C172 RG Retractable Gear System

[Trever Oakes]

Hello everyone!

I am in the middle of commercial, and just about to get my complex endorsement. I have been flying the 172RG. I'm pretty solid with the CS Prop, but the landing gear system is still a little unclear to me. Using the diagram in the systems section of the POH. Can somebody help explain how this system works? I understand the basics of it, but I am a little confused on the specifics (the effect of switches in the system on the different lines, etc.)

 

[dmspilot]

I'm not sure anyone is going to explain it to you from square one without you paying them. Might want to ask more specific questions on what exactly you're confused by.

 

[RyanShort1]

Hello everyone!

I am in the middle of commercial, and just about to get my complex endorsement. I have been flying the 172RG. I'm pretty solid with the CS Prop, but the landing gear system is still a little unclear to me. Using the diagram in the systems section of the POH. Can somebody help explain how this system works? I understand the basics of it, but I am a little confused on the specifics (the effect of switches in the system on the different lines, etc.)

It's basically similar to the Cardinal and the 210 as well (with some differences). Best to get out to the aircraft with the diagram and try to figure out which point does what. Also, you should really get the instructor to let you do a simulated emergency extension.

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[Dan Thomas]

Hello everyone!

I am in the middle of commercial, and just about to get my complex endorsement. I have been flying the 172RG. I'm pretty solid with the CS Prop, but the landing gear system is still a little unclear to me. Using the diagram in the systems section of the POH. Can somebody help explain how this system works? I understand the basics of it, but I am a little confused on the specifics (the effect of switches in the system on the different lines, etc.)

Go here https://www.redskyventures.org/doc/...RG_F177RG_Cardinal_1971-1975_MM_D991-3-13.pdf and scroll to page 5-1. Lots of detailed description and diagrams.

The POH should have a simplified version of that. You have read it, right?

Edit: Wrong manual. Wrong system. See post #6. Sorry. Caffeine deficiency again.

 

[Clip4]

The gear lever is a valve. The gear pump has a switch. When the pressure in the gear system is below the specified PSI, the motor runs. When you move the gear lever, the flow of fluid to the actuator is changed and the changes from up to down. When the gear is down, pressure is restored and the switch turns off the pump. The gear is held up buy pressure. The main gears has a locking mechanism. The nose gear does not have a down lock. 6 switches (3 switches in series for up and 3 for down). indicate the the gear position. A squat switch in the nose gear prevents the gear motor from running when there is weight on the nose wheel and prevent pump operation on the ground. An hand pump is provided for gear extension, but does not work for retraction. The gear warning will sound when the down light is not lit and with the flaps extended to more than 20 degrees or the power is reduced below 14”. There are switches on the flaps and the throttle that make this happen via a control unit. You can test the warning by depressing the gear down light.

 

[Dan Thomas]

The nose gear does not have a down lock.

It does. The actuating scissors go a little past overcenter and a spring holds them there. You never want to rely on hydraulic pressure for downlocks.

Edit: Sorry, everybody. I misread the thread title. I saw 177RG instead of 172RG. The correct manual is here: http://www.aeroelectric.com/Referen...manuals/Cessna_172RG_1980-1985_D2066-1-13.pdf

There are considerable differences in the two systems. The 172RG is similar to the 182RG and shares a lot of design with the 210. The nosegear downlock mechanism is shown on pages 5-68 and 5-77 of the correct manual. It's not an easy thing to understand, and IIRC the 182RG manual had a better layout and description of its operation. The downlock hooks are operated by some fore-aft slop in the hydraulic cylinder rod end that shifts the forward upper ends of the hooks so that they move up and down to lock or unlock to the pegs in the cylinder fork. It works well. Those pegs need checking at annual/100 hour inspections; they have grooves in them for the spring pins that keep them in the fork, and they can crack through that groove. Slamming the nosewheel down hard on landing puts plenty of stress on them. An accident report with a couple of good pictures of the problem: https://www.atsb.gov.au/media/5364274/AO-2015-013 Final.pdf

 

[Clip4]

It does. The actuating scissors go a little past overcenter and a spring holds them there. You never want to rely on hydraulic pressure for downlocks.

Edit: Sorry, everybody. I misread the thread title. I saw 177RG instead of 172RG. The correct manual is here: http://www.aeroelectric.com/Referen...manuals/Cessna_172RG_1980-1985_D2066-1-13.pdf

There are considerable differences in the two systems. The 172RG is similar to the 182RG and shares a lot of design with the 210. The nosegear downlock mechanism is shown on pages 5-68 and 5-77 of the correct manual. It's not an easy thing to understand, and IIRC the 182RG manual had a better layout and description of its operation. The downlock hooks are operated by some fore-aft slop in the hydraulic cylinder rod end that shifts the forward upper ends of the hooks so that they move up and down to lock or unlock to the pegs in the cylinder fork. It works well. Those pegs need checking at annual/100 hour inspections; they have grooves in them for the spring pins that keep them in the fork, and they can crack through that groove. Slamming the nosewheel down hard on landing puts plenty of stress on them. An accident report with a couple of good pictures of the problem: https://www.atsb.gov.au/media/5364274/AO-2015-013 Final.pdf

So if you have a 172rg on jacks gear up, pull the gear motor breaker, turn on the master and select gear down the nose gear doesn’t free fall out?

 

[Dan Thomas]

So if you have a 172rg on jacks gear up, pull the gear motor breaker, turn on the master and select gear down the nose gear doesn’t free fall out?

It will. It's not locked up; it's locked down. Pressure holds all three legs up, and latches hold them all down. Older 210s had uplocks as well. Downlocks are needed to ensure the gear stays extended if the hydraulic pressure fails.