Rotary Reverse
Helicopter rear speed limits.
Not sure if any factual info is wanted on the subject, but as its post Christmas and I'm full of mince pies ... can I add some actual numbers to the discussion.
The PFM's stopped quoting actual 'crosswind/rearward' limits a while ago, (probably due to an accident below the quoted numbers and a legal claim) so these days they simply declare that the machine in question has been 'demonstrated at ....? (usually circa 17 knots)
Having looked into the situation we all appreciate the rearward 'disc flapping' limit where the cyclic reaches the rearward limiting stops and further airspeed increase simply tucks the nose down with no further aft control movement available to correct.
This assumes the pilot retains an approximate horizontal 'flapped back' disc attitude with translational/then transitional airflow acting conventionally. I've found in my display routine, that a firmer aft movement of cyclic before translational effect kicks in results in a pronounced change of disc attitude (nose well up and T/R down) to the point where the further transitional flow is replaced by an 'induced' airflow so that the disc no longer 'flaps.' In this attitude perhaps 90% of the flow is now through the disc and the actual limit is only the available collective (power) and speed at which the drag equals the thrust. Anti torque pedal control is significantly INCREASED !! We've all seen the Antarctic Chinook's attitude as it pulls through the ice !!
I know that Charlie Zimmerman and Herman Fuchs had 'rearward reading' ASI's on their B105's for their 1986 Championship routines and I'd quite like one for the Enstrom/Hughes.
The best I have is a GPS reading and subtract the known wind but I have seen a 75knot indication along the crowd line downwind. As 2005 will be my last display year, I'm hoping some younger 'guns' will take up the display scene soon and no doubt investigate the numbers further.
Good wishes to all ppruners for 2005.