What do you think of these EGTs.

[nickjaxe]

3000rpm 525c
3500 575c
4000 625c
4500 625c
5000 560c
5500 600c
6000 610c
6300 650c or 1200f rotax max.

All with the a/c on the ground 503 ducati s/c,

Around 4000rpm there seems a temp spike upwards, then 5000rpm-6000rpm a drop, then at WOT I get the Rotax max allowed 650c or 1200f, the OAT was 12c so those temps were are 25c high when the correction for temps are made,

Its a new duel gauge and sender both cylinders read more or less the same through out the range,

I am puzzled by the jump around 4000rpm, just the engine speed I normally use on landing,

I have just de-coked this engine but I had the same fig before hand.

Nick.

[Duck Rogers]

Nick, the spike is normal. Some engines have this at a different rpm range than others.
It's the way the carburettors work in our 2 strokes. These carbs are rather simple fuel measuring devices and can't compensate for all the variations encountered.
I have a technical article on this somewhere. Just now tried to find it in order to post it. I'll send it to you separately.

[nickjaxe]

Thanks Duck that would interesting to read,

They maybe seemingly simple little engines but there is more to them than meets the eye.

Nick.

[Morph]

This is the exact reason why it is important to have EGT sensors and a gauge. You have already seen that there are ranges of revs in the middle that are hotspots. Now the idea is never to run the motor at these rpm's for extended periods of time, on a long cruise decent for example. Rather move the throttle slightly up or down to get a cooler rpm.

Your carb is a 3 stage device, it has an idle jet, for idling, a main jet, for full throttle, and then the jet needle and needle jet, for everything else. It is the unevenness of the needle jet, caused perhaps though wear and vibration, that allows varying fuel/air mixes through at different revs. If your EGT's are too hot at full throttle, go one up on the main jet.

Here is a pic of all the jets. Your standard settings for a 503 at sea level is Main Jet 158, Jet Needle 11K2, Circlip in the 2nd position, Needle Jet 2,70 and Idle Jet 55 for a dual carb. I don't have the single carb settings

[Duck Rogers]

Nick, PM sent

[nickjaxe]

Hi Morph checked all my jets they are std as per the book, although some of my figs are high non of the go over the limit 650c/1200f so I don't really know if it worth meddling with it and they will go down as our days warm up over here,

I have just fitted a new duel EGT and a new duel CHT gauges as before I only had one of each, I was happy though that on my 30 min test run all readings where within 10c of each other,

I did try a bigger main jet well it was the next size up a 170 and it made no difference to my climb out EGT so I have gone back to the std 165 main jet.

Nick.

[Morph]

absolutely,

they are within spec, leave it alone

[nickjaxe]

Thanks Morph, I was bothered by the EGTs at the 4000rpm mark which is my powered landing revs, I was worried about uneven cooling, cylinders cooling off pistons getting hot a bigger and if a go around was needed back on full power with those cooler cylinders.....cold seize??? or am I thinking the wrong way about that?

Nick.

[Morph]

The 503 cylinder is made of steel and the piston, alluminium. Alluminium expands at a higher rate than steel

To me there are only two possibilities of a "cold seizure",
1. Startup, whack open full throttle and take off immediately without warming up, The piston will expand faster than the sleeve and viola, seizure.
2. on a long extended decent, low rpm, the piston sleeve's cool off, then if you suddenly go to full throttle you stand the chance of a seize depending n how cold the sleeves are.

The first one is easily managed, I never used to take off until the CHT temps were a min 70deg C. Idle to warm up, not rev at 4000rpm

The second one, is managed by revving the motor every few minutes or so to keep the cylinder sleeve temps up. This also helps to clear any icing that might be forming in the throat of the carbs. If you have CHT probes you can monitor the cylinder head temps.

Normal operating temps, 180 to 220 deg C, and a max difference of 20 deg C

I don't believe that the decent on base and final in the circuit is long enough to allow the cylinders to cool sufficiently to result in "cold seizure" on the go around. I feel I can safely say that 1000's of 503's are being used safely at flight schools, with a high rate of circuits and never suffer from a cold seize.

I have also heard of "Shock cooling" namely, you start your engine, but are held on idle, in queue for clearance. By the time you get to line up, your CHT's are cooking, as a result of zero air movement across the heads. Then you go to full throttle, tons of ice cold fuel pours into the pistons, resulting in a seize. Now this is anecdotal, heard in hangar and pub talk, I personally have not experienced this, nor seen it, perhaps others have?

PS I thought I had seen an example of this one year at the Saldanha flyin. The field is normally unmanaged, but for the day they created an ATZ, with ATC's to man the tower as an exercise. You had to call for start up, taxi, takeoff, en-route and landing instructions. Unfortunately the ATC was so busy that guys were standing idling for up to 20 minutes, in high temperatures. Wargames entered, lined up, took off and had sudden power loss at 300ft, he declared an emergency, and landed safely ahead in a field. I was sure it was "shock cooling", but it turned out he had just installed a fuel flow sensor, and put the wrong size jet in, resulting in field starvation.

[Duck Rogers]

......and put the wrong size jet in, resulting in field starvation.

Sorry Morph........no offense meant. I just couldn't help myself

[Morph]

well he did starve in the field after being stranded with fuel starvation