Bob Llewellyn

Flashy thing...

Yes, but barely - the energy transfer into the induction air is quite small. The reduction in engine power due to icing is much greater! As aeroplane engines are often operated at less than 15 degrees C and density altitudes above sea level, they ought to be designed to meet their rated power at, say, 5000' ISA with de-icing on. But nobody ever starts there with a design, so bad luck to all pilots...

i can pay you in IOUs, if you can deliver the aeroplane...

Drugs? what drugs? i say what I think of saying when the special chocolates the little green men give me, make me happy!!!

Madness is taking its toll - how does one NOT post a reply? Other than to not start it...

Flow straightening generally requires long straight runners; it's well studied in wind tunnel design. Achieving a flow-straightened system that'll curl up into a cowl is, to say the least, challenging. Motorbikes settled on one carby per cylinder, long ago; many big bikes now feature four CV Mikunis - but a single Bing is cheaper and lighter. A solenoid valve, a la EFI, can only deliver acceptable droplet sizes over a flow range of <4:1; in order to run from idle to full power, EFI systems use controlled variable feed pressure (some cars have dual-speed or multi-speed pumps, others use electrically controlled regulators). If the regulator fails high, or pump ditto, there is a chance of an over-rich situation. The probability would depend upon the system in question. (if the EFI does nothing below ~50% power, that's a failure mode that can be eliminated - no doubt Oscar has already entered it into his FMEA ) If the fuel/air ratio is optimised in all cylinders at all times, the ignition can relax.

It's the other way up - traditionally the engine heat is dumped into the engine bay, and leaks out the back somewhere (generally the bottom, in opposition to good sense); so when aeroplanes started to fall out of the sky due to carby icing, a bit of the existing heat was sucked off the exhaust system to make the carby comfy. Cooling is badly done because it's tradition, and ya can't go wrong with tradition!

In reverse order: I repeat: I suspect that FMEA is the way to prove, not condemn, what may be termed the usage of electronically regulated high power jets in a Jabiru carby system. Now Oscar, it's a matter of record that you can find your way around Excel, so how about a 24 hour ritual fast; smear yourself with Woad, and wrap yourself in a bullock hide; have a smoke, drink a strong coffee, and start listing failure modes. Once you've been through a few iterations, you may PM me the result, and I'll inject some figures if that's what it takes to stop yer b----y whinging! A water pump is not directly comparable to a complete EFI system but I agree, Rotax seem prepared to settle for sub-optimal (but lucrative) solutions... Chucking buckets of fuel on the engine is generally a GOOD THING, particularly during takeoff / climb - during this period the mixture generally does not need fiddling with below 5000 ft (or more), because as long as the engine is richer than stoichometric, it's good. The behavior, which is consisten for pretty much all hydrocarbon fuels, is that the engine develops maximum power and reduced tendency to detonate at 10~15% rich. The reason is that the hydrogen burns off the hydrocarbons before much any carbon has burned; and hydrogen burns about 500C cooler than carbon. So, running rich means a cooler combustion chamber; and the carbon association-disassociation cycle linked to detonation occurs later in cycle; both of which vastly reduce the chance of destructive detonation. The lighties I've seen have the mixture control next to the throttle, so the vast paw of the pilot can shove both fowards together - "full rich, full power". Once the climb rate is reduced by pulling power, the cool combustion and unburnt carbon requires the mixture to be leaned off a bit, lest the plugs become foul and the noise erratic. Leaning the mixture a tad further reduces fuel burn, and in the cooler higher airs (and at reduced power) the CHTs stay in the green; but the EGTs tend to creep up, and the combination of high EGT and unburned oxygen can singe the valves, shortening valve seat life and possibly burning valves between overhauls. Lindberging the mixture a lot leaner still, and the EGTs drop again; but if the CHTs are kept warm by closing the cowl flaps, flying the Atlantic becomes possible. However, the extreme oxidising environment in the cylinders now eradicates sparkplugs with ruthless efficiency - hence the onboard oscilliscope displays for the flight engineer on Super Connies and DC-6's. Now, Cessnoids have no cowl flaps, and not enough adjustment to really lean them out anyway (if running on the idle jet, they can be cut by leaning, but not at flight powers... mostly...); this is to "simplify" things for poor dumb recreational (GA) pilots. The second generation of GA - what we call Recreational Aviation these days - has shifted away from allowing the pilot to fool with the mixture in flight; but is this more good than bad? Oscar, seek ye some woad...

A few fundamental points arise. (1) Aero engines have never had the luxury of excessive robustness; the Brotherhood-Ricardo auxiliary engines (for industrial, marine, and generation applications) were considered startlingly light at ~22lb (10kg) per hp. Whilst some may find merit in an 800kg Jabiru engine, it'll never fly. This means that aero engines will always be susceptible to operator technique; which has, once again, been made manifest by the copious discussions on jabiru engine reliability (and esp. cooling) on this website. Furthermore, because of the extremely rapid changes in operating environment - aero engines have substantial changes in ambient pressure and temperature, and often humidity, every takeoff and landing at least; and the role changes - during takeoff, aero engines are called upon for the absolute maximum power to weight, despite said rapid environment changes; during cruise, the role is absolute maximum fuel efficiency at 110% reliability, in a cool and low-density environment; it's not so simple to keep the engine in whatever may be the optimum configuration / tune at the time (have a look at petrol viscosity vs temp curves - this is one area EFI* does not handle well, but MFI does). *EGO sensors, or a similar loop-closing feedback system, are used to compensate in cars. This adds a critical single-failure mode... cars also use fuel tank pressure sensors, or complex pressure regulation - extra systems - to help reduce variability. The best results have always been had by intelligent engine management - see Charles Lindberg. Humans have long held the belief that the educated human mind is capable of more sophisticated reasoning than, say, an Engine Control Module. Without digressing into the levels of specialised training required or available, I would posit that practicable aero engines still require enlightened usage - and who better to provide that, than the highest expression of human evolution to date, the pilot? (2) Neither Oscar's dogma, nor Dafydd's considered conservatism, dismiss FMEA. It would be most enlightening if substantive and verifiable data could be analysed on the actual effects of less-than-optimal operator techniques; but such data is hard to come by, and many engine suppliers (a certain Austro-Canadian manufacturer comes to mind) will resort to implausibly ludicrous assertions in defence of their products. I suspect some indicators could be had from US Transport Safety data, but even professional accident investigation organisations are pretty dodgy when it comes to correctly approportioning causality. Setting this aside, Oscar is actually using a non-quantified form of FMEA to justify his mixed fuel supply proposal; I don't understand why he gets a rash when I suggest he quantify it, because such an approach is - when well supported - acceptable to National Airworthiness Authorities. (3) Simplification does not equal reliability. By far the most reliable engine of WW1 - NOT such a long time ago, in piston engine development - was the Rolls-Royce Eagle, which had the highest parts count of any serving Allied engine, and probably any serving engine at all. It also had twice or more the TBO of any of its peers. The design philosophy was to design each subsystem optimally for its sole task - and sacrifice no reliability or performance in the name of profit or cheapness - or appearing "smart"! The current simile is found in the enormous car recalls of Toyota, GM, and VW - the computer/software packages are now so insidious and incestuous that people are dying due to combined E-failure modes that disable the airbags or power steering or brakes, whilst simultaneously either cutting or freezing the power levels of the engine. Car stats do not add confidence in electronically removing control from operators. By far the most simple recreational aero engines of recent times - the single-cylinder Fujis and Rotax 277s - have, for some reason, not maintained a high market presence. Despite their simplicity, they have not earned awards for high reliability either. This does not mean that I am advocating complexity; rather, any system or subsystem must be just as complex as necessary to achieve the target reliability in any real operational situation, and no more. In spark ignition engines, MFI gives a better fuel/air ratio over the operating range than any non-temperature-compensated carby can, and need not be made from cast zinc and ---ing brass!; and both these mechanical systems achieve a very comparable result to EFI (either with multi carbys or really well developed manifolding). Given a choice between MFI with an aneroid for MAP sensing, six carbys, or an ex-car EFI system, I think parts count, parts reliability predictability, and performance (in the aeronautical role) go to the MFI. I do not see how an EFI plus carby wins on these terms, even if - as Oscar says (and may be able to substantiate?) the overall fleet safety would be enhanced by using MPCEFIRS (MultiPointCarbyElectronicFuelInjectionRedundantSystem) technology. (4) Fuel is the joker in the pack. There is a huge body of research on the enormous range of variability of behaviour of various hydrocarbon blends during combustion in a spark-ignition engine, which led to very tight and rigid specifications for all forms of Avgas. Car engines compensate by having significant margins of excess cooling, strength, and extreme combustion gas flow development (thus can't sustain the power to weight). Petrol companies ("how do you justify this level of renumeration?" - "I don't"...)have extremely negative reactions when anyone starts to test the qualities of their extortion - pardon me, products; so I don't see this situation changing in the forseeable future. If anyone is aware of an EFI unit that does on-the-fly analyses of dissociation - reassociation gaseous reactions during partial combustion, I'd LOVE to hear about it. Or even an EFI with a form of active knock detection that doesn't require "incipient" knock to function? How about an active fuel viscosity detector? Rotax use small (and highly developed) combustion chambers, liquid cooled heads, high crankshaft RPM, and judicious mixture enrichment to provide a margin of safety from PULP variability; and they're still struggling to better 2lb / hp, which Contacoming had 50 years ago on AVGAS (with similar TBOs, too). Jabiru engines are simpler, can be made at a competitive price on a far smaller fiscal base, are power to weight competitive, but do not tolerate variable fuel without enlightened operator handling. In the present environment, the most tolerant fuel supply system regulates the mixture, guided by multiple EGT / CHT and knowledge of what's in the tanks, using a trained human brain. It does not matter if the fuel is delivered by EFI, MFI, carby, or little green men with buckets. Engines are neither perfect, nor as good as they could be. Fuel is far from perfect, or as good as it could be, and big money is keeping it that way, so you better not have a problem with that. But we fly with our brains - don't we? So surely we can out-think our noisemakers?

...wonder what happens if you overhaul 'em on the same schedule?

I've already been told this is simplistic, but the simpletons in life are often the best...

I"VE ALREADY EXPLAINED IT: look, it was sucked up by an alien spacecraft and taken away, and the whole search thing is just a smokescreen because China has been negotiating with the aliens, and Vladimir Pootin is afraid the aliens would accept the CCP's world view, whilst Assad is trying to make Syria an Alien Economic Zone; Iran has got into bed with the USofA, who are negotiating with DIFFERENT aliens.... it's SO obvious... everyone knows the Anzani engines on the Handley-Page 777 overheat if flown over the ocean for more than 2 hours. The reason for the lack of radar evidence is because the French were testing their new radar cloaking device fitted to the Mirage-4s, which are intended to let them nuke Madagascar with plausible deniability, to get rid of the bubonic plague. In the meantime, the Australian Greens are losing ground in Tasphobia because the aliens in contact with the USA have given a demo of their mass mind control ray to the republicans... Bob Llewellyn, Wednesday at 3:08 PM Report #48 Reply

No, we couldn't agree on a uniform...

silly boy, didn't look up ac23.1309, did you? a crash is a Didn't look up the AC, didja? I know they're big words, but a "crash" is a "Hazardous" or "Catastrophic" failure. Your prolixty is well known, DO try to keep up...

Actually it does, if you exercise that imagination when writing up potential failure modes - the redundant system you are proposing should show, on FMEA, to be superior. The single carby is accepted because they are known to deliver the "acceptable probability of safety when maintained in accordance with the (certified!) engine manufacturer's data. Note that the LSA-compliant engines are considered to meet this requirement, although I am not sure if the manufacturer's maintenance instructions really cover the carby. The twin engined argument is that, even though the twin has twice the probability of failing an engine per hour / flight, the probability of failing both in the same flight, is minute. AC23.1309 has a higher acceptable probability of failure for single reciprocating engined aeroplanes (than any other class), due to the nature of typical operations.

You keep talking about EFI failure that stops the EFI delivering fuel. What if the EFI fails such to deliver too much fuel? There are a few Continentals around, which suffer rich cut - i.e. they stop whilst at TO power, full rich - if the boost pump and engine pumps are fully functional (in event of an engine pump failure on takeoff, the pilot automatically turns the boost pump on... see, certification = safety...). Now I agree that the maximum EFI delivery can be limited - but if the failure mode of over-delivery is eliminated by introducing a failure mode of some auxiliary electromechanical device, the FMEA gets no smaller. One simply works out every possible failure mode - however unlikely; and its effect(s) on the operation of the aeroplane. Summing the probabilities of each failure mode to cause, say, an AC23.1309 "serious" effect, shows the overall probability of occurence of this class of event; which is then compared with the acceptable probability of failure. Since probability of failure is related to time, one generally reduces the inspection or maintenance intervals until the target acceptable pof is reached. The job is not to say, "my injected car is better than my carby car was, therefore..." anything; the job is to say, "based upon this data, according to this table, the Soggysquish injection setup when tied up with string, gives half the PO (serious) F of the certified carby setup".

Here... here... and here... now a thumbprint... and the deeds to your house... thank you! CASA "We are here to help you". And don't you forget it. The number of times I've had this sort of dialogue: me: "The Regulations say (thus and so), and here is how I've shown compliance..." CASA bod: "That's good, but we also want to know (blah blah blah)..." me: "How do you want me to show that?" CASA bod: "That's up to you - put a package together, make a proposal, and then we'll consider it..." They could not tell me why they wanted more than the regs required. They could not provide me with their interpretation of the regs. They could not tell me what they required; and they would not accept any justification that required judgement on their part without unjustifiable multiple submissions. This is because they are the experts. This has remained constant under three directors at least, and in multiple departments within CASA. Our tax dollars at work...

Ron, I fly a T-83 mostly, which will not penetrate plate glass; but that transonic monstrosity of yours represents a danger to skyscrapers everywhere... don't you think that, perhaps, you owe it to the nation, to get an ASIC?

An engineer in CASA ESB once told me "well, you can't trust pilots, you know"... how do you guys live with yourselves? (as a rec pilot only, I choose not to trust myself with small things like beer.... I mean, icecream...)

Mmmm, ta, I'd appreciate that... Cheers, Bob.

But... but... safety is achieved by Compliance With Regulations.... airworthiness is only relevant if there's a Regulation about it! For that matter, your engine would never suffer fuel exhaustion, except some idiot wrote a regulation about it...

Rich cut.

The let-out is that very light aeroplanes are slow enough that you can eyeball the TOR / TOD; and it's true with the early ultralights - the minature Cessnoids, however, kind of invalidate the concept. The Aeronca Chief POH (it didn't have one) is a relic of the same philosophy. As the laws of physics are pretty reliable, there is a good process for modelling P charts, given only a few measured performance data points - the more you have, the less conservative the chart gets.

Nasty. Those diggers oughta be banned... just menaces to life & limb...

Hey Flygirl, could you do Ceconite bags? I'm thinking about a future project... hopefully not too future....