Question about gear up/down indications

[Ragsf15e]

Hello, 

I have a 1968 M20F that was modified with electric gear at the factory in 1968.  It has 3 gear indications - a green light and a red light on the panel, and the green "gear down" indicator on the floor between the seats.  

 

What exactly do these mean?  If the green light is on, are all 3 gear down - i.e. is there a squat switch on all 3 gear and the light doesn't come on unless they are all good?  Is there a switch on just one gear and they are all assumed down if the one gear is good?

 

What about the red light?  It's on when I pull up the gear... does that mean all my gear are up and the nose gear doors are closed?

 

I'm just curious so that I'm more ready to deal with any faulty indications or problems before they happen.

 

Thanks,

Rags

[cbarry]

Red light usually means "gear unsafe"--meaning the gear is not at either stop point (fully retracted or fully extended). A green light/lights usually means "gear safe"--meaning gear is extended. If I'm not mistaken, since all three gear are activated by the same system/gear motor, the indicator switch for the lights is on the activation tube behind the gear actuator/motor. Also, the indicator in the floor works on the same principle.

[cliffy]

Is there nothing describing your gear system in your Pilot Hand Book?

[Ragsf15e]

Yep, I read through the 1968 POH and the gear indications are slightly different than I'm use to in the more "modern" aircraft I fly...  The red light in the M20F is on continuously when the gear is retracted.  The green light is on when the gear is down and locked.

 

I guess my question is more about where the sensor is for these indications?  I realize the gear are mechanically linked, but is there any failure mode that would have a green indication when all 3 weren't completely down?  Is the green indication on only 1 gear and it assumes the others?

 

According to the manual, the floor indication works on the same principle as the green light, so it indicates the same thing.

 

Thanks,

Rags

[tony]

The light on the floor is a plastic thing that is attached to a bar that shows the position of the gear mechanism or carraige .  At night a light that shines through the plastic giving  you a red or green indicator. 

 

The green and red lights on the instrument panel each are a separate bulb which are illuminated by two limit switches that indicates the end of travel of the actuator. They are not on any one gear.

 

Red light does not mean gear unsafe, it means its up and stowed.  Green light means the gear is down.  There are no switches for the doors or the position of each gear. 

 

The next annual when the belly is off, crawl under there and go find the stuff I described. 

 

This is an almost 50 year old design, nothing modern under there. Hope that helps. 

[cbarry]

If your craft has a one piece belly panel, it's very educational to drop the panel and take a look for yourself. If it doesn't have the one piece panel, then you should still be able to pull enough panels to still get a good look at the mechanism. If the "green" light switch were to stick in the closed circuit/on position (with the gear retracted) then you would have a false indication--thus the reason for the purely mechanical floor indicator (the only electrical switch for the floor is for the light that illuminates the "window"). The system has "one for all" indicator meaning that all gear is down or up.

[MB65E]

In the floor boards access thru the belly, you"ll find 2 push button switches one for up and one for down limits. ( I would not say micro switches) The switches are activated by a rod with stops on it. About 4-6 wires on each of them that go to the relays that are also next to the gear motor. It's the mechanical positioning of the rod that moves the switch and sends voltage to the lights. It's a bit crude, and there could be a potential for incorrectly positioned stops, bends or brakes in the rods, and failure of wiring, switches or bulbs... The indicator on the floor is there to make sure the main torque tube for the gear rods moves correctly. Rigging is not to be taken lightly! I've pulled all the bent hardware out of ours and have replaced many parts in the last 2 years that were incorrect. It sounds like your system is working normally...

Best,

-Matt

[cbarry]

Tony, the red light can mean the gear is "unsafe"--at least on the "F" model and the "S" models I've owned. I'm sure you are correct on the prior to '74 model being discussed here.

[tony]

Tony, the red light can mean the gear is "unsafe"--at least on the "F" model and the "S" models I've owned. I'm sure you are correct on the prior to '74 model being discussed here.

I was specifically taking about the 1968 M20F, I was only trying to explain how that system works.  Please don't infer that to be true on other aircraft. 

[N201MKTurbo]

The lights are controlled by the limit switches on the actuator.

[Hank]

The push buttons are not on a wheel, but on the central bar in the gear mechanism under the belly. Our electric gear uses the same mechanism as the manual birds, we just don't have the extension coming up through the floor.

Red light on panel and red floor indication = gear up.

Green light on panel and green floor indication = gear down.

Red light on panel, red/white stripe floor indicator, buzz in headset = one or more wheels not all the way up. This is usually fixed by replacing old pucks that have lost elasticity, which shows up with this failure mode during cold weather.

Bonanzas have switches, motors and lights for each wheel. Mooneys have one motor with a solid mechanical linkage to all three wheels. Something large would have to break for only two Mooney gear to move.

[Ragsf15e]

Tony and Hank (and the others too...  ) - Thanks for your responses.  That cleared up my understanding of the mechanism.  I'll definitely take the next opportunity when the belly panels are off (no single piece panel here) to check it out.  I'll also not take the rigging for granted.  That's one of the reasons I had DMax do my pre-buy and annual when I bought it this year.  I think I'll keep using a good MSC to keep myself out of trouble.

Thanks again!

Rags

[Seth]

In addition, and this may be different for the 1968, in my former 1967 F the Red and Green light on the instrument panel can be twirled to adjust brightness (night time vs day time flights). 

 

Also I forget, but someone here can verify.  If you press the light toward the panel, you can check to see if it is lights.  I'm trying to remember if that was the Mooney or a different aircraft.

 

The F is a great plane.

 

-Seth

[Ragsf15e]

Seth - You're right on all three counts... the brightness is adjusted by twisting, you can press to test them, and the F is a great airplane!  Thanks for the input.

 

Rags

[mooniac15u]

On the manual gear system those lights are hooked to a switch in the block on the panel where the Johnson bar locks when the gear is down.  With the gear up you can reach up into the block and activate the switch with your finger.  If something like a pushrod were to break you would still get a nice green light even though some, or all, or your gear wasn't down.  Overall, not very informative.  It's a good thing that system is completely bulletproof.