Rigging issue?

[futr_alaskaflyer]

My 170b has a problem...

When the yoke is held in a neutral position and feet off the pedals it flies straight and level with the ball centered. Both ailerons line up with the trailing edge of the flaps more or less.

Let go of the yoke and the yoke rotates to the left, the left aileron goes up about two inches, right one goes down two inches, and the plane goes into an uncommanded slow left roll. Left to its own devices it continues the roll past 70 degrees. Maybe more but I've never let it go further

Push a little left pedal and it is a beautifully coordinated left turn

My usual A&P and his partner are good at this stuff - one of them owns a 170 and is a member here - and I took it for a second opinion to an IA who has been through the CPA rigging workshop. She checked the usual stuff, zeroed and leveled everything to no avail. Rudder is centered. Adjusted the eccentrics to correct for left wing heavy. STILL no better no worse. Now we are all collectively scratching our heads.

The effect is lessened at slower speeds. Power off or on seems to make no appreciable difference, it seems more an issue of airspeed.

Some other data points to consider: this plane previously flew hands off, or very nearly so. Then the engine was removed and sent for overhaul, the motor mount was removed, inspected,stripped and powder coated and reinstalled along with the engine. And (I know this will be a big aha for some) the left wing was rebuilt and reskinned to address corrosion issues. It was rebuilt on a well-known and well used Cessna jig by someone who forms and reskins a lot of Cessna aluminum. It seems to measure out with the correct 3d twist. The original control surfaces (flap and aileron) were not reskinned and reinstalled as is.

Any thoughts before we start drilling rivets?

[Bruce Fenstermacher]

Richard, my first 170 had a heavy wing. If aileron was not held it would turn. Yes the ailerons would move when the yoke pressure required for level flight was released but it wasn't that much. 2 inches up and down is extreme. How could it do that? It is like there is some pressure pulling in a cable or something.

I can't even remember any airplane that when flown extremely out of trim with rudder, would cause the ailerons to be deflected like that. So I can't imagine an engine alignment issue causing this. And if the engine alignment was not right power changes would change the problem.

It would seem that something has to be acting on the ailerons themselves. Think of an trim tab pushing an aileron. OK you don't have a trim tab but could either aileron be twisted or maybe just the trailing edges or corners bent that are acting like a trim tab.

I know it is not correct procedure but I have a friend who would tweak the corners of his 170B ailerons to effect some trim so I know just bending the corners does make a small effect.

Could it be that now the left wing is correct after repair but a bent aileron which was at one time compensating for a bad wing, is now causing this trim problem.

[GAHorn]

Bruce is on the correct track. Ailerons will "fair" or "streamline" with relative-wind when flown hands-off, regardless of eccentrics or most wings (in-fact, regardless of whether they were in alignment with flaps/tips/etc. while at-rest in the hangar....all that test does is confirm the cable's are equally-tensioned and the bellcranks are properly adjusted. It does/says nothing about the shape of the aileron airfoils and how they will behave in-flight.)
Think about this...they are out there in the relative-wind...which in-turn affects where they reside in-flight. If one is twisted or has an upper-skin not parallel with a lower-skin then it will behave accordingly....and, being physically connected to its opposite, will affect where its opposite will reside.

[futr_alaskaflyer]

Both ailerons are less than perfect but they were less than perfect before too. They look like many with some bent trailing edges from wing covers, small dents etc.

But we will take a closer look. One might have a concavity that could really be adversely affecting the airflow.

[c170b53]

I'm with Bruce with respect to the amount of deflection. The flaps are symmetrical, and equally retracted, the left wing trailing edge is dialed all the way down, the right wing dialed all the way up, both inbd aileron ends meet the flap and the outb have equal gaps at the tips; and you have visible deflection to maintain level flight? Ouch!

[mit]

Would you like to barrow an aileron?

[futr_alaskaflyer]

Would you like to barrow an aileron?

I might take you up on that - would be great to test drive before I "buy."

You aren't using it yet?

I'll call Vicki in the morn.

[mit]

The Right one is off. I just want it back before the snow starts piling up. If the right one doesn't change anything we can pull the Left one off and try that too. It would be another trouble shooting tool. My wing is in the Brooks jig. I can't get my mechanic off the computer!

[futr_alaskaflyer]

The Right one is off. I just want it back before the snow starts piling up. If the right one doesn't change anything we can pull the Left one off and try that too. It would be another trouble shooting tool. My wing is in the Brooks jig. I can't get my mechanic off the computer!

Well, that's where mine was rebuilt too. Keep your fingers crossed Just kidding he does good work and the more people I talk to (in addition to the excellent advice provided above, of course) the more I think the aileron(s) are trashed and causing this phenomenon.

[futr_alaskaflyer]

Update for anyone who is interested: Both ailerons were removed and put on a jig. They measured out correctly but severe "dishing" exists on the underside of the left (less severe on the right )

Tim's were installed and after rigging everything back to book neutral the problem has mostly gone away, though some minor correction is probably needed on the rudder tab and eccentrics to get it perfect. Conclusion? The concavity on the underside of the aileron was most likeley the culprit, causing abnormal airflow over the control surface resulting in left banking.

Next up: repair. Apparently there is a tool out there with prong(s) which are inserted into the ends of the skin corrugations which can then be used to apply downward pressure on the skin from the inside, without having to drill rivets to access it. Anyone ever heard of such an animal?

Beware wing cover bungi tension

[Bruce Fenstermacher]

Apparently there is a tool out there with prong(s) which are inserted into the ends of the skin corrugations which can then be used to apply downward pressure on the skin from the inside, without having to drill rivets to access it. Anyone ever heard of such an animal?

Yes. And I've even attempted to make one but have thus far not produced anything I'm proud off (or that actually worked ).

[futr_alaskaflyer]

I think this company stopped making them. If anyone finds a source, please let me know.

R.A.T. (Rib Alignment Tool) http://www.generalaviationnews.com/2009 ... ol-debuts/

I believe that is the tool. Here's another view of it:

http://www.youtube.com/watch?v=1yHGQzhm ... ata_player

Great idea, though it appears Mr Harris has moved on to other opportunities Maybe I'll kick around the internet some more in search of, but in the meantime we'll probably try the tried and true screwdriver method (carefully!)

[n2582d]

And (I know this will be a big aha for some) the left wing was rebuilt and reskinned to address corrosion issues. It was rebuilt on a well-known and well used Cessna jig by someone who forms and reskins a lot of Cessna aluminum. It seems to measure out with the correct 3d twist. The original control surfaces (flap and aileron) were not reskinned and reinstalled as is.

Any thoughts before we start drilling rivets?

Richard,
It sounds like your problem lay with the ailerons. But it seems strange that your plane flew level hands off before the rebuild using the same ailerons. Any idea why? I thought of your rigging issue when I ran across this old Cessna Service Letter which concerns the landing light on the SkyMaster. How good of a job did they do in rebuilding the landing light area on your plane? Is there any chance the lense cover is sticking up too much?

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[futr_alaskaflyer]

3/16 inch square key stock with one end smoothed nice and round on a grinding wheel, and a large cork bottle stopper with a hole drilled through the center on the other for a handle, has worked pretty darn well along with a hot air gun and a bucket of cold water and a sponge. I used two of these homemade rods, and leapfrogged down the surface two ribs at a time.

In the absence of a tool that allows for leverage on the rods inserted into the end of the ribs such as the red tube part of the RAT above, the trick was putting the trailing edges about 1 inch from the edge of my workbench and using the edge of the bench for the levering action. Of course this is not an option if they are still attached to the plane. As it is things turned out very well.

Tim is getting his ailerons back this weekend and I look forward to getting mine back on and rigged next week.

[futr_alaskaflyer]

Richard,
It sounds like your problem lay with the ailerons. But it seems strange that your plane flew level hands off before the rebuild using the same ailerons. Any idea why? I thought of your rigging issue when I ran across this old Cessna Service Letter which concerns the landing light on the SkyMaster. How good of a job did they do in rebuilding the landing light area on your plane? Is there any chance the lense cover is sticking up too much?

SL66-21.png

SL 66-21A.png

I don't know. Another winter with bungi wing covers? Uncareful handling of the aileron when the wing was being rebuilt? Who knows?

I did look at the landing light assembly - all seems ok there.