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Bruce Tuncks

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Everything posted by Bruce Tuncks

  1. Bruce Tuncks
    There is some good stuff on this site. I was helped a lot. Also there is Limbach tech bulletin 44 well worth a read.
  2. Bruce Tuncks
    Good thinking guys. I recommend measuring differential pressures with a water-filled U tube. This will enable you to see how well the lower cowl is sucking from the ducts. It also enabled me to see how the 2 ducts were different, something which I thought had to be caused by the prop rotation but further testing this idea proved negative. The airflows under the cowl are not intuitive. I think it was Yenn who did some tufting and took pics to show just how different the airflow was from our intuition. But the goal of cool and even temperatures sure is worth a bit of work.
  3. Bruce Tuncks
    I tried out my Bunnings type detector by holding it near the car exhaust. Sure enough, it emitted a shrill noise and indicated co. It is a bit too big for the panel tho so it was mounted on the fuse upper rhs above the fuel tank. I was going to run a power cable to it but apparently the batteries last a long time and so this probably will not happen. I think it was cheaper than Bunnings on Ebay. Old K, how about trying your detector out by using car exhaust?
  4. Bruce Tuncks
    My temperatures were evened out and lowered by doing a lot of tweaking with the ducts. It took years. Examples include blocking off holes or gaps where cooling air could escape without coming close to the metal surfaces of the engine and joining left and right side ducts with a pipe, as well as adding rivetted aluminium duct extensions. This was experimental stuff and not everything worked at first. But it was fun and satisfying. I also added a smallish skirt to the lower cowl and baffled the oil cooler so as to avoid any higher than necessary lower cowl pressures. If you think about the physics of air flow and heat transfer you will get things better and you should do this before putting new engine bits in to suffer the same fate as the old bits.
  5. Bruce Tuncks
    I did the same with my kids and grandkids. They drove off the roads as soon as they could reach the pedals. My kids are nearing 50 now and so far have not had a prang. ( touching wood here) My experience of teaching agriculture students convinced me though about intelligence and driving. We went for many years with zero loss of students on the road, and the statistics said that this was very improbable, in fact millions to one against. BUT we were getting the smart kids from the classes and not the dumb ones. Then I read somewhere about the 10% dumbest causing 90 percent of the fatalities and it all became clear.
  6. Bruce Tuncks
    Of course garfly... the smartest of pilots can do the dumbest of things. But only 10% as often as the dumbest pilots. That is , if the figures follow those of driving. Driving is not that safe compared with flying. Here at Gawler we don't lose people from flying but we do from driving.
  7. Bruce Tuncks
    Of course you do better testing, including using simulators. My guess is that this would keep some mentally deficient off the roads. But the hoons would easily pass any such test and proceed to kill themselves and others later. Only an IQ type test would keep the worst of them off the road. Disguised as a physics of cars test of course.
  8. Bruce Tuncks
    You are missing my point garfly. My point is to keep the really stupid off the roads. It is those people who do most of the killing. Anyway, I don't agree with you. Whatever you do in life, more knowledge will help. That is why is the theory of flight is part of the commercial pilot's license.
  9. Bruce Tuncks
    Why has this never been tried anywhere? Making a driver's license dependent on understanding physics like OME does? I reckon that doing this would reduce the road toll by about 90%. Most fatalities are caused by those too stupid to ever understand elementary physics. My guess is that the fat lady vegetarian lesbian politically correct lot have successfully destroyed good sense everywhere.
  10. Bruce Tuncks
    But here is a better idea.. get the local pet food guy to come out and harvest those roos.
  11. Bruce Tuncks
    How about something on the ground, activated by radio like the lights can be? I can imagine a line of these along the runway. If they all suddenly sounded, I can imagine the roos running away, well at least for the first few times.
  12. Bruce Tuncks
    Well I reckon your aircraft choice is fine. And there is a lot of regulation surrounding those figures. There is a set of CASA directions defining weights etc. I can say with certainty that the figures would be at legal MTOW. The atmospheric conditions would also be specified but I didnt see them on a quick look. My guess is that they would be for a "standard atmosphere" and you should de-rate the figures for hot and high. Not relevant, but once I watched a 2.2 Jabiru take off in company with a Cessna GA plane. The Jabiru was a good hundred feet higher before they reached the cross-strip. There was no comparison between them regarding take-off distances, the Jabiru was so much better.
  13. Bruce Tuncks
    OME, while I liked your posting, I have to say that I have never heard of centrifugal and centripetal forces as "imaginary ". Gosh, there is 7000g's at a Jabiru's prop tip! That really can unpeel tape I can say for sure.
  14. Bruce Tuncks
    The force impulse which changes the momentum comes from the bank angle used in the turn. If you were to simply and quickly rotate the helicopter 180 degrees, you would suddenly have a reverse airflow. In the example, with a 50 knot asi and a 50 knot wind on the nose initially, you would now have a 50 knot wind from the tail and the asi would now show minus 50 knots but the helicopter would have zero groundspeed just as before. Note that the rotor disk which was tilted into the wind has not changed so to do this swivel, the helicopter would now be nose-up and "flying backwards". Also note that the groundspeed is not relevant. Of course, if you lowered the nose and applied more collective ( and power) you could accelerate downwind and the impulse of the new force would equal the momentum change. In this case the force would not come from the bank angle but from the tilted rotor. I guess this stuff really is rocket science.
  15. Bruce Tuncks
    Here is a point of confusion which I have noticed in this discussion... the velocity reference appears by some to be assumed to be the ground. In fact it is the air. So a 50 knot asi helicopter in a 50 knot wind on the nose has zero groundspeed... so what? If it turns to fly downwind still at 50 knots it will have 100 knots groundspeed but unless it interacts with the ground ( like trying to land) , this is irrelevant. the momentum of the helicopter has changed dramatically of course, and this is the result of the force times time applied to make it turn. The momentum has reversed. We should however always state the frame of reference we are using. Absolute velocity? There is no such thing. The planet Earth has about 100,000 knots speed with respect to the galactic center. Just as well we don't notice that in our Jabirus huh.
  16. Bruce Tuncks
    I can see the argument in favor of hand propping, but could you actually do enough to make a difference? It seems to take a long time using the starter before oil pressure comes up. This is the technique I use after a layup... crank with the mags off until oil pressure comes up. I would do this every time but I don't want to wear out the starter system. It is a quite an indirect way to just operate the oil pump, but it sure adds no complexity. It is turning the engine over dry, but there are no combustion forces. I would prefer a small and light add-on electrical oil pump but his is probably not necessary.
  17. Bruce Tuncks
    Nev beat me to it, but the point is important: If you have a long nose plane, at circuit speed everything in front of you gets hidden. So you have no choice but to fly a curved base leg, you see much better this way. Learning in a glider, the main thing drummed in was " safe speed near the ground" . This was 1.5 times stall speed as a minimum. Most of us gave it a few knots more, those big dive brakes are wonderful . We never had a stall-spin in a glider. On take-off behind the tug you have no control over the speed of course, except to let go if it gets too wrong. At the 70 knots tow speed, a glider can do a climbing 180 turn if needed. Sometimes they do an exercise where a tug failure is simulated. Once, solo and at 600 ft, the tug did a diving turn and I had to let go. It turned out that the elderly tuggie had forgotten which part of the tow he was doing ... this was the last day he ever towed. I never complained, and I don't think anybody else noticed. I think he just felt unwell and knew it was time to retire. I hope to be as smart one day.
  18. Bruce Tuncks
    Is there an add-on electric oil pump? This could also be used before start-up to ensure there was no time where the bearings went dry. I have never heard of such a thing, but the idea is so obvious that it must have been used.
  19. Bruce Tuncks
    Those vids made me feel like a wimp. Here am I at the farm where I gave up on a 550m strip to use the 1000m bitumen strip at the town.
  20. Bruce Tuncks
    Thanks Nev, just 3 questions: 1. What temp do you remember aiming for? 2. were you using straight or multigrade oil ? 3. do you know of incidents in Australia due to this? I too have spent time waiting for the oil to warm up. And yes I wished I had cowl flaps. And I can see why engine heaters are used in cold climates.
  21. Bruce Tuncks
    Gosh there is different stuff out there... I have read " 100 degrees F minimum oil temperature for take-off" in the Lancair stuff. I can dig out the reference if you like. I wonder why " the engine not faltering on throttle application" means that the oil is warm enough to lubricate properly.
  22. Bruce Tuncks
    There seems to be little standardization about this. Jabiru say that the oil temp should be over 15 degrees C, while I was taught to see the needle move off the stop ( at about 50 degrees.) The Lancair with the Lycoming 360 has a much higher temp specified.n Yes its funny old units on the meter, but for sure its a lot hotter. In neither case do they have a lower allowed temperature if using a multigrade oil, but it seems that 15/50 would lubricate cold much better than straight w100. So I would lower the specified temperature for the Lycoming if using 15/50. Of course, we don't have real cold here in Australia, and I have never heard of any damage as a result of taking off too fast before the oil is hot enough for the spec. I can just imagine wrecking an engine if the oil was too viscous to flow to the bearings and full power was used. What do you guys do?
  23. Bruce Tuncks
    Mine was the first Jabiru kit to be supplied with an oil cooler, while an earlier plane had its builder asking for one for years. This guy was a motor-bike racing mechanic and I reckon he knew his stuff. My Jabiru ( 1998) has never had any oil-related problems, not even a leak.
  24. Bruce Tuncks
    The finned sump was never enough. There was too-short an oil temp sensor which gave Stiffy the idea it was ok for awhile till he wised up. Fins on the inside? Has this ever been tried? I can see some drawbacks.
  25. Bruce Tuncks
    Enlightening stuff Jerry. All good reason for Brexit I reckon. Now could be a good time to lobby over there for more sensible regulation. I reckon South Africa has better aviation regulation than the EU, and after reading your stuff, I am even more convinced that the EU has gone the nasty overly-bureaucratic and expensive way. I have seen plaintive letters from German sailplane manufacturers apologizing for charges brought on by this nastiness.
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