Camit engines - anyone got one?

[Oscar]

Look, if we were MEANT to use EFI, Kugelfischer wouldn't have made mechanical fuel injection for petrol engines!

Owned one (Pug 504I), and it did work better than the standard Solex on a 504 - but then, a tuned oil-can and a fast thumb would have worked better than the standard Solex. However, a mechanical FI pump is a right complex bastard, heavy, expensive to manufacture and repair, requires extremely precise timing input via gear or chain drive. Any 'tuning' capability ( e.g. for altitude) requires extra mechanical devices to alter the mixture delivery. There is NO capability of redundancy in the installation.

 

Electronics are cheap for the capability - ridiculously cheap. You could carry a spare (programmed) motherboard and a couple of injectors and have a back-up dedicated LiFePo4 power supply installed - all for less than 2kgs. With reasonably sophisticated algorithms, an individual sensor failure can be accommodated. Hell, with the capabilities of a moderately sophisticated EFI, you could ingest a seagull in one cooling intake and probably limp to a safe landing without damaging the engine!

 

With a decently-designed electrical supply system (not something cobbled-up by a bush electrician), the only real serious failure mode that won't be normally detected on initial start-up would be lightning strike. RAA aircraft are not supposed to fly in areas likely to have lightning strike. I postulate that the incidence of lightning strike is statistically FAR less than the incidence of below-spec. fuel delivery - for which the EFI system can compensate.

 

The whole use of EFI is a matter of risk management assessment - and there has been way too little analysis of the chain of risk in a 'conventional' - i.e. carburettored - fuel delivery system vs. EFI. The potential additional benefits over and above the mechanical improvements CAMit have made to the basic Jabiru engine in terms of reducing the vulnerability of the engine to varying fuel quality and cooling installations is something that - in my opinion - every 19-reg (or VH-exp. certificate) Jab-engined aircraft owner might seriously want to consider.

 

 

[deadstick]

Yes none of the tweaks really worked very well, even higher cost like new plenums etc did little in sorting it out. Anything BUT repeatable!I did ask Ian a while ago but dont think he had achieved much either.

I do know lots of hours has gone into sorting this problem out with little result. By design, having plenum end fed by basic carb isnt a good position to start with in getting even flows.

 

Isnt a new issue auto makers struggled for years getting carb plenums and runners working right, if their R&D budget couldn't sort it out what hope does Jabiru or Camit have?

 

Auto makers love multipoint EFI as many of these issues including average design, poor grade fuel, cold starts, altitude and hot weather problems just disappear.

 

I still believe much of Jabiru failures can be linked to detonation and overtemp running. EFI solves much of it.

Jetjr, I have developed a theory over the years dealing with split EGT's and unrepeatable results, it really only twigged when I heard from an operator of the solid lifter engine that his EGT's some split are always the same. It occurred to me that not all Hyd lifters are the same! one lifter to another may have slightly different characteristic's, some pump up fast others slower, tolerances are just that a limit for uneven duplication, so I theorised that each valve is seeing a different amount of lift or slight delay, I noticed on inspection that lifter preload is different across the lifters. just a theory!

 

 

[Bob Llewellyn]

Owned one (Pug 504I), and it did work better than the standard Solex on a 504 - but then, a tuned oil-can and a fast thumb would have worked better than the standard Solex. However, a mechanical FI pump is a right complex bastard, heavy, expensive to manufacture and repair, requires extremely precise timing input via gear or chain drive. Any 'tuning' capability ( e.g. for altitude) requires extra mechanical devices to alter the mixture delivery. There is NO capability of redundancy in the installation.Electronics are cheap for the capability - ridiculously cheap. You could carry a spare (programmed) motherboard and a couple of injectors and have a back-up dedicated LiFePo4 power supply installed - all for less than 2kgs. With reasonably sophisticated algorithms, an individual sensor failure can be accommodated. Hell, with the capabilities of a moderately sophisticated EFI, you could ingest a seagull in one cooling intake and probably limp to a safe landing without damaging the engine!

 

With a decently-designed electrical supply system (not something cobbled-up by a bush electrician), the only real serious failure mode that won't be normally detected on initial start-up would be lightning strike. RAA aircraft are not supposed to fly in areas likely to have lightning strike. I postulate that the incidence of lightning strike is statistically FAR less than the incidence of below-spec. fuel delivery - for which the EFI system can compensate.

 

The whole use of EFI is a matter of risk management assessment - and there has been way too little analysis of the chain of risk in a 'conventional' - i.e. carburettored - fuel delivery system vs. EFI. The potential additional benefits over and above the mechanical improvements CAMit have made to the basic Jabiru engine in terms of reducing the vulnerability of the engine to varying fuel quality and cooling installations is something that - in my opinion - every 19-reg (or VH-exp. certificate) Jab-engined aircraft owner might seriously want to consider.

Electronic reliability is assessed under MIL-HDBK-217; to do which, you have to have the circuit diagrams AND electrical loadings of all components. Without these things, the aviation FMEA cannot be done. Without a credible FMEA, no basis for Approval exists.

Carburrettors are mechanical, and FMEAs are simple; also, stacks of failure probability data exists.

 

Mechanical fuel injection is as simple to analyse, and generally will have a lower probability of failure, than a carby. If Ian Bent couldn't produce a simple, light, cheap mechanical injection pump - remember, it's very low pressure compared to a diesel pump (which is what Kugelfischer adapted, hence size & weight) - then I'll eat a CAMIT 2200 (with salt)...

 

 

[Oscar]

I would have no doubt that CAMit could make a simple mechanical FI pump - but that would be providing a solution to a problem that isn't looking for one.

 

We don't need a 'better carburettor', we need a fuel delivery system that is continuously and very rapidly adaptable to specific changes in the delivery of the fuel/air mixture to each pot. I accept that in theory, the ability to provide individual injectors at a late point in the intake tract to each cylinder does allow for a more effective intake tract arrangement than the squashed-up single-plenum-into intake-tubes we have at the moment - but that arrangement does allow for some fairly simple redundancy capability to be integrated into the overall system, whether this be by retaining a carby or having a back-up single-point injection device (e.g. a megasquirt-style independent arrangement) in the plenum intake.

 

 

[jetjr]

On the idea of carby back up, A Rotec TBI would be perfect as the throttle body/backup carb, bit too expensive for this job though.

 

On the concept of certification, if the carb setup was the primary fuel delivery system, could the EFI not be supplementary and therefore not need certification?

 

 

[Oscar]

Good grief, man - next thing, you'll be proposing that one should keep the carby set-up but tune it so that it is delivering a consistently lean-of-optimal mixture (jet and needle combination..) and use the EFI as a 'mixture top-up' mechanism to deliver a tightly controlled and optimised mixture to each pot.

 

Then I suppose you'd argue that one might use the choke facility (re-tuned to provide a 'safely rich', not a 'starting rich' solution) as the fall-back 'get you out of trouble' device if the EFi goes to silicon heaven - since in normal operation the EFI would supply the ideal rich starting mixture, the 'normal' choke isn't required. So, you're flying along, the EFI dies, you pull 'combat rich' and start looking for a suitable bug-out site - and fly appropriately.

 

If all of that could be achieved - and the hardware to do it is a set of injector tubes on the intake runners plus the EFI controller and the high-pressure fuel delivery circuit - CASA might find it damn hard to argue. Putting CASA in a difficult position to enforce its prejudices is a very dangerous game - probably the best option is to make a break for the tree-line...

 

 

[jetjr]

Yes agreed crazy stuff.

 

Carby, choke and carb heat arent required, but as they exist, leave them there.

 

If the EFI plays up, turn off ECU and pump switches, turn on Carb fuel maybe elect boost boost pump, keep flying....zactly like they are running today.

 

Could possibly run both at once and ECU would wind down on mix adjustment then turn it off. If your slick enough wouldnt need restart.

 

You would implement some system of 1 x circuit running on carb alone per month or so to make sure it all still functions and keep carb full of fuel and gaskets wet.

 

Hows the engine driven fuel pump going to go running without fuel most of the time?

 

Your correct about hardware to do it and its pictured on the SDS website

 

Who doesnt like poking a bees nest, so long as you can run fast

 

 

[Oscar]

Actually, in my idea, the carby is still supplying partial fuel mix all the time so the entire carby fuel delivery system remains operative - just running at a lower fuel delivery quantity. You could probably do a double-check of both systems on run-up by starting her up (using both systems ON, to provide the choke), then do a second mag drop check with the EFI switched off - if it splutters and dies, the carby-fed circuit isn't working..

 

If the injectors can be sized so that they can provide full fuel mix in the case that the carby is iced/otherwise inoperative without being over-sized when it isn't, then you have added security (though I think it'd be wise to retain carby heat to ensure that great gobs of ice don't build up in the carby and then get sucked into the valves..)

 

All this seems too simple in concept to be reality. There has to be a huge Catch-22 somewhere lurking..

 

 

[Bob Llewellyn]

Actually, in my idea, the carby is still supplying partial fuel mix all the time so the entire carby fuel delivery system remains operative - just running at a lower fuel delivery quantity. You could probably do a double-check of both systems on run-up by starting her up (using both systems ON, to provide the choke), then do a second mag drop check with the EFI switched off - if it splutters and dies, the carby-fed circuit isn't working..If the injectors can be sized so that they can provide full fuel mix in the case that the carby is iced/otherwise inoperative without being over-sized when it isn't, then you have added security (though I think it'd be wise to retain carby heat to ensure that great gobs of ice don't build up in the carby and then get sucked into the valves..)

 

All this seems too simple in concept to be reality. There has to be a huge Catch-22 somewhere lurking..

Rich cut.

 

 

[Oscar]

Rich cut.

Good response - concise. However, unless you are referring to the current governmental fad for taxation breaks to high-level income earners, I'm not QUITE sure how it applies...

 

Can I just re-state the proposition: you have a complete, operational carby-fed fuel system that is set up to provide, let us say, 75% of the fuel required at 75% power. You have a supplementary EFI system that is capable of supplying all of the extra fuel for 100% power. The EFI system is sufficiently sophisticated that it can vary mixture to each pot as required to keep egt's within limits, stop detonation etc.

 

That gives you - I believe - optimal mixture delivered to each pot for all phases of flight. You therefore get the advantages of both best achievable economy and safe engine management, no matter what the quality of the fuel you happen to have filled your tank with, any peculiarities in cooling airflow / inlet tract variations / single plug failure etc. in any momentary change of circumstances.

 

Your back-up in case of EFI failure - particularly at a critical point in the flight - is use of the 'choke' function of the carby which is now set up to be capable of adding sufficient extra fuel when selected for 100% fuel at 75% power, or perhaps even at say 85% power. Hell, if you routinely fly out of a site that absolutely mandates max. ROC on climb-out, you may want to set it at 100% power. In this extreme case, you may even want to adopt an operating regime that incorporates not switching on the EFI until climb-out is completed so you remove the added worry of perhaps having to pull 'choke' (let's call it 'combat rich' for a giggle) at a critical part of the climb-out - because it's already on. Then, once in 'cruise climb' or above, you select EFI-ON and 'combat rich' off. In theory at least, if you DO have a '100% fuel delivery' setting on the 'combat rich' jet, then the EFI won't be delivering any additional fuel anyway, thus negating any effect from EFI malfunction until you close the 'combat rich' selector. The transition to EFI-efficient cruise in normal situations would be completely automatic on closing the 'combat rich' selector.

 

I don't see any of this as being more complicated than managing carby heat and boost pump operation. You use the EFI for start-up to provide starting choke fuel mixture condition - and if the damn EFI is O/S then the engine won't start, which should be enough to keep you out of trouble unless you're seriously inventive.

 

Would the additional EFI system be cost-effective to add? Probably depends on how you typically operate your aircraft, but I suggest there are some fairly decent arguments to say that for Jab-based engines, it would be very well worth consideration. Here's a few ideas I'd like to throw into the mix:

 

Jab. engines do not tolerate out-of-limits heat situations at all well, as we know. If you can eliminate all occurrences of an out-of-limit heat situation, typically (it appears) you can get double or more the time between overhauls, and just ONE overhaul is going to (in all likelihood) cost more than the complete EFI installation.

 

Fuel quality: the future for 100LL manufacture - at least on the East Coast - appears precarious, with both the Shell refinery at Geelong and the BP refinery in Qld. changing ownership. I think it is highly likely that it will only get more difficult to obtain 100LL elsewhere than at major airports where RAA aircraft can't go; and the usual pattern of RAA aircraft use is such that it is highly likely that on any decent trip you are going to have to use fuel from the local servo of unknown quality (age, composition etc.). You are very likely to end up with a hybrid mix of fuel at some point.

 

Economy (aka - range). Anecdotally at least, it seems that you can expect at least several litres/hour saving with an EFI system over a pure carby system, so for a say four-hour flight you gain an extra 8 litres of 'free' fuel - extending your effective useful range by around 50 nm. That's not much, really - but if most of your flying is around the Eastern area, from the coast across to the 'middle of the bush' area, it could be the difference of having several refuelling sites available, or not. You might not save much per litre on the purchase cost of the fuel itself, but if you can save a $50 call-out charge / expensive taxi-rides to and from the fuel station by having a wider selection of potential refuelling sites, it could quite quickly mount up to a decent amount even on just one several-days trip. Not worth it for just tootling around a well-supplied local site but worth consideration for those who use their aircraft for more serious touring.

 

 

[jetjr]

Anecdotal evidence says more like 6-8 lph saving with the SDS setup

 

Basic numbers says it will pay for itself before 200 hrs and you get the other benefits

 

The system has a mixture adjustment knob, also they are looking for AFR unit to provide even more data for tuning. Will work with 100ll for hundreds of hours.

 

More info in May hopefully

 

Using more variable fuel would be far less of a problem than with carb as you correctly say

 

Edge performance in EU is doing much of the kit work and they also run a turbo 2200 and EFI.

 

 

[Bob Llewellyn]

Good response - concise. However, unless you are referring to the current governmental fad for taxation breaks to high-level income earners, I'm not QUITE sure how it applies...Can I just re-state the proposition: you have a complete, operational carby-fed fuel system that is set up to provide, let us say, 75% of the fuel required at 75% power. You have a supplementary EFI system that is capable of supplying all of the extra fuel for 100% power. The EFI system is sufficiently sophisticated that it can vary mixture to each pot as required to keep egt's within limits, stop detonation etc.

 

That gives you - I believe - optimal mixture delivered to each pot for all phases of flight. You therefore get the advantages of both best achievable economy and safe engine management, no matter what the quality of the fuel you happen to have filled your tank with, any peculiarities in cooling airflow / inlet tract variations / single plug failure etc. in any momentary change of circumstances.

 

Your back-up in case of EFI failure - particularly at a critical point in the flight - is use of the 'choke' function of the carby which is now set up to be capable of adding sufficient extra fuel when selected for 100% fuel at 75% power, or perhaps even at say 85% power. Hell, if you routinely fly out of a site that absolutely mandates max. ROC on climb-out, you may want to set it at 100% power. In this extreme case, you may even want to adopt an operating regime that incorporates not switching on the EFI until climb-out is completed so you remove the added worry of perhaps having to pull 'choke' (let's call it 'combat rich' for a giggle) at a critical part of the climb-out - because it's already on. Then, once in 'cruise climb' or above, you select EFI-ON and 'combat rich' off. In theory at least, if you DO have a '100% fuel delivery' setting on the 'combat rich' jet, then the EFI won't be delivering any additional fuel anyway, thus negating any effect from EFI malfunction until you close the 'combat rich' selector. The transition to EFI-efficient cruise in normal situations would be completely automatic on closing the 'combat rich' selector.

 

I don't see any of this as being more complicated than managing carby heat and boost pump operation. You use the EFI for start-up to provide starting choke fuel mixture condition - and if the damn EFI is O/S then the engine won't start, which should be enough to keep you out of trouble unless you're seriously inventive.

 

Would the additional EFI system be cost-effective to add? Probably depends on how you typically operate your aircraft, but I suggest there are some fairly decent arguments to say that for Jab-based engines, it would be very well worth consideration. Here's a few ideas I'd like to throw into the mix:

 

Jab. engines do not tolerate out-of-limits heat situations at all well, as we know. If you can eliminate all occurrences of an out-of-limit heat situation, typically (it appears) you can get double or more the time between overhauls, and just ONE overhaul is going to (in all likelihood) cost more than the complete EFI installation.

 

Fuel quality: the future for 100LL manufacture - at least on the East Coast - appears precarious, with both the Shell refinery at Geelong and the BP refinery in Qld. changing ownership. I think it is highly likely that it will only get more difficult to obtain 100LL elsewhere than at major airports where RAA aircraft can't go; and the usual pattern of RAA aircraft use is such that it is highly likely that on any decent trip you are going to have to use fuel from the local servo of unknown quality (age, composition etc.). You are very likely to end up with a hybrid mix of fuel at some point.

 

Economy (aka - range). Anecdotally at least, it seems that you can expect at least several litres/hour saving with an EFI system over a pure carby system, so for a say four-hour flight you gain an extra 8 litres of 'free' fuel - extending your effective useful range by around 50 nm. That's not much, really - but if most of your flying is around the Eastern area, from the coast across to the 'middle of the bush' area, it could be the difference of having several refuelling sites available, or not. You might not save much per litre on the purchase cost of the fuel itself, but if you can save a $50 call-out charge / expensive taxi-rides to and from the fuel station by having a wider selection of potential refuelling sites, it could quite quickly mount up to a decent amount even on just one several-days trip. Not worth it for just tootling around a well-supplied local site but worth consideration for those who use their aircraft for more serious touring.

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".

 

 

[Oscar]

Maybe 6 for the 3300, say 4 for the 2200? (let's be conservative here and treat our engines with lavish love..) Depending on the flight profile, that's getting up towards 80+ nm for a four-hour flight, which is starting to be a useful improvement in range, because if you think about it, for a full day's flying, you get about a 100-nm circle of options for your mid-point fuel stop at the very least!

 

I do believe that there's more to look at than just 'basic' numbers here, though. For careful owner/operators, things like economy and better protection against odd batches of fuel would be significant, but for operators who have their aircraft on the line, I suspect that just the improvement in engine management that would happen automatically instead of having to rely on the user consideration factor could be a real bonus. Let's face it - if you don't know about/ train the aircraft hirer on the finer points of engine management, having a system on board that limits the possible damage from ham-fisted operation just has to be a worthwhile investment in the potential cost of repairs and downtime.

 

And that's without the added potential cost of a mid-air cessation of noise due to really BAD engine management, in that flight or any before it..

 

 

[Oscar]

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 occurrence 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".

Aha - ok, now I understand the 'rich cut' comment. I thought that SOP for take-off is boost pump ON anyway, not 'boost pump ON if it hiccups', so over-delivery should, surely, happen before lift-off.

 

However, in terms of the 'overall' system delivering a manageable situation in case of failure of a critical component at a critical moment: assuming that the EFI system maximum fuel delivery capability is sized appropriately, which happens faster: damage through over-lean situation or loss of power through over-rich? We cannot ever assume that any system can be made foolproof, since by definition fools can exceed the imagination of those with the intelligence to be tasked to design the 'fool-proof' system.

 

I'm no expert on Human Factors, but I suspect that there is a vast gulf between having to react in around two seconds or less to a sudden overtemp situation heading towards detonation and terminal failure of the engine, and say ten seconds of increasingly rough running, scanning the egt's, realising that they are woefully low and deciding that there is too much fuel being delivered and hitting an EFI-OFF switch. The equation here is not JUST the POF figure, but the degree to which F is manageable.

 

Despite what the chattering media (and the fillums) suggests, there is an interval between engine failure and a crash. Gracious me, there is actually NOT an impenetrable nexus between 'noise-off ' and 'smash into the ground in a ball of fire'! I know I'm being radical here, but I dare to suggest that with a level of redundancy in fuel delivery systems - with the optimal mix of redundancy determined and applied - we could actually IMPROVE safety by adopting a hybrid system.

 

Anybody who grew up with carburettored cars knows that carbies CAN fail. I had a Renault R8 that regularly died when the spray-bar on the Solex became dislodged - to the point where I could re-engage it in the bloody dark, by feel, and I always carried the necessary screw-driver. We have redundant ignition systems, redundant fuel pump systems - but we fly without any redundancy for the carby! - and that is accepted, because nobody has come up with a system that can provide redundancy for the carby.

 

Electronic systems have a bloody fantastic reliability rate in real-life terms - and the added security of self-checking PLUS 'limp-home' failure mode. The use of basic POF statistics simply doesn't cover the full gamut of the potential of a hybrid system to reduce the risk of a component failure resulting in a crash.

 

 

[Bob Llewellyn]

Aha - ok, now I understand the 'rich cut' comment. I thought that SOP for take-off is boost pump ON anyway, not 'boost pump ON if it hiccups', so over-delivery should, surely, happen before lift-off. However, in terms of the 'overall' system delivering a manageable situation in case of failure of a critical component at a critical moment: assuming that the EFI system maximum fuel delivery capability is sized appropriately, which happens faster: damage through over-lean situation or loss of power through over-rich? We cannot ever assume that any system can be made foolproof, since by definition fools can exceed the imagination of those with the intelligence to be tasked to design the 'fool-proof' system.

 

I'm no expert on Human Factors, but I suspect that there is a vast gulf between having to react in around two seconds or less to a sudden overtemp situation heading towards detonation and terminal failure of the engine, and say ten seconds of increasingly rough running, scanning the egt's, realising that they are woefully low and deciding that there is too much fuel being delivered and hitting an EFI-OFF switch. The equation here is not JUST the POF figure, but the degree to which F is manageable.

 

Despite what the chattering media (and the fillums) suggests, there is an interval between engine failure and a crash. Gracious me, there is actually NOT an impenetrable nexus between 'noise-off ' and 'smash into the ground in a ball of fire'! I know I'm being radical here, but I dare to suggest that with a level of redundancy in fuel delivery systems - with the optimal mix of redundancy determined and applied - we could actually IMPROVE safety by adopting a hybrid system.

 

Anybody who grew up with carburettored cars knows that carbies CAN fail. I had a Renault R8 that regularly died when the spray-bar on the Solex became dislodged - to the point where I could re-engage it in the bloody dark, by feel, and I always carried the necessary screw-driver. We have redundant ignition systems, redundant fuel pump systems - but we fly without any redundancy for the carby! - and that is accepted, because nobody has come up with a system that can provide redundancy for the carby.

 

Electronic systems have a bloody fantastic reliability rate in real-life terms - and the added security of self-checking PLUS 'limp-home' failure mode. The use of basic POF statistics simply doesn't cover the full gamut of the potential of a hybrid system to reduce the risk of a component failure resulting in a crash.

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.

 

 

[Oscar]

No, actually it damn well doesn't. Bloody engineers... can't hear the train for the whistle. You are talking failure rates, I am talking crashes. Do try to -ing LISTEN.

 

Yes, more systems delivering fuel increases the statistical probability of a component failure. What you numerically-retentive types fail to accept is the potential for outcome. An instantaneous engine failure during a high-risk period of flight - let's say, at 500 foot off the deck when maintenance of Vx is crucial to survival has an entirely different impact on the likely outcome than a prolonged engine shut-down event that starts when cruising at 8,000 AGL over open, flat country. Both will score 100% on the 'engine stopped because of component failure' table, which is where you are coming from. However, the result of an instantaneous failure that ends up with the aircraft in a crumpled ball of flame on the side of a steep hill vs. a gradual failure that results in an annoyed PIC landing deadstick at an unfamiliar airstrip and seeking the assistance of the local L2 to get the noise working again is a very different animal, from every POV other than the POF statistical one.

 

 

[Bob Llewellyn]

No, actually it damn well doesn't. Bloody engineers... can't hear the train for the whistle. You are talking failure rates, I am talking crashes. Do try to -ing LISTEN.Yes, more systems delivering fuel increases the statistical probability of a component failure. What you numerically-retentive types fail to accept is the potential for outcome. An instantaneous engine failure during a high-risk period of flight - let's say, at 500 foot off the deck when maintenance of Vx is crucial to survival has an entirely different impact on the likely outcome than a prolonged engine shut-down event that starts when cruising at 8,000 AGL over open, flat country. Both will score 100% on the 'engine stopped because of component failure' table, which is where you are coming from. However, the result of an instantaneous failure that ends up with the aircraft in a crumpled ball of flame on the side of a steep hill vs. a gradual failure that results in an annoyed PIC landing deadstick at an unfamiliar airstrip and seeking the assistance of the local L2 to get the noise working again is a very different animal, from every POV other than the POF statistical one.

silly boy, didn't look up ac23.1309, did you? a crash is a

 

No, actually it damn well doesn't. Bloody engineers... can't hear the train for the whistle. You are talking failure rates, I am talking crashes. Do try to -ing LISTEN.Yes, more systems delivering fuel increases the statistical probability of a component failure. What you numerically-retentive types fail to accept is the potential for outcome. An instantaneous engine failure during a high-risk period of flight - let's say, at 500 foot off the deck when maintenance of Vx is crucial to survival has an entirely different impact on the likely outcome than a prolonged engine shut-down event that starts when cruising at 8,000 AGL over open, flat country. Both will score 100% on the 'engine stopped because of component failure' table, which is where you are coming from. However, the result of an instantaneous failure that ends up with the aircraft in a crumpled ball of flame on the side of a steep hill vs. a gradual failure that results in an annoyed PIC landing deadstick at an unfamiliar airstrip and seeking the assistance of the local L2 to get the noise working again is a very different animal, from every POV other than the POF statistical one.

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...

 

 

[Dafydd Llewellyn]

Let me see if I have this right . . . this most erudite debate began from a discussion of how to increase the engine reliability by reducing mixture mal-distribution, which causes uneven cylinder temperatures, and can provoke detonation, etc, didn't it? And it wandered off into the by-ways of being able to contend with off-spec fuel, improve overall fuel consumption, etc, which are by-products of an EFI system ?

 

IF that's so - and I've always been of the view that the top three criteria out of ten for an aero engine were, in order, reliability, reliability, and reliability . . . then should we not consider the causes of unreliability? We always tend to jump to a "New" solution before we finish getting the bugs out of the old system. This has never made total sense to me; but it seems to be a fundamental human behaviour.

 

One of the main arguments in favour of a fuel injection system over a carburettor, is that most people do not feel competent to tamper with a FI system, whereas anybody who has owned a lawnmower feels competent to muck about with a carburettor. So should we go to mechanical and electronic complexity as a means of reducing finger-trouble? This is sane?

 

The same reason applies to the use of constant-depression carbies; they are, to a degree (roughly 50% by my figuring, but it can be better than that, depending on the needle profiling) inherently altitude-compensated, so the manufacturer can leave out a mixture control that the pilot can abuse - at least, for the density altitude range allowed for RAA aircraft. Also, the richening that occurs despite the CD carbie's inherent compensation, provides a mite of extra cooling as the air gets thinner. That's not all bad.

 

That's where we are right now; the biggest cause of engine unreliability - at least, in the view of the manufacturers - is finger trouble. BMW were talking about sealing the bonnets of their cars at one time, I seem to recall. The "No user-serviceable parts inside" syndrome suggests there is more than a little validity in this point of view - at least, until the warranty runs out.

 

If you look at a Marvel-Schebler (now Facet) carburettor from a Lyconental, you will find a damn near bullet-proof device of almost aggressively basic simplicity; but it requires competence on the part of the pilot. That's one way to achieve reliability - use the KISS principle. It's worked pretty well, for around sixty years, but it's not idiot-resistant. Getting rid of the mixture control by using CD carburettors is a further step in this direction; it gets the pilot's digit out of the equation, at the cost of adding the potential unreliability of the rubber diaphragm. Further, nobody, but NOBODY, is allowed to strip a GA aircraft carbie except a licenced carburettor overhaul shop. Over-regulation? No, I don't really think so. It's about the only practical way to control the hazard from finger-trouble.

 

What causes mixture mal-distribution from a CD carburettor? We could do with some intelligent research into this. However, several aspects are known:

 

Firstly, the fuel spray moves up and down as it enters the manifold, according to the butterfly position. If you only feed two cylinders per carburettor, and the dividing edge in the manifold is vertical, and the carburettor is installed accurately horizontal, this need not cause a mal-distribution between the cylinders. However, this will only be true if there is no swirl in the airflow as it exits from the carburettor. Swirl can be (usually is) introduced in the airbox upstream of the carburettor; and it can be largely removed by flow-straighteners in the duct between the airbox and the carbie. How many installations have this feature? Ian McPhee drew it to my attention for a Jabiru installation in a Motorfalke; I've not seen it used anywhere else. It made a huge difference in that installation.

 

Feeding more than two cylinders from one carburettor poses much greater difficulty. Rotax uses two CD carbies on its 912 - but is the dividing edge at the start of the manifold vertical? If not, I think they missed a point in the design.

 

I take the view there is scope for further improvement in the way we use carburettors; and aircraft engines do not have to meet the pollution constraints over the enormous range of operating conditions of a car engine, so the full scope of EFI is not necessary to get an aircraft engine to market. The common perception that "it's gotta be EFI" is, I think, somewhat short-sighted - but it may be forced onto the engine manufacturers by popular (but pig-headed) perception, whether or not that is the best answer.

 

 

[Bob Llewellyn]

Let me see if I have this right . . . this most erudite debate began from a discussion of how to increase the engine reliability by reducing mixture mal-distribution, which causes uneven cylinder temperatures, and can provoke detonation, etc, didn't it? And it wandered off into the by-ways of being able to contend with off-spec fuel, improve overall fuel consumption, etc, which are by-products of an EFI system ?IF that's so - and I've always been of the view that the top three criteria out of ten for an aero engine were, in order, reliability, reliability, and reliability . . . then should we not consider the causes of unreliability? We always tend to jump to a "New" solution before we finish getting the bugs out of the old system. This has never made total sense to me; but it seems to be a fundamental human behaviour.

 

One of the main arguments in favour of a fuel injection system over a carburettor, is that most people do not feel competent to tamper with a FI system, whereas anybody who has owned a lawnmower feels competent to muck about with a carburettor. So should we go to mechanical and electronic complexity as a means of reducing finger-trouble? This is sane?

 

The same reason applies to the use of constant-depression carbies; they are, to a degree (roughly 50% by my figuring, but it can be better than that, depending on the needle profiling) inherently altitude-compensated, so the manufacturer can leave out a mixture control that the pilot can abuse - at least, for the density altitude range allowed for RAA aircraft. Also, the richening that occurs despite the CD carbie's inherent compensation, provides a mite of extra cooling as the air gets thinner. That's not all bad.

 

That's where we are right now; the biggest cause of engine unreliability - at least, in the view of the manufacturers - is finger trouble. BMW were talking about sealing the bonnets of their cars at one time, I seem to recall. The "No user-serviceable parts inside" syndrome suggests there is more than a little validity in this point of view - at least, until the warranty runs out.

 

If you look at a Marvel-Schebler (now Facet) carburettor from a Lyconental, you will find a damn near bullet-proof device of almost aggressively basic simplicity; but it requires competence on the part of the pilot. That's one way to achieve reliability - use the KISS principle. It's worked pretty well, for around sixty years, but it's not idiot-resistant. Getting rid of the mixture control by using CD carburettors is a further step in this direction; it gets the pilot's digit out of the equation, at the cost of adding the potential unreliability of the rubber diaphragm. Further, nobody, but NOBODY, is allowed to strip a GA aircraft carbie except a licenced carburettor overhaul shop. Over-regulation? No, I don't really think so. It's about the only practical way to control the hazard from finger-trouble.

 

What causes mixture mal-distribution from a CD carburettor? We could do with some intelligent research into this. However, several aspects are known:

 

Firstly, the fuel spray moves up and down as it enters the manifold, according to the butterfly position. If you only feed two cylinders per carburettor, and the dividing edge in the manifold is vertical, and the carburettor is installed accurately horizontal, this need not cause a mal-distribution between the cylinders. However, this will only be true if there is no swirl in the airflow as it exits from the carburettor. Swirl can be (usually is) introduced in the airbox upstream of the carburettor; and it can be largely removed by flow-straighteners in the duct between the airbox and the carbie. How many installations have this feature? Ian McPhee drew it to my attention for a Jabiru installation in a Motorfalke; I've not seen it used anywhere else. It made a huge difference in that installation.

 

Feeding more than two cylinders from one carburettor poses much greater difficulty. Rotax uses two CD carbies on its 912 - but is the dividing edge at the start of the manifold vertical? If not, I think they missed a point in the design.

 

I take the view there is scope for further improvement in the way we use carburettors; and aircraft engines do not have to meet the pollution constraints over the enormous range of operating conditions of a car engine, so the full scope of EFI is not necessary to get an aircraft engine to market. The common perception that "it's gotta be EFI" is, I think, somewhat short-sighted - but it may be forced onto the engine manufacturers by popular (but pig-headed) perception, whether or not that is the best answer.

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?

 

 

[Dafydd Llewellyn]

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?

Yes, indeed - and that's how it has been done, in GA; the pilot has a manual mixture control; the carby or multi-point mechanical fuel-injection system is set up to give the correct result (on quality-controlled fuel) at standard sea-level conditions, and the pilot is supposed to use his brain to adjust the mixture at altitude. The carburettors and MFI systems are tightly controlled as to who is allowed to fiddle with them. The pilots get some training as to what the mixture knob is there for; but flying-training schools mainly tell the trainees to leave the mixture full rich, because that saves engines in basic circuit training, so it's debatable whether it is driven sufficiently firmly into some pilot's skulls. Given an EGT and CHT on every cylinder, and proper knowledge of what they mean and how to use the mixture control, this system works very well; but there are still engines being wrecked in GA due to finger trouble, especially now fuel price is seen as a major part of the direct operating cost - so this approach is not perfect, either. However, scratch almost any experienced ex-GA pilot and I wager you'll find he'll prefer to have a manual mixture control.

The RAA scene is rather different; firstly, the available engines all use CD carbies and do not have a mixture control - so pilots are not trained to use one, unless they come from a GA background, which may or may not have driven the knowledge into them successfully. Secondly, the maintenance requirements for RAA aircraft do nothing to control the knowledge and competence of people who want to fiddle with their engines. Why did the engine manufacturers choose to make it impossible to train RAA pilots about the use of mixture controls? (One guess). If I were an engine manufacturer in this environment, I'd make the same choice; product liability really leaves no other option.

 

Multi-point mechanical fuel injection - provided everything is working as it should - improves the mixture distribution; and it lessens the induction icing problem (tho not as completely as people generally imagine; an alternate source of warm air is still required). However, there are more things to go wrong in even the stone-axe mechanical systems used in contacomings, than in the carburettors they replace; and I've seen some truly bizarre engine failure modes from them - the Continental "rich-cut" mode is one that few pilots comprehend, and it beats me how it ever got past certification. So the "educated operator" approach has large holes in it, too.

 

On the whole, I consider the adoption of the CD carburettor to be one of the choices that has made recreational aviation possible, and I think it should be recognised as such. No, they're not perfect - and there are still some shortcomings in our knowledge of how to best use them, such as de-swirling the air entering them, and how to design a really effective way to distribute the fuel spray. But I suspect they're the least-worst option; and we need to be just a bit smarter in how they are applied.

 

 

[Russ]

All this is one good read, the lot....

 

 

[Oscar]

Well, hot damn, where is the smiley for 'Don't Poke the Engineers?' Don't give me 'prolix', sunshine, you're not an ex-PFC...

 

A couple of quick points. The flow-straightening improvement for Jab. engines is more broadly known than just the work done by Ian McPhee; at least one member of the Sonex Jab-user group ( Lyn Matheson, I think is his name) has been working on those for at least several years, and I THINK I saw a reference somewhere recently to Jab. USA having an OTS flow straightener available, though don't stake me with yer slide-rule if this isn't so. Without doubt, it's one step that every Jab. owner should consider (and preferably implement, with due attention to testing).

 

Adding complexity to any system is fundamentally undesirable, I yield the field there. However, in every situation one should look at the cost-benefit ratio before dismissing potential solutions to a problem. The point made that we are seeing more and more problems with cars recalled because of faults in the electronics is, I suggest, because the level of complexity they now have has gone over the top of the 'benefit' curve to the point where they try to be everything to everyone at the push of a button. When you have hulking great SUVs with 'Comfort - Normal - Sport - Track' settings that vary everything from the engine response through the gearbox change points, proportional diversion of power through the differentials to every damn wheel, plus steering response and suspension compliance adjustment, it's getting ridiculous - no, I correct myself - it's gotten ridiculous..

 

In this particular case, I believe we are faced with several major problems - and these are real problems, not the manufacturer's PR department dreams for product differentiation.

 

The first of these is dealing with varying fuel quality - and that is a problem that is, I very strongly suspect, going to only get worse for RAA-class aircraft operators. What we have here is a developing situation where the capability of auto EFI systems to deal with varying fuel quality has allowed the fuel suppliers to get away with sloppier standards and Australia is particularly bad for this - just about every high-performance vehicle sold in Australia has its engine de-rated because of our known poor-quality fuel. Even so, we get reports of auto-engines destroyed - recently, the NSW Police destroyed a high-performance Falcon engine with one fill of lower-grade fuel than recommended (cracked the block!). Some manufacturers go so far as to recommend only certain brands of PULP - the Golf GTI, for example, effectively mandates Shell, I think it is.

 

As far as I am aware, Jabiru has withdrawn the higher-comp. barrels it used to supply so they can accommodate PULP. One small step etc. - but ironically, Jabiru not so long ago indicated in their Jabachat section, that they were getting a statistically significant number of reports of problems with the aromatics in Shell V-Power PULP attacking the fuel tanks. So by trying to solve one problem, another one arose. What to do if you're in need of fuel in Didjabringabeeralong and the only servo around is a Shell station? Do you restrict your operation to airfields where 100LL is available - and can you even access airfields where 100LL is available?

 

Next problem: yes, mixture-adjustable carbies obviously exist, but they are only as effective in maintaining acceptable fuel mixture ratios as the competence of the operator to monitor and adjust mixture correctly. Of course, the time when doing that is most critical is initial climb-out - exactly the time when one ought, I think, to be (mostly) looking outside the damn cockpit,not to mention playing around with speed, revs, trim, flap settings, etc. For an experienced pilot well in tune with the aircraft, I imagine this is a deeply-ingrained dance done by second nature, but statistics suggest that the majority of RAA pilots don't really do enough hours to keep the fine edge sharp. Perhaps when my own experience is adequate for me to make that judgement I'll change my opinion - I'm sure others can provide better guidance.

 

Third problem: particularly with RAA-class aircraft, we are often juggling with trying to squeeze the best performance out of a pretty (weight) limited amount of fuel and as-safe-as-possible operation. Just chucking buckets of fuel at the engine to keep the temps down is not necessarily an optimal solution.

 

Is a hybrid system necessarily the bastard child of a 'last lady in the pub at closing time' encounter? Well, the Rotax has been mentioned. Now it is a hybrid system: you have air-cooling plus water cooling, which improves tolerance to differing fuel quality but introduces an additional failure potential: a broken hose, a failed water pump.. oh, and two carbies, doubling the potential carby failure situation. I'm not at all sure that a Rotax represents a free launch..

 

The EFI'd carby hybrid I'm postulating is possible to incorporate on a standard Jab. engine without changes to the existing installation. I think it's worth a bit more consideration than just being damned by a thousand FMEA cuts.

 

 

[Dafydd Llewellyn]

Diesels, with basic mechanical injection systems. If somebody could only build one that's affordable, and light enough, and does not need to be blown to 3 atmospheres to get a reasonable power to weight . . .

 

There's no simple best way. A chaque un, son gout.

 

 

[Oscar]

Oh, agreed. HOWEVER - this thread is about CAMit engines (and by default, I suggest, getting the maximum utility from them). One of the highly-attractive things about the CAMit engines is the fact that they don't require changes to the basic installation and therefore the cost of them can be directly compared to the cost of a Jab replacement / rebuild engine - you don't have to go through the torture of re-engineering from the firewall forwards to plug one in. Additionally - there is a 100% 'back-up' available in terms of a standard Jab. engine. These are features not to be lightly ignored.

 

So the genesis of the hybrid discussion came from curiosity about how one could achieve further improvements to operational reliability etc. within fairly small parameters of further modification and in the broader context of applicability to ALL Jabiru-based engines. The obvious candidates, I suggest, are improvements in cooling arrangements and improvements in fuelling management - with the over-riding caveat being that it be reasonably 'do-able'. That, of course, means compromise - it's highly unlikely, I think, that one could make quantum leaps without significant changes to the underlying engineering.

 

Compromise inevitably introduces value judgement as to the priority for one factor over another vs. the benefit / cost of other factor/s. Compromise is, I think, de facto exclusive of the possibility of a 'silver bullet' emerging. Add in things like regulations and liability issues and it gets really damn complicated, but that doesn't necessarily mean we shouldn't have the fun of talking about it.

 

 

[Dafydd Llewellyn]

Yep. I'll be happy with a CAMIT engine with a CD carbie.