always sad to see a machine get wadded up. At least in helo's more often than not, the soft filling gets to walk out of the wreck or carried.
Wind: the video shows negligible wind in the grass near the camera (phone..). What there is, appears to be from the left of the viewpoint, in the direction of the first translation. The 1st translation was reasonably undertaken and doesn't look like it was intended to be a take-off that was aborted, it looks like positioning for the turnaround. Only the pilot knows for certain, but it looks like positioning for the actual take-off.
Path: The final flight path looks like it went over a descending field, which also had a transition from short grass to long grass. For a running take-off, the disk height needs to be as low as is possible until achieving ETL, with the power requirement increasing rapidly with even small changes of the disk height from the ground. In the image, it appears that the flight path did not follow the terrain to maintain a constant level of the disk, so power requirement would have increased just because of the height above the ground. The path went from short grass to long grass, and that results in an increasing demand for hover power, The change is due to the attenuation of ground effect by the surface material, so the absolute change is dependent on the effect of the grass height, but as the helicopter is translating across the changed conditions, the rate of change is dependent on translation speed.
CG: 4 onboard and some gas will give a forward CG, heavy dudes in the front will bring it well forward. In the hover, absent wind, a CG outside of limits would be evident as a low nose condition, and if the cyclic limit is reached, then translation will occur that cannot be checked. To achieve a case like that, you are well outside of the CG envelope, but that is what happens. In this case, the helicopter first translates and then stops, pedal turns, and then sets off again, suggesting that the CG was not a significant factor. For a semi-rigid rotor (OK, one with a hybrid coning/teeter head...) A CG at a limit won't make a whole lot of difference to the power required. Within reasonable body pitch angles, the TR arm isn't going to shift a whole lot; a forward CG will induce a slight roll component increase, but not much, and the lateral cyclic demand isn't much. Power required won't change any significant amount.
Running take-off with increasing skid height below ETL; The terrain falling away seems to have let the driver enter an increase in his skid (disk) height, and the outcome suggests that they were likely still under ETL. That would have increased power requirement. The ground falling away would have required an increase in forward cyclic to maintain a constant height. Going from zero speed towards higher speed, the cyclic demand for level accelerating flight follows a reverse "S" shape, (with all motion forward), the flap back even at low speed, results in an increase in forward cyclic and if not made, e.g., a constant longitudinal cyclic is held, then the helicopter longitudinal acceleration will reduce. Nothing new in any of these issues, but coupled with ground contour falling away, a lot of things are occurring that happen to need care in handling to avoid an increase in power. For most take-offs, we don't get to the absolute limits of power required, which is a good thing, as when it starts to go bad, the problems compound quickly. (Mason tells the story of a messed up slick running takeoff that ended up in the razor wire inside a minefield, lots of stuff can happen...)
RPM: Low RPM sucks, and shows up in the coning angle if observed, and rapidly decaying TR authority, reducing cyclic authority, and some other stuff related to inertial-aero effects, most giving degraded HQ's. As the engine power output is dependent on RPM, low RPM really sucks. Recovery from low RPM in the hover is one thing, recovery below ETL is another, the translating case is going to have some interest in the surface conditions/contour etc... and the cyclic inputs at all times.MIlking the collective works like a hot dog in a hover, in a messed up running takeoff, lots of other dynamic stuff will come up rapidly and limit any effective gains from that technique.
Turns; a gentle turn to the right with minimal lateral cyclic, and a reduction in the left pedal will recover power, and RPM, but needs clear terrain, and judicious control on the rates, but the reduction in tail rotor power required will recover available power to the main rotor.
Leaving the bodyguard on the ground would have been a good start to a happy day flying.
This incident happened when someone answered the phone and accepted the task, the planning allowing weight above IGE is not reliable in the outcome in the field.
Helicopters, every flight an adventure into physics.
Last edited by fdr; 18th October 2020 at 15:32.