At 17:15 20 June 2012, Bill D wrote:
On Jun 20, 10:36=A0am, John Cochrane
wrote:
Ramy

Lark manual with scratched in hard to read W&B numbers for that
particu=
lar
ship:http://www.clubplaneadoresbari.com.a...ark_Manual.pdf

Seems to me that a tail dolly heavy enough to put it out of the aft
lim=
it would have to be very heavy.

The manual is interesting. P. 7 says the minimum front seat weight is
183 lbs. it also gives 22-47% mac range
The chart on the last page--an obvious reference if you're taking
light passengers in the front seat -- says 90 lbs in the front seat is
ok
The calculation on the second to last page says 183 in the front seat
is fine at 37%, and 121 in each seat is fine at 39%
Why is the placard 183 lbs then?
Somebody who knows how much a lark dolly weighs could certainly tell
us minimum front seat weight with dolly on given this chart
I surely hope we're not replaying this
onehttp://www.ntsb.gov/aviationque=
ry/brief.aspx?ev_id=3D20001208X06614

John Cochrane

I hope not as well. Both cockpits are well ahead of the aerodynamic
center so I would expect the CG to be well forward with three souls on
board. I don't think the tail dolly had much effect in this accident
as long as it was not unusually heavy. In fact, it may have prevented
a forward-of-limit CG.

That said, the Twin Lark has some 'interesting' trim/pitch stability
behaviors. At higher speeds, even with negative flaps, the glider
becomes progressively nose heavy requiring significant aft stick
pressure to prevent a steeper dive. If re-trimmed for the higher
speed, slowing down causes increasing tail heaviness. This indicates
that pitch stability becomes divergent under normal flight conditions
which is not what I would expect from a standard category glider.

Bill D - former Lark owner.

Some of the gliders I fly will take a far greater weight of water in the
fin tank than even the heaviest dolly I have seen, getting airborne with
the tail dolly still attached is more embarassing than a danger.