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Bruce Tuncks

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Everything posted by Bruce Tuncks

  1. Bruce Tuncks
    Great pic glen. It looks to me as if there was something scratching the surface. But it also looks like the scratches are longer than the rockers would make.
  2. Bruce Tuncks
    I too never heard of a cock-eyed bob before. Whirywinds, thermals, willy-willies, mini-tornados ( for really strong ones). Strange we haven't got a proper word huh.
  3. Bruce Tuncks
    Skippy, you got some good replies there. Can you do an experiment? On a nice dry day, arrange a temporary cool air supply to the engine and see if there is a difference in straight and level speed? On my Jabiru, I can't tell the difference with carb heat on or off, but then I'm not very good at picking stuff like that.
  4. Bruce Tuncks
    Why not carry a few liters of water to spray on the engine when it needed it?
  5. Bruce Tuncks
    7000 g's at a Jabiru props tips... I was told this but didn't believe it so I dug out an old physics text and got the same answer. Still I find it hard to believe.
  6. Bruce Tuncks
    I have been trying to find out about fuel additives. One article said that you can't just run a leaded-fuel engine on unleaded without risking the engine, and that you needed some substitute chemicals. That's not what I've heard about Jabiru engines. Maybe they have a low enough compression ratio ( 8 to one, maybe 8.3 to 1 ) that detonation is not a problem with 98 mogas? They did say that it was detonation and not valve-seat recession that was the problem. The only negative thing I found about the 2 stroke oil was that it didn't help the exhaust valve seats, on account of having been burned before getting there. I also read that some petrols already have oil added... how would you know?
  7. Bruce Tuncks
    I think its a trend that the fleet is going better than on avgas. I didn't know there are different versions of mogas 98. I'll look into it. So far, I have just bought at service stations and only checked for the absence of ethanol. But here's a question... it seems to me that Yenn is quite right to add a bit of 2 stroke oil to the fuel. How else is the very top of the cylinder going to get any oil? Yet if this was such a good idea, why is it so discouraged?
  8. Bruce Tuncks
    A Jabiru at our club is showing improved leakdowns after about 100 hours of mogas. The oil is darker than usual at change time, so it may well be cleaning up stuff. Too early for me to tell I know. I might age-out before the engine cleans out.
  9. Bruce Tuncks
    I gotta defend OME. I reckon his stuff is standard mechanics, like they once taught in physics classes. Can you give an example of a " false theory?"
  10. Bruce Tuncks
    Back on topic... After 5 hours on mogas, the compressions were checked and they varied from 65/80 to 72/80. There was no big reduction at 15 degrees either side of TDC. A borescope look inside the cylinders still showed beige crap lightly crusting the combustion chamber. I think this beige stuff is unscavanged lead bromide. My plan is to repeat the leakdown in another 20 hours or so to see if it gets better or not.
  11. Bruce Tuncks
    Academics don't fight on account of having a foolproof method of dealing with disagreements. Its called experimentation. The rivalry between the Wright brothers and professor Langley is a great example. The Wrights were the best scientists by far. They used more and better experiments.
  12. Bruce Tuncks
    Are you sure that is Jesus? I am pretty sure he had brown hair and beard and a thinner face. I have seen pictures. He did make a second coming, running the shoe repair and key-cut stall for a few years at my local mall. I was the only person to notice.
  13. Bruce Tuncks
    Mike, the narrowest runway I have ever used was in the USA, at the Hilton ranch in Nevada. And here at Gawler, we use take-off pads which are real narrow, but it doesn't matter if you stray off them. The common thing is the private funding . Why go for narrow if somebody else is paying? You can see both these things on Google I reckon. At the Hilton ranch, I went off the narrow strip on my first landing with an LS4. These gliders have funny heel-brakes and using them stops you using the rudder. Experienced LS4 guys pull the rudder pedals up as close as they can go before landing, but I found out the trick the hard way. Going off the strip was not too bad, although the gravel there was very coarse.
  14. Bruce Tuncks
    Sorry for going off-topic, but I have to say how trading in an old Deutz for a new Massey Ferguson was the biggest mistake since we got the farm. The MF was a heap of #### compared to the Deutz.
  15. Bruce Tuncks
    I remember reading that the underwing campers got dust from aircraft taking off due to their site allocation. This would have slowed me down as another thing to check out before going. How far is the camping area from the tie-down area this year?
  16. Bruce Tuncks
    Onetrack, I like your use of neverseeze but I was surprised at only a 10% reduction in applied torque. I would have thought maybe 25% but this is just a wild guess.
  17. Bruce Tuncks
    I agree about the wankel Nev. AND its hard enough to seal a circular cylinder, I've never seen an old wankel, but I bet they would fare worse when they got old and leaky.
  18. Bruce Tuncks
    There is a youtube on the duke engine and the guy says that the swash-plate is not as robust or as simple as the crankshaft. He likens the action to how we naturally turn a crank. On the other simplifications, I think that idea of eliminating poppet valves and camshafts and push-rods is so good that it is surprising to me that a 2 stroke engine is not more reliable than a 4. These ideas can of course be done with a crankshaft engine.
  19. Bruce Tuncks
    Remember the Sarich engine? same thing. I have flown in a self-launching glider powered by a wankel though, and it was very smooth. On the Duke engine, it was not clear to me how the reciprocator worked. I wonder if this was not the downfall.
  20. Bruce Tuncks
    My engine is an avgas one, nearly 700 hours now. It does nothing on applying carby heat or on turning off a mag. I decided that it must be doing things which I'm not sensitive enough to notice.
  21. Bruce Tuncks
    Wow good point rfguy. Yes I know that you should do leakdowns at more than one spot. But I have been lazy so I just have done the one reading. On the deposits stuff. ... my book ( Skyranch ) says to get a lab test of the deposits stuff. I have asked about oil analysis on Jabiru engines and have been told that there is not enough database for this. Skyranch has 50 years of experience with Lycomings and Continentals, they have been around a long time huh. And thruster, I think you are right. My endoscope was pretty cheap but it will go down a spark plug hole so I am going to try it. I am hoping to see a cleaned up engine from the mogas running. In the meantime, the leakdowns, done more carefully, will be the main thing for sure. Mike Busch implies that leakage past the rings is not real bad , but leakage past the valves is bad. Only a leakdown can help you pinpoint this.
  22. Bruce Tuncks
    I remember as a kid that car engines needed decoking at 40,000 miles. That is thankfully a thing of the past, I wonder what changed... was it the oil or the fuel or the engines? My Jab has gone 700 hours just fine on avgas and although I'm not planning on doing a decoke, I will be looking in the pots soon with an endoscope.
  23. Bruce Tuncks
    Don't use a pressure system to transfer fuel from a drum to the plane. Some years ago, a guy wrote up this system he had been using where he put compressed air into the drum to force the fuel out. The editor unwisely published the article and then all hell broke loose. Apparently this is a fire/explosion hazard. Ken's fuel pump is ok though. I might get one, on account of finding 20 litres quite heavy to lift just so all the time.
  24. Bruce Tuncks
    thanks OME. My son-in-law is a shooter and although he knows his stuff, he will like to see it displayed like that. I personally don't think a flaring and floating Jabiru though is ballistic. If so, you would feel the lack of g force. I reckon the float comes from the conservative approach speed of 60 knots compared with the touch-down speed of 40 knots or a bit less. But I have to admit that a slightly high flare can end with a decisive drop. On the topic of speed control on landing... A glider exercise was to cover the ASI and see how well the pilot flew and in particular maintained a safe speed near the ground. Most pilots flew the circuit about 5 knots faster with no ASI. After flying gliders, I never thought that the Jabiru had a long float time. In a glider, you would float right along and past the airstrip without those nice airbrakes.
  25. Bruce Tuncks
    My ASI is already marked. But I need an audio warning in case I forget to look at it... Oops, I have just re-invented the stall warning. When I installed that stall-warning, I didn't like how far it was around on the underside of the wing, so I moved it up a few mm to go off earlier. What's the use of a warning if it happens too late, thought I. The result is that I can make the warning go off at altitude easily enough, but I still never hear it go off on landing. I think the Jabiru just doesn't reach anything like stalling A of A on landing... if you draw a line from the sub-fin to the main wheels, you will see what I mean.
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