Trim wheel ratio reducer

[S Lathrop]

There have been many comments about how sensitive the trim wheel system is to adjustments. There was a drawing a number of years ago for a worm and roller system. If some one were to design a gear reduction system, how much of a reduction would be desirable? Would twice the wheel movement for the same change at the elevator trim flap be correct or something else?

I fly a C180 and I would like my Bearhawk trim to be close to the feel of the C180.

[tailwind]

Attached is a 2:1 reduction gear system that I designed. I do not know how it will function in real life as I have not flown that plane yet. I hope to fly it this spring and will report on it function at that time. It was designed so that if it does not work all that is needed is to remove it and replace the chain with a longer length along with the sprocket and wheel.

[S Lathrop]

I came up with a with a trim wheel and gear reduction for 2:1. I have added a spring ball detent to control the force to move the wheel and lock it at a setting.

I have not been able to upload a picture.

[S Lathrop]

Here is a rendering of the trim wheel with the gear reduction. The wheel is 6" dia. and the width of the wheel and the reduction box is 13/16 ".

[Gerhard Rieger]

Hi all, I gave what you said a lot of thought and came up with the following( pic attached) If it doesn't function as planned, it will be easy to change back to what the plans dictate, Look at it and I'd like to hear what comments good or bad you have. It cost $15,00 to make and with chains complete weigh in at 2 pounds.

[jaredyates]

Is $15 the cost of the raw materials?

[Gerhard Rieger]

Yes, that is for the raw materials, what I like about this is that its simple and not something that can break and let you down.

[S Lathrop]

I see one advantage to what you have done. If you leave the large speocket exposed, you have the option of using that to trim as well.


With the Cessna 180 I fly, re-trimming for a go around or touch and go is a struggle to move the trim fast enough to bring the back plane to trim with full power.

[alaskabearhawk]

Russ Erb was the one that came up with a screw drive for his trim and it's in his CD. I'm looking at potentially using a planetary reduction gearbox from an R/C truck. These things are about indestructible and small. Input one side, output the other. But, I may just install per plans and fly it as-is and put one in later.

[S Lathrop]

Here is a picture of my gear reduction trim wheel setup, installed, and a rendering of what I finally built with the mounting brackets included. This unit reduces the trim wheel movement 33.3% vs. the 50% I originally designed. For perspective, the wheel is 6" diameter and the reduction box is 3.2" x L, 1.25" x W and 0.5" x W. The mounting block is 3/4 by 1.5 stock. I originally had hopped to make something that would mount as Bob had in the drawings but this is what I ended up with instead..

The next trick is to come up with a position indicator for the trim position.

I have a ball detent that runs against the small gear, the one operated by the wheel to give a feel for the amount of movement and to give a positive stop.

[Gavin Chester]

Trim is easy to get used to. But you could do a cable reduction and double the trim wheel movement.

[patrickh99]

This is what a trim system from a C172 looks like installed on the BH. I can't say how it works in flight yet, but it looks like it should work good.
Thanks to Dan R for engineering this.

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