Balls !

So, does the inclinometer (aka ball of the turn coordinator) show ROLL or YAW?

It measure lateral acceleration. i.e., acceleration along the lateral axis. This can measure sideslip (not yaw), because sideslip generates an acceleration long the lateral axis. An aircraft in a steady, ball-centered turn is yawing and will yaw 360 degrees for every circle, but will never encounter a sideslip. Same with a roll.

However, if I roll left without using left rudder, the nose will yaw right. The fuselage sideforce will work against the centripetal force of the turn, decreasing my rate of turn for the given bank angle. This means that the apparent gravity inside the airplane will not be in the plane of symmetry (perpendicular to the lateral axis) and will instead have a component along the lateral axis, forcing the ball to move down the curved tube until equlibrium is reached. Each ball width is worth .08g, according to Malcom Azbug in "Airplane Stability and Control."
 
Acceleration about the LA huh? Thats deep and over my head. Third grade please.

Oh, sorry, the lateral axis runs from wing tip to wing tip. When you pitch, you pitch about the lateral axis. However, this is accelerating ALONG the lateral axis...uhm, scooting left or right? If your aircraft nose is pointing North, but the aircraft starts sliding East or West, you're moving along the lateral axis. This isn't normal. :)

When you're flying a ME aircraft with an engine out and you bank to eliminate the sideslip, the ball will be 1/2 out of center. This is a measure of the portion of gravity which is acting along the wing....the lateral axis.
 
Mr. Mavencamp is a very good, and very fair examiner ... but so is Barb Mack. I used to have the Mavencamp gouge, but don't have it on me right now, I know he used to ask that question though about the ball. If you end up going with him PM me and I will dig around for it!
 
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