Harder to stall in a steep turn?

In his book Gliding, p100, Derek Piggott writes:

"In most modern gliders, the elevator power is not adequate to pull
the wing beyond the stalling angle in a steep bank and it is only just
possible to reach the pre-stall buffet with the stick right back.
This is very different from straight flight and gentle turns where a
movement right back on the stick would definitely stall the aircraft,
requiring a significant loss of height to pick up speed before full
control is regained."

If this is the case, what are the aerodynamics that account for
this? Does it have something to do with the elevator's limited
power to deal with the load factor resulting from a steep, level turn?

Jim writes:

In his book Gliding, p100, Derek Piggott writes:

"In most modern gliders, the elevator power is not adequate to pull
the wing beyond the stalling angle in a steep bank and it is only just
possible to reach the pre-stall buffet with the stick right back.
This is very different from straight flight and gentle turns where a
movement right back on the stick would definitely stall the aircraft,
requiring a significant loss of height to pick up speed before full
control is regained."

Please be patient with a long-time power pilot attempting to make the
transition to gliders, but I am having considerable difficulty imagining
that any aircraft which can be brought to a stalling angle of attack with
the elevators at a given speed should have so much more difficulty doing so
in one attitude than another. Surely what we have here is a statement by
Piggot the truth of which rests upon some unspoken assumptions and a rather
more specific scenario than we are attributing to him.

I have not read "Gliding" by Piggot, but I am currently reading his
"Understanding Gliding". His explanations of maneuvering flight regimes seem
to suffer from an attempt to explain flight dynamics in layman's terms.
Piggot, for all his vast experience in gliding and teaching, is sometimes as
awkward to read as was Langewiesche with his references to "flippers"
instead of "ailerons".



Jack

In article ,
Jack wrote:

Piggot, for all his vast experience in gliding and teaching, is sometimes as
awkward to read as was Langewiesche with his references to "flippers"
instead of "ailerons".

Perhaps because the term "flippers" was referring to the elevator?

-- Bruce

The danger here is that we are talking theory where
we may start to confuse pilots. It is harder to stall
with 60 degrees of bank. Gliders like the K13, by
design run out of elevator in straight and level flight.
They are difficult when flown with heavy pilots to
develop more than a mushing stall in sraight and level
flight.

Put light -- bottom weigh pilots in and they become
a different glider.

The Puchacz on the other hand has plenty of rear elevator
even when banked, quite steeply.

There can be some dangerous assumptions that gliders
will not spin.

The pilot must know the limitations and characteristics
of the glider he/she is flying. This can only be achieved
by carefully experimenting with different configurations
and different flight situations.

Gliders with reputations that they will not spin, can
catch pilots out who load them wrongly, fly them badly
or worse combine both.

Dave Martin

Get some empirical experience. Hop in a G-103, circle
at 60deg bank and
bring the stick back to the stop. If properly rigged,
it will not stall.
Do the same in straight and level flight. It will
stall, in a mushy sort of
way depending on loading. Also, in a G-103, you will
get more elevator
authority in tight turns by moving the trim forward.

This is not true of all gliders, but clearly in a 60deg
bank, the G-103 is
stall proof by design.

Frank Whiteley

I fully agree, and I might add that entering a spin from a 60 deg bank -
when it happens - is a totally different story than spinning out of a
shallow bank. The difference in behaviour increases as wing span increases.
Spinning a 25m glider out of a 60 deg bank is something I experienced once
and I don't want to experience it another time.

Whether or not a specific glider will spin out of a steep bank is nothing to
learn from books. When you're low on a ridge, or centering a strong core at
600ft agl in flat country, there is more to flight dynamics that elevator
authority - a strongs gust or wind shear in such a situation makes any
sailplane stall.

--
Bert Willing

ASW20 "TW"
"Dave Martin" a écrit dans le message
de ...
The danger here is that we are talking theory where
we may start to confuse pilots. It is harder to stall
with 60 degrees of bank. Gliders like the K13, by
design run out of elevator in straight and level flight.
They are difficult when flown with heavy pilots to
develop more than a mushing stall in sraight and level
flight.

Put light -- bottom weigh pilots in and they become
a different glider.

The Puchacz on the other hand has plenty of rear elevator
even when banked, quite steeply.

There can be some dangerous assumptions that gliders
will not spin.

The pilot must know the limitations and characteristics
of the glider he/she is flying. This can only be achieved
by carefully experimenting with different configurations
and different flight situations.

Gliders with reputations that they will not spin, can
catch pilots out who load them wrongly, fly them badly
or worse combine both.

Dave Martin

Get some empirical experience. Hop in a G-103, circle
at 60deg bank and
bring the stick back to the stop. If properly rigged,
it will not stall.
Do the same in straight and level flight. It will
stall, in a mushy sort of
way depending on loading. Also, in a G-103, you will
get more elevator
authority in tight turns by moving the trim forward.

This is not true of all gliders, but clearly in a 60deg
bank, the G-103 is
stall proof by design.

Frank Whiteley

That's why I gave a very specific example and also mentioned proper rigging,
which includes that the elevator actually moves within the design
deflections at annual time. There's also no accounting for pilots that
can't coordinate a 60deg bank or think a 45deg bank is 60degs. Of course
there are gliders that will flick into a spin with little or no warning from
this attitude, so try it at altitude, away from the crowd, and with your
instructor if necessary.

Frank

"Dave Martin" wrote in message
...
The danger here is that we are talking theory where
we may start to confuse pilots. It is harder to stall
with 60 degrees of bank. Gliders like the K13, by
design run out of elevator in straight and level flight.
They are difficult when flown with heavy pilots to
develop more than a mushing stall in sraight and level
flight.

Put light -- bottom weigh pilots in and they become
a different glider.

The Puchacz on the other hand has plenty of rear elevator
even when banked, quite steeply.

There can be some dangerous assumptions that gliders
will not spin.

The pilot must know the limitations and characteristics
of the glider he/she is flying. This can only be achieved
by carefully experimenting with different configurations
and different flight situations.

Gliders with reputations that they will not spin, can
catch pilots out who load them wrongly, fly them badly
or worse combine both.

Dave Martin

Get some empirical experience. Hop in a G-103, circle
at 60deg bank and
bring the stick back to the stop. If properly rigged,
it will not stall.
Do the same in straight and level flight. It will
stall, in a mushy sort of
way depending on loading. Also, in a G-103, you will
get more elevator
authority in tight turns by moving the trim forward.

This is not true of all gliders, but clearly in a 60deg
bank, the G-103 is
stall proof by design.

Frank Whiteley

"Dave Martin" wrote in message
...
The danger here is that we are talking theory where
we may start to confuse pilots. It is harder to stall
with 60 degrees of bank. Gliders like the K13, by
design run out of elevator in straight and level flight.
They are difficult when flown with heavy pilots to
develop more than a mushing stall in sraight and level
flight.

Put light -- bottom weigh pilots in and they become
a different glider.

The Puchacz on the other hand has plenty of rear elevator
even when banked, quite steeply.

There can be some dangerous assumptions that gliders
will not spin.

The pilot must know the limitations and characteristics
of the glider he/she is flying. This can only be achieved
by carefully experimenting with different configurations
and different flight situations.

Gliders with reputations that they will not spin, can
catch pilots out who load them wrongly, fly them badly
or worse combine both.

Dave Martin

You make a good point. Some gliders are very resistant to stalls and others
will stall readily - especially with light pilots. It seems that trainers
made in Eastern Europe come equipped with large, effective elevators that
can stall the wing in any attitude. On the other hand, many German single
place glass gliders often have small elevators with limited up authority.

For example the Blanik L-23, IS28 b2 Lark and, as another poster pointed out
the Puchacz, can be stalled from a steep bank easily. For this reason, they
make good trainers since the student must learn to be constantly aware of
pre-stall buffet.

However, the point the Derek was making is that it is more difficult, but
not impossible, to stall in a steep turn. I've had this discussion with
pilots who feared steep banks. I suggest that thermalling is steep banks is
easier in that the glider is more difficult to stall and fewer corrections
are needed to stay in the thermal since the turn diameter is smaller.

Bill Daniels

On Tue, 29 Jul 2003 08:05:21 -0600, "Bill Daniels"
wrote:


"Dave Martin" wrote in message
...
The danger here is that we are talking theory where
we may start to confuse pilots. It is harder to stall
with 60 degrees of bank. Gliders like the K13, by
design run out of elevator in straight and level flight.
They are difficult when flown with heavy pilots to
develop more than a mushing stall in sraight and level
flight.

Put light -- bottom weigh pilots in and they become
a different glider.

The Puchacz on the other hand has plenty of rear elevator
even when banked, quite steeply.

There can be some dangerous assumptions that gliders
will not spin.

The pilot must know the limitations and characteristics
of the glider he/she is flying. This can only be achieved
by carefully experimenting with different configurations
and different flight situations.

Gliders with reputations that they will not spin, can
catch pilots out who load them wrongly, fly them badly
or worse combine both.

Dave Martin

You make a good point. Some gliders are very resistant to stalls and others
will stall readily - especially with light pilots. It seems that trainers
made in Eastern Europe come equipped with large, effective elevators that
can stall the wing in any attitude. On the other hand, many German single
place glass gliders often have small elevators with limited up authority.

For example the Blanik L-23, IS28 b2 Lark and, as another poster pointed out
the Puchacz, can be stalled from a steep bank easily. For this reason, they
make good trainers since the student must learn to be constantly aware of
pre-stall buffet.

However, the point the Derek was making is that it is more difficult, but
not impossible, to stall in a steep turn. I've had this discussion with
pilots who feared steep banks. I suggest that thermalling is steep banks is
easier in that the glider is more difficult to stall and fewer corrections
are needed to stay in the thermal since the turn diameter is smaller.

Bill Daniels

This is an extremely important caution. Gliders do not all have the
same behavior. Along this line, I have been cautioned that in a turn,
the inside wing, even in a coordinated turn, is flying at a higher
angle of attack than the outside wing. The degree of difference would
vary with the bank angle. Thus, some gliders may not only stall in a
steep turn, they can flick into a spin "out the bottom" in the blink
of an eye. This may not be the case with many (most?) "modern"
ships, but none-the-less is worth keeping in mind I guess.

With regard to the original message,

I don't think Derek is arguing specifically that the effectiveness of the
elevator depends on the angle of bank, rather that pulling back on the stick
with the wings level or in a shallow bank leads to a nose high attitude from
which the glider will slow down and stall. In a steeply banked turn, pulling
back on the stick tightens the turn more than it raises the nose so you
won't slow the glider down very much, any pre-stall buffet is more likely to
be the result of stall speed increasing with higher g.

Its easier to reach that pre-stall buffet (inadvertently or otherwise) by
slowing down than by pulling g, thus it is easier to use the elevator to
stall a glider from straight flight or in a gentle turn than in a steep
bank. Either way, the recovery is the same, ease the stick forward.

If your instructor asks you why its harder to stall a glider in a steep bank
and you reply that the extra g makes the glider nose heavy, you are liable
to get a few demonstrations as to why that isn't true. The reason why its
hard to stall in a 60 degree bank is not because the glider is nose heavy
but because you are using virtually all the elevator authority to make it
nose heavy.

I'm sure its not what Bill meant to suggest, but its important that you
understand that just because you're pulling 2g, the glider is not too nose
heavy to stall.

Ed