Diagnose this ...

[APenNameAndThatA]

47 minutes ago, old man emu said:

OK. Let's call quits. I set a scenario without ensuring that it was completely debugged. I'm sorry that no one had the ability to look for the main point, but focused on wind, fuel and trim.

 

I was going to pose another question on something else, but I can't be bothered to minutely inspect every syllable to ensure that what I write is blatantly obvious.  Maybe I should work backwards. Provide the answer, then ask people what the question is.

You still don't get it. When you wrote the scenario, what was in your mind was engine power. But once you posted the question, the answers depended on the question not what your intention. The correct answer was wind. If then engine lost power, the aircraft would have lost height (and you did not give enough detail to suggest that a different less likely outcome would have arisen). You were wrong and lacked the grace to admit it. That is the fault of you and your question, not the fault of the people who responded to the question.

 

Re: "I'm sorry no one had the ability to look at the main point." If you had said "I am setting a question and I want you to guess the answer, but you need to remember that the objective is for you to work out what I am thinking, not what the best answer is based on the question," then that would have been more honest and more insightful.

 

Stated differently, it doesn't matter if the question is not debugged when you post it. The question would have given you a different answer to the one you expected. You lacked the humility and mental flexibility to say, *very* early on, "Oh, s-, wind is the obvious answer". That's on you.

 

Re "I was going to pose another question on something else, but I can't be bothered to minutely inspect every syllable to ensure that what I write is blatantly obvious.  Maybe I should work backwards. Provide the answer, then ask people what the question is", the obvious solution is to pose the question and see if you were right. Why on earth do you suppose that the answer has to be certain before you post the question? You. Still. Don't. Get. It.

 

[M61A1]

How about an actual problem?

 

I had this issue a couple of weeks ago.

The aircraft has a Rotax 912 with standard Bings with vent hoses as per Rotax instruction. The installation is pretty normal. A single throttle cable from the dual throttle linkage to a splitter which goes to each carb. 

The installation has an Air/Fuel Ratio gauge fitted. A let over from some previous testing.

The exhaust is not standard Rotax but appears similar in design.

Engine mounts are standard for the aircraft  design, which has a bed mount.

 

The whole installation has been functioning normally for around 400 hours.

 

One afternoon on a normal sort of day with a normal takeoff, about mile from the strip, I reduce the throttle to cruise at 5200 RPM. Moments later power drops to 4800 RPM. After turning back immediately I cycle the throttle a little and find that 4800 RPM is all I'm going to get and the mixture is extremely rich at high power settings. If I reduce power the mixture returns to normal levels.

After landing the engine idles and throttles up normally, but will not produce power above 4800RPM. After shutdown ( having a check under the cowl at various bits) and restarting everything appears to run normally, including ground run, but does the same again after taking off.

 

I fixed it after four hours of troubleshooting and multiple ground runs and test flights.

 

Any takers?

[Blueadventures]

Partially blocked fuel filter or fuel tank vent.

[Thruster88]

Just now, Blueadventures said:

Partially blocked fuel filter or fuel tank vent.

That would cause the mixture to lean, it has to be a blockage of air intake or a float problem.

[M61A1]

23 minutes ago, Blueadventures said:

Partially blocked fuel filter or fuel tank vent.

Both checked, just to rule out.

 

20 minutes ago, Thruster88 said:

it has to be a blockage of air intake or a float problem.

Exactly what I thought.....Pod filters fitted. even swapped them with another set.

After checking plugs it was noted that both sets on the left hand side were sooty while the ones on the right were normal. So float levels were checked, needles and seats tested and floats replaced with a spare set and float bowl vents and galleries were cleaned with compressed air. Also slide diaphragms and needles were inspected with no faults found as part of troubleshooting.

All with no result. 

Then during a ground run there was an abrupt power reduction at full throttle, a mixture reading less than 10:1 (it only reads between 10 and 20:1) while still idling normally and low power operation normal (including air/fuel ratio)).

[planesmaker]

Seal in choke mechanism?

[Blueadventures]

52 minutes ago, M61A1 said:

Both checked, just to rule out.

 

Exactly what I thought.....Pod filters fitted. even swapped them with another set.

After checking plugs it was noted that both sets on the left hand side were sooty while the ones on the right were normal. So float levels were checked, needles and seats tested and floats replaced with a spare set and float bowl vents and galleries were cleaned with compressed air. Also slide diaphragms and needles were inspected with no faults found as part of troubleshooting.

All with no result. 

Then during a ground run there was an abrupt power reduction at full throttle, a mixture reading less than 10:1 (it only reads between 10 and 20:1) while still idling normally and low power operation normal (including air/fuel ratio)).

Next checks perhaps an ignition switch or wiring chaffed and grounding out one ignition or similar type looseness in the soft start circuit.

Edited October 18, 2020 by Blueadventures

[M61A1]

2 minutes ago, planesmaker said:

Seal in choke mechanism?

Checked as well.

 

No fault found.

[M61A1]

3 minutes ago, Blueadventures said:

Next checks perhaps an ignition switch or wiring chaffed and grounding out one ignition or similar type looseness in the soft start circuit.

Mags checked out serv. Wiring all good.  Intermittent problem still there

[Blueadventures]

1 minute ago, M61A1 said:

Mags checked out serv. Wiring all good.  Intermittent problem still there

I'd now check the plugs, ohms etc as could be a failed plug.

[Jase T]

Something is reducing the amount of air you are getting at full suction. Do you have ducting that is collapsing? Oil or other body blocking an air filter? Out on a wing here as you didn't mention the environmental conditions... Inlet icing? 

[M61A1]

I will add at this time an acquaintance came over when I was faultfinding and leaned on the prop. He then started moving the prop back and forwards listening to the tiny amount of backlash in the gears and commented that he could hear that when it was idling. 

It's not the problem but it's a clue.

[onetrack]

Internal lining of intake hose peeling off, bunching up and restricting air flow - but only at high RPM. Throttle closure reduces air flow, and separated hose lining returns to a more normal position, allowing full air flow in intake manifold.

[M61A1]

1 minute ago, Jase T said:

Something is reducing the amount of air you are getting at full suction. Do you have ducting that is collapsing? Oil or other body blocking an air filter? Out on a wing here as you didn't mention the environmental conditions... Inlet icing? 

It has pod filters which are in good condition and it is in the high 20's low 30's in temp with about 25% humidity.

[planesmaker]

Seems like carbs are going out of balance, I don't believe it is electrical but carb related

[planesmaker]

I did have an aircraft with vibrations which seemed to be carb related turned out to be gearbox. Vibrations caused carb flooding. 

Edited October 18, 2020 by planesmaker

[Jase T]

Did the power actually drop to 4800RPM? i.e. was there a commensurate performance drop? Looking at indicating system errors? Tell me about the fuel? Are you getting complete combustion or a reduction due to contamination or incorrect fuel? What was the EGT / CHT doing?

[Blueadventures]

13 minutes ago, M61A1 said:

I will add at this time an acquaintance came over when I was faultfinding and leaned on the prop. He then started moving the prop back and forwards listening to the tiny amount of backlash in the gears and commented that he could hear that when it was idling. 

It's not the problem but it's a clue.

Loose trigger coil pickup just touching , no air gap.

[M61A1]

15 minutes ago, Jase T said:

Did the power actually drop to 4800RPM? i.e. was there a commensurate performance drop? Looking at indicating system errors? Tell me about the fuel? Are you getting complete combustion or a reduction due to contamination or incorrect fuel? What was the EGT / CHT doing?

Power certainly did drop, fortunately being a hot day there was plenty of lift about. I had fresh 98 in it, and then put some fresh 100LL in it. 

Filter is clean. Float bowls clean and correct levels. CHT was normal for the weather, EGTs may have indicated differently if they were fitted, but this installation has none.

14 minutes ago, Blueadventures said:

Loose trigger coil pickup just touching , no air gap.

I didn't even think of that, but probably because there were no weird noises when turning by hand.

 

21 minutes ago, planesmaker said:

I did have an aircraft with vibrations which seemed to be carb related turned out to be gearbox. Vibrations caused carb flooding. 

I have experienced this also, but only at idle. Float bowls were checked immediately after shutdown when the abrupt power drop occurred on ground run. No anomalies were found.

 

27 minutes ago, planesmaker said:

Seems like carbs are going out of balance, I don't believe it is electrical but carb related

I thought that also and the carbs and fuel system were the focus of my troubleshooting. Cables and stops have been checked and rechecked. Slides, diaphragms, needles and spring lengths checked and rechecked also. 

 Everything seems to point carbs or induction.

I'm just about tearing my hair out because I can't find a solid fault and I was planning to fly out at first light.

[M61A1]

It has been good to see that the responses are generally the same as the path I took.

While working on it, I knocked the exhaust pipe with my knee and thought I heard a faint rattle. I gave it a thump on the side and sure enough something was adrift inside the muffler can.

I cut the end off and found a largish piece of baffle had been floating about in there. The design of the can allowed the piece to partially block the outlet and likely one side of the can at times depending on where it got stuck. I was likely the rattle heard at idle was the loose piece, but it wasn't audible from the cockpit.

A big sigh of relief as I've got a solid fault to work with.

The exhaust was removed, a welded repair was carried out and re-installed

The aircraft was ground run and test flown with no further problems.

 

A borescope up the muffler will become part of my 50 hr inspections.

[planesmaker]

Good to know, thanks for sharing 

[Thruster88]

9 hours ago, M61A1 said:

It has been good to see that the responses are generally the same as the path I took.

While working on it, I knocked the exhaust pipe with my knee and thought I heard a faint rattle. I gave it a thump on the side and sure enough something was adrift inside the muffler can.

I cut the end off and found a largish piece of baffle had been floating about in there. The design of the can allowed the piece to partially block the outlet and likely one side of the can at times depending on where it got stuck. I was likely the rattle heard at idle was the loose piece, but it wasn't audible from the cockpit.

A big sigh of relief as I've got a solid fault to work with.

The exhaust was removed, a welded repair was carried out and re-installed

The aircraft was ground run and test flown with no further problems.

 

A borescope up the muffler will become part of my 50 hr inspections.

The loss of power is easy to understand. Why the mixture became very rich is a mystery to me. I would assume that when the engine was being "throttled" by the exhaust the constant depression carburetor's slide would drop and the fuel air ratio would be maintained?  Anyone got an explanation? 

Edited October 18, 2020 by Thruster88

[APenNameAndThatA]

15 hours ago, M61A1 said:

How about an actual problem?

 

I had this issue a couple of weeks ago.

The aircraft has a Rotax 912 with standard Bings with vent hoses as per Rotax instruction. The installation is pretty normal. A single throttle cable from the dual throttle linkage to a splitter which goes to each carb. 

The installation has an Air/Fuel Ratio gauge fitted. A let over from some previous testing.

The exhaust is not standard Rotax but appears similar in design.

Engine mounts are standard for the aircraft  design, which has a bed mount.

 

The whole installation has been functioning normally for around 400 hours.

 

One afternoon on a normal sort of day with a normal takeoff, about mile from the strip, I reduce the throttle to cruise at 5200 RPM. Moments later power drops to 4800 RPM. After turning back immediately I cycle the throttle a little and find that 4800 RPM is all I'm going to get and the mixture is extremely rich at high power settings. If I reduce power the mixture returns to normal levels.

After landing the engine idles and throttles up normally, but will not produce power above 4800RPM. After shutdown ( having a check under the cowl at various bits) and restarting everything appears to run normally, including ground run, but does the same again after taking off.

 

I fixed it after four hours of troubleshooting and multiple ground runs and test flights.

 

Any takers?

No one here is capable of realising that it is the magneto. 😡

[M61A1]

2 hours ago, Thruster88 said:

The loss of power is easy to understand. Why the mixture became very rich is a mystery to me. I would assume that when the engine was being "throttled" by the exhaust the constant depression carburetor's slide would drop and the fuel air ratio would be maintained?  Anyone got an explanation? 

My best explanation would be that when you put more fuel in than the engine Can use, there is more unburned fuel leaving through the Exhaust. 

[old man emu]

3 hours ago, APenNameAndThatA said:

No one here is capable of realising that it is the magneto. 😡

Right-O. You've had your joke. You can drop it now.