CG and spins

[Big Pistons Forever]

Originally Posted by Pilot DAR

I'm going to guess that the "save" was not entirely successful, if the outcome was fatal...

We are evolving into a stage in GA where modifications are more common, and multiple modifications a factor too. It is a sad oversight that mod upon mod(s) are stacked up on airplanes, perhaps in the effort to modernize legacy types, and the inter relationship is overlooked, or poorly considered. Sure, the gross weight increase is STC'd, but was it considered for compliance (spin characteristics) when combined with other mods - like tip fuel tanks (Flint) or extra wing tanks (Monarch)? The now longer range plane, with the gross weight increase, will probably say that the weight above a certain weight must be carried as fuel (for landing weight considerations), but has anyone properly evaluated the changed handling characteristics (spin recovery) at a higher weight, and with fuel weight further away from the C of G (by span, rather than fuselage station)? Might you be flying a multi mod plane, and not be entirely aware of the compliance of the combined mods? The first clue would be: If there is not a flight manual supplement which relates all of the aerodynamic/weight/power mods to the airplane in ONE flight manual supplement, it's likely that you're flying a plane which has not had the combination correctly reviewed together. Each STC tells the installer to consider the relation of each mod to the others, but it is often not done, and if done, not completely done. Your Cessna 210 gets several mods installed together, does the installation shop require that the plane be test spun for confirmation of compliance following multi mods? Rarely, though I have done it for shops following major mods.

When you get in an unmodified certified single engine plane, you know that it has compliant spin recovery characteristics, whether spin approved or not. Once you install more than one mod on it, that assurity of handling characteristic compliance goes way down. The flight manual supplement will be your clue - if it does not describe the compliance of the modified configuration you're flying, beware!

So, though BPF and I do not entirely agree about spin training, I will certainly agree that it should be taught by an aerobatic or spin competent instructor, and treated as a practiced emergency procedure, not something which is "fun", unless aerobatics is your fun, in which case, get trained properly, and go for it. But I do feel that every pilot should be exposed to an incipient spin entry and recovery, just to bring understanding. After that, yes, train avoidance, as long as that training promotes stall recovery by application of nose down elevator (as opposed to adding power) and highlights the need to keep the ball in the middle all the time.



No modern certified and properly rigged airplane will spin if yaw is controlled......

I've flown a few homebuilt types which had a pretty unforgiving stall, I've flown a couple of horribly rigged planes, that would rather spin than stall, no matter how centered the ball is maintained, and I've flown a few antique types with no washout in the wing (DC-3) who have an unforgiving stall. But, yes, generally, keeping the ball in the middle is the best step toward preventing a spin entry. Thereafter, don't accidentally stall it! And, be aware, is the type of flying you're about to do a higher risk? Turns during aerial photography or ground observation at slower speeds, tightening a turn to base or final, or low speed parachute jump runs, where jumpers are going to gang up on the outside of the plane before departing...

Yes obviously keeping the ball centred is good practice at all times but that is not what I was getting at. What is important is that Yaw is controlled after the airplane stalls, which will often require an immediate full rudder input. This is where pilots get into trouble. The airplane unexpectedly stalls and starts to yaw and the pilot freezes. By the time they wake up it is too late as they are probably too close to the ground to recover from the inadvertent spin.

What training has to emphasize is developing the muscle memory so that if the airplane starts to depart controlled flight there is the instinctive push forward on the stick and application of rudder opposing the yaw. I stand by my contention that there are no airplanes that a reader of this forum is likely to fly where this technique will not always avoid a spin entry. However some unforgiving airplanes will give you very little time to intervene so the stall recognition and recovery is especially important.

Finally I would suggest a practical definition of a “spin” is where classic stall recovery control inputs will not recover the airplane and indeed will exacerbate the situation. Only spin recovery inputs will recover the airplane. However I have never seen an airplane that will not recover with a conventional stall recovery technique if the stall recovery inputs are correctly and forcefully applied before the airplane has completed more than 180 degrees of yaw after departing controlled flight.