On 8/15/2011 2:57 PM, Walt Connelly wrote:
Well about half of the posts re flaps only gliders made me feel positive
about the possibility of finding a glider with flaps only, and the other
half made me feel just the opposite. I guess you could dump flaps on
final rather quickly if your speed was above stall for all ranges of the
flaps as they came up but the purpose of flaps is to create more lift
allowing for a lower approach speed or am I mistaken?

The 'purpose of flaps' - Is this where philosophy enters the aerodynamic world
definable by flaps' effect on a glider's polar? To me, viewed most generally,
the purpose of (large deflection landing) flaps is identical to the purpose of
spoilers, i.e. to ease Joe Glider Pilot's task of safely making a landing
pattern into 'glider-size' fields...different ways to skin the ease/safety cat.

Beyond that, both options come with their pros & cons. Again to my way of
thinking, it would be a 'glider shame' to wantonly disregard/not use the
flap-related effect of increasing the max lift inherent in the use of the
simply-hinged flaps used on (say) every 15-meter FAI-class ship around and
most 15-meter span ships. That's true even if the ship uses its flaps 'only'
for optimizing the drag bucket of the airfoil in cruise (i.e. they don't
deflect much beyond ~20-degrees). Stated another way, if Joe Glider Pilot's
ship has (small deflection, 'intended for cruise optimization-only') flaps, in
conjunction with intended-for-landing spoilers, why *wouldn't* JGP go to max
positive deflection flaps before then using spoilers for primary glidepath
control? He still would (could) obtain a theoretical lower touchdown speed
benefit contrasted to not using the flaps.

Where I'm headed with this is, one can reasonably conclude the 'purpose of
flaps' is whatever JGP decides, within their aerodynamic capabilities. You've
noted above, one possible purpose...and others have (and probably will again!)
note this particular purpose comes with its own safety-based 'recommended user
guidelines!' In other words, there's nothing about having (only) large
deflection landing flaps that *insists* one make the whole approach below the
flaps-off stalling speed. I generally did so only under absolutely benign
conditions, otherwise until 'somewhere around' flare altitude keeping my speed
at or above the flaps-off stall speed, less from fear of 'falling out of the
sky like a brick' should I (for whatever reason) instantaneously dump the
flaps, and more because it simply provides a larger margin (margins being good
in my book). However, in any pattern conditions that I thought safely
permitted, I also sought to minimize my touchdown speed (whether on or off
airport) by *using* the extra lift inherent with flaps to minimize my
*touchdown* speed...easiest on the the equipment, if nothing else.

Apparently beyond
a certain point the flaps cease to provide lift and are only a drag
device.

"Roger that...and folks will probably 'O-beer-thirty' argue if that point is
30-degrees, 45-degrees, or more." Pick whatever number you like for now!

It would make sense that a quick move from the drag area back
to the maximum deflection for lift could be accomplished quickly with
little problem.

....and beyond, if you have the height margin and hand-eye skills...


I guess the best option is for a glider with both flaps and
spoilers/airbrakes but I don't think there are a lot of those out there.

Only the AS W-20A in the large deflection w. spoiler field that I know of, but
lotsa designs with small-deflection flaps with spoilers. And, of course, the
'don't fit precisely into either category' ships like Mosquito, Vega, Mini
Nimbii, early Ventii, etc., which have their own devils in their own details!
Such fun!!!

Sometimes too many opinions from too many people are a bad thing.

Heh!

Regards,
Bob W.