Low approaches in ground effect

Imagine you get things wrong and are caught out low on final,
still a fair distance out, and it looks marginal whether you
are going to reach the runway or not.

One technique I have sometimes heard described is to dive for
the deck and complete the remaining distance in ground effect.
For the sake of the argument we can assume fairly flat ground,
free of obstacles, though not necessarily landable.


A few years ago Soaring Magazine reported experiments on this
undertaken (I believe) by the airforce glider program. They used
Blaniks and a very long runway. The conclusion was that it was better
to stay at max glide and not dive for the ground. I forget though how
much wind they had -- there is some headwind (50 mph) and gradient (to
zero at ground level) where it has to be better to dive. And Blaniks
are pretty bad at high speed -- though will have more induced drag at
any speed in ground effect too.

John Cochrane BB

An additional concern to those who dive to go into ground effect is that you
are giving up the ability to choose a touchdown point. Once in ground
effect, the pilot loses the ability to turn and must touch down straight
ahead. Altitude, however, gives the pilot the option of turning slightly to
avoid something hard.

If you cannot make the airport, pilots must select the best option as soon
as possible, using the aircraft as a bargaining chip. Walking away is the
concern rather than making the airport. From that standpoint, altitude
gives us the most options for the longest time.

Colin N12HS


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