Loss of power

[Steve Brown]

Actually I think partial loss for between one and two seconds.

It was a short flight of 0.6 flight hours. At the turn around I climbed from 3500 to 4500 for the return flight. The climb was strong, but after leveling off and while still accelerating power was significantly reduced for about 1-to-2 seconds.

I could hear it and feel the change in acceleration which went from positive to negative.

All engine gauges were nominal. I checked the mags and both were normal. The rest of the flight was without incident.

The fuel samples from both wings had been clean at pre-flight.

The air temperature was pretty hot, but not close to the hottest I've flown this airplane in. Usually I start leaning in the climb, but this time the mixture was full rich. Density altitude was over 6000 at 4500 MSL. I don't think this is related, but it is different from usual.

Also, I had left the fuel pump on due to a traffic distraction departing the pattern. I don't think this is related and certainly not the first time I have done it.

I'm thinking it was a fuel issue, either some water, contamination, or a bubble (vapor lock). The sound and feeling was similar to over leaning an engine.

This was Murphy's law at play. My passenger was my daughter in law. Her first in a small airplane and she is a afraid of flying. The dialog went something like this:
Me - Did you feel that?
Her - Yes, what was it?
Me - It felt like we momentarily lost power.
Her - What caused it?
Me - I don't know.
Her - What usually causes it?
Me - In 1300 hours of flying, this is the first time it has happened.
Her - Oh

Whoops, too much information. Then I moved on to explaining how far we could glide and what we would do if the motor stopped altogether. She seemed content and the family got a laugh about it once we got home.

My current current best guess is a fuel vapor bubble and planned course of action is to wait and see if it happens again.

I am very interested in any thoughtful speculation about what may have caused this and what to do, if anything.

[N941WR]

Steve,

Is there any chance it could have been a slug of water that worked its way through?

It is unlikely that it is an ignition issue as they both wouldn't go out at the same time.

That leaves either fuel or air and my guess is fuel.

[osxuser]

Originally Posted by Steve Brown

Actually I think partial loss for between one and two seconds.

It was a short flight of 0.6 flight hours. At the turn around I climbed from 3500 to 4500 for the return flight. The climb was strong, but after leveling off and while still accelerating power was significantly reduced for about 1-to-2 seconds.

I could hear it and feel the change in acceleration which went from positive to negative.

All engine gauges were nominal. I checked the mags and both were normal. The rest of the flight was without incident.

The fuel samples from both wings had been clean at pre-flight.

The air temperature was pretty hot, but not close to the hottest I've flown this airplane in. Usually I start leaning in the climb, but this time the mixture was full rich. Density altitude was over 6000 at 4500 MSL. I don't think this is related, but it is different from usual.

Also, I had left the fuel pump on due to a traffic distraction departing the pattern. I don't think this is related and certainly not the first time I have done it.

I'm thinking it was a fuel issue, either some water, contamination, or a bubble (vapor lock). The sound and feeling was similar to over leaning an engine.

This was Murphy's law at play. My passenger was my daughter in law. Her first in a small airplane and she is a afraid of flying. The dialog went something like this:
Me - Did you feel that?
Her - Yes, what was it?
Me - It felt like we momentarily lost power.
Her - What caused it?
Me - I don't know.
Her - What usually causes it?
Me - In 1300 hours of flying, this is the first time it has happened.
Her - Oh

Whoops, too much information. Then I moved on to explaining how far we could glide and what we would do if the motor stopped altogether. She seemed content and the family got a laugh about it once we got home.

My current current best guess is a fuel vapor bubble and planned course of action is to wait and see if it happens again.

I am very interested in any thoughtful speculation about what may have caused this and what to do, if anything.

What was the relative humidity? I could have been a little chunk of carb ice that got ingested... wouldn't be the first time. RV's aren't prone to carb ice, but it does happen on occation, and high temp+high relative humidity is perfect conditions.

[DeltaRomeo]

Could have been a 'lead ball'. Tiny piece of lead breaks off the side of a plug and momentarily shorts out that plug - feels like a 1-2 second dip in power.

I've had it happen and it feels kinda like what you described. Just an idea...

[Sam Buchanan]

Had the same thing occur last year, the only such occurrence in ~850 hrs of flight in the RV-6 (O-320, carbed, mags). I decided it must have been carb ice since the OAT was ~35*F with high humidity. I didn't think about the possibility of a lead ball, but I believe the drop in power was too significant to explain with the loss of just one plug. If a valve had been sticking, I believe the engine would have been running quite rough. But this episode was smooth, like pulling the throttle back 150 rpm for a couple of seconds. By the time I reflexively switched tanks and started turning toward a nearby private airstrip, the engine was running fine. It surprised me so much I forgot to apply carb heat (never use it in this plane except to test it during runnup) but that will be my first action if it happens again.

It definitely got my attention.....but has not happened since.

[RV8N]

Sounds like a slug of water to me. Water can settle out and sit on those stiffeners that are between the ribs on the bottom of the tank. It would take something significant to get it down to the pick-up. The climb you described may have done it.

Karl

[Steve Brown]

And I'll keep monitoring the thread for additional input.

Every suggestion has an element of plausibility, but also problems:

-The led ball. The power loss felt greater than switching off one of the mags, which takes 4 plugs out of action. Of course, when I've done that I was in steady cruise. It may be more noticeable if accelerating. I don't believe it could have been one plug. Maybe the E/P mags shut down the whole mag if there is a short, until its cleared.

-Water in fuel. No water at preflight and no exposure to water recently. I had been on the left tank for about 10 minutes. I think that is about the right amount of time for something to work its was through. I pulled the plans and noticed the pickup tube seems like it could hold water on its own, though how it could get in there is a mystery. Then there is the vestigial gascolator. I've never emptied it and I wonder if it could have gradually filled with water that just "spilled" in the line????????????? Also Karl's suggestion but I though my leveling off was petty gentle.

-Carb ice. It was about 80F at altitude. I had been in the air about 20 minutes, cruising ~65%. At the point of the problem I had been at full throttle for about 1 minute from 3500-4500 climb and still accelerating at full throttle in level flight. Doesn't seem to meet the textbook carb ice scenario, but the symptoms do agree.

At this point I'm not eliminating any of these, but hoping that it doesn't happen again.

[L.Adamson]

Originally Posted by Steve Brown

-Carb ice. It was about 80F at altitude. I had been in the air about 20 minutes, cruising ~65%. At the point of the problem I had been at full throttle for about 1 minute from 3500-4500 climb and still accelerating at full throttle in level flight. Doesn't seem to meet the textbook carb ice scenario, but the symptoms do agree.

At this point I'm not eliminating any of these, but hoping that it doesn't happen again.

One thing about the Lyc, is that it's carb is mounted to the "warm" oil sump (as opposed to the Continental), which slightly warms the carb for additional icing protection. This can only lead to farther speculation...

L.Adamson

[rvbuilder2002]

Originally Posted by Steve Brown

And I'll keep monitoring the thread for additional input.

Every suggestion has an element of plausibility, but also problems:

-The led ball. The power loss felt greater than switching off one of the mags, which takes 4 plugs out of action. Of course, when I've done that I was in steady cruise. It may be more noticeable if accelerating. I don't believe it could have been one plug. Maybe the E/P mags shut down the whole mag if there is a short, until its cleared.

-Water in fuel. No water at preflight and no exposure to water recently. I had been on the left tank for about 10 minutes. I think that is about the right amount of time for something to work its was through. I pulled the plans and noticed the pickup tube seems like it could hold water on its own, though how it could get in there is a mystery. Then there is the vestigial gascolator. I've never emptied it and I wonder if it could have gradually filled with water that just "spilled" in the line????????????? Also Karl's suggestion but I though my leveling off was petty gentle.

-Carb ice. It was about 80F at altitude. I had been in the air about 20 minutes, cruising ~65%. At the point of the problem I had been at full throttle for about 1 minute from 3500-4500 climb and still accelerating at full throttle in level flight. Doesn't seem to meet the textbook carb ice scenario, but the symptoms do agree.

At this point I'm not eliminating any of these, but hoping that it doesn't happen again.

I think it would be a good idea to sump your gascolator.
It is not likely to be full of water but it is possible.
I sump mine during every oil change or if the airplane has been outside with a lot of rain. I have a hole in the cowl bottom that allows sumping without cowl removal.

[rrd1_99]

[quote=Steve Brown;248532] Usually I start leaning in the climb, but this time the mixture was full rich. Density altitude was over 6000 at 4500 MSL. QUOTE]

This question is as much for my knowledge as it is for trying to help figure out what happened. Is it possible that simply running too rich would manifest itself like this? We would expect it to just result in a reduced power output at that altitude and not just "disappear" after 1-2 seconds, but did you maybe adjust the mixture shortly after it happened?

I agree that while it sounds just like carb ice, it doesn't seem to fit the scenario since you had been at full throttle for a while.

Roger Barnes
-9A slow QB