Scary situation... M20K Encore not making full power

[nickmatic]

Had a scary situation last night... I took off at night from a fairly short field (2600ft). I had just filled the tanks and had pax on board so I wasn't super surprised the takeoff roll was long. But we got off and I right away I had to keep the nose up and airspeed down to climb even slowly. I focused on keeping the speed above stalling and getting some altitude and finally noticed I was only seeing about 25" of manifold pressure at full throttle instead of the usual 39". I had neglected to check full power during the roll (where I check airspeed alive and engine green). Big oops. Lucky we got off the ground.

After about 5-10 minutes, the engine bounced up to 39" on its own and the flight continued normally.

Any ideas what might have caused this?

[cbarry]

This situation sounds a lot like the turbocharger was not spooling up.  

 

[nickmatic]

This situation sounds a lot like the turbocharger was not spooling up.  

 

I had this thought as well. Is there a way to know definitively?

[ArtVandelay]

I had this thought as well. Is there a way to know definitively?

I would start with downloading the engine monitor data.

[nickmatic]

I would start with downloading the engine monitor data.

Good suggestion, thanks! There is a CF card in the monitor. I'll have to check that out.

[carusoam]

Oil flow to the bearings would be of interest. The heat of the turbine has a tendency to burn the oil.  It would make sense to have a mechanic clean out the oil lines to make sure they are flowing, catch anything that is in that oil. Then inspect the bearings and the rotor for proper operation.

It would not be normal to think it is going to fix itself. You want to know what caused that happen to get it fixed properly.

You may also want to mention what waste gate you have, is it fixed or variable.  When was the system's last OH?

I am a PP, not a mechanic, not even a TC or TN'd pilot.

best regards,

-a-

Edited October 18, 2015 by carusoam

[nickmatic]

Oil flow to the bearings would be of interest. The heat of the turbine has a tendency to burn the oil.  It would make sense to have a mechanic clean out the oil lines to make sure they are flowing, catch anything that is in that oil. Then inspect the bearings and the rotor for proper operation.

It would not be normal to think it is going to fix itself. You want to know what caused that happen to get it fixed properly.

You may also want to mention what waste gate you have, is it fixed or variable

I am a PP, not a mechanic, not even a TC or TN'd pilot.

best regards,

-a-

Yes, definitely getting this checked out. Not good. The Encore/252 has an automatic wastegate. Thanks for the advice.

[carqwik]

Same thing happened to me in a 252 back in the early 1990s at Van Nuys.  This was on a rental 252.  I just flew the pattern and landed.  IIRC from what I was later told, it was a stuck wastegate.

[FlyDave]

Had a scary situation last night... I took off at night from a fairly short field (2600ft). I had just filled the tanks and had pax on board so I wasn't super surprised the takeoff roll was long. But we got off and I right away I had to keep the nose up and airspeed down to climb even slowly. I focused on keeping the speed above stalling and getting some altitude and finally noticed I was only seeing about 25" of manifold pressure at full throttle instead of the usual 39". I had neglected to check full power during the roll (where I check airspeed alive and engine green). Big oops. Lucky we got off the ground.

After about 5-10 minutes, the engine bounced up to 39" on its own and the flight continued normally.

Any ideas what might have caused this?

To me this definitely sounds like the turbocharger not spooling up. I would not fly it again until this issue is reviewed by a mechanic and <hopefully> resolved.

If you were only making 25" MP why didn't you stay in the pattern and land immediately instead of flying for 5-10 minutes more - at night, with passengers (or did I mis-read your post)?

[Guest]

Stuck or sticking wastegate, lubricate with Mouse Milk at every 30 hour oil change.  A defective throttle cable also a possibility.

Clarence

[jackn]

While it could be the turbo/wastegate, I'd first check the throttle. When you go full throttle, you open the butterfly full and a cam on the throttle plate pushes a piston in. This in turn closes off the oil coming from the wategate thereby closing the wastegate. I lubricate the throttle mechanism with some LPS2 while a friend moves the throttle back and forth everytime I change the oil. Just make sure everything moves freely.

[Yooper Rocketman]

To me this definitely sounds like the turbocharger not spooling up. I would not fly it again until this issue is reviewed by a mechanic and <hopefully> resolved.

If you were only making 25" MP why didn't you stay in the pattern and land immediately instead of flying for 5-10 minutes more - at night, with passengers (or did I mis-read your post)?

Agree with the first statement.

Don't agree with the second.  Not sure I would want to land on a 2600' runway, at night, with an engine that had very marginal climbing ability (a problem if I had to go missed) when it's still making enough power to stay airborne while I figured out my options.  I would have likely stayed in the airport area in the event it got worse, or until I was high enough to make it to a larger airport.

[nickmatic]

Great suggestions, thanks all. Definitely feel better knowing some of the possibilities. Think it's pretty safe to fly it to my regular mechanic 45 minutes away (assuming I can get full power before takeoff)?

As for the decision to not land immediately, I wasn't far from home and the power returned at the same time I started to feel safe about altitude. It was probably 5 minutes but felt like an eternity. Being night I opted for the longer and well lit runway with emergency equipment over the podunk airport from which I had departed. 

[CoachTom]

Turbo will be spinning at whichever speed it is allowed to spin at due to exhaust flow through its vanes.  If the turbo was starved of oil, or if there was any bearing issue, the turbo would seize rather quickly due to its high RPM.  It would not "fix" itself with time and oil...

I would posit your first place to look would be at the wastegate's ability to open and close.  I am sure if there was 60psi of oil pressure, the sequence of throttle application, the wastegate would operate normally, so look into the exhaust side to see if any carbon has built up restricting the full operation. The other issue would be that the wastegate was failing in an "open" position as you could not generate boost and subsequent take off power.  If it was closed, you would have all the power and you would have to use he throttle to adjust the boost.  hard to do and chase the power settings, but do-able.

Mouse Milk is a lubricant designed for high heat applications and is usually sprayed into wastgates to aid in their operation.  This is not an approved lubricant for Merlyn wastegates. Let us know how you faired with its resolution.

 

[carusoam]

Nick,  Do you have any JPI data that you can review?

EGTs and TIT may help indicate what else (if anything) may have been going on at the same time...

When the POH says try a restart below 12k', this is the point when there is enough N/A MP for the low compression (TC'd) engine to have enough compression to generate some power in the event the TC system is broken or a hose comes off.

 

Questions for turbo charged engine flyers....

You get 15 seconds to answer the following... (Approximate Ground roll time)

What instruments do TC'd pilots usually check before committing to Flight?  (MP, FF)

Does the run-up give a fair indication of the TC's operation?

Best regards,

-a-

 

[chrisk]

Manifold pressure is always on my list.  I push the throttle in, wait a few seconds and feel the turbo kick in, and glance at the gauge to make sure I don't over boost.  This gets checked a time or two on the roll and around  50 feet.

As for instruments before committing on the take off roll.   Airspeed, Manifold pressure, and RPM.  And if it is a touch and go or go around, throw in the VSI.  (it gets really busy, especially if you had full flaps)  

 

[nickmatic]

Nick,  Do you have any JPI data that you can review?

EGTs and TIT may help indicate what else (if anything) may have been going on at the same time...

I have an Insight G3. I'll have to see what kind of data it records when I next get out to the plane.

What instruments do TC'd pilots usually check before committing to Flight?  (MP, FF)

I always check airspeed coming alive and oil temp and pressure in green. BIG MISTAKE to not check that manifold pressure comes up to full. The 252/Encore has an automatic wastegate so I'm used to just opening the throttle and rolling. Huge lesson learned.