Flap settings for Dummies

wrote in message
...
On 30 Mar, 03:30, Frank wrote:
Bill,

I like the 'neutral-force' idea, and I think I have actually felt that
a little bit on my Ventus. I'll keep looking at that. As for
building a drag meter, I looked through the articles you referenced
and beat a quick retreat. I would be much more likely to do serious
damage to my glider (and/or me) than I would be to do anything
positive! ;-)

Frank

The neutral-force force idea has been around for decades but there is
no particular reason to think that it gives the best glide angle for
the aircraft as a whole for a given speed - not least because it takes
no account of the fuselage drag .

The trailing edge drag probe is useful for research but completely
useless as a real time flap guide during sporting flight - there are
just too many variables and too much noise in the reading.
Furthermore, once again, there is no reason to think that the flap
setting that gives the lowest drag probe reading for that one station
on the wing span is going to be the flap setting that maximises glide
performance for the aircraft as a whole. If anyone believes otherwise
they are welcome to make me an offer for my old Replogle drag probe
and meter but they will be wasting their money:-)

All the optimum settings change with wingloading (as well as air
density, bugs etc).

So, I would change the question round and ask "what is the best speed
for each flap setting"? For each flap setting/wing-loading
combination there will be an optimum airspeed when the fuselage is a
its minimum drag angle of attack. Find information on the minimum
drag angle of attack for the fuselage, set up the glider C of G to
mimimize elevator drag, choose the ballast load depending on
conditions and/or contest tactics, choose the cruise flap setting
depending on the degree of pilot optimism and let the glider run at
whatever speed corresponds to the fuselage angle of attack for lowest
drag - using your handy fuselage angle of attack meter or wool canopy
tufts. This will still be an approximation to the ideal but at least
it is simple to use.

In this way you end a choice of 2 or 3 three of inter-thermal cruise
speeds - just like Ingo Renner advised all those years ago.

Iain


If the Idaflieg has the data for your ship---you can, for a small handling
fee, get that data. They have carefully measured polars for each flap
setting, faired together. Adjust for your flying mass, and viola, the best
flap settings for you.

Hartley Falbaum
USA "KF"

wrote:
On 30 Mar, 03:30, Frank wrote:
Bill,

I like the 'neutral-force' idea, and I think I have actually felt that
a little bit on my Ventus. I'll keep looking at that. As for
building a drag meter, I looked through the articles you referenced
and beat a quick retreat. I would be much more likely to do serious
damage to my glider (and/or me) than I would be to do anything
positive! ;-)

Frank

The neutral-force force idea has been around for decades but there is
no particular reason to think that it gives the best glide angle for
the aircraft as a whole for a given speed - not least because it takes
no account of the fuselage drag .

It's an appalling idea because of it's simplicity, but I've seen no
support for it from glider designers - why put in the flap setting
detents instead of letting the lever float, if that is best?

The idea seems to be the flap is just there to "streamline" the rest of
the wing and doesn't provide any lift itself. Aerodynamicists never
mention this reason for having flaps, nor do they suggest using the
"trail" position, either. And, if you look at airfoil charts showing
pressure distributions, you will see there is a net force on the last
few inches of the airfoil, where the control surfaces are.

If you don't want to trust your handbook settings, you can make
comparison runs with another glider of the same performance. This is
much easier to do accurately than a complete flight test - no math, no
instrument calibration, no high tows, no smooth air or wind free
conditions needed.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Iain

If the Idaflieg has the data for your ship---you can, for a small handling
fee, get that data. They have carefully measured polars for each flap
setting, faired together. Adjust for your flying mass, and viola, the best
flap settings for you.

Hartley Falbaum
USA "KF"

Thanks - I emailed them about the Ventus 2bx

Frank (TA)

On Mar 29, 7:14 pm, Frank wrote:
At the risk of having my ignorance exposed (again), is there any way a
reasonably competant (another problem in my case) can determine
"optimum" flap settings for the most commonly used speeds/
configurations, without resorting to a full-blown Johnson-style test
program?

I have been flying my new (to me) Ventus 2bx for a year now, and am
reasonably comfortable with the following flap settings (speeds in
kt):

40-60 Flaps L, +2, +1 dep on thermal characteristics
60-80 Flaps 0
80-100 Flaps -1
100+ Flaps -2, only happens on badly planned final glides or with
ballast.

However, I'm not sure how efficient these values are for my glider.
Should I stay with 0 all the way to 90kt, or maybe switch to -1
earlier? I mean, I've already give everyone else a big lead just due
to the IQ drop I experience immediately after release, so I'd hate to
think that I'm costing myself even more with poor flap settings!

I have played around some with watching the vario in cruise (TE) mode
to see if it makes much difference between 0 and -1 at say, 70kt, but
it's awful hard for me to tell. Anything else I should be looking
for?

TIA,

Frank (TA)

Frank - Use the values in the manual. You should not use the "0"
position on this glider (either -n cruise or +n thermal). No problem
to
use the "L" setting for landing, but it would be a rough tight thermal
that would benefit from "L".
Best Regards, Dave "YO electric"

On Mar 30, 9:29*am, wrote:
On 30 Mar, 03:30, Frank wrote: Bill,

I like the 'neutral-force' idea, and I think I have actually felt that
a little bit on my Ventus. *I'll keep looking at that. *As for
building a drag meter, I looked through the articles you referenced
and beat a quick retreat. *I would be much more likely to do serious
damage to my glider (and/or me) than I would be to do anything
positive! ;-)

Frank

The neutral-force force idea has been around for decades but there is
no particular reason to think that it gives the best glide angle for
the aircraft as a whole for a given speed - not least because it takes
no account of the fuselage drag .

The trailing edge drag probe is useful for research but completely
useless as a real time flap guide during sporting flight - there are
just too many variables and too much noise in the reading.
Furthermore, once again, there is no reason to think that the flap
setting that gives the lowest drag probe reading for that one station
on the wing span is going to be the flap setting that maximises glide
performance for the aircraft as a whole. *If anyone believes otherwise
they are welcome to make me an offer for my old Replogle drag probe
and meter but they will be wasting their money:-)

All the optimum settings change with wingloading (as well as air
density, bugs etc).

So, I would change the question round and ask "what is the best speed
for each flap setting"? *For each flap setting/wing-loading
combination there will be an optimum airspeed when the fuselage is a
its minimum drag angle of attack. *Find information on the minimum
drag angle of attack for the fuselage, set up the glider C of G to
mimimize elevator drag, choose the ballast load depending on
conditions and/or contest tactics, choose the cruise flap setting
depending on the degree of pilot optimism and let the glider run at
whatever speed corresponds to the fuselage angle of attack for lowest
drag - using your handy fuselage angle of attack meter or wool canopy
tufts. *This will still be an approximation to the ideal but at least
it is simple to use.

In this way you end a choice of 2 or 3 three of inter-thermal cruise
speeds - just like Ingo Renner advised all those years ago.

Iain

Lain,

Yes, I believe you have hit the nail on the head. We all drive around
in our flapped gliders, and all we really know is the thermalling and
high-speed flap settings. Interthermal cruise flap settings appear to
be a mystery for everyone, even though we all try to maximize the time
spent in interthermal cruise, and minimize the time spent at
thermalling speeds. And, even if we have good data for a particular
type of glider (V2bx in my case), that really doesn't mean that the
data is completely applicable for a particular glider of that type,
given that they are all essentially hand-made.

It may be that what we wind up with is a recognition that inter-
thermal cruise is pretty low-loss over a broad range of flap settings,
and the difference between 'optimum' and 'good' in the inter-thermal
phase gets lost in the noise between 'good' and 'optimum' thermalling
techniques/performance, as others have pointed out in the past.

Frank (TA)

On Mar 29, 7:14�pm, Frank wrote:
At the risk of having my ignorance exposed (again), is there any way a
reasonably competant (another problem in my case) can determine
"optimum" flap settings for the most commonly used speeds/
configurations, without resorting to a full-blown Johnson-style test
program?

I have been flying my new (to me) Ventus 2bx for a year now, and am
reasonably comfortable with the following flap settings (speeds in
kt):

40-60 Flaps L, +2, +1 dep on thermal characteristics
60-80 Flaps 0
80-100 Flaps -1
100+ Flaps -2, only happens on badly planned final glides or with
ballast.

However, I'm not sure how efficient these values are for my glider.
Should I stay with 0 all the way to 90kt, or maybe switch to -1
earlier? �I mean, I've already give everyone else a big lead just due
to the IQ drop I experience immediately after release, so I'd hate to
think that I'm costing myself even more with poor flap settings!

I have played around some with watching the vario in cruise (TE) mode
to see if it makes much difference between 0 and -1 at say, 70kt, but
it's awful hard for me to tell. �Anything else I should be looking
for?

TIA,

Frank (TA)

Flying my V2C(15) I have found that the -1 setting is the one I use
most often inter-thermal . In thermals I've tried L but definitely do
not feel it works for thermalling . I land generally using L , but
sometimes +2 in cross wind conditions . Then again my contest record
might not mean these are the absolutely best settings !

ZA.

On Sat, 29 Mar 2008 18:45:55 -0600, "Bill Daniels"
bildan@comcast-dot-net wrote:

Some will suggest feeling for the aerodynamic neutral-force point with the
flap handle. The idea is that the lowest drag configuration is with the
flaps in trail. I think I remember reading that minimum drag is slightly
positive from the neutral force point.

I'm pretty sure this applies only to the classical airfoils FX67-x and
FX62-x.
The ASW-27 definitely needs a strong push into the optimum negative
value, and even the older ASW-22 has a pretty non-intuitive
flap-handle force curve.



Bye
Andreas

On Sat, 29 Mar 2008 19:44:45 -0700 (PDT), Frank
wrote:

Hmm thanks for the tip about the 'L' setting: I have started using L
for thermalling in strong thermals, in the belief that it allows me to
core better, and to use no more than +2 for landings. If the mylar
seal is being overstressed any time the flaps are in 'L', I may want
to reconsider its use at all.

Don't worry about overstressing the mylar tape - this is not going to
happen. Mylar tape even survives on ASW-20s with its 55-degree
setting...
Bye
Andreas

Frank,

Read your Flight Manual and follow its guidance. BTW, there is no reason to
ever fly in flap setting "0" in a Ventus 2. "-1" is the optimal setting for
best L/D (which also happens to be min sink). And of course, your positions
change with speed according to wing loading. This too is in the manual. I
copied the chart and keep it in the cockpit for occasional reference.



"Frank" wrote in message
...
At the risk of having my ignorance exposed (again), is there any way a
reasonably competant (another problem in my case) can determine
"optimum" flap settings for the most commonly used speeds/
configurations, without resorting to a full-blown Johnson-style test
program?

I have been flying my new (to me) Ventus 2bx for a year now, and am
reasonably comfortable with the following flap settings (speeds in
kt):

40-60 Flaps L, +2, +1 dep on thermal characteristics
60-80 Flaps 0
80-100 Flaps -1
100+ Flaps -2, only happens on badly planned final glides or with
ballast.

However, I'm not sure how efficient these values are for my glider.
Should I stay with 0 all the way to 90kt, or maybe switch to -1
earlier? I mean, I've already give everyone else a big lead just due
to the IQ drop I experience immediately after release, so I'd hate to
think that I'm costing myself even more with poor flap settings!

I have played around some with watching the vario in cruise (TE) mode
to see if it makes much difference between 0 and -1 at say, 70kt, but
it's awful hard for me to tell. Anything else I should be looking
for?

TIA,

Frank (TA)