Spiraling Slipstream...right rolling tendency?

[flyTotheSky]

Was reading an article online the other day and saw that in addition to the left yawing tendency it produces, it can produce a right rolling tendency about the longitudinal axis.

The only way I can fathom this is if the slipstream is hitting some upper portion of the fuselage before it finally reaches the tail causing it to roll to the right. Still would seem to be negligible to me...

Thoughts?

[tgrayson]

Originally Posted by flyTotheSky

The only way I can fathom this is if the slipstream is hitting some upper portion of the fuselage before it finally reaches the tail causing it to roll to the right. Still would seem to be negligible to me...

This is exactly what happens, but the main culprit actually is a high vertical stabilizer, one mounted well above the longitudinal axis. This has been a problem in some airplanes.

[flyguy]

The slipstream pushes on the left side of the horizontal stabalizer which pushes the tail to the right, and you get left yaw. It also pushes the horizontal stabalizer over and rolls it to the right, and you get right roll.

[moxiepilot]

Originally Posted by flyguy

The slipstream pushes on the left side of the horizontal stabalizer which pushes the tail to the right, and you get left yaw. It also pushes the horizontal stabalizer over and rolls it to the right, and you get right roll.

dont you think it would also be caused due to the yaw, the right wing will speed up producing more lift, hence roll? (think about sweepback - that's where i'm coming from)

[tgrayson]

Originally Posted by moxiepilot

dont you think it would also be caused due to the yaw, the right wing will speed up producing more lift, hence roll? (think about sweepback - that's where i'm coming from)

The roll you mention would be a left roll; the OP is discussing right roll.

[moxiepilot]

Originally Posted by tgrayson

The roll you mention would be a left roll; the OP is discussing right roll.

yes, although not enough coffee is running through me yet that was what i was focusing on. if the right wing speeds up causing left roll, would that offset the left roll on the stabilizer?

[tgrayson]

Originally Posted by moxiepilot

yes, although not enough coffee is running through me yet that was what i was focusing on. if the right wing speeds up causing left roll, would that offset the left roll on the stabilizer?

You mean would the left roll offset the *right* roll on the vertical stabilizer?

In the scenario presented, if the yaw is allowed to happen, then sure, the yawing velocity could very well override the right rolling tendency.

But: once the aircraft is yawed, the right wing stops moving, so that goes away. However, the aircraft is in a yawed condition and the dihedral effect will produce the same effect.

Realistically, though, the pilot stops the yaw with the rudder and the rudder lift can produce a rolling moment as well to the left.

[nosehair]

AARrrggg!! You're gonna rip the airplane apart with all these "opposing" forces! Stoppit !!

[flyguy]

It would depend on the airplane. If it has a very tall stabalizer there would be more moment creating a stronger right rolling force. If the stab is smaller it may not be much force and the accelerating wing might roll it to the left more than the stab rolls to the right. Different designs would have different characteristics. Personally I've never flown an airplane where I felt any discernable right rolling tendency, (accepet for some where the aileron trim was off) but that's probably mostly due to the fact that there are several other left rolling tendencies that if the accelerating wing didn't overcome, the other rolling tendecies certainly would.

[JDP]

Realistically, though, the pilot stops the yaw with the rudder and the rudder lift can produce a rolling moment as well to the left.[/quote]

Could someone further explain the rudder lift and how it produce's a rolling moment, or is it like a two dimensional physics problem where your only looking/thinking about the x-axis and the spiraling slipstream hitting the underside of the rudder?

[nosehair]

Originally Posted by JDP

Could someone further explain the rudder lift and how it produce's a rolling moment, ?

Think of the rudder as a vertical elevator. Right rudder is like down elevator. Increased camber on the left side of rudder increases lift in perpendicular direction of rudder which is left rolling moment.

[JDP]

Crystal Clear now thanks