slip or skid?

[Daveman]

just deleted a drunk post, keep scrolling.

 

[Singlecoil]

No Mu-2 time, but the Dash-8 was the same way. It used to drive me up and down the wall to see the person you're flying with (Capts and FO's) yank the power back with their feet flat on the floor, watch their coffee almost spill out the cup as the airplane gets completely uncoordinated, then start tweaking the rudder trim, all while keeping their feet on the floor.

I don't mean to be ranting here, but Jeez that drove me nuts.

 

[airpix]

slip or skid on climbout

No I'm just wondering what to tell the student on takeoff. Climbing out, wings are level, balls pegged to the right, headings constant. They won't use enough right rudder!! Are they skidding the plane or slipping it?

STEP ON THE BALL, THE PLANE'S IN A _______________?

 

[airpix]

Yep, Airplane Flying Handbook p 4-5.

Is that chapter 4, page 5? I can't find it.

 

[Donsa320]

Good info Donsa320. Man you have flown everything

Lets say that a 172 is climbing out with a 15kt crosswind, and you are holding constant heading with level wings (no crab angle, being blown to the left). How would the plane be coordinated then?

I have a feeling that is what airpix meant.

The WIND has no effect on what the ball instrument is displaying.

~DC

 

[Donsa320]

No I'm just wondering what to tell the student on takeoff. Climbing out, wings are level, balls pegged to the right, headings constant. They won't use enough right rudder!! Are they skidding the plane or slipping it?

STEP ON THE BALL, THE PLANE'S IN A _______________?

As I mentioned, your description above is an impossibility. You cannot have the wings level, NO heading change and the ball off to the side. Either the wings are NOT level (slipping), or you must be turning (skidding).

BTW, either condition is costing you performance.

~DC

 

[JB74]

Is that chapter 4, page 5? I can't find it.

Yes, chapter 4, p 5, figure 4.7 "Indications of a slip and skid". The far right TC shows the wings level, the ball to the right and is labeled a "slip".

I am trying to get a link so anyone interested can see what I am talking about.

Oh, by the way, I have the '99 edition.

 

[Donsa320]

Airpix, JB74 and all:

I'd like to liven this thread up a little....

If Airpix convinces his student to counter the yaw in the climb with enough right rudder and finally gets the ball exactly in the center with the wings exactly level is the airplane then moving exactly straight through the air??

~DC

 

[nosehair]

If Airpix convinces his student to counter the yaw in the climb with enough right rudder and finally gets the ball exactly in the center with the wings exactly level is the airplane then moving exactly straight through the air??

No, it is not. Think about the P-Factor. A single engine propeller airplane will not, repeat, NOT have the ball centered in a straight climb holding right rudder for a constant heading with the wings level. Center of thrust has moved to the right of center and would require a slight right wing down to counter this off-set thrust. Since we teach keeping the wings level and holding a constant heading, the ball will be slightly to the left. The airplane is slipping slightly to the left as a result of the off-center thrust. This is not very noticeable in small engine airplane at normal climb speeds, but it is there, and becomes more noticeable when practicing power-on stalls. Watch the ball slide about a half ball width out when holding a constant heading winds level when approaching a stall. If you try to keep the ball centered with the wings exactly level, you will yaw to the left.

In the figure 4-7, page 4-5 of the AFH, the picture depicting the wings level with the ball out to the right, this airplane might be in a climb (P-Factor) and correcting for yaw with aileron only, no rudder. (slipping)

 

[Donsa320]

No, it is not. Think about the P-Factor. A single engine propeller airplane will not, repeat, NOT have the ball centered in a straight climb holding right rudder for a constant heading with the wings level. Center of thrust has moved to the right of center and would require a slight right wing down to counter this off-set thrust. Since we teach keeping the wings level and holding a constant heading, the ball will be slightly to the left. The airplane is slipping slightly to the left as a result of the off-center thrust. This is not very noticeable in small engine airplane at normal climb speeds, but it is there, and becomes more noticeable when practicing power-on stalls. Watch the ball slide about a half ball width out when holding a constant heading winds level when approaching a stall. If you try to keep the ball centered with the wings exactly level, you will yaw to the left.

In the figure 4-7, page 4-5 of the AFH, the picture depicting the wings level with the ball out to the right, this airplane might be in a climb (P-Factor) and correcting for yaw with aileron only, no rudder. (slipping)

You were doing fine, good buddy, but I'm afraid you got a little off track (no pun) at the end.
True, the thrust line is offset due to asymetric disk loading. The right side pulls harder on most engine/prop combinations in the USA. So far so good. Centering the ball to keep the wings level and heading constant, however, does not result in straight flight, just as you said. The airplane is NOT turning, the ball stays in the center whilst the airplane moves slightly LEFT through the air if it is right rudder you are holding. The ball does NOT move left however, because there is no force to put it there, i.e. no turn, wings level...ball centered, gravity pulls straight down. The only way to detect that sideways movement is a yaw string, but they don't work with the engine on the nose.
If you wish to eliminate that sideways movement, called "leeway" to differentiate it from slip/skid, then yes put a little wing down into the rudder. Then the ball will be out to the right slightly again. Whether drag is greater while making leeway or with a little wing down (a little slip) in a single engine airplane is a good question. I suspect it's a toss up. There are other variables too, like vertical fin offset and wing twist that are set to negate the off set thrust, more or less, and may work against you in descent, for example.
For instructional purposes I'd say wings level, ball centered, and you can't go wrong.

BTW, leeway becomes much more pronounced in multi-engine airplanes with an engine out. Beechcraft gave some guidence on that a while back. The old 5 degrees of bank into the good engine is usually excessive. On their twins, Beechcraft recommended 1/2 ball width into the good engine if the critical engine is failed and 1/4th ball width if it was the non-critical engine out. In the counter-rotating airplanes then, 1/4th ball width worked for either side. This would be for low speeds, down around Vyse.
One can see then that in a single the leeway must be very slight.
In every case, the faster you go, the less the effect. I've see multi-students trying to keep that wing down into the good engine right up to max single-engine cruise speed. Hilarious.

~DC