Flaps VS Airbrakes/Spoilers

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

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

Walt

On Aug 15, 2:57*pm, Walt Connelly 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? *Apparently beyond
a certain point the flaps cease to provide lift and are only a drag
device. *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.

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

Walt

--
Walt Connelly

Check out the Mini Nimbus, Mosquito and early Ventus.

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.

On Aug 15, 10:55*pm, BobW wrote:

The 'purpose of flaps' - Is this where philosophy enters the aerodynamic world
definable by flaps' effect on a glider's polar?
....
Where I'm headed with this is, one can reasonably conclude the 'purpose of
flaps' is whatever JGP decides, within their aerodynamic capabilities. ....

Joe Pilot didn't put the flaps there, Bob the designer did. He had a
"purpose", which was probably to lower the stall speed and thus the
approach speed and all the other good things that come from that.

On Aug 16, 10:26*pm, toad wrote:
On Aug 15, 10:55*pm, BobW wrote:



The 'purpose of flaps' - Is this where philosophy enters the aerodynamic world
definable by flaps' effect on a glider's polar?
...
Where I'm headed with this is, one can reasonably conclude the 'purpose of
flaps' is whatever JGP decides, within their aerodynamic capabilities. ....

Joe Pilot didn't put the flaps there, Bob the designer did. *He had a
"purpose", which was probably to lower the stall speed and thus the
approach speed and all the other good things that come from that.

I kind of disagree.
From my experience, the benefit of "real" landing flaps is very high
drag such that speed increases only slightly when approach is
steepened and drops off quickly during round out and landing.
They also have the very positive effect of reducing the angle of
attack at the tip, giving much better roll response. Look at a '20 in
full "crow" mode and the tips almost look like they are bending down
relative to inboard part of the wing.
My View FWIW.
UH
(Don't try what I've done at home)

On 8/17/2011 5:47 AM, wrote:

Joe Pilot didn't put the flaps there, Bob the designer did. He had a
"purpose", which was probably to lower the stall speed and thus the
approach speed and all the other good things that come from that.

I kind of disagree.
From my experience, the benefit of "real" landing flaps is very high
drag such that speed increases only slightly when approach is
steepened and drops off quickly during round out and landing.
They also have the very positive effect of reducing the angle of
attack at the tip, giving much better roll response. Look at a '20 in
full "crow" mode and the tips almost look like they are bending down
relative to inboard part of the wing.

Not only do they look like it, they are, in fact, bent down a bit. I saw
that on my ASW 20 C, and I see it on my ASH 26 E.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

On 18/08/2011 00:44, Eric Greenwell wrote:

Not only do they look like it, they are, in fact, bent down a bit. I saw
that on my ASW 20 C, and I see it on my ASH 26 E.

But that's not really due to the flaps. The clever Schleicher mixer
design raises the ailerons as the flaps move to landing. ASH-25s show
it best of all.

That's why longer span Schleicher gliders are significantly easier to
manoeuvre on final than some other contemporary designs.

GC

On Aug 17, 8:47*am, wrote:
On Aug 16, 10:26*pm, toad wrote:

On Aug 15, 10:55*pm, BobW wrote:

The 'purpose of flaps' - Is this where philosophy enters the aerodynamic world
definable by flaps' effect on a glider's polar?
...
Where I'm headed with this is, one can reasonably conclude the 'purpose of
flaps' is whatever JGP decides, within their aerodynamic capabilities.. ...

Joe Pilot didn't put the flaps there, Bob the designer did. *He had a
"purpose", which was probably to lower the stall speed and thus the
approach speed and all the other good things that come from that.

I kind of disagree.
From my experience, the benefit of "real" landing flaps is very high
drag such that speed increases only slightly when approach is
steepened and drops off quickly during round out and landing.
They also have the very positive effect of reducing the angle of
attack at the tip, giving much better roll response. Look at a '20 in
full "crow" mode and the tips almost look like they are bending down
relative to inboard part of the wing.
My View FWIW.
*UH
(Don't try what I've done at home)

I actually kind of agree with you. The purpose of the initial
deflection is lift increase/stall speed decrease. By increasing the
flap deflection available to the "real landing flap" range, the
designer got the high drag/glide-slope control feature without adding
a second system. Obviously some designers have chosen having 2
systems instead.

If all the designer wanted was the drag, he would have used a drag
device. IMHO.

Todd

Here is a video example of flaps...(on powered planes)

http://freedom4um.com/cgi-bin/readart.cgi?ArtNum=133255

Scott

The "Flap-only" system appear most often on homebuilt sailplanes. (Schreder
series, BG-12-16, etc) I am sure the designers realized that simplifying
wing construction was one of the advantages of the flaps-only system.

BTW, I don't use the flaps to fly a lower my approach speed. I use them for
the massive amount of drag that they produce.

Wayne
HP-14 "6F"
http://tinyrul.com/N990-6F


"toad" wrote in message
...

On Aug 15, 10:55 pm, BobW wrote:

The 'purpose of flaps' - Is this where philosophy enters the aerodynamic
world
definable by flaps' effect on a glider's polar?
....
Where I'm headed with this is, one can reasonably conclude the 'purpose of
flaps' is whatever JGP decides, within their aerodynamic capabilities. ...

Joe Pilot didn't put the flaps there, Bob the designer did. He had a
"purpose", which was probably to lower the stall speed and thus the
approach speed and all the other good things that come from that.