Bump in the night

[Guilly]

Two flights today in 1997 M20R. 20 minutes into first flight felt a "bump". It felt like like the engine missed, no indication on engine monitor of anything amiss. The remainder of the flight was normal and I wrote it off. Second flight was similar but when the "event" occurred, the rear seat passenger reported a thump from under the seat. It was a 40 min flight but felt the bump two more times. Lowered the gear early and no issues. Thought I may have an issue with a gear door but everything was tight on inspection...Again, nothing unusual on the GEM or other engine gauges. 3000 hr in the "R" and never seen this one...any ideas on where to start would be greatly appreciated.

[PT20J]

Did it sound/feel like the sound the gear makes when it reaches the end of the retract cycle? Did you happen to notice if the gear unsafe annunciator illuminated momentarily?

[Guilly]

I can't say for sure but I would not rule that out regarding the retract cycle. No gear unsafe light during any of the events. Passengers both pro pilots and said it felt like King Air hydraulic's "sucking the gear back up".

 

[PT20J]

The Mooney landing gear has no up locks. The no-back spring in the actuator keeps the weight of the gear from back driving the actuator ball screw and allowing the gear to move down. If the actuator slips and the gear moves down with the gear switch in the up position, the actuator motor should suck it back up. I would expect the gear unsafe light to come on until the gear fully retracted, though, but it might be a quick flash since the motor would immediately raise the gear once the gear moves enough to deactivate the up limit switch.

If it were mine, I would put it on jacks and check out the gear. It might be something else entirely making the bump, but I would want to rule out a gear issue. 

Skip

[ArtVandelay]

I would put it on jacks, retract the gear, then pull the gear motor circuit breaker, so it won’t be able to retract if it’s slipping. Then leave it overnight to see what happens.

[N201MKTurbo]

It may not happen on jacks. The bumps and vibration probably help bring it down.

[Hank]

19 minutes ago, N201MKTurbo said:

It may not happen on jacks. The bumps and vibration probably help bring it down.

Or ram air pressure at speed.

They could try wiggling the leading edge of the doors, see if they're loose.

[Guilly]

Sounds like a good place to start. I'll update my progress...

 

[anthonydesmet]

Guilly,

im going back to your first comment that it felt like the motor missed a beat just as an alternative. A few years back I was flying from Va Beach to Florida. On climb out and after level off my engine “missed a beat” but at first I thought something was thumping or a little pocket of light chop.  After the third time I could tell it was definitely the engine but no indications on the JPI or fuel flow.  When I leveled off it happened again then stopped. I spoke to Paul K at Savvy and he said it sounds like water in the fuel system.  Then I remembered a couple days before I topped off and as I was finishing there started a very light mist.  I even covered up the fuel port with my hand. Also before flight when I sumped there was no water.  Paul explained to me that in Mooney tanks water droplets can get caught in and behind the ribs and pockets  inside the the tank and not find their way down to the sump. But with change in aircraft attitude (climbing) or turbulence they get dis-lodged and make their way to the engine and would manifest itself as a hiccup.

he recommended putting some HEAT in each tank.  Paul also saw slight anomalies on the JPI I couldn’t see real time.  So good idea to download your data. After I added HEAT- no issues.

anyway that was long winded but just a thought if you have any reason to believe you might have water intrusion……plane stayed outside recently? how new are your fuel cap gaskets, etc, 

[Guilly]

Very interesting. Gas cap gaskets are less than mo and plane is kept hangered. I sumped prior to first flight and very throughly before 2nd (night) flight. I had recently added 80 gal. 
 

I’ll look into this further…thank you for sharing your experience. 

[shawnd]

What’s this HEAT you speak of in the fuel tanks?

[philip_g]

1 hour ago, shawnd said:

What’s this HEAT you speak of in the fuel tanks?

Heet

It's a water remover for gas tanks and lines 

[neilpilot]

3 hours ago, philip_g said:

Heet

It's a water remover for gas tanks and lines 

Search Heet in MS for additional info.  It’s critical you use the red label Heet and not the yellow label.

[philip_g]

5 hours ago, neilpilot said:

Search Heet in MS for additional info.  It’s critical you use the red label Heet and not the yellow label.

flying around colorado for 20 years in and out of mountains and the flight levels in 4 turbo aircraft, not once have I used nor needed it. Even in crappy winter weather in fiki planes.

Edited November 22, 2021 by philip_g

[neilpilot]

1 hour ago, philip_g said:

flying around colorado for 20 years in and out of mountains and the flight levels in 4 turbo aircraft, not once have I used nor needed it. Even in crappy winter weather in fiki planes.

Good for you.  It's not something you typically need to do if you fuel & fly in cold environments.  It's indicated primarily when you've fueled in a relatively warm area and plan to either hanger that fuel thru a deep freeze cycle or will then venture into subfreezing conditions.  Water is slightly soluble in 100LL when it's warm, the solubility drops as the fuel temperature plummets, and very fine ice crystals can form.  Those ice crystals can bind a filter and seriously restrict fuel flow.    

[philip_g]

40 minutes ago, neilpilot said:

Good for you.  It's not something you typically need to do if you fuel & fly in cold environments.  It's indicated primarily when you've fueled in a relatively warm area and plan to either hanger that fuel thru a deep freeze cycle or will then venture into subfreezing conditions.  Water is slightly soluble in 100LL when it's warm, the solubility drops as the fuel temperature plummets, and very fine ice crystals can form.  Those ice crystals can bind a filter and seriously restrict fuel flow.    

Yeah, still not buying it.

[Shadrach]

On 11/20/2021 at 8:51 AM, anthonydesmet said:

Guilly,

im going back to your first comment that it felt like the motor missed a beat just as an alternative. A few years back I was flying from Va Beach to Florida. On climb out and after level off my engine “missed a beat” but at first I thought something was thumping or a little pocket of light chop.  After the third time I could tell it was definitely the engine but no indications on the JPI or fuel flow.  When I leveled off it happened again then stopped. I spoke to Paul K at Savvy and he said it sounds like water in the fuel system.  Then I remembered a couple days before I topped off and as I was finishing there started a very light mist.  I even covered up the fuel port with my hand. Also before flight when I sumped there was no water.  Paul explained to me that in Mooney tanks water droplets can get caught in and behind the ribs and pockets  inside the the tank and not find their way down to the sump. But with change in aircraft attitude (climbing) or turbulence they get dis-lodged and make their way to the engine and would manifest itself as a hiccup.

he recommended putting some HEAT in each tank.  Paul also saw slight anomalies on the JPI I couldn’t see real time.  So good idea to download your data. After I added HEAT- no issues.

anyway that was long winded but just a thought if you have any reason to believe you might have water intrusion……plane stayed outside recently? how new are your fuel cap gaskets, etc, 

Being more familiar with the inside of Mooney tanks than I would like to be, I am interested in how this happens.  The fuel pick up is more than an inch higher than the sump outlet.  Water temporarily trapped behind a rib assembly or stiffener should still flow downhill towards the sump.  I am not doubting it happens. I would just like to understand how. It would take a significant quantity of resting water to get anywhere near the fuel pick up. I am curious how a small amount suspends itself in a liquid that weighs less.

Edited November 23, 2021 by Shadrach

[neilpilot]

1 hour ago, philip_g said:

Yeah, still not buying it.

Guess you can't believe everything you read, even M20-64:

 

sim20-64.pdf

[PT20J]

2 hours ago, neilpilot said:

Guess you can't believe everything you read, even M20-64:

 

sim20-64.pdf 13.52 kB · 2 downloads

When I was in Anchorage we used to add isopropyl alcohol to the fuel seasonally in the flight school airplanes. 

I don't see HEET mentioned in the service instruction.

Skip

[Dustin Kurath]

On 11/19/2021 at 9:05 PM, Guilly said:

Two flights today in 1997 M20R. 20 minutes into first flight felt a "bump". It felt like like the engine missed, no indication on engine monitor of anything amiss. The remainder of the flight was normal and I wrote it off. Second flight was similar but when the "event" occurred, the rear seat passenger reported a thump from under the seat. It was a 40 min flight but felt the bump two more times. Lowered the gear early and no issues. Thought I may have an issue with a gear door but everything was tight on inspection...Again, nothing unusual on the GEM or other engine gauges. 3000 hr in the "R" and never seen this one...any ideas on where to start would be greatly appreciated.

Might be worth checking the plugs. I had the same problem. 2 of the plugs were barely firing. Also, make sure that nobody used aluminum anti seize on the plugs. Graphite or copper is the best choice. Aluminum keeps the plugs from dissipating the heat.

[carusoam]

Let’s see…

1) Effects of water in the fuel tanks….

2) Gear not going up all the way, then deciding to go up on its own….

3) Ignition system challenge… or fuel system challenge…?

 

1a) Download engine data, post here… and send to Savvy.  If the engine actually skips a beat, Savvy is the best resource to find it… water is always in fuel, significant changing of temps can make it fall out of solution…

The O POH has a paragraph for fuel additives…

2a) Time for a gear bump is really slow and deliberate, compared to the time of an engine skip…. Engine skips are scary, and eye opening…. Gear bumps make you wonder what is that..?

3a) Inflight mag checks are the best defense against unknown ignition challenges….  Gami spread test is the best way to see if the fuel system needs a closer look… it takes two spark plugs in one cylinder to cause a skip… a slow deliberate run-up may show anomalies if they exist…

If you have Champion spark plugs… check their resistance…

If you have the other type of spark plug… check their center electrodes… to see if they are still there…

 

Sooo…..

What else can go bump in the flight..?

Anything holding the tail trim, then releasing…?  A small amount of uncommanded tail movement could cause a surprising bump…

Be on the look-out for loose plane parts… to see if anything loose is causing a thump… significant pre-flight inspection…

 

It is uncommon for the landing gear to get out of whack… but, there are occasions where checking the rigging is required…

 

Under what conditions of flight did the bump occur?

Some changes of aerodynamic forces occur when the AOA changes…

 

Last thought…

The alt air door can cause a simple thump that may be detected by experienced pilots…  sometimes the magnets holding it closed lose their strength… hmmmmm….. 

 

PP thoughts only, not a mechanic…

Best regards,

-a-