the ideal modified jab engine

[RFguy]

I have come to a conclusion that the best engine combo for J230, 160, 170 all of them....is :

2200 Gen3 upgraded engine with LCH ( liquid cooled heads)  (series 2 rotec)

the new high temperature  fancy exhaust valves ($75 a pop)

The marle forged pistons (need very slight overbore) 

and a turbo charger... maybe up to 38". 

ideally, an Airmaster IFA Prop.

 

why ?

1) LCH provides the thermal margin for higher power operation

2) The turbo can work well with an 8:1 compression engine. gets you that extra 20-30h you always wanted , or needed when operating from Jindabyne in summer (DA 5k-6k)  

3) The new valves can take the extra heat , espesh in conjunction with the LCH

4) Those pistons are a good upgrade

 

and what do you have ? you have a 914 rotax equiv (80hp engine with turbo) ........

 

I am wholly convinced now that Jab engine troubles are mostly inappropriate/ unfamiliar /unsuitable  mechanical staff  operating on them, and in many cases, a lack of CHT/EGT on all cylinders, which thus operators, not faced with red flags on their panels, are oblivious to their inappropriate engine control styles. Yes, the factory are responsible for some clangers, like the flywheel. Jabiru would have saved alot of bad press on themselves  by putting all cylinder EGT/CHT on all engines. Jabiru's secrecy and lack of communication has not done them any favours, either.

 

 

Edited November 2, 2022 by RFguy

[Old Koreelah]

Yes Glen, always liked the LC heads but their electric water pump needs some sort of backup.

Relocating the ring gear and flywheel to the front is probably beyond mere mortals. 

 

Amazes me why Jabiru thought a single CHT sensor would do the job, when they must have known their head metal couldn’t cope with the temperatures tolerated by most cast heads. 

 

I’d love to see your ideal engine built; SA or NZ are innovative enought to do it. 

[RFguy]

I dont think the water pump is a big issue if the water pump has good QC to start with and is derated sufficiently, and probably might be good to vibration isolate the mount. 

I had a cunning plan that when I go full electronic ignition, the 2 x distributor drive shafts might be useful for something else. (pump)  but I dont know at all how much work those coupling gears could do.  

I think that oil rather than water cooling is good but I would not like to see an oil cooler input hose come astray under the heads amongst the exhuast headers.... The Rotec head input is OK for low pressure but I reall ylike to see AN hoses for oil.

 

[facthunter]

Starter drive to behind the Prop Priority, You don't want a flywheel at both ends of the crank. One works against the other. Later HEADS/NikasilCylinders  and good pistons should be good enough. Injection near ports should prevent damaging backfiring.  Nev

[RFguy]

Fortunately, the Jab crank has alot of bearings.  I will update the viewers shortly onmy vibration analysis kit I've built.

 

Nev, talking about flywheels, I have read a little of dual mass flywheels. IE 2nd mass in a spring

https://en.wikipedia.org/wiki/Dual-mass_flywheel

 

Now doubt Jabirus problem with the steel bolts elongating the aluminium crankshaft holes in the 4 cylinder would have been bad. 

Jabiru has a low limit on the MMoI of the prop. It's the same as their heaviest prop. I always wondered if the low MMoI was of convenience, or whether there was some concern about ending up with dual flywheels. 

If someone has one and can measure the weight and the thickness and any radius steps, I'll calculate the MMoI of the flywheel and see how to compares to the prop.

 

[RFguy]

Nev, there appears to be quite a bit written about this for boats

- IE the propellor - (long) drive shaft with various bearings, couplings, gearbox, and the engine at the far other end

 

https://www.tandfonline.com/doi/pdf/10.1080/20464177.2017.1419705

 

But, here we are - the gold- 

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_20-66B.pdf

 

the appendix is most interesting

[facthunter]

The "Extra" bearings make the crank more rubbery and prone to torsional harmonics. Worse in the flat four as the pistons all stop at the same time. Most flat four cranks seem more prone to breakage. You could argue those engines don't need all the Main bearings it has. The CASE is probably not strong enough to restrain it either. Crankcases with separate cylinders are inherently lacking in strength/stiffness as well.. Nev

Edited November 3, 2022 by facthunter

[RFguy]

VWs break alot of crankshafts by all accounts (in aircraft use ) . But I have never heard of a broken Jabiru crankshaft EVER except one that had had a prop strike what wasnt enough to put more than a decent nick in the prop but the crank failed some time later

[facthunter]

VW's and Borgward's and Jowett etc. Never a Cont or Lycoming four either. . Many  aero cranks have dynamic torsion dampers and  the Jab generally runs a wooden prop for good reason(s). . They are not doing very high ours generally either. My point is extra bearings make it LONGER effectively.  Nev

[onetrack]

Oil cooling would be undesirable, as it allows higher head operating temperatures. Deutz make an oil-cooled diesel engine, it runs hotter than any water-cooled engine.

 

Edited November 3, 2022 by onetrack

[turboplanner]

5 hours ago, RFguy said:

I have come to a conclusion that the best engine combo for J230, 160, 170 all of them....is etc.

 

What do you think about the main jet size?

 

[kgwilson]

The Gen 3 6 cyl engine installed in an airframe that has decent airflow through the heads and ability to climb at 1000 -1500 fpm at 80 knots (aka my aircraft) means you don't need to monitor all cylinders or have any EGT gauge at all. All the early Cessnas & Pipers had terrible rubbery gauges, some with no CHT or EGT at all and were flown all over the world in scorching and freezing conditions. Now everyone is obsessed with monitoring every cylinder and freaking out when they all show different values. I've got news for you all. They always have and it hasn't made them all fall out of the sky.

 

I decided on a Jab 3300A when the Gen 3 was released. I got number 14 I think in early 2013. At the time overheating seemed to be the big problem with Jabiru engines. In reality a lot of the problem was new recreational pilots had never been taught how to treat an air cooled aero engine, not warming them up properly and assuming you could just climb out at full power on a hot day or idling in for a glide approach without thinking about  shock cooling and everything would be fine just like driving a car. The rest was poor airflow in Jabiru airframes. At one point Jabiru had a negative pressure lip kit to install on the lower cowl air exhaust to try & suck more air through.

 

I did something different. I did some research. The best information came from NASA and it was produced in 1981. It is the NASA Contractor report CR3405 entitled "An Experimental Investigation of the Aerodynamics and Cooling of a Horizontally-Opposed Air-Cooled Aircraft Engine Installation". The 152 page document has everything you thought you knew but didn't and everything you had no idea existed. So I spent a lot of time making sure airflow was right, sucking it through with good air sealing, appropriately located and angled vanes, a huge air exhaust with negative pressure lip and keeping the oil cooler completely separate with its own cool air intake and exhaust. I have 1 CHT which I have shifted around all cylinders & finally left it on No 3. I had 2 EGTs & they were on Nos 5 & 6 & were close all the time till the probes failed so now I have none. Oil temp, oil pressure & CHT is all I have and is all I need.

 

 

[facthunter]

Having a more "slippery" plane helps. Increase the climb speed before the engine gets too hot, (not wait till it has).  Know how to retension the heads properly. Run a non hydraulic lifter set up.  Nev

[Old Koreelah]

11 hours ago, kgwilson said:

The best information came from NASA and it was produced in 1981. It is the NASA Contractor report CR3405 entitled "An Experimental Investigation of the Aerodynamics and Cooling of a Horizontally-Opposed Air-Cooled Aircraft Engine Installation"...

Just skimmed this report, KG. Pleasantly surprised to find all measurement to be metric, even altitude! 

[facthunter]

Metric is the measurement of Scientists. (Even the un-american ones). Nev

[RossK]

I saw something recently from a home builder who was having overheating issues with his lycoming.

he eventually settled on the intake to the engine, and worked out the engine at WOT was consuming 6L/sec of the available cooling air.

He made a separate air intake for the airbox and saw CHT drop by 30deg.

[facthunter]

Most have a separate intake  for air consumed. That's the proper way of installing these engines. The installation has to comply with the engine makers recommendations to be legal. Nev

[spenaroo]

probably had a nice power bump too from it sucking cold air instead. surprised anyone wouldn't be running an airbox style set-up on an aircraft. especially with ram air

[Old Koreelah]

Jabiru are said to have done extensive testing and found ram air intakes problematic. They ended up with an air intake flush with the skin, behind the engine.

[spenaroo]

interesting, I wonder how the prop effects the intake with ram air.
its not exactly still air being funneled in like a motorcycle.

still better then what I assume was an open carb in the engine bay

[RFguy]

KG, I think you are wrong about the need for multipel EGT probes. I think it is #1 for requirement is multiple EGT probes. 

 

Jabirus can have some wild mixture distribution. need multiple probes. also, single EGT probe and setup means single point of readout error if there is a problem with that probe.

also, multiple EGT probes enables a user to spot a bad cylinder

EITHER WAY having multiple EGT probes I think is important because NON TECHNICAL opereators will see a single or multiple high EGTs and maybe report it. A single EGT probe will allow out of bound cylinders to continue and self destruct which if the user had all the EGTs showing, would be reported or noticed.

 

[RFguy]

On 03/11/2022 at 12:57 PM, turboplanner said:

What do you think about the main jet size?

 

I dunno.  Some users I know have done alot of work  with different main jets.  Jabiru have fiddled with the jet sizes from the beginnning of time....

 

too lean and you will cook something, for sure  IE beyond exhaust valve sustained capability at WOT .  Too rich and  the chambers etc will tend to cake up more, and also power will be left on the table if too rich... bore and ring wear can increase also since the fuel dissolves the lubricant. 

I am no expert or even have much experience with knowing how much main jet size different will affect WOT EGTs by how much. But others have that knowledge. 

 

I dont like to see any more than 680C under any weather condition at WOT.

 

Edited November 4, 2022 by RFguy

[Old Koreelah]

1 hour ago, spenaroo said:

interesting, I wonder how the prop effects the intake with ram air...

When I first installed my Jab engine I cleverly crafted an air filter that sat on top of the engine, drawing air from below the spinner. 

 

It was a waste of time- wouldn’t rev out, so I consulted the factory.

Don Richter said it would never work; they’d tried all sorts of intake locations and the best was a flush inlet way back on the left side.

 

Works for me.

[kgwilson]

I had dual probes and gauge initially on No 5 & 6 cylinders. I have a bulbous cobra head between the airbox & carburettor which sits horizontally with the air from the airbox exiting on the left with the cobra head expansion chamber about 350mm long and it narrows to the diameter of the carb intake and clamped on directly. I have installed a vertical vane at the carb end to split the air left and right and with a combination of moving the carb itself in the horizontal plane and bending the vane I got the airflow through the intake plenum and induction tubes almost spot on so the CHT & EGTs were even. Once I got it right I didn't need the EGTs & didn't bother replacing the probes when they failed. Jabirus just have a bit of scat hose between the airbox & carburettor.

 

This is the cobra head set up.

 

This is the vane installation which is curved vertically to get the R/L airflow laminar. When I got it right I sealed the top.

[spenaroo]

Which then brings the question of how much better these engines could perform with ITB or quad carbs.
certainly makes things more complicated, but I know the rear carb on my Jet ski is set richer then the front to keep CHT down, as is the vertical cylinder on my Ducati