Looking for advice on power problems

[nugs314]

Hey Gents, looking for advice before speaking with my mech. Flew my F on a long xcountry and on my return trip experienced some strange and alarming issues. The IAS was about 10 kts lower than what would be normal for the flight conditions and this matched up with what was indicated on the GPS so ruling out a problem with the AS indicator. Engine ran smooth, temps normal etc. here is the mystery, every so often ( about 4 times over a 4 hr flight) the indicated AS and gps derived GS would go back to what would be considered normal with no changes in engine settings. I just had a new prop (scimitar) installed and it had been producing great results up to this point. Anyone else ever see/ hear about this? Take-off power/ acceleration seemed normal but I did notice prop RPM slightly lower than normal on take-off (26 vice 27). Appreciate any thoughts.

[adamsboomer]

I am no expert and in fact I am very new to the Mooney however I would look into RPM/prop control personally.

[jackn]

The winds have been very strong along the East Coast this week. Mountain waves can reach 100s of miles away from the Appalachian Mtns. Could you have been flying somewhat parrallel to them?

[cliffy]

Were you in altitude hold on autopilot when this happened? If so you could have been in a down draft and the nose was pulled up to maintain altitude losing airspeed. Not knowing all your conditions at the time makes diagnosis difficult.

[orionflt]

to add to the questions, do you have a fuel flow gauge, and if you do did you see any change? also what were your CHT and EGT's doing?

 

Brian

[nugs314]

I was actually flying alongside the Appalachians at the end of the trip but the problem was noticed when I was in Texas. My instinct was that the plane was not producing the power it normally does. I would usually be indicating around 130 kts at the power settings I always fly on xcountry and was consistently 10-15 kts IAS slower backed up with the GPS with at 12kt tail wind the entire flt. Almost like I was flying at normal power settings with a speed break out ( yes the gear was up, I know someone will ask). Just seems odd that this started about 10 hours after the Top Prop Overhaul.

[nugs314]

to add to the questions, do you have a fuel flow gauge, and if you do did you see any change? also what were your CHT and EGT's doing?

 

Brian

Hey Brian, Temps were steady and normal as was the fuel flow. Fuel flow was my first thought as well.

[EDNR-Cruiser]

Did you check if both magnetos were working? Could be that you were flying on one magnet only... - all temperatures steady but less performance at the same fuel flow. The EGTs would be higher though but I'm not sure if that is visible on the factory gauges... - an engine monitor would clearly show this.

[nugs314]

Did you check if both magnetos were working? Could be that you were flying on one magnet only... - all temperatures steady but less performance at the same fuel flow. The EGTs would be higher though but I'm not sure if that is visible on the factory gauges... - an engine monitor would clearly show this.

I did have to burn one of the MAGs a bit before takeoff but it was the first thing I checked when I landed and both seemed to be in limits. I'm scratching my head on this one and I hate going to my MECH with no clue. Just spoke with him and the MAGs are where he is going to start.

[N9405V]

I've got a new to me 1970 M20E.  It's in the shop right now getting both mags rebuilt and a new wiring harness.  At 1700-1800 rpm mag check was normal.  At 2600 rpm (I know, it hurt to do it) the right mag just couldn't keep up.  Lost tons of rpm, but when the switch went back to both, it smoothed out.  

[Marauder]

I had a similar experience in August. My airspeed loss was in the 5-7 KIAS range. I downloaded the engine data from the JPI and sent it over to SaavyAviator to have a look at it. They saw nothing in the data and couldn't explain the loss of speed from an engine perspective.

[Guest]

I too have seen this in my E model, it drove me nuts for a while. I would be flying loose formation with my buddy when suddenly I would lose up to 10 knots. I worked my way through everything and finally re did my new magnetos on my recently overhauled engine. Lots of issues within, once corrected the speeds were normal.

Clarence

[Piloto]

How is the climb rate? Power changes are more noticeable during climb. One factor that affect IAS is weight. Did you have the same amount of fuel and cargo?. Some autopilots have no auto trim and this can cause an out of trim condition when in altitude hold that will slow the plane. Check for a slight pitch up/dn when A/P disengaged. Verify the flaps are raised in cruise.

 

José 

[Mooneymite]

It could simply be "atmospherics", I.E. wind/temp/thermals/etc.

 

Fly a few more flights, preferably in the early morning/late evening when the air is calm.  If the problem persists, you can rule out atmospherics.

[nugs314]

Gents thanks for all the help/ info. I am going to have the mags checked out. I was loosing my mind for the 4 hour flight trying to figure out what the heck was going on. I would almost feel better if I saw some engine abnormalities other than the airspeed issues. I'll update after my mech digs through it and I get her up flying again.

S/F,

Nugs

[takair]

You mentioned gear is up. Was watching another Mooney take off just last week, gear up, but nose gear doors were down! I suspect in cruise, they would float around. This is the second time I've seen this on a Mooney. I bet that would be worth a few knots. Do you have vacuum step? Could your step be floating down? Did you say there was no change in RPM or MP? Check your exhaust too, I'm not sure what the indications would look like, but flame tubes could break off and partially block the exhaust.

[nugs314]

You mentioned gear is up. Was watching another Mooney take off just last week, gear up, but nose gear doors were down! I suspect in cruise, they would float around. This is the second time I've seen this on a Mooney. I bet that would be worth a few knots. Do you have vacuum step? Could your step be floating down? Did you say there was no change in RPM or MP? Check your exhaust too, I'm not sure what the indications would look like, but flame tubes could break off and partially block the exhaust.

Good stuff, step was up. Didn't consider the gear door. I'm pretty sure it would have ripped off on my decent though. The exhaust is something I definitely will have checked. Thanks!

[DanM20C]

Take a look at the small tube running from the manifold pressure gauge to the manifold. Mine once developed a crack up by the manifold. My gauge would read somewhere in between atmospheric and actual manifold pressure. Making me think I was flying my normal power settings but I wasn't. I was 10kts slow. If your fuel flow was normal this probably isn't the problem but could be worth a look.

[John Pleisse]

I am assuming you meant true air speed. Unless you are at an atmosphere of 2,000 or lower, they (ground speed and indicated) should never match up. I like the down draft-up draft notion given above. On a windy day, up to 30 miles down range from the Appalachains, you can get these all the time...they can go on for a good 10 miles. Typical from DC to FL.

[FloridaMan]

I have experienced this a handful of times:

 

• As some people have mentioned, if you are in areas of descending air, you will be climbing to maintain altitude which will affect your airspeed/groundspeed. If you are using an AP/hand fly the airplane and you will notice the adjustments that you have to make. 
• I have experienced this when I had a failing magneto coil. EGTs were not necessarily going off the chart, depending on the mixture setting. Also, the coil behaved weirdly in that it would idle, but not be able to produce spark at run up settings. I would recommend trying mag checks and noting temps on the ground at full power. 
• I have also experienced similar behavior when I had a clogged injector. In that case, the issue was also intermittent. I happened consistently one day, then I was unable to reproduce it the next day, then it came back with a vengeance. The problem manifested itself in flight as surging that went away with mixture adjustments. 
• A fourth item, that most mechanics suggested was the issue before I discovered the obstructed injector, is the fuel servo (throttle body). My understanding of the servo is that it consists of a couple diaphragms that can become stiff over time, making an engine slow to respond. Byron posted a schematic of the part here: http://mooneyspace.com/topic/5317-question-about-the-fuel-servo-on-injected-engines/
  • Another method of failure I investigated with the fuel servo was to verify the o-rings were not failing. My understanding of the process is as follows: (this is done with engine off) Open your Ram-Air door, so you can look directly into the fuel servo and look at the impact tubes (I assume you can do this with the standard Cowl; I have the LoPresti cowling). With the mixture at idle cut-off, open the throttle all the way and turn on your electric boost pump. Look through the ram air door and see if you have any fuel leaking out of those tubes. You will likely have fuel running out of your intake vent tube (under the belly) onto the ground after several seconds. This is normal, as is loading of fuel into one of the cylinders if you pull your plugs. 

[nugs314]

I am assuming you meant true air speed. Unless you are at an atmosphere of 2,000 or lower, they (ground speed and indicated) should never match up. I like the down draft-up draft notion given above. On a windy day, up to 30 miles down range from the Appalachains, you can get these all the time...they can go on for a good 10 miles. Typical from DC to FL.

Definitely not atmospherics. The the IAS was far less than normal for the flight conditions and the GS from the GPS backed up what I would expect to see with the indicated airspeed reading slow with the atmospherics and a 10kt tail wind. Trust me, I have been scratching my head. My mech is on it today. Anxious to get this sorted.

[nugs314]

I have experienced this a handful of times:

 

• As some people have mentioned, if you are in areas of descending air, you will be climbing to maintain altitude which will affect your airspeed/groundspeed. If you are using an AP/hand fly the airplane and you will notice the adjustments that you have to make. 
• I have experienced this when I had a failing magneto coil. EGTs were not necessarily going off the chart, depending on the mixture setting. Also, the coil behaved weirdly in that it would idle, but not be able to produce spark at run up settings. I would recommend trying mag checks and noting temps on the ground at full power. 
• I have also experienced similar behavior when I had a clogged injector. In that case, the issue was also intermittent. I happened consistently one day, then I was unable to reproduce it the next day, then it came back with a vengeance. The problem manifested itself in flight as surging that went away with mixture adjustments. 
• A fourth item, that most mechanics suggested was the issue before I discovered the obstructed injector, is the fuel servo (throttle body). My understanding of the servo is that it consists of a couple diaphragms that can become stiff over time, making an engine slow to respond. Byron posted a schematic of the part here: http://mooneyspace.com/topic/5317-question-about-the-fuel-servo-on-injected-engines/

• Another method of failure I investigated with the fuel servo was to verify the o-rings were not failing. My understanding of the process is as follows: (this is done with engine off) Open your Ram-Air door, so you can look directly into the fuel servo and look at the impact tubes (I assume you can do this with the standard Cowl; I have the LoPresti cowling). With the mixture at idle cut-off, open the throttle all the way and turn on your electric boost pump. Look through the ram air door and see if you have any fuel leaking out of those tubes. You will likely have fuel running out of your intake vent tube (under the belly) onto the ground after several seconds. This is normal, as is loading of fuel into one of the cylinders if you pull your plugs. 

Thanks Antares, the servo was mentioned by my mech but not the injector. I will ask about that. Good info!

[FloridaMan]

If it is an injector, you'll probably see an EGT on that cylinder that is much higher or lower than the others. Like I said, in my case, the injector obstruction was inconsistent. 

[philiplane]

Was your CG different that normal? Forward CG will cost 5-7 knots. Mid to aft CG gives book performance. Most Mooneys are flown at forward CG unless pilots ensure there is enough aft baggage weight to offset pilots and fuel. It can take as much as 80 pounds in the baggage to offset full fuel and two pilots with no passengers. 

[Piloto]

That is a good observation Philiplane, specially if you are heavy. Try moving the pilot seat all the way back and check on the speed. The seat positioning may cause a speed change in flight.

 

José