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185 stab trim/CG question

Tom3holer

Tom3holer

MEMBER
Cape Cod
I have had my 185 for just under 2 years now and have learned a ton form the many questions I've posted here and want to say thanks again to all of you.

My IA and I rebuilt the stab last year as it has a bit of slop in it. The trim issue was in play before we rebuilt it. We replaced a bunch of stuff and aligned the stab jack screw bushings. It has no wiggle and trims quite smoothly until the speed get up to around 140mph and higher. In a descent I cannot trim into the yellow as it gets very hard and will start to trim nose up on its own slightly. Trim cable tension was checked and it was fine. Basically aerodynamically it does not want to trim nose down as speed increases. I realize this is a common issue with the 180/185. Had a 58 180 many years ago and do not recall the trim issue to the extent I am having now. I know the 185 is nose heave although I have the battery in the back and carry a 20-25lb tool bag in the back of the extended baggage compartment. It would seem that additional weight in the rear would make the matter worse although there is probably more aerodynamic forces at play than I realize. Have read in posts in the past where some owners report no issues with higher speed nose down trim.
Any thoughts or suggestions would be greatly appreciated.

Tom
 
I find with my 54 180 that just neutralizing the elevator by letting go will make trimming easy. If there is pressure from up or down forces, then the jackscrews don't want to turn and I worry about breaking the little roll pin in the trim wheel.
 
images


put one of these on trim wheel when it wants to run away
 
If I apply back pressure it will make the trim a bit easier but there is a strong tendency to trim back nose up after I release it. As I approach the yellow on the AS indicator the force to trim forward is so much so that I am afraid I will break something. I just can't believe this is normal. Like I said, I have had pilots tell me their trim was fairly easy to move at the higher speeds.
 
never was a problem in my 185, if trim pin breaks reduce power and drop some flaps(I know because it happened to me and scared the crap out of me)
 
Tom3holer said:
If I apply back pressure it will make the trim a bit easier but there is a strong tendency to trim back nose up after I release it. As I approach the yellow on the AS indicator the force to trim forward is so much so that I am afraid I will break something. I just can't believe this is normal. Like I said, I have had pilots tell me their trim was fairly easy to move at the higher speeds.
Click to expand...

does you model have the adjustable helper cable & spring interconnect between front of stabilizer and elevator tube??
 
Mine is a 73 A185F

There was a interconnect for the rudder as it was a seaplane in a previous life but that has been removed being a landplane only now.
Mike, was that interconnect you asked about to help elevator pressure or for stab trim assistance?
 
My trim wheel effort is greater to roll it forward than to roll it back when in high speed cruise but it's not a problem. If I roll it forward it may rebound a half a click but it's easy to feel it come back to a catch point. I don't describe that as the trim wheel rolling back without me moving it. If it did? To the mechanic it would go.

There's a chapter in the Skywagon Service Manual about trim. Here's what the troubleshooting chart says.

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Thank you for the info and we have done most of that. The trim is very easy at 120mph but aIt has it gets up past 140 becomes very hard to trim nose down getting worse with speed.
It is where I feel something might break if I try and trim. I know it had to have been certified and as new could not have behaved like this.
It has the Sportsman cuff and VG's but don't think that had this effect. It must be a binding at higher speeds but we loaded the stab LE with 60 or so lbs in the shop and was able to trim it nose down with relative ease.
 
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Put big tires and a big tailwheel on it. With enough drag the speed thing becomes moot. Trim works better. :)

Maybe you need to stop babying it and just turn the wheel. Unless you're a fan of high forward yoke pressure your adjustment will only be a couple of clicks. Just because it offers resistance doesn't mean there's something wrong with it.
 
stewartb said:
Put big tires and a big tailwheel on it. With enough drag the speed thing becomes moot. Trim works better. :)

Maybe you need to stop babying it and just turn the wheel. Unless you're a fan of high forward yoke pressure your adjustment will only be a couple of clicks. Just because it offers resistance doesn't mean there's something wrong with it.
Click to expand...

What he said. Geeez, going that fast in a 185 isn’t even legal is it?

MTV
 
The issue comes into play when descending. It trims OK up to 145-150 mph at cruise. No, I am not babying it I am afraid I might break the roll pin or something.
 
Tom3holer said:
Mine is a 73 A185F

There was a interconnect for the rudder as it was a seaplane in a previous life but that has been removed being a landplane only now.
Mike, was that interconnect you asked about to help elevator pressure or for stab trim assistance?
Click to expand...

73, you definitely have the adjustable helper cable.. adjust it
 
I sheared a Cessna trim roll pin once. Two weeks on Alaska's North Slope on floats with a filed down nail from a found 50 year old Blazo box in the hole. When the mechanic put in a replacement he put safety wire through the pin's center. Said it might take me longer to break it next time.

Gary
 
BC12D-4-85 said:
I sheared a Cessna trim roll pin once. Two weeks on Alaska's North Slope on floats with a filed down nail from a found 50 year old Blazo box in the hole. When the mechanic put in a replacement he put safety wire through the pin's center. Said it might take me longer to break it next time.

Gary
Click to expand...

we'd buy those pins by the bag from ying-ling
 
Had another pin shear I think going downhill to land. Been some time but probably right. Rolled the trim deal forward and it kept on going....the stabilizer that is while the trim wheel didn't move in my hand. Wierd. Landed ok and got it fixed. Not sure what made the tail screws keep turning some on their own but they did. Always thought electricity would make a better trim system than that goofy wheel.

Gary
 
BC12D-4-85 said:
I sheared a Cessna trim roll pin once. Two weeks on Alaska's North Slope on floats with a filed down nail from a found 50 year old Blazo box in the hole. When the mechanic put in a replacement he put safety wire through the pin's center. Said it might take me longer to break it next time.

Gary
Click to expand...
I had a roll pin fall out of the trim wheel at cruise speed. The stab rapidly went to the full nose up stop. Wild ride which fortunately was close to the airport. Reinstalled the roll pin with safety wire holding it in.
 
The service manual for my 180 (and 185s) specifies that the 2 roll pins in the trim wheel shaft be safety wired. Earlier model pins are supposed to be staked on both ends.
 
stewartb said:
The service manual for my 180 (and 185s) specifies that the 2 roll pins in the trim wheel shaft be safety wired. Earlier model pins are supposed to be staked on both ends.
Click to expand...
That's good. I also had a roll pin fall out of one of the jack screws under the stabilizer on a 180. Both of these airplanes were relatively new and came from the factory without​ safety wire.
 
Gotta love an iPhone. In a cab on the way to the airport in the wee hours and I can open the Skywagon service manual in Files in just a few seconds. Bam!
 
Mike that you for all the suggestions. Are you talking about the elevator down spring? I will have my mech look into that. How does that effect the stab trim. It seems that as you trim nose down it would put more tension on the elevator in a nose down position. In flight pushing nose down actually increases the effort to trim nose down.

One thing I noticed is the trim wheel wanting to move aft when I adjust it nose down seems more noticeable flying in the cold temps. I guess this is due to the ariframe somewhat shrinking causing the cables to have less tension.
 
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There are some spring loaded catches that rub against the trim wheel and add friction to hold it- that is the 'clicking' when you turn the wheel. Sounds like those or the indents in the wheel are wearing. I had that issue at work and that was what they found, and replaced. Problem solved. Your mechanic will hate you by the time he is done I suspect.

Roll pins? Mike is right. We had issues with those all the time.
 
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