Devices for avoiding VNE?

Good if that's what makes YOU feel safe !


"Todd Pattist" wrote in message
...
"Arnold Pieper" wrote:

These reports led you to the wrong conclusion.
Overstress is the key here, weahter with or without airbrakes.

My load limit is 5 G's brakes closed, 3.5 G's brakes open.
If you want to pull the nose up at 5 G's to avoid hitting
the ground, you can do it brakes closed, but not brakes
open. If your adrenaline kicks in as you pull back, you can
pull until you feel 5 G's if you leave the brakes closed,
but only to 3.5G's if you open them.
Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

Okay - point taken on designs with lots of tip washout
or inbord flaps deployed. But the wing twist discussion
was really a secondary point in the dialog about pitch
stability overall, and I'm not sure that a twisting
at the tip would contribute very much to making the
glider unstable overall.

I still think it's not reasonable to expect that a
glider would be certified where you'd get enough structural
twisting to upset the overall stability of the aircraft.
More broadly, I doubt that you'll find a certified
aircraft that has a pitching moment that becomes more
nose down with increasing speed no matter what the
reason. The feds are unlikely to smile on a design
with static instability at any speed.

I remain convinced that if your sailplane exhibits
pitch instability you have a c.g. problem, a rigging
problem, your aircraft has been modified or you are
outside the certified operating limits.


At 18:42 02 April 2004, Jj Sinclair wrote:

I a bit suspicious of this whole wing twist thing.

Take a K-6 up to 100 and look at the tips.

Take an ASH-25 up to 80 with landing flaps on and
look at the tips.

In the case of the K-6, she does have a few degrees
of tip wash-out (leading
edge down)

In the case of the ASH-25 with landing flaps on, Only
the inboard flaps go
down, the outboard flaps and ailerons go up to produce
a negative angle of
attack.

So why do the wings in both cases bend down?

Why does the B-52 use spoilers instead of ailerons?
Because at higher airspeeds
an aileron input causes the wing to bend and can cause
the ship to turn in the
opposite direction (wing twist)

Even in a *certified* ship, if the wings start to tuck
under and you don't
catch it right away, you could find yourself in a situation
where elevator
won't stop the pitch down action. Now, all of this
is at or above VNE, so if we
are flying our glass slippers within limits, we should
be OK.
JJ Sinclair

Well,

Although not directly related to gliders (except really fast ones), look up
"mach tuck" and you will find several certified aircraft that tend to nose
down as speed increases.

Critical mach is a aeronautics term that refers to the speed at which some
of the airflow on a wing becomes supersonic. When this occurs the
distribution of forces on the wing changes suddenly and dramatically,
typically leading to a strong nose-down force on the aircraft. This effect
led to a number of accidents in the 1930s and 1940s, when aircraft in a dive
would hit critical mach and continue to push over into a steeper and steeper
dive. This problem is often lumped in with the catch-all phrase
compressibility.

Wings generate much of their lift due to the Bernoulli effect; by speeding
up the airflow over the top of the wing, the air has less density on top
than on the bottom, leading to a net upward force. The relative difference
in speed is due largely to the wing's shape, so the difference in speed
remains a fairly constant ratio over a wide range of speeds.

But if the air speed on the top of the wing is faster than on the bottom,
there will be some speed where the air on top reaches the speed of sound.
This is the critical mach. When this happens shock waves form on the upper
wing at the point where the flow becomes supersonic, typically behind the
midline of the chord. Shock waves generate lift of their own, so the lift of
the wing suddenly moves rearward, twisting it down. This effect is known as
mach tuck.

;0)

Allan

"Andy Blackburn" wrote in message
...
Okay - point taken on designs with lots of tip washout
or inbord flaps deployed. But the wing twist discussion
was really a secondary point in the dialog about pitch
stability overall, and I'm not sure that a twisting
at the tip would contribute very much to making the
glider unstable overall.

I still think it's not reasonable to expect that a
glider would be certified where you'd get enough structural
twisting to upset the overall stability of the aircraft.
More broadly, I doubt that you'll find a certified
aircraft that has a pitching moment that becomes more
nose down with increasing speed no matter what the
reason. The feds are unlikely to smile on a design
with static instability at any speed.

On 02 Apr 2004 14:51:49 GMT, (JJ Sinclair) wrote:


It's not all BS, there was this Doctor that extended the wing span on his ship,
back in the '70's. He brought a new meaning to the term, *final glide* as the
wing tips dug-in and he almost completed an outside loop, with the stick full
back, but the ground got in the way. Wing twist at high speed is real.

Basic rule #2 in aviation:
Better know what you are doing if you want to become an old pilot.

Any airfoil with a negative Cm0 (this means any glider with a tail)
will twist at high speed and low CL's... but the wing needs to be
strong enough to prevent excessive twist.
If it is not (because of a design flaw or a modification - see above)
your day is going to be ruined.

And if the wing is able to twist enough to make the ship unstable, I
am absolutely sure that it will not get a certificate. Certainly not
by German authorities.





Bye
Andreas

On 02 Apr 2004 16:17:09 GMT, (Mark Navarre)
wrote:


I have seen it myself, my ship was not out of CG limits, the effect is subtle,
but present nevertheless. Other pliots with AS-W20's may not experience the
tuck due to flying with a further forward CG and resulting trim speed change,
thereby canceling the aeroelastic twist of the wings. 20 B's have stiffer
wings than the A or C, by the way, and may not twist as much.
The speed at which this begins to occur on my ship is out of the normal range
of efficient cruising speed anyway. Just fly the plane...put the stick where
it gives you the speed you want and keep it there until you want a different
speed. It's not autopilot!

Interesting. The 20's I was flying could all be trimmed to about 230
kp/h with the CG at about 90 percent (different CG's, only my club's
20L was optimized for my weight and allowed a truly tail-heavy CG),
independent of the configuration (15 or 16.60 meters). I never felt
the need to go back further with the CG - are you flying yours with a
CG at the end if the allowed range? I guess you carried no water,
correct?


Bye
Andreas

A+ for research initiative, D- for applicability.

Mach tuck affects certain high speed aircraft (high mach numbers, jets only)
with swept back wings, when they exceed their Mmo.
When flying within their normal certified speed ranges, they do not present
this abnormality.

As someone already posted, no aircraft would be certified with instability
being a part of its normal flight envelope.

"ADP" wrote in message
...
Well,

Although not directly related to gliders (except really fast ones), look
up
"mach tuck" and you will find several certified aircraft that tend to nose
down as speed increases.

Critical mach is a aeronautics term that refers to the speed at which some
of the airflow on a wing becomes supersonic. When this occurs the
distribution of forces on the wing changes suddenly and dramatically,
typically leading to a strong nose-down force on the aircraft. This effect
led to a number of accidents in the 1930s and 1940s, when aircraft in a
dive
would hit critical mach and continue to push over into a steeper and
steeper
dive. This problem is often lumped in with the catch-all phrase
compressibility.

Wings generate much of their lift due to the Bernoulli effect; by speeding
up the airflow over the top of the wing, the air has less density on top
than on the bottom, leading to a net upward force. The relative difference
in speed is due largely to the wing's shape, so the difference in speed
remains a fairly constant ratio over a wide range of speeds.

But if the air speed on the top of the wing is faster than on the bottom,
there will be some speed where the air on top reaches the speed of sound.
This is the critical mach. When this happens shock waves form on the upper
wing at the point where the flow becomes supersonic, typically behind the
midline of the chord. Shock waves generate lift of their own, so the lift
of
the wing suddenly moves rearward, twisting it down. This effect is known
as
mach tuck.

;0)

Allan

"Andy Blackburn" wrote in message
...
Okay - point taken on designs with lots of tip washout
or inbord flaps deployed. But the wing twist discussion
was really a secondary point in the dialog about pitch
stability overall, and I'm not sure that a twisting
at the tip would contribute very much to making the
glider unstable overall.

I still think it's not reasonable to expect that a
glider would be certified where you'd get enough structural
twisting to upset the overall stability of the aircraft.
More broadly, I doubt that you'll find a certified
aircraft that has a pitching moment that becomes more
nose down with increasing speed no matter what the
reason. The feds are unlikely to smile on a design
with static instability at any speed.

Do you include rudder lock as an instability? How about dynamic stability?
What about downsprings, bob weights and other stability enhancement devices?
Stability is a really broad subject.


In article , "Arnold Pieper"
wrote:
A+ for research initiative, D- for applicability.

Mach tuck affects certain high speed aircraft (high mach numbers, jets only)
with swept back wings, when they exceed their Mmo.
When flying within their normal certified speed ranges, they do not present
this abnormality.

As someone already posted, no aircraft would be certified with instability
being a part of its normal flight envelope.

"ADP" wrote in message
...
Well,

Although not directly related to gliders (except really fast ones), look
up
"mach tuck" and you will find several certified aircraft that tend to nose
down as speed increases.

Critical mach is a aeronautics term that refers to the speed at which some
of the airflow on a wing becomes supersonic. When this occurs the
distribution of forces on the wing changes suddenly and dramatically,
typically leading to a strong nose-down force on the aircraft. This effect
led to a number of accidents in the 1930s and 1940s, when aircraft in a
dive
would hit critical mach and continue to push over into a steeper and
steeper
dive. This problem is often lumped in with the catch-all phrase
compressibility.

Wings generate much of their lift due to the Bernoulli effect; by speeding
up the airflow over the top of the wing, the air has less density on top
than on the bottom, leading to a net upward force. The relative difference
in speed is due largely to the wing's shape, so the difference in speed
remains a fairly constant ratio over a wide range of speeds.

But if the air speed on the top of the wing is faster than on the bottom,
there will be some speed where the air on top reaches the speed of sound.
This is the critical mach. When this happens shock waves form on the upper
wing at the point where the flow becomes supersonic, typically behind the
midline of the chord. Shock waves generate lift of their own, so the lift
of
the wing suddenly moves rearward, twisting it down. This effect is known
as
mach tuck.

;0)

Allan

"Andy Blackburn" wrote in message
...
Okay - point taken on designs with lots of tip washout
or inbord flaps deployed. But the wing twist discussion
was really a secondary point in the dialog about pitch
stability overall, and I'm not sure that a twisting
at the tip would contribute very much to making the
glider unstable overall.

I still think it's not reasonable to expect that a
glider would be certified where you'd get enough structural
twisting to upset the overall stability of the aircraft.
More broadly, I doubt that you'll find a certified
aircraft that has a pitching moment that becomes more
nose down with increasing speed no matter what the
reason. The feds are unlikely to smile on a design
with static instability at any speed.

"ADP" wrote in message ...
Well,

Although not directly related to gliders (except really fast ones), look up
"mach tuck" and you will find several certified aircraft that tend to nose
down as speed increases.

Critical mach is a aeronautics term that refers to the speed at which some
of the airflow on a wing becomes supersonic. When this occurs the
distribution of forces on the wing changes suddenly and dramatically,
typically leading to a strong nose-down force on the aircraft. This effect
led to a number of accidents in the 1930s and 1940s, when aircraft in a dive
would hit critical mach and continue to push over into a steeper and steeper
dive. This problem is often lumped in with the catch-all phrase
compressibility.

Wings generate much of their lift due to the Bernoulli effect; by speeding
up the airflow over the top of the wing, the air has less density on top
than on the bottom, leading to a net upward force. The relative difference
in speed is due largely to the wing's shape, so the difference in speed
remains a fairly constant ratio over a wide range of speeds.

But if the air speed on the top of the wing is faster than on the bottom,
there will be some speed where the air on top reaches the speed of sound.
This is the critical mach. When this happens shock waves form on the upper
wing at the point where the flow becomes supersonic, typically behind the
midline of the chord. Shock waves generate lift of their own, so the lift of
the wing suddenly moves rearward, twisting it down. This effect is known as
mach tuck.


How do you fly inverted using "Bernoulli Effect"?


Jan-Olov Newborg

A for effort, D for accuracy. The DC-8 Could not be flown at altitude with
out it's PTC (Pitch Trim Compensator) being operative.
The function of the PTC was to protect against mach tuck.

Since the DC-8 was undoubtedly certified, the argument is invalid.

Had you read my post you would have noticed the reference to supersonic
airflow which presumably does not apply to gliders.
On the other hand, a P-38 with a critical mach number of .69 is hardly a jet
and has straight wings.
Several were lost in early testing because the phenomenon of mach tuck was
not well known.

In fact, sweepback is a design factor that helps delay critical mach to
higher numbers.

Not to make too fine a point but any aircraft, if flown fast enough without
breaking up, can be subject to mach tuck.

Allan

"Arnold Pieper" wrote in message
m...
A+ for research initiative, D- for applicability.

Mach tuck affects certain high speed aircraft (high mach numbers, jets
only)
with swept back wings, when they exceed their Mmo.
When flying within their normal certified speed ranges, they do not
present
this abnormality.

As someone already posted, no aircraft would be certified with instability
being a part of its normal flight envelope.

"ADP" wrote in message
...
Well,

Although not directly related to gliders (except really fast ones), look
up
"mach tuck" and you will find several certified aircraft that tend to
nose
down as speed increases.

Critical mach is a aeronautics term that refers to the speed at which
some
of the airflow on a wing becomes supersonic. When this occurs the
distribution of forces on the wing changes suddenly and dramatically,
typically leading to a strong nose-down force on the aircraft. This
effect
led to a number of accidents in the 1930s and 1940s, when aircraft in a
dive
would hit critical mach and continue to push over into a steeper and
steeper
dive. This problem is often lumped in with the catch-all phrase
compressibility.

Wings generate much of their lift due to the Bernoulli effect; by
speeding
up the airflow over the top of the wing, the air has less density on top
than on the bottom, leading to a net upward force. The relative
difference
in speed is due largely to the wing's shape, so the difference in speed
remains a fairly constant ratio over a wide range of speeds.

But if the air speed on the top of the wing is faster than on the bottom,
there will be some speed where the air on top reaches the speed of sound.
This is the critical mach. When this happens shock waves form on the
upper
wing at the point where the flow becomes supersonic, typically behind the
midline of the chord. Shock waves generate lift of their own, so the lift
of
the wing suddenly moves rearward, twisting it down. This effect is known
as
mach tuck.

;0)

Allan

It's called angle of attack.

Allan

"Jan-Olov Newborg" wrote in message
om...
"ADP" wrote in message
...
Well,



How do you fly inverted using "Bernoulli Effect"?


Jan-Olov Newborg