helicopter transverse flow effect ????

[flame_bringer]

Been reading about the helicopters aerodynamics lately and i came accross this discrepancy :
a decrease in lift in the aft portion of the rotor disk occurs in hovering conditions or slow speed forward motion , when the helicopter conducts a forward motion at a low airspeed typically between 10 to 15 knots the airflow across the aft portion of the disk is accelerated for a longer time than the fore portion , which results in the air moving more vertically in the aft portion than the fore portion and consequentally a decrease in the angle of attack on the aft rotor portion and a decrease in lift and gives the helicopter a tendency to pitch the nose up .

hows the air accelerated for a longer time ? and what does that got to do with altering the angle of attack of the blades ?
please anyone explain
Thanks in advance

[flame_bringer]

Anyone ? =(

[Widewoodenwingswork]

Hey buddy, you might want to ask that question on Rotorheads, there will be a few more authorities there who should be able to clear it up for you. Otherwise check out Wagdentonks (sp?) Helicopter Principles of Flight. That sounds like a rather complicated way of explaining the phenomenon.

[Garfs]

The air hitting the aft section of the disc is accelerated for a longer amount of time than the air hitting the front portion as it has further to travel I guess, so as a consequence, the perpendicular flow of air through the disc at the rear is more pronounced than at the front of the disc.

This will cause a difference in angles of attack between the front and rear of the disc and give u the transverse flow effect.

I think thats right, and hopefully it makes sense, maybe someone can explain it better than me :ok:

[flame_bringer]

Seemingly i posted this topic in the wrong section :suspect:
Anyhow thanks for all the replies and attempts to help

[tony 1969]

If you picture the helicopter moving slowly forwards, the air at the front of the disc meets it horizontally whereas as the air moves towards the back of the disc the induced flow (air being pulled down through the disc) has more time to act on the air flow so the rear portion of the disc experiences a more vertical flow, this reduces the angle of attack which equals less lift at the rear of the disc, the effect is felt 90 degrees later so will cause a roll to the left (on american helicopters)
hope this helps