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Takeoff anomaly.

Richard Connell

Richard Connell

Well Known Member
Question for the engine experts:

I went away on a trip this week.
Bit of a long story, but the airport I'm flying out of is short one of 3 runways due maintenance, so there are large ground delays. I had about a 30min delay on the ground while awaiting various clearances. It was quite a warm day. On takeoff I had a noticeable stumble at about 3/4 throttle which cleared almost as quickly as I noticed it and arrived at full throttle. By this time I was airborne. No other issues noticed for the flight.
I put it down to fouling due to the protracted ground running.
It repeated on the subsequent takeoff . So clearly there's something amiss and we are now grounded. I pulled the data and to my surprise, both 4 and 6 appear to have gone quite cold momentarily.
My first thought is it must be fuel related but Im curious to hear where others think I should start.
Its a IO540 with one mag and one surefly. AFP FI. Aircraft plugs.
I recently installed turbo rails but I've done around a dozen flights since with no issues.

Screen Shot 2023-11-20 at 8.56.27 am.png
 
Richard - what was the ambient temperature? A very brief stumble and then full power sounds a lot like a bit of fuel vapor went through the system.

Perhaps on the runway try about half throttle for maybe 10s, holding with brakes. Then release and go full throttle. That might clear any vapor in the system, if it should be that.
 
Hi Alex. Yes that definitely crossed my mind for the first event but the second was down south. OAT about 12c and only a few mins from startup to takeoff.
Plus I’ve never had a vapor issue before and have done lots of flying in very hot conditions recently.
 
Can you share the savvy link? The behavior of #4 and #6 are slightly different but the FF overlay makes it a little hard to determine.

I don't think it's ignition related -- especially since you are running with two different systems. Ignition related issues usually manifest as an abnormally elevated EGT compared to cohorts.

An issue with Fuel/Air delivery could cause the "cold cylinder" syndrome - A plugged or dry injector, or a stuck valve, or a floating valve could also be the culprit.
 
bjdecker said:
Can you share the savvy link? The behavior of #4 and #6 are slightly different but the FF overlay makes it a little hard to determine.

I don't think it's ignition related -- especially since you are running with two different systems. Ignition related issues usually manifest as an abnormally elevated EGT compared to cohorts.

An issue with Fuel/Air delivery could cause the "cold cylinder" syndrome - A plugged or dry injector, or a stuck valve, or a floating valve could also be the culprit.
Click to expand...

here you go

https://apps.savvyaviation.com/flights/shared/flight/7579466/8c66d93d-d3bc-4433-b501-cdaee159136c
 
Data...

Richard Connell said:
here you go

https://apps.savvyaviation.com/flights/shared/flight/7579466/8c66d93d-d3bc-4433-b501-cdaee159136c
Click to expand...

Richard,

I think the injectors on #4 & 6 went dry -- perhaps debris in the fuel distribution spider.

See anomalous events at 07:53 - 07:55 -- EGT 6 falls precipitously at low MAP, RPM and FF -- not indicative of a floating valve.

On another note -- the physics of air must be different down under :) How on earth are you getting 25" MAP at 9K ft? Got a turbo lurking under the hood?

Check your MAP transducer and make sure there's no gunk blocking the orifice.
 
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Yes I think you are right. I’ll pull the spider and take a look next.

Re the MAP, it’s the snubber I think. Ive pulled it and cleaned it a few times as this came up a few months ago. It kind of acts like a one way valve I think.
But without it, the readings are unreadable. So it’s a problem for future me.
 
Richard Connell said:
Yes I think you are right. I’ll pull the spider and take a look next.

Re the MAP, it’s the snubber I think. Ive pulled it and cleaned it a few times as this came up a few months ago. It kind of acts like a one way valve I think.
But without it, the readings are unreadable. So it’s a problem for future me.
Click to expand...

Get rid of the Omega PS-8g snubber. Install a .008” restrictor instead. This solved the steadily increasing MAP issue on my G3X…
 
Just to close out this thread, I pulled the spider and the lines/nozzles/restrictors for 4/6.

Dissasembled and gave it all a clean. There was no obvious sign of contamination, but I assume that it dosent take much. The filters were all clean too.

Anyway, we are now back to regular programming. No stumbling and a nice tight GAMI spread again.

Thanks all.
 
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