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Jaba-who

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Jaba-who last won the day on November 18

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About Jaba-who

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    Well-Known Member

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  • Occupation
    Jabiru 430
  • Location
    Cairns, Atherton
  • Country
    Australia
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    male

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  1. Jaba-who

    How to improve the reliability of the 6 Cylinder Jab

    ooooh kaaay! 🤐
  2. Jaba-who

    How to improve the reliability of the 6 Cylinder Jab

    I have to concur with Jetjr here. (Of course I am assuming you are referring to the typical AF ratio sensor system where it selectively samples gas from one site only. As has been stated here and on many sites and threads on this forum - the major problem with Jabiru engines is that there is not uniform mixing in the after carby plenum chamber. This then means that depending on the amount of mixing that has occurred gas that is aspirated by the individual cylinders can vary dramatically. This is actually similar on many engines, its just that the massive heatsinks of Lycs and continentals can cope happily with some cylinders running lean. Jabs are a fine light engine and the cause of many problems is they can't tolerate the same as the heavy old ones. There are a bunch of reasons why they run uneven: Typically the richest (laden with the heaviest droplets of fuel) air has the highest inertia and is carried forward to the front cylinders. The air on the sides of the column of flow through the throat of the carby tends to be the leanest and this air is the least dense and has least inertia and is preferentially directed toward the rear cylinder intakes. There's a further complicating factor - The direction of air rotation in the carby intake SCAT hose. Typically it rotates in a clockwise direction and as it passes through the carby picks up the fuel (in an uneven concentration) as as it passes out the carby tends to throw the densest fuel laden air to the right. Then there's a further complication: In the intake plenum chamber there's an airfoil shaped post in front of the carby outlet. The role of that is to try to stop the swirl of air - but it also can produce complex coanda effects (gas flow sticking to the surface and then leaving at a more pronounced angle in the original direction) which may over-enhance the negative effect in some situations. Without getting into what can be done to ameliorate these - The point is that all these things serve to either improve or mess up the mixing depending on lots of factors. Often they impede mixing. The lack of mixing is what finally ends up with significant variation of ratios at each cylinder. So a Fuel Air ratio gauge is not going to tell you which cylinders are rich and which are lean unless you have one at each and every inlet because as JetJR said an average tells you nothing about the individuals cylinders.
  3. Jaba-who

    How to improve the reliability of the 6 Cylinder Jab

    Jabiru maintain that changing the intake structure and location makes a positive difference in most set ups. ( both 3300 as well as 2200. ) The standard air filter is just an auto one. At one time I had over rich in some cylinders ( can’t remember whether it was all or some or which) and had black soot exhaust. In discussions with stiffy we tried changing to effectively no filter. Essentially to lower the fuel:air ratio. What we used Was actually a very open large hole foam (filter foam made to withstand oil and petrol) coated in filter oil. It made a difference but didn’t cure it completely. Repitched the prop to a finer prop and that made the most difference.
  4. Jaba-who

    How to improve the reliability of the 6 Cylinder Jab

    Sorry I didn’t make it clear. I did the initial blockage with card and cut a hole the same circular size as the duct. But it was in same site as the naca duct. Then flew it for about ten hours with all data collated ( 6 x egt, chts) charting temps against altitudes and rpms and OATs. All compared to similar data done for previous 10 hours. Talked to Jamie at Jabiru about it. He told me they did pressure transducer tests all along the cowel and the reason they moved it so far back was there was still some Higher pressure forward due to ram air on the cowel surface. They moved it back till they found the spot where the pressure drops off. Perhaps mine would get better if it was moved. So since I’ve been doing other stuff that meant glass work and painting, I’d give it another go. Since it’s not a huge amount of extra work I’ve done the move. But in the new position I have yet to fly it it. So as yet can’t say if there’ll be any benefit. something that I’ve found though is that so many times one person will swear that some mod made a difference but others ( including myself) will do it and it makes no difference. Equally I have done mods that made a difference and I have done significant testing to prove it but when we did the same in another jab it made no difference. There are just so many differences in people’s set ups.
  5. Jaba-who

    How to improve the reliability of the 6 Cylinder Jab

    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.
  6. Jaba-who

    How to improve the reliability of the 6 Cylinder Jab

    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.
  7. Jaba-who

    Lower your MTOW

    I’m confused by that statement. Sounds like you’re saying ( but I could be wrong) Your GP will send you to someone who will then send you to someone else. Your GP can refer you ( legally) to the final guy direct. I’m not sure what the middle guy does. The statement “who ever is on” is an unusual setup in private medicine. It’s the standard in public (free) medicine. The whole principle being you chose your own surgeon rather than be forced to accept any surgeon who may or may not be any good. Odd set up.
  8. Jaba-who

    jabiru radio noise

    Did you need to do anything tricky to ensure insulation between the engine, the engine mount frame and the firewall? On mine the frame bolts to the firewall so that’s a connection. Just wondering (can’t remember it’s been so long since I installed the engine) whether the big rubbers between the engine and frame were open circuit as they are. or does it need some further insulation for where the bolts go through the frame.
  9. Jaba-who

    How to improve the reliability of the 6 Cylinder Jab

    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.
  10. Jaba-who

    Lower your MTOW

    Mmm. I know nothing of said doctor and may be casting him in a wrong light but .... but as a specialist anaesthetist who anaesthetises for a range of surgeons in the private world- there’s a reason some surgeons charge way less, or have short waiting lists. - charge nothing because that’s the only way GPs will refer to them and patients will see them. You get what you pay for I’m afraid. The other thing is waiting times - I have heard people say they had to wait x weeks to see Dr. A but they can get in to see Dr. B tomorrow. Well there’s a reason for that too. Dr A is a fine surgeon who all the GPs want their patients to see while Dr B is a nitwit who stays just one jump ahead of the malpractice suits and no caring GP will let their patients go near.
  11. Jaba-who

    Multiple avionics - panel replacement

    Hi Bob send me a pm. Either on the site pm or to j-martin@bigpond.net.au Cheers
  12. Dynon D180 & dash cradle Dynon Autopilot panel AP74 & dash cradle Dynon EDC 10a ( external magnetometer for D180) $2500 the Dynon lot. Garmin 296 Carry case chargers external mouse antenna manual AirGizmo Panel mount $200 the GPS lot Microair 760 transceiver PM501 4 place intercom $500 All items in working order - redundant due to upgrading panel to Skyview system. Some cables and looms for the above. No AP servos ( retaining & using those with new system)
  13. Jaba-who

    Lower your MTOW

    You're not alone. Broadly speaking (according to the previously mentioned follow up studies) about 85% of people who lose weight put it back on within about 5 years. ( now I can't recall if it was 5 years but that figure sticks in my head). The psychology of "weight regain" is a whole world of its own.
  14. Jaba-who

    Lower your MTOW

    Try ANY diet ( and even the weight loss surgeries) you like - free or otherwise. Published Follow up studies ( and there’s a lot of them) for pretty much every diet, good scientific nutritionally sound, fad and wacko. They all basically show that generally the same result happens. Everyone on them, who follows them, loses weight. Broadly they all rely on you eating less and moving more in some way or other. The complex theories and notions on which they are based are often wrong but that’s irrelevant. They all make you become more aware of how much you eat and cut it down. The problem is the long term keeping it off. It’s the maintaining the lifestyle and dietary change in the long term that is the kicker.
  15. Jaba-who

    Lower your MTOW

    Nope. My understanding ( could be wrong since I didn’t go into it fully). It’s free -if you lose weight. You pays the money. Go on the diet and lose weight and get the money back. You only lose the money if you don’t lose the weight. That’s part of the psychological incentive to work through the diet properly.
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