Elevator trim mechanism

[Monty1950]

Mock up of elevator trim mechanism.

 

[Aviacs]

Interesting looking. I like the idea.

That said, without a scale, it looks beefier (heavier?) than necessary?
What size is the acme screw?

Would a phenolic pulley be lighter? (& still adequate?)

smt

 

[Monty1950]

The top/bottom plate in the mock up is 1/4” plywood however it will be 3/32” 4130 chromoly. The jack screw is 5/8” but a 1/2” would work fine. The pulley is 2 1/2” and I feel that works best. The connecting rods to the elevator are 1/4” tube.

 

[Aviacs]

Aha!
Seeing the parts like that further understanding dawned.
I was absentmindedly thinking the jack screw was threaded in the bronze bushings & the nut pinned to rise and fall with the screw.

Looking more closely back at the mock-up that would be impossible because the nut is fixed from rotating where the pin "ears" carry a strut to move the horizontal stab up and down.

Hence, all the metal parts could be quite reduced except the necessary threaded area?

thanks for posting!
smt

 

[dcstrng]

That was essentially the set-up in my long-gone IIS project, except that the screwjack was higher in the airframe so the links were only about 4-5" long as I recall (could be my geriatric eyes are fooling me, tho')

 

[Monty1950]

Works well, thanks

 

[kennyw]

I found some pics of Scott's trim mechanism in his old media folders.

I don't know if he machined the jackscrew himself, of scavenged one out of an old Cub. But, I'm told it looks just like a cub's trim system.

I'm gonna go through his build log and see what it says about it.

 

[soneraifred]

Scott’s trim system is a copy of the design i came up with for my airplane. The jackscrew is a piece of 1/2” all-thread rod that is fixed to the stab leading edge with a bent 4130 bracket. The jackscrew moves up and down in a threaded fitting mounted in the pulley which is sandwiched between two bushings. The bushings are mounted in two 4130 triangular plates that are bolted to the original stab mounting bushings in the fuselage. I have drawings if anyone is interested.

 

[[email protected]]

i have used freds design it works great

 

[Val_895]

This is an old thread but wondering if anybody has followed up, finished, of tried out any trim systems mounted in the lower fuse area. As mush as I have tried to fold lil cardboard cutout designs into the upper space none have been spectacular or accessible after install.
I don’t want to cut my fabric, and I like the ease of inspection and maintenance from the lower area after the access plate is off.
Any further developments?

 

[Bil4381]

This is an old thread but wondering if anybody has followed up, finished, of tried out any trim systems mounted in the lower fuse area. As mush as I have tried to fold lil cardboard cutout designs into the upper space none have been spectacular or accessible after install.
I don’t want to cut my fabric, and I like the ease of inspection and maintenance from the lower area after the access plate is off.
Any further developments?

The elevator trim on My Sonerai II is so small that it does not trim the airrcraft for 2 up. My flight advisior insisted that I create a Horizontal Stab trim system. I used a Jabiru flap actuator through a 100/1 bellcrank to reduce the travel. I have a drawing somewhere. Photos attached. It has a POwer on Sw and direction switch. Even at 100/1 if you operate it in flight there is a "bumP" which will likely improve your prayer life. You see 2 vertical rods. One is attachment the other is a damper which eliminates play. BillE

 

[vhbill]

The arrangement below is relatively simple as all you need is a 2 wire cable to connect to the pilot's control column.

The two rod ends on the right are for push rods connected to the leading edge of the horizontal stabilizer. The two connections instead of one to the leading edge provides some lateral stability to the horizontal stabilizer leading edge.

It is all accessible from the removable panels on the sides of the rear fuselage.


The actuator was bought online. It most likely uses a a nylon nut and alloy threaded shaft. So far it has worked without any problems. There is another one in use that has flown over 200h without a problem.

The main risk with the actuator is it sticking or running away due to a switch failure. This has caused loss of control in the past. During the test flight it was found that on this aircraft there was enough elevator control to counteract the actuator at the extreme positions within a limited speed range.



It adds weight to the tail where you don't want it. I moved my lithium battery to the front to compensate. That saved a lot of weight and compensated for the CofG shift due to the actuator and mechanism.

If you plan to cruise at more than about 130kt you may need more nose down trim than shown in the plans.


To do that you may need to lower the rear spar of the Horizontal stabilizer. That is doable, but it is not a simple change.

While this system works on one aircraft, it may not work on another as each aircraft is different. Also changes like this result an aircraft that is different from the plans and has not been test flown before.

 

[Chucker]

Here is an option that actually weighs less than the original fixed installation. The weight savings comes because the original cross tube is removed while the jackscrew is anchored to the leading edge of the vertical tail.

https://www.sonerai.net/threads/chuckers-sonerai-ii-minus.4109/page-2

 

[Val_895]

Here is an option that actually weighs less than the original fixed installation. The weight savings comes because the original cross tube is removed while the jackscrew is anchored to the leading edge of the vertical tail.

https://www.sonerai.net/threads/chuckers-sonerai-ii-minus.4109/page-2

I like the simple design of this and weight savings but again this would require removing the fabric and servicing it would be very difficult as well.

I have been looking at actuators online and they are cheap and plentiful from china. And some are fairly “light-ish”. It really depends on how much load you need. I can’t see using more than 40 lbs to 100lbs trim in level flight. The one listed at 4.5 amps is closer to 800lbs. I think lighter is better. If a stop switch fails. I don’t want to spread my frame. The unit should hold several hundred pounds when stationary as they are used for all manner of items from snow blowers to lounger chairs.
As for safety I think I would add a dampener as well. If the unit failed and fell apart the elevator would not flutter but rather move very slowly top to bottom.

The welding would all have to be able to be tig welded (low heat transfer) and accessible from the cover plate.
I think it can be done. Will play with some card board patterns and see what works.

Thanks for all the ideas.

 

[Chopndrag]

I actually just installed the aeroconversion trim system. Cheap and does the trick until I make a trim tab in my tail for the ray allen system

 

[Chopndrag]

Has anyone made a actual trim tab instead of the jack screw design?

 

[soneraifred]

Elevator trim tabs have been installed several times over the years.

 

[Bil4381]

Has anyone made a actual trim tab instead of the jack screw design?

My Sonerai II LS has both an Elevator trim Tab on the left elevator. Its operated by a cable ina tube. The control lever is below the throttle, left side. of Pilot.
The Tab is maybe 1 foot wide and 3-4" Long. It pivots on a piano hinge. The rub is that when you adjust the travel for solo flight then take a passenger the travel is not enough to trim for a pax. It needs to be bigger, say 4" long by 16-18" " wide. (my guess) That change is a Major modification.
Send me your email of cell number and I can take a photo or 2 and send them.
BillE

 

[Chopndrag]

My Sonerai II LS has both an Elevator trim Tab on the left elevator. Its operated by a cable ina tube. The control lever is below the throttle, left side. of Pilot.
The Tab is maybe 1 foot wide and 3-4" Long. It pivots on a piano hinge. The rub is that when you adjust the travel for solo flight then take a passenger the travel is not enough to trim for a pax. It needs to be bigger, say 4" long by 16-18" " wide. (my guess) That change is a Major modification.
Send me your email of cell number and I can take a photo or 2 and send them.
BillE

I'd like to see your set up even in the Cockpit. [email protected]

 

[Chopndrag]

Scott’s trim system is a copy of the design i came up with for my airplane. The jackscrew is a piece of 1/2” all-thread rod that is fixed to the stab leading edge with a bent 4130 bracket. The jackscrew moves up and down in a threaded fitting mounted in the pulley which is sandwiched between two bushings. The bushings are mounted in two 4130 triangular plates that are bolted to the original stab mounting bushings in the fuselage. I have drawings if anyone is interested.

Can you send me the drawings of yours?