negative flaps--what speeds?

The manual for my 303 Mosquito is silent as to when the use of negative
flaps becomes beneficial during cruise. Any pointers as to what speeds are
associated with -1 and -2 flap positions? Any data on the LD benefits of
negative flaps at higher speeds?

I read Dick Johnson's flight eval (Aug '79) and my take away is that it
makes sense to go to -1 (4.6 degrees) at around 80 kts and that there's
little difference between -1 and -2. I also understood that article to say
that the speed of best LD could be increased by 5 kts by using -1. Is my
understanding on these two points correct? Dick says the weather was poor
and there was a lot of scatter in the data--does anyone have experience that
agrees/disagrees with Johnson's report?

Any help appreciated--specific to the 303 or regarding flap use during
cruise in general. Hey, I'm transitioning from a PW5 to a 15M and it's got
a lot of new thingies to get used to--retractable wheel, flaps, water,
LEGS!!! ;-)

Brent

I would recommend a flap setting for the FX 67 170 of
-4 deg. starting at ~50 kt and changing over to - 8 at 70-75 Kt.
The Airfoil analysis agrees with the R.Johnson statement,
the L/D is better with -4 Flap
Udo

"303pilot" brentUNDERSCOREsullivanATbmcDOTcom wrote in message ...
The manual for my 303 Mosquito is silent as to when the use of negative
flaps becomes beneficial during cruise. Any pointers as to what speeds are
associated with -1 and -2 flap positions? Any data on the LD benefits of
negative flaps at higher speeds?

I read Dick Johnson's flight eval (Aug '79) and my take away is that it
makes sense to go to -1 (4.6 degrees) at around 80 kts and that there's
little difference between -1 and -2. I also understood that article to say
that the speed of best LD could be increased by 5 kts by using -1. Is my
understanding on these two points correct? Dick says the weather was poor
and there was a lot of scatter in the data--does anyone have experience that
agrees/disagrees with Johnson's report?

Any help appreciated--specific to the 303 or regarding flap use during
cruise in general. Hey, I'm transitioning from a PW5 to a 15M and it's got
a lot of new thingies to get used to--retractable wheel, flaps, water,
LEGS!!! ;-)

Brent

At 18:36 24 July 2003, 303pilot wrote:
The manual for my 303 Mosquito is silent as to when
the use of negative
Hi Brent

I am a Mosquito owner.
I have found that normal thermalling is best done at
around the 45-50kt range with +1 flap. I have flown
in weak wave where at around 50knots the glider was
sinking and putting the flaps up to 0 enabled the glider
to climb. The drag is obviously less in the higher
(up) flap setting

When cruising I put the flaps in whatever position
feels comfortable with little reference to the ASI,
other than to monitor the chosen cruise speed. The
way to do this is quite simple, once you start to increase
speed move the flap lever into the free position and
without letting go, let it float. You will find that
it adopts a set position which can be felt, for a given
speed, then you can drop it into the closest notch.
After a while this becomes automatic.

Two other simple techniques are

1. When leaving a thermal put the flaps right up
before you accelerate, on some gliders like the ASW20
putting the flaps up causes a quite marked speed increase,
the Mosquito is not quite so marked and need a little
help from the stick. One you have reached your chosen
cruise speed you can then reset the flaps as required.

2. Only put the flaps down when you have slowed after
your pull up into the next thermal.

This means you are accelerating and decelerating with
minimum drag and do not have to worry about the speed
settings as you speed up and slow down.

Landing the Mosquito is a whole new ball game!! The
was a thread running a few months ago on this subject.

Hope this helps

Dave Martin

Someone (I do not remember the name) wrote in last years Soaring magazine about quite contrary
approach (not related to specific glider). The idea was that one has to put flaps down WHILE slowing
down, not after. And the reasoning was that flap position is not that much depending on the speed of
the glider, but on angle of attack. So if one attacks thermals aggressively making serious pull-ups,
the increased AOA means one has to advance in flap settings beforehand the lowering speeds. Same
applies to leaving the thermal cause then the AOA decreases. It was told to be making huge
differences.


Regards,
Kaido, who doesn't fly flapped gliders currently.



2. Only put the flaps down when you have slowed after
your pull up into the next thermal.

This means you are accelerating and decelerating with
minimum drag and do not have to worry about the speed
settings as you speed up and slow down.

Sorry, It was in 2001, but I still don't remember the specific article and the writer.


"iPilot" wrote in message ...
Someone (I do not remember the name) wrote in last years Soaring magazine about quite contrary
approach (not related to specific glider). The idea was that one has to put flaps down WHILE
slowing
down, not after. And the reasoning was that flap position is not that much depending on the speed
of
the glider, but on angle of attack. So if one attacks thermals aggressively making serious
pull-ups,
the increased AOA means one has to advance in flap settings beforehand the lowering speeds. Same
applies to leaving the thermal cause then the AOA decreases. It was told to be making huge
differences.


Regards,
Kaido, who doesn't fly flapped gliders currently.



2. Only put the flaps down when you have slowed after
your pull up into the next thermal.

This means you are accelerating and decelerating with
minimum drag and do not have to worry about the speed
settings as you speed up and slow down.

Kaido

Read, 'Advance Cross Country Soaring' by John Delafield.
Pages 81 Flaps

John gives a detailed account of the use of flaps,
which agrees with what I said, or more to the point,
there were few articles written on the correct use
of flaps in 1983 and the information from John helped
me learn how to use the flaps.

In summary he says, 'Flaps should be not be regarded
as anything other than an auxilary control to enable
the pilot to operate the wing efficiently throughout
the speed range. The are straight forward in use and
will become instinctive after only a few hours' practice.'

The method described is simple and reduces the movements
to a minimum and saves the pilot worrying what the
next setting should be.

Flaps UP to slow down. Flaps UP to accelerate, then
once the
required speed has been achieved set them to support
flight at that speed.

The only word of caution is that in large pull ups
and push overs with reduced G at the top and increased
stall speed because of the negative flap setting the
pilot may be in serious danger of spinning.



At 08:24 25 July 2003, Ipilot wrote:
Someone (I do not remember the name) wrote in last
years Soaring magazine about quite contrary
approach (not related to specific glider). The idea
was that one has to put flaps down WHILE slowing
down, not after. And the reasoning was that flap position
is not that much depending on the speed of
the glider, but on angle of attack. So if one attacks
thermals aggressively making serious pull-ups,
the increased AOA means one has to advance in flap
settings beforehand the lowering speeds. Same
applies to leaving the thermal cause then the AOA decreases.
It was told to be making huge
differences.


Regards,
Kaido, who doesn't fly flapped gliders currently.



2. Only put the flaps down when you have slowed after
your pull up into the next thermal.

This means you are accelerating and decelerating with
minimum drag and do not have to worry about the speed
settings as you speed up and slow down.

Thanks all and I'm interested in any other opinions/data.

"Robert Ehrlich" wrote in message
...
justification. The appropriate setting should be derived
from the various polars corresponding to the various settings.
This is what I was trying to do with the three polars in Dick Johnson's
flight eval--the problem is that the weather wasn't optimal, producing a lot
of scatter in the polar curves.

Whilst all this theory makes sense ---- to some, my
glider manual only has the single polar curve which
itself is a guestimate from a comparison flight with
a 16 metre Standard Cirrus B

I like to keep my flying simple, John Delafields method
works it is simple and in flight uncomplicated. I
suspect the savings on drag produced by speeding up
or slowing down with flaps in a negative, up, position
is relatively small.

Whereas putting flaps down at speed to slow down appears
very inefficient.

Still if you are happy with this loss of energy then
fine.

Dave Martin

Robert raises some good points about interpolating between the
different polars, and it points towards a question that I've been
wondering for a while:

Why have none of the established manufacturers come out with an
auto-flap system that uses a computer to assess several parameters
(speed, angle of attack, G loading, air density, etc), and an actuator
to adjust the flaps to an appropriate setting?

I suspect that the answer might be, because it really doesn't matter
all that much. Look at the difference between the LS6 and the LS8 -
you can barely tell them apart until you get to about 85 knots.

However, that autoflap arrangement has a lot of whiz-bang appeal, and
I'd like to see someone give it a try.

Thanks, and best regards

Bob K.
http://www.hpaircraft.com

In article ,
Robert Ehrlich wrote:

If you consider
two polars, e.g. for zero setting and the first negative setting,
they intersect each other at some point. At speed above the
speed of this point, clearly the negative setting is better,
at speed below this point, the zero setting is better. But it
is not optimal to switch the setting juste when you cross this
speed. Above the intersection, the two polars have a common
tangent which meets each polar at some point, corresponding
to some speed, a low one for zero setting and a high one
for negative setting. You should never fly a speed between these
both speed

Another alternative is to use a flap setting between the detents while
in that speed range.

The performance difference is likely to be minor in any case.

When I fly the Janus -- the only flapped ship I fly, and which (as you
note) gives individual polars in the manual -- I tend to choose between
the lower and higher flap setting based on what I and the air are likely
to be doing. For example, when flying in the 50 - 60 knot range, if the
air is smooth (e.g. in wave) I'll fly in zero flap. If the air is bumpy
and I'm turning from side to side looking for a thermal then I'll use +6
becasue I figure that the better response and performance at the higher
AOA in a gust will outweigh the little extra drag the rest of the time.

At the other end, it was I think the Dick Johnson report that claimed
that there was no speed range in which -4 was better than both 0 and -7,
so don't use it.

-- Bruce