Flap Settings

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 |

I find with my PIK that my pull ups are much better with the flaps
full negative until I get below 65 kts. I then slowly transition them
to +8 if I'm going to circle, but only to 0 if I'm going to pass
through the lift and go on. It seems that I waste less time and energy
if I go ahead and transition back to -8 as I nose over to go on. I've
often wondered if I'm doing this correctly, but it seems to work.

Jack Womack

2 cents, I've personally noticed generally good performance in my 20B
when I "float" the flaps while driving. The 20 seems to be fairly well
suited for this proceedure as other ships may not be for a variety of
reasons as noted in one of the posts.

RC-21


On Jul 10, 9:49 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 Jul 11, 11:01 am, Rick Culbertson wrote:
2 cents, I've personally noticed generally good performance in my 20B
when I "float" the flaps while driving. The 20 seems to be fairly well
suited for this proceedure as other ships may not be for a variety of
reasons as noted in one of the posts.

RC-21

Please describe exactly what you mean by "floating" the flaps.

Jack

Hi Jack,

I'll attempt to clarify;
My 1985 asw20b has the following five flap settings;

#1 = -12' (high speed cruise)
#2 = -6'
#3 = 0
#4 = +9 (thermalling)
#L = +38'/-8' (landing flaps)

I also have an additional after market thermal setting between flap
settings #3 & 4

When I speak of "floating the flaps" I'm referring to setting #1
through #3 but most often between the negative flap settings #1 & 2.

Dick Johnson (as I recall) noted in his 1978 asw20 report that he
notice the #2 flap setting didn't seem to produce a noticeable
performance improvement verses the #1 setting and suggested perhaps a
different/better flap setting was in order in this specific speed
range. Additionally, some very talented former 20 drivers told me
they "allowed" the flap handle to "float" between the negative
settings with good results. Meaning, to the location of the least
resistance.

In practice I have found the handle will fairly easily slide to the
next detent (flap setting) with increased speed and not as easily
slide back to the previous one when speed is decreased. I generally
keep my hand on the flap handle and feel for the change in pressure
and assist it with slight pressure for or aft to stay in the area of
least resistance. Of course when I leave a thermal and need to "get up
to speed" quickly, I always lead or set the flaps in advance to the
anticipated cruise speed setting. So what I'm generally referring to
is not when your driving for the next 10 kt thermal at 100+ kts or
when your floating along at best LD but when your varying between 70
and 90 kts. Additionaly I attempt to adjust subtile speed adjustments
within this range with the flap handle verses using the elevator as
has been sugested by some talented published pilots.

My 1985 asw20b seems (IMHO) to be ideally suited for this practice and
the feed back is quite pronounced. Conversely the same "former 20
drivers" have stated the ships they fly today, an asw27 and ash26e do
not accept this kind of flap assistance at all. So this may be unique
to the asw20 or similar ships of its era. In any event it seems to
work well with my ship.

I hope that's helpful,

Rick - 21



On Jul 11, 6:21 pm, Jack wrote:
On Jul 11, 11:01 am, Rick Culbertson wrote:

2 cents, I've personally noticed generally good performance in my 20B
when I "float" the flaps while driving. The 20 seems to be fairly well
suited for this proceedure as other ships may not be for a variety of
reasons as noted in one of the posts.

RC-21

Please describe exactly what you mean by "floating" the flaps.

Jack