Re: Question: Vertical speed on landing?

Date:         18 Mar 97 03:14:52 
From: (Kim Hackett)
Organization: Your Organization
References:   1 2
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>As the FAR's show, the vertical decent rate limit is governed
>by max landing weight.  The 12 fps is taken as an ultimate (failure)
>condition, and 10fps is limit (i.e. yielding).  I don't know
>if gear is actually _tested_ to 12, I think only to 10.
>(I've seen the drop test videos - what an explosive event!)
>BTW, that rate applies to all jet transport airplanes.

At Cessna, we drop test gears to 10 fps limit and
also test the gear to 12 fps for reserve energy to meet FAR 25.723(b).
In fact we are drop testing the main gear for the new Citation Excel
sometime next month. I wrote the drop test proposal.

>For any sort of a max takeoff weight landing
>situation, the airplane is already committed to flight and
>would dump fuel to get the weight down to landing weight
>before it tried to land again.  I don't
>think _any_ airplane could land at more than 7 or 8 fps (approx)
>at max takeoff.

Citations are limited to sink rate of 6 fps for weights above the
maximum landing weight.  The term maximum landing weight means the
maximum weight you can land at 10 fps.  We perform gear loads analysis
for maximum takeoff weight landings at 6 fps.  For our aircraft
the loads are higher for MLW at 10 fps than for MTOW at 6 fps.

Kim Hackett
Cessna Aircraft
Wichita, Kansas