bildan wrote:
On Sep 10, 8:27 am, Frank Whiteley wrote:
On Sep 10, 2:37 am, (Alan) wrote:



In article Jim Beckman writes:
At 14:13 08 September 2009, FBCompton wrote:
Important Timing Aspect: The glider (in low tow) must not touch down
much before the towplane -- this can be a hazardous aspect -- touching
down well before the towplane and stalling it. The glider wings are
still carrying the weight of the glider while it is flying. Once the
glider touches the wings stop lifting and the glider creates more
weight drag on the towplane, which if still well above the runway will
be slowed and may stall.
This seems counterintuitive to me. When the wings stop lifting, the
induced drag goes away, so the drag on the towplane should decrease. The
only added drag is friction in the glider's main gear. What am I missing
here?
Jim Beckman
It seems backwards to me, too, but I have asked tow pilots about this,
and I was told that they feel the drag decrease when the glider comes off
the ground on the takeoff roll.
I guess those wheels have a lot of drag.
Alan
Behind less powerful tow planes, I generally note a 3-5 knot jump in
airspeed immediately following glider lift off.

Frank Whiteley

Brake pucks and shoes are always in light contact with the disks or
drums to eliminate 'lost motion' so as to provide immediate braking
action. Although small, this friction is not negligible.

Aircraft tires are made from natural rubber which has very good wet
and dry traction but also has higher rolling resistance than synthetic
rubber. A single glider tire is also loaded heavily - sometimes
beyond the load rating limit which increases rolling resistance still
further.

It's reasonable to expect these taken together would result in
noticeable rolling resistance.

On a slightly different tack, I've had badly worn drum brakes lock up
on touchdown all on their own without input from me. Normally, this
is not a problem and serves as a reminder to service the brakes. If
the brake locked and/or a tire blew while landing on tow, the results
might be 'interesting'.
Very interesting - the white stripe on the runway costs about $100/m...
(Pictures available)

Tost Lilliput 4" rim failed radially around the pressed in liner as I
touched down in my Std Cirrus. Air pressure forced the two parts apart
against the frame. Instant locked wheel.
The tar ate a hole right through the Tost 4.00x4 that I could fit a
thumb through.

Certainly the only time the Lilliput ever stopped 66 fast though - can't
have gone much more than 50" ground roll.

Have adjusted the replacement rim to give the normal useless level of
braking force.

Bruce