Aileron rigging on a 172P

[aterry1067]

I am currently getting my PPL. Today the CFI and I take a particular aircraft out. The plane just came out of an extensive annual/100hr and mx stated they completely rigged the flight controls. We go up and there is a hard right roll. Flying straight and level, let go of the yoke and we immediately go into a progressive right roll. We are only doing pattern work today, and on first final I am all over the place. There is a 6ish knot crosswind, and it requires full left rudder to bring the nose around to centerline. I land, but it's not pretty. The CFI is critiquing my technique. I ask if he has landed this plane since it came out of annual and he states no. I ask him to perform a landing. He does so, and as we are on roll out he agrees, something isn't right. We get back to chocks and I install the control lock and have a look at the ailerons. The right aileron is about 1/4 to 3/8" below wingtip and flap. Left aileron is flat even with wingtip and flap. It appears to be rigged for a slight left roll (which I assume to be normal), but we are still rolling right.


So.....the question. What is normal aileron rig for 172P? What are the rig limits? Any suggestions or thoughts?


For reference, I have years of experience rigging F-15 and A-10 flight controls. I also have years of experience of rigging F-35 flight controls, but that is simply pushing a button and measuring a surface....about as easy as it gets. I fully understand rigging, rigging bias, hysteresis, etc.

 

[Magman]

I’m suspecting there is more to the story of why all flight controls were re-rigged.

Possibly the right wing heaviness was already present?

Normally the flaps are rigged and ailerons aligned with them.

There are eccentrics on the Aft Spar/Fuselage Attach that allow the trailing edge

of the wing to be moved up or down slightly.

That is how wing heaviness is addressed.


It is possible that the wing was repaired at some point and may not have the

correct amount of twist or “wash-out”.

The SM illustrates a simple method of checking this in the Structural Repair

section.

 

[AggieMike88]

For the curious, here is a video where John Efinger of CessnaRigging.com discusses rigging.

 

[Oldmanb777]

You just gained valuable experience. A plane coming out of that kind of maintenance should be test flown by someone experienced and expecting things to not operate correctly. Second, you flew a plane that wasn't correct and survived. Third, maybe you should have caught this on the preflight, or control check prior to take off. Lots a valuable learning went on there, make the most of it.

 

[Bell206]

So.....the question. What is normal aileron rig for 172P? What are the rig limits? Any suggestions or thoughts?

The limits are in the service manual which can be found online. I trust you brought this to the attention of the mechanic who performed the work? May also want to ask the person who performed/signed off the ops check flight and returned the aircraft to service flight on what they felt on that initial flight.

 

[Dan Thomas]

A broken left rudder bar spring will do this.

Wing heaviness cannot be corrected with aileron rigging. If you rig one aileron down, the aerodynamic load on it pushes it up and forces the other aileron down until they're the same. Nothing is accomplished.

Like Bell206 says, the manual must be followed.

 

[aterry1067]

I’m suspecting there is more to the story of why all flight controls were re-rigged.

Possibly the right wing heaviness was already present?

Normally the flaps are rigged and ailerons aligned with them.

There are eccentrics on the Aft Spar/Fuselage Attach that allow the trailing edge

of the wing to be moved up or down slightly.

That is how wing heaviness is addressed.


It is possible that the wing was repaired at some point and may not have the

correct amount of twist or “wash-out”.

The SM illustrates a simple method of checking this in the Structural Repair

section.

Thanks!!! ["Normally the flaps are rigged and ailerons aligned with them. There are eccentrics on the Aft Spar/Fuselage Attach that allow the trailing edge of the wing to be moved up or down slightly."] That's what I was looking for. I appreciate the information.


And yeah, I believe there is a lot more to the story.


Thanks again!

 

[Jeff Oslick]

IMHO, any plane that just had rigging work done on it should not be first-flown by a student pilot, regardless if there is a CFI next to them.

After we had rigging work done on our plane, I spent at least an hour doing a preflight inspection to be as confident a possible that I wouldn't have a surprise in the air. Same should be true for any annual inspection. I once found an aileron cable pulley rubbing against interior doorpost trim by noticing some unusual friction during a preflight inspection.

 

[bnt83]

Most recent 91.407 flights I have logged:

Cessna 177 post dual Garmin G5 installation.

Cessna 182L Post CGR-30P engine monitor installation.
Cessna 182L Post Dual Garmin G5 installation.
Cessna 182L Post GFC 500 autopilot installation.

 

[aterry1067]

For the curious, here is a video where John Efinger of CessnaRigging.com discusses rigging.

Thanks! Great video!

 

[bnt83]

Some 135 operators use a checklist, any items disturbed on the list automatically requires OCF and it don't matter if the MM doesn't require it because its a company policy.

 

[Jim Carpenter]

If the plane flew straight before the flight control maintenance, I would not mess with the spar attachment eccentric adjustment. That tweak was presumably never touched, and is unlikely to be the cause of the new problem.

 

[Dan Thomas]

I will say it again: a broken left rudder bar spring will do this. It will result in the right rudder bar spring pulling the rudder to the right and causing the right roll. Some pilots never notice the pedal displacement and automatically blame the wing or ailerons.

Proper diagnosis MUST be made before the systems are corrected. Before you fly the thing, make sure the turn coordinator is properly level in the instrument panel. There are slots in the panel for the instrument screws. With a level across the doors sills or seat rails and the airplane jacked as necessary (or a tire deflated a bit) to get it level, the ball should be centered. If not, level that instrument. Take it up, get it flying level and trimmed, and hold the ball centered with the rudder, and hold the wings level with the ailerons. Now let go of the control wheel. If it rolls, you have a wing problem. If it stays level, hold the control wheel and let go of the rudder. If the ball goes off center you have a rudder problem.

If it's the rudder, the first suspect is that spring. The left one gets stretched far more often that the right; it gets stretched every time right rudder is applied, which is in every takeoff and climb. It fatigues and eventually breaks. On high-time airplanes, the anchor bracket on the left tunnel wall gets worn by the spring hook pulling and rocking in it, and the hole tears out. With the left spring failed, the right spring applies right rudder.

Easy to prove. Push the tail down so the nosegear centers the rudder system. If the rudder is off to the right, the spring might be busted. Go open the pilot's door and reach in and pull the left rudder pedal back. It will flop back easily if the spring is gone. Pull the right pedal back for comparison. It should snap forward when released.

One thing the manuals don't mention: Turning the eccentrics at the rear wing spar roots not only moves the spar up and down, it moves it in and out as well. This messes up the flap and aileron cable tensions, so they must be rerigged as well. Aileron rigging is much more complicated than some folks realize, and the manual, again, must be followed. Same with rudder rigging in a Cessna; it starts at the nosewheel, not at the rudder. And the pedals must be clamped as per manual, too, for rigging.

There's a cam on the nosewheel that centers the rudder system. I've seen the rubbing block on the lower torque link so badly worn that it doesn't center when the airplane lifts off, and can hold whatever right rudder was in at liftoff. That now means an airplane that will want to roll right as soon as you release the control wheel.

BTW, the "yoke" (or "yolk" as some call it) is the big control system part hidden behind the panel that connects the control wheels and their shafts to the elevator and aileron systems. A check of the parts manual will confirm this.

 

[aterry1067]

I will say it again: a broken left rudder bar spring will do this. It will result in the right rudder bar spring pulling the rudder to the right and causing the right roll. Some pilots never notice the pedal displacement and automatically blame the wing or ailerons.

Proper diagnosis MUST be made before the systems are corrected. Before you fly the thing, make sure the turn coordinator is properly level in the instrument panel. There are slots in the panel for the instrument screws. With a level across the doors sills or seat rails and the airplane jacked as necessary (or a tire deflated a bit) to get it level, the ball should be centered. If not, level that instrument. Take it up, get it flying level and trimmed, and hold the ball centered with the rudder, and hold the wings level with the ailerons. Now let go of the control wheel. If it rolls, you have a wing problem. If it stays level, hold the control wheel and let go of the rudder. If the ball goes off center you have a rudder problem.

If it's the rudder, the first suspect is that spring. The left one gets stretched far more often that the right; it gets stretched every time right rudder is applied, which is in every takeoff and climb. It fatigues and eventually breaks. On high-time airplanes, the anchor bracket on the left tunnel wall gets worn by the spring hook pulling and rocking in it, and the hole tears out. With the left spring failed, the right spring applies right rudder.

Easy to prove. Push the tail down so the nosegear centers the rudder system. If the rudder is off to the right, the spring might be busted. Go open the pilot's door and reach in and pull the left rudder pedal back. It will flop back easily if the spring is gone. Pull the right pedal back for comparison. It should snap forward when released.

One thing the manuals don't mention: Turning the eccentrics at the rear wing spar roots not only moves the spar up and down, it moves it in and out as well. This messes up the flap and aileron cable tensions, so they must be rerigged as well. Aileron rigging is much more complicated than some folks realize, and the manual, again, must be followed. Same with rudder rigging in a Cessna; it starts at the nosewheel, not at the rudder. And the pedals must be clamped as per manual, too, for rigging.

There's a cam on the nosewheel that centers the rudder system. I've seen the rubbing block on the lower torque link so badly worn that it doesn't center when the airplane lifts off, and can hold whatever right rudder was in at liftoff. That now means an airplane that will want to roll right as soon as you release the control wheel.

BTW, the "yoke" (or "yolk" of the OP) is the big control system part hidden behind the panel that connects the control wheels and their shafts to the elevator and aileron systems. A check of the parts manual will confirm this.

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Thanks! That is all great info. If I ever get a Cessna, I would certainly take this into account. (airplane belongs to a flight school, it's not mine. Sorry for any confusion).

LOL, can you show me where "yolk" is in any of the posts?


I certainly agree that often times during rigging, many folks think they can rig one surface and be done. I don't know how many F-15s I had to re-rig because of other mechanics making this mistake. Changing one surface or actuator required pinning the stick, the PRCA and ARI, and the bellcranks to that surface, at a minimum. It was a short cut to just pin the bellcrank of that surface, rig the control rods to bring the new surface or actuator into rig, and then call it good. A few days later, we would be called out to do it right. What's the old saying?...If we can't find the time to do it right, we will find the time to do it over. I always enjoyed the Phase II inspection on a 15, because that was a full acft rig from stick to surface of every flight control. That was always fun and could be challenging depending on what mx had taken place in the 400 hours since the last Phase II.

That said, I don't see how any mechanic could think they could only change the eccentric cams on the Cessna wing, and not be required to re-rig the rest of the aircraft. But, I am sure it happens. The intent of my OP was simply to ask about the rig process of a Cessna 172 because i was curious. For one, I didn't know about the eccentric cams, but now that I do, it makes sense. It seems that the ailerons are rigged from the flap TE tips, which of course must be rigged correctly prior to aileron rig. Watching the video posted by @AggieMike88 answered a LOT of questions. That guy rigged Harriers...and I thought A-10 ailerons/speed brakes were a headache! LOL. A hat tip to Mr. Effinger.

 

[Magman]

As Dan said the eccentrics are nothing to play with.

If front and rear not turn simultaneously you will tear spar!!

 

[Dan Thomas]

LOL, can you show me where "yolk" is in any of the posts?

Sorry. I saw it in one of the posts or another thread about the same time I read yours. I didn't reply to yours right away so got mixed up somewhat. I AM retired, after all, and hadn't had nearly enough coffee yet when I posted that.

 

[aterry1067]

Sorry. I saw it in one of the posts or another thread about the same time I read yours. I didn't reply to yours right away so got mixed up somewhat. I AM retired, after all, and hadn't had nearly enough coffee yet when I posted that.

No worries, bud. I do the same. Anything I say "pre-coffee" or "post-beer" has to be checked for accuracy.


Again though, thank you for the information and experience. It's valuable and I love learning new stuff!

 

[Southpaw]

I will say it again: a broken left rudder bar spring will do this. It will result in the right rudder bar spring pulling the rudder to the right and causing the right roll. Some pilots never notice the pedal displacement and automatically blame the wing or ailerons.

Proper diagnosis MUST be made before the systems are corrected. Before you fly the thing, make sure the turn coordinator is properly level in the instrument panel. There are slots in the panel for the instrument screws. With a level across the doors sills or seat rails and the airplane jacked as necessary (or a tire deflated a bit) to get it level, the ball should be centered. If not, level that instrument. Take it up, get it flying level and trimmed, and hold the ball centered with the rudder, and hold the wings level with the ailerons. Now let go of the control wheel. If it rolls, you have a wing problem. If it stays level, hold the control wheel and let go of the rudder. If the ball goes off center you have a rudder problem.

If it's the rudder, the first suspect is that spring. The left one gets stretched far more often that the right; it gets stretched every time right rudder is applied, which is in every takeoff and climb. It fatigues and eventually breaks. On high-time airplanes, the anchor bracket on the left tunnel wall gets worn by the spring hook pulling and rocking in it, and the hole tears out. With the left spring failed, the right spring applies right rudder.

Easy to prove. Push the tail down so the nosegear centers the rudder system. If the rudder is off to the right, the spring might be busted. Go open the pilot's door and reach in and pull the left rudder pedal back. It will flop back easily if the spring is gone. Pull the right pedal back for comparison. It should snap forward when released.

One thing the manuals don't mention: Turning the eccentrics at the rear wing spar roots not only moves the spar up and down, it moves it in and out as well. This messes up the flap and aileron cable tensions, so they must be rerigged as well. Aileron rigging is much more complicated than some folks realize, and the manual, again, must be followed. Same with rudder rigging in a Cessna; it starts at the nosewheel, not at the rudder. And the pedals must be clamped as per manual, too, for rigging.

There's a cam on the nosewheel that centers the rudder system. I've seen the rubbing block on the lower torque link so badly worn that it doesn't center when the airplane lifts off, and can hold whatever right rudder was in at liftoff. That now means an airplane that will want to roll right as soon as you release the control wheel.

BTW, the "yoke" (or "yolk" of the OP) is the big control system part hidden behind the panel that connects the control wheels and their shafts to the elevator and aileron systems. A check of the parts manual will confirm this.

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Thank you for that information .
Yesterday I was doing touch and goes and full stop landings at local airport . Traffic was getting a bit heavy so I ventured off to have a look see at the Farm and the son-in-laws Ranch.
I took a couple pictures along the way and had to let go go yoke to hold camera .
The Aircraft kept wanting to roll to right . First time that ever happened, with ball centered I kept having to hold left aileron . Came in for the day ,taxied parallel to front of Hanger.
I noticed the nose wheel was slightly to the right when I did my post flight walk around.
Airport manager and CFI (Same person) came along to help me push it back in to hanger . I mentioned what was going on . He didn't know what to say other than "It's an airplane."
This old 1959 C172 previously would fly hands off when trimmed.
Heading back down today to have a another look and try what what you suggested .
Again ,Thank You Dan for that timely information .