# What is a rough estimate for a sideslip angle for a Dutch Roll?

I previously asked: Is there a regulatory maximum side slip angle for commercial aircraft?

Apart from a regulatory maximum, can anyone give me a rough value to assume for sideslip angle during a dutch roll? Is it less than 1?

• Does this answer your question? Maximum Side Slip angle for commercial aircraft
– Ralph J
Commented May 1, 2022 at 13:02
• I think the question is ok on basic principles (and not a duplicate) but I'm confused about your units. "1" what? Commented May 2, 2022 at 18:20

It seems like you are starting at the end here. Sideslip angles will be a result of rolling, and will increase, decrease, or stay the same depending on the design, speed, altitude, center of gravity, weight distribution, and (possibly) configuration of the aircraft.

So, starting from your chosen aircraft, it may be best to determine its tendency to Dutch Roll under normal parameters.

Normally, aircraft oscillations stabilize after a few cycles by a process known as "damping". Imagine a spring attached to a board in your hand. Bend it once and it will flip back and forth for a while before it stops.

Do this under water and see if you get even one cycle of oscillation. The drag of the fluid resists motion.

Now take your board out into a hurricane and see what happens. The oscillations become greater and greater because energy input into the spring is greater than the damping forces.

There are many factors involved with Dutch Rolling, but knowledge of maximum slip angles at what speeds would be very useful, lest someone gets heavy on the rudder at 250 knots and overstresses the vertical stabilizer.

• I think the question is fine at least as far as its fundamental philosphy. Presumably the author means a self-sustaining Dutch roll oscillation that is continuing with no pilot input. Presumably for any given aircraft at any given airspeed one could specify the max sideslip angle observed in a typical self-sustaining Dutch roll oscillation, if the aircraft is prone to that sort of thing. Perhaps the results would vary wildly from aircraft to aircraft but-- if so, that observation could be the basis of an answer as well. Commented May 2, 2022 at 18:19
• In the analysis we might find that a "slip angle" (or a roll angle) might reduce Dutch Roll tendency, as aircraft become more spirally unstable when bank angle increases. So, I wonder if coordinating the rudder with the roll rather than trying to fight it is better. Commented May 2, 2022 at 19:09