Slips and Skids

Trever Oakes

Trever Oakes

Filing Flight Plan
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Jul 10, 2019
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KimJongUncle
Hello there!

I am doing some research for a paper, and I am doing research to further understand slips and skids. What makes them specifically different, and why if allowed does the stall occur the way it does in each situation. I think this is something that a lot of students don't ever really grasp in depth.
 
Both involve the airplane not tracking in line with the flight path. In the context of turns, slips have the airplane sideways to the inside in the turn, skids are to the outside.
 
The other two are really good, but this one too. This person has a great way of showing it, and also (similar to the other video above) demonstrating how to think about it, using a model.

 
Skid, too much inside rudder. Slip, too much outside rudder. Sort of like oversteer and understeer, or loose and tight, if we make car references.
 
The simplest definitions, off the top of my head:

A skid is when the rate of turn is too great for the angle of bank.

A slip is when the rate of turn is too small for the angle of bank.

Or turned around (but saying the same thing)...

A skid is when the angle of bank is too small for the rate of turn.

A slip is when the angle of bank is too great for the rate of turn.
 
I don't think that's the simplest by any means.
 
A skid is when your tail get's ahead of your turn. Think of drifting the rear wheels in a car.

A slip is when your wings are banked but you're not turning as much as you should.
 
EdFred said:
Skid, too much inside rudder. Slip, too much outside rudder. Sort of like oversteer and understeer, or loose and tight, if we make car references.
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Excellent example.
Oversteer: When the front tires slip and the rear tires grip. (This may also be called "pushing").
Understeer: When the rear tires skid and front tires grip.
 
Trever Oakes said:
Hello there!

I am doing some research for a paper, and I am doing research to further understand slips and skids. What makes them specifically different, and why if allowed does the stall occur the way it does in each situation. I think this is something that a lot of students don't ever really grasp in depth.
Click to expand...

I think most students have a good grasp of the difference by the time they are ready for their checkride. Are you basing your opinion on anything in particular?
 
Is there ever any reason to intentionally skid an airplane. Except of course to tighten up that base to final turn or get a good look at that moose (disclaimer: those are jokes, do not take them seriously)
 
alfadog said:
Is there ever any reason to intentionally skid an airplane. Except of course to tighten up that base to final turn or get a good look at that moose (disclaimer: those are jokes, do not take them seriously)
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Box Canyon
 
write-stuff said:
View attachment 80442
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God I hate this one :)

from the picture and tail I thought left is a skid, right a slip.
But I get messed up by the bank indicator that I seem to recall I think exactly wrong about, just using IT I would think left was slip, right skid.
But since I know I think 100% wrong about bank indicator, I’m going with left = skid as my final answer.
 
LongRoadBob said:
God I hate this one :)

from the picture and tail I thought left is a skid, right a slip.
But I get messed up by the bank indicator that I seem to recall I think exactly wrong about, just using IT I would think left was slip, right skid.
But since I know I think 100% wrong about bank indicator, I’m going with left = skid as my final answer.
Click to expand...

Left pic, tail outside = skid. Also left turn with right ball = too much left rudder = skid.

edit: also, the ball is "skidding" to the outside of the turn.
 
FastEddieB said:
Yep! Looks pretty clear to me, so why the hate?
Click to expand...

it reminds me I have to spend some time to figure out the bank indicator ball and what it’s telling me.
Like I mention, currently remembering the ball is opposite what I think, and not sure why.

Maybe a good time to ask for help here. I’m thinking now, the ball is sliding to the side the airplane is wanting to go because of forces on it. So on the left the ball is showing the airplane has forced on it to the outside of the turn. In a slip the ball is showing the plane wants to “slide” down into the turn.

Am I right so far? That the ball is more easily moved (less inertia, because less mass?) and the plane also is tending to move that direction.

and I think I get that the forces are gravity, and centrifugal/centripetal, but then...
In an uncoordinated turn, say a left bank the ball will be low, telling us to step on the ball (left rudder) to get coordinated. But that is a situation where the skid/slip indications I mention above are suddenly opposite. The plane is yawing to the right say, but the ball is to the left, we need to put more left rudder in. Seems here the plane has moved “under” the ball, like a magician quickly removing a tablecloth and the plates stay in place.

What is different between skid/slip and uncoordinated turns, as far as the indicator? I’m thinking I’m wrong on the forces in the skid or slip.
 
Skidding...slipping...yawn...

...now, on a moonless night over a hazy ocean with light frost on the wings...now we're talking a challenge!!
 
LongRoadBob said:
it reminds me I have to spend some time to figure out the bank indicator ball and what it’s telling me.
Like I mention, currently remembering the ball is opposite what I think, and not sure why.
Click to expand...

Be warned, this may over complicate things, but it works for me.

Imagine a race track that’s banked for a car going 100 mph. At 100 mph g-forces would be pushing the car straight onto the track. Fuzzy dice hanging from the mirror would hang straight down. The car’s rate of turn at 100 mph would be appropriate for the track’s banking.

Now slow to 80 mph. Suddenly the bank is too great for the rate of turn, the definition of a slip. If held to the same line, the fuzzy dice would move towards the inside of the turn. Which is what the ball does in a slip.

Now speed up to 120 mph. Now you’re going faster than the track designers figured, and your rate of turn is too great for the banking. Fuzzy dice will move towards the outside of the turn, like the ball does in a skid.

As an aside, I had a piece of yarn attached to the canopy of my Sky Arrow for a while as a slip/skid indicator. First time I slipped or skidded, it moved opposite to what I had imagined. It makes sense now, but like the ball for you it seemed backwards at first.

You can see in this video the yarn moves exactly opposite the ball when slipping back and forth across the runway.

 
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@LongRoadBob you might be overthinking it a bit. It's not about the inertia in the ball. Forget about that. The ball is telling you the same thing the seat of your pants would be telling you.

The position of the ball in the tube is a function of the angle of bank and the nature i.e. speed / radius, of the turn. If the ball is going out to the outside of the turn, it's telling you in a sense that you don't have enough bank angle for your turn. You can back off the inside rudder or you can increase the bank angle; either of those will move the ball back toward the center.

An analogy would be a race car on a banked track. If the race car is drifting toward the top of the bank or the outside of the turn, it means that the bank is not steep enough for the nature of the turn, radius and speed. That would be analogous to a skidding turn.
 
FastEddieB said:
Be warned, this may over complicate things, but it works for me.

Imagine a race track that’s banked for a car going 100 mph. At 100 mph g-forces would be pushing the car straight onto the track. Fuzzy dice hanging from the mirror would hang straight down. The car’s rate of turn at 100 mph would be appropriate for the track’s banking.

Now slow to 80 mph. Suddenly the bank is too great for the rate of turn, the definition of a slip. If held to the same line, the fuzzy dice would move towards the inside of the turn. Which is what the ball does in a slip.

Now speed up to 120 mph. Now you’re going faster than the track designers figured, and your rate of turn is too great for the banking. Fuzzy dice will move towards the outside of the turn, like the ball does in a slip.

As an aside, I had a piece of yarn attached to the canopy of my Sky Arrow for a while as a slip/skid indicator. First time I slipped or skidded, it moved opposite to what I had imagined. It makes sense now, but like the ball for you it seemed backwards at first.

You can see in this video the yarn moves exactly opposite the ball when slipping back and forth across the runway.

Click to expand...

alfadog said:
@LongRoadBob you might be overthinking it a bit. It's not about the inertia in the ball. Forget about that. The ball is telling you the same thing the seat of your pants would be telling you.

The position of the ball in the tube is a function of the angle of bank and the nature i.e. speed / radius, of the turn. If the ball is going out to the outside of the turn, it's telling you in a sense that you don't have enough bank angle for your turn. You can back off the inside rudder or you can increase the bank angle; either of those will move the ball back toward the center.

An analogy would be a race car on a banked track. If the race car is drifting toward the top of the bank or the outside of the turn, it means that the bank is not steep enough for the nature of the turn, radius and speed. That would be analogous to a skidding turn.
Click to expand...

Thanks to both of you guys, that helped a LOT!
Also realized that yes, still want to “step on the ball” to get aligned again for coordinated.
Which also made me realize the typical left bank, if you didn’t use any rudder, would be then a slight slip, not a skid. I think. Somehow I wasn’t thinking of uncoordinated as slip in that instance.

I think I’ve got it now! Liked the fuzzy dice!
 
write-stuff said:
The ball represents the airplane's tail. The two-bars/cage represent the airplane's nose. When they are together in the inclinometer, the tail is tracking the nose and the airplane is enjoying coordinated flight.
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I don’t think I’ve ever heard that interpretation before, nor do I recall reading it anywhere.

Is that original? Just curious. If that visualization works for someone, go for it!
 
In a skid, the ass end is coming around in the turn, In a slip your nose pushes through the turn. Y'all sure like to overcomplicate things with fuzzy dice and balls chasing noses.
 
write-stuff said:
The ball represents the airplane's tail. The two-bars/cage represent the airplane's nose. When they are together in the inclinometer, the tail is tracking the nose and the airplane is enjoying coordinated flight.
Click to expand...

Damn, those three sentences exactly as written ought to have been in my ground school books, and the FAA student pilots flight manual! When you write it like that, of course it does. I just had not put it together.
THANKS! That makes perfect sense to me, and is exactly how I’m going to be thinking of it from now on.
I hope you are a CFI, that kind of teaching is priceless!

FastEddieB said:
I don’t think I’ve ever heard that interpretation before, nor do I recall reading it anywhere.

Is that original? Just curious. If that visualization works for someone, go for it!
Click to expand...

Yes, I don’t feel quite as bad now after you wrote that for not realizing that. The visualization works perfectly for me. Also though “step on the ball” probably should have led me to realize it, I hadn’t.

for myself, the photo quiz here with the blue line of flight path, along with where the tail is sitting and the bank indicator and cage inclinometer all make sense, from the description write-stuff wrote. I had to study the pictures and “think on it” but this just makes it all more intuitive.

I’m very glad I asked!
 
part of the problem is that the ball isn’t actually a yaw instrument...we just use it as such, and it works most of the time.
 
A slip is a useful maneuver to control your descent (i.e. add drag). Used properly, it is a very safe and stable maneuver.

A skid is what kills pilots in the dreaded turn-to-final stall/spin crashes.

- Martin
 
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