Wingdrop while stalling

Hi,

there is a HAL HPT-32 (pistonengined 2 seater trainer light a/c)
which, when attempting a stall, does not pitch down correctly. Instead
one of the wings (either port or starboard (50/50)... no gyro problems
due to engine) almost always drops, and this genreally results in the
a/c entering a spin (which the rookie pilots are unable to handle,
generally). There is no inherent imbalance in the c.g. location due to
the fuel tanks ot fuel flow. What could be causing such a wing drop
while stalling? Is it soem inherent instability in the roll axis?

Any help/advice/recollection of previous such problems and what you
did to fix it will be greatly appreciated.

Lars

drake wrote:
Hi,

there is a HAL HPT-32 (pistonengined 2 seater trainer light a/c)
which, when attempting a stall, does not pitch down correctly. Instead
one of the wings (either port or starboard (50/50)... no gyro problems
due to engine) almost always drops, and this genreally results in the
a/c entering a spin (which the rookie pilots are unable to handle,
generally).

Sounds like a great trainer aircraft! If this problem common to the
type, or just this particular A/C?

The 50/50 part is interesting. Normally, if a plane is bent, it'll favor
one side or 'tuther.

Stall strips are a common way to improve stall performance, so as to
keep the tips flying (and ailerons working) while the root stalls. Does
the type have them?

Good luck...

In article ,
Todd Pattist wrote:

(drake) wrote:

there is a HAL HPT-32 (pistonengined 2 seater trainer light a/c)
which, when attempting a stall, does not pitch down correctly. Instead
one of the wings (either port or starboard (50/50)... no gyro problems
due to engine) almost always drops, and this genreally results in the
a/c entering a spin

A strong wing drop that occurs on either side can be caused
by the wing tips stalling too early. As the tip stalls, the
wing with the stalled tip begins to drop, the AOA increases
on the dropping wing and the entire wing stalls. Washout
(wing twist to reduce tip AOA) or a carefully selected
airfoil for the tip (that stalls at a higher AOA than inner
parts of the wing) may be used by the designer to prevent
this undesirable phenomenon. Careful comparison of washout
angle and/or the airfoil at the tip with the plans might
detect some rigging or construction problems. Any tendency
of the wing to twist, while in flight, can exacerbate the
problem.
Todd Pattist
(Remove DONTSPAMME from address to email reply.)
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Share what you learn.

If the wing drop is 50/50 L/R on the same plane, I would think that
somebody is holding in a little aileron or rudder, without knowing it.

I am not familiar with the type, so I cannot speculate further.

I would attach some stall strips to the inboard leading edges of both
wings, so they would induce turbulence at high angles of attack. They
need be 4" to 6" long, which would induce root stall before tip stall.

In article , drake says...

Hi,

there is a HAL HPT-32 (pistonengined 2 seater trainer light a/c)
which, when attempting a stall, does not pitch down correctly. Instead
one of the wings (either port or starboard (50/50)... no gyro problems
due to engine) almost always drops, and this genreally results in the
a/c entering a spin (which the rookie pilots are unable to handle,
generally). There is no inherent imbalance in the c.g. location due to
the fuel tanks ot fuel flow. What could be causing such a wing drop
while stalling? Is it soem inherent instability in the roll axis?

Any help/advice/recollection of previous such problems and what you
did to fix it will be greatly appreciated.

Lars

Bet you don't have any wash out in the wings.If it was always the same wing then
it could be rigging. That's a starting point .

See ya

Chuck

nafod40 wrote in message ...
drake wrote:
Hi,

there is a HAL HPT-32 (pistonengined 2 seater trainer light a/c)
which, when attempting a stall, does not pitch down correctly. Instead
one of the wings (either port or starboard (50/50)... no gyro problems
due to engine) almost always drops, and this genreally results in the
a/c entering a spin (which the rookie pilots are unable to handle,
generally).

Sounds like a great trainer aircraft! If this problem common to the
type, or just this particular A/C?

The 50/50 part is interesting. Normally, if a plane is bent, it'll favor
one side or 'tuther.

Stall strips are a common way to improve stall performance, so as to
keep the tips flying (and ailerons working) while the root stalls. Does
the type have them?

Good luck...

Some airplanes might have some nasty stall characteristics
caused by wing design, and sometimes such design is intentional to get
good aerobatic performance and to teach advanced flight maneuvers.
Most training airplanes are designed to have straightforward stalling
behaviour, some so forgiving that there is no real stall at all.
Newbie pilot students can get into big trouble real quick with stall
behaviour that drops one wing or the other.
Any certified airplane will have a straight-ahead stall break.
Wing drop is caused by one wing stalling slighty earlier, or the stall
on that side has progressed more than on the other, and if the wing
isn't out of rig, it's caused by uncoordinated flight. The nose of the
airplane isn't pointing straight ahead so that the airplane is sliding
slightly sideways as it stalls, and the wingtip that's farther aft
will stall first and drop. The same holds true for skidding turns; the
inside wing will drop first.
A power-on stall will most often drop the wing on the side that
has the upgoing prop blade; in North America, that's the left wing.
The rotating propwash strikes the wing root and causes a higher angle
of attack on that side, causing an earlier stall.

Dan

"Todd Pattist" wrote in message
...
(drake) wrote:

there is a HAL HPT-32 (pistonengined 2 seater trainer light a/c)
which, when attempting a stall, does not pitch down correctly. Instead
one of the wings (either port or starboard (50/50)... no gyro problems
due to engine) almost always drops, and this genreally results in the
a/c entering a spin

A strong wing drop that occurs on either side can be caused
by the wing tips stalling too early. As the tip stalls, the
wing with the stalled tip begins to drop, the AOA increases
on the dropping wing and the entire wing stalls. Washout
(wing twist to reduce tip AOA) or a carefully selected
airfoil for the tip (that stalls at a higher AOA than inner
parts of the wing) may be used by the designer to prevent
this undesirable phenomenon. Careful comparison of washout
angle and/or the airfoil at the tip with the plans might
detect some rigging or construction problems. Any tendency
of the wing to twist, while in flight, can exacerbate the
problem.
Todd Pattist
(Remove DONTSPAMME from address to email reply.)
___
Make a commitment to learn something from every flight.
Share what you learn.

It occurs to me that they might want to check the aileron rigging.
If both ailerons were "drooped", it would reduce the washout.

Tim Ward

I once heard a neat story about stall spin characteristics.

It seems that a light airplane manufacturer wanted a piece of the two seat
training market that Cessna dominated with the C150/152. They designed and
built a nifty little low wing prototype that flew real nice with much better
performance than the 150/152 with the same power. Then they invited a bunch
of CFI's to fly it and asked, "How'd you like it?" "It doesn't spin - we
want to teach spins", they said.

The manufacturer hired some engineering consultants and said, "Make it
spin". The consultants added stall strips on the outboard wing to make the
wing tips stall first - and boy, did it spin. The manufacturer brought the
CFI's back and let them fly it again. The CFI's said, "Boy, does it spin".
"We like it", they said.

So, the manufacturer built some little airplanes and the CFI's and their
students started making smoking holes in the ground as they spun in.

"Wow", said the manufacturer, "we got to fix this". So, they hired another
bunch of aeronautical consultants who looked up "how to fix bad stall/spin
characteristics" in their "how to design little airplanes" book. The book
said, "add stall strips to the inboard wing", so that's what they did. Now
the little airplane would still spin, but not as enthusiastically as before.
With FOUR stall strips on the wing, it didn't perform worth a damn either.

Still, the manufacturer built a bunch of them before exiting the market.

Makes you wonder.

Bill Daniels

"Morgans" wrote in message
...

"Tim Ward" wrote

It occurs to me that they might want to check the aileron rigging.
If both ailerons were "drooped", it would reduce the washout.

Tim Ward


I believe you have it backwards. Droop decreases overall AOA, and acts as
washout, right?
--
Jim in NC


I don't think so. I'm using "droop" here to indicate that the trailing
edges are lower than normal.
If it's lower in back, the AOA should be larger, and the washout less.
If they were both _reflexed_, it would be higher on the trailing edge, and
increase the washout.

Tim Ward

"Tim Ward" wrote

It occurs to me that they might want to check the aileron rigging.
If both ailerons were "drooped", it would reduce the washout.

Tim Ward


I believe you have it backwards. Droop decreases overall AOA, and acts as
washout, right?
--
Jim in NC

"Tim Ward" wrote in message
...

"Morgans" wrote in message
...

"Tim Ward" wrote

It occurs to me that they might want to check the aileron rigging.
If both ailerons were "drooped", it would reduce the washout.

Tim Ward


I believe you have it backwards. Droop decreases overall AOA, and acts
as
washout, right?
--
Jim in NC


I don't think so. I'm using "droop" here to indicate that the trailing
edges are lower than normal.
If it's lower in back, the AOA should be larger, and the washout less.
If they were both _reflexed_, it would be higher on the trailing edge, and
increase the washout.

Tim

Right. I had to do some hand flying to get that figured! g
--
Jim in NC