212; You made me spill my coffee.... thanks.
Manadasys... 212, herod and co are quite correct. The inertial and aerodynamic forces that act on an aircraft result in "autorotation" the difference in incipient to developed spin is essentially the axis direction of flight, (and that can be argued) both can be stable or oscillatory (er, incipient is generally not a stable case over any time frame),. The B/A ratio is an expression of the inertial moments on the longitudinal and lateral axis, which affects how cross-coupling will develop in passing. B/A is suggestive of the ease of entry or exit of a spin, and of the impact of a control input to the spin. Supposedly. Weird stuff can happen anyway. In a spin, there are continuous changes in accelerations on all axis, and as the apple dropping showed, that has to take forces to change, those forces come from the autorotative moments of inertia and from drag and lift variations that will either be pro rotation or anti-rotation. Break one of the axis moments will change the spin mode and establish into a recovery. (well, kind of...)
For the B737, that was a new "improved" function for that sim, it was eye-watering to see. the takeaway was that an off-axis entry into a microburst is exciting, it adds to the common or garden initial pitch up, (speed/aoa stability) the yaw component, and that is a blast. None of these are a deal-breaker by themselves, but being ham-fisted, pulling through to stall gives a memorably wild ride, yelps and a face plant (sim freeze after the 1st one) DL did Dallas, and that data shows an off-axis entry, the guys had a lot going on. A probability of entry angle relative to the core will show that the least likely entry is the one we practiced previously, which gives a pitch effect mainly. It is easier to simulate, but it doesn't reinforce the point that if y'all iz wobbling in yaw, respecting the aerodynamic stall is of more than passing interest.
Observed roll rates in excess of control authority suggest its time to lower AOA.... so when the accident data shows 180 deg/sec roll rates (not an uncommon rate in the recovered data) , with up-elevator, it's a given as to what is occurring. your ailerons will give a certain rate, and rudder another, both are non linear functions, rudder effectiveness increases at higher AOA, and lower speeds if a limiter is involved, up to the tail falling off.... ailerons increase in effectiveness as AOA reduces and as speed increases. But at any time, there is a limit to what they can give, and above that, you are having a wild ride from autorotation. [fixed wing thingys]
When that crew came back from coffee, the techs and I showed them the QTG overlay and what we had looked at and recorded in the coffee break. they redid the same entries with a bit more care on pitch control and had a pleasant ride out the other side. The downside was, the IPs got around to avoiding the simulation of off-axis entry, which seemed to be a missed opportunity to get a learning point across. The set up for the IP had a set of entry geometries that seemed to be a good idea.
For helos, autorotation merely indicates that there is a derived torque to the rotor to drive the system. As the books show that is achieved through the magic of relative airflow inflow angles to the blade and happens to give a drive force in the mid-span of the rotor blade, to offset the drag force at the tip and at the root section of the blade. That brings up some wacky twist oddities that are interesting to read about, martin Hollman had a nice graph on that I seem to recall.
Last edited by fdr; 9th Feb 2021 at 02:21.