negative flaps--what speeds?

It's been the Akaflieg Munich, and the glider was/is the Mü 28 (single
seater aerobatics).

Bert

"Mike Borgelt" a écrit dans le message de
...
On 25 Jul 2003 10:01:38 -0700, (Bob Kuykendall)
wrote:

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


Bob,
You don't need a computer. About 20 years ago the Akaflieg
Braunschweig had an auto flap sustem in an LS3. Essentially a weight
on an arm - more g more flapdown. Less g and the faster you go the
airloads push the flap up more. Do this correctly and it all works
nicely I'm told. You do need a damper as you are un mass balancing the
flaps and might be prone to flutter.

The flaps on the LS6 barely work according to the DLR polar I have
which is of course why the LS8 works so well.

Mike Borgelt

On Mon, 28 Jul 2003 09:58:51 +0200, "Bert Willing"
wrote:

It's been the Akaflieg Munich, and the glider was/is the Mü 28 (single
seater aerobatics).

Bert

You are right it was Munich but they did have an LS3 as well with the
auto flap.

Mike Borgelt

The method Dave described is what I normally do in my LS-3a. Yesterday
I was trying some different settings and noticed that at 100 knots,
the flaps could be moved between 0 and -7 with no issues. At 120 knots
the flaps wanted to stay at about -3 and when I moved them to -7,
which required some pressure, it created a humming noise. Seems that
-7 should be better at higher speeds but the noise and pressure on the
flap handle tells me otherwise.

Also, the LS-3a Flight Manual has the following instructions:

Up to 103 knots - Flaps should be between 0 and -7, depending on
desired speed. Once the aircraft is trimmed for thermaling, no
additional trim adjustment is required for high speed flight. Any
stick forces can be removed by adjusting the flap position. This
results in the correct flap position for all speeds.

103 ~ 146 knots - Flap position -7. Stick forces should be reduced to
zero through trim adjustment.

All the best,
Steve

Dave Martin wrote in message ...

snip

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.

snip

Dave Martin

Andreas Maurer wrote:
...
Yup. Always keep the AoA constant by using the flaps.
I think the procedure that is described in the ASW-20's manual
describes the physics very well.

Isn't the attitude rather than the AoA you are keeping constant?
As far as I can say from experience on LS6, it flies with nearly
the same attitude at high speed with negative flaps and at low speeds
with zero or positive flaps, which means that the Aoa (defined as the
angle between the direction of the airflow and the wing chord, i.e.
the line frm leading to (moving) trailing edge) varies.

Bob Kuykendall wrote:

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 think one of the reason for not doing that is that it would make the
use of some (probably eletrical) power supply mandatory. I don't know
if it is a part of the certification requirements, but the fact is that
in all gliders, the basic operation is always possible without any such
power. E.g. in France at least only the basic pneumatic instruments are
mandatory, and they must be pneumatic.

The flaps on the LS6 barely work according to the DLR polar I have
which is of course why the LS8 works so well.

Mike Borgelt

Mike any idea where I can get polar data on the V2C?

I have seen a mirror with a level type of device attached to the panel to help
set flap positions, Sean Franke's Ventus has this. I I do not know how it
works but was hoping someone has used sucha device and could comment.

Craig