Flap Settings

I understand, a wing will perform optimally when the flap is set at
the proper angle for the airspeed ... any mismatch of flap to airspeed
will result in some performance losses vs. the correct setting. Of
course, we have a couple of compromises here ... the flaps are set at
fixed increments and the airspeed varies continuously ... so by
design, you will rarely have the flap and airspeed matched up
perfectly.

I remember seeing a story where one of the German schools modified an
LS-3 with springs, etc. so it automatically put in the correct amount
of flap for the airspeed ... did this result in a measurable
improvement?

Along the same lines, I have heard some pilots say they put the flap
in a position where they feel no pressure ... does this work?

I myself tend to go negative quicker or maintain a negative setting
longer ... then pulling in positive flap ... thinking being too
positive is more costly then too negative ... is this valid?

KK

Good, question. I'll follow this thread with interest.

I can make one comment. My Nimbus 2C has a complex set of trim/flap
interconnect springs and gas struts that probably to more to effect the
"feel" of the flap handle than aerodynamic forces. Even so, the neutral
force point on the flap handle "seems" to be about right. Most of the time
I keep my left hand on the flap handle with the setting at some intermediate
position between detents that "feels about right". The only time I use the
detents is when I need to use my left hand for something else.

I expect the only way to know for sure the flap setting is right is to
install a "drag meter" pitot rake on the flap trailing edge.

Bill Daniels


"Ken Kochanski (KK)" wrote in message
ups.com...
I understand, a wing will perform optimally when the flap is set at
the proper angle for the airspeed ... any mismatch of flap to airspeed
will result in some performance losses vs. the correct setting. Of
course, we have a couple of compromises here ... the flaps are set at
fixed increments and the airspeed varies continuously ... so by
design, you will rarely have the flap and airspeed matched up
perfectly.

I remember seeing a story where one of the German schools modified an
LS-3 with springs, etc. so it automatically put in the correct amount
of flap for the airspeed ... did this result in a measurable
improvement?

Along the same lines, I have heard some pilots say they put the flap
in a position where they feel no pressure ... does this work?

I myself tend to go negative quicker or maintain a negative setting
longer ... then pulling in positive flap ... thinking being too
positive is more costly then too negative ... is this valid?

KK

I'm reaching back a bit in my memory here so apologies
to the real practitioners if I miss anything.

I believe optimal flap settings are a function of angle
of attack, not airspeed, though obviously there is
a relationship between the two if you adjust for weight,
density, etc.

Second, the 'feel' on the flap handle is determined
by the hinge moment on the flap/flaperon. Again, minimum
hinge moment does not necessarily correspond to minimum
drag, maximum lift coeficient or maximum L/D. You might
want to optimize for any one of these at a given airspeed.
Each would require a different flap setting I think.

9B

At 16:24 10 July 2007, Bill Daniels wrote:
Good, question. I'll follow this thread with interest.

I can make one comment. My Nimbus 2C has a complex
set of trim/flap
interconnect springs and gas struts that probably to
more to effect the
'feel' of the flap handle than aerodynamic forces.
Even so, the neutral
force point on the flap handle 'seems' to be about
right. Most of the time
I keep my left hand on the flap handle with the setting
at some intermediate
position between detents that 'feels about right'.
The only time I use the
detents is when I need to use my left hand for something
else.

I expect the only way to know for sure the flap setting
is right is to
install a 'drag meter' pitot rake on the flap trailing
edge.

Bill Daniels


'Ken Kochanski (KK)' wrote in message
oups.com...
I understand, a wing will perform optimally when the
flap is set at
the proper angle for the airspeed ... any mismatch
of flap to airspeed
will result in some performance losses vs. the correct
setting. Of
course, we have a couple of compromises here ... the
flaps are set at
fixed increments and the airspeed varies continuously
... so by
design, you will rarely have the flap and airspeed
matched up
perfectly.

I remember seeing a story where one of the German
schools modified an
LS-3 with springs, etc. so it automatically put in
the correct amount
of flap for the airspeed ... did this result in a
measurable
improvement?

Along the same lines, I have heard some pilots say
they put the flap
in a position where they feel no pressure ... does
this work?

I myself tend to go negative quicker or maintain a
negative setting
longer ... then pulling in positive flap ... thinking
being too
positive is more costly then too negative ... is this
valid?

KK

Unfortunately we do not have A of A meter. I have come to the
conclusion that using the flight manual for specific flap setting and
speeds and wing loading is the way to go.
For example: At a gross of 800 lb and a flap setting of +20 the
optimum speed range is about 5-7 kt, about the same in a 45 deg. bank
with the needed extra speed added for that bank.
But in level cruise the minimum drag has a range from about 70 kt to
95 kt at zero flap and 800 lb gross. You will feel the aft loading
of the airfoil in climb at the Flap handle , but no load in cruise.
Due to friction this " flap handle feel", as an indicator is
unreliable and depending on the airfoil also misleading.
I can speak from practical experience. On my past projects I had to
calculate the speeds for each flap setting as well as wing loading
In case of that airfoil it had a very narrow speed range in each flap
setting to maximize performance but it comes at a cost of having to
pay attention to the flaps to get the most out of each setting.
Udo

On Jul 10, 11:49 am, "Ken Kochanski (KK)"
wrote:
I understand, a wing will perform optimally when the flap is set at
the proper angle for the airspeed ... any mismatch of flap to airspeed
will result in some performance losses vs. the correct setting. Of
course, we have a couple of compromises here ... the flaps are set at
fixed increments and the airspeed varies continuously ... so by
design, you will rarely have the flap and airspeed matched up
perfectly.

I remember seeing a story where one of the German schools modified an
LS-3 with springs, etc. so it automatically put in the correct amount
of flap for the airspeed ... did this result in a measurable
improvement?

Along the same lines, I have heard some pilots say they put the flap
in a position where they feel no pressure ... does this work?

I myself tend to go negative quicker or maintain a negative setting
longer ... then pulling in positive flap ... thinking being too
positive is more costly then too negative ... is this valid?

KK

On Tue, 10 Jul 2007 08:49:17 -0700, "Ken Kochanski (KK)"
wrote:

Along the same lines, I have heard some pilots say they put the flap
in a position where they feel no pressure ... does this work?

Indeed this works for most gliders with the FX62-K... (ASW-20, LS-6
etc.) and FX-67-K...x (Nimbus-2, LS-3, Pik-20 etc.) airfoils, but most
later airfoils (ASH-25, ASW-27 etc.), need a firm "push" towards
negative settings.


Bye
Andreas

Ken Kochanski (KK) wrote:
I understand, a wing will perform optimally when the flap is set at
the proper angle for the airspeed ... any mismatch of flap to airspeed
will result in some performance losses vs. the correct setting. Of
course, we have a couple of compromises here ... the flaps are set at
fixed increments and the airspeed varies continuously ... so by
design, you will rarely have the flap and airspeed matched up
perfectly.

I remember seeing a story where one of the German schools modified an
LS-3 with springs, etc. so it automatically put in the correct amount
of flap for the airspeed ... did this result in a measurable
improvement?

Along the same lines, I have heard some pilots say they put the flap
in a position where they feel no pressure ... does this work?

I myself tend to go negative quicker or maintain a negative setting
longer ... then pulling in positive flap ... thinking being too
positive is more costly then too negative ... is this valid?

Its well worth digging out Dick Johnson's reports on flapped gliders and
looking at the combined polar he plots - the one showing polars for all
flap settings.

The polars for the ASW-20 blend quite nicely except at the ends of the
speed range for each setting and the available speed range gets smaller
for each setting at more positive settings. The implication, I suppose,
is that selecting the right flap is more critical at lower airspeeds.

The same may apply to other gliders too: I haven't looked.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Jul 10, 11:49 am, "Ken Kochanski (KK)"
wrote:
I understand, a wing will perform optimally when the flap is set at
the proper angle for the airspeed ... any mismatch of flap to airspeed
will result in some performance losses vs. the correct setting. Of
course, we have a couple of compromises here ... the flaps are set at
fixed increments and the airspeed varies continuously ... so by
design, you will rarely have the flap and airspeed matched up
perfectly.

I remember seeing a story where one of the German schools modified an
LS-3 with springs, etc. so it automatically put in the correct amount
of flap for the airspeed ... did this result in a measurable
improvement?

Along the same lines, I have heard some pilots say they put the flap
in a position where they feel no pressure ... does this work?

I myself tend to go negative quicker or maintain a negative setting
longer ... then pulling in positive flap ... thinking being too
positive is more costly then too negative ... is this valid?

KK

Hi Ken - It depends very much on the glider. The Antares manual
specifically says "do not let the flap handle move to the position
of no force, as you will have the wrong flap setting" (I'm on the
road so that's an approximate quote). In other gliders I've flown
this is sort-of the correct flap setting (but far from exactly right).

Factors include the mechanics of the flap system, any trim
spring interconnect to flap, airfoil, etc...

To your second question, correct flap setting depends on CL
not airspeed. Again, the Antares manual specifically warns
against pulling the flap down during a pull-up. Because of the
flat polar and consequent high cruise speed, you would end
up with the flaps down way too soon and incur much extra
drag during the pull-up - more so than older designs.

Hope that helps,
Best Regards, Dave "YO"

On my want to do list is to build a flap controller for my HP16T.

I have been using PIC Microprocessers and pressure sensors that could
easily be adapted to do this. My initial Idea was to install a drag
rake that the microprocesser would read the pressure difference from
and would adjust the flaps accordingly. Alternate ideas are to connect
directly the the Pitot/Static system or build an AoA Sensor. All are
pretty easy to do but good low pressure sensors are in about $100
range and so far my budget hasn't made it to that. I really hadn't
considered AoA sensors until reading this thread, That might be a
cheaper way of doing this.

Brian Case
HP16T N16VP.



On Jul 10, 11:25 am, Udo wrote:
Unfortunately we do not have A of A meter. I have come to the
conclusion that using the flight manual for specific flap setting and
speeds and wing loading is the way to go.
For example: At a gross of 800 lb and a flap setting of +20 the
optimum speed range is about 5-7 kt, about the same in a 45 deg. bank
with the needed extra speed added for that bank.
But in level cruise the minimum drag has a range from about 70 kt to
95 kt at zero flap and 800 lb gross. You will feel the aft loading
of the airfoil in climb at the Flap handle , but no load in cruise.
Due to friction this " flap handle feel", as an indicator is
unreliable and depending on the airfoil also misleading.
I can speak from practical experience. On my past projects I had to
calculate the speeds for each flap setting as well as wing loading
In case of that airfoil it had a very narrow speed range in each flap
setting to maximize performance but it comes at a cost of having to
pay attention to the flaps to get the most out of each setting.
Udo

On Jul 10, 11:49 am, "Ken Kochanski (KK)"
wrote:

I've noted that there are AoA probes that use two pressure ports on 45
degree faces. Such as:
http://www.cgmasi.com/aviation/index.html although this one is also a pitot
probe.

I've wondered if pressure ports on the top and bottom of the fuselage nose
where the nose contours are at about 45 degrees to the airstream wouldn't
give about the same pressure diferential that could be used to compute AoA.

Bill Daniels


"Brian" wrote in message
oups.com...

On my want to do list is to build a flap controller for my HP16T.

I have been using PIC Microprocessers and pressure sensors that could
easily be adapted to do this. My initial Idea was to install a drag
rake that the microprocesser would read the pressure difference from
and would adjust the flaps accordingly. Alternate ideas are to connect
directly the the Pitot/Static system or build an AoA Sensor. All are
pretty easy to do but good low pressure sensors are in about $100
range and so far my budget hasn't made it to that. I really hadn't
considered AoA sensors until reading this thread, That might be a
cheaper way of doing this.

Brian Case
HP16T N16VP.



On Jul 10, 11:25 am, Udo wrote:
Unfortunately we do not have A of A meter. I have come to the
conclusion that using the flight manual for specific flap setting and
speeds and wing loading is the way to go.
For example: At a gross of 800 lb and a flap setting of +20 the
optimum speed range is about 5-7 kt, about the same in a 45 deg. bank
with the needed extra speed added for that bank.
But in level cruise the minimum drag has a range from about 70 kt to
95 kt at zero flap and 800 lb gross. You will feel the aft loading
of the airfoil in climb at the Flap handle , but no load in cruise.
Due to friction this " flap handle feel", as an indicator is
unreliable and depending on the airfoil also misleading.
I can speak from practical experience. On my past projects I had to
calculate the speeds for each flap setting as well as wing loading
In case of that airfoil it had a very narrow speed range in each flap
setting to maximize performance but it comes at a cost of having to
pay attention to the flaps to get the most out of each setting.
Udo

On Jul 10, 11:49 am, "Ken Kochanski (KK)"
wrote:

Bill Daniels wrote:
I've wondered if pressure ports on the top and bottom of the fuselage nose
where the nose contours are at about 45 degrees to the airstream wouldn't
give about the same pressure diferential that could be used to compute AoA.

The factory AOA meter in my DG-600 uses cross-connected pairs of
fuselage static ports just above the wing root, one set just aft of the
leading edge, and another at roughly 50% chord. The meter appears to be
a slightly modified electronic vario.

Marc