On 5/20/2026 6:48 PM, Larry Flesner via KRnet wrote:
Bottom line. If *all* your numbers are correct, I don't think you
have a C.G. problem. Did you change the gear geometry at all? Does
the airplane start to feel light at rotation or do you have to
initiate rotation with back stick. The airplane should be telling you
what its doing.
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My earlier post may have seemed a bit off the wall but here is where the
logic originated.
*What causes an airplane to lift off?*
The total lift exceeds the gross weight of the airplane. How the
airplane handles at that point is determined by the relationship of
"center of lift" to "center of gravity". If the C.of L. is within the
design C.of G. range the airplane is flyable. If not, bad things happen.
*Why a sudden lift off?*
If the transition from weight on wheels to weight on wing is too sudden,
the airplane leaps in to the air. As the *weight* from ramp to liftoff
doesn't change it must be the *lift generated* changes too suddenly.
This change in lift only takes place with airspeed or angle of attack of
the wing. As airspeed is generally a smooth transition it must be angle
of attack. Angle of attack is determined by the stance on the main gear
or is changed by pilot input. Properly designed gear allows the lift to
increase smoothly during acceleration and the airplane tends to lift off
on its own with very little pilot input. Holding the airplane weight on
the gear to above lift off speed can cause a sudden lift off with little
input from the pilot. Bottom line, with properly designed gear,
acceptable C.G. location, and acceptable pilot input, the entire process
from application of power to lift off should be a very smooth event and
99% of the time it is. There are times when we want the event to be
sudden as in a crosswind take off. We want to keep maximum weight on
the wheels to eliminate side drift and then very quickly transition to
weight on the wing.
On my tailwheel KR it took me a while to realize how that tiny little
elevator generated enough lift to raise the tail on takeoff with the
amount of weight on the tailwheel. I finally realized that the center
of lift on the wing is behind the main gear pivot point of weight on the
wheels. As the takeoff run accelerates it is the increasing lift
generated by the wing, not the elevator alone, that raises the tail. An
airplane flies based on geometry and physics. No real surprises here.
Larry Flesner
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