RFguy

hmm OK the dipole is definetly VHF the stub end fed antenna with the ground plane- that ground plane looks like it could be used for VHf or UHF, so it depends what is on the other side of the fibreglass. if it is ~ 16cm long skinny , that would be a UHF stubby whip. If it is perhaps 30cm long and appears to have a coil or spring in it, probably VHF. -glen RF Engineer.

thanks all the interesting observations and comments . Nev before I extract it, I will get it under the microscope and see if I observe any trapping of the ring. Thruster what's the ring land gap on the 2nd ring in a O320 ?

Given the simple construction of the antennas, the UHF antenna will be the smaller. got any photos ?

dlegg -Yes, 95/98 ULP is the best fuel for Jabirus. no argument from me on that. keep them clean and they wont get much buildup, which means less /no stuck rings, no red hot buildup coals, etc etc less of everything undesireable. OME : It's significant that the sticking wasnt random. they're stuck within a few degrees of precisely the centre of the minor thrust side. ther eis significant temperature difference between the top and underside of the barrel, so its not that. So was it an event that causes this to occur, or is the clearance such that the buildup will just kill it in time. An event might be... sudden barrel cooling where the piston goes almost interference fit ? Or ...is the lower pressure on the piston on the minor thrust side, make the scraping of the barrels is not as effective / different and it scrapes junk into the ring lands ? something goes on here. If I can get it out without damaging the ring , I'll take a look under the microscopes.

I'm overhauling a jabiru 6 cylinder engine, and it has on #1 and #2, the middle ring stuck on both....... both stuck on the minor thrust side . the last Jab 6 cylinder I overhauled, it ALSO had the middle ring stuck on 3 of 6 cylinders. Does this 2nd ring in the jab not get enough pressure across it (IE first ring does all the work ) to move , extend and seal (and do something useful) ? I've heard muttering about insufficient ring land clearance being an issue. I am interesting in commentary on this . and guesses Can someone with a bit of experience particularly with seeing this on non aircraft engines please comment ? has any one seen this on only unleaded petrol only jab engines ?, or is it just an avgas fun thing. -glen

yep

Jabirus are fine, just that the jabiru engine doesnt have the capacity to absorb faults and abuse. - The engine should have the head + barrel pulled for inspection of leakdown < 70. That in my book is the maintenance trigger. - the engine should be grounded for leakdown less than 65 for any cylinder. - fit EGT sensors to all cylinders since again jabiru engine cant tolerate out of limits EGT. One sensor is not enough for this engine. - CHT < 160C. there is a culture of ignoring the bad news by many concerned.

I think the up front purchase price for the rotax is good value for money. "The Rotax " is a good engine . But the way spares are priced, the manufacturer does not encourage rebuilding/overhauling. I see it as a method of ensuring a busy factory pumping out new engines. They dont want you to fix it. So the upfront buy engine cost is really not too bad since it should need much all the way to 2k TBP. Oil filters and spark plugs and oil for "The Rotax" are cheap. that's all it should need over the 2000 hours.

but he's a rotax owner Don, when a set of rings for a rotax is $250, money is no object. (I just bought 6 ring sets for a jab project for less than the cost of a single ring set for the rotax) .

but , no fire. I'm thinking the pilot and home owner, and neighbours all pinch themselves and go buy a lottery ticket or two. that the pilot survived its likely it didnt fall from far or wasnt going too fast. maybe was best effort for autorotation landing over the suburbs. I'd prefer a Jetranger in a crash over a squirrel.

Bruce the main error is the lack of a battery isolation relay/contactor at the battery. Needs to be an enclosed contactor (no free air spark) . every certified aircraft I've looked at is done this way. The factory has the hot battery wire goes into the cockpit wiring mess. same for alternator- needs to be fused and have its own wiring in the engine bay. alternator generators enough energy to make a fire also, but the battery is the king fire generator. needs a fuse between battery and alternator chargign output. regulator goes bad and puts battery V+ onto the shorted stator. woof.

dunno, I'd do some reading... others might be able to advise. there might be some minimum temperature it has to be at to operate correctly, and location might influence that.

I would not blame the pilot- it is a helicopter !. to stay airborne you just need to put in enough rudder, balance pitch and roll, and pull on enough collective. how hard can it be. so, no I do not think it was the pilot. Jabiru's likely burn because of their haphazard, dangerous wiring practices, and poorly engineering wiring paths (happy to stand in a court of law with that one) . there is no way those airframes should fly without electrical mods. IMO. I have commented to Jabiru about it with no response.

home owner and neighbours are fortunate that there wasnt a fire.

I've had the jabiru ice up on the ground at high idle on a foggy cold morning. ...

rightio then , sounds like just needs methodical approach to figure out what is going on. Yeah the O2 sensor (ULP only - no lead) would be a handy diagnostic I think.

This is a good read https://www.rotax-owner.com/pdf/UNDERSTANDING THE 914 ROTAX.pdf Particularly sections : the ENRICHER SOLENOID SECTION (9) and FUEL REGULATOR- AIR BOX PRESSURE (14) Rudder - take a good look at those two sections. I reckon you will find your demon there.

Carb heat is common oncarbed Rotax, Brendan, depends on manufacturers implementation of WHERE they get the inlet air from. Most Tecnam seem to have dual air filters on the carbs inside the engine bay. so, somewhat preheated air. You'd want carb heat if deriving inlet air fresh from front of aircraft. disadvantage of internal air source is you leave performance on the table with the warmer air intake . rudder, I'd suggest persisting in finding the problem. I'd be looking for the enrichment circuit sticking, or carbs not well balanced in those RPM ranges. After thoroughly cleaning all the plugs, did the behaviour change ? The 914 runs tricks on the carb bowl pressure when in boost. at MAP28- that's a transiiton area where you like are starting to get the boost of coming online. Maybe the float bowl pressure boost compensation is not working currectly. Is it generally smooth at any setting where there is a couple of inches of boost ?

if you have not as yet, do consult the book on recommended loading (manifold pressure, fuel flow ) versus RPM in the 914 ops manual,

iT'S SUCH A LOAD OF CRAP, JUST DID IT. Remember the try on by the gov back in the 80s- the "Australia Card" and they got rejected. So then they just came up with the ATO TFN instead as the number...

mmm dunno that will help that much you can get an idea of mixture just from the EGTs ... what did you find re my above questions ?

105C and 20 deg ambient ?. hmmm might be hot on a hot day. but all planes have similar issues.

what's the thermofan fan for ? airplanes generate plenty of airflow and pressure... rotax is happy for much higher temps than that. and if you let it get hotter, cooling effectiveness improves enormously (higher Tdiff) . IMO the airplane should have enough cowling airflow stationary at engine idle to deal with any heat it makes.

another gear up landing. gather the empenage buckled when the front of the airplane stopped. cant imagine the passengers bodies faired well to the decel.

Thanks CC for the nicely written input. I did have to look up "Azeotrope". My year 12 chemistry is a long time ago... An azeotrope is a mixture of compounds with the same composition in the vapour as in the liquid. In other words, an azeotrope is a liquid mixture that has a constant boiling point and whose vapour has the same composition as the liquid.