On 8/9/2011 10:19 PM, Bruce Hoult wrote:
On Aug 2, 2:15 pm, wrote:
As for the rollout, how many 1-26 drivers
routinely roll no more than 300 feet on a hard surface after touchdown? (And
how long does your skid plate last?)

I haven't flown one of those in anger, but most of my genuine landouts
have been in a PW5.

I always pace out the distances afterwards. The usual figures are
about 30 paces from a standard cattle farm fence to the main wheel
touchdown point, and another 30 paces to the point where I'm stopped.

If I call the paces 1m each then that's 200 feet -- from the fence,
not from touchdown.

Pacing off - or otherwise striving to find some realistic method of
quantifying - one's landing rolls is a highly worthwhile activity, whether at
the gliderport (establishes one's required-field-length 'baseline'), or
eventually in fields (the field distance *will* be shorter due to the higher
drag of the unpaved surface). I usually found my 15-meter Zuni's off-field
rolls ranged from 150' to 200', probably averaging 180'. Field surfaces ranged
from plowed/disked/dry fields (my personal favorite) to hard-packed dirt
(occasionally) and reverting-to-prairie (once). The one G-102 (w. 2 aboard)
OFL I made in a plowed/disked/dry field, albeit very slightly downhill but
into a good breeze, paced out at 220'. All those distances are for summer
conditions at ~5,000' msl. They would've all been less at sea-level, I reckon.


Most of the rest of my landouts were in a Club Libelle. I'd say the
distances were quite similar. It, of course, has speed limiting
trailing edge airbrakes, which also have enough flap effect to lower
the stall by ~5 knots.

And it's that stall-speed-lowering capability I so love about landing flaps
(and their close cousins found on some Glasflugel & Schempp-Hirth designs),
when it comes to reducing off-field roll-out risks!

IMHO, large deflection landing flaps on gliders are the best kept sailplane
secret in the last half century.

I'd love to have some! But the trailing edge brakes as on the Club
Libelle, Hornet, Mosquito and I think also the Mini Nimbus and early
Ventus seem to give most of the same benefits, plus some extra ones.

Lacking any experience with those designs' 'flaplike' landing aids, I've
resorted to picking pilots' brains whenever I could, trying to get a handle on
the ships' drag-devices' pros & cons. One of my broad-brush, tentative,
conclusions eventually became few 'club-based' pilots ever really learned (or
strove to learn?) how to consistently extract the lowest energy touchdowns
from the devices. The conclusion was based on probing, trying to understand
the pilots' knowledge limits (both practical and theoretical), and then - when
I could - continuing to watch their landings.

FWIW, I routinely thought and flew as if the biggest 'unknown risk', directly
influence-able by me, in soaring was off-field landings, and - once committed
to a given field - the most pertinent thing I could do to minimize the
landing-surface-related 'unknowns risk' was to achieve as short a rollout as
safely possible. Hence the theoretical attraction to me of landing flaps.
Learning their 'unanticipated benefits' was pure gravy!

Regards,
Bob W.