Lateral stability...

[muddyboots]

what is it and why is it good to improve it?

[RyanShort1]

what is it and why is it good to improve it?

So your warbird stays on course and doesn't lean to much to the left... or right.

Ryan

[skydaddy61]

If I recall my aero engineering lessons, it's the tendency for the aircraft to return itself to wings-level flight when disturbed in roll, generally accomplished by building dihedral into the wings.

Or did I miss part of a joke? (It IS kinda basic stuff.)

[bdk]

what is it and why is it good to improve it?

Stability in general is good in a bomber and not always so useful in a fighter.

Lateral stability is a resistance to upset about the longitudinal axis of the aircraft. A laterally unstable plane will tend to roll off left or right at the slightest provocation. If an aircraft is too stable it will be resistant to maneuvering. Too unstable and it will be difficult for the pilot to control.

[RyanShort1]

Yeah, the above was a joke...

Basically, when you alter the angle of the wings - an aircraft with the right amount of dihedral will experience a "change" in the chord of the wings - relative to the forces of lift and gravity thus allowing the "low" wing to produce more lift and theoretically re-establish level flight.
It may not be fully desirable in fighters nowadays, but most WWII single seat fighters had a fairly significant amount of dihedral.

Ryan

[jet1]

...wearing a knee brace when I ski....

[skydaddy61]

...wearing a knee brace when I ski....

Visited my dad some years ago; he was using a cane. "Dad, did you fall again?" (He'd broken an ankle a year before.)

The old man shook his head. "Nope. Don't want to."

[Steve Nelson]

The Wright Brothers actually designed their Flyer to be inherently UNstable. They felt that inherent stability would negatively effect an aircraft's controllability.

SN

[skydaddy61]

The Wright Brothers actually designed their Flyer to be inherently UNstable. They felt that inherent stability would negatively effect an aircraft's controllability.

SN

And they were right, to a point. That point being the difference between the local airflow's propensity to induce a rolling moment, the pilot's abilty to detect it, and the control system's ability to impart a compensatory moment in response to the pilot's input.

IOW, you can make an airplane so nimble that no human can keep it from departing controlled flight. Hence the fly-by-wire system of the F-16 and its successors.

[muddyboots]

so it has t do with roll
or swinging side to side
or porpoising front to back



this is a serious question btw. It may be obvious to you pilot types but to us ground pounders lateral stability is about sex with fat chicks.

[Wheels up]

There's the definitions....

[RyanShort1]

Muddy - I did take your question seriously, just couldn't resist the joke.

Here's a different way of explaining it. An aircraft has three imaginary "axis."

The Lateral axis runs from the pilot's left to right in piloted aircraft, and parallel to the wings of a winged aircraft
The Longitudinal axis runs through the body of the vehicle from tail to nose in the normal direction of flight, or the direction the pilot faces
The Vertical axis runs from top to bottom, and perpendicular to the other two axes
Essentially these would work around the aircraft's center of gravity - which is why CG is important.

Lateral stability is especially helpful for directional control (because aircraft generally turn and change course by rolling into a bank in the direction of the turn) and involves rolling moments.

Ryan

[skydaddy61]

So referring to the drawing,

Lateral (roll) stability is stability around the longitudinal axis.

Longitudinal (pitch) stability is stability around the lateral axis.

Yaw stability is stability around the vertical axis.

A stable aircraft will fly hands-off. An unstable aircraft will depart controlled flight easily. Modern fighters are designed to be unstable, because its digital flight control system can make the hundreds of minute corrections per second needed to keep the pointy end forward.

An aircraft with poor pitch stability (for example, one with a CG that is too far aft) will tend to porpoise. It's easy to get into a pilot-induced-oscillation, pitch up into a stall, or pitch down into a power dive.

[muddyboots]

ah HAH! I understand roll and pitch and yaw

the fact that longitutdinal stablity was about the lateral axis was confusing me. Thanks everybody! I am now ready to jump in a mustang and fly it!:rolleyes:

[muddyboots]

Muddy - I did take your question seriously, just couldn't resist the joke.


Ryan

but you didn't get my joke about staying on top of the fat chick. did you?