Marske Flying Wings do not stall

I did a modest cross country in the Pioneer IId yesterday but what is most
interesting was that I am exploring all of the flight envelope and yesterday
was stalls. When I pulled the stick all the way back slowly I suddenly found
that my airspeed had fallen to zero where I held it for quite some time and
my sink rate was 100 down. And I have it on video! I did this many times
although there was tendency to turn to the left since we have a left turn in
the glider.

The airspeed system was calibrated recently, both the airspeed instrument
and the installation, however I did not do the calibration for zero
airspeed... so it could be off slightly.

I have posted a picture on the web site showing the airspeed near zero and
will post a video shortly.

http://www.continuo.com/marske/pione...%20pioneer.htm

This is rather a long address so if this does not work go to our web site
and find "Marske Pioneer IId"

-mat

I have been recording all of this on video to give some credibillity to my
claims.
--
Marske Flying Wings
http://www.continuo.com/marske

Earlier, Mat Redsell wrote:

the air going over the top is separating
due to the high angle of attack...

Sounds like a stalled condition to me.

Bob K.

"Bob Kuykendall" wrote in message
...
Earlier, Mat Redsell wrote:

the air going over the top is separating
due to the high angle of attack...

Sounds like a stalled condition to me.

Bob K.

Again, not quite. Mat is describing an incipient stall, not a full stall.

The PII is under-elevatored with respect to stalling the aircraft but not
with respect to achieving CLmax. The Marske PII elevator authority
limitation is directly related to the incipient stalling of the wing. At
airspeeds above stall, the elevator authority is as large or larger than
conventional gliders. But as the incipient stall begins, the elevator
authority is sharply limited. (Another way to say this is that there is a
large non-linearity in elevator authority that sharply reduces elevator
effectiveness as the incipient stall begins.) This is not a linear function
of AOA or airspeed. As far as I know, this behavior is unique to plank-type
flying wings - particularly those with the elevators on the inboard trailing
edge of the wing such as the Marske planform.

On the other hand, with a conventional tailed aircraft, there is no link
between the elevator authority and the stalling behavior of the wing. In
the case of a conventional glider with a horizontal tail located some
distance aft of the wing, the wing may be fully stalled or fully flying, or
anywhere in between, with no effect on the elevator authority. Depending on
the elevator area, up angle limit, airspeed and CG location, the elevator
may be able to bring the wing to stall or beyond without the wing stall
imposing any limits on the up elevator authority at all. The designer may
choose to impose limits on up elevator authority to achieve benign stalling
behavior - this is not the case with the Marske planform.

As to Mat's report of near zero airspeeds, there are certainly large ASI
errors involved and the true airspeed is almost certainly not zero. To get
a true reading, Mat would need a nose boom with a gimballing pitot/static
probe and a sensitive calibrated ASI.

However, there are many reports of special conditions where a spanwise
vortex forms above the wing at high AOA preserving a large amount of lift.
One prototype of the Velocity canard pusher encountered this phenomenon with
the forward wing which resulted in the aircraft settling in a flat attitude
at low sink rates. The aircraft was not recoverable from this condition and
the test pilot elected to ride it into Tampa Bay at 200FPM sink and lived
to tell the tale. The Kasper Wing apparently can do this as well but is
recoverable.

It would be interesting to see a video of yarn tufts on the upper wing
surface to help visualize the flow with near-zero indicated airspeed.

Bill Daniels

Marske Flying Wings wrote:

I did a modest cross country in the Pioneer IId yesterday but what is most
interesting was that I am exploring all of the flight envelope and yesterday
was stalls. When I pulled the stick all the way back slowly I suddenly found
that my airspeed had fallen to zero where I held it for quite some time and
my sink rate was 100 down. And I have it on video! I did this many times
although there was tendency to turn to the left since we have a left turn in
the glider.

The airspeed system was calibrated recently, both the airspeed instrument
and the installation, however I did not do the calibration for zero
airspeed... so it could be off slightly.

I have posted a picture on the web site showing the airspeed near zero and
will post a video shortly.

http://www.continuo.com/marske/pione...%20pioneer.htm

This is rather a long address so if this does not work go to our web site
and find "Marske Pioneer IId"

-mat

I have been recording all of this on video to give some credibillity to my
claims.
--
Marske Flying Wings
http://www.continuo.com/marske

A zero speed indication is not surprising in these conditions, and doesn't
mean the speed (or even its horizontal component) is zero, but rather that
the pitot tube used by the ASI for total pressure is no more at the stagnation
point in these conditions and so you don't get the true total pressure. I guess
that the pitot is in the nose and when near stall angle the stagnation point
is well below, with a nice round nose like on the Pioneer IId, the pitot may even
be at a point where the airflow is accelerated at a speed higher than the freestream
speed, so the pressure is lower than the static pressure and the ASI should show
a negative speed if it could. Isn't that the reason for what modern gliders with
a nose pitot have a sharp nose (ASW20, Pegases) and many other ones have a pitot
in the fin?

"BD5ER" wrote in message
...
Doesn't this kind of depend on your definition of flight? The Kaspar wing
can
enter and recover from a controlled vertical decent. In this case the
forward
airspeed is zero but you are still in the air and in control.......and if
that
air is rising fast enough....


There is no such thing as "forward airspeed". Just Airspeed.
The speed of the air over the wing is completely independent
of ground reference points. If you want to use a ground
reference, use GROUND SPEED. Airspeed and Groundspeed
are easily confused when you try to describe things so don't take it so
hard. To use your illustration, push the nose down 100 degrees from
vertical, you are now slightly inverted and traveling backwards
over the ground. Do you now have NEGATIVE AIRSPEED?
Don't think so.............

Scott

There is no such thing as "forward airspeed". Just Airspeed.
The speed of the air over the wing is completely independent
of ground reference points. If you want to use a ground
reference, use GROUND SPEED. Airspeed and Groundspeed
are easily confused when you try to describe things so don't take it so
hard. To use your illustration, push the nose down 100 degrees from
vertical, you are now slightly inverted and traveling backwards
over the ground. Do you now have NEGATIVE AIRSPEED?
Don't think so.............

Scott

But what happens when you cock up a chandelle and don't get the nose down
before you loose forward airspeed? Seems like negative (or backwards)
airspeed to me! 8-)

Keith

There is no such thing as "forward airspeed".

All depends on where your point of referance is if the vector is positive or
negative. All of the planes I have flown had the pitot somewhere in the front
and I tend to have that stuck in my mind as the referance point. Substitute
"ground speed" solar speed or what ever speed you like but da ting duz wat is
duz G

"Marske Flying Wings" wrote in message

When I pulled the stick all the way back slowly I suddenly found
that my airspeed had fallen to zero where I held it for quite some time and
my sink rate was 100 down.

Must be that antigravity effect that flying wings are famous for...or
maybe you had an inadvertent deployment of a recovery parachute.

Seriously, Matt, what you probably saw is the same thing most gliders
do when put into a severe slip - the pitot gets masked or moves into
turbulent airflow and no longer indicates your actual airspeed. Ditto
with the rate of sink, perhaps (static port location?). Where is your
pitot located?

Do you have a GPS logger trace of this event? That should show what
your actual groundspeed (and sink rate, with the right software) was.
Repeat the exercise upwind and downwind, then tell us what really
happened.

Meanwhile, enjoy your wing!

Kirk
Happy with the nice, long, beautiful tail of my LS6

We have a pitot tube.. 1/4 " slightly protruding out from the front of the
nose inside a 2 " vent tube in the normal nose location. As I said before, I
will check my GPS ground speed on the next attempt.

I fly all kinds of gliders so I do know a slip well... but this is no slip.
Watch for that video!

I started at 40 mph and slowly went from 35 to 30 to 25 then 20 and then
zero. The video will show all of this on the instrument panel.....and I did
this more than once. I doubt that I actually got to zero..... but the
forward speed was definitely down about 20 or lower. I have boom mounted
turbine and will attach that on one of next flights.

-mat

"Kirk Stant" wrote in message
om...
"Marske Flying Wings" wrote in message

When I pulled the stick all the way back slowly I suddenly found
that my airspeed had fallen to zero where I held it for quite some time
and
my sink rate was 100 down.

Must be that antigravity effect that flying wings are famous for...or
maybe you had an inadvertent deployment of a recovery parachute.

Seriously, Matt, what you probably saw is the same thing most gliders
do when put into a severe slip - the pitot gets masked or moves into
turbulent airflow and no longer indicates your actual airspeed. Ditto
with the rate of sink, perhaps (static port location?). Where is your
pitot located?

Do you have a GPS logger trace of this event? That should show what
your actual groundspeed (and sink rate, with the right software) was.
Repeat the exercise upwind and downwind, then tell us what really
happened.

Meanwhile, enjoy your wing!

Kirk
Happy with the nice, long, beautiful tail of my LS6