Side Slip Exercise

[FastEddieB]

Over on the Pilots of America site there's quite a discussion on this topic - be warned, a very frustrating one if you choose to delve into it!

http://www.pilotsofamerica.com/forum/sh ... hp?t=79926

In any case, much discussion was being had about what was and was not possible when slipping side to side on a runway.

Anyway, I thought I'd share this video I took today:

https://www.youtube.com/watch?v=D4gnd_gF9F4

My arrangement is near perfect for this sort of thing, with a very sensitive ball prominently displayed at the top of the panel.

I also experimented around with a "yaw string", which my pusher configuration makes easy to install and use.

Not to mention it was a gorgeous day to fly in the mountains, and I did not mind an excuse to do so!

[3Dreaming]

I'm not going to waste my time reading the whole thread over there, but I'm fairly certain that I could do it without any problem. Kind of like alternating between lefr and right wheels on landing.

[SportPilot]

.......

[FastEddieB]

I'm not going to waste my time reading the whole thread over there, but I'm fairly certain that I could do it without any problem. Kind of like alternating between lefr and right wheels on landing.

My impression was its something we all do as we maneuver left and right to stay on the runway centerline if we drift off a little. This is just an exaggerated version of that.

And instructors do it all the time, "saving" many a landing that's gone astray by slipping back to the center of the runway.

In that thread, I think it boils down to poor communication, for instance not even agreeing on what a "turn" is.

[Merlinspop]

I could be completely wrong, and please correct me if so, but I've looked at it thusly:

(In the horizontal plane), straight and level gives you straight line travel, aligned with the nose of the airplane (take wind out for the moment). A turn gives you an arc. A side slip gives you diagonal travel. All three, in various combinations, give you the control authority needed to precisely maneuver and aircraft across the ground with the orientation you need. At 1000' agl, you don't really care if your nose is pointed 20* left or right of your direction of travel. At .5' ... you kinda do.

[CharlieTango]

Maintain heading with rudder and control drift with aileron is all we need to know to land without side loading.

Fully grasping the physics is another matter.

Primary issues that prevent grasping are:

1) you can turn up to ~15* while maintaining the runway heading
2) you fly and drift along with the air mass until you touch down
3) you cannot fly sideways but it sure looks like it, you are flying relative to the moving air mass but you are seeing this portion of the flight relative to the ground.

[FastEddieB]

1) you can turn up to ~15* while maintaining the runway heading

This is where it can get confusing, and it was not my intent to have that lengthy discussion spill over to this forum.

My allegation would be that, by definition, if one is flying runway heading throughout, one cannot be "turning", in spite of a changing ground path.

I think it was expanding on what a "turn" can be that led to a lot of the confusion.

[CharlieTango]

1) you can turn up to ~15* while maintaining the runway heading

This is where it can get confusing, and it was not my intent to have that lengthy discussion spill over to this forum.

My allegation would be that, by definition, if one is flying runway heading throughout, one cannot be "turning", in spite of a changing ground path.

I think it was expanding on what a "turn" can be that led to a lot of the confusion.

My allegation would be that if you are changing your flight path, like you do in your video then you are doing turns. Lack of agreement on this point makes us unable to agree that the plane can or cannot fly sideways.

BTW its ultimately the changing path through the air-mass that determines the turn not the changing ground path. Throw in some shear and the ground path becomes irrelevant. We fly in the relative wind, relative to the wind not the ground.

What if you did the same track 1,000' AGL with a cloud deck below? Would the ground track be determining the turns or lack of them?

...My allegation would be that, by definition, if one is flying runway heading throughout, one cannot be "turning", in spite of a changing ground path...

Where does this definition exist?

[FastEddieB]

I'll have to delve into an official definition of "turn".

I would say it's generally any change in heading. Though one counter example would be a forward slip where you intentionally change heading but cross control to prevent a turn.

My mental image for this exercise*, and the one I would try to instill in a student, would be something like...

"Use your ailerons to move the plane laterally back and forth across the runway. But feed in just enough opposite rudder to keep the plane from turning. If you do it just right, the plane will never turn away from the runway heading in spite of all the lateral movement."

Anyway, it's what I was attempting to do in my video. I would say the Sky Arrow never "turned" off runway heading.


*As an aside, I don't recall ever doing this exact exercise before.

[CharlieTango]

When you take the runway out of it and simplify it to a change in heading not caused by a slip we agree but your video doesn't match that definition.

Might be helpful to consider the track described by the center of mass of the aircraft. When that track bends a turn has occurred and any slip is irrelevant. Slips and slipping turns were continuously employed in order to maintain alignment.

With this thinking I see you approach the runway sideline and then do a slipping turn to a new heading that allows drift to the other sideline and then a slipping turn to a new heading that allows you to track the right sideline, rinse and repeat.

[FastEddieB]

This is headed down the exact path the PofA thread took.

I don't see any point rehashing that mess.

If anyone cares to discuss the maneuver itself, I'm game.

The minutea of what defines a "turn", not so much.

[SportPilot]

.......

[CharlieTango]

This is headed down the exact path the PofA thread took.

I don't see any point rehashing that mess.

If anyone cares to discuss the maneuver itself, I'm game.

The minutea of what defines a "turn", not so much.

You make it hard to not respond after saying:

...My allegation would be that, by definition, if one is flying runway heading throughout, one cannot be "turning", in spite of a changing ground path...

In a steady state wind a changing ground path indicates a changing flight path through the air mass as well. You seem to be alleging that you cannot be turning even if you are.

Some definitions of 'turn' are more useful than others. The one you rely on allows you to fly at least 3 different headings without turning to the new heading.

[CharlieTango]

To me, drifting left or right is not a turn. Side slipping left or right is not a turn. A turn would be a change in heading resulting in a change in direction.

Didn't you see Eddie fly 3 different directions over the runway?

1) runway heading when he was tracking either sideline.
2) a heading to the right that allowed him to drift from left side line to right side line
3) a heading to the left that allowed him to drift from the right side line to the left side line.

I saw a series of slipping turns that as you say '[where] a change in heading resulting in a change in direction'

The counter is that there was no change in direction except we saw them in the video. You can't hold the sidelines and then drift to the opposite without changes in direction.

[SportPilot]

.......