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Ground effect

  • aviatrix
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aviatrix created the topic: Ground effect

hey everybody,
got a question on ground effect that i need clarification on;

which of the following could be attribute to ground effect
A)the aircraft may become airborne at a speed well below a safe climbing speed
B)the aircraft may be difficult to rotate
C)the float between round out and touchdown may be shorter than usual
D)the initial climb just after takeoff will be greatly improved
im torn between A or D

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  • Cranenium
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Cranenium replied the topic: Ground effect

As you leave ground effect the Induced drag increases to it's normal value and so climb performance decreases right after takeoff. Ground effect only plays well when equivalent to one wing span down to ground level. Remember also that during ground effect the ASI and Altimeter may tend to over read due to the change in pressure at the static vent. This will give the illusion that you can climb and when you do, the aircraft will suddenly have a nose up attitude as well as reduction in longitudinal stability. Then boom drop. Hope this helps

I would go for (A) but not climb yet till VToss is reached

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  • John.Heddles
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  • ATPL/consulting aero engineer
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John.Heddles replied the topic: Ground effect

Some observations ..

(a) the lift curve slope changes and, IGE, one sees more lift than OGE. In addition the stall speed is reduced somewhat IGE. Hence this is a potentially dangerous possibility during an undisciplined takeoff procedure. Of interest, it would be worth reading the report on the 2011 G650 flight test crash for which GE was a critical factor. So (a) is a possible.

(b) more relevant to larger aircraft, where the rotation may hesitate as the tailplane gets close to the ground prior to liftoff. While this is a minor training load for the newly transitioning pilot, it rapidly becomes a learned response to increase stick loads at the appropriate pitch attitude to accommodate the effect. So, (b) is a possible.

(c) the opposite happens depending on the actual heights of the flare manoeuvre. GE sees an increase in lift and decrease in drag .. so bin this option

(d) once OGE, climb performance will decrease. Normally not a problem due to the short period IGE and adherence to SOP protects the pilot against too much excitement. The option is poorly worded and it is not clear whether it refers to after lift off or post screen. Probably can be discounted.

My guess is that (a), rather than (b), is the answer sought.

Engineering specialist in aircraft performance and weight control.

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