## Tyre slip angle question

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As I understand it, sideslip is a condition. sideslip angle, on the other hand...

They're really the same thing applied in different contexts. Essentially, both are the angle between the yaw direction vector and the direction of travel. we just typically use slip angle for tires and sideslip angle for aircraft.

In a crosswind landing, an aircraft will be in level flight with respect to roll, but there will be a yaw angle to counteract wind force and prevent drift. As in the diagram JT posted, the aircraft will be oriented at an angle to its direction of travel, similar to a tire in a turn. We can call this sideslip angle.

There is also a technique typically used by glider pilots called "sideslipping". It is performed by crossing the yaw and roll controls and is normally used to shed excess speed/altitude for a landing. In this case in plan view the craft will have a slip angle in that there is an angle between the direction the aircraft is facing and the direction in which it is travelling. The difference is in this case, the aircraft will have a significant amount of roll to increase drag.

I hope we are all clear now and can get back to discussing tyres.
Lycoming

Joined: 25 Aug 2011

hardingfv32 wrote:What is the relationship of side slip to slip angles? Is side slip a subset of slip angles?

Brian

Sideslip angle... slip angle.. same thing in my mind.
Grip is a four letter word.

2 is the new #1.
Jersey Tom

Joined: 29 May 2006
Location: Huntersville, NC

In vehicle dynamics, body side slip angle uses the symbol BETA and is the ratio of lateral to longitudinal velocity at the CG.

The slip angle at any given tyre is the ratio of the lateral to longitudinal velocity at the tyre itself. Knowing BETA (i.e. the lateral and longitudinal velocity at the CG) can be useful in calculating this.

Ben
ubrben

Joined: 28 Feb 2009

The B-52 is crabbing. The net of the crosswind velocity and plane velocity is a velocity parallel to the runway.

Side slipping is a crossed controls (ailerons and rudder) condition that causes the plane to literally slip sideways.

But back to tires, it’s just a matter of definition. Anybody have an authoritative one?
olefud

Joined: 12 Mar 2011

olefud wrote:The B-52 is crabbing. The net of the crosswind velocity and plane velocity is a velocity parallel to the runway.

Yup. But it's not pointed in that direction. That difference... call it a yaw angle, whatever.. is the analog to slip angle.

But back to tires, it’s just a matter of definition. Anybody have an authoritative one?

Have we not hit on this multiple times already? Inverse tangent of lateral velocity over longitudinal velocity in the top view wheel orientation... which in simpler terms, is the angular difference between the orientation of the wheel and its overall velocity vector.

Tire deformation or twist or whatever you want to call is not part of the definition. Period.
Grip is a four letter word.

2 is the new #1.
Jersey Tom

Joined: 29 May 2006
Location: Huntersville, NC

Jersey Tom wrote:...
Yup. But it's not pointed in that direction. That difference... call it a yaw angle, whatever.. is the analog to slip angle.
...

I think what yo'all refer to is called "Planck's angle" in SI-terms?
"Bernoulli is a nine-letter name"
xpensive

Joined: 22 Nov 2008

What made the B52 such a hand full to land? Do any other large aircraft have wheel carriage systems that steer to correct this type of landing issue?

Brian
hardingfv32

Joined: 3 Apr 2011

hardingfv32 wrote:What made the B52 such a hand full to land? Do any other large aircraft have wheel carriage systems that steer to correct this type of landing issue?

Brian

The B-47 may have had a similar system. Now the commercial heavies now pretty much crab through the final approach and kick into alignment with the runway as they're about to set down. I'd guess that it's a matter of gear strength and gross weight - but I'm sure there's more expert knowledge on the specifics.
olefud

Joined: 12 Mar 2011