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Old 29th Nov 2017, 02:32
  #115 (permalink)  
BOBAKAT
 
Join Date: Jun 2013
Location: Thaïland
Age: 62
Posts: 183
One of the perfect example of SWP it is a few years ago a 747 Captain, freshly dual rated on helicopters . One day he fly with friends on an Alouette 2 ( turbine engine remember..) He check the weight and balance, check the abacus with Zp and OAT : everything is limit, but ok !
Full passengers, no doors but just at limit on the MTOW, smooth take off on the limit off power and climbing at 500 ft...few minutes later, one passengers ask him to make an hovering in front of his house to take picture.
The Captain say OK ! He slow the speed until stop at 300ft and....Surprise, the helicopter settling with power...and finish in a pond, nobody hurt ...

Why ?
He take off at the power limit IGE, In Ground Effect = Right !
Few minutes later and few liters of kerozen burned but not enough to change the chart......
He stop (try to stop ) his helicopter OGE : Out Ground Effect...FAULT ! he don't check the abacus for OGE, only IGE...
He was a young pilot on helicopter and don't feel the limit when he reach the hovering. If he can , it was easy to escape, just take some speed....
If you follow a French helicopter Course, you learn the hovering power difference between IGE and OGE is around 7% ( or 7% oflift weight capacity)
If you have the power to standard hovering ( 5 ft) IGE at 100%, that's really at the limit but enough for take off...BUT if you want to make an hovering OGE, you need 107% at the same place ( Zp/OAT ) and same load...
If you don't have the 7%....You go sure in SWP...
For sling or the hoist, if the charge weight augmentation exceed the max power available, you know it immediatly ! : the NG (turbine engine) NR ( piston engine) decrease, when you want to lift more than you can.
At this point you have 2 choice ! ....
You continue to increase the pitch and sure, you go down slowly....
OR
you decrease the pitch a little be , the NG/Nr increase and you reach the OGE hovering... your are safe. End of the story..
No one can talk about VRS, it's only a power story and abacus good reading ....
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