[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Ground Effect & Gliding Q



Bill Hunt wrote:
> 
> Brown Pelicans, Black Skimmers and Swallows employ ground effects in flight.
> But then these are already excellent fliers with high aspect wings to begin
> with.

I agree.  Though ground effect will do more to reduce total drag in a
flyer with a low aspect ratio wing than in one with a high aspect ratio
wing, because induced drag is already a smaller component of total drag
in the animal with the high aspect ratio wing.

>  And these birds have to be moving at a pretty good clip for the
> ground effects to take place.

Actually, that's not quite the case.  What they have to do is be flying
at a relatively high lift coefficient, and simultaneously flying at a
speed that allows the aoa to be somewhat less than stall aoa.  The
faster they fly, the lower the aoa and consequently the lower the lift
coefficient.  So ground effect has much less effect on total drag at
higher airspeeds than at lower, because the induced drag is much lower
at higher airspeeds, by the inverse square of the airspeed.

>  I wouldn't think it would be something that a
> novice flyer would use immediately;  evolutionarily speaking that is.  -

I agree, thinking mostly of the pitch control issues.  I promise you
that when flying in ground effect, it is very easy to fly into the
ground (or water).  Usually, you just bounce when you do so, but not
always.  And it isn't the ground effect you are bouncing off of, it is
the ground or water.  And again, you don't always bounce.

> Bill