How to improve the reliability of the 6 Cylinder Jab

[hyundai]

I read a lot of suggestions of what you should do. I can tell you from experience the 3300 and 2200 are a very good engine the problem is they run to lean an air cooled engine rely on fuel and mixture to keep cool. and one of the problems is the nacka duct intake the engine cant have forsted air into the carb. jabiru have fixed this by a

 

flat intake on the side no forced air to carb. I owned a 2200 4 cyl i fitted a air fuel ratio gauge with all the other gauges is indicated if it was running lean or rich. To ajust mixture I fitted a butter fly in the intake just after the nacka duck the old coarse fin heads where cool same the EGT. I done 600 or more hrs no trouble. Jabiru tryed to

 

build a air cooled engine that we could start and fly with no ajustments lycoming and cont could,nt do that. I am not sure as to the new intake mod if this solves the problem but I would not fly a jab without the air fuel ratio gauge and some means of rich or lean device and your engine will last. I am not nocking jabiu they have done a

 

great job manufacturing the engine. I hope in the future buy a skyfox and fit a 3300 6 cyl.

 

 

[facthunter]

Don't bother doing that. The engine is too heavy and the Vne is too low to use the power. .

 

re the mixtures the variation is the problem. No one can design a manifold to keep them even. Nev

 

 

[Bruce Tuncks]

The other thing is that EFI needs electricity to work, and this introduces a potential for unreliability.

 

I would like a non-electric solution to the variation problem. But even an electric solution, like putting a fan into the intake plenum, would be acceptable provided the engine still ran if the fan stopped.

 

 

[hyundai]

Don't bother doing that. The engine is too heavy and the Vne is too low to use the power. .re the mixtures the variation is the problem. No one can design a manifold to keep them even. Nev

Mate you want to read my reply you don’t get it

 

 

[hyundai]

A 6 cyl jab into a skyfox has already been done, kitfox in the USA have up to 180 HP.

 

Have a nice day.

 

 

[facthunter]

Do a lot of research and do it right then. It's not the right plane as it stands structurally and aerodynamically. Have you flown a kitfox and a jabiru XP with the 6 cyl motor.? The kitfox originally used 2 stroke motors of very light weight and the undercambered wing has serious speed limitations in the standard plane which only cruised at around mid 70's knots at best.. It's a lighter build than the tricycle U/C Gazelle. They are not overstrong. .You will need a lot of weight in the tail and perhaps a larger fin or extended fuselage. Ie this is extensive modification. which would require much research to do. properly.

 

A heavier engine with more weight added at the tail has adverse possibilities for spin recovery as well. Nev

 

 

[Thruster88]

Kitfox is up to series 7 now.

 

https://www.google.com.au/url?sa=t&source=web&rct=j&url=https://www.youtube.com/watch%3Fv%3DOHlfsT-DWAs&ved=2ahUKEwibtpe2x5jeAhXFRo8KHe54DlsQjjgwAXoECAgQAQ&usg=AOvVaw00VZYqGWICzAF-5rF8DDdx

 

 

[Blueadventures]

Hyundai In my opinion the standard Skyfox is not the airframe to put speed / hp into. I expect you may have read that skyfox max cruise speed in smooth air is 86 kts. (Would rarely get that speed WOT S&L in my experience flying both variants) Vne is only 93 kts. Wing design is not conducive to going faster than 75 to 86 kts. There is one on the VH register with modified wing cord shape and by all accounts it would meet your plan goal. Matt may give details if you ask him. Coastal aviation have a better wing design but advised a few years back that they would not be tooling up to make them. Most likely due to limited market for that type of construction. By all means build your modified design but if designing not available put the time and effort into a proven robust design. To reinforce Nevs comment the Ca21 airframes are lighter tube in the lower cabin construction where the under carriage hangers are attached (welded on) and the 25 variants are beefed up in that area. Cheers and good building of your dream. Mike

 

 

[planedriver]

JabSP6 .Sounds logical to my way of thinking. If the exhaust valves are a tad too small, the CHT would surely run a bit higher which has been a bit of an issue with some Jabiru installations especially in pusher configeration, apart from the normal required airflow to assist the cooling of the engine.

 

It will be interesting to know more about the mods the NZ guys come up with. Improving gas-flow can only improve the situation and engine efficiency. Gas flowing and ironing out the lumps and bumps do more than just restricting an engines output. ie temperatures.

 

 

[jetjr]

Jab engines can be made to run cool, its been proven. Not easy though and as its presented in factory aircraft is pretty poor and variable.

 

Its EGT and fuel/air distribution that's the bear. It was ignored for many years and only fairly recently with multi channel monitoring been seen for how bad it is.

 

 

[Yenn]

The reason that EGT was ignored was because Jab have no means of adjusting mixture in flight, so the CHT is your only guide.

 

 

[Thruster88]

Maybe if they were jetted to burn an extra 2-3 litres per hour they would be more reliable, fuel is cheap

 

 

[frank marriott]

fuel is cheap

I wouldn’t call $2.30 per ltr cheap.

 

 

[jetjr]

There are ways to adjust mixture in flight, use carb heat or fit leaning device and then various carb options

 

The problem is the unevenness of the distribution. Some cylinders are on high EGT limits and some too low

 

Being able to control mixture doesn't help if spread is too big

 

When I first raised this was told "you have too much info, just confusing yourself" They sell this D180 as an option now

 

 

[hyundai]

The problem with jab engines they run lean. Monitor the air fuel ratio and be able to adjust and you wont

 

Have any problems. Lycoming and Continental need mixture ajusment.

 

 

[jetjr]

Do they? Jetting should be altered to fix that. Good numbers on where EGT should be to avoid lean running

 

What if some cylinders running rich and others lean, single AFR isn't going to help.

 

Even out the egt, then AFR and mixture control would be helpful

 

 

[Bruce Tuncks]

how do you monitor this Hyundai?

 

 

[Yenn]

So how do you adjust mixture on a Jab?

 

 

[Jaba-who]

The problem with jab engines they run lean. Monitor the air fuel ratio and be able to adjust and you wont

Have any problems. Lycoming and Continental need mixture ajusment.

That’s unfortunately not  the case Hyundai. Jabs don’t run lean. 

 

Jabs run run all over the place. In the unmodified carb intake they tend to run right cylinders rich while the left  cylinders run leaner  with the forward cylinders richer than the rear cylinders. 

 

This changes with throttle settings. These are most pronounced on most ( but not all) in wide open throttle. 

 

If you put a crossed vane in the cobra head you usually get rid of the right to left imbalance but still have forward aft imbalance. 

 

If  you change the plenum chamber centre vane from an airfoil to a cylinder you may alter the front back and the side to side ratios but in a variable manner. 

 

If you tilt the carby you get alteration in the air stream around the plenum vane and may change the flows in variable directions. 

 

If you measure the fuel air ratios by means of one of the several monitors that measure oxygen and or air and fuel in a single location ( usually  the exhaust) you get no information about individual cylinder ratios. You get a bunch of  figures that makes you think you are onto something but that don’t tell you anything about individual cylinder ratios. 

 

Unless you are suggesting measuring each air fuel ratio at each and every intake port then you you actually don’t get any useful info in Jabirus. 

 

 

[hyundai]

I am writing from hands on expereance my jab 2200 flew over 600 hrs with out any problems how much has all the other 

 

commenters have. You all have to read my first comment.

 

 

[Jaba-who]

We’ve been working on and rebuilding jab engines here since about 2007 and done heaps of trials with both cobrahead  modifications and plenum chamber modifications. 

 

When I had my original engine and had issues with over rich on the right and lean on the left I spent quite a lot of time with Don Richter at jabiru modifying them and trialling them. We even tried sieve like grids in the intake ducts but they were a lot of work for no gain in mine (J430 with a 3300) but made a big difference in a Corby Starlet with a 2200 in a very unusual intake path. 

 

But overall the plenum chamber ( which has had several redesigns over the years is still the limiting factor.

 

There is a central  shaft of air with high density  of fuel droplets that carries it forward preferentially to the front cylinders and delivers leaner air to the rear cylinders.

 

Short of some major changes nothing much will change that. Stiffy was always reluctant to change to a more complex system for a lot of reasons. 

 

 

[hyundai]

The first thing you have to do is change the intake from nakaduct to side intake. Jabiru has finely done this,

 

A naturaly asperated engine can’t have pressure into the intake. The best thing is fuel injections people say 

 

it won’t be reliable how many cars stop because of the computer injection.

 

 

[jetjr]

Changed from NACA to side duct and achieved nothing

 

 

[Jaba-who]

The first thing you have to do is change the intake from nakaduct to side intake. Jabiru has finely done this,

A naturaly asperated engine can’t have pressure into the intake. The best thing is fuel injections people say 

 

it won’t be reliable how many cars stop because of the computer injection.

 

 

Changed from NACA to side duct and achieved nothing

I’ve done the initial experiment of blocking up naca duct inlet with a slab of cardboard and just cutting a circular hole. After discussions with Jamie 

 

And as jetjr found made not a single bit of difference. 

 

Since then I have done some other work on the cowl so I have filled and moved the hole to a flush one in the new position. 

 

The aircraft is yet to fly since doing it so will report then. 

 

 

[jetjr]

things run more even with heated air on

 

Havent really tried but just using air from inside cowl might work

 

Im convinced its ram and swirl which changes as velocity changes through intake system - in which case every build will be quite possibly different