On Mar 19, 5:49*pm, Martin Gregorie
wrote:
On Thu, 19 Mar 2009 15:41:38 -0700, bildan wrote:
As the glider leaves the ground, the inertial rotation will begin but if
the acceleration continues, the elevator effectiveness will also
continue to increase with the square of the airspeed. *Rotation can't
happen instantly because the glider has mass and rotational inertia. In
fact, the pilot has to start backing off the down elevator to allow the
glider to rotate into the climb.

That depends on what you're flying and how lead footed the winch driver
is. I have an early (H.201) Std Libelle.

I remember having a fairly 'vigorous' launch on a calm day from a V8
Supacat. I started with full forward trim as usual but possibly with not
quite as much additional forward pressure as I normally use. The glider
started to pitch up shortly after lifting off. Applying full down
elevator maintained but didn't reduce the pitch-up rate until the full
climb attitude, when rotation eased off and I was able to ease back to no
stick pressure. This started to happen around 50 kts, the rotation rate
was acceptable and the full climb angle post rotation was steep but not
excessive. I had around 65 kts when rotation had stopped.

My Std. Libelle normally lifts off both wheels almost simultaneously,
even with full forward trim plus a bit of forward pressure. I usually
have no problems holding or reducing that attitude as the speed builds up
past 50 kts. However, on this occasion I want to emphasize that I went
fairly briskly to full forward stick as rotation started and REMAINED
THERE through rotation into full climb. At that attitude when I eased
back to the trimmed position as the rotation slowed. If the acceleration
had been higher I could have been in real trouble.

Now, I always ask to be launched "like a Junior but 10 kts slower", which
gives a nice lift-off and constant attitude until 50 kts and rising is on
the clock. At that point a reduction in forward pressure gives a nice,
controllable rotation into full climb. Easing the stick back as the
rotation slows gives a nice full climb attitude at just over 60 kts.
Vwinch is 65.

Caveat: I've never winched an H.201B, which has a bigger tail than the
H.201, so its winch behavior may be different.

--
martin@ * | Martin Gregorie
gregorie. | Essex, UK
org * * * |

Martin, your post has all the ingredients I'm talking about. If you
know your glider, you'll know if it will require down elevator and
roughly how much. It's probably a good idea to start the roll with
full down elevator to eliminate 'reaction time'. The problem occurs
when the nose is allowed to rise too far and the pilot then tries to
correct the situation.

This has been a hard fought discussion but I kept at it because there
is a lot of good things in it that winch novices need to think about.