Extreme CHT temps immediately after takeoff - 2nd post-maint flight that day - Mayday.

[Ragsf15e]

5 hours ago, PT20J said:

Thanks for the updated link. I went back and looked at the data for a flight where I accidentally took off in my M20J with the mixture leaned. My fuel flow during initial climb from sea level was about 12 gph (yours during the incident was about 15). Normal sea level takeoff fuel flow is around 18 gph. The highest the CHT reached during my climb was 367 F during a 2 min climb before I richened the mixture. My timing is set to 20 BTDC which might give it more detonation margin than one set to 25 degrees. Still, I doubt that you could get that kind of thermal runaway by restricting fuel flow to 15 gph as it takes time for things to heat up enough to get the point of detonation. Your #2 cylinder exceeded redline CHT after a little over 1 minute at an altitude of about 300' AGL. Both cyl 1 and cyl 2 are showing a temperature rise of around 180 F/min. 

Skip

Thinking about your situation vs his… 12gph could possibly have been lean of peak vs our normal ~18gph+ on takeoff. Warm, yes, but lean enough it didn’t detonate and do damage.  His at 15, maybe closer to 50 rich of peak?

I agree there’s probably more to it with how fast his went downhill, but yours may have been just lean enough.

[PT20J]

8 minutes ago, Ragsf15e said:

Thinking about your situation vs his… 12gph could possibly have been lean of peak vs our normal ~18gph+ on takeoff. Warm, yes, but lean enough it didn’t detonate and do damage.  His at 15, maybe closer to 50 rich of peak?

I agree there’s probably more to it with how fast his went downhill, but yours may have been just lean enough.

I suppose that’s possible. But, if my takeoff was LOP, then the power would have been 12 * 15 = 180 hp and I’m pretty certain that I would have noticed the loss of 20 hp during the takeoff roll and climb. But everything seemed normal until I did a scan and noticed that the mixture wasn’t full rich.

According to the Lycoming Operator’s Manual best power mixture fuel flow at rated power is 15.7 gph. 

 

 

[mhrivnak]

Just an observation: EGT 1 and 2 started to run away exactly at the moment of rotation. The engine ran full power for 18 seconds with similar parameters to the former flight. But just when IAS stopped increasing and altitude started rising, that's where the EGTs take off. That could be consistent with a theory that the physical pitch change at rotation contributed to dislodging some rust or debris in the fuel system, or maybe there's some other connection, or maybe it's a coincidence.

[Shadrach]

10 hours ago, PT20J said:

I suppose that’s possible. But, if my takeoff was LOP, then the power would have been 12 * 15 = 180 hp and I’m pretty certain that I would have noticed the loss of 20 hp during the takeoff roll and climb. But everything seemed normal until I did a scan and noticed that the mixture wasn’t full rich.

According to the Lycoming Operator’s Manual best power mixture fuel flow at rated power is 15.7 gph. 

If your FF number is correct, the most power you could have made at 12gph is ~180hp.  You had to have been down at least 20hp. It takes a little over 13gph to get 200hp at best BSFC.

[David Lloyd]

12 hours ago, PT20J said:

Thanks for the updated link. I went back and looked at the data for a flight where I accidentally took off in my M20J with the mixture leaned. My fuel flow during initial climb from sea level was about 12 gph (yours during the incident was about 15). Normal sea level takeoff fuel flow is around 18 gph. The highest the CHT reached during my climb was 367 F during a 2 min climb before I richened the mixture. My timing is set to 20 BTDC which might give it more detonation margin than one set to 25 degrees. Still, I doubt that you could get that kind of thermal runaway by restricting fuel flow to 15 gph as it takes time for things to heat up enough to get the point of detonation. Your #2 cylinder exceeded redline CHT after a little over 1 minute at an altitude of about 300' AGL. Both cyl 1 and cyl 2 are showing a temperature rise of around 180 F/min. 

Skip

One of the mags was incorrectly set at 27 degrees, even less detonation margin.  

[PT20J]

7 hours ago, Shadrach said:

If your FF number is correct, the most power you could have made at 12gph is -180hp.  You had to have been down at least 20hp. It takes a little over 13gph to get 200hp at best BSFC.

Good point. 

[Shadrach]

3 hours ago, David Lloyd said:

One of the mags was incorrectly set at 27 degrees, even less detonation margin.  

Maybe this was the cumulative effect of many things.  
 

I don’t think one mag set 2° advance of spec would make much difference. Half the flame front initializing two degrees early is not very significant.

[TheMooneyAnomaly]

11 hours ago, mhrivnak said:

Just an observation: EGT 1 and 2 started to run away exactly at the moment of rotation. The engine ran full power for 18 seconds with similar parameters to the former flight. But just when IAS stopped increasing and altitude started rising, that's where the EGTs take off. That could be consistent with a theory that the physical pitch change at rotation contributed to dislodging some rust or debris in the fuel system, or maybe there's some other connection, or maybe it's a coincidence.

That one has been on my mind.  This still irritates me.  Why was flight #1 perfect?

Switch tanks on ground just after start for flight #2.  Could that have dislodged things, like someone noted earlier?

 

I didn't make any aggressive moves and my takeoff was gentle... so I don't think it was uniquely capable of dislodging debris, compared to the prior flight.

 

It will be interesting to get fuel contamination ruled in/out when we get the lab results.  They do not tell us what is in the fuel, but they will tell us characteristics of the fuel vs. what it should be.

[David Lloyd]

1 hour ago, Shadrach said:

Maybe this was the cumulative effect of many things.  
 

I don’t think one mag set 2° advance of spec would make much difference. Half the flame front initializing two degrees early is not very significant.

By itself, no, but combined with a slightly low fuel flow, the need for higher than normal flow (Power Flow exhaust), some other unknown factors I think that potential is there.  You’d think something relatively minor would not cause something like this.  Why aren’t other engines doing the same thing? I don’t have an answer.

I did have an IO360 with 10:1 pistons and would detonate sometimes when timed at 25* but never when timing was set to 23*.

All the fixes listed may or may not take care of the problem.  I would also have a shop inspect both mags. At least 4 plugs need replacing, I would replace all 8.

[mhrivnak]

59 minutes ago, StPeteM20F said:

I didn't make any aggressive moves and my takeoff was gentle... so I don't think it was uniquely capable of dislodging debris, compared to the prior flight.

The smoothest Mooney takeoff still feels every bump in the runway. We get used to it, but even a runway in excellent condition can shake things around.

What do you make of the big MAP swings that started in the middle of the earlier flight? Looks like the airplane leveled off from climb, reduced RPM from 2500 to 2400, and that's the moment when MAP started oscillating in a fairly consistent pattern with 12-15s between peaks. At 16m in, they start a descent, and while descending the oscillations speed up to 5 second periods with a smaller amplitude. When they level off, the oscillation slows down again with a bigger amplitude. The descent at 20m follows the same pattern: faster and smaller oscillation during descent, returning to slower and bigger at level-off.

Comparing the warm-up data from the beginning of each flight when the engine was running about 1000 rpm, the MAP seems noticeably more volatile on the second flight. Then during your takeoff roll, it was jumping around A LOT. There were three peaks even above ambient (measured at 30 prior to engine start): 30.4, 31, then 30.6. Is it possible that something was pressurizing the intake manifold?

It sure seems like this data is trying to tell us something. I wish I knew what it was!

But it does seem like something went awry with the intake system first. It may have started during the first flight, but not caused harm at cruise power and below.

Your first post said the team reported "No intake leaks",  but I wonder how they determined that. It seems like much of this might be explained with an intake leak affecting cyls 1 and 2 where the leak was moderate for a while, then whatever gap was the source of the leak physically opened up wider at rotation, leading to a very lean condition. For example, just speculating: if someone loosened intake pipe hardware on the front cylinders for some reason while installing the new exhaust, that might result in forgetting to re-tighten, and/or damaging the old-and-crusty intake gasket that needed to be replaced if disturbed, or something like that. It could have partially shaken loose during the prior flight, then further let go at rotation in your flight.

The MAP sensor installation is also a consideration. I don't know where it's plumbed in on your engine, but I suspect the engine monitor displayed on the g3x touch required new engine sensors to be installed. That's another opportunity to introduce an intake leak.

Speaking of sensors, did you have new fuel sensors installed? Anything different about the fuel line routing, for example to accommodate a new fuel flow sensor? Forgetting about MAP for a second, I wonder if a fuel line too close to the new exhaust could cause issues of vaporization or similar. Speculating wildly now: maybe with the pitch change at rotation, whatever liquid fuel was in the divider would pool in the back, feeding the lines to cylinders 3 and 4 normally, while the front cylinders got the vapor.

[Will.iam]

5 minutes ago, mhrivnak said:

The smoothest Mooney takeoff still feels every bump in the runway. We get used to it, but even a runway in excellent condition can shake things around.

What do you make of the big MAP swings that started in the middle of the earlier flight? Looks like the airplane leveled off from climb, reduced RPM from 2500 to 2400, and that's the moment when MAP started oscillating in a fairly consistent pattern with 12-15s between peaks. At 16m in, they start a descent, and while descending the oscillations speed up to 5 second periods with a smaller amplitude. When they level off, the oscillation slows down again with a bigger amplitude. The descent at 20m follows the same pattern: faster and smaller oscillation during descent, returning to slower and bigger at level-off.

Comparing the warm-up data from the beginning of each flight when the engine was running about 1000 rpm, the MAP seems noticeably more volatile on the second flight. Then during your takeoff roll, it was jumping around A LOT. There were three peaks even above ambient (measured at 30 prior to engine start): 30.4, 31, then 30.6. Is it possible that something was pressurizing the intake manifold?

It sure seems like this data is trying to tell us something. I wish I knew what it was!

But it does seem like something went awry with the intake system first. It may have started during the first flight, but not caused harm at cruise power and below.

Your first post said the team reported "No intake leaks",  but I wonder how they determined that. It seems like much of this might be explained with an intake leak affecting cyls 1 and 2 where the leak was moderate for a while, then whatever gap was the source of the leak physically opened up wider at rotation, leading to a very lean condition. For example, just speculating: if someone loosened intake pipe hardware on the front cylinders for some reason while installing the new exhaust, that might result in forgetting to re-tighten, and/or damaging the old-and-crusty intake gasket that needed to be replaced if disturbed, or something like that. It could have partially shaken loose during the prior flight, then further let go at rotation in your flight.

The MAP sensor installation is also a consideration. I don't know where it's plumbed in on your engine, but I suspect the engine monitor displayed on the g3x touch required new engine sensors to be installed. That's another opportunity to introduce an intake leak.

Speaking of sensors, did you have new fuel sensors installed? Anything different about the fuel line routing, for example to accommodate a new fuel flow sensor? Forgetting about MAP for a second, I wonder if a fuel line too close to the new exhaust could cause issues of vaporization or similar. Speculating wildly now: maybe with the pitch change at rotation, whatever liquid fuel was in the divider would pool in the back, feeding the lines to cylinders 3 and 4 normally, while the front cylinders got the vapor.

I thought a manifold air leak doesn’t matter at WOT. As all the cylinders are getting as much air as possible so a leak isn’t going to effect the air side of the equation until you start to “throttle” back then all the cylinders that are not leaking will be restricted but the cylinders with an air leak will then get more air than they should for the amount of fuel being metered and thus go lean. 

[mhrivnak]

24 minutes ago, Will.iam said:

I thought a manifold air leak doesn’t matter at WOT. As all the cylinders are getting as much air as possible so a leak isn’t going to effect the air side of the equation until you start to “throttle” back then all the cylinders that are not leaking will be restricted but the cylinders with an air leak will then get more air than they should for the amount of fuel being metered and thus go lean. 

Good point. Though of course the induction system introduces significant and measurable airflow restriction even at WOT, which is AIUI why we don't see MAP get higher than about 1" below ambient air pressure for normally aspirated engines. But it's a fair question: if a leak was so bad that it could deliver full ambient pressure to a cylinder, or slightly more if coming from a pressurized area within the cowling, would that be enough of a difference at WOT to cause a cylinder to be lean enough for detonation? Perhaps if combined with lower fuel flow than usual, as seems like the case here, and timing found to be advanced by 2 degrees, that could all add up to be enough to cause it.

[EricJ]

2 hours ago, Will.iam said:

I thought a manifold air leak doesn’t matter at WOT. As all the cylinders are getting as much air as possible so a leak isn’t going to effect the air side of the equation until you start to “throttle” back then all the cylinders that are not leaking will be restricted but the cylinders with an air leak will then get more air than they should for the amount of fuel being metered and thus go lean. 

Manifold leaks matter after the fuel metering device (servo, carburetor), because any additional air that comes in will be unmetered and lean the mixture more to potentially one cylinder or so than the rest (depending on the location of the leak).   The amount of air leaking will be less on a naturally aspirated engine because at WOT the difference in pressure from outside the manifold to inside will be less, so there will be less pressure differential driving the leak.    On a turbocharged aircraft the leak will be from the manifold out to the outside world, so it'll potentially richen the mixture at one cylinder rather than another as well as potentially limiting boost.

 

[PT20J]

I tried a little experiment today with my IO-360-A3B6 in a M20J with 20 deg BTDC timing. Full power run up at sea level. Leaned mixture to peak EGT which was at about 12.5 gph. The engine ran smoothly with no apparent detonation. I didn't stay there long because the CHTs started to rise after about 30 seconds (there is poor cooling when the airplane isn't moving) but they did not rise rapidly. I've seen rapid rising CHTs when I had a preignition event caused by a faulty spark plug, so I know what that looks like.

Skip

 

 

[Shadrach]

1 hour ago, PT20J said:

I tried a little experiment today with my IO-360-A3B6 in a M20J with 20 deg BTDC timing. Full power run up at sea level. Leaned mixture to peak EGT which was at about 12.5 gph. The engine ran smoothly with no apparent detonation. I didn't stay there long because the CHTs started to rise after about 30 seconds (there is poor cooling when the airplane isn't moving) but they did not rise rapidly. I've seen rapid rising CHTs when I had a preignition event caused by a faulty spark plug, so I know what that looks like.

Skip

 

 

That is an experiment best conducted using the richest cylinder as a reference.

[Shadrach]

1 hour ago, PT20J said:

I tried a little experiment today with my IO-360-A3B6 in a M20J with 20 deg BTDC timing. Full power run up at sea level. Leaned mixture to peak EGT which was at about 12.5 gph. The engine ran smoothly with no apparent detonation. I didn't stay there long because the CHTs started to rise after about 30 seconds (there is poor cooling when the airplane isn't moving) but they did not rise rapidly. I've seen rapid rising CHTs when I had a preignition event caused by a faulty spark plug, so I know what that looks like.

Skip

 

 

What was full finch fuel flow.?

[PT20J]

19 minutes ago, Shadrach said:

What was full finch fuel flow.?

17.6

[carusoam]

Thanks for posting the link to Savvy….

 

PP thoughts only, not a mechanic or data analyst….

 

1) First flight is showing some details…

• The run-up is quick, faster than the JPI can collect a lot of data….  Both mag peaks appear to be similar, but, may not have been given enough time to show a difference…. The peaks will differ when the timing is different between mags….  Allowing the EGTs to peak when testing the mags is a really good idea… more like 15-20 seconds on each switch position…
• As the throttle gets pushed in, FF comes up to a relatively low number for an IO360….
• EGT 1 is playing a different game than the other EGTs….
• Raw EGT data is often challenging to get any detail out of… but, we are not given a Gami spread.
• This 100°F higher value stands out as a look into me kind of moment… check the Gami spread… possible FI blockage…

 

2) Second flight really shows the details….

• The run-up is even harder to find amongst the data….
• Same EGT 1 quirk as the throttle comes up….
• EGT 2,3 both wait 20 seconds before they distinctly start to move… even higher.  This is really unique… as something changed in a step wise fashion for both fuel injectors…
• EGT 2 and 3 are both 100°F higher than EGT1
• Making an EGT spread of about 200°F (again raw numbers, but graphically very meaningful…)
• FF is really standing out asking to be looked at…

 

As mentioned above… full rich, T/O power, near seal level… is usually closer to 10gph per 100 hp…. (Really rich setting for great CHT control)

Flight 1: max FF is 17gph…. But begins tailing off quickly… (?)

Flight 2: max FF is 16.5gph… and continuously goes lower over time…  probably matching rpm that is decreasing…. (?)

Max rpm seems to be showing 2650

Looking at MP… and FF…

For the second flight…

Max FF shows about 16.5gph…  

MP data seems a bit noisy, showing 29.5”

 

 

Posted in reverse order… flight 2 is first, flight 1 follows….  Third graph is MP and FF….

questions…

• how long were all knobs full forwards?
• when did any of the knobs get adjusted?

 

People looking to define how well their fuel injectors are working, often perform a baby food jar test… capturing fuel that has been run through the fuel injectors and measuring any differences…

This is odd… because something changed in 20 seconds of adding power for T/O….

No bumps required… the ship’s acceleration alone can move things….

PP guessing only, not a mechanic or skilled aviator…

Best regards,

-a-