185 horiz trim question

[Tom3holer]

Thank you all for all the help on getting my newly acquired 73 185 up to speed.
The horiz trim wheel was fairly easy to run fore and aft to stops on the ground. We lubed all hinges and the jack screws with a needle. It runs very free now end to end on the ground. In flight if I exceed 150mph or so it becomes VERY difficult to trim nose down. I have read all the posts and understand this is an issue. We did not check the eccentric bushing alignment however.
Could these cause that excessive difficulty in trimming nose down at speed?

Tom

 

[85Mike]

My 185 was the same. At relatively high speed down trim was very stiff. I found that holding slight back pressure on the yoke it made a world of difference applying down trim.

Mike

 

[gntw]

My 185 was the same. At relatively high speed down trim was very stiff. I found that holding slight back pressure on the yoke it made a world of difference applying down trim.

Mike

I have a 77 180 520 3 blade battery on firewall. Moved c of g forward. Flying empty it does that. Put weight in baggage move c of g back way better. Go on a long trip I load aft c of g flys the best . Was a big change when I moved battery on firewall.

 

[OLDCROWE]

I have a 77 180 520 3 blade battery on firewall. Moved c of g forward. Flying empty it does that. Put weight in baggage move c of g back way better. Go on a long trip I load aft c of g flys the best . Was a big change when I moved battery on firewall.

Yep, 25# min and 50 all the way back in the aft baggage is magic.

 

[Tom3holer]

Thanks everyone.
I do fly most of the time alone and have the extended baggage and will try putting my case of oil back there.
Battery is in the back as I was told moving it forward was not a good idea in a 185.

 

[stewartb]

Hmm. You complain that nose down trim is hard and you think weight on the tail will help? All Cessnas fly a little faster with weight aft but it makes them less nimble. No skywagon guy even sat on a short strip and looked for weight to toss in the tail to help his performance. To your trim question? They're all easier to trim nose up than nose down when in flight.

 

[Gordon Misch]

Maybe because more aft CG will reduce the pitch trim and control forces.

 

[mike mcs repair]

also remember the elevator to stabilizer trim cable(clamp on elevator actuator rod) helper spring is relocatable to where it is most helpful to you & your mission

 

[Tom3holer]

It doesn't seem to make sense to me either that more weight in the tail would make it easier to roll in nose down trim which is bringing the stab up for more lift.
I had read somewhere a report where someone weighted the H spar to simulate inflight loads on the stab then readjusted the eccentric bushings to find the "sweet spot".
He said it made a difference since now both jackscrews were taking equal load. That was going to be our next step. Has anyone had experience doing this?

 

[OLDCROWE]

I start trimming forward as I accelerate so once at cruise speed it's just fine tuning and the trim wheel isn't so overloaded. Kind of like leaning in a climb once you figure out what it likes you just work up a routeen and do it, give it a try.

But to Stuart's anti-point about a little ballast, moving the CG aft a bit seems to help balance the trim but it's not equal up to down unless you're mid-speed or less and remember the ballast reduces or comes out with load.

 

[stewartb]

It wasn't an anti-ballast comment. I've loaded stuff in the back to improve cruise speed since I've owned Cessnas, at least when speed is the priority. If short fields are your thing aft loading is not your friend. I was pointing out that the original trim question and the ballast comments were two different topics.

 

[skywagon8a]

If short fields are your thing aft loading is not your friend.

I assume that you are referring to the additional drag of the tail wheel in soft ground?

 

[OLDCROWE]

IMO aft loading and a bit of aft ballast to offset a CG near the forward limit (which in my experience is what you get with a big engine on a 180 and just a front seat load) are two significantly different conditions. If you want to work short a little help with the CG sure helps to both pick up a few knots in cruise but also to help balance the elevator forces so when you get it slow it will fully flare when you're out or near out of trim.

Personally, I think the POH comment to trim neutral on final should be a required plackard!

 

[stewartb]

Data point. My own 180, 0-520 and 86" 3-blade, battery on the firewall, hydraulic tank on the firewall, 29" mains, BBW- Arm is 38.8". If I fly it solo with a totally empty plane and 20 gallons in the tanks the CG is 39.03. If I toss my approx 40# of survival gear and tools back there the CG is 40.4".

 

[Cub junkie]

deleted

 

[hotrod180]

In my 180, it seems like if I am applying back pressure it's harder to turn the trim wheel for nose up-- if I relax the back pressure, it makes it easier. Maybe the same thing the other way, never noticed. .
I think its normal for the trim wheel to get harder to turn at higher speeds-- after all, you're putting more air load on the stabilizer.
Just like the ailerons & elevator get stiffer at high speeds.

 

[Tom3holer]

Yes it is the same for nose down trim; using back pressure will help with the nose down trim a bit.

Thanks again everyone, guess the jackscrew bushing alignment is not a common issue for relief.

 

[Tom3holer]

Update:

We removed the vert fin and rudder and replaced much hardware and tighened the horiz stab right pivot bracket which was quite loose New pivot bolts torqued. Disconnected the jack screws and regreased although they were well lubed. Did weight the LE of the stab and adjust one bushing to match the other. No slop at all now and the flight test showed a stab trim that was MUCH earier to move nose down at speed.

 

[flywhatever]

Thank you all for all the help on getting my newly acquired 73 185 up to speed.
The horiz trim wheel was fairly easy to run fore and aft to stops on the ground. We lubed all hinges and the jack screws with a needle. It runs very free now end to end on the ground. In flight if I exceed 150mph or so it becomes VERY difficult to trim nose down. I have read all the posts and understand this is an issue. We did not check the eccentric bushing alignment however.
Could these cause that excessive difficulty in trimming nose down at speed?

Tom

exceeding 150mph not a bad problem to have...I used to fly 185's up on the glaciers year round, and for descents I would push the airspeed to 140kts, cowflaps closed and power set to hold temps on the engine/no shock cooling for the high speed descent, one time, the nose immediately pitched up as if I immediately ran out of down trim. We changed the grease in the jackscrew bags, one that didn't have a propensity to freeze, never experienced that issue again...something to think about is all...

 

[BC12D-4-85]

One time I had a weird runaway trim in a C-185. On reaching my visual descent point in cruise on floats (~125-130 mph) I rolled in some forward trim. The trim wheel kept turning while calling for nose down all the way to the stop. I cranked it back ok and it never happened again. Unloading the tail elevator down must have let the stab LE rise on it's own.

Gary