On 8/2/2011 8:25 AM, Willy VINKEN wrote:


Lots have been said about flaps-reducing while on final.
I know at least of one other ASH25 pilot who has done it
gently without harmful effects (on final).
Last week, I've tried it in calm evening air at 1500 feet,
checking 2 independent digital altimeters.
A gentle reduction from from 'L' position to neutral made us
loose about 10 feet (natural ~5 second descent included).
A brutal 'L' to 'N' caused a 25-30 feet loss.
Some sailplanes are probably less forgiving.
I'd be glad to hear about pilots who have tried it for real.
wv

I have no ASH 25 experience, but many times (in an HP-14 and a Zuni [think
American design 'PIK-20']) I've gone from full flaps to zero flaps, by way of
learning 'useful bits' about plane/self. All initial experiments, of course,
well distant from the earth...

My HP had hydraulic flaps, which I considered a 'one-shot' in the landing
pattern, due to the 'somewhat funky' valve controlling the hydraulic system
(resetting it in flight was a contortionist's act). Best guess is it lost
perhaps 50 feet when you dumped the flaps, which blew to zero
'instantaneously' at 45 knots indicated. In any event, it distinctly 'settled'
if the stick position was maintained. Simultaneously pulling aft on the stick
when dumping its flaps at 'normal approach speeds' (attempting to maintain the
previous IAS) *seemed* as if it might reduce altitude lost, but that wasn't an
experiment I would've voluntarily tried 'on short final' to verify my surmise!
That said, the HP is the only glider in which I've ever done a 'go-around'.
Youthful stupidity combined with 'contest get-home-itis' brought me and a
nasty T-storm cell overhead the field simultaneously. I wound up dumping full
flaps no more than 300' agl on what I'd intended to be short final but which
transformed to an imminent overshoot due to a positive climb rate with full
flaps (!); the rain obscuring the view directly ahead combined with landing
crosswind on featureless prairie and the sheer (never seen before/since)
unlikely possibility of NOT descending w. full flaps in that ship, combined to
delay my detection of the worsening situation. The hardest part of 'getting
away with it' was resetting the flap valve, which I did on my second downwind
after successfully pulling off the instantaneous-flap-dump/180-degree turn.
(Yes, I re-ran the entire scenario in my mind lots!)

My (flap control mechanisms vary) Zuni's flaps are controlled by a handle
which moves through an arc of ~45-degrees from zero-to-full (~75-degrees), so
flaps can be pulled on/removed as rapidly as one can move arm/handle. It's
essentially pretty simple in the Zuni to dump the flaps while maintaining IAS
within a knot or so as the ship settles. Because the Zuni's flaps are
considerably weaker than were the HP-14's (as in, distinctly less effective
than those of the PIK-20A/Bs I've seen), its 50%/full-flap approach angles are
distinctly shallower than were the HP's. One not-so-great (IMHO) consequence
is, Joe Pilot is more likely to *have to* remove large amounts of flap on
short final in the Zuni if one encounters (say) heavy sink along the way.
BTDT, and removing flaps was never an issue.

In both ships I always simply attempted to fly speed stabilized approaches
regardless of flap position, which - in my experience - is not particularly
difficult. American pilots who've flown (say) Schweizer 1-34s or 2-32s can
easily relate, since with their speed-limiting dive brakes, Joe Pilot has to
effect pitch changes to maintain a constant speed as one modulates their
(very) effective spoilers.

HTH.

Regards,
Bob W.