Aero D: IGE vs OGE

[Gunpilot]

Can anyone tell me why the sum angle of attack is the same for any given helicopter hovering both IGE and OGE. I would appreciate. Or if in fact this is the case.

[Shawn Coyle]

Hmmmm. What do you mean by 'sum angle of attack'?

[C4]

GPilot,

The amount of lift required to hover in or out of ground effect is the same (Amount of Lift needed to carry the aircraft weight does not change). Thus the sum angle of attack needs to be the same during all profiles of hover to carry the weight.

The difference being, as the angle of the RAF (relative airflow) changes due to being IGE or OGE, this requires more (or less) pitch angle to supply the requisite lift to counter the aircraft weight.

I hope this makes sense to you..

Over to you Shawn!!!!

[Gunpilot]

Thanks guys. I am with you on these explinations. They are pretty standard. I was just looking for a little spice to teach to my guys.

[delta3]

Gunpilot

The Angle off attack as measured at the rotorhead (collective) will be bigger OGE, because the induced airspeed is bigger (not blocked by ground). This also explains the greater power need.

Of course for the same weight the relative angle of attack, taking the induced airspeed into account, will be more or less the same (if it is that what you mean by the sum..)

d3