Elevator Turbulator tape question

I find this a very interesting subject (LS stab stalls) I have a lot of time
in the LS-6 and found no stab stall problems at all. The LS-7 was the same
until I put zig-zag on, then got an abrupt nasty stall. I only have about 50
hours in the LS-8, but I could feel and hear stab separation a good 5 knots
above wing stall when flying with 9 lb wg loading. My CG on all 3 was about 85%
of allowable range.

All three use a thin stab section and none come with zig-zag on the stab. If
I'm getting separation (nervous stick) a good 5 knots above wing stall, doesn't
that mean I'm getting close to stalling the stab? If I put zig-zag on the stab
and delay the stall, won't I be masking the tell-tail sings of stab stall?
JJ Sinclair

I find this a very interesting subject (LS stab stalls) I have a lot of time in
the 6 & 7. I found NO stab stall problem at all in my LS-6. The LS-7 was the
same until I put zig-zag on, then I got an abrupt, nasty stall. I only have
about 50 hours in the LS-8, but I could feel and hear stab separation, a good 5
knots above wing stall, when flying at 9 lb wg loading. The CG on all 3 was
about 85% of allowable range.

All 3 use a thin section and none of my ships came with zig-zag on the stab. If
I'm getting separation (nervous stick) a good 5 knots above wing stall, doesn't
that mean I'm getting close to stalling the stab? If I put zig-zag on the stab
and delay the stall, won't I be masking the tell-tail signs of stab stall? Are
we investigating something that LS already knows?
JJ Sinclair

JJ Sinclair wrote:

I find this a very interesting subject (LS stab stalls) I have a lot of time in
the 6 & 7. I found NO stab stall problem at all in my LS-6. The LS-7 was the
same until I put zig-zag on, then I got an abrupt, nasty stall. I only have
about 50 hours in the LS-8, but I could feel and hear stab separation, a good 5
knots above wing stall, when flying at 9 lb wg loading. The CG on all 3 was
about 85% of allowable range.

All 3 use a thin section and none of my ships came with zig-zag on the stab. If
I'm getting separation (nervous stick) a good 5 knots above wing stall, doesn't
that mean I'm getting close to stalling the stab? If I put zig-zag on the stab
and delay the stall, won't I be masking the tell-tail signs of stab stall? Are
we investigating something that LS already knows?
JJ Sinclair

How do you know that your feeling and hearing comes from the stab
and not the wing ? I can't believe the stab is stalling before the
wing, for the reasons I tried to explain in my previous post. This
happens only on canard stabs. But separaion beginning on the wing
before full stal is much more likely and this can also cause nervous
stick.

On Thu, 16 Oct 2003 10:49:22 +0000, Robert Ehrlich
wrote:

JJ Sinclair wrote:

I find this a very interesting subject (LS stab stalls) I have a lot of time in
the 6 & 7. I found NO stab stall problem at all in my LS-6. The LS-7 was the
same until I put zig-zag on, then I got an abrupt, nasty stall. I only have
about 50 hours in the LS-8, but I could feel and hear stab separation, a good 5
knots above wing stall, when flying at 9 lb wg loading. The CG on all 3 was
about 85% of allowable range.

All 3 use a thin section and none of my ships came with zig-zag on the stab. If
I'm getting separation (nervous stick) a good 5 knots above wing stall, doesn't
that mean I'm getting close to stalling the stab? If I put zig-zag on the stab
and delay the stall, won't I be masking the tell-tail signs of stab stall? Are
we investigating something that LS already knows?
JJ Sinclair

How do you know that your feeling and hearing comes from the stab
and not the wing ? I can't believe the stab is stalling before the
wing, for the reasons I tried to explain in my previous post. This
happens only on canard stabs. But separaion beginning on the wing
before full stal is much more likely and this can also cause nervous
stick.

I'd expect major flow separation under the tailplane at the elevator
hinge under these conditions (low airspeed, fully deflected elevator).
If the tailplane doesn't actually stall, I'd at least expect a sudden
reduction in elevator effectiveness as the flow separated. That might
be all that's needed to give the fairly gentle pitch down we all
associate with a typical glider stall.

Ob. question: what have I missed?

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

Martin Gregorie wrote:

I'd expect major flow separation under the tailplane at the elevator
hinge under these conditions (low airspeed, fully deflected elevator).
If the tailplane doesn't actually stall, I'd at least expect a sudden
reduction in elevator effectiveness as the flow separated. That might
be all that's needed to give the fairly gentle pitch down we all
associate with a typical glider stall.


Low airspeed is not a factor, stalling is related to angle of attack,
not to airspeed. For the wing there is a relationship between angle
of attack and airspeed due to the fact that the lift must remain equal to
the weight, so lower airspeed implies higher lift coeefficent, i.e.
higher angle of attack, as long as increasinng the angle of attack
increases the lift coeefficent, i.e. up to stall angle. But nothing
like this exists concerning the tail plane.

Unless the stops on the elevator allows an execessive excursion,
there should be no separation at the hinge. Even in this case
this should occur before the nose up attitude is obtained, at the
moment when the elevator is deflected in order to obtain the
rotation providing this nose up attitude because at this moment the
(negative) angle of attack is higher (in absolute value) than when
the nose up attitude is obtained.

The pitch down associated with a typical glider stall is not due
to stalling or separation at the elevator, but on the contrary
to the fact that the wing is stalled and not the elevator, both
having positive angles of attack. Only on canards the elvvator+
stabiliser has a higher incidence than the main wing and so stalls
before the main wing, and this is well known to completeley avoid
wing stalls. On aircratfs with conventional tailplanes the main
wing stalls before the tailplane and the ensuing pitch down
decreases the angle of attack on both the main wing
and the tailplane and should avoid stall on the tailplane as
well as recover from stall on the main wing.

Robert wrote
How do you know that your feeling and hearing comes from the stab
and not the wing ?

In the LS-8, I can feel it in the stick a good 5 knots above stall. I don't
believe it is separated air coming from the wing, because the T-tail is just
too high to allow that. I have felt the same thing about 3 knots above stall in
a 301 libelle which has a low tail and it was *dirty air* coming from the
wing.

BTW, I only felt the nervous stick with a load of water and I wasn't trying to
stall the ship, It happened when I was thermalling.
JJ Sinclair

Where should I put turbulator tape on the all-flying
stabilator on my LS-1d? Right now, there is a the
head of a big 'ol hex-head bolt, safety pin, and peg
(to anchor the safety pin) that sticks out in the breeze
on the upper surface of the stabilator.
(This is asked with tongue in cheek)

By the way, when it stalls, just a very quick foreward
movement on the stick gets it going again. No warning
before it stalls.

Ray Lovinggood
Carrboro, North Carolina, USA

At 13:54 16 October 2003, Jj Sinclair wrote:
Robert wrote
How do you know that your feeling and hearing comes
from the stab
and not the wing ?

In the LS-8, I can feel it in the stick a good 5 knots
above stall. I don't
believe it is separated air coming from the wing, because
the T-tail is just
too high to allow that. I have felt the same thing
about 3 knots above stall in
a 301 libelle which has a low tail and it was *dirty
air* coming from the
wing.

BTW, I only felt the nervous stick with a load of
water and I wasn't trying to
stall the ship, It happened when I was thermalling.
JJ Sinclair

Robert,
If the stab isn't stalling, can you explain the sharp stall in the LS-7 after
adding zig-zag and the elevator buffet in the LS-8, a good 5 knots above wing
stall?

Could it be this LS-8 wasn't set with the proper declanage? With all the
sloppy workmanship we are seeing these days, it wouldn't surprise me, a bit.
:(
JJ Sinclair

In article ,
says...
Robert wrote
How do you know that your feeling and hearing comes from the stab
and not the wing ?

In the LS-8, I can feel it in the stick a good 5 knots above stall. I don't
believe it is separated air coming from the wing, because the T-tail is just
too high to allow that. I have felt the same thing about 3 knots above stall in
a 301 libelle which has a low tail and it was *dirty air* coming from the
wing.

BTW, I only felt the nervous stick with a load of water and I wasn't trying to
stall the ship, It happened when I was thermalling.
JJ Sinclair

If it happened while thermalling, this suggests it isn't the elevator
stalling. Here's why:

While circling, the elevator's angle of attack (AOA) is greater than
the wing's AOA, because of the differing airflow directions.

This greater AOA tends to increase the upward force on the elevator
(or reduce it's downward force), which is why it is more difficult to
stall a glider in a turn.

Or, if we think of the elevator as an "upside down" wing that is
producing lift downward (pushing the tail down), it's AOA is
_reduced_.

With a lower AOA, it's not going to stall in a turn if it can't do it
in straight ahead flight.

Question: with water, was the CG kept in the same place as without
water, or did it move forward?

--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

On Thu, 16 Oct 2003 12:59:05 +0000, Robert Ehrlich
wrote:

Low airspeed is not a factor, stalling is related to angle of attack,
not to airspeed.

Yes, of course, but airspeed does affect the energy in the boundary
layer and that in turn does control where (and if) the airflow
separates from the surface.

That's why turbulation works - it energises the BL, thus preventing
flow separation.


--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :