EGT vs CHT

[Wargames]

Hi,

Was just wondering. If you can choose only one of above, which will it be and why?? eg. Which will give you the earliest warnings if something is going wrong in engine??

[Morph]

I'm assuming a 503, 2 stroke

EGT,

The CHT only is useful in telling you the plane is hot enough to take off, thereafter you need to watch your EGT's to get an idea of how well the engine is running

Hi EGT will indicate (generally very bad for the motor)
a) lean mixture
b) Low loading, low prop pitch (corrected - Morph)
c) holes in the fuel pipes sucking air
d) cracks in the carb rubbers sucking air etc
e) incorrect carb settings, i.e. needle jet etc
f) the engine will seem to run better and then stop, with a hole in the piston

Low EGT will indicate
a) rich mixture
b) high loading, i.e. too high prop pitch(corrected - Morph)
c) leaking choke piston gasket, i.e. choke not closing.
d) the richer the mixture the engine performance will decrease

So an EGT will be able to tell you in flight, how well the motor is running, where there are hot spots, i.e. on a long decent you might have a setting that leans the motor out and could burn a hole in the piston. The only way to know this is to have egt's

If you want to balance your carbs out, the only real way is to get the EGT's within 25deg of each other. To correctly set up the pitch of the props again, the egt guage is essential.

Now for a 582 the same is true except you will also need a water temp guage, not CHT's

[Wargames]

Thanks, Think I will get myself that EGT. I think that I have 2 problems on my engine. 1. Prop pitch is too rough. 2. Settings on carbs need some fine tuning and I need to balance carbs as well.

Other than what I mentioned here, is there some other tips on how to improve my fuel consumption. Other wise the high petrol price is going to force me to take my trike for a sunday walk every week. No flying allowed. Currently with pax I get about 15 litres an hour on my 503. or is this about par??

Regards,

[Duck Rogers]

Currently with pax I get about 15 litres an hour on my 503. or is this about par??

That's about right

[Wargames]

Currently with pax I get about 15 litres an hour on my 503. or is this about par??

That's about right

Thanks. Still a bit shocked. I thought it was better.

[Morph]

Do yourself favour and get the MGL EMS-503. It's a full engine management system for your 503 engine. He has a 582 version as well

It gives you
2 EGT, 2 CHT, Hobbs, RPM plus alarms if anything is exceeded.

As far as fuel consumption goes the MGL FF1 will let you know exactly how much you are burning plus what your range is. Both are in small 2.5" packages.

I used to get 10l per hour on my short wing Challenger at 60mph. However then I was running at about 4800rpm and very nose high. once trimmed properly I cruised at 75mph and burned about 13l per hour at 5200 to 5400. My WOT rpm on takeoff was 6250

On decent I had a hot-spot at about 4200rpm. I only discovered this while monitoring the temps. The EGT's would shoot up. so I avoided this rpm.

I also noticed at WOT on climb the EGT's would be nice and cool so I was happy to be able to run it at full throttle pratically all day. Here I was burning 22l/h

[Wargames]

Hi Morph,

Thanks for the info. I had a good look at mgl instruments. The engine monitor is definitely on my wish list. I am reasoning that it is better to spend few grand for instruments before I have engine seize. Then we are talking of mega grands. Will be interesting though to get my fuel consumption solo. I'll let you know.

Regards,

[skybound®]

My understanding is that an EGT will warn you of an impending problem quite a bit before a CHT. The CHT will lag a little.

[Morph]

Yes I think by the time the CHT's actually show you that there is a problem the damage is done. I would only use the CHT during the warmup. I gave myself a number of 70degC before starting to taxi. If you do an extended taxi and have to hold for ages it will also tell you if the engine is too hot for takeof. If it is too hot and you crank it open to WOT you could get the motor cooling suddenly because of all the nice fuel/oil and you could get shock cooling, also resulting in a seizure.

In a 582, CHT means nothing as it's all governed by water temps. Now in this case, these are very critical

[Wargames]

Hi Morph,

Wanted to ask you whether there is any reason as to why your egt is higher at 4200rpm??

[Morph]

Idiosyncrasies in the carbs.

The carbs have 3 stages, idle, controlled by the Idle jets, WOT controlled by the main jets and in between controlled by the jet needle and needle jet. The various rpm settings lift/drop the jet needle, opening or closing the hole to increase/reduce the amount of fuel. There could be a bump on the needle at a point that suddenly leans the air fuel/oil mix. The result is that you could inadvertantly burn a hole in a piston over an extended decent.

I flew back from Swellendam, over the Theewaterskloof and had to decend into the Franshoek valley from 8500 to 1500ft this took a good 10 minutes, more than enough time to run lean and damage the motor. Fortunately I could see the effect on the EGT's and moved the throttle settings accordingly.

[German]

On the 912 100hp. What would the ideal egt readings be at say 5500ft and at 4700rpm?

[Morph]

Between 800 and 900 deg C

[wingnut]

Thanks for sharing all this information, Morph. I am curious as to why a prop that is too coarse thus causing a high loading will increase the EGT's? I thought that the EGT's would be more a function of the RPM for a given engine/carb setup. If nothing else changes, will a specific engine/carb setup at a specific RPM have higher EGTs when the prop pitch is coarser than would be the case for same setup at same RPM, but with a finer pitched prop?

If so, WHY?

My windlass's 503DCDI had static WOT RPM of around 6000 at microlands 5300ft elevation. I considered this to be a good thing even though I couldn't get to say 6500rpm for more power, because I reasoned that the lower RPM (and lower EGT's I thought) would be better for my engine. I don't have EGT instruments, but will probably get some soon when starting to fly here in Brisbane (sea level) with my same windlass. I do know about the lean condition on long descents and reduced RPM which is one of the main reasons why I want EGT's now.

Thanks again for all the info!
W

[Morph]

Got the loading mixed up again

Hi loading, i.e. high prop pitch, Low static RPM, low EGT's. A high loading will require more fuel to maintain the same level of rpm. Since the motor uses fuel to cool and lubricate itself, this will result in lower EGT's

Low loading i.e. low prop pitch, high static rpm, high EGT's

I did a test once, by increasing the loading to a point that my static was 6000. This gave me lower climb ability and supposed to give a better cruise, but also used more fuel. I then went the other way and set the static to 6800 rpm, better climb, but dangerous because you can easily overrev the motor.

I finally settled on a static of 6250. This gave me no more then 6500 on takeoff. I noticed that my engine ran nice and cool at 6500 and at cruise I actually got a better fuel consumption than when the prop was highly loaded.