Oscar

is it ok to fit 6 x CHT senders to a 24 reg?

Isn't this where the regs get stupid... but if it's a 'C' model, then a Part 21M engineer should be able to approve it instantly under 'nil adverse effects'; and if it's not and Jabiru don't approve, they should be taken out the back of the shed and kicked at 'inappropriate response' level.

 

 

Oh, yes - and generators in the Antarctic, buses, major league trucks... and that's the point. I love them. But you don't get 85 hp continuous from 55 kgs without pushing the envelope.. and people who don't understand that they're pushing the envelope and treat them accordingly, are destined to be disappointed.

 

 

We know that Jab cooling can be very uneven between pots, if one doesn't have CHT's on all cylinders then it's easy to assume - incorrectly - that temps have all been within limits. Once one pot gets overtemp, it's entirely possible to get an accumulation of effects, and if the dissipation of heat from one exhaust valve goes awry, you'll probably get a build-up of fried oil on that rocker supply every time the engine shuts down and the oil remaining in the rocker supply line stops flowing but the heat-sink effect remains. That will close off the oil supply to that rocker and the effect will simply grow with use.

 

The dissipation of heat - particularly in an air-cooled engine - of individual elements is a highly complex situation and unless you have the diagnostic capabilities of a CAMit, the inter-relationships of things like the cooling airflow, the heat-transference capability of the valve guide and valve-seat material et al is way beyond the appreciation of we end-users of the product.

 

For the cost of installing full engine CHT and EGT monitoring for every pot - preferably with a recording facility that allows post-use examination of the flight conditions and early-intervention remedial work vs. more frequent overhauls - it's a damn no-brainer. As with everything on an aircraft, 'systems' are always a compromise. In the case of Jab engines, the compromise is between light weight (allowing more usable weight within the class limits), cost, and fuel economy. If you want to have your engine Gardner-class unbreakable, it will cost you Gardner-class weight and cost. I'm talking (from personal experience!) 750 kgs engine weight for 140 HP continuous for 40k hours of operation and a price of about $40k... They are magnificent pieces of engineering, but they've never flown.

 

 

I flew the sole example of a Rallye Commodore in Australia a bit, and I'll never forget landing it on the 06 runway at Camden, at light weight one afternoon, into about a ten knot breeze - it stopped literally within the length of the piano keys; the student waiting to line-up in a 150 gave me a staggered look as I turned off under his wingtip. One of those moments, it was . . . However, I came to agree with Randy Green, who had done the first-of-type testing of the first Rallye into Australia, that it was essentially a landing-and-taking off device, rather than a thing for going places.

 

If that was the same Rallye I flew in from Canberra to Tocumwal with you, it was absolutely a horrible thing for cross-country - too directionally stable and weaved everywhere every time it hit a gust from one side. The nearest thing I've ever been in for an unpleasant travelling motion was a Spray-inspired yacht with a vastly too small rudder and a steering wheel that was slipping on the shaft in a nasty following sea with added side-chop. We did several 360's from broaching between Sydney Heads and Barrenjoey Head, and that was with one person playing the main sheet and another playing the jib - and the mainsheet hand was a highly-experienced racing yacht crew member!

 

 

From all of the above, it occurs to me that one should be very prudent about flying in a 19 (or CH-exp) reg aircraft that has had vg's attached - because the range of effects may not have been properly tested. It is, I think, one of those areas where a little knowledge can be a dangerous thing, and there is a bit of a perception that vg's are a marvellous cure for any sort of undesirable stall behaviour, or just a silver bullet for improving stall speed.

 

Human nature being what it is and vg's being cheap to buy and easy to attach, inevitably some people will adopt the 'more the merrier' approach, and also assume that what they see working on one aircraft will translate to the same effects on another. We've all seen that syndrome over and over - remember the fad for enormously wider tyres than standard on cars years ago? Many people assumed that more rubber meant more cornering power, and then found that things like camber change meant that the tyres would suddenly lose huge amounts of grip as the tread became removed from the road, that they aquaplaned like curling pucks on spit or simply slid uncontrollably on gravel patches etc.

 

I think it would be useful information if RAA were to produce a 'beginner's guide to vg's' that would give people some sort of idea of what they are looking at before they jump into a modified aircraft - and perhaps some idea of the sort of questions they should ask of the owner of the aircraft re the testing that's been done. Just because something looks like an excited hedgehog obviously doesn't mean it's necessarily going to fly like a cuddly puppy...

 

 

CAMit sell a much-improved rocker bush with grooving designed to ensure the oil gets to the right places: http://camitaeroengines.myshopify.com/collections/engine-components/products/rocker-bush

 

Obviously, even they won't help if there's no oil getting to the rocker in the first place, but if you looking at having to replace a bush, at the cost of a set, I'd go the lot. If you want to really do the job nicely, add the new CAMit rocker arms with the better geometry. If that exhaust valve has been running hot, as you suggest, then I'd be suspicious of a build-up of fried oil in the rocker supply.

 

 

If all other 'normal' tests don't show anything untowards, as a long shot I'd be checking the airbox to see that everything is ticketty-boo. I have an ST1, early production number aircraft, and the airbox is, to be polite, not the most inspiring thing.

 

 

The poor think was probably feeling overawed by all those rough, tough ag-ro types and just wanted its tummy tickled... but that's a pretty amazing forward roll it did there - didn't even dent the spinner!

 

So many small aircraft crashes end up with the thing upside down, it's enough to make one think hard about the level of protection some of the swoopy low-wing types offer against neck compression injuries - not to mention the problems of getting out if they are upside down. Plus, the desirability of five or six point harnesses, even for just recreational flying.

 

 

Add to checklist: LOOK at the damn landing site, recognise potential hazards, and plan accordingly?

 

 

What a bugger!.

 

 

Aha, well that's all good then! If the old pump was running ok on the old engine, it'd be interesting to know why suddenly not on the new one though, to add to the sum of Jab knowledge around!

 

 

Frank - great that you have sorted the problem, but I have a question: if the Type 1 fuel pump was re-installed, was that with the longer push rod? If so, then I think we can assume that the mechanical pump diaphragm was not being allowed to settle properly back to its 'empty' position, so not sucking enough fuel in to pump forward. That makes me wonder - if the longer push rod was used, has the cam lobe been damaged?

 

 

Um, surely it's pretty clear that the port wingtip passed something like 10 metres from the tower ( see 0.04 of the video). Since it has a nearly 68 metre span, that makes the other one maybe 78 metres away, if my calculator isn't lying to me. If I were flying a Galaxy - or anything, really - closely past a tower, I'd want to be able to see the bleeding tower out my side window..

 

 

Nope, it was a genuine NASA test - here's a similar one they did on a C-5A:

 

 

 

Model Aircraft Association of Australia, Aaaargh!

Well, Thruster Abominable Aircraft Anonymous was already taken.

 

 

The standard Jab. oil pressure relief valve can go into 'float' under certain conditions, which keeps it mostly open - reducing oil pressure markedly. It's a known problem that CAMit have addressed with a superior design. The conventional wisdom was to add a washer under the relief valve spring, but that just moved the problem further up the chain, as it were.

 

At the AMSL of Kingaroy, 98 MON - even if it's fresh from the refinery - is in reality about 95. If it's a bit stale - more than two weeks since production - it's basically expensive ULP.

 

 

I remember having a problem with a mechanical fuel pump on one of my cars, everything seemed to spec, then (finally) I discovered that the spacer between the pump and the engine block was the incorrect thickness - too thick! Have you tried disconnecting the fuel delivery line to the carby and pulling the engine through say 10 revolutions and seeing what the delivered fuel quantity is? That might not be enough to do an accurate conversion to the required delivery rate / revs but if it's definitely on the marginal side it might show up. I've also experienced a fuel line on the suction side that, because it was twisted when installed, actually managed to pretty much close itself off due to the change in radius of the curve from the suction pressure.

 

 

tsk, tsk... this from a man who used to ride a 6-cylinder Honda motorbike...

'Twas expensive, but wasn't slow (no, NOT a Leadwing!)

 

 

Only for the Sport edition.... The standard Thruster doesn't take off, the ground under it rejects the noise.

 

 

Yep, I always wanted to be slow and expensive, but I never managed it.

 

 

According to the Encyclopaedia of Commercial Aircraft, the AN-14 was developed to replace Aeroflot's AN-2 fleet - so they must have had one? (fleet that is...)My T-83, with the 503 de-tuned to ~40hp because of the crap points ignition system and single carb, gets 3.1 gallons/hour (per seat, also) at 45kts, so the AN-2 is cheaper on fuel... perhaps a little more costly on engine overhaul?

3.1 gph? So, 3.1 gallons, or 11 litres or so, per 25 kilometers OTG in still air, per seat?? Makes my Jabiru look like a bloody Prius for economy and a WRX for performance.

 

May I suggest you move to a plastic deck chair and some weather balloons for a massive boost in range and economy? Or, walking.

 

 

Been there, did that, you try to help a Thruster owner and you pay the price. So much for charity.

 

 

Engine overhaul may be as cheap as doing up an early Victa mower engine ( a fair comparison in terms of quality etc.), but fixing up the T-83 ghastlies isn't cheap unless you have a benefactor who will work for CX500's in exchange, and have no shame in ripping him off.

 

 

Great stuff!. I had it ALMOST correct... but as always, there's no better advice than you will get from 'the horses mouth', as it were. That response is 'classic' Ian Bent - not just what, but why and how things interact to produce results. If I sound overly enthusiastic, I probably should apologise to Ian if other people take this as unwarranted - but as a business systems analyst by (previous) profession, I spent a considerable part of my professional life looking at 'systems' to make sure that any changes were not just a band-aid to an obvious problem but did not introduce new problems ('the law of unintended consequences'). I suspect that there are quite a number of Jabiru engine owners who wonder if the same intellectual rigor had been applied to the introduction of hydraulic lifters...

 

The keen-eyed will note that Ian Bent's response contains an extract from another document. Suffice it to say that such a document might be a step along the way to a wider application for CAMit engines than for 19-reg aircraft. I'm guessing here, but having been involved in the preparation of an extensive EO for modifications and repairs to our aircraft so it can remain in 55-reg., there's a vague familiarity. Maybe presumptuous to say 'watch this space', but I'll be watching nonetheless.

 

 

Rotating the pistons 180* ( reverse the offset ) according to an engineer, makes good sense to jab engines. ( gave me the reasons why......long story )

Yes, the physics behind reversing the pistons appears pretty sound, though has certainly been the subject of debate (arguing slap vs thrust line). Additionally, Jabiru use a tighter piston-cylinder tolerance than most piston manufacturers recommend for an air-cooled engine, which I suspect may be a part of the reason that the standard Jab engine tends to be very tight just after shutdown; however I am not an engineer and my reasoning here may not be correct.