Effect of Density Altitude on Crosswinds

[RotorDude]

Notice how your nose wanders off heading? Those are forward slips not sideslips.

dtuuri

The only difference between "forward slip" and (non-turning) "side slip" is your reference point or frame of reference. Physically they are one and the same.

 

[dtuuri]

The only difference between "forward slip" and (non-turning) "side slip" is your reference point or frame of reference. Physically they are one and the same.

Aerodynamically they are the same. The difference lies in the the point of view of the observer. In this case the runway is the reference of interest and the longitudinal axis does not remain parallel with it. That's a forward slip.

dtuuri

 

[whifferdill]

Aerodynamically they are the same. The difference lies in the the point of view of the observer. In this case the runway is the reference of interest and the longitudinal axis does not remain parallel with it. That's a forward slip.

dtuuri

Which type of slip is a slipping turn?

 

[dtuuri]

Which type of slip is a slipping turn?

Neither? The terms don't apply, they describe landing slips. "Skids" and "slips" describe bad turns.

dtuuri

 

[whifferdill]

Neither? The terms don't apply, they describe landing slips.

Who the heck actually approaches to land in an angled "side slip" as shown in that picture above? I fail to understand why anyone would want to do that. There are two reasons to slip - to lose altitude, and to align the airplane in a x-wind. What kind of slip is it if you're doing both at the same time? I don't understand why you'd want to fly along, do a slipping turn to a new flight path, and then turn back and reestablish the original flight path, only displaced a bit - as that "side slip" picture shows. Classic academic overcomplication.

 

[Lindberg]

Who the heck actually approaches to land in an angled "side slip" as shown in that picture above?

I did a bunch of times today. And I'm sure you have too. That's exactly what you're doing when you use a slip for crosswind correction; the only difference being that if you are doing it right, the crosswind exactly cancels out your angled (relative to the airmass) flight path. The diagrams above specifically state there's no wind.

Neither of those slips is a slipping turn because the aircraft is not turning. The nose is pointed in the same direction at the entry and exit of the slip. You will note that if you could cut out the side slip drawing and rotate it, it would be exactly the same as the forward slip drawing.

 

[dtuuri]

Who the heck actually approaches to land in an angled "side slip" as shown in that picture above?

Maybe there's a cow grazing on the end of the runway and you don't want to curdle its milk? Or a sailboat mast? Or a sycamore tree? The list seems endless...

dtuuri

 

[whifferdill]

I did a bunch of times today. And I'm sure you have too. That's exactly what you're doing when you use a slip for crosswind correction; the only difference being that if you are doing it right, the crosswind exactly cancels out your angled (relative to the airmass) flight path. The diagrams above specifically state there's no wind.

Neither of those slips is a slipping turn because the aircraft is not turning. The nose is pointed in the same direction at the entry and exit of the slip. You will note that if you could cut out the side slip drawing and rotate it, it would be exactly the same as the front slip drawing.

To make the airplane do this (below), slip or no slip, requires a flight path change - turning. Sure you can do this if you want, but it's not a realistic illustration of what you normally do in a x-wind. I've done plenty of x-wind landings, and I crab along tracking the runway, and then slip the airplane close to the runway without changing my flight path, using the exact same inputs I used in my video above.

The inputs above (no wind) require different inputs from doing this below (in x-wind). Below there is no slipping turn required, and no flight path change required. I still fail to see how that "side slip drill" illustration above has any bearing on realistic x-wind ops. Below, you're not changing your flight path through the air, or with respect to the ground. Luckily my original instructor never mentioned a word about this "side" vs. "forward" slip nonsense. But it does seem lots of pilots like to make a big deal about the "difference".

 

[Lindberg]

I was taught not to crab down final in a taildragger, too likely that you land with some sideload. Better to stabilize in a slip and take it all the way to the runway.

The "runway sideslip drill" is exactly how you use a slip to counter a crosswind. If there was a crosswind from the left in your picture, then the plane would track the centerline instead of moving left (given the correct amount of slip). Without the slip, it would move to the right.

Here's some videos of aircraft moving laterally through the air. And no engines to complicate the issue. These are slipping to lose altitude, and you can clearly see that the plane is moving laterally through the air. Note that when they kick out of the slip, they are still on the same flightpath:

https://www.youtube.com/watch?v=xheubh4LeFY
https://www.youtube.com/watch?v=5t7xnls2w5k
https://www.youtube.com/watch?v=hTF3M80d27Y

 

[whifferdill]

The "runway sideslip drill" is exactly how you use a slip to counter a crosswind.

OK, so here is how you would use that "drill" to land in a left (for example) x-wind: You would line up with the runway to your right, airplane heading matching the runway heading. The x-wind would cause you to drift along an angled flight path to the right toward the runway - flight path not tracking the runway heading. Then as the airplane drifts into the extended runway centerline, you would apply slipping (left) turn inputs to change your flight path such that the airplane is now tracking the runway. If you did not do a slipping turn (or a turn of some sort), you would be slipping along the same drifting track and miss the runway. It could be done, but I don't know anyone who approaches a x-wind landing like that.

 

[Silvaire]

...It could be done, but I don't know anyone who approaches a x-wind landing like that.

Dude, you just told us a few posts ago that it was impossible

 

[whifferdill]

Dude, you just told us a few posts ago that it was impossible

What was? Re-read post #208 dude.

 

[Silvaire]

What was? Re-read post #208 dude.

Where you tell us that a side slip with no heading change is a turn?

I give up, there's no point continuing this.

 

[whifferdill]

No kidding

 

[dtuuri]

To make the airplane do this (below), slip or no slip, requires a flight path change - turning deflecting.

FTFY.

dtuuri

 

[dtuuri]

Here's some videos of aircraft moving laterally through the air.
https://www.youtube.com/watch?v=xheubh4LeFY
https://www.youtube.com/watch?v=5t7xnls2w5k
https://www.youtube.com/watch?v=hTF3M80d27Y

More forward slips. Can't anybody do a real sideslip anymore?

dtuuri

 

[Lindberg]

More forward slips. Can't anybody do a real sideslip anymore?

Yeah, ignore the YouTube captions. Those are all deliberate forward slips to lose altitude. Very effective, and necessary in a glider if you lose spoilers or approach too high.

I think some posters in the thread could benefit from a glider ride and a demonstration of aggressive slips.

 

[vintage cessna]

Luckily my original instructor never mentioned a word about this "side" vs. "forward" slip nonsense. But it does seem lots of pilots like to make a big deal about the "difference".

[/QUOTE]

That explains a lot. The FAA Airplane Flying Handbook differentiates the two, every training manual I have seen does also. The Private Pilot PTS has a task titled "Forward Slip to Landing". Wonder why his instructor didn't see fit to teach the difference?

 

[whifferdill]

That explains a lot.

Sure does. It explains that my original CFI had some freakin common sense, and was not one of these book thumping regurgitative monkeys on this particular subject. He was an excellent CFI. And I have a bookshelf full of flying knowledge books that I've read, so you can cut the academic superiority act. I learned to fly in a tailwheel airplane with a big rudder and no flaps. Want to steepen your approach? Slip. Want to land in a x-wind without wadding the airplane up? Slip at some point before touchdown. Please inform me what I'm missing.

I know what this made up "book" difference is between side and forward slip that people get their panties twisted up about. It doesn't make a bit of difference. I never made an effort to try very hard to remember which is which. Back when Wolfgang Langeweische wrote 'Stick and Rudder' (which BTW beautifully and comprehensively nails every fundamental flight control concept that pilots should know) there was none of this side vs. forward slip nonsense. There was only the term sideslip - used to describe what you do to lose altitude or to touch down properly in a x-wind. Somewhere along the way the FAA felt the need to invent a problem that doesn't really exist.

Of course, according to dturri, nobody can do a real sideslip anymore. Millions of flying videos on Youtube, and apparently this is demonstrated nowhere. But I guess I, like so many others, have this fundamental hole in my flying knowledge and ability that's going to cause me to wad up my Pitts someday.

 

[Lindberg]

Sure does. It explains that my original CFI had some freakin common sense, and was not one of these book thumping regurgitative monkeys on this particular subject. He was an excellent CFI. And I have a bookshelf full of flying knowledge books that I've read, so you can cut the academic superiority act. I learned to fly in a tailwheel airplane with a big rudder and no flaps. Want to steepen your approach? Slip. Want to land in a x-wind without wadding the airplane up? Slip at some point before touchdown. Please inform me what I'm missing.

I know what this made up "book" difference is between side and forward slip that people get their panties twisted up about. It doesn't make a bit of difference. I never made an effort to try very hard to remember which is which. Back when Wolfgang Langeweische wrote 'Stick and Rudder' (which BTW beautifully and comprehensively nails every fundamental flight control concept that pilots should know) there was none of this side vs. forward slip nonsense. There was only the term sideslip - used to describe what you do to lose altitude or to touch down properly in a x-wind. Somewhere along the way the FAA felt the need to invent a problem that doesn't really exist.

Of course, according to dturri, nobody can do a real sideslip anymore. Millions of flying videos on Youtube, and apparently this is demonstrated nowhere. But I guess I, like so many others, have this fundamental hole in my flying knowledge and ability that's going to cause me to wad up my Pitts someday.

I'm confused. In post #166, you said:

To me, moving sideways would be like trucking along in flight andall of a sudden causing the airplane's flight path to start moving in a different direction without changing the alignment of the airplane - like a car shifting lanes without any amount of turning of the vehicle. Airplanes can't do that.

But that's exactly what a side slip is. Using the ailerons to bank the airplane and change the direction of flight, while using rudder to maintain heading.

So I'm confused as to what you're calling a side slip if it isn't that.

Forward slip and side slip in the same aircraft (with proper captions):

http://youtu.be/v_f0KnXyExU?t=10s
http://youtu.be/YOiUmoGb4no?t=1m8s

Both show the aircraft "changing lanes" to use your metaphor. It's just that in the second video, because of a crosswind, the airplane tracks the extended centerline despite flying "sideways" through the air. In neither video does the plane turn, i.e., change direction of flight.

 

[Silvaire]

I don't mean to infer that you have a hole in your flying knowledge, You may be perfectly capable of flying and I'd rather keep this as impersonal as possible but for the benefit of others reading this thread I am compelled to point out that in your post #154 you make a number of statements that are just flat out wrong.

Among them is this:

It is physically impossible to move an airplane "laterally" through the air at a constant heading.

If that statement were true it would be impossible to land an airplane in a crosswind.

As I've said a number of times it is perfectly possible to enter a slip without changing your heading. Simply keep the nose on point with the rudder as you apply opposite aileron. Don't try tell me once again that this is not possible because it certainly is and once you have full opposite aileron and rudder inputs what would you call that flight condition if not a slip?

What I am not able to understand is why you repeatedly fail to grasp such a simple concept

 

[RotorDude]

I don't mean to infer that you have a hole in your flying knowledge, You may be perfectly capable of flying and I'd rather keep this as impersonal as possible but for the benefit of others reading this thread I am compelled to point out that in your post #154 you make a number of statements that are just flat out wrong.

Among them is this:



If that statement were true it would be impossible to land an airplane in a crosswind.

As I've said a number of times it is perfectly possible to enter a slip without changing your heading. Simply keep the nose on point with the rudder as you apply opposite aileron. Don't try tell me once again that this is not possible because it certainly is and once you have full opposite aileron and rudder inputs what would you call that flight condition if not a slip?

What I am not able to understand is why you repeatedly fail to grasp such a simple concept

I think if you do what you suggest, you will turn onto a new track, even if your indicated heading is the same. Try to do this over a straight road in zero wind (keeping the nose pointed down the road), and you'll see it's impossible.

 

[Silvaire]

I think if you do what you suggest, you will turn onto a new track, even if your indicated heading is the same. Try to do this over a straight road in zero wind (keeping the nose pointed down the road), and you'll see it's impossible.

Learned how to do that in 1969, when did it become "impossible"?

I'd like for you to demonstrate to me how you can make a turn without changing your heading. That would be real interesting.

 

[RotorDude]

Learned how to do that in 1969, when did it become "impossible"?

I'd like for you to demonstrate to me how you can make a turn without changing your heading. That would be real interesting.

Easy. Do what you suggested above: roll in a left bank, crank in right rudder to keep your indicated heading. Depending on the relative amounts of roll and yaw, you would end up either on a continuous turn, or a short one onto a new "real" heading (where the airframe is headed), or track.
You will not be able to keep the nose on the road with a wing low, guaranteed (under no wind conditions).

 

[whifferdill]

I went out today and tried that silly "runway sideslip drill" as shown below. No wind. Here's the problem with how it's presented - It implies that you can fly along on runway heading, displaced a bit, and then slip diagonally toward the runway until you want to stop, at which point you neutralize the controls and the airplane automatically returns to its original flight path, on runway heading, just displaced a bit. It doesn't work that way.

So I set it up like in the picture below, to the right of the runway, on runway heading. No wind. Then I start to slip. To move toward the runway requires a flight path change. The only way to do that is to do a slipping turn. Yes, you can manage a slipping turn such that the nose basically stays on runway heading. So I do that, and start my angled path toward the runway. Now guess what happens when you neutralize the controls and end the slip? You keep trucking along on your new angled flight path right past the runway. In order to cause the airplane to start tracking the runway again, as shown in this "slip drill" picture, you must turn the airplane to the right, back to your original flight path. You could make it a slipping turn such that the heading stays pretty much constant, but it's still a turn - not "sideways" movement.

You cannot just fly along in coordinated flight, enter a slip, instantaneously start flying "sideways", along a new flight path, then neutralize the slip and immediately and automatically return to your original flight path tracking the runway. Doesn't work that way. I'd be happy to have someone show me. This is about the only maneuver I've not done in my Pitts. I'm open to learning new things.

So given all that, I ask again - who the hell lands while manipulating the controls in this fashion? Again, to use this "technique" in a real x-wind would require you to fly an angled (drifting) approach toward the runway and then do a slipping turn to change your flight path to match the runway track once you've reached the extended centerline. Who does that??

 

[Silvaire]

...Now guess what happens when you neutralize the controls and end the slip? You keep trucking along on your new angled flight path right past the runway...

Assuming no wind how do you do this with the controls neutral (not crossed)? How does your airplane continue to fly a path other than where the nose is pointed?

As you describe it if you are on short final with a 15 kt crosswind from the left, the nose aligned with the runway and no drift (normal crosswind landing) you are turning?

I'm sorry but what you are saying doesn't make any sense. It doesn't matter to me how you think it works but when you make incorrect statements I'm just going to point that out.

 

[Silvaire]

Easy. Do what you suggested above: roll in a left bank, crank in right rudder to keep your indicated heading. Depending on the relative amounts of roll and yaw, you would end up either on a continuous turn, or a short one onto a new "real" heading (where the airframe is headed), or track.
You will not be able to keep the nose on the road with a wing low, guaranteed (under no wind conditions).

Nope, you end up in a slip. You cross the controls and you slip, plain and simple. You don't keep the nose on the road because you'll be slipping either left or right off of it, you keep the same heading. This is such basic stuff I can't fathom how you guys can make it seem so complicated?

 

[whifferdill]

I'm not going to try to keep this up. RotorDude gets it. Lots of others too, probably, but they just have the sense to try to let this thread die. I'm a glutton for punishment I guess, but I give up.

 

[Silvaire]

That's fine. If you don't say stuff that's wrong then I won't comment on it.

 

[vintage cessna]

Easy. Do what you suggested above: roll in a left bank, crank in right rudder to keep your indicated heading. Depending on the relative amounts of roll and yaw, you would end up either on a continuous turn, or a short one onto a new "real" heading (where the airframe is headed), or track.
You will not be able to keep the nose on the road with a wing low, guaranteed (under no wind conditions).

Correct. The plane will move sideways in the direction of the slip in a no wind condition. That is why you would employ a slip in a cross wind landing, to offset
the drift. You don't slip a plane to only align the nose with the centerline but also to prevent drift.

 

[vintage cessna]

Now guess what happens when you neutralize the controls and end the slip? You keep trucking along on your new angled flight path right past the runway.

[/QUOTE]

That is called inertia. Part of the drill would be to anticipate inertia, just like learning to roll out of turn early on a specified heading.

 

[RotorDude]

Nope, you end up in a slip. You cross the controls and you slip, plain and simple. You don't keep the nose on the road because you'll be slipping either left or right off of it, you keep the same heading. This is such basic stuff I can't fathom how you guys can make it seem so complicated?

I agree that it's simple.
And I agree that if you keep the heading using rudder and roll in some aileron, you'd be slipping.
But my point was that in zero wind conditions, flying over a straight road, you cannot stay over that road if you keep the nose pointed down the road, roll in some aileron and lower a wing, regardless of what you do with your rudder.
And if you deviate from that road, you have obviously turned away from it, regardless of the "ugliness" of said turn.

So I am not sure what your "nope" refers to.

 

[vintage cessna]

I agree that it's simple.
And I agree that if you keep the heading using rudder and roll in some aileron, you'd be slipping.
But my point was that in zero wind conditions, flying over a straight road, you cannot stay over that road if you keep the nose pointed down the road, roll in some aileron and lower a wing, regardless of what you do with your rudder.
And if you deviate from that road, you have obviously turned away from it, regardless of the "ugliness" of said turn.

So I am not sure what your "nope" refers to.

I don't think Silvaire has been talking about landing in a slip condition in no wind, or the ability to track centerline in a slip with no wind.

 

[dtuuri]

Of course, according to dturri, nobody can do a real sideslip anymore. ... But I guess I, like so many others, have this fundamental hole in my flying knowledge...

Aw shucks, there I go again hurting everybody's feelings. Here, have a tissue.

At least you are going out there and doing this stuff. That's more than I can say for Jaybird180. Do you know how long I've been waiting for a tuft report? Neutralizing, i.e., "releasing" the controls when in a slip will change the heading, so I don't know what that's supposed to prove. Once you arrive over the runway after sideslipping to it you need to stop the lateral motion in order to land without event. I'm sure anyone who can land a Pitts (you can, can't you? ) knows how to unslip it back along the runway centerline. Do that.

dtuuri

 

[RotorDude]

I don't think Silvaire has been talking about landing in a slip condition in no wind, or the ability to track centerline in a slip with no wind.

So what does his "nope" refer to?
And I was addressing his statement above, "I'd like for you to demonstrate to me how you can make a turn without changing your heading. That would be real interesting."

 

[vintage cessna]

So what does his "nope" refer to?

To me, it appears the "nope" is in response to your contention that placing an airplane in a slip is turning the airplane. He agrees with you about the no wind condition. Everyone knows, I think , that you would not want to land an airplane in a slipped condition with no wind becuase of the sideways ( in relation to the centerline) movement of the aircraft.

 

[RotorDude]

To me, it appears the "nope" is in response to your contention that placing an airplane in a slip is turning the airplane. He agrees with you about the no wind condition. Everyone knows, I think , that you would not want to land an airplane in a slipped condition with no wind becuase of the sideways ( in relation to the centerline) movement of the aircraft.

I made no such contention. I simply said that if you lower your wing and keep the nose pointed down the road (or runway), you'll turn away from your present track, regardless of your rudder inputs.

 

[vintage cessna]

I made no such contention. I simply said that if you lower your wing and keep the nose pointed down the road (or runway), you'll turn away from your present track, regardless of your rudder inputs.

Well that is the problem, you just used the word "turn" to describe the motion in a slip. I now know what you mean when you say that. In the vocabulary of aviation, I (and probably Silvaire, and most others) have never seen the word " turn" used that way. To us, turn means a change of heading, not a change of flight path. What does your rate of turn instrument indicate in a slip?

 

[Silvaire]

I agree that it's simple.
And I agree that if you keep the heading using rudder and roll in some aileron, you'd be slipping.
But my point was that in zero wind conditions, flying over a straight road, you cannot stay over that road if you keep the nose pointed down the road, roll in some aileron and lower a wing, regardless of what you do with your rudder.
And if you deviate from that road, you have obviously turned away from it, regardless of the "ugliness" of said turn.

So I am not sure what your "nope" refers to.

My "nope" is in regards to you saying the slip is a turn. It's not a turn, you can hold it all day long and your heading will not change and you will certainly not fly in a curved path. I never said you would remain over the road, you will drift with respect to the ground (in a no wind condition) in the direction of the slip. I said your heading would remain constant. It's not a turn, it's a slip. It's exactly what you do every time you land in a cross wind, you slip the amount necessary to counteract the cross wind movement of the air but since there is no wind n this example you will drift left or right.

I don't understand why you are calling it a "turn" if I were turning my heading would change.

 

[vintage cessna]

I made no such contention. I simply said that if you lower your wing and keep the nose pointed down the road (or runway), you'll turn away from your present track, regardless of your rudder inputs.

If there is a wind of 270 degrees at 40 kts, and you fly and maintain a heading of 360 degrees, you will of course drift right. Are you in a continuos right "turn"?