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Bruce Tuncks

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Bruce Tuncks last won the day on October 12

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About Bruce Tuncks

  • Rank
    Well-Known Member
  • Birthday 08/08/1945

More Information

  • Occupation
    Jabiru SK, Libelle
  • Location
    Gawler, South Australia
  • Country
    Australia
  • Gender
    male
  1. Bruce Tuncks

    How to improve the reliability of the 6 Cylinder Jab

    That is interesting onetrack. It confirms the droplet theory. Unfortunately the Jabiru intake plenum is too close to the carby for such a thing to work. Turbs, are you thinking about tuned inlet pipe lengths? I haven't got the figures anymore, but I did work out that the inlet pipes on my engine were much less than the displacement of each piston. That means the flow is through the carby through the plenum and the pipe and into the sucking cylinder for the time the inlet valve is open.
  2. Bruce Tuncks

    Tell us about your last flight

    Thanks for posting that , I especially liked the good landings. Great video work.
  3. Bruce Tuncks

    How to improve the reliability of the 6 Cylinder Jab

    Jaba is right about the droplets of fuel in my experience. Of course the job of the carby is to convert the fuel to vapour in the intake plenum, but nothing is perfect. How else would you explain how cylinders 1 and 2 originally had lower EHT's than 3 and 4? I imagine those droplets overshooting the branches going off to 3 and 4, and hitting the end of the plenum to be probably now vapour which is then sucked into 1 and 2. (sorry but the engine is a 4) In fact I made some little vanes just downstream of the carby to deflect these droplets into 3 and 4 and there was a big change for the better. (thanks to jetjr for the comment about how nothing much upstream of the carby would work ) But my vanes are not perfect either and while the EGT's are quite even now, the CHT's for 1 and 3 ( stbd side) run about 20 degrees cooler than 2 and 4. Yep, 3 now is cooler on CHT than 2, even though 2 is at the front. But the whole engine is much more even now than before the exercise so it was all worthwhile. I would still like to reduce the difference to 10 degrees though. One thing I considered was putting more distance between the carby and the intake plenum, it is interesting to know that Rotax does just this. I have also wondered about putting an electrical agitator ( tiny fan ) into the plenum but both these things would be very hard to do.
  4. Bruce Tuncks

    How to improve the reliability of the 6 Cylinder Jab

    how do you monitor this Hyundai?
  5. Bruce Tuncks

    "Phantom" radio reception

    Have a look at filtering the power supply to the radio. I use a 4wd filter.
  6. Bruce Tuncks

    Guess This Aircraft ?

    Thats real professional red. There is a shop in Adelaide advertises that service for photos. I think its quite expensive.
  7. Bruce Tuncks

    Guess This Aircraft ?

    Red, how are the rego letters etc taken out from these pics?
  8. good points Nev. Yes, the Jabiru has an oil system which can't go negative. Nor can the carby.
  9. I have wondered about the negative G capacity of the Jabiru struts. There is a story ( I can't vouch for its truthfulness) about a guy ( south of Adelaide) who began doing loops in a Jabiru. Then he got a bit bored and started to do a bit of inverted at the top of the loop. Inverted flight in a strut plane is something I never would contemplate, but if the story is true, then he got away with it. Of course you can design compression struts, the Pawnee being an example. But those struts are a lot fatter than the Jabiru struts.
  10. Bruce Tuncks

    Guess This Aircraft ?

    I give up red. I even tried to google it up. The u/c looks really good and being a tail dragger it should perform well. I'd put a Jabiru engine in it if I built one, and I reckon an extra stringer to give the fuselage more shape would be good too.
  11. Bruce Tuncks

    Guess This Aircraft ?

    where are the doors? I don't think I would like to climb in if that is a tilting canopy. Otherwise it looks logically designed, but those slab sides might vibrate.
  12. Good point djpacro. The strut would have to be placed just right for there to be zero up or down on the wing attach points. Just far enough inboard of 50% to allow for tip effects to balance out. If I were designing a strut wing, I would like for the wing attach points to be carrying a bit of upload, mind you this would make the strut longer which is not good... And Turbs, being scientific is not at all the same as being academic. The Wright bros were good scientists, better than professor Langley. There are some good scientists posting on this forum who have not been to any academies. I reckon this is the best site by far to get good technical comments on my ideas and proposals.
  13. Wow turbs, you have seen ROTTED fibreglass? That might be a world first. Maybe you mean water ingress between laminations in a poorly made layup. Please try to be clearer and more polite in your postings.
  14. Good comments HIC. What happens is that the conservative assumptions add up with glass and the final structure is greatly over strength, so the only way out is to test-load. And yes, I agree about flexibility effects. This flexibility is what gives fibreglass its toughness as measured by the energy required to fracture. Remember the Janus fatigue project? They had to double the applied loadings to get anything to happen. Gosh in 50 years of flying, I never saw wingtips deflected so much and this machine was doing it every few seconds, all day and week after week. What happened was that the fatigue machine broke. Then they did some deliberately poor-quality repairs. Finally they got some action in that the metal embedded fittings began to come loose. Fatigue in fibreglass is a furphy disseminated by those who have something to gain by frightening the scientifically challenged.
  15. Here's an example of calculations.. the bolts in the Jabiru struts. The strut-bolts are AN4 =1692kg ultimate in single shear. At the Jabiru strut angle, this gives 813.6kg upwards ultimate force times 4 (for 2 struts each in double shear.) This gives 3254 kg or 6 G at 544kg. ( actually 5.98 G) The next step is the mainspar assembly with the wing skin contribution. I would bet that the extra contributed by the wing skins was ignored at the design calculation stage on account of how it would complicate the calculations. There is no doubt that the Jabiru has plenty of strength. Another reason is that fiberglass is a variable material and so the design strength is well below the actual due to conservative assumptions. One example I have already told of is when a Jabiru collapsed onto a wing when a u/c leg failed. Almost that same week, a Technam had a very similar collapse. The result? No damage to the Jabiru, but a new wing needed for the Technam. I am not saying the Technam is badly designed, on the contrary, it is accurately designed and the Jabiru is over-designed.
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