TRIM WHEELS ON A 737 TQ

[manhattan]

Hi everybody.

Does anybody know how the trim wheels on a 737 TQ work? I would like to know why they need to spin so fast, and what this action achieves? I know that it is easy to operate trim from the yoke, but interfacing the actual wheels themselves, would be a lot more authentic. It is difficult to see how a spinning wheel is read by a device that can translate the movement into a trim position?
Those with original aircraft TQ's, must either not activate the wheels, or at least know how to interface them with FS?

Maybe nobody out there bothers with these wheels?

All help appreciated.

TONY Plymouth UK

[metamarty]

The 737 trim system (originating in the 707 trim system) is a system that is directly linked to the horizontal stabilizer. With all power off, you can take the trim wheel and turn it around, and you will in fact move the whole horizontal stabilizer structure in the tail. It is designed to allow a human to operate it and will therefor need a lot of rotations to achieve a minor stabilizer adjustment. It has electric motors to do the heavy lifting for you under normal circumstances.

Next to allowing an operator to turn the wheel, the wheel serves a second purpose: It clearly indicates the pilots when the stabilizer is being adjusted, since this is something that a pilot should know about.

It is possible to recreate this system for a simulator, but you would need a high gear ratio to move a pot meter and have the potmeter control the FS trim directly. A tricky problem here is that most autopilots will fly the plane by trim control and will therefor mess with your pot meter reading. The pot meter should follow the FS trim whenever an external source is writing to it. This will lead to massive up and down trimming which is hard to control. This is why most TQ's will have 'fake' trimewheels that only show trim actions and are not hardlinked to a trim value.

[birdyguy]

Hi everybody.

Does anybody know how the trim wheels on a 737 TQ work? I would like to know why they need to spin so fast, and what this action achieves? I know that it is easy to operate trim from the yoke, but interfacing the actual wheels themselves, would be a lot more authentic. It is difficult to see how a spinning wheel is read by a device that can translate the movement into a trim position?
Those with original aircraft TQ's, must either not activate the wheels, or at least know how to interface them with FS?

Maybe nobody out there bothers with these wheels?

All help appreciated.

TONY Plymouth UK

Hi Manhatton,

On my homebuilt TQ I can adjust the trim . I have no needle showing where the trim is at, I have to refer to the PMDG software for that. But looking at the trim wheel software and moving my trim wheel I can easily adjust it for takeoff. If I'm doing a short hop around the port,or any other flight not using the autopilot, I can adjust the trim using my wheels as well. While flying , I dont need the software , the nose attitude tells me where I am with the trim when I want to use the tq wheels. When on Otto, I just leave it do it's own thing and dont really have any issues with it. I used a set of gears and a pulse switch on each wheel. Off the top of my head, I think the ratio was one turn of the big gear equals four turns of the little gear which in turn equalled one mark on the graduation scale. Some day I may put a needle to show the actual position on the tq, but would be very difficult and I have more projects on the go right now that need my attention.

Metamarty's advice is pretty well spot on. It's very difficult to get the trim to work as the real one. I think there may be motorized tq's out there that will do this, but you're talking big bucks, and for me, I am one of those that have to build with budget restrictions.

All the best

[Westozy]

G'day Manhattan!
I have made the trim wheels fully functional on my TQ including the trim indicators via a rather complex reduction drive. The trim pot is driven by the trim indicator so I will be able to calibrate it accurately to the scale. When I researched the operation I was told that there are 45 turns of full travel from one end of the scale to the other. At full speed they spin pretty close to 100rpm and that is what I have geared my drive motors to do. We have not yet decided whether the Aerosim Solutions TQ will be come a product fulltime but there are three units in production at the moment and one will be offered for sale on completion. If you need a pair of high quality trim wheels we are selling them here - eBay Australia: Buy new & used fashion, electronics & home d The starting bid is only AU$300. I have seven pairs available.

Cheers Gwyn
Aerosim Solutions

[manhattan]

Hi Manhatton,

On my homebuilt TQ I can adjust the trim . I have no needle showing where the trim is at, I have to refer to the PMDG software for that. But looking at the trim wheel software and moving my trim wheel I can easily adjust it for takeoff. If I'm doing a short hop around the port,or any other flight not using the autopilot, I can adjust the trim using my wheels as well. While flying , I dont need the software , the nose attitude tells me where I am with the trim when I want to use the tq wheels. When on Otto, I just leave it do it's own thing and dont really have any issues with it. I used a set of gears and a pulse switch on each wheel. Off the top of my head, I think the ratio was one turn of the big gear equals four turns of the little gear which in turn equalled one mark on the graduation scale. Some day I may put a needle to show the actual position on the tq, but would be very difficult and I have more projects on the go right now that need my attention.

Metamarty's advice is pretty well spot on. It's very difficult to get the trim to work as the real one. I think there may be motorized tq's out there that will do this, but you're talking big bucks, and for me, I am one of those that have to build with budget restrictions.

All the best

Hi Ed.

Thanks for the info on trim wheels. I would be interestd to know about the set of gears and the pulse switch? Could you explain how the gears interact with the trim wheel, and how the pulse switch works? Sorry to seem dim - my technical expertise is limited.

I hope you don't mind me asking. You seem to be very busy.

Regards,

TONY Plymouth UK

[manhattan]

The 737 trim system (originating in the 707 trim system) is a system that is directly linked to the horizontal stabilizer. With all power off, you can take the trim wheel and turn it around, and you will in fact move the whole horizontal stabilizer structure in the tail. It is designed to allow a human to operate it and will therefor need a lot of rotations to achieve a minor stabilizer adjustment. It has electric motors to do the heavy lifting for you under normal circumstances.

Next to allowing an operator to turn the wheel, the wheel serves a second purpose: It clearly indicates the pilots when the stabilizer is being adjusted, since this is something that a pilot should know about.

It is possible to recreate this system for a simulator, but you would need a high gear ratio to move a pot meter and have the potmeter control the FS trim directly. A tricky problem here is that most autopilots will fly the plane by trim control and will therefor mess with your pot meter reading. The pot meter should follow the FS trim whenever an external source is writing to it. This will lead to massive up and down trimming which is hard to control. This is why most TQ's will have 'fake' trimewheels that only show trim actions and are not hardlinked to a trim value.

Hi Metamarty

Thanks for your input. You say that fake trim wheels are used to show trim actions. Can you expand on this a little, to explain how the actions are shown if the wheels are not connected in any way?

Many thanks.

TONY.

[birdyguy]

Hi Ed.

Thanks for the info on trim wheels. I would be interestd to know about the set of gears and the pulse switch? Could you explain how the gears interact with the trim wheel, and how the pulse switch works? Sorry to seem dim - my technical expertise is limited.

I hope you don't mind me asking. You seem to be very busy.

Regards,

TONY Plymouth UK

Hi Tony,

The gears are plastic. The large gear has 58 teeth and a diameter of 60mm. I drilled out the center to fit . The small gear has 18 teeth and a diameter of 20 mm. Look on my website under the throttle section. I have about 7 pictures showing how I set mine up. I have a link to the gear store on my Links page. It's a model railroad company in the UK so you should be able to get them quite handily, The link wont take you directly to the gears, you'll have to monkey about the site until you find them, but they are there.

The pulse switch data can be found on Ian's site COCKPIT BUILDING Components .. Boeing B737NG. This is where I got the idea to use the pulse switches for my trim wheels. Ian's site is so full of information, that you will be a long time leaving it. The pulse switches can be purchased through Mouser. The pulse switch is unique, it works in both directions, which is what allows you to use it for a bi directional function like the trim wheel. I have mine wired to a Bodnar card and then through FSUIPC to talk to PMDM737.

Hope this starts to give you an idea. It's not a perfect setup but it works well enough for me and the cost is minimal.

If you have any other questions, on the trim set up, dont be shy.


PS: The link on my website to the gear wheels no longer works. This one should: Railwayscenics model railway accessories - Plastic gear with 4mm bore centre 18 Tooth - 217-304 - Motors, gears and Accessories - Railwayscenics online model shop