Tolerating an un-airworthy aircraft. Wing drops at stall
 

Australian Flying magazine November-December 2020, published an article by the editor Steve Hitchin where he talks about brushing up his stall recovery skills using a Piper Warrior at Victorian counttry flying school. The article was well written and entertaining until the bit that said "We had deliberately chosen a Piper Warrior with an unrelenting habit of dropping the right wing at the stall. No point in making this easy" wrote the author.

Later in the article his instructor said " This aircraft has a tendency to drop a wing to the right in a stall"

Certification flight tests by the manufacturer's test pilot require the approach to the stall be flown at one knot reduction per second. In other words not a rapid loss of airspeed as might be expected if the nose was initially pulled up too quickly. In addition the maximum wing drop permitted at the point of stall is 15 degrees.

While the article does not record how many degrees of wing drop on that particular Piper Warrior constituted "an unrelenting habit of dropping the right wing at the stall", the description by the author would suggest it was considerably more than 15 degrees.
That being the case, assuming the approach to the stall was correctly flown at one knot per second speed reduction,the amount of reported wing drop would indicate the aircraft was un-airworthy and the maintenance release so endorsed.

Sharp wingdrops at the point of stall could be due to any number of reasons. For example, damage to the wings, pilot faulty technique, icing on the wings or defective or incorrect rigging. The latter is the most likely in this case.
Rogue flying school aircraft with a reputation for a marked wing drop at the point of stall are often not only tolerated by flying school operators but even encouraged to be used for stall training. Perhaps this is what the author implied when he wrote "We had deliberately chosen a Piper Warrior with an unrelenting habit of dropping the right wing in a stall?" Was this defect recorded in the maintenance release? Buckleys..
An unexpected sharp wing drop during hold-off could lead to an accident; particularly if the aircraft is flown by a student pilot.

Makes me think of the C172 "my" flying school used for introducing us to stalling - stalled left. It needed a bit more than full right rudder to stall straight - I was glad I had flown a lot of RC, felt it when lifting it off, and asked the instructor what kind of stalls we were to perform. "What kind of stalls - what do you mean?".
Just traight ahead, I asked. "Would do nicely", he answered, so I knew that he knew, but knew too that he didn't know that I knew..
I managed to perform three almost straight ahead stalls before he noticed the rudder foot. Then we did some without rudder - felt to me as if a church fell on left wing, with a 60 - 70 degrees wing drop. He asked about spinning, but I decided against it, I would rather be sure we could get it ot of spin too.
It was later sold and had a "landing incident" shortly after.
What I would like to know is, is it normal for flying schools to have something bad-mannered for "waking up people"?

I think it is "normal" for cash strapped flying schools to spend minimum $$$ on aircraft maintenance and to leave some inexplicable items like excessive wing drops at stall to " it always has done that". Particularly with aged aircraft with a phone book list of ex owners and a less than clear maintenance history. I am not saying that this is acceptable, but I have experienced this with a few schools, and I think it is more common than it ought to be, at least in Australia.

it's certified under a different and older certification so it's not obliged to meet new requirements. Archers have very benign stall characteristics in comparison to Warriors..but Never, ever spin an Archer but she really fights the stall both power on or power off even in turns

Maybe the student was on the heavier side. I haven’t flown a flight school Cessna, other than a brand new cirrus, that didn’t drop a wing on stall.

On the day, the stall that tries to kill you will not be some genteel church tea party thing, with perfect manners and plenty of notice. It'll probably be at low altitude, in marginal weather while you are craning over your shoulder looking for the threshold. You'll be out of balance, at low power and missing all the cues. And that's when you'll be glad you understood that correcting a wing drop and recovering needs to be instinctive, whichever way the aircraft takes you. If you can't do that, it's probably not the aircraft that's "un-airworthy" but the pilot.

Not that heavy, 73kg - the instructor was heavier

I disagree.
These aircraft still need to meet their original design and certification requirements.
A consistent wing drop is a sign of a crooked or incorrectly repaired or incorrectly rigged aircraft.
That should not be tolerated.
Unfortunately we’re all guilty of being too eager to fly.

The comments section in the log book allow a pilot to write any defects on the flight . Did the article writer consider putting the wing drop in the log book ?
Snagging an airplane allows maintenance the opportunity to correct defects before they become expensive . Checking the rigging takes minutes , looking at the spar box for damage might require some seats to be removed . But it is always better and cheaper to find a problem on the ground than take a problem flying where it will get real expensive.

I wonder how the pilot discovering the fault and not snagging it , might feel if the next pilot came to grief over his inactions to ground the aircraft or at least prevent stall practice until maintenance has a look . I have grounded lots of airplanes . And Ferried wounded birds home to get fixed .One Cessna Caravan I grounded without looking at it when the pilot told me she saw it move when the forklift went past it . Just a small scratch on the elevator, might not have noticed . the small scratch through a ten foot fulcrum did massive damage to the internals . Not visible until the tail cone was removed . That particular plane repair was way cheaper than the insurance premium increases the company would have suffered if we just let it go to the next inspection . Or we might have lost more revenue through fear from a passenger market that is more frightened by death and dismembering than delays .
When in doubt talk to maintenance and write it in the book . Next Pilot might not be as lucky .

I would disagree with your statement - the aircraft can have never been repaired and correctly rigged & still drop a wing.

Care to explain to us how that would aerodynamically happen in a power off straight ahead wings level coordinated stall as per certification requirements?

A wing drop indicates an asymmetry in how the stall propagates from the wing root to the tip.
A generic light SE GA airplane does not experience a full wing stall just a partial wing stall as indicated by aileron effectiveness well into the buffet.

Unless we are flying an elliptical wing planform with rounded wingtips but that’s not what the original poster was asking about.

I had wondered about that when I read the article. But the author did not "suggest it was considerably more than 15 degrees" nor was there an "amount of reported wing drop". Perhaps he would respond to the question in the next issue of the magazine?

The regulation states something like "it must be possible to prevent more than 15 degrees of roll or yaw by the normal use of controls". It refers to the test pilot not an average pilot as other sections of the regulations require. It therefore does not preclude the behaviour that the author described.

Warriors don't normally behave like that so it seems that there is something not right about the airplane anyway so should be rectified, in my opinion.

Yes, my guess too. I have flown a Decathlon which had a couple of degrees of washin instead of nil to a tad of washout which resulted in unacceptable (to me) behaviour at the stall with a sharp, substantial wing drop which I was unable to prevent. It had been a few years since I had flown that particular one and it had behaved normally before. I can only guess as to how it got like that. It didn't take long to fix it - rig it per the service manual.

Some factors also adding to a wing drop are P factor, slipstream and gyroscopic effects at low airspeed....the warrior is ancient so it's not required to meet current FARs. Although I'm not entirely sure about that, to be absolutely sure one would have to check the FARs that are applicable to the airplane in question. I mean the Warrior is ancient.

Really? I would've thought they'd be almost the same.

They better write the Boeing 717 up as un-airworthy then! :E

Aircraft as mentioned have rigging tolerances of the control surfaces - typically +/- 2 degrees. Unlike other types there is no max between the L/H and R/H, so you can be correctly rigged with a 4 degree difference with the ailerons. There can also be the difference in cable tensions between L/H and R/H, this will have a lesser effect but still an effect.

Then you add in the flaps with a tolerance in L/H and R/H rigging - often streamlined to the aileron so adding to the aileron bias.

The nosewheel can act like a rudder, many owners elect to remove the wheel boots which would normally provide an aerodynamic restoring force to align the nose wheel with the slipstream.

I though the PA28 was a 1950s design and certification basis, CAR 3 ?

Yes, the stall requirements in CAR 3 at the amendment status per the Warrior's (I'm guessing the particular model) Type Certificate Data Sheet are pretty much as I stated in my post #12.

There was allegedly a flying school out there somewhere in our big world, that had one of these aircraft that “violently” dropped a wing at the stall and the aircraft was labelled by the boss as not to be used for student stalls and incipient spin entry, however one day, that aircraft was used for such a lesson and one of the flight crew was fatally injured from a spin that wasn’t able to be recovered from.

Be careful out there, I cringe when I hear stories like the one above!

Huh? Please elaborate. I’ve flown both, and I thought them to be the same airframe, just O-320 engine in the Warrior and O-360 in the Archer, a 20-hp difference. I don’t know them to be different, but if they are, I would expect the Archer to be a bit busier at power-on stalls, but no different with power off. I certainly prefer their tapered wing to the earlier Cherokee wing (commonly called a Hershey bar wing, its shape resembling the chocolate bar, and with similar drag characteristics).