Gear bump when activated

[Vaughn]

I'm a new Mooney driver and my 1969 M20F seems to bump, push up a bit on the floor when the gear is activated. Happens when I retract or extended the gear. Is this usual?

Thanks,

[kpaul]

2 minutes ago, Vaughn said:

I'm a new Mooney driver and my 1969 M20F seems to bump, push up a bit on the floor when the gear is activated. Happens when I retract or extended the gear. Is this usual?

Thanks,

Nope...you need to get the plane to a shop with the proper Mooney gear tools and have them checked. Your gear is out of rig!

Where are you located?

Edited July 23, 2021 by kpaul

[Ron McBride]

This was quite normal in my 69F when I had 40:1 gears.   When I replaced the gears with 20:1 it was much less noticeable.

take the plane to a Mooney shop.  There is a repetitive AD note on the gear motor and gears, inspection and lubrication with special grease. 
 

Ron

 

[Shadrach]

16 minutes ago, Ron McBride said:

This was quite normal in my 69F when I had 40:1 gears.   When I replaced the gears with 20:1 it was much less noticeable.

take the plane to a Mooney shop.  There is a repetitive AD note on the gear motor and gears, inspection and lubrication with special grease. 
 

Ron

 

I would have thought it more noticeable with 20:1 gears not less so…

[Vance Harral]

The bracket on the airframe which your gear actuator mounts to, is in turn mounted to the floor pan directly under the pilot's seat.  As the gear goes over center, compression of the springs in the system cause the rods to compress against the actuator on both the fore (nose gear) and aft (main gear) ends.  This compression, combined with the aluminum floor pan not being perfectly rigid, will cause a "bump" under your butt in the left seat.

Our 1976 M20F has consistently done this for the last 16 years, through numerous gear rigging checks, with no long-term ill effects.  I've come to think of it as an additional "gear is down and locked" indicator.  When I put the gear down, in addition to looking for the green light on the panel and checking the floor indicator alignment bars, I expect to feel a kick in the butt.

On edit: if your log books indicate recent completion of Mooney Service Bulletin M20-190 (the AD that @Ron McBride refers to), I would not do anything at this time.  If there is no record of this inspection being done recently, then yes, you ought to have the gear actuator checked out.  But that is true independent of the "bump in the butt" observation.  For further info, see https://www.donmaxwell.com/ad-75-23-04-sb-m20-190

Edited July 23, 2021 by Vance Harral

[N201MKTurbo]

You obviously have electric gear. It indicates that you are overdriving the actuator. You need to have someone who understands the Mooney gear get it set up right.

[Ron McBride]

35 minutes ago, Shadrach said:

I would have thought it more noticeable with 20:1 gears not less so…

Shadrach, you may be right, I noticed more with the original gears. 

[Shadrach]

Just now, Ron McBride said:

Shadrach, you may be right, I noticed more with the original gears. 

I don’t have electric gear but I thought the originals were 20:1 and the SB called for 40:1 which should slow the retraction.

[BrianWilkins]

I agree with what Vance said above.  Electric gear in my 69 E has been this way since I bought it and the gear rigging has been checked multiple times including by an MSC.  Normal for my plane. 

[Vaughn]

Thanks everyone for the rapid feedback. I'm in Western Arkansas so a short hop to
Maxwell if needed but my A&P is very competent and very busy. The last annual was done by Air Mods, a solid shop. Logs show that AD 75-23-04 is "NA pin installed." Could still have my mechanic swing the gear and see what he thinks? Thoughts?

[Vance Harral]

15 hours ago, N201MKTurbo said:

It indicates that you are overdriving the actuator

I'm trying to understand why you would say this.

Both the mains and the nose gear linkages in these systems incorporate heavy springs, which get compressed when the gear pivot links pass over center.  The gear rigging checks effectively measure the spring compression force in the locked position, and there is a minimum standard below which is unsafe.  Therefore, it is completely normal to have transitory loads during the time the pivots are going over center, which put the entire linkage system in compression, and therefore induce some amount of flex in the connections to the airframe.  It is not true that these compressive loads and flex in the system mean the actuator is being driven beyond normal limits.

It is true that excessive loads and flex indicate a problem, perhaps that's what you're getting at.  But as we see from the postings here, multiple owners with correctly rigged gear report this "butt bump" in the seat pan when the gear transitions.

[Vance Harral]

6 hours ago, Vaughn said:

Logs show that AD 75-23-04 is "NA pin installed."

That makes absolutely no sense to me, unless a "pin" is installed somewhere that prevents the landing gear from retracting at all.

AD 75-23-04 makes Mooney Service Bulletin M20-190 mandatory.  That SB requires removing and inspecting the landing gear actuator for worn internal gears.  There is no "pin" involved, and I'm extremely skeptical that AD 75-23-04 is actually N/A to your airplane.  Strongly suggest you have your mechanic research the AD and SB in detail.

[Vaughn]

I agree Vance. I'm going to first give Maxwell a call.

[N201MKTurbo]

15 minutes ago, Vance Harral said:

I'm trying to understand why you would say this.

Both the mains and the nose gear linkages in these systems incorporate heavy springs, which get compressed when the gear pivot links pass over center.  The gear rigging checks effectively measure the spring compression force in the locked position, and there is a minimum standard below which is unsafe.  Therefore, it is completely normal to have transitory loads during the time the pivots are going over center, which put the entire linkage system in compression, and therefore induce some amount of flex in the connections to the airframe.  It is not true that these compressive loads and flex in the system mean the actuator is being driven beyond normal limits.

It is true that excessive loads and flex indicate a problem, perhaps that's what you're getting at.  But as we see from the postings here, multiple owners with correctly rigged gear report this "butt bump" in the seat pan when the gear transitions.

When I got my current Mooney, it would warp the floor when the gear was actuated. The plane had been repaired from a gear up and it wasn't assembled properly. After I put it together right and adjusted the gear properly, it doesn't do it any more, you can't even feel it except you can feel the motor running a little. 

Who says they are all correctly rigged? I've seen a few that worked fine and were probably safe, but were all jacked up.

The last Mooney Gear that I did was Brice's M20C with a Johnson bar. It had always been hard to put the wheels down. I ferried it home when he bought it and I mentioned to him then that it shouldn't be that hard. Fast forward three years and he installs a new up lock block. He asked me to inspect it and sign it off. At that point I re-rigged his nose gear, one rod was being over driven and the other was doing nothing. I got them equalized and now the preloads are spot on and you can work the Johnson bar with your finger tips. I'm just saying that there is a lot of ways to get the Mooney gear all cattywhampus and still meet the preload specs.

[Ragsf15e]

52 minutes ago, N201MKTurbo said:

When I got my current Mooney, it would warp the floor when the gear was actuated. The plane had been repaired from a gear up and it wasn't assembled properly. After I put it together right and adjusted the gear properly, it doesn't do it any more, you can't even feel it except you can feel the motor running a little. 

Who says they are all correctly rigged? I've seen a few that worked fine and were probably safe, but were all jacked up.

The last Mooney Gear that I did was Brice's M20C with a Johnson bar. It had always been hard to put the wheels down. I ferried it home when he bought it and I mentioned to him then that it shouldn't be that hard. Fast forward three years and he installs a new up lock block. He asked me to inspect it and sign it off. At that point I re-rigged his nose gear, one rod was being over driven and the other was doing nothing. I got them equalized and now the preloads are spot on and you can work the Johnson bar with your finger tips. I'm just saying that there is a lot of ways to get the Mooney gear all cattywhampus and still meet the preload specs.

I’m about to bring mine too you!  Are you all the way south in Phoenix?

[N201MKTurbo]

4 minutes ago, Ragsf15e said:

I’m about to bring mine too you!  Are you all the way south in Phoenix?

I'm in Tempe, on the South side of Phoenix.

If you are serious, we will have to wait a while. I have a 172 I have to get fixed up and I'm on the hook to get the 310 in my picture airworthy again, not to mention the Mooney can use some attention. I promised @Boilermonkey a gauge that I have to swap out of the Mooney this weekend. Not to mention that I have a day job who would love to have me work 60 hours a week. 

[Vance Harral]

3 hours ago, N201MKTurbo said:

Who says they are all correctly rigged? I've seen a few that worked fine and were probably safe, but were all jacked up.

Fair enough, but when I say our airplane is rigged correctly, I don't just mean the preload torque; I mean the full procedure described in the maintenance manual, last performed when we removed the main gear to install new pivot link bushings from LASAR.  I think the only thing that can be said is either some airplanes which flex the floor pan are operating as designed by the factory, or that the gear rigging procedure can be correctly followed and still "overdrive" the system by your standards.

[Yetti]

Start with the simple things like greasing the gear.   all of the zerts.  This is the first step in solving gear issues.

[MikeOH]

Another data point:  I've had my '70F, with electric gear, for 4 years and NEVER have felt ANY kind of 'butt bump'. Personally, I'd freak out if that happened and fly it, with gear down, to the nearest EXPERIENCED Mooney mechanic.

If this 'bump' was in any way normal, EVERY electric gear Mooney would be doing it.  Something is NOT rigged right.

IMHO, naturally

[Hank]

My C has thumped against the floor since I bought it in `07. A genius IA decided on his one and only annual to (among other indiscretions) adjust my nose gear door so that there was lots of noise and a jerk in the yoke when the wheels went up and down. So off the KDNN for Joey Cole to look into it. He said I was lucky the gear didn't jam . . . .

Now there's still a bump, more so when it goes down than up, maybe half of what it was the dozen years before Joey fixed it. Smooth, quick, and a satisfying feel as the gear lock down.