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About RFguy

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  • Birthday 27/12/1970


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  1. 10 thou. wow. . My pistons rocked up and down I think about 8 thou cold clearance at the crown on the thrust axis. apparently rather normal, and inside the jab spec. Here is a rotax 912 ULS piston . solid skirt, note the drilled ports *I think* behind the oil ring.
  2. It seems that, getting clearances right and the oval, slotted piston just the right fit in the bore at some workload/temperature is rather tricky indeed. Not to be guessed. If the cold oval pistons are round at just a small range of operating temperatures, where the expansion has provided the correct fit in the bore for cooling, and not too tight during conditions that deviate slightly from the optimal, this is very tricky indeed (from my POV). Too much clearance , poor cooling. IE small contact area, small heat transfer area ... That is : IE then piston expands to fit
  3. Shajen OK hmmm. alright. more questions. 1) you said "Although the few times I’ve contacted melb centre they have been quite scratchy and unreadable" Were you on the right frequency and good line of site to the central base station at the time ? 2) you said "Can usually hear aircraft ok, about 3, so readable for most. " is that 3 aircraft, or on average readability 3 even when they are close ? 3) do you ever hear other same aerodrome aircraft readibility 5 or your mate on the portable radio readibility 5 ??
  4. first thing, dont get too close with your test radio, most portables (and some fixed) will saturate, and you will hear carrier, but no modulation if too close, so minimum distance 30 meters I'd suggest. Your description does not sound like a radio problem, more a system problem.. what do you mean "Still can’t understand all the Chinese ones though.". The chinese radios, are for the 99% part, complete rubbish, the chinese know nothing about audio. u get what you pay for. First question do you always hear other transmission about as well as expected , I
  5. fault find logically. First.....do you have another radio , portable or another aircraft on site that you can test with ? glen
  6. OK on that. In terms of reducing piston temps, for this engine, any other suggestions ? Worthwhile for cruise/takeoff to use some EGR and or varying timing ? I know that advancing timing reduces EGTs but increases cylinder pressure and temps. retarding timing increases EGT, and decreases the other two, very roughly.... EGR does need to be servoed pretty well, looking at all the charts I read, but I cant help thinking that you might as well just put a throttle early stop (not quite wide open) or limit RPM and acheive similar. -glen
  7. there isnt really a kicker, would be a project just to stir up interest. all cost. Wearing an extra few kg in the motor, one can use a far less pricey motor than the super rare earth motor. Cost factor 3:1 ! 70kw motor in rare earths, 20kg, maybe $12k, 70kW motor in other , 30kg $4k ... controller for either 3k-5k. but use 2 x 35kW motors. - I propose put two motors on the same shaft, duplicate motor and motor controller This has a good advantage that its easier to get the heat out of a motor half the size. and redundancy. batteries are cheap now, just h
  8. I have been looking for someone to do a electric project with. so far , no takers. Jabiru not very interested, Brumby sort of, trying to find myself a low wing brumby airframe with no engine. I am told....Need seems to be for schools to run the plane continuously, so ity needs battery swap out. and that is HARD but if it was 1 hour on, 1 hour off, then that is entirely practical. 1 hour , or 6 circuits, then 1 hour to charge is practical. I;'ve run all the numbers,, know how to do it... 130kg of batteries is required for 1 hour, next year 120kg, next year 100
  9. All that aside BRUCE I think jts good you extended the air flow to the base of the cylinders, give them every bit of chance to get heat out. My guess is the top and sides of the bores are doing all the cooling work they have some airflow, with the bottom side staying hot and not doing much cooling work, and perhaps lending itself to a hot side of the piston due to a lack of cooling . Let's see. even side, skirt thrust is on.. the top . Odd side, skirt thrust is on the bottom. I think that's right . As is said, different shapes of pistons lend themselves to dif
  10. Turbs, WHen I was a lad (18) I experimented with asymmetrical constrictions (IE different resistance out than in) in inlet ram tubes to change the behaviour of the inlet any in prescence of the reflection wave from the closing- closed inlet valve. It ended up being VERY dependent on gas velocity , and had a very small sweet spot. Going to much larger inlet open time reduced the reflection pressure wave ALOT. IE the inlet gas velocity was slowed down by the action of the slowing and reversed direction piston as it got through BDC in intake stroke, with the
  11. Great description OME. and that is why Jab's tend to float, with the high aspect wing the spiraling tip airflow doesnt get a chance to get on top of the wing , (time) , the wing is not deep , so the first spiral of air is off the back of the wing... so the increase in induced drag is not abrupt.. So it just keeps on flying, - drag doesnt increase rapidly....and as it slows down, the lift just slowly reduces without drag increasing much. For low aspect wings, like an RV, a deep chord, the induced drag increases rather quickly with reducing airspeed, this is because the spi
  12. Oh this is gold . Nice post, Jetboy. In "Synopsis"...... "See Figure 1. RPM history, from takeoff to landing. Max RPM 3330." Oil is up to operating temp, CHTs have stabilized, and engine goes to maximum stress conditions - engine max RPM and WOT. "Burned pistons". well, nasty...
  13. head come off ? !!!$#$%^#%^!
  14. Ipads dont emit much energy. radios are well shielded but they are not completely 'air tight'. the metalwork has gaps. however radios also have antennas..... The pickup of an antenna is approx 10,000,000 (yes ,real numbers) times more sensitive than energy getting in the gaps. There are two main ways noise gets into aircraft radios 1) direct pickup- the antenna can pickup the radiated noise.. IE the radiated noise from a device has enough energy to reach the antenna and be greater than other noises. Antenna placement AWAY from the cockpit is the real sol
  15. overheated valves (as above) stuck ring. hole in the crown. crack. recession of bore sleeve into head follwed by cool down and shrink and loss of compression due to lack of head seal. ha ha how many do ya want.
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