANEUVERING AND PITCH SETTINGS DO NOT ALLOW THIS TO HAPPEN. IN THIS RESPECT, THE ROBINSON HEAD IS JUST LIKE A SIKORSKY HEAD THAT HAS OFFSET HINGES.
NOW, IF YOU UNDERSTAND THIS, YOU WILL ALSO UNDERSTAND WHY I STATED THAT FRANK ROBINSON WAS HANDING OUT A LINE OF BULL WHEN HE INDICATED,THAT HE HAD CONSIDERED THE 90-DEGREE PITCH,HORN EVEN THOUGH HIS ROTOR SYSTEM IN EFFECT HAD AN OFFSET HINGE AS A PART OF THE DESIGN FROM DAY ONE.
YOU MAY HAVE NOTICED THAT I HAVE CHANGED MY STORY A BIT ABOUT WHAT HAPPENS IF YOU HAVE A 90-DEGREE PITCH HORN ON A RIOBINSON HEAD. THIS COMES FROM YOUR INPUT THAT CAUSED ME TO EXAMINE THE PROBLEM FROM A DIFFERENT PERSPECTIVE.
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The Cat
[This message has been edited by Lu Zuckerman (edited 01 January 2001).]