engine instruments

[Bruce Tuncks]

My 2.2 jab has been going fine for years, but lately I've been wondering if it has all the instruments it needs, since it doesn't have an EGT and a fuel pressure meter.

 

The argument against an EGT is that the Jabiru doesn't have a mixture control, so the weight and complexity are not worth the payoff in information supplied.

 

A similar argument can be made against the fuel pressure meter... If the engine runs rough and improves on switching on the electric fuel pump, then what more could you do anyway?

 

But on the pro side, there is the possibility that an earlier warning is worth heaps. For example, was anyone alerted to a lean running condition by the EGT?

 

I'd be grateful for any comments .

 

Bruce

 

 

[facthunter]

EGT gauge

 

It's not a 2-stroke and with the Bing CV, mixture should not change unless you change the needle etc. Also EGT gauges rarely work for long. I wouldn't spend the money cluttering up the panel. Nev

 

 

[jetjr]

Theres pages of posts elsewhere regarding Jabiru engines and EGT spread, that is differences between cylinders

 

Having all of them watched will pick up a wide variety if problems and be able to improve the engines running and longevity. Yes the EGT guages will alert you to a problem. By the time the engine runs rough you could have easily burn out a valve of something like that. You need to make sure you are watching hottest CHT and EGT cylinder as they can vary A LOT!!!

 

Having these monitors also brings on all kinds of paranoia regarding impending disaster

 

 

[frank marriott]

The LSA J230 has a fuel pressure warning light fitted. The factory tells me it is a CASA requirement for the LSA category.

 

Frank

 

 

[Bruce Tuncks]

I didn't know about the warning light, the LSA regulator obviously thinks a fuel pressure indicator matters.

 

But a gauge is obviously better than a light, and not much more weight when you consider that the light needs a sender unit.

 

thanks, Bruce

 

 

[Alan]

EGT - Temperature Spread

 

My 230 has EGTs on Nos 3 and 4 Cylinders only, but even when cruising throttled way back because of FNQ turbulence the EGT temps never go above 1300°F. However, my No 4 is always some 50°F below No 3. On those two cylinders anyway I don not seem to get the high EGTs we are warned about at low rpm. NB Weather permitting I use 2850-2900rpm most of the time.

 

Just wondering what others had experienced as a typical EGT temperature spread for the Jab 3300 cylinders and for those with six EGTs whether there is a consensus as to which cylinder positions run hotter (leaner) than others (possible as a result of the different paths lengths in the inlet manifold to the single carb).

 

Many years ago I rode a trials bike (Greeves Scottish) this had two inlet manifolds,a short one for road work and a long one for trials; the long one increased the torque. So I assume the manifold length must change the mixture or charge somehow, as the jab has three different inlet manifold lengths. I wondered whether this was contributing to the reported Jab EGT temperature spread - Anybody?

 

Alan

 

 

[facthunter]

Different Mixtures.

 

With ONE carburettor and numerous branches in the manifold you are never going to get even fuel distribution. Within 50. degrees doesn't sound too badThe more vapourised the fuel the better. Fuel injection is the only way, and there would be some calibration required in that, too. Nev.

 

 

[jetjr]

50 deg F sounds quite close, mine can have up to 100 deg C

 

I have hotter front than back and also left to right, ie 1 is hottest, 5 is coolest

 

The spread changes at different rpm

 

Its fairly well documented the CHT and EGT differences being an issue its just no one has clear solution. Theres some kind of swirl and preferential feeding to cylinders but it changes with load and rpm.

 

Im pretty convinced 6 EGT and CHT COULD help prevent some problems by picking up a problem cylinder and managing things according to it,

 

 

[facthunter]

Multiple EGT's.

 

The trouble with that is that you are flying an airborne test bed. That is OK if you want to check them, but someone would want to be flying the plane. You are dealing with pulses and pressure waves, which as you say, changes every time you adjust the engine setting. In any case, what are you going to do about it? You can only enrichen the carb so that the worst. cylinder is catered for, and you have to cop what happens to the rest. I still don't believe that you need an EGT in a Jab.once the engine is set up. I think I would have a fuel flowmeter first, but you always keep track of your rates of fuel consumption when you refuel. (Amount against flight time), so why do you need that, even.. Two strokes are a different thing as aerodrome altitude affects them .(flight altitude too, but T/O is more critical)..anyhow we are talking about Jabiru's. Nev

 

 

[jetjr]

Flying test bed...What are you testing?

 

An entire EMS screen takes no longer to check than any other std set of gauges and has set alerts so lets you know if somethings out of limits.

 

Most have Fuel flow too, but these can give variable results.

 

I think you are right regarding no need for EGT ..... IF everythings set up right. I doubt many Jabs are that well sorted. They are still fighting the problem in factory and have been since day 1.

 

If they had used this sort of gear when developing engines we would have better products today.

 

I just installed recommended Carb needle and jet upgrades, first flight indicated EGT on 3 front cylinders rising to over 800 deg C, Alarms went off at 720, I throttled back, they went up further, pulled carb heat and increase rpm and got temps down to normal levels, landed and started to work on the problem. Im still working on it but things are now much better. Jets were simply too small for my setup - no idea why. No EGT's and I could have smoked the engine or at least a few valves.

 

Having all six monitored you can see changes in conditions due to all sorts of engine conditions / problems. You also need this to help to get engine setup working right.

 

 

[facthunter]

I think we agree, really. BUT.....This sort of situation should be sorted out ON THE GROUND. I know the Jabs have problems with the valves which only seemed to become chronic after the lean jetting set-up was in vogue. IF I have problems with Two strokes and EGT's I prefer to do a lot of ground running first, to prove them within limits, before committing aviation. Warnings coming on distract you from flying. Nev

 

 

[jetjr]

My problem was not the lean jet kit but the latest version and the high EGT only came on in flight

 

Jabs dont reach same rpm on the ground as in flight, and seems needle doesnt move the same either. Mine will only run for 60 sec at WOT on the ground then go over temp on CHT so can only achieve so much testing there. I did this thoroughly too and still found unplanned problems in flight

 

Without multiple EGT how would you sort it out on the ground?

 

Warnings in flight shouldnt happen, if they do you bet Im distracted and rightly so. They may avoid a really distracting silence...........

 

 

[facthunter]

I'm not suggesting that you don't have a problem, and yes you would need multiple EGT's, and I am sympathetic. Good luck. I think Jabiru have tried to get a manifold to work. I have had a fair bit to do with branched manifolds with carbs and some of the effects are totally unsatisfactory. Firing order, interferance, and length and the way the branch itself works. Sometimes the ugliest looking thing works better than one that has all the smooth curves. Trouble is that it has to be right in an aero engine, and you shouldn't have to go through this with a standard engine. Nev