Elevator bungee springs

[cruiserflyer]

Hello all. I am finally an owner. I recently purchased M20F 3288F, a 1967 model. I love the aircraft and ferried it back from Washington state with my A&P/CFI. Two issues that are demanding attention are an oil leak which is "lubricating" the nose gear, and what appears to be weak elevator bungee springs. I will be at the hangar with my A&P this Thursday to start addressing these issues. I did buy the service manuals (but I left them in the aircraft an hour away) but I'd like to know if this is something that can be solved by opening up the bungees and replacing springs. Both the A&P who last looked at the aircraft and my A&P think this needs to be addressed so I'm 100% on board, just trying to get a lead on part sourcing. Any guidance would be helpful. Can the bungee assemblies be opened up and, what I presume are springs, be replaced?

Thanks!
Paul

 

[47U]

19 minutes ago, cruiserflyer said:

I did buy the service manuals (but I left them in the aircraft an hour away)

There are copies of the service manuals in the downloads section…

[N201MKTurbo]

How did he determine the springs were weak? I don’t think there is a way to know that from the handling of the plane. Considering there is one for each elevator, which one is weak? The left or right?

The springs can break. If you remove the bungee, they are easy to disassemble. If you do disassemble them, clean, repaint and grease them. They probably haven’t been serviced since they left the factory.

[cruiserflyer]

I think just by feel, that there does not appear to be any resistance or spring pushback. I was honestly deferring to them, but I didn’t feel any slack or troubling feeling in the controls. From pushing gently up and down on the elevator the bolt moves all the way out and in. Since I am deferring to them I took it on faith that it must be wrong, but maybe it’s fine. My A&P has owned about a dozen Mooney’s so I just listen to them. The pics are of me pushing and pulling.

[N201MKTurbo]

There were a few different elevator arrangements in the Mooneys. Some of them have a definite force while sitting on the ground. The arrangement you have does not. It will just center around the trimmed position. The bungees put a spring bias to the elevator depending on trim position. The bungees are responsible for the elevator not lining up with horizontal stabilizer in cruise. The bungees put the elevators in the optimal position for minimum drag, which is not lined up.

[Ragsf15e]

4 hours ago, cruiserflyer said:

I think just by feel, that there does not appear to be any resistance or spring pushback. I was honestly deferring to them, but I didn’t feel any slack or troubling feeling in the controls. From pushing gently up and down on the elevator the bolt moves all the way out and in. Since I am deferring to them I took it on faith that it must be wrong, but maybe it’s fine. My A&P has owned about a dozen Mooney’s so I just listen to them. The pics are of me pushing and pulling.

I had an F, now i have a K, the elevator arrangement is completely different.  I’m saying this because maybe your mechanic had different models and the elevator was set up differently.  My F looked just like yours, it should roughly center the elevator to the horizontal stab on the ground.  If it’s not broke, maybe it doesn’t need fixed?  If they really want to take it apart, maybe the goal should be to clean it up?

Heres the real point… is there somewhere in the maintenance manual telling you (or your mechanic) how much spring force there should be and what the limit is?  I don’t think there is, but you can look.  And if they still think it’s not right, maybe ask why they think that?  

[Ragsf15e]

6 hours ago, cruiserflyer said:

Hello all. I am finally an owner. I recently purchased M20F 3288F, a 1967 model. I love the aircraft and ferried it back from Washington state with my A&P/CFI. Two issues that are demanding attention are an oil leak which is "lubricating" the nose gear, and what appears to be weak elevator bungee springs. I will be at the hangar with my A&P this Thursday to start addressing these issues. I did buy the service manuals (but I left them in the aircraft an hour away) but I'd like to know if this is something that can be solved by opening up the bungees and replacing springs. Both the A&P who last looked at the aircraft and my A&P think this needs to be addressed so I'm 100% on board, just trying to get a lead on part sourcing. Any guidance would be helpful. Can the bungee assemblies be opened up and, what I presume are springs, be replaced?

Thanks!
Paul

 

To your second question, they all leak on the nose a little.  A tiny bit of oil makes a big mess.  How bad is it?  It might be worth searching for but you might decide to live with it.  Also, there are three tubes coming out of the cowling near the nose tire.  The case vent, a drain for the mechanical fuel pump and the sniffle valve drain.  There’s a drain for the electric fuel pump and the gascolator farther aft (under the pilots feet roughly).  You need to see if the oil drips are from these drains because that will guide your troubleshooting.  Oil will normally drip out the case “breather” tube.  That’s normal.  The sniffle valve might drip a little fuel but shouldn’t drip much.  Oil out the mechanical fuel pump drain is a sign of a failing pump diaphragm on your mechanical pump.

Unfortunately, almost all the oil leaks in the engine find their way to the nose gear.

[cruiserflyer]

Great responses, thank you! The elevator is perfectly in line with the horizontal stab on the ground. I am definitely not in favor of unnecessary maintenance and will take all these answers to the hangar on Thursday. My main goal at the moment is to locate the oil leak source. My A&P mentioned it might be the fuel pump diaphragm but we'll clean it up first, then run it and see if we can source it. On our ferry flight from Spokane to eastern Montana we only were down half a quart, hardly anything to worry about.

[PT20J]

All M20 models through the M20J have trim assist bungees (later models have a different system not relevant to this discussion). The Mooney trims primarily by adjusting the angle of incidence of the horizontal stabilizers which is a common trimming method used on many airplanes. What makes the Mooney different is that rather than adjusting the horizontal stabilizer itself (like a Piper Cub, Cessna 180 and many jets) the Mooney stabilizer is rigidly attached to the empennage and the trim, through a jackscrew arrangement, pivots the entire empennage. Since the trim has to move a considerable amount of structure, it has to have a lot of mechanical advantage to keep trim forces within reason. But, that also means that it would take a lot of turns of the trim wheel to adjust the stabilizer angle through the range necessary for all trim conditions. So, the bungees are added to add an additional force to the elevator to assist trimming so that the stabilizer doesn't have to move as much. The bungees also act as centering springs on the stick which improves longitudinal stability. 

You can see the effect of the bungees if you move the trim while sitting on the ground. With the trim set to the takeoff position, the elevator should be approximately aligned with the stabilizer. If you set full nose up trim the elevator should move trailing edge up. If you move the trim full nose down the elevator should move trailing edge down.

The TCDS (and service manual) will have rigging information for adjusting the bungees. I would check this before doing anything else.

[PT20J]

8 minutes ago, cruiserflyer said:

My A&P mentioned it might be the fuel pump diaphragm but we'll clean it up first, then run it and see if we can source it.

The fuel pump has two diaphragms for redundancy. There is a drain line between the diaphragms that should exit behind the left cowl flap. It's a good preflight item to check this line as it should be dry. It can be wet with fuel or oil depending on which diaphragm has failed. Be sure you are checking the correct hose. There should also be hoses for the intake manifold drain (sniffle valve), the crankcase breather and perhaps the vacuum pump in the same area.