I have a question relating to the following exam question:

Select the situation in which ground effect is most pronounced:

During the take off run

At 50 feet during the approach to land

Immediately after take off

During the landing roll.

Answer given as correct is "immediately after take off".

From Ops and performance the definition given is that take off ends at 50 feet above the runway (or clearway). As ground effect diminishes rapidly more than a wingspan above the ground I answered with the choice of "50 feet during the approach" as this would be closer to the ground.

Any thought on this?

Hi Peter,

It's really a lot to do with the wording. You can immediately discount A and D. B states "AT 50 feet". As you've said, ground effect disappears very quickly once the aircraft is higher than it's own wingspan above the ground (after takeoff or before landing), so at 50 feet (in most GA aircraft) ground effect wouldn't be noticeable.

Ground effect is more pronounced immediately after takeoff, while the aircraft is still within that wingspan from the ground. This is the reason pilots of overloaded aircraft seem to think all is good because the aircraft has become airborne, but once out of ground effect, the increased induced drag then comes to the party and lo and behold, the aircraft struggles to climb.

I think I see where you're coming from using the performance data but the answers given included immediately after takeoff and at 50 feet during approach to land, not after (the definition of;) the takeoff.

Hope this helps,

Cheers

Actually Peter, you have made a good point. I'll rewrite that question to say 'immediately after lift-off'. Thanks for the feed-back.

Bob