Cruise EGT.

14 posts in this topic

Posted (edited)

Another Question to the veterns.

Have a rotax 582 on a kitfox3.  5100rpm seems like a comfortable economical cruise rpm. However as the aircraft accelerates the egt peaks as the prop unloads when throttling back at top of climb.

Pitching up and loading the prop causes egt to reduce as does increasing throttle.

I have reduced static to 6000rpm to try and cure this. But I feel the prop needs to be coarsened more in order to ensure its suitably loaded in cruise.

Tried going up a size in the needle jet and this helped but I feel its curing the symptom and not the cause.  

If I increase pitch some more my fear is that I will be lugging the engine and cause damage(or worse!) And take off power will be outside the power band for the 582

I estimate the  the next degree increase in pitch will leave me with approx 5800rpm max static.

Main Jet 165..needle jet 2.74..needle 11g

Idle.45

 

Thanks in advance guys

L.

 

Edited by Lorax

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Posted

I'll throw out a few questions.  What are your EGTs in actual numbers at the different rpms?  What temps are you seeing when you say it peaks?  Are you seeing the same EGTs on both cylinders?   Did you go to a larger needle jet after you raised the needle as much as you could and needed to go further?  What are you seeing for rpms at full throttle climb out?  JImChuk

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Posted (edited)

EGT varies at different RPMs but peaks at 1200 after a few seconds at 5100..5200rpm I never let it go higher. I either throttle back and land or increase RPM to 6000 and it backs off to 1150 or there abouts.

If I fly around dragging my ass pitched up keeping prop loaded it stays at 1100

needle is in third slot from top. One more to go.

I feel the prop. New to me, is unloading very much after transition to cruise

Edited by Lorax
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Posted

OAT 59 Degrees F

Airfield elevation 200feer also.

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Posted (edited)

Dont we set static rpm on the ground at 6250? What is it set at now? keepin the prop loaded helps with egt temps right? 

Edited by Buckchop

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Posted

According to the factory chart, the circlip should be in the third notch from top.  What happens if you put it in the bottom notch and reinstall the 2.72 jet needle.  That would then be just one notch from stock. Still have some unanswered questions as well? Like full throttle climb out rpm, ect.  Also, do both cylinders read the same EGTs.

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Posted

Static 6000

Full throttle climb out 6000 55mph

WOT 6200 in flight

Both cyls same temp. Swapped egt probe wires both same temp.

 

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Posted

MTOW   .....Two fat guys...problem seems Less as obviously prop is loaded more

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Posted

So it looks like I can cure this problem by coarsning pitch one last time and go back to standard carb jetting rather than flood the engine with fuel....but I'm unhappy about the low static rpm and reduced take off performance. And lugging the engine

 

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Posted

Adding more pitch will reduce performance across the board.  Richening the mid range one notch will lower egts at cruise where you have the issue, and not hurt your full throttle performance.  Is there any chance you have a small air leak that may be leaning the mixture just a bit.  It would be more obvious at mid range than full throttle perhaps??  With dual carbs it is more likely to show up on one side rather then both, but something to think about none the less.   Also, where are your egt probes located?  Should be 100 MM (3 15/16") from piston to probe.  Another thing I would do is run the plane on the ground at the rpm I was concerned with for a couple of minutes, and kill engine with ignition.  Then look at the plugs to see how rich or lean the engine seems to be running.  Something else to consider is the accuracy of the tach.  Some of the round gauges are not very accurate.  Tiny tac is usually real good.  JImChuk

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Posted

Your jetting looks fine and you are loading the engine way more than you should have to in my opinion. Have you checked for air leaks?

On a 2-stroke, if the crank seals are starting to go it will suck air and start to lean. Likewise, carb boots cracked will do the same. Really anywhere there is a leak on the engine it will suck air and lean it. You can check by doing a crankcase pressure test. This involves blocking exhaust, intake, and fuel pump pulse line and pressurizing the engine to about 5 psi. It should hold that 5 psi for minutes. I just did this on my newly acquired project 582 and I have a leak. A little later I can get some pictures of my setup, but it is basically 2 plates drilled to block the exhaust and siliconed to seal, a pair of forceps to pinch the pulse line, and a couple plugs to go in the carb boots. One plug has a 0-15 psi pressure gauge, and the other has a tire valve stem. I use a bike pump to pressurize, not an air compressor.

This video shows what I do. https://www.youtube.com/watch?v=r-ffJVbpeAs&ab_channel=Paisteboy

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Posted

Tach is correct as has been checked with an optical tach.

Seals only have 20 hours on them. Installed 13 months ago. New carb boots, tight jubilee clips..

Plugs are grey..not black or brown ?

Fuel, I've used 95 octane E5, Avgas 100ll, and avgas 91unleaded...

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Posted

brown is more of a preferred color, white to gray is lean

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Posted

Yes..the bing manual says grey is the correct colour. But that's no consolation. The egts are high. I'm thinking on trying a different prop...the present one is designed specifically for a 582 but it unloads noticeably at top of climb.

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