# Runway Sideslip Drill?

Discussion in 'Flight Following' started by whifferdill, Feb 27, 2015.

1. ### whifferdillLine Up and Wait

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I know - groan. But I have a dead serious, non-loaded question for those of you with slicker marbles than me. Not trying to continue that density altitude slip thread. Too many tangents, and nothing accomplished. This question is honestly something I've never thought about in my years of blissful ignorance of such convoluted sideslip complexity. I cannot for the life of me think of a reason to ever perform this "drill", but I'm interested in the academics.

Here it is - I'm trying to figure out how to recreate this "runway sideslip drill" exactly as shown in the picture below. I shot a new video below starting out in coordinated flight, tracking the right edge of the runway, and then entering a slip. I used enough rudder for the bank angle to prevent the airplane from turning or modifying its flight path. I could have continued this slip in that constant fight path state until I ran out of fuel.

Now I know that this is not the runway slip exercise. Suppose from this starting position that I was trying to "side slip" the airplane and move it toward the left side of the runway, starting as I show in the video. Oops - too much rudder, or too little aileron. Nothing is happening. No flight path change. So how do we change our flight path from here? There are only two ways I can think of - either reduce the rudder deflection, or increase the aileron deflection. So in the video, I slightly reduce the right rudder deflection, but only enough to cause the airplane to do something different. Then I hold that input. I am still slipping. But unless I need to be locked in a padded cell, it sure appears to me that the airplane is turning (slipping turn) at a constant rate (curved flight path) and not simply adopting a new and constant flight path as shown in the picture. You can see my hand, and I did not make any further inputs with the stick from the initial slip.

So looking back at the picture below, it shows the airplane starting in coordinated flight, fuselage aligned with the flight path, and then "side slipping" to the left along a straight, but diagonal flight path, moving the airplane laterally to the left. Then it shows a point at which "controls are neutralized", and boom - the airplane returns to the original flight path, in coordinated flight, just displaced a bit to the left. Never in my short 13 years of flying have I neutralized slip inputs to find the airplane's flight path instantaneously redirected as a result of removing the slip.

In this video, I made the airplane move to the left across the runway in a turn, but when I neutralized the controls and exited the slip, the airplane was of course flying a new flight path, not aligned with the runway - and continued that way. Duh...because the airplane was turning. A turn was required in the opposite direction to return the airplane's flight path parallel to the runway.

This "runway sideslip drill" is shown nowhere in the sacred FAA Handbook, but some seem to take it as gospel. It is also claimed that no turning is required in order to perform this drill and its two flight path changes - one to move the airplane in a new direction to the left, and another to return the flight path to the original direction. Can anyone explain this mysterious sideslip drill? I'm wondering if there's a good reason no videos can be found showing an aircraft replicating the movements depicted in this diagram. To me, it seems at odds with the laws of physics. But I'm open to education.

2. ### HenningEjection Handle Pulled

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This picture is incorrectly drawn, the angle of the flight aircraft to the flight path has to change with the flight path due to the aerodynamic influence of the fuselage, that's why it's called a slip and it can be used to slow down. The aerodynamics of flight do not change because you are in a slip, the efficiency just changes is all. This whole premise is not well thought out. The only difference between a forward slip and side slip is the result you are looking for. The only way the zig zag thing works is if you have a cross wind, and then it's just a difference in the rate of slip being adequate, or inadequate, to compensate for the drift rate of the cross wind.

Last edited: Feb 27, 2015
3. ### FastEddieBFinal Approach

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If the weather is nice tomorrow I may attempt it in my Sky Arrow and video it.

I can picture mimicking the diagram - I think I can.

After all, on a normal landing, with the plane aligned with the runway, do we not routine "sideslip" left and right as necessary to stay on the centerline without letting the nose yaw? This should just be an exaggerated example of that.

We'll see!

Last edited: Feb 27, 2015
4. ### HenningEjection Handle Pulled

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The only way to mimic the Runway Sideslip Drill as it is drawn is if you have a crosswind.

5. ### whifferdillLine Up and Wait

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But even in a x-wind, how do you change your flight path twice without turning, and instantaneously redirect your flight path upon removing the slip? I don't see how the x-wind or no x-wind changes anything. But this segways right into the other question of what happens if, in x-wind while perfectly slipped, aligned with, and tracking the runway, you remove that slip? Or even enter a slip in the opposite direction? You still track the runway...unless you deliberately turn the airplane. Otherwise, no flight path change. Others have said that you cannot fly a right banked slip in a left x-wind and track the runway. I disagree, of course. I'm just waiting or a stiff enough x-wind where you can actually see the crab angle in the Pitts.

6. ### HenningEjection Handle Pulled

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Because you don't change the flight path, the wind does, all you need to do is increase or decrease drag as the response. You just vary the amout of total slip, not the proportion of rudder/aileron. It would require a stiff crosswind or a long runway to see a good result. The whole premise of the drill is actually weak and incorrect to try to teach.

Last edited: Feb 27, 2015
7. ### whifferdillLine Up and Wait

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Maybe someone can redraw the picture "correctly" so we're all clear on what's being described. I think that's where these discussions break down.

8. ### HenningEjection Handle Pulled

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We really need to end the whole 'side slip-forward slip' thing, it's stupid, there is only one slip, the difference is the result we are looking for when we use it.

9. ### HenningEjection Handle Pulled

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You can't redraw the picture correctly because the base premise they are working under is false. He is not understanding what is going on therefore has created a drill that can't really be done.

10. ### whifferdillLine Up and Wait

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Agreed! For pure ****s, I was just trying to figure out how some felt an airplane could do things that made no sense to me from a physics standpoint.

BTW, here is the FAA Handbook illustrating the difference between forward and sideslip. See the difference? Sure hope nobody forgets which is which when it comes time to make your next x-wind landing.

Agreed again.

11. ### FastEddieBFinal Approach

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I still think I can manage it, crosswind or not.

For the sake of argument, let's imagine a right crosswind.

I will approach and line up with the left runway edge, in enough of a slip to track the edge, as if I were landing there but won't. Then I'll increase right bank, with a commensurate amount of left rudder, to move laterally across the runway left to right, then track down the right runway edge. Reverse the process by decreasing bank and opposite rudder to drift back to the left edge, all the while lined up with the runway.

It's clear enough in my mind. If I can't do it, it should be readily apparent.

12. ### janikpilotPre-Flight

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This really messed me up when I went through training. My instructor put it like this:

A side slip is used to keep your nose pointed in the direction of travel. It is used in crosswinds.

The forward slip is NOT used in crosswinds. It is designed to descend quickly. You are using the side of the aircraft as a kind of spoiler to slow you down.

The picture in the FAA book is confusing, I agree.

At the OP:

Perhaps the issue is letting lift increase and not doing anything about it? I noticed your nose pitches up when you reduce right rudder. I believe instead of reducing rudder, you should actually increase both aileron and rudder, thus increasing the overall effect of the slip.

Also, your Pitts is sexy, I hope you spin her right

13. ### whifferdillLine Up and Wait

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Just be sure that the simple removal of the slip inputs causes the airplane to stop moving right, and then re-track the runway on the right side. If you must make a slipping turn BACK in the other direction (to the left) to re-track the runway, this is counter to the 'idea' behind the runway slip drill and of course disproves the ability to perform it. Good luck!

14. ### FastEddieBFinal Approach

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Thanks!

Nice to have a mission, and I'll learn something either way!

15. ### whifferdillLine Up and Wait

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But all that would do is cause me to continue along the right edge of the runway, as my video started with, but with a steeper bank angle. I'd just be flying along, tracking the runway looking like Skip Stewart on takeoff. If you don't know what I'm talking about, youtube him.

I freakin love the airplane. And yes, I spin it on occasion. -

16. ### HenningEjection Handle Pulled

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BINGO! You have to have the crosswind. The drill is not predicate on a crosswind.

17. ### FastEddieBFinal Approach

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No.

The fact that I can (I hope) move laterally across the runway either into or with the wind would imply I could do it with no wind as well.

We shall see.

18. ### janikpilotPre-Flight

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If that's the case, then less slip would cause you to also maintain straight down the runway? Perhaps even no slip at all?

I can just personally remember many times in xwind training where I would slip too little or too less and drift away from centerline. Perhaps the maneuver has to be done in a less-than-aerobatic aircraft in order to work (or at least be a lot easier).

The reason Skip Stewart can do what he does (who doesn't know Skip, by the way? ) is because Prometheus has a 400 hp beast on the front.

And that's really nice flying. I like to see a good, tight pilot. Superb aerobatics!

19. ### HenningEjection Handle Pulled

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Let's see what you get.

20. ### whifferdillLine Up and Wait

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I agree the 'drill' should work the same, wind or no wind. I can move the airplane laterally each way, as drawn in the drill, but I'm unable to do it without making turns (slipping or otherwise) to each new flight path. The path is shown as a 'zig-zag'. There was about 5KT of wind blowing across the runway today when I shot the video, but not enough to really see a crab angle.

21. ### HenningEjection Handle Pulled

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Exactly, your slip is not changing your flight path, the cross wind is changing your flight path. Your slip is altering your relationship to the wind, not the relationship to your flight path. There is no such thing as a side slip if there is no crosswind, because a side slip is defined as a slip used to correct for a crosswind.

22. ### HenningEjection Handle Pulled

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Your instructor is correct. We define them by the result we are seeking, not by what we are doing. It's not only confusing, it's useless information on top of it. It should be abandoned and replaced with 'slip' plain and simple.

23. ### pilot1956Pre-Flight

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Eddie - my thoughts on the topic. The runway sideslip drill, as pictured, can't be done (and by "as pictured", I mean flying the airplane so that it tracks left and right, over the runway centerline, with no change in yaw (i.e., no change in heading)).

I think it is true that for any given crosswind, there is only one configuration of aileron and rudder that will both keep the long axis of the airplane parallel with the centerline of the runway (so that if it were to land, there would be no side load on the gear) AND maintain a constant distance from the centerline of the runway. Change rudder or aileron alone, and the plane will enter turning flight and change both (i.e., increase slip) and the plane must yaw as it assumes a new non-turning ground track (a track that would also not be parallel to the runway centerline).

Use your example, crosswind from the right and flight with the long axis of the airplane aligned with the runway centerline and with the airplane maintaining a constant distance from the centerline. If you increase the bank angle (with more right aileron) with commensurate increase in left rudder, as you indicated, the plane will yaw left and establish a new track to the right of the original path. It can't happen any other way.

If you think it doesn't happen in flight, then it was too subtle to observe. That didn't mean it didn't happen.

[Edit: Assumes no change in crosswind component and no change in IAS during drill]

Last edited: Feb 27, 2015
24. ### whifferdillLine Up and Wait

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Of course. I can maintain runway track with no slip, a small slip, a large slip, alternating in either direction, constantly varying, doesn't matter. I shot a video of just that in that 'other' thread. I don't suggest going to look for it, though.

But in this case, all that 400 hp is doing is allowing him to do that near knife edge slip at a lower airspeed. I could do the exact same thing on takeoff down the runway, but my 180 hp would require more airspeed, and it wouldn't look as cool as Skip's. BTW, if his engine ever takes a crap while he's doing that, it will not be pretty.

Very generous. Now if we can get some decent Wx, I can get back to practicing.

Last edited: Feb 27, 2015
25. ### asechrestEn-Route

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So then yourr issue with the drill is actually the transition points, correct? Because what I know of slips should make everything in between perfectly doable as diagramed, I'd think.

26. ### HenningEjection Handle Pulled

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Exactly, it's the variation in forward airspeed in relationship to a cross wind that allows you to move back and forth across the runway by varying the slip without turning.

27. ### whifferdillLine Up and Wait

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That is a new take on this - are you saying that you're using the slip to simply add drag and slow down such that the x-wind correction requirement becomes greater, thus causing drift? If so, moving in alternating directions left and right, as shown in the slip drill picture would require speeding up and slowing down with either power changes or altitude variations. Interesting idea, though not sure if this is what is intended by the 'drill.'

You could even do the same thing without slip - in coordinated crabbed flight. Set up crabbed and tracking the runway at a certain speed, and then pull power (or climb) and slow down - you will drift downwind. Add power and speed up (faster than your original 'entry' speed) and you will drift toward the upwind side, all with no turning through the airmass. But if this is your point, the slip isn't changing anything, the speed is. At a constant speed, a turn would still be required, since zig zagging over the ground (at a constant airspeed) also requires zig zagging through the airmass.

Or maybe I'm misunderstanding what you're trying to say. Happens a lot in these discussions.

Last edited: Feb 27, 2015
28. ### dtuuriEn-Route

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Don't forget the yaw string.

dtuuri

29. ### dmspilotPattern Altitude

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It sure looks possible to me.

30. ### HenningEjection Handle Pulled

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Exactly, all it is is an exercise in angular geometry at varying speed that is dependent on the <strong> crosswind do make an effective demonstration of. It's a good exercise for teaching cross wind landings as it teaches them that it is safe to maneuver like this next to the runway, and to develope the feel to do so accurately. The guy just didn't really understand what was going on, or failed to explain it.

31. ### HenningEjection Handle Pulled

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What that video shows is not what the drill issue is.

32. ### whifferdillLine Up and Wait

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Thanks - looks like slipping turns back and forth to me, and that he didn't let each turn go far enough in each direction to show that in fact, the airplane would continue to turn to the point where heading could no longer be maintained with rudder. He is still stopping the slipping turn such that he continues on a new constant slipped flight path. Then he's doing a slipping turn in the opposite direction to turn to a small new heading change, then stopping the slipping turn, and continuing the slip along the new flight path. Back and forth.

All I was trying to show in my video was that in order to cause the airplane to move in a new direction, you must turn it. Releasing the slip will just cause you to continue on along that new flight path you turned to until your TURN the airplane (slipped or not) back in the other direction.

We may be headed for another circular semantics discussion, with different folks having different ideas about what the slip is actually accomplishing. I strongly feel it's misleading for folks like Martha here to say that in a x-wind, you're using the bank to make the airplane drift into the wind. You know that it's perfectly possible to be attempting to land in a x-wind with the right amount of slip bank and rudder deflection, but still be drifting downwind right? It's not that you need more bank in the slip, you might just need to TURN your flight path more into the wind. This could be done one of two ways - with ailerons and a MOMENTARY bank, or a constant bank angle and a rudder reduction. It does not have to be all about bank angle. So you turn such that your new flight path allows you to track the runway. Then once you've reset your FLIGHT PATH (by turning - with ailerons), you can either relax your aileron input back to what you started with, or if you used decreased rudder to turn the airplane, re-apply the amount of rudder you had before. Then you can be set up for a perfect slipped x-wind landing.

Again, maybe you, me, Martha, etc. are all saying the same thing in a different way, but I strongly feel that for those wanting a good understanding of the mechanics, that it needs to be clear in their minds that turning (and stopping that turn) is taking place here - anytime a flight path change takes place. In reality, maybe none of this matters. People will learn to fly airplanes just fine, just the same. This is academia.

Last edited: Feb 28, 2015
33. ### eetrojanCleared for Takeoff

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Why not? Can you elaborate?

34. ### HenningEjection Handle Pulled

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Because they are turning the flight path, not moving the airplane sideways.

35. ### eetrojanCleared for Takeoff

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Hmmm. Don't totally follow. It's being performed in a crosswind (a prerequisite to being able to move sideways if I understand you), and it looks to my like the plane is pretty much moving sideways, back and forth.

Help.

36. ### HenningEjection Handle Pulled

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Correct, now go back to the OP and the drill as drawn.

Last edited: Feb 27, 2015
37. ### eetrojanCleared for Takeoff

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Oh, I see. The legend next to the "Runway Sideslip Drill" in the OP's illustration says "because there is no wind..." and, if that were true, then the slipping plane wouldn't be capable of sliding left and right relative to the runway, it would necessarily transit a curved path relative to the runway. Yes?

38. ### HenningEjection Handle Pulled

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.

39. ### LindbergPattern Altitude

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Your video looks like a knife-edge demonstration. And that runway looks a bit narrow for the side-slip drill. Did you watch the videos posted in the other thread, which clearly show aircraft moving laterally?

The King video seems to perfectly demonstrate the side-slip drill, and the nose never changes direction. So whether or not you want to call what you're seeing a "turn," but you're wrong about the controls. You may be able to do it in the manner you describe, but that isn't what's being taught, and I doubt that's what John is doing in the video. It sure isn't what I do. If I'm landing in a crosswind and am too far downwind, I absolutely increase bank and opposite rudder simultaneously to bring it back on the centerline without ever turning.

Only if you aren't aligned with the centerline to begin with. In which case, yes, you'd need a turn to get lined up and then apply your crosswind correction. But once you are lined up, you can absolutely go side to side without turning (i.e., changing heading). You can even do it with or without wind, the difference being that with no crosswind, you'll have to slip in both directions, but with crosswind you can just relax the slip to drift downwind.

If the King video didn't convince you of that, probably nothing will. Certainly not another video. But maybe you can get someone to take you up and demonstrate. I'd be happy to if you were in the area.

Last edited: Feb 28, 2015
40. ### HenningEjection Handle Pulled

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This thread has the potential of going treadmill on us, where's Nick?