negative flaps--what speeds?

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 Fri, 25 Jul 2003 14:31:35 +0200, "Bert Willing"
wrote:

Flaps are just a pitch control which is more direct than the stick. I do
accelerate by pushing the flaps to negativ, and I deccelerate by pulling
them to positive settings. Works very nicely (but still using the stick :-)
I don't see why I should use negativ flaps to pull up.

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.

Bye
Andreas

Andreas,

Without wanting to prolong the argument
There appear to be two ways of achieving the same objective,
pilots should just chose the one they are happy with.
I trust the John Delafield theory and find it works,
others prefer yours and Berts

Dave
14:06 26 July 2003, Andreas Maurer wrote:
On Fri, 25 Jul 2003 14:31:35 +0200, 'Bert Willing'
wrote:

Flaps are just a pitch control which is more direct
than the stick. I do
accelerate by pushing the flaps to negativ, and I deccelerate
by pulling
them to positive settings. Works very nicely (but still
using the stick :-)
I don't see why I should use negativ flaps to pull
up.

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.

Bye
Andreas

Dave Martin wrote in message
Kirk invited comments -- obviously an aerotow man.

A man of all tastes - I have winch launched (in Germany) and would do
it if available out here, but in the US aerotow is more common. I'm
also a tow pilot, so have seen it from both ends.


Kirk try this in your machine at height I suggest several
thousand feet.

Fly at 60 knots and then pull hard back to about 45
degrees climb attitude, as the speed decays push hard
forwards, as you attain straight and level flight turn
quickly left or right . If you do it correctly you
can enter a spin nicely, IN any machine!!!!!!!

Interesting maneuver. Sounds like a rolling departure - which would
take some real mishandling of the glider to do! I also so some
aerobatics (Grobs, Swifts, Pilatus etc) so I'm a bit familiar with
what a glider will do in unusual attitudes.

It is the classic spin off a winch launch failure.
Pulling up hard into thermals and pushing hard over
is no different. As an instructor it requires a
little practice to make it work every time. Somehow
students do it with ease

Sounds like you are forcing a negative AOA stall then rolling, causing
an inverted spin from right side up.

If your description of how you pull up is true then
I will steer clear of you in the sky! May be you were
just taking the p***


Well, In my description I never lose control of my glider, despite a
badly misjudged pullup to well below stall speed - in yours you depart
into a spin! I think I will steer clear of you, too!

Dave Martin

Cheers,

Kirk

At 18:48 26 July 2003, Kirk Stant wrote:
Dave Martin wrote in message

Kirk

The exercise I described is one of the BGA stall reinforcement
exercises. The common cause following a winch launch
failure, pushing hard forward, then as the attitude
looks correct and as the glider is in a reduced G situation
starting a turn. (Without getting the books out that
is as simple as I can describe it) This has caused
several accidents in the UK some of them fatal.

The danger also exists when pulling up sharply in to
a thermal and pushing over hard at the top of the pull
up then starting a turn in reduced G.

Fingers crossed as yet I have never entered a spin
pulling up into thermals. But as an instructor at
a winch launch site, it something you need to be able
to demonstrate.

But we are getting away from the thread...........

Regards


Dave

In article ,
says...

The danger also exists when pulling up sharply in to
a thermal and pushing over hard at the top of the pull
up then starting a turn in reduced G.

Do people really enter thermals this way? I've never seen anyone do
this. I might pull up at as much as 1.5 g momentarily, but just let it
bleed down to 1 g and start a turn. What is the value in pushing hard
at the top, instead of just entering a turn?
--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

"Dave Martin" wrote in message
...

The exercise I described is one of the BGA stall reinforcement
exercises. The common cause following a winch launch
failure, pushing hard forward, then as the attitude
looks correct and as the glider is in a reduced G situation
starting a turn. (Without getting the books out that
is as simple as I can describe it) This has caused
several accidents in the UK some of them fatal.

The danger also exists when pulling up sharply in to
a thermal and pushing over hard at the top of the pull
up then starting a turn in reduced G.

Fingers crossed as yet I have never entered a spin
pulling up into thermals. But as an instructor at
a winch launch site, it something you need to be able
to demonstrate.

But we are getting away from the thread...........

Regards


Dave

These are fun maneuvers. I find a Blanik L-23 to be a prefect trainer for
them - it spins easily, recovers easily with little altitude loss or
airspeed gain.

My winch stall maneuver is done at a safe altitude (of course). First, I
ask the student to dive then zoom up at 45 - 50 degrees, then when the
airspeed drops to about 55Kts, I yell "wire break" and expect the student to
push over smartly in a simulated wire break recovery. (This gets the
student used to the attitude and feel of a wire break and the control inputs
needed for a recovery before trying it for real on the winch.)

If the student doesn't screw it up on his own, I will demonstrate a botched
recovery by doing nothing until the nose falls on its own then stopping the
pitch-down at the normal gliding attitude. This results in the airspeed at
about 15 knots with the glider held level with near full-up elevator. The
L-23 will usually oblige with a quick flip into a spin even if no turn is
attempted - try a turn and it will spin for sure. No student observing this
has failed to appreciate that the wings should be level and the nose needs
to be well below the normal glide attitude and held there until a safe
airspeed is achieved.

The thermal entry stall/spin only requires that the pilot hold into-the-turn
rudder a second or two longer than needed while trying to reduce airspeed
still further. In most cases, this is a full cross-controlled accelerated
stall from a 45 degree bank - wheee! (I've caught some high time pilots
with this one.)

Bill Daniels

"Eric Greenwell" wrote in message
.. .
In article ,
says...

The danger also exists when pulling up sharply in to
a thermal and pushing over hard at the top of the pull
up then starting a turn in reduced G.

Do people really enter thermals this way? I've never seen anyone do
this. I might pull up at as much as 1.5 g momentarily, but just let it
bleed down to 1 g and start a turn. What is the value in pushing hard
at the top, instead of just entering a turn?
--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

Depends on how long you hold the 1.5G. Hold it long enough and you might
get a steep pitch up that requires forward stick to get the nose down for
the turn. Rush it and things get interesting.

Bill Daniels

"Bill Daniels" wrote in message

The thermal entry stall/spin only requires that the pilot hold into-the-turn
rudder a second or two longer than needed while trying to reduce airspeed
still further. In most cases, this is a full cross-controlled accelerated
stall from a 45 degree bank - wheee! (I've caught some high time pilots
with this one.)

Bill Daniels

Interesting exercise. Also sounds like a good way to teach
low-G/low-AOA affects on stall speeds. I can see how it would work
well in something like a Blanik, with a huge elevator. How do
competition ships with small elevators react? I'll have to try with
my LS6, but I have the feeling that the elevator is not powerful
enough to keep the nose from falling through and causing a stall/spin.

On the other hand, in the same nose high/close to stall speed
situation, the LS6 (and any other glider, I'm sure) reacts perfectly
well to an unloaded (low-G) roll in the direction of the intended
turn, followed by an easy nose down acceleration to a safe speed
before pulling on the G necessary for the turn. Not a recommended
normal thermal entry by any means, but a way to recover from a
botched, overenthusiastic zoom-in.

The obvious key is the G (or AOA) versus airspeed relationship.
Trying to turn when the airspeed is down in the teens would show that
the pilot has a certain lack of situational awareness!

Kirk
66

"Kirk Stant" wrote in message
om...
"Bill Daniels" wrote in message

The thermal entry stall/spin only requires that the pilot hold
into-the-turn
rudder a second or two longer than needed while trying to reduce
airspeed
still further. In most cases, this is a full cross-controlled
accelerated
stall from a 45 degree bank - wheee! (I've caught some high time pilots
with this one.)

Bill Daniels

Interesting exercise. Also sounds like a good way to teach
low-G/low-AOA affects on stall speeds. I can see how it would work
well in something like a Blanik, with a huge elevator. How do
competition ships with small elevators react? I'll have to try with
my LS6, but I have the feeling that the elevator is not powerful
enough to keep the nose from falling through and causing a stall/spin.

On the other hand, in the same nose high/close to stall speed
situation, the LS6 (and any other glider, I'm sure) reacts perfectly
well to an unloaded (low-G) roll in the direction of the intended
turn, followed by an easy nose down acceleration to a safe speed
before pulling on the G necessary for the turn. Not a recommended
normal thermal entry by any means, but a way to recover from a
botched, overenthusiastic zoom-in.

The obvious key is the G (or AOA) versus airspeed relationship.
Trying to turn when the airspeed is down in the teens would show that
the pilot has a certain lack of situational awareness!

Kirk
66

A stall occurs only when the AOA exceeds about 16 degrees for most airfoils.
Low G, by itself, isn't dangerous and, in fact, reduces the stall speed
since the wing isn't loaded. The stalling AOA comes in at the transition
from low G to one G.

Most competition ships fly with the CG well aft so, even with small
elevators, they have plenty of elevator authority for some interesting
stalls. I do worry that many competition pilots get very close to a
stall/spin departure without realizing it during an aggressive thermal
entry. This is particularly dangerous when down low (I've GOT to center
this thermal or land out.) Desperately and aggressively trying to center a
small core when under the stress of a pending outlanding is a bad
combination - there have been a more than a few bad outcomes to this
situation.

Bill Daniels