T/O Downwind -v- power available ?
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ACORN,
This is a good thread, with lots of opposing views (always better than all those "me too" posts from which nothing new is learned)
Acorn said:
"Downwind departure or arrival may mean the ground effect in the hover is reduced (blown away) therefore a larger power requirement. ................ a groundspeed of variable speeds up to 30kts therefore achieving no ground effect. Although you may be close to the ground you will recieve no help from either translationl lift of ground effect therefore effectively requiring out of ground effect power requirements."
Nick sez:
It is good old fashioned pilot lore that ground effect can be "blown away" or that a large groundspeed will negate ground effect. This is quite mistaken, as the ground effect is related only to the proximity to the ground relative to the wing or rotor span, and the amount of induced power that is being consumed. A previous post on the thread discussed this more fully, you might want to peek back.
[ 17 September 2001: Message edited by: Nick Lappos ]
This is a good thread, with lots of opposing views (always better than all those "me too" posts from which nothing new is learned)
Acorn said:
"Downwind departure or arrival may mean the ground effect in the hover is reduced (blown away) therefore a larger power requirement. ................ a groundspeed of variable speeds up to 30kts therefore achieving no ground effect. Although you may be close to the ground you will recieve no help from either translationl lift of ground effect therefore effectively requiring out of ground effect power requirements."
Nick sez:
It is good old fashioned pilot lore that ground effect can be "blown away" or that a large groundspeed will negate ground effect. This is quite mistaken, as the ground effect is related only to the proximity to the ground relative to the wing or rotor span, and the amount of induced power that is being consumed. A previous post on the thread discussed this more fully, you might want to peek back.
[ 17 September 2001: Message edited by: Nick Lappos ]
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What about these two thoughts on power requirements in a downwind hover. As the tail wind acts on the horizontal stabilizer forcing the nose down, the cyclic has to be moved aft and therefore tilting the lift vector away from the vertical. Also the airflow from the tail rotor is blown toward the main rotor and effects the induced flow thru the rear of the disc. Both of these effects reduce the total rotor thrust and would require more applied power to maintain a hover height.
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when hovering. i think slight winds from any direction, would require more power than no wind because the rotor is tilted into wind reducing lift, until the wind exeeds translational lift speed. just because when accelerating from still, more power is needed to hold level. same thing or not?
less power would be required when just holding a slow speed i spose.
less power would be required when just holding a slow speed i spose.
Senis Semper Fidelis
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Hi Rotorheads
After another exciting afternoon flying the length of the Uk (well almost) I had again the chance to try the downwind hover and taxi in one of the new(400hrs) Hydraulic R44's, with three people on board and the wind at 7/8knts I yet again ran out of stick in the attempt to bring the R44 to a halt, and had to perform a turn on the spot to get the help of the little wind available, the problem was also that I reached the max limit of the power and was in danger of going into the overpitch situation, all this at about 6/8 ft from the ground, all this was overseen by my friendly Cfi who was quite happy for me to undetake this little test, we also tried the creeping take of at about 30% down wind, we hovered at about 12/14ft the distance travelled before we started to lift was incredibly long compared to a normal into wind T/O with the same A/C.
But thanks to all your inputs and thoughts I feel I know a lot more now than I did a few weeks ago, Could it be renamed the "PPrune Educational Forum " I have not had chance to try this in the B206, at this low amount of Tail wind would it too run out of rear stick with three up?
After another exciting afternoon flying the length of the Uk (well almost) I had again the chance to try the downwind hover and taxi in one of the new(400hrs) Hydraulic R44's, with three people on board and the wind at 7/8knts I yet again ran out of stick in the attempt to bring the R44 to a halt, and had to perform a turn on the spot to get the help of the little wind available, the problem was also that I reached the max limit of the power and was in danger of going into the overpitch situation, all this at about 6/8 ft from the ground, all this was overseen by my friendly Cfi who was quite happy for me to undetake this little test, we also tried the creeping take of at about 30% down wind, we hovered at about 12/14ft the distance travelled before we started to lift was incredibly long compared to a normal into wind T/O with the same A/C.
But thanks to all your inputs and thoughts I feel I know a lot more now than I did a few weeks ago, Could it be renamed the "PPrune Educational Forum " I have not had chance to try this in the B206, at this low amount of Tail wind would it too run out of rear stick with three up?
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Vorticey, whilst i agree with your thoughts re any tilting of the disc will require slightly more power, perhaps the less streamlined fuselage that a tailwind meets will create more requirement for power. The other consideration in a crosswind situation is, of course, that a right crosswind will require more power absorbing left pedal (US built heli's!!) to maintain heading and vice-versa. Then we could get into the topic of strong left crosswinds and LTE.....but lets save that for another day.
And to vfrpilot?? (spelling??) yes a B206 will run out of aft cyclic in a tailwind quiet easily, depending on loading etc.
And to vfrpilot?? (spelling??) yes a B206 will run out of aft cyclic in a tailwind quiet easily, depending on loading etc.
VFRpilotbb
206 is not good down wind as for the R44 - fly a proper helicopter !!!!!
Seriously, lots of helicopters will run out of rear cyclic, eg Hughes 300 with 2 x 200lb people and less than about 10g of fuel will run out of rear cyclic with 25 kts plus wind in the hover, although weight and balance has to be considered here.
206 is not good down wind as for the R44 - fly a proper helicopter !!!!!
Seriously, lots of helicopters will run out of rear cyclic, eg Hughes 300 with 2 x 200lb people and less than about 10g of fuel will run out of rear cyclic with 25 kts plus wind in the hover, although weight and balance has to be considered here.
