Oscar

Yes, my apologies to Airborne there; they've been doing well.

 

 

Lol, sorry Tom, rant is focused on the engine! I love the airframe, albeit not of Rods design but wouldn't be here without his initial throuput. ( I have been known to rant ) so when ya bringing that Rotax powered beast up Tamworth way, would love to see it in person!!!

Factually false and typically malicious.

 

While it is true that Rod Stiff and Phil Ainsworth contracted highly experienced engineering assistance in the development of the Jabiru line, the basic design and perhaps more importantly, the design philosophy for the airframe is attributable to Rod Stiff. Key points that the entire ultralight movement in Australia can thank Rod for include:

 

• a remarkably robust and crash-worthy airframe that is also cheap (in aircraft terms) to repair, with commensurate advantages for running costs including insurance;
   
   
  

 

 

 

 

• very competitive performance that can be realistically used in Australian conditions;
   
   
  

 

 

 

 

• benign if not necessarily exciting handling with no nasties lurking in the woodpile for the unwary / inexperienced;
   
   
  

 

 

 

 

• straightforward maintenance and the ability to have many things that may be subject to damage from 'usual' operational circumstances field-repairable so one can keep going / get back from remote sites.
   
   
  

 

 

 

Rod and Phil developed an aircraft line that has produced more aircraft than any other Australian manufacturer ever, that has international recognition ( and worldwide sales) as a 'good' product, and that has put more people into happy ownership of an aircraft that they can use effectively for just generally aviating than any other. At the same time they managed to develop a business model that is a significant contributor to the economy of the local area.

 

Jabiru is now the only Australian manufacturer of aircraft with any significant international sales that is Australian-owned. Gippsland Aero and Seabird have both been taken over by overseas owners.

 

We have no Australian-owned automotive industry any more - and it looks as if we shortly will have no Australian automotive industry at all. That Jabiru have been able to continue as an indigenous and viable hi-tech manufacturer is very much a product of Rod Stiff's and Phil Ainsworth's initial vision and testament to the capability of Rod's basic design and the business model they both embraced for its manufacture.

 

Jabirus are not perfect - nobody who owns one would suggest they are. However, before casting the first (of an apparently unending sequence of) stones, show us a perfect aircraft.

 

 

Just read the whole blub on Jaba chat written by Rod Stiff. http://www.jabiru.net.au/images/jaba/Contrary_to_local_rumour.docx.I think when the engine manufacturer (Camit ) recognizes the engines has faults and has decided to fix them, then Mr Rod Stiff better watch out as his engine has a bad reputation and he is doing nothing but whinging. He needs to embrace the modifications. I think he will be the big looser in the end. I wish Camit all the best.

It's not as simple as that. Jabiru holds a TCDS for the 2200 engine that took a lot of certification runs to obtain; CAMit will have to go through the same rigmarole to obtain a TCDS for its engine. However, accepted demonstration (by calibrated test runs) that modifications to a TCDS'd Jab engine have at least the equivalent 'quality' will allow substitution - by an Engineering Order - of CAMit modifications for original Jabiru parts. However, since in the case of a 24-D reg. Jab. every component is 'warrantied' by the manufacturer, an EO cannot apply.

 

The issue of whether 'Jabiru' as the aircraft and engine manufacturer should embrace and authorise the use of a revised version of their engine by CAMit, is entirely separate. We all have opinions; perhaps Jabiru will recognise the market forces if CAMit engines prove to be 'superior' ( and most readers of this forum will know my own position on that question) - but FWIW, it's not unreasonable for Jabiru corporate to withhold their blessing until there is clear evidence that it is deserved.

 

 

Nick, you mean Jaba Chat, of course- on the Jabiru company website.

 

Holy crap, this opens up a lot of stuff. Rod Stiff's comments are entirely correct (as far as I understand it, and I'm not an expert) for LSA-class 24-reg aircraft - but NOT correct for 24-reg 'Certificated' aircraft (e.g. 160Cs). In the case of 160Ds, it IS correct: Jabiru as the manufacturer is held responsible for every component on the aircraft, and that includes the engine as defined, down to the last nut and bolt.

 

HOWEVER: since a 'C' ('Certificated') aircraft is NOT an LSA per se but a national airworthiness authority certificated aircraft, it can be modified by an Engineering Order supplied by a Part 21M engineer. Without going into chapter and verse (because that's longer than 'War and Peace'), the essential basis is (broadly speaking) that any modification does not invalidate the basis of Certification. LSA-registered aircraft are NOT 'certificated' - they are warrantied (as it were) by the manufacturer to comply with the (ASTM) LSA standard. The manufacturer is required to take the liability for compliance with the LSA standard, and this is an important distinction in terms of legal liability. Rod Stiff's comments are - I suspect - an entirely reasonable response to the liability Jabiru accepts for the supply of aircraft to be registered as LSA-compliant, with the advantages that bestows: higher MTOW etc..

 

There is - I think - also absolute truth in Rod Stiff's comments that stating to an insurer (or other authority) that your aircraft has a 'Jabiru' engine as defined in the TCDS if it has been modified in any way, is false. HOWEVER (again..) if you are running an engine that has received an Engineering Order for modification (which cannot be issued for an LSA-reg aircraft unless the manufacturer accepts it), then it is qualitatively equivalent to the original TCDS for the engine. Rod Stiff is( I think) almost certainly correct that notification to your insurer etc. of the changed status of your engine is required - but that does not mean that it is a lesser-quality engine. By definition, the issue of an EO for modification of a TCDS engine renders it in no way inferior to the engine for which the TCDS was issued - and your insurer should not impose any penalty for the substitution of components subject to the EO.

 

With respect to the CAMit modifications to Jabiru engines, it will be shortly be the case that an EO can be issued for such modifications, on an individual-engine basis. The work to provide the substantiation for the EO is well underway. It requires running a CAMit-modified engine through the full regime of conditions for certification against the JAR-22h requirement under which the original Jab. engine TCDS was issued. It is entirely not a trivial task. I have no information of intentions / activity to do the same for any other manufacturer's mods. - e.g. Rotec.

 

 

I think this might represent a breakthrough; the FAA has (apparently) accepted that there are grounds for acceptance of aircraft that do not conform to a non-FAA standard ( the ASTM LSA standard) into the LSA class. The whole MTOW thing has always been an arbitrary number imposed as an intellectually lazy way of defining a performance envelope (not dissimilar to speed limits being defined as a 'safe/unsafe' determinant with no acceptance of the driving environment actually existing in any specific case).

 

We could hope that this will filter down to individual national airworthiness authorities (read, for us, CASA) accepting that an aircraft that utilises a greater MTOW than defined in the ASTM standard for the inclusion of greater safety (particularly for structural improvements, rather than extending 'performance'). That could lead to very considerable improvements in things such as crash-worthiness, repair cost, insurance premium cost etc. for useful aircraft that still remain fundamentally LSA-class aircraft.

 

We have all seen evidence of the lack of crash-worthiness of LSA-class aircraft that have been built to extract the maximum performance within the restrictive LSA standards. A carbon-fibre composite cabin structure simply explodes on severe impact like a smashed bottle, whereas a lower-tech but heavier cabin structure can absorb the same sorts of loads with a resilience that provides a far better chance of minimal injury.

 

We have seen the weight of passenger vehicles increase with additional occupant-safety measures quite considerably over the last, what - 10 - 15 years? It's time that aircraft regulations accepted occupant safety measures - just for a start - as valid reasons to accept increased MTOWs. The operational environment in a country like Australia (or probably also South Africa) is considerably more demanding than for much of Europe: gust loads, outback airstrip conditions - even distance between airstrips etc. We need rugged aircraft, more fuel, strong landing gear, big wheels etc.

 

The ASTM standard requires that 'one size fits all'. It should be regarded as a minimum set of characteristics - not a box into which everything has to fit. It appears that he FAA has broken through the mind-set of blind obedience to that standard; I'd like to think that CASA could embrace the same idea. Perhaps with the replacement of McCormick as head of CASA, we might just see that happening.

 

 

It might help if someone ( David Isaac seems very qualified) could produce a matrix of Lithium battery characteristics ( cost, weight, charging risk, discharging risk, cranking power, charge system complexity etc). I believe LiFePo4 batteries are in general terms 'safe' in an aircraft environment - though I'll be encasing mine in a fire-resistant housing - if the charging system is reliable and they have a proper isolating switch.

 

 

I see I have received a 'last warning'.

 

Fair enough - I don't respond well to snarky criticism that is completely incorrect in fact. I'm out of here.

 

 

For the less educated amongst us, what is the thermal expansion rate of the cylinder heads, compared with the crank case?

Um, Merv, the cylinder heads aren't held on by the through bolts.... different system..

 

 

just for the record; it's not my technique ,that's the way jab does it , or did it .( last engine revisit was 2 1/2 years ago.

I wasn't aware that it's being done as you say ,or camits assembly procedures .

 

my engines that were done in front of me all had the cases inspected for flatness and were either accepted or rejected .

 

cheers mike

Mike - dry assembly is absolutely NOT the Jab recommended technique: see: http://www.jabiru.net.au/eula/eula.php?u=/Manuals/Engine/JEM0001-6_Overhaul_Manual.pdf I don't have knowledge of early times, but I understand that the Loctite 515 assembly material has been the recommended technique for a long time - others may well be more knowledgeable than me there.

 

Given the precision of everything required for effective use of Loctite 515, I'd personally hate to have to use the stuff, and quite possibly dry assembly has a lower potential of problems - but given the clamping design, I suspect some form of sealing between the cases is required to ensure you don't lose oil pressure from inadequate inter-case sealing. You'd certainly want no less than perfect case-face flatness to be confident of dry assembly.

 

The Hylomar alternative ( if used correctly) is far more tolerant of anything less than perfect assembly technique. I believe that CAMit will fairly soon produce an assembly manual for their modded engine that will detail what is required; personally, I have that on my list of required reading..

 

 

Indeed, I have rebuilt one. Under the watchful eyes, the instruction and with the help of the guys who build them all, not only showing/checking what was done but explaining all the things that matter about what was being done. With the guy who manufacturers them telling me what to do and teaching me how to do the machining and inspecting my work (and even hand-making some tools just to do my old engine to the new specifications). With the guy who measures each and every engine for production checking my work every step of the way, in a laser-measuring-equipped, temp. controlled measurement room. In the build room that every new Jabiru engine comes out of, using the tools, the benches, all the gear that every new Jabiru engine is assembled with. Following the assembly procedure from dedicated bench to dedicated bench, starting with the crankshaft and down to the electrics.

 

Got a 'tick' from those guys. Would I suggest I can do it for a living? - NO. I learned so much from the experience of being there, I know how precise and experienced one needs to be, and I certainly know that I don't have that level of experience, nor do I have the very specialised tools for doing certain procedures correctly..

 

Not from books, little Noddy, but from DOING IT. Spent two weeks learning and doing it, making mistakes, learning from them, fixing them.

 

So suck it up, princess, and get off your own high horse.

 

 

Not Jab bashing ...way beyond that now, besides I don't need to now as everybody else does it for me.As I 've said before I believe the very basis of the Jab engine problem is the CNC machines alum case. Highest rate of thermal expansion with steel cylinders hanging off it, and a hot steel rotating crankshaft within, trying to get out. No wonder through-studs break and valve trains can't keep up ..!

 

There is a good reason most aero engine cases are either cast or forged alloy....IE: Lycomong, Contenentals and Rotax

 

Alf...with you all the way there mate...and feeling your pain..

 

End of my rant ................Maj....

You are so completely wrong about the crankcase material and manufacturing technique as being a problem, that it is not just risable but woeful. Your fundamental lack of understanding of engine manufacturing and metallurgy is so far wrong as to place you in the realm of the wilfully ignorant. Possibly, you would be better to stick to commenting on parachute packing - I have no doubt you are extremely well qualified there.

 

BTW, it's Lycoming and Continental - but at least you got Rotax correct. In the circumstances, one out of three is about par for your course.

 

 

So let's say you do a perfect fit before it has cured: Loctite 515 has the same expansion factor as the through bolts has it?

Turbs, you miss the essential point of pre-tension of the studs: if correctly designed and tensioned, you don't get expansion of the gasket material because the studs themselves do not expand sufficiently to allow movement, that is taken up by the pre-tension. However, if the pre-tension falls off for any reason - and there are several reasons why this can occur, incorrect preparation /assembly being two of them - then a chain of circumstances starts to happen that can lead to: hammering of the studs (especially in the case of even mild detonation), bending of the barrel bottom flange, bending of the stud end and rapid fatigue cracking of the stud. There are some even more non-intuitive problems that can happen: as I said earlier, the whole case securing thing is a 'system' and the 'weak link' principle applies.

 

That when everything in that system is correct, Jab engines will hold together is evidenced by the fact that a fair proportion of them DO hold together. However I'd be daft to suggest that there is not way too much evidence that if anything in the system isn't right, then they damn well don't. Not even the most one-eyed Jab. 'fan' ( and I rather assume that I am seen as such) could deny that and seriously believe what he or she is saying. I certainly wouldn't and don't. The extremely finicky nature of the basic Jab 'system' that requires everything to be absolutely dead-on, balls accurate (it's an industry term ) is the reason why CAMit have completely modified that system. The crankcases themselves are fine for purpose - it's what holds them together that is their Archilles heel.

 

I believe that some shops are using a Hylomar aerosol as a non-setting case jointing compound and achieving very good results. It has a much longer working time than 515

Funny you should say that... and it makes sure the oil passes between the crankcase halves properly without loss of oil pressure (I'd be worried to use AVOCET's dry assembly technique, for that reason). It for sure takes some of the pressure off (little assembler's joke there) when a circlip goes 'Jesus Christ' on one when assembling the engine and it flies off into the corner of the workshop and hides under the edge of the linoleum. (Ask me how I know? - go on, live dangerously.) BUT: it does need to be used in conjunction with the proper techniques and tools. Once again, kiddies: DO NOT TRY THIS AT HOME, and then come crying back that Hylomar is a crap case sealant. There is no such thing as a mechanic in a can, and if one knows about all of the effects of using WD40, mostly one bans it from one's workshop.

 

 

Oscar, out of interest why is the gasket clean off so hard? Is it some sort of epoxy? I ask as a motorcycle rebuilder who has cleaned plenty of gasket material off but obviously not in such a fastidious way. Do you examine under a strong lens to see? Are you scraping or doing it with a rag and solvent? I admit I'm just curious.

pm: it's a Loctite product - Loctite 515 - and it sets as hard as rock after a while, I'm not aware of any useful solvent. Yes, scraping (very, very carefully, plus polishing with 1200-grit paper on a piece of machined flat steel bar) - and strong, low-angle light shining on a fully cleaned and dried surface continually shows up small patches of micron-thin residue that you can only see by the slight discolouration of the alloy.

 

It also sets damn quickly on assembly - the Jab. manual states:

 

Note that the entire crankcase assembly process including the fitting of pistons and cylinders MUST be completed in one continuous operation otherwise the Loctite 515 Sealant around the crankcase join can dry before uniform pressure is applied to the crankcase join by the cylinder nuts, so make sure that you have all parts ready for completion up to this stage (i.e. pistons and cylinders) before starting to fit the crankcase halves to the crankshaft.

 

7.8.1 Crankcase Joining

 

 During the joining process various sealants will be used which will cure quickly – therefore it is essential that the overhauler be thoroughly organised before starting this task and that they work efficiently and quickly once they have begun. If too much time is taken the engine must be disassembled and re-cleaned, ready for another attempt at joining.

 

Watching the CAMit engine shop guys assembling Jab. engines is an experience - two-person job, both of whom have done it hundreds of times - move so damn fast you'd think that the engine was coming together in a step-motion photography replay. Less than 5 minutes from everything on the bench to the cases (and cylinder barrels, obviously) bolted together. Every part is laid out ready before they start, every tool is placed ready for instant use.

 

It's absolutely a two-person job, and they need to be experienced people - Jab. really ought to say 'Don't try this at home - we really, really mean it! in the manual. If the 515 dries anywhere before the assembly is torqued down, you can't get full, even pressure on the sealing compound, and it will later crack and some fall out, which backs-off the pre-tension on the studs, which then allow the cases to fret and shock loadings to occur to the studs and bang-oh, another stud failure.

 

 

Merv - using the same through-bolts for both crankcase and cylinder retention is not that unusual (UL Power engines, for instance, do the same) - but it does impose disciplines that simply must be observed. Without going into obsessive detail, it's a 'system', and everything in that system has to be spot-on. Suffice it to say that just about every aspect of that particular system has been researched, analysed and modified by CAMit.

 

 

To Alf - I was well aware of your terrible family situation and join with everybody else in absolutely hoping for the best outcome, and didn't take the comment as anything but a bit of fun at Jabs. expense, which I agree is deserved.

 

Interesting comment oscar. Doesnt reflect conversations Ive had with him, and probably about the actual engine which is the star of this thread:).

Merv, if that engine is the one we're both thinking /talking about, David has pictures of the damage done to the crankcases by someone pulling them up to tension (the only purpose of which would be to measure the main and cam bearing tunnels) without washers under the nuts on the studs used for the job. That procedure is normally (and correctly) done using about 40mm diameter x 6mm or 8mm packers (thick washers) to distribute the load properly into the crankcase and protect the crankcase material. A quick look at the Jab. Engine Overhaul Manual, p.92, shows what I am talking about.

 

In the case of the engine in question, NO washers were used and the nuts were wound down into the crankcase material, tearing the alloy badly in the process.

 

If that doesn't constitute butchery, I don't know what would qualify.

 

That crankcase should never have been allowed back into service. FWIW, when we disassembled our own engine (also an EFATO through through-bolt failure), we found more than sufficient evidence of bad practice in re-building (dents on the crankcase mating surfaces that could only have come from it being parted using small cold-chisels or a screw-driver hammered in as a parting tool and not even dressed-out, meaning the crankcases could not have been properly pulled down on assembly, and certainly it did not - and could not have when previously assembled - measure up. It was discarded.

 

Given that Jabiru use a non-gasket crankcase jointing technique , anything less than a perfect mate between crankcase halves is critical to maintaining proper tension on the through-bolts - without which they will, sooner or later, fail. Even without any 'butchery', just cleaning the old jointing material off the crankcase faces is such a time-consuming process and so difficult to get right ( and I can personally attest to that - we're talking many, many hours of excruciatingly patient work, inspection, saying 'oh, bugger' under one's breath and returning to the task) that CAMit simply do not re-use the existing crankcases - whether they have been subject to failure or not - in their re-builds. It is more economic to make new cases than to try to prepare used ones for re-use in the CAMit situation. I would not have believed that until I did the work myself, but I damn well understood why by the time I had finished. If you are supplying the labour and can take the time to do a prep. job on the cases properly, it's possible to get them right if they have not been abused, but it's an almost Sisyphean task. Anything less than 'proper' prep work is simply building in the next failure.

 

 

Had some interesting discussion with the LAMEs. Seems the Jabiru engine is not exactly their favourite.

David Dent and his lads have good reason to have reservations about Jab. engines; I've seen (at least some of) the evidence. However: most of that is - as he will tell you - also evidence of some absolute butchery in rebuilding, not fundamental design. You can blow a hi-spec. Ford V8 engine apart by filling the thing with the wrong fuel - imagine what sort of buggerisation you can do to a Jab. engine by using brute force and wilful ignorance.

 

 

Expect the real-life experience of the CAMit modded-engines to start to come into focus very soon and an important step forward in the ability to put CAMit engines into 'C'-reg / 55-reg. Jabs. in a couple of months (CASA willing to process the paperwork..)

 

 

Many years ago, a bloke I know used to routinely land using car headlights as his lighting at YMIG, (when his was the only aircraft using the strip, for years before and after) in the winter months.

 

HOWEVER: firstly, flying from YMIG was his daily commute to/from work, he'd done it a vast number of times. He knew where every damn tree was on the way in, from rote memory. Secondly, an Auster comes in steep and slow - especially if flown by someone who spends his weekends as a glider tug pilot and does maybe 20-30 landings in a day - several hundred (plus on average, 8-10 per week for the daily commute) in a year.

 

He's well over 70 years old now, and has never had a crash. Forced landings? - yes. Broken aircraft/injuries? - nil. Old and Bold? - absolutely not - and he's been a CASA certified test pilot. for maybe 30 years now

 

Would he try that in a Cirrus? - well, I think no - in fact, you'd probably find it hard to get him INTO a Cirrus in any circumstances other than with all spark plugs removed - they're about second only to a Lancair 320/340/360 as stupidly dangerous aircraft (assuming one accepts that the published statistics of fatal crashes are not a conspiracy theory).

 

So, a blanket statement of: 'landing using car headlights is stupid' is simplistic - but a good guideline if one does not have both the aircraft and the expertise to make it safe. Sadly, this was a case where probably BOTH of those criteria were not present.

 

 

121 kts cruise? Typical website fluff..

Merv - once again, I agree with you (that's twice this year alone, but don't consider it the start of a bromance just yet..)

 

Still, at least the Pipistrel figures are available: I note that the Flight Design brochure for the CTLS has 7 pages of illustrations of the available colour schemes, but gives just two V-speed figures: VH and VNE.

 

What does that say about the target market for the aircraft that I think claims to be the 'world's most popular'?

 

In fact - when one tracks down the CTLS POH - the Va at max. weight is a very reasonable 99 kts (reducing to 90 at lightest weight) for a VH of 120 kts, so probably a cruise of around, what - 110 kts? Vb is good - above VH by a healthy margin.

 

So, perhaps the FD people can be excused for not bothering to quote the relevant figures in their advertising, since the thing is less likely to fly one into trouble than some others. Quite possibly, this is fair enough - but if the things are selling at a very high rate, does that mean that there are a lot of people out there as buyers who do not care - or possibly, do not understand - that these flight limitations are important in real-life?

 

And if that IS the case: is pilot education lacking in getting the message across that one has to accept and apply the structural limits when flying? HITC in post #48 recounted an instance of an educated, sensible and generally cautious pilot basically ignoring the limitations predicated by the conditions because 'Jabirus are built tough'. I think (and don't jump on me here as a 'Jab. lover', most people agree about the ruggedness of the airframe at least) that that is pretty much 'conventional wisdom' - but it's not something one should use as an excuse to ignore the limits Jab. place on their aircraft and endanger oneself and one's pax. Hilux utes are 'built tough' - but they can be broken and so can Jabs. 'Bugger' is not useful if some of the airframe has departed..

 

 

I suggest that, in some cases, 'push the edge' is a somewhat kindly phrase. Take the Pipistrel Virus 912 (figures from the website): 75% power cruise: 121 kts. Vb: 76 kts. ( No Va given and no indication of whether those speeds are KIAS or CAS, draw your own conclusions). 45 kts difference - or looked at another way, a 37% reduction in speed required between smooth and rough conditions. I understand that they are a very nice aircraft to fly, but jeez, you'd feel a bit as if you were getting out and walking in turbulence.

 

 

They should factor it in when they buy the plane. Nev

Yes - but do they? I mean that seriously. Here, on the one hand, you have a pretty plain-Jane little Jab, it's fairly obviously just a somewhat tarted-up version of the original LSA55 with what I suspect most pilots would consider to be pretty much the 'baseline' of performance for RAA aircraft, somewhat on the 'cheap and cheerful' side. You look at the performance figures quoted on the Jab. web-site, and there are plenty of other aircraft claiming better figures, with nicer looks and finish etc. (and let's be honest here, everybody keeps a bit of 'reserve' about Jab. engine reliability in mind, with good reason).

 

If you have paid (or are prepared to pay) quite a considerable chunk of extra $$ for something that is quite a bit more 'attractive' than a J120, are you really going to consider that, when the going gets a bit 'rough', you will routinely pull back your speed (and that little Jab will, albeit not remarkably quickly, waddle off into the distance if on the same flight path?)

 

It seems to me that this discussion of understanding and applying knowledge of Va is very important.

 

 

The whole thing of improving knowledge of what Va means and how it exceeding it can be disastrous, is of immense importance. However, can I intrude slightly and ask - does the average pilot understand and take into account in her/his flying, of Va as a serious factor in conducting their flight behaviour?

 

Here is what I am trying to suggest.

 

In the case of a Tecnam P96 - for which the possibility (absolutely unproven as yet) of in-flight structural failure as a consequence of exceeding VA is being considered - from what I have been able to glean the normal cruise speed is around 110 -112 KIAS. From the P96 POH, that is actually about 102 kts CAS. VA for the P96 is 81 KIAS, 79 CAS.

 

So what? So what is: if the pilot suddenly has the need to employ full control deflection, he/she may well need to wash off nearly 30 KIAS speed before doing that, if simply cruising along at the available cruise speed. I suggest that the conditions requiring full control deflection and the 'envelope' of washing off nearly 20% of the cruise speed, (or, from a reaction pov, 30 kts off the clock speed) are likely to be inimical.

 

By comparison, the Jabiru J120 example given above, has a Vno of 113 KIAS and a Va of 103 KIAS. From the J120 POH, allowing for airspeed position error, 113 KIAS is 108 CAS and 103 KIAS is about 98 CAS. In broad general terms, I think most people cruise their J120s at around 2850 rpm, giving an indicated KIAS of 110, or a CAS of around 104.

 

What's the point I am trying to make here? There are a couple, actually.

 

Firstly, in the case of the Jab, the potential for unintentionally exceeding Va when a situation requiring full control deflection suddenly arises is about 6 - 7 % in a 'normal' flight situation (and Vb is extremely close to Vno). By comparison, in the p96 would be 'normally' cruising at something around 20% above its Va. I have no idea of the Vb for the P96 but conventional wisdom suggests Vb is usually fairly close to Va.

 

In terms of pilot behaviour - or in this case, the approach to selecting cruise speed in conditions that require prudence, the J120 pilot ought to knock off maybe 5 kts. It appears to me that the P96 pilot should knock off around 20 kts - which is a pretty decent chunk of speed to throw away when trying to get across the ground in a country as large as ours. We get, particularly in summer, some pretty serious CAT, 'blue-air' thermals etc.

 

So my question is this: do pilots routinely factor in their aircraft's Va as a factor in selecting a safe cruise speed for the conditions - especially the 'likely' or 'possible' conditions over and above the apparent conditions?

 

 

FFS, look at the photo referenced in post #16.

 

Both flaps are missing. The entire section of the starboard wing outside the flap end is missing. The thing obviously hit in a spiraling, almost vertical descent, that smashed the starboard wing behind the elevator and horizontal stabiliser.

 

 

Years ago, Phil Ainsworth, when with Jabiru, wrote an article for the University of Sydney Aero-mech. school explaining why Jabiru decided to build their own engine when KFM pulled the plug on the 1600, and why they didn't just go for a Rotax then. http://www.aeromech.usyd.edu.au/AERO1400/Jabiru_Construction/jabiru.html It's very well worth reading.

 

Jabiru confirmed to me some time ago, when I sought information as to whether I could do anything to increase the MTOW of my STI (which is a 55-reg LSA) that the placarded MTOW was a result of the stall speed, not a limit imposed by the structural considerations. As I understand it, the UL was a development necessary to meet the lower European stall speed requirement.

 

However, the various regs. - which in regard to at least some of the limitations appear to have been developed by people in authority plucking a handy figure out of the air (pun intended) provide a 'box' within which the designer has to operate. Phil's article shows up rather well the compromises the designer has to grapple with.

 

 

The Gypsy had MOUNTS? Get away, it had BOLTS. Mounts were an effete, latte-sippimg and chardonnay-swilling metro-sexual affectation of years later. Real men had their teeth fillings lock-wired and were proud of it.