Question for my 180/185 flyers with STOL modifications. I recently purchased a 1966 A185E. It came with the MASA LE cuffs and the full Micro VG’s on the wings, and Vert/Horiz. stabilizers. Both appear correctly installed. Everything else aerodynamically is Cessna stock. At speeds around approximately 130 knots and above the trim starts to get progressively harder to trim nose down. This has been true from day-one of my ownership (2021). We have removed the stabilizer and fin for the AD, replaced all hardware, overhauled both trim actuators, adjusted tensions, cleaned, inspected, lubed everywhere, and inspected for correct parts/installations/adjustments, etc. We can duplicate this issue on the ground by loading the LE of the Horiz. Stabilizer. My AP/IA suspects that the VG’s on the lower surface of the TE of the Horiz. Stabilizer are putting ‘non-factory’ aerodynamic loads on the stabilizer, and causing the trim issue. Anyone else having this ‘phenomena?’

My Skywagon does not have VG's but I had the same issue you did with trim binding at higher airspeeds.

I installed new brackets, chains, jackscrew actuators, and similar steps you've taken, none of it worked.

The fix ended up being fixing the bushings in the horizontal attach pivots. Kenmore air did fix on it and made it great again.

Did the bolts attaching the stab to the jack screws come in without the least need of lifting or pushing down on the stab?
They should slide in easy.
Surprising how uneven load on jack screws can create the problem you describe.

Less tension on the cables can sometimes also help.

[email protected] wrote:Did the bolts attaching the stab to the jack screws come in without the least need of lifting or pushing down on the stab?
They should slide in easy.
Surprising how uneven load on jack screws can create the problem you describe.

Less tension on the cables can sometimes also help.

This^^^

Those eccentric bushings at the top of the jackscrews will only absorb slight differences in screw height. Those bolts need to just slide in during installation. Easy to get them off half a turn.

I’d be very surprised to see the VGs have an appreciable impact on stabilizer movement.


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I agree on the jack screw assessment. If VGs caused a problem it would show on all the 180s that have them, and ive never heard of them causing such an issue.

Before you start chasing this down, you might have an experienced Skywagon pilot fly your airplane. The amount of force normally required in a Skywagon would be scary in just about anything else. The trick is to trim in anticipation of leveling off, rather than in reaction to it.

The fact that you can reproduce it on the ground seems like maybe something really is wrong. But there’s a chance that everything is normal.

I had similar concerns and experience as mine is the only I have flown. How much load are you applying? A little push probably a problem, alot of force probably not. Assuming you've checked the trim wheel, roll pin, detents, etc, I think you've covered it all. It should move freely stop to stop on the ground. I use a quick burst of back pressure on the yoke with each few clicks forward before leveling off. You are probably also light. They are made to be loaded so put weight in the baggage area and you should find it moves easier and cruises a little faster as you take some of the negative lift burden off the horizontal. Mine got quite a bit better when setting trim cable tension to 24 lbs and some tools back there when not hauling. A lot of float planes are probably going around loose because they don't see the speeds for this to be noticeable. Any engineers here to speculate on VG effect?

Stu makes an excellent point all.

MW

I spent countless hours trying to correct very stiff (almost binding) trim down at cruise speed in a Cessna 180J (without VGs). At lower speeds the trim was easy to move. Replaced with McFarlane jackscrews, lubed with correct grease as specified in service manual, checked cable tensions and new eccentric bushings (these are forward at jackscrew attachment). Did on-the-ground testing using milk jugs filled with water placed on along horizontal stabilizer spar which worked really well to reproduce the problem. These efforts did improve trim operation at cruise but did not fully resolve to my satisfaction. I've since learned this can be caused by worn hing bushings as @nickelb reported above and if I were doing this again I would replace these bushings first if other components such as jackscrews, cable, chain, sprockets appear healthy upon inspection. Would like to learn exactly how worn hing bushings cause this trim problem. Does busing wear lead to misalignment that causes unequal load on the jackscrews or something else?

Man, don’t you guys get nosebleeds going that fast?
You obviously need bigger tires, skis and/or floats.

MTV

Maybe a chance someone worked on the Jack screws and they aren’t. I bet one is half a turn off.

VG's have no effect on the wing load at cruise. VG's only create turbulence not he wing at slow speed and high AOA to prevent boundary layer separation. They would not have any effect whatsoever on the amount of force required to trim at higher cruise speeds.

MW

flybaker family wrote:Question for my 180/185 flyers with STOL modifications. I recently purchased a 1966 A185E. It came with the MASA LE cuffs and the full Micro VG’s on the wings, and Vert/Horiz. stabilizers. Both appear correctly installed. Everything else aerodynamically is Cessna stock. At speeds around approximately 130 knots and above the trim starts to get progressively harder to trim nose down. This has been true from day-one of my ownership (2021). We have removed the stabilizer and fin for the AD, replaced all hardware, overhauled both trim actuators, adjusted tensions, cleaned, inspected, lubed everywhere, and inspected for correct parts/installations/adjustments, etc. We can duplicate this issue on the ground by loading the LE of the Horiz. Stabilizer. My AP/IA suspects that the VG’s on the lower surface of the TE of the Horiz. Stabilizer are putting ‘non-factory’ aerodynamic loads on the stabilizer, and causing the trim issue. Anyone else having this ‘phenomena?’

Just curious but how much time do you have in 180/185? Seems about normal to have a more resistance trimming at higher IAS regardless of VG's and or other modifications. Just asking so we can help you discern your issue better.

MW

Skywagons are for manly men and girls with admirable strength. The trim wheel is just heavy. Staying ahead of the airplane with inputs helps. Start trimming just before you level off in the climb. Just before levelling off in the descent. You’ll learn where the trim needs to be for any given configuration and speed and know to dial it in as the airplane settles into the commanded pitch and speed. This will lessen the required force considerably. Can’t say I’ve got it 100% figured out, but I’m trying, and it seems to be getting easier.

A little bit of back pressure will take a lot of the aerodynamic load off adding forward trim at cruise, I find. Worth a try if everything else checks out OK.

JohnH and I both ran into the same issue and presented notes on bushings if you read above posts.