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Hi am currently trying to run Dutch roll simulations for a proposed 35 seat twin engine turboprop aircraft.

I was just trying to work out what sideslip angle might be appropriate to use. Is there a maximum side slip angle for commercial aircrafts, if so I would like to use it to access the aircrafts performance at that angle. I heard something about 15 degrees.

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    $\begingroup$ Dutch Roll might not involve huge sideslip angles - some of course - are you talking about maximum slip angle that a/c systems permit? Or that a/c can tolerate w/o breaking? Is yaw damper on? What is pilot doing with rudder pedals? Etc- need more info. Or are you asking about a regulation? $\endgroup$ Apr 30, 2022 at 16:14
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    $\begingroup$ @quietflyer yes more talking about regulation $\endgroup$ Apr 30, 2022 at 18:59

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There is no regulatory maximum for side-slip angle. There are requirements that there be sufficient lateral control in an engine out condition.

§ 25.147 Directional and lateral control.

(a) Directional control; general. It must be possible, with the wings level, to yaw into the operative engine and to safely make a reasonably sudden change in heading of up to 15 degrees in the direction of the critical inoperative engine. This must be shown at 1.3 VSR1 for heading changes up to 15 degrees (except that the heading change at which the rudder pedal force is 150 pounds need not be exceeded), and with -

(1) The critical engine inoperative and its propeller in the minimum drag position;

(2) The power required for level flight at 1.3 VSR1, but not more than maximum continuous power;

(3) The most unfavorable center of gravity;

(4) Landing gear retracted;

(5) Flaps in the approach position; and

(6) Maximum landing weight.

So a minimum of 15 degrees is expected in the above conditions.

It also goes on to require (I skipped (b) as it addresses 4 engine a/c);

(c) Lateral control; general. It must be possible to make 20° banked turns, with and against the inoperative engine, from steady flight at a speed equal to 1.3 VSR1, with -

(1) The critical engine inoperative and its propeller (if applicable) in the minimum drag position;

(2) The remaining engines at maximum continuous power;

(3) The most unfavorable center of gravity;

(4) Landing gear

(i) retracted and

(ii) extended;

(5) Flaps in the most favorable climb position; and

(6) Maximum takeoff weight.

Again, with an engine out, the slip angle can be significant.

It's also not unusual to see similar slip angles when de-crabbing during the flare of a crosswind landing.

There are requirements for static lateral-directional stability § 25.177 Static lateral-directional stability. and dynamic stability (including Dutch roll) § 25.181 Dynamic stability..

But all of these are based on the flight characteristics of the aircraft that is being certificated. What you need to model is the aircraft flight characteristics. It will determine what type of Dutch roll behavior the aircraft has. You don't model a Dutch roll and apply it to the aircraft. Different aircraft can have very different Dutch roll modes.

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