Guide to Aircraft Coordinates: Roll, Pitch & Heading

[senmeis]

Hi,

I’ve read a set of coordinate elements: „roll, pitch and heading“ for aircrafts. What’s the difference to „roll, pitch and yaw“?

Senmeis

 

[anorlunda]

Heading is the compass direction in which the longitudinal axis of a ship or aircraft points.

Roll and pitch both have a natural zero point, relative to the Earth below. Yaw has no natural zero point. So yaw control refers to which direction the nose points, but there is no easy way to define zero yaw. That makes heading more useful.

Note by the way that heading is not necessarily the direction the pane moves. There can be cross winds coming from the side. The actual direction of motion is called track.

It is the same on boats.

 

[pbuk]

It is the same on boats.

Except on boats we don't use the term "yaw" (in English). Instead we refer to "leeway" which does have a zero point, the heading.

Also on boats there is the added complication of motion through two fluid media, air and water. Because of this we usually refer to the actual direction of motion unambiguously as "course over the ground" (COG). A boat's track is is the path that it follows through the water and is usually less significant than its COG (but more significant when recovering a man or cargo lost overboard).

 

[FactChecker]

In aero engineering, it is common to call the Euler angles Pitch, Roll, and Yaw, or Theta, Phi, Psi (as opposed to Psi-nav). In this context, the actual compass heading is usually not important. They are using the Euler angles to indicate the orientation of the airplane in some "locally level" coordinate system.

 

[anorlunda]

Except on boats we don't use the term "yaw" (in English). Instead we refer to "leeway" which does have a zero point, the heading.

I always thought of leeway as sideways velocity rather than an angle. Related but not identical.

An amusing anecdote involving leeway. I once coached a new sailor who had a 28 foot sailboat. He was going to cross the Gulf Stream from Florida to The Bahamas. The Gulf Stream is a powerful ocean current that flows northward past Florida.

I was shocked to hear that he turned back the first day out because "his compass went crazy." He was caught by surprise by leeway as fast as his forward speed, which made his heading deviate from his track by 45 degrees. He correctly compensated by turning the bow of the boat southward, but that made the deviation worse. He could have gotten into a situation where his net velocity was zero and the direction of his GPS track indeterminate, and that would really make him fear being lost out at sea.

 

[sandy stone]

I always thought of leeway as sideways velocity rather than an angle.

To go a bit further, I always thought of leeway as a sideways movement through the water, as opposed to being carried sideways by the movement of the water (which I would call "set"). And I have heard references to boats making, for instance, five degrees of leeway.

 

[anorlunda]

I never heard the word "set" used that way. When you are at sea, out of sight of land, how do you tell the difference between sideslip (leeway) and current? The only sure way is to stop the boat dead and measure the velocity. Don't try that in an airplane.

IMO five degrees leeway is wrong. I found this forum thread that used "10 degrees of leeway" but that was challenged in a reply that said that usage was wrong. But, in English, we have no language police, so there can be no wrong answers.

 

[sandy stone]

When you are at sea, out of sight of land, how do you tell the difference between sideslip (leeway) and current?

Actually, I think the traditional way is to look aft, at the angle your wake makes to the centerline of the boat; certainly not very accurate, but still helpful for navigation.

 

[pbuk]

I never heard the word "set" used that way. When you are at sea, out of sight of land, how do you tell the difference between sideslip (leeway) and current?

Actually, I think the traditional way is to look aft, at the angle your wake makes to the centerline of the boat; certainly not very accurate, but still helpful for navigation.

Exactly that, and in practice I have found it accurate to better than ±5° which is similar to the accuracy with which it is possible to steer a boat by compass. So if you are trying to steer a course of 90° in a Northerly breeze and you can see you are making 5° of leeway then you will steer 85° and be confident that your track is 90°±5° (you will of course have allowed for tidal set in calculating the 90° course to steer (CTS)).

IMO five degrees leeway is wrong. I found this forum thread that used "10 degrees of leeway" but that was challenged in a reply that said that usage was wrong. But, in English, we have no language police, so there can be no wrong answers.

No, but we can have answers that are correct by convention, and at least in the British maritime convention '10 degrees of leeway' is correct (although, as mentioned in that thread, rather a lot).