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. 

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.

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.

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.

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.

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

2 minutes ago, planesmaker said:

Seal in choke mechanism?

Checked as well.

No fault found.

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)).

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?

12 minutes ago, old man emu said:

I'm sorry that no one had the ability to look for the main point,

Oakey says PPR on ERSA. When I phoned ops to get permission, the standard answer is "You can't".

They gave up some of their airspace when Wellcamp opened. Now the are very protective of what they have left.

At least the deactivate on weekends and usually for 2 hours late afternoon.

1 hour ago, old man emu said:

Made ya think, didn't I?

Pretty sure you don't want to know what it made me think....😵

40 minutes ago, old man emu said:

WILL YOU STOP GOING ON ABOUT THE WIND!

 

 

Why.....It's the simplest and most logical reason for indicated speed not matching ground speed.

You said it a simple solution.

3 hours ago, Kyle Communications said:

All of the people so far using them have all stated that they have had to modify the landing phase a little as you dont get the same braking force now so glide should be a lot further.

This could cause me some issues.....I frequently use my prop as a brake.😱

51 minutes ago, old man emu said:

I know I have learned a lot from this about how people read and comprehend stuff. I ran what I had written through a style analyser and it concluded that the content would be comprehensible to a Year 6 student. 

The content was perfectly comprehensible. You just didn't write what you actually meant.

3 hours ago, Thruster88 said:

Agree with a fixed pitch prop. If the aircraft had a constant speed and the power was set at 23inch manifold pressure and 2300rpm and one mag failed what would the two gauges show and why. The engine should still run smoothly but there would be a power loss.

RPM should still be 2300 ( constant speed),  manifold pressure should slightly lower as the as the engine would have unloaded slightly when the prop fined up to compensate unless the pilot increased power to compensate for reduced airspeed, in which case the manifold pressure would be higher.

That would be my best guess. I’m not educated on constant speed props, ask me about helicopters and I may be more helpful. 

It's either MIB or DR Evil....Both of those use them. I saw it on telly.

10 minutes ago, old man emu said:

No there wasn't

 

BECAUSE THE FIRST THING THE PILOT NOTED WAS THAT HE WAS LATE ON HIS ETA. 

 

HAVING NOTED THAT, WHAT WOULD A PILOT DO?

Check the wind.

Power loss would have been noticed the moment it occurred.

1 hour ago, Yenn said:

My flights are spent with one hand on the throttle all the time. The cockpit is too small for it to be anywhere else.

On Saturday I was stooging along and all of a sudden saw that my Tiny tach was indicating over 5000rpm.

That is the only tach I use and it was new only a few hours ago. The Jab engine will not run to 5000rpm.

I know what happened, do you? I will fix it before next flight.

Either the tach was switched over to a different setting or you are getting extra signals from other cables with AC or other plug leads.

2 hours ago, IBob said:

In fairness, OME, you said:

"RPM set to 75% cruise power."

and

"The arrow of the ASI points directly at your desired value."

 

I assumed from your scenario that was also the case 30minutes later, since I can't imagine any pilot would set and forget the throttle. Would they?

 

Clearly, if ground speed is less than expected, then either the air speed is down, or there is some wind situation impacting the ground speed.

Your scenario implied (to me) that the air speed was not down.

Perhaps that was why the responses were not as you had expected?

I have experienced this exact situation when cross checking another altimeter in flight. I have two instruments that read airspeed and disconnected the static off one to connect to the altimeter being tested. It was noted immediately that the ASI with cockpit static pressure was overreading significantly compare to the one with a proper static port and the GPS.... Virtually this exact scenario.

1 hour ago, rgmwa said:

Being in good company always makes me feel less of a failure. 🙂

Don't feel a failure. The failure occurred when the question was written. Not when it was answered.

I have had an instructor that used to asked such vague and broad questions. it seemed as that way he could always be right and you would always be wrong, because the answer could be whatever he wanted it to be.

21 minutes ago, old man emu said:

OK. Not one of you has provided a systematic scheme for working out what is going on here, and, despite my saying that knowledge of aircraft systems would solve the problem, the best that people have come up with is a faulty ASI.

 

Here's the original data, so let's go through it:

 

It's Sunday morning and you and your "significant other" decide to take a flight to get a $100 hamburger at a beach side airport. You check the weather and find that your intended flight path is dominated by a strong high pressure cell of up to 1024 hPa and winds are light and variable below 5000. Temperature is in the low 20's; humidity in the 40's and dew point is below 10C.

 

You take off and set for cruise, checking that you have "Carby - Cold; Friction Nut - firm; fuel On and sufficient quantity; oil pressure and temp "in the green"; RPM set to 75% cruise power. The aircraft is trimmed nicely. The needle of the VSI isn't moving away from Zero. The arrow of the ASI points directly at your desired value.  God's in His heaven and all's well with the world.

 

1.  The flight will be through a very strong High pressure area within which winds will be light and variable. Light and variable means there's no meaningful wind speed or direction.  It will also mean that the aircraft will be very stable - nothing to knock it off straight and level flight.

2.  The air temperature is nicely above freezing level and humidity is low, so you won't need to constantly watch for carby icing.

3.  At Top of Climb you have established the aircraft on course and in straight and level flight with engine power set.

4.  You fly along for 30 minutes, watching the scenery and notice nothing untoward. However, after 30 minutes of smooth flight you determine that, while you are on your intended track, you are behind your ETA.

 

The flight has been smooth and you are on track, but late. That could indicate a head wind, but wind doesn't blow in a steady stream. Any wind acting on the aircraft would have caused some degree of buffeting. You dismiss the head wind theory and look elsewhere.

 

You scan the instruments and see that the ASI is reading less than what you expected. What can cause this? It could be a problem in the pitot system, or it could be reduced thrust.

 

The simplest reason is that the engine is not producing the thrust normally expected at a certain throttle setting. Then take a look at the tachometer. If it is showing a reading lower than what was set at top of climb, there could be a problem with the engine.

 

Three things could be the simple cause of that. Check are the throttle friction nut. If the nut has wound itself out, the throttle rod could have walked backwards, reducing power. Check that the nut is tight. Likewise the mixture control could have wound itself out. Check that. the carburettor heat could have started to bring itself on. Check that.

 

To run an engine, you need two things - an air/fuel mixture and a spark. You've checked the things that affect the air/fuel mixture (the assumption is that since the flight has been smooth and unremarkable, that the fuel supply is OK). That only leaves the spark.

 

Remember when you did the pre-takeoff engine checks? You ran the engine to 1500 RPM, or whatever fast idle was for the engine, then you checked the magnetos, carefully noting the drop in revs as you switched from Both to Left of Right. At fast idle we expect a rev drop whose size is dependent on the engine.

 

A 75% cruise power setting results in engine RPM well above those of fast idle.  If shutting off a magneto at, say 1500 RPM gives a 50 RPM drop, what sort of RPM drop would you get at the higher RPM of 75% cruise? That RPM drop would result in less thrust, resulting in a lower air speed and hence a lower ground speed. That's could be why you are behind ETA. One of the magnetos has failed.

 

Remember I said that this diagnosis depended on your knowledge of aircraft systems.

 

I think I'd accept that I had a failed magneto, in accordance with Occam's Razor. The redundancy in the ignition system gives me faith that I can complete my flight, but maintain greater vigilance, and I'll look at the magnetos after I land at the beach side airport while my significant other is having a hamburger.

 

 

 

I was going to make no further comment but, you've demonstrated clearly your own lack of understanding....You stated that the ASI was reading exactly where it should and that the ground speed was slightly less than than anticipated, which rules out the engine straight away. Then in your explanation you tell us that you have a lower airspeed....contradicting what was said previously. This is nothing to do with Occam's Razor, and there would have been a more clues than a couple of knots of missing ground speed.

Next time I'll know better and not bother.

1 hour ago, old man emu said:

You had better strop Occam's razor, 'cause it's as blunt as.

 

As you are told in all examinations - read the question carefully and think about the information it gives you.

Maybe you really should write exam questions for CASA....They are always written in a vague manner with little relevance to the real world.

I won't be giving it any more thought. I have actual things to fix.

2 hours ago, old man emu said:

Why? What will that tell you?

That if it gets any worse you might actually take a look at the static system and do a leak check and cal your ASI at your next service.

If you consider it enough of a problem, the answer would lie somewhere in the static system or the GPS. Since the GPS is unlikely, that leaves the static system. You can leak check the static system which will lead the a leak in the aircraft plumbing or a fault with the instrument. Depending on the aircraft type the little sleeve on the pitot used to calibrate the static system could have moved.

You could get a job writing CASA exam questions OME.