My Socata Wants to Kill Me!

[subsonicsubic]

Hi,

I own a MS893E. It appears to be a great wee plane but it has some quirks.

At less that 70 KIAS, turning left from base onto final, it suddenly rolls to port, quite violently. This usually coincides with the air operated leading edge slats.

My mechanics think its a rigging/pulley issue. Any ideas?

Best,

SSS

[Jan Olieslagers]

You are the pilot, you are the boss. Plane tries to kill you? => You try to kill the plane. Teach her who is the boss.

Now on a serious note :) : "rigging" is a rather general term, it can mean many things, though usually involving cables. But, for as little as I know about this particular plane type, these slats have neither pulleys nor cables nor rigging; I seem to remember they are controlled only by springs, pushing against the induced drag. Surely you have already checked them for free movement? Added a tad of oil/grease at crucial points, according to maintenance manual? Compared activating forces port/starboard? Checked for birds nests/scorpions/illegal migrants hidden behind the slats?

[subsonicsubic]

Thanks, Jan. The slats are fine. They are linked by a cable and therefore deploy simultaneously. I guess there may be a delay or advance between right and left deployment. I'm usually busy at this stage of the flight so I can't focus in the leading edge devices. If they are deploying at different times, this shouldn't be occurring.

In my feeble mind, if this was the case, the right side would be deploying generating more lift initially.

Thanks for your response.

Best,

SSS

[Jan Olieslagers]

They are linked by a cable Ah, that's new to me.

I guess there may be a delay or advance between right and left deployment. If that be sooth, something must be wrong with the a/m cable. But perhaps there is damping, through springs or such.

Anyway, it seems obvious my little bit of insight is not really adding much... thanks for bearing with me...

[sycamore]

Suggest you try going to altitude and do some straight stalls,power on and off,making sure you are balanced..Check which slats operate first,or together.Is the aircraft in trim,or are you holding a wing up...?Are the u/c fairings `square`...?Possibly got a snake in one wing,fuel balanced,etc....might be an idea to check the ASI...? make right turn only...!

[BoeingBoy]

Whilst my thoughts would turn to rigging initially I would also want to conduct a full set of stall checks at altitude including approach configuration replicating that you have set up on the problem turns.
For the left wing to drop it must be losing lift in comparison to the right which could either be early deployment of the right slats, or late deployment of the left. If the rigging is set correctly the only other way of producing this would be out of balance flying, slipping into or skidding out of the turn. Whilst most people regard nose wheel spam cans as not needing rudder I find it quite the opposite. The rudder should be in use in all turns and to assist maintenance of heading in straight flight.

Are you perhaps introducing too much rudder into the turn? Or not using any when it's actually needed? I have a colleague who's concentration and absorbance into the approach see's him at almost full left rudder by the time we get to short final. I could do with a pin to reach over and prod his thigh to release it.

If you have a friendly instructor to hand maybe an hour spent exploring the aircraft and your handling might reveal results. You could count it towards your SEP validation.

Hope you find the answer anyway. Good Luck.

[Ultranomad]

SSS, just to check, does this wing drop occur when the ball is centred? The situation you describe looks like a skidding turn, and it's easy to acquire a bad habit of asymmetric leg work, when the ball is always shifted to one side, or when you centre the ball correctly in the right turns but not in the left ones.
Here (https://www.boldmethod.com/learn-to-fly/aerodynamics/slip-skid-stall/) is a detailed article on the subject.

[rjtjrt]

Base to final turn, slats extend and un-commanded roll.

I wonder if we talking about a base to final turn STALL.
As suggested above, maybe go to altitude with an experienced instructor, and see how aircraft reacts in same circumstances. Look at the skid ball when it all happens.

[Pilot DAR]

Certified GA aircraft will have met a design requirement similar to or as this:

Sec. 23.203

Stall characteristics.

(a) For level wing stalls--
(1) For an airplane with independently controlled rolling and directional controls, it must be possible to produce and to correct roll by unreversed use of the rolling control and to produce and correct yaw by unreversed use of the directional control, up to the time the airplane pitches in the maneuver prescribed in Sec. 23.201(b);
(2) For an airplane with interconnected lateral and directional controls (two control), for an airplane with only one of these controls, it must be possible to produce and correct roll by unreversed use of the rolling control without producing excessive yaw, up to the time the airplane pitches in the manuever prescribed in Sec. 23.201(b); and
(3) During the recovery part of the manuever prescribed in Sec. 23.201(b), it must be possible to prevent more than 15 degrees of roll or yaw by the normal use of the controls.
(b) For turning flight stalls, when stalled during a coordinated turn with 30 degrees of bank, 75 percent maximum continuous power on each engine, and flaps and landing gear retracted, it must be possible to regain normal level flight without excessive loss of altitude or uncontrollable rolling or spinning tendencies.
(c) For limited elevator control stalls, it must be possible, when stalled from an excessive climb attitude, to recover without exceeding airspeed or acceleration limits.

Note, in particular, point 3. This is for power off stalls, power on, will introduce torque, which will require extra attention to rudder use. Without applying unusual pilot skill and attention, this should be achievable. If you're having trouble making the plane stay within these limits, and you're applying proper skill and technique, you should be looking for a rigging error with the plane. There will be rigging adjustments possible, though for that plane I don't know what they are. It would be common for a rigging error to appear as a cruise flight problem as well, but not always. Following a rigging adjustment, a test flight with stalls will be required to verify.

You should be comfortable stalling - well, all pilots should - but particularly for this testing. If your plane is mis-rigged, then stalls at altitude will be great practice for you! Remeber, when you have planned stalls at suitably high altitudes, it is not necessary to minimize altitude loss during recovery, let it descend, and build a little speed, then recover, you're not in a hurry. In a stall, or incipient spin recovery, the nose pointing down is good - flat is bad, let the nose go down.

I have maintenance check flown many planes with either known, or I found stall handling deficiencies. It's not great that they get this way, but that's why we check. Every plane for which I have flown a post maintenance check flight, I have stalled several times, just to confirm handling. I have found some horrendous handling defects, one in a brand new (3 hours TTSN) plane - that was a manufacturing defect, and failure to detect during production/acceptance test flying. The plane spun violently, no matter how precisely it was stalled. In that case, I found and reported the defect. The owner's pilot acknowledged it, after flying himself, and then before returning the aircraft to the manufacturer for rectification, killed himself and another person in a stall spin after takeoff. The "evidence" was destroyed, so only my report remained to prompt the investigation. Stall handling defects should be corrected without delay. Though you can compensate for stall defects, when you most need the plane to behave, it could let you down badly.

[Vilters]

I have many hrs in Socata's.

Normally these slats come out pretty gently if all rollers and guides are properly lubricated.
We could fly all day with the slats gently moving in intermediate positions, just by changing airspeed by a knot or 2.
During normal operations they are completely out long before the stall happens, even in banking.

My guess :
Check the slats for FREE movement and listen to any abnormal noise from the guides, rollers or interconnecting system.
Disassemble and grease properly, and re-check the torque values of the rollers bolts. The rollers MUST roll freely.

What can happen with these older aircraft.
Some of the tubes wear off and have tread marks (grooves) in them where the rollers are. => Check, cross check and triple check. => The tube you are looking for is about 1inch in diameter.
Most of these older planes have wear marks and if the tubes are not replaced in time they "can" be the reason of the binding, and the slats coming out too late.

[Vilters]

What I see in this video would be a reason for inspection for full free movement and proper greasing..
https://www.youtube.com/watch?v=zSzXOpG52VY

[piperboy84]

I’d flog it and get something with more benign stall characteristics, that base to final uncommanded roll could be a killer, no point trying to be a test pilot or not having full confidence in your machine.

[subsonicsubic]

Thanks for all the replies. I'm going to investigate further in approach configuration at altitude. I'll also pay closer attention to my inputs, especially when turning final, however, I'm certain it's aircraft-related as I haven't had the issue with another 893 I've flown.

Best,

SSS

[Piper.Classique]

I've done a fair bit of aerotowing in rallyes. This is very odd behaviour for the type. I think I would also do some careful measurement of the general wing rigging and aileron, rudder and flap deflections, and look at the aircraft's accident history. Don't just leap to the conclusion it's the slats. Sounds like something is twisted.

[IFollowRoads]

Well it's French, and you're (presumably) not, so it is either going to try to kill you or surrender:)

[subsonicsubic]

I've done a fair bit of aerotowing in rallyes. This is very odd behaviour for the type. I think I would also do some careful measurement of the general wing rigging and aileron, rudder and flap deflections, and look at the aircraft's accident history. Don't just leap to the conclusion it's the slats. Sounds like something is twisted.

Thanks, PC. It's good to know its not common of the type. I'm going to ask my guys to pull the whole rigging, and slats apart, clean, relubricate etc. I have stalled the aircraft and the stall characteristics were very benign.

Thanks for your input. I've just bought the plane and only put a few hours on her. Out of interest, did you often conduct stall training in the approach configuration?

Best,

SSS

[DaveUnwin]

I must second Piper.Classique. I've also got a reasonable amount of time in Rallyes, again usually aerotowing. Its one of the most benign aeroplanes ever built, which is why its sometimes referred to as the 'Tin Parachute'. Something is definitely not right with yours, I'd carefully and with reference to the maintenance manual check and measure every angle, deflection etc before flying it again.

[N707ZS]

Think back in the mid 80s in the UK one of these aircraft had a fatality due to I think only one side of the slats deploying. Hong Kong must be a good place for corrosion and these aircraft sufferer seriously from it inside the wings were you cannot see, if I remember. Sorry 80s seems a long time ago.

[Fl1ingfrog]

The only way of satisfying the condition of the slats is following a full inspection of them of course. I'm not sure from what you say if the engineers have done this.

You say the slats deploy during the turn at: "less than 70 kts" what do you mean by that? The slats should not be activating at speeds around seventy knots.?

I would not expect the slats to deploy until approaching the stall. The slats are aerodynamic and activated by the angle of attack. They are a fantastic and reliable indicator of the approach to the stall. The wing drop to the left during a turn to the left is symptomatic of a stall. HAVE THE ASI CHECKED BEFORE YOU FLY AGAIN, this is quick and simple check for the engineers to perform and could save your life.

[Piper.Classique]

Hi, subsonicsubic. I never taught anyone to fly on a rallye, but yes, i did stall them in the approach configuration. Well, I got them to mush down. Never ever got a wing drop without being very proactive with the rudder, and even then it was reluctant to give any sort of break.
The slats extend on a normal approach. Quite a long way off the stall, such as it is.

[Fl1ingfrog]

I must confess that it is a long time since I last flew any of this series of aircraft but there was a time when I flew them regularly including instructing on them. From memory I wouldn't expect the slats to deploy much above 55 kts, certainly not when turning onto final at speeds close to 70 kts, why would they need to. The aircraft ASI should be checked in the first instance in my view. An over reading ASI is not uncommon.

[subsonicsubic]

I must confess that it is a long time since I last flew any of this series of aircraft but there was a time when I flew them regularly including instructing on them. From memory I wouldn't expect the slats to deploy much above 55 kts, certainly not when turning onto final at speeds close to 70 kts, why would they need to. The aircraft ASI should be checked in the first instance in my view. An over reading ASI is not uncommon.

Thank you for your input and concern. I'm going to have the ASI checked immediately.

Best,

SSS

[nonsense]

Can you reproduce the behaviour at a safe altitude?
If so, can you rig a pair of cameras, such as GoPros to see what the slats on each wing are doing, as per the video in an earlier post?
If the cameras don't have audio you would need a synchronising signal to align the two videos in time such as a simple camera flash illuminating the cockpit interior fired off before and after the events you're interested in.
This way you can determine whether there is any uneven movement or, more importantly, asymmetrical operation of the slats.
If you're really keen, you could film either the cockpit controls or the rudder (ailerons already being in view of a camera filming the slats) to check for unconsious/inadvertant control inputs. Mind you, I'm not sure where you would put a camera to see the rudder from a Socata cockpit!

Suggest you try going to altitude and do some straight stalls,power on and off,making sure you are balanced..Check which slats operate first,or together. Is the aircraft in trim,or are you holding a wing up...?Are the u/c fairings `square`...?Possibly got a snake in one wing,fuel balanced,etc....might be an idea to check the ASI...? make right turn only...!

Obviously if you can assess the slat synchronisation visually, without cameras, do that first!

[BackPacker]

Oh, and obviously, while you are investigating this issue, DO NOT let yourself get into the same situation as before. So make sure the aircraft is fully settled in the approach configuration (slats extended, flaps extended, power properly set for flight in that envelope) before you descend below the altitude from which you can safely recover from a wing drop. If at all possible, try to avoid having to make turns once below that altitude, so try to fly a long final, traffic permitting. An ILS-like profile, where you are in the landing configuration and at a reasonable approach speed, 6 nm/2000' out, would be ideal.

[DaveUnwin]

I'm not sure I see the relevance of being at 2000ft and 6nm from the threshold in a Rallye. In fact, it seems like a very poor idea, as with slats out, flaps down and any sort of headwind you could be on final for about eight minutes!

[treadigraph]

Legend has it that ace French test pilot Maurice Seree once got a Rallye to go backwards at a particularly windy Biggin Air Fair...

[DaveUnwin]

That sounds perfectly plausible to me Treaders!

[subsonicsubic]

That sounds perfectly plausible to me Treaders!
It's my first plane guys. I know she's not a rocket ship but I'm proud of her despite her issues. Be sensitive ;)

[treadigraph]

They are lovely aeroplanes. You have time to watch the world go by underneath. I had a flight in one many years ago and have a mutual acquaintance with the owner of one of the older examples on the UK register - hoping for a ride, it's an old friend from my spotting and spotty school days!

Hope you sort the slats out without much bother.

[Piper.Classique]

They are very good aeroplanes. Rugged, good visibility, great load carriers and forgive much. Even their best friend wouldn't accuse them off being fast or light on the controls. BTW, slats extend around 110 kph. I've usually got full flap and engine to idle by then. It will probably make a slight difference to slat extension speed but I've never bothered to look. Do your own conversion to your preferred units. Then just fly enough nose up that they don't retract again until you are ready to round out. Close your eyes and pull hard. Return for the next glider while opening the canopy for a breath of air, setting flaps to half and doing whatever you need to with the fiddly bits.
maybe don't do that if it's not flying right though.....
Seriously, if it rolls into a turn at 70 knots something is very wrong. Where are you based? I fancy a bit of a cross country with the not a Cub.

[subsonicsubic]

They are very good aeroplanes. Rugged, good visibility, great load carriers and forgive much. Even their best friend wouldn't accuse them off being fast or light on the controls. BTW, slats extend around 110 kph. I've usually got full flap and engine to idle by then. It will probably make a slight difference to slat extension speed but I've never bothered to look. Do your own conversion to your preferred units. Then just fly enough nose up that they don't retract again until you are ready to round out. Close your eyes and pull hard. Return for the next glider while opening the canopy for a breath of air, setting flaps to half and doing whatever you need to with the fiddly bits.
maybe don't do that if it's not flying right though.....
Seriously, if it rolls into a turn at 70 knots something is very wrong. Where are you based? I fancy a bit of a cross country with the not a Cub.
Dear PC. Based in HK It's a great place to aviate. I'm amazed at the helpful contributions to my initial post from your good self and fellow GA pilots. If you are ever down and South East, pls. drop me a PM. Best, SSS

[Fly Aiprt]

The only way of satisfying the condition of the slats is following a full inspection of them of course. I'm not sure from what you say if the engineers have done this.

You say the slats deploy during the turn at: "less than 70 kts" what do you mean by that? The slats should not be activating at speeds around seventy knots.?

I would not expect the slats to deploy until approaching the stall. The slats are aerodynamic and activated by the angle of attack. They are a fantastic and reliable indicator of the approach to the stall. The wing drop to the left during a turn to the left is symptomatic of a stall. HAVE THE ASI CHECKED BEFORE YOU FLY AGAIN, this is quick and simple check for the engineers to perform and could save your life.

I would agree 100% with the above.
I logged lots of flight time on type, both flying and instructing, and the stall characteristics are quite benign. Nice safe draggy little airplane. Very good for short landings.
BTW, according to the flight manual, you should not turn final much under 70 kt.

The slats usually open in short final.
Not sure I can post pictures or links to the flight manual

[subsonicsubic]

I would agree 100% with the above.
I logged lots of flight time on type, both flying and instructing, and the stall characteristics are quite benign. Nice safe draggy little airplane. Very good for short landings.
BTW, according to the flight manual, you should not turn final much under 70 kt.

The slats usually open in short final.
Not sure I can post pictures or links to the flight manual
Yes. My POH says turn final @ 70. I'll post here when I know more. Thanks, everyone.

[Piper.Classique]

70 knots for the final turn sounds right for max weight. A bit less solo and half tanks. Should be nowhere near the stall at that, so I'm coming round to the idea of an asi problem. Though I would definitely look for something bent as well, as they are (should be) very docile at the stall. What does the attitude look like?: And is the stick close to the back stop? Hong Kong is a wee bit far to come and take a look, sorry.