Gear horn on takeoff

[spitzfyre]

Hello all, I'm hoping there's someone out there who's experienced something similar to my problem and can relay what their solution was. 

It used to be an intermittent issue, but now it happens nearly every time. I take off and put my (electric) gear up. I have a 74 F model with only 2 lights, green down and amber up. The amber up light will flicker but not remain lit, and the gear horn will start blaring. Weird thing is, pulling the gear horn CB does not shut it up. It will silence the horn when I have low power (below the microswitch in the throttle quadrant) with my gear up, though, so the CB does in fact work. I pulled the belly panel and pushed the gear up limit switch with my finger and had a friend watch the amber 'gear up' light, which did not illuminate. I also put my ohmmeter to it just for the heck of it and it checked out fine. Also to be clear, my gear is moving, evidenced by the floor sight glass and the fact that I can feel them swing. Sometimes like on my way home today, the amber 'gear up' light decided to come on halfway through the flight, and the blaring stopped. I've tried cycling the gear several times after takeoff, but this doesn't fix anything.

I don't have jacks so I haven't been able to simulate this on the ground for troubleshooting, but I'm hoping someone else has some idea of where I should start. 

Thanks

[N201MKTurbo]

Try lubricating the down switch in the belly. It may not be springing all the way out when the gear comes up.

[spitzfyre]

I will try that, thank you

[larryb]

Are you sure it’s not the stall horn?

[Hank]

Once upon a time, my C was doing that. It would get better and worse, then I noticed when it finally quit that my airspeed would jump about 10 mph higher. One solo trip, the durn thing buzzed and slowed me down 15 mph for an hour,  finally going away just a few minutes before I began descending, running late by then of course. Yes that was a mid-winter flight.

It got better all summer, cured I thought. That next fall when temperatures dropped it came back with a vengeance. I-forget-who said the check my donuts; it looked like the manufacture date molded in was "09-96" (the ones I could see were upside down). Upon removal, it was "06-69"!

The four from a main gear were almost 1/2" shorter than a stack of new ones. No trouble with that annoying horn and no lost airspeed since. The pucks were replaced in Dec 2012, I think. My landings immediately improved, too! Forty years is too long for a set of gear pucks!

[spitzfyre]

12 hours ago, larryb said:

Are you sure it’s not the stall horn?

Yes I'm sure. When the "gear up" light eventually illuminates, the horn shuts up. 

[spitzfyre]

2 hours ago, Hank said:

Once upon a time, my C was doing that. It would get better and worse, then I noticed when it finally quit that my airspeed would jump about 10 mph higher. One solo trip, the durn thing buzzed and slowed me down 15 mph for an hour,  finally going away just a few minutes before I began descending, running late by then of course. Yes that was a mid-winter flight.

It got better all summer, cured I thought. That next fall when temperatures dropped it came back with a vengeance. I-forget-who said the check my donuts; it looked like the manufacture date molded in was "09-96" (the ones I could see were upside down). Upon removal, it was "06-69"!

The four from a main gear were almost 1/2" shorter than a stack of new ones. No trouble with that annoying horn and no lost airspeed since. The pucks were replaced in Dec 2012, I think. My landings immediately improved, too! Forty years is too long for a set of gear pucks!

Interesting! Does your C have a squat switch? Maybe that's where the issue lies, and the logic thinks the gear is still down? Maybe it's a "gear unsafe" horn even though I don't have a light for it. I've been trying to find a wiring diagram for my plane but so far no joy.

 

Looks like my donuts are from 1998. Might be time for a new set

[Hank]

1 hour ago, spitzfyre said:

Interesting! Does your C have a squat switch? Maybe that's where the issue lies, and the logic thinks the gear is still down? Might be time for a new set.

Yes it does. There's a puck test in the Maintenance Manual, jack the plane and measure the gap. Mine failed.

[spitzfyre]

40 minutes ago, Hank said:

Yes it does. There's a puck test in the Maintenance Manual, jack the plane and measure the gap. Mine failed.

Hmm. I don't have jacks, but the Mx manual says full fuel, weight on wheels. I'll be back out at the airport either later today or tomorrow and will take a look

[Ragsf15e]

4 hours ago, spitzfyre said:

Interesting! Does your C have a squat switch? Maybe that's where the issue lies, and the logic thinks the gear is still down? Maybe it's a "gear unsafe" horn even though I don't have a light for it. I've been trying to find a wiring diagram for my plane but so far no joy.

 

Looks like my donuts are from 1998. Might be time for a new set

If you definitely have the squat switch, those are pretty sensitive to the donuts, so maybe that’s your issue.  However, there are only a couple years with squat switches, most have airspeed switches. Typically squat switch issues lead to the gear not coming up which is not what you indicated.

[LANCECASPER]

4 hours ago, spitzfyre said:

Looks like my donuts are from 1998. Might be time for a new set

I think 24 years says you’ve gotten your money’s worth from those shock discs. Your landing gear parts will thank you, your fuel tanks will thank you, your back will thank you . . . etc, etc.

You might donate them to a kids hockey league. After that long they have the elasticity of a puck.

[Ragsf15e]

2 hours ago, LANCECASPER said:

I think 24 years says you’ve gotten your money’s worth from those shock discs. Your landing gear parts will thank you, your fuel tanks will thank you, your back will thank you . . . etc, etc.

You might donate them to a kids hockey league. After that long they have the elasticity of a puck.

I don’t disagree about the donuts but I’m not convinced they’re causing his gear horn… they typically cause the gear to not come up if the squat switch isn’t being compressed/released properly.  No?

[Hank]

1 hour ago, Ragsf15e said:

I don’t disagree about the donuts but I’m not convinced they’re causing his gear horn… they typically cause the gear to not come up if the squat switch isn’t being compressed/released properly.  No?

They cause my gear to.come up most of the way. The floor indicator was barber poles instead of red or green. 

[spitzfyre]

*Her* gear horn :-)

Rags, yeah I definitely have a squat switch. I went back to the airport earlier this evening and found no gap at the top of the donuts with weight on wheels, as the manual instructs. But that doesn't make much sense to me doing it with weight on them; you'll never have a gap. So I used my bottle jack and lifted one side (wish I could lift both at the same time for gear swings!), measured the gap. Came up with 86 thou, which is supposedly within tolerances. Unless the manual limit of .6 is a typo and should be .06"

I have a scheduled flight tomorrow, I'm thinking I'll pull the belly panel beforehand and lube the two limit switches. And look into getting new donuts. My annuals coming up in December so that'd be a good time to do them. Thanks for all the replies, guys

[Ragsf15e]

35 minutes ago, spitzfyre said:

*Her* gear horn :-)

Rags, yeah I definitely have a squat switch. I went back to the airport earlier this evening and found no gap at the top of the donuts with weight on wheels, as the manual instructs. But that doesn't make much sense to me doing it with weight on them; you'll never have a gap. So I used my bottle jack and lifted one side (wish I could lift both at the same time for gear swings!), measured the gap. Came up with 86 thou, which is supposedly within tolerances. Unless the manual limit of .6 is a typo and should be .06"

I have a scheduled flight tomorrow, I'm thinking I'll pull the belly panel beforehand and lube the two limit switches. And look into getting new donuts. My annuals coming up in December so that'd be a good time to do them. Thanks for all the replies, guys

Yes lubing the belly limit switches is always good.  Lube the squat switch while you’re at it.

I don’t have a squat switch, but I recall @Marauder saying his gear got intermittent as weather got colder with old donuts.  Theory was that they didn’t expand enough (or quickly enough) to trigger the switch after the weight was off the wheels.

[Hank]

28 minutes ago, Ragsf15e said:

Yes lubing the belly limit switches is always good.  Lube the squat switch while you’re at it.

I don’t have a squat switch, but I recall @Marauder saying his gear got intermittent as weather got colder with old donuts.  Theory was that they didn’t expand enough (or quickly enough) to trigger the switch after the weight was off the wheels.

Exactly!

Use some contact cleaner spray on the squat switch, clean it thoroughly. Push it several times and clean it again. The spray isn't cheap except when compared to the price of 11 new donuts.

[spitzfyre]

Just a followup

I'm not sure if its the result of the warmer weather or my lubing all 3 switches, but the horn and light are behaving better. Now it shuts up shortly after takeoff as opposed to 20-25 minutes after. We'll see if it continues to improve, especially when the weather starts getting cooler again

[Marauder]

3 hours ago, spitzfyre said:

Just a followup

I'm not sure if it’s the result of the warmer weather or my lubing all 3 switches, but the horn and light are behaving better. Now it shuts up shortly after takeoff as opposed to 20-25 minutes after. We'll see if it continues to improve, especially when the weather starts getting cooler again gear squat switch 

In my plane, when the gear squat switch was the culprit, the gear will not come up and the gear unsafe light would stay on. It sounds like the gap on yours is within tolerances. 
My gear unsafe issue was due to really cold flights (like below 10°F). The donuts wouldn’t expand enough to activate the squat switch and the gear stayed down. 
Mooney recognized this was an issue with the squat switch design and offered a retrofit called the “Gear Bypass” kit. I installed it in my plane.