RFguy

skippy are you sure that pulling choke closes the throttle? I have never seen any aircraft do that. I learned quite a but abotu them after doing the Dunstone Bing Masterclass. read about it here : http://www.bingpower.de/download/datenblaetter/type94e.pdf

While Bing DO call it a choke, yes I will accept that, The Bing cold start assist is not a choke like the traditional restriction of old automotive carbs. Actually the reference manual calls it a starting jet- but - It's really a completely independent carburettor. Opening the enrichment path allows vaccuum on the engine side of the throttle to pull fuel via the enrichment jet into the engine. This is why Bing carbs enrichment does not work without the throttle closed- it needs vaccuum to suck fuel.

you only need the ENRICHMENT (since it is not actually a choke) briefly. Skippy, how about a magnetic solenoid that just pulls against the spring in the engine bay. you either want it on or off.... since the throttle being closed is what activates it. (or allows it to activate, more truly) . certainly yes does need a spring. enrichment shafts and the shaft o rings can get sticky due to fuel products that solidify.

Jab are iron. (I thought) . or a stainless type I am not familiar with.

mmmmmm what does the street advice say on sensor location with a turbocharger ?

agreed Nev. There is a tenuous relationship between piston expansion and barrel expansion.... I did run some numbers for another when considering scenarios of go around and say, top of climb WOT >> flight idle. ************************************************************** Jab cromo 4140bores : 175deg C rise (25C >> 200C) (12.2ppm/mK up to 400 deg C) assumes unifrom temp , Though I would expect the bore to go non circular because the undersides are far hotter than the top sides (40 deg difference haphazardly measured) . IE pear shaped however, if uniform, is about 0.2mm growth. so...say start at 97.6mm >> 97.8mm 4032... I know pistons have irregular expansion (due to lots of things.) worst it would be 19.4ppm/m/K . pretty steady rise in CTE with temperature. linear to 300C... 20ppm at 100C, 21ppm at 250C we'll call it 20.5 ppm . so 97.5mm room temperature piston worst case assuming uniform temperature (is NOT- bad assumption !!) would be 97.85mm - a 0.34mm growth at 200C (175degC rise) --------------- Now, 2618. that has quite a different CTE curve CTE 22.3ppm 25-100C, 23.2ppm 20-200C, 24ppm 20-300C. We'll use 23.2ppm. so above numbers for 2618 is ---- 97.89 or 0.39mm growth. Therm conductivity for 2618 is 146. for 4032, is 138 (lower due to Si).

Hi Carbon. your insight is useful. yes glass like indeed. " Is the assumption that the rings are seized onto the piston at operating temperature as well ?" you basturd (french accent) you just introduced another unknown ! 🙂 it would be useful to measure BMP etc on each cylinder eh instead of in a lab. I would have thought spark plugs could have done that . well you can of course with measuring breakdown voltage of the plug etc, and various breakdown emission corona modes..

So ! oxygen sensors.... They seem to be located on the headers where the cylinders combine. some are exhaust heated (must get to min 350C, pref 500C) most with more than 2 wires are internal heater type (a couple of amps at 12V) . and wideband are 5 wire usually. has a current output and requires 2-5 V depending on the sensor + heater. I bought a wideband sensor from ebay. we'll see what it does eh ? But if you want simple : use a narrow band sensor. IE you just get a "above stoich" and "below stoich" output. VERY simple to use with just a multimeter reading voltage. and a 12V source for the heater. wideband sensor provides more 'linear' output from rich to lean- but most cars just want to know if they need to go one way or the other. Titanium sensors (rather than zirconia) more tolerant of crap in the gas.

so, if the ring becomes stuck - (and the stuck rings are all the way in against the inner radius) IE flush with the piston outer- then it would stop effectively conducting (its share of the ) heat to the barrel on that side of the piston , and just get hotter.

new Jabiru rocket engine ? what ?

diamonds are made under super temperature and pressure , I guess we have the right conditions.... (yeah I know its not real diamond- but has glass appearance.)

spacecraft ?

yeah , UHF. BNC is fine . make sure you buy 50 ohm connectors, not 75 ohm BNCs.... Be aware, when you talk on UHF from 1000' above the ground, you'll be heard 150km + .... you might find it easier to place the whole run, instead of a join... https://www.minikits.com.au/BNP01 and https://www.minikits.com.au/BNS02 https://www.minikits.com.au/HT336 and https://www.minikits.com.au/JAW336D2 https://www.ebay.com.au/itm/321637603591

Hi jetboy, thanks for the input. Jabiru have used 'various' pistons. Interesting on your thoughts of the heat narrowed lands hypo. When I cleaned out the lands of the last engine , the middle ring lands had what looked like black glass in them... it was tough like diamond. took a month of sundays of scraping with the end of a ring to clean all the lands pristine.

for small ground planes, like these, being a solid or approximated with thin elements wont make any difference in this application. the only time this is important is if, for example, you have some sensitive electronics underneath the antenna- the solid plane will be an electrostatic shield and prevent possible interactions. also, noise from the cockpit can get on the coax cable outer and be brought into the antenna pickup field. The complete ground plane (solid) reduces the pickup from garbage on the cable. in this application, the minimum you need in thin elements is two wires in opposite directions to acheive symmetry. The coax cable should come away at 90 deg to the antenna, ideally, in the two wire scenario.

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.