M20F electric landing gear flexing down at high speed

[Ronnie Pool]

I wanted to create a new topic as an offshoot to “slowest Mooney M20F ever”. A recent picture on a high speed pass shows that my landing gear is flexing downward in flight at higher speeds causing a huge airspeed loss. My gear is rigged per the book with some but minimal clearance to the bumpers when up. The doors are snug and seemingly flush when up on jacks. On takeoff when the gear is selected up, the gear up light comes on as it should. In flight and at speeds seemingly above 110 kts, even when in level flight, the gear up light goes off indicating that all the gear linkage up to the motor is flexing. Has anyone had any experience with this? Maybe due to the doors being too tight and having a slight bow causing suction? Worn out heim bearings and linkages? Issues with the motor and worm gear (they were recently inspected per the AD)? See pictures below. In a few days I will remove the gear doors and fly without them to see if the issue goes away to prove if the doors or gear linkages are at fault. See pictures below taken at around 130 kts.

 

 

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[EricJ]

Have you tried pulling on the gear legs while in the up position when on jacks?    If it moves, pop the belly off and see if the jack screw is back-driving somehow.   It may be a bad relay or something dumb like that, or components on the jack screw or actuator gears may be worn that allow it to back-drive.

 

[Ronnie Pool]

Have you tried pulling on the gear legs while in the up position when on jacks?    If it moves, pop the belly off and see if the jack screw is back-driving somehow.   It may be a bad relay or something dumb like that, or components on the jack screw or actuator gears may be worn that allow it to back-drive.
 

I have the belly open now and on jacks. Pulling on the gear (with as much force as I dare) when up does not seem to affect the switch. The gear does move slightly downward due to the bungee tension as I would expect as they do not have a load when up per the MM. There must be a huge amount of force when in air for it to flex…. Thinking about it now, there may be just enough movement from the bungees to where a slight gap opens in the gear doors causing an exaggerated flex once air starts rushing in. What I am looking for is any one else that may have experienced the same or near same thing, and it there were any parts replacements that eliminated the issue. I’m kind of expecting to have to replace all of the rod ends.


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[EricJ]

10 minutes ago, Ronnie Pool said:

I have the belly open now and on jacks. Pulling on the gear (with as much force as I dare) when up does not seem to affect the switch. The gear does move slightly downward due to the bungee tension as I would expect as they do not have a load when up per the MM. There must be a huge amount of force when in air for it to flex…. Thinking about it now, there may be just enough movement from the bungees to where a slight gap opens in the gear doors causing an exaggerated flex once air starts rushing in. What I am looking for is any one else that may have experienced the same or near same thing, and it there were any parts replacements that eliminated the issue. I’m kind of expecting to have to replace all of the rod ends.

Usually one expects positive pressure on the doors, not negative.   The M20J/K gear pulls down with aero because the inner doors are canted outward in transit, but you don't have those.

There isn't much of a spec on how tight the doors have to be against the bottom of the wing, so I don't think aero is your problem.    If it was, it'd be seen across many Mooneys that don't have properly rigged doors, i.e., it'd be a fairly common problem.   If you're already finding the doors snug against the bottom, I suspect that's not the issue.

You might try turning the power on and pulling on things or bumping on them while it's on stands and see if a relay isn't turning on intermittently or something.    This seems like a pretty unusual problem.   If you have an airspeed switch, maybe that's involved since it seems airspeed dependent.   That may involve a mis-wire, but I think that sort of thing may be in play.    

[N201MKTurbo]

I would just adjust the up limit switch to suck them up a bit tighter. The bungees are for preload on extension, they should be fully extended on retraction and have no compliance.

[N201MKTurbo]

You may just need new bolts and bushings (mostly bolts) in your retraction links, but that wouldn’t explain the nose gear doors being opened the same as the mains.

[PT20J]

I might put it on jacks and retract the gear and then pull on each main wheel and see if I could duplicate the effect. If so, I’d watch all the linkages and see what’s going on. 

[Ragsf15e]

2 hours ago, Ronnie Pool said:

 

I wanted to create a new topic as an offshoot to “slowest Mooney M20F ever”. A recent picture on a high speed pass shows that my landing gear is flexing downward in flight at higher speeds causing a huge airspeed loss. My gear is rigged per the book with some but minimal clearance to the bumpers when up. The doors are snug and seemingly flush when up on jacks. On takeoff when the gear is selected up, the gear up light comes on as it should. In flight and at speeds seemingly above 110 kts, even when in level flight, the gear up light goes off indicating that all the gear linkage up to the motor is flexing. Has anyone had any experience with this? Maybe due to the doors being too tight and having a slight bow causing suction? Worn out heim bearings and linkages? Issues with the motor and worm gear (they were recently inspected per the AD)? See pictures below. In a few days I will remove the gear doors and fly without them to see if the issue goes away to prove if the doors or gear linkages are at fault. See pictures below taken at around 130 kts.

 

 

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I’ve been on MS for ~10 years and have an F model with electric gear as well, but I’ve never seen that happen before!  It’s definitely going to be faster once you figure it out!  Im glad you found the problem, good luck!

[Bolter]

If you pull the breaker while the up-gear indicator is still on (low speed), and make another low pass "inspection: or see if you achieve higher speeds than before.  This will confirm the gear motor or somethign electrical is not activating.  

Put a flag on your panel or something to remind you that you pulled that breaker before turning for home!

[PT20J]

Also, it wouldn’t hurt to call Don Maxwell. He’s happy to answer questions and share his knowledge and he’s seen just about everything.

[Ronnie Pool]

Also, it wouldn’t hurt to call Don Maxwell. He’s happy to answer questions and share his knowledge and he’s seen just about everything.

What’s his contract info?


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[PT20J]

5 hours ago, Ronnie Pool said:

What’s his contract info?


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903-643-9902

dmaxwell@donmaxwell.com

www.donmaxwell.com

[Ronnie Pool]

Had an epiphany late last night and confirmed the issue today after replacing a failed aircraft jack. It seems that the main gear shock discs are worn out enough that the weight on wheel switch can make contact when the gear is in transition in flight and with a wind load pushing the main tires back. This is causing the gear to not fully retract after takeoff, but is not a problem when on jacks. While retracting today, pushing on the tire causes the gear to hault retraction. Time for some new shock discs….


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[Ragsf15e]

55 minutes ago, Ronnie Pool said:

Had an epiphany late last night and confirmed the issue today after replacing a failed aircraft jack. It seems that the main gear shock discs are worn out enough that the weight on wheel switch can make contact when the gear is in transition in flight and with a wind load pushing the main tires back. This is causing the gear to not fully retract after takeoff, but is not a problem when on jacks. While retracting today, pushing on the tire causes the gear to hault retraction. Time for some new shock discs….


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Ahh, glad you found it!  Only a couple of years in the mid 70s Use a switch there. Most models use an airspeed switch which isn’t affected by the donuts but can have its own drawbacks.

[Ronnie Pool]

Ahh, glad you found it!  Only a couple of years in the mid 70s Use a switch there. Most models use an airspeed switch which isn’t affected by the donuts but can have its own drawbacks.

Can’t imagine why the went away from the WOW switch…lol


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[Flyler]

I was going to say- shouldnt the gear motor turn back on if that "gear up" lights goes out, and pull it back in?  Glad you found the ghost!! That must be a relief. That plane is way too pretty to be slow

[Ragsf15e]

1 hour ago, Ronnie Pool said:

Can’t imagine why the went away from the WOW switch…lol


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Yeah the gear design isn’t great for a wow switch since it doesn’t compress nearly as much as something with a piston or spring.  Well it doesn’t compress much if your donuts are good, maybe yours does ;)?

The airspeed switch seems a more reliable way to keep the gear down when you’re on the ground and allow them to come up in the air.

[BillyT0020]

On 11/16/2024 at 12:36 PM, Ronnie Pool said:

 

I wanted to create a new topic as an offshoot to “slowest Mooney M20F ever”. A recent picture on a high speed pass shows that my landing gear is flexing downward in flight at higher speeds causing a huge airspeed loss. My gear is rigged per the book with some but minimal clearance to the bumpers when up. The doors are snug and seemingly flush when up on jacks. On takeoff when the gear is selected up, the gear up light comes on as it should. In flight and at speeds seemingly above 110 kts, even when in level flight, the gear up light goes off indicating that all the gear linkage up to the motor is flexing. Has anyone had any experience with this? Maybe due to the doors being too tight and having a slight bow causing suction? Worn out heim bearings and linkages? Issues with the motor and worm gear (they were recently inspected per the AD)? See pictures below. In a few days I will remove the gear doors and fly without them to see if the issue goes away to prove if the doors or gear linkages are at fault. See pictures below taken at around 130 kts.

 

 

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Is your step down on the low flight picture? 

[Ragsf15e]

1 hour ago, BillyT0020 said:

Is your step down on the low flight picture? 

My F has a fixed step (1968 model), so I think his is fixed too.

[Slick Nick]

On 11/17/2024 at 4:07 PM, Ronnie Pool said:

Can’t imagine why the went away from the WOW switch…lol


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But you’ll often see posts here on Mooneyspace where guys are saying “the airspeed switch idea is so stupid! Why wouldn’t Mooney just use a squat switch like everyone else?”

[Utah20Gflyer]

On 11/21/2024 at 7:06 PM, Ragsf15e said:

My F has a fixed step (1968 model), so I think his is fixed too.

It’s interesting that a 68 F model would have a fixed step while my 68 G model has the retractable step.  Is your fixed step one of the more aerodynamic types like on J models?  My square non aerodynamic step costs me 2-3 knots when it’s down.  

[Ragsf15e]

10 hours ago, Utah20Gflyer said:

It’s interesting that a 68 F model would have a fixed step while my 68 G model has the retractable step.  Is your fixed step one of the more aerodynamic types like on J models?  My square non aerodynamic step costs me 2-3 knots when it’s down.  

No, it’s not as good as the J step, but it looks a little more aerodynamic than the retractable step?  Hard to tell though because it’s a thick tube sticking out with a chunky step on it.  Im sure it’s worth a knot or 3.  It is weird how they changed the designs rapidly even within year groups.

[Yetti]

On my 75F there is a brake on the back of the motor that prevents the motor from chattering.  So I think this is a known issue with a fix.     The fourth lug on the Ford 8N tractor solenoid releases the brake when the motor puts the gear down.    Sometimes the contacts for the brake become unstaked in the motor.