Camit engines - anyone got one?

[Russ]

An engineering point I ponder why???

 

My jab and others jabs I have seen under the cowl of.......is the routing of the cabin heat hose.....it deflects HOT air from the exhaust pipe flange then that hose routes up to the top area of the firewall to a mechanical flap arrangement. To utilise the available hot air on a cold day you pull the push/pull cable and it closes a flap, thus opening the available hot air into the cab.....great, but when cab heat is no longer needed , which is 99% of the time! that entry flap into the cab rotates and closes cab entry! but goes back to funnelling all that hot air back into the engine bay.

 

Heat, we do our best to minimise/ control, so why pump heat back into the engine bay??

 

Just wundering....

 

 

[Bob Llewellyn]

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.

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...

 

 

[Bob Llewellyn]

An engineering point I ponder why???My jab and others jabs I have seen under the cowl of.......is the routing of the cabin heat hose.....it deflects HOT air from the exhaust pipe flange then that hose routes up to the top area of the firewall to a mechanical flap arrangement. To utilise the available hot air on a cold day you pull the push/pull cable and it closes a flap, thus opening the available hot air into the cab.....great, but when cab heat is no longer needed , which is 99% of the time! that entry flap into the cab rotates and closes cab entry! but goes back to funnelling all that hot air back into the engine bay.

Heat, we do our best to minimise/ control, so why pump heat back into the engine bay??

 

Just wundering....

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!

 

 

[jetjr]

Solid lot of opinions there, all valid

 

A few points

 

I have two flow straightners in my Jab engine, small improvement, still have 100 deg C variation in EGT

 

EGT spread is undoubtedly caused by swirl etc in the intake but fixing it is not easy. Plenty of people including me have been trying for many years. Discussions with older Jab people say its been an issue sinc ethe engine was first concieved.

 

I have tried three factory jet and needle kits, and maybe 10-15 different jetting arrangements, NONE deliver a good even mixture for all conditions and the best can be hoped is a "safe" range of operation, which invariable means running rich.

 

There is mixture control in Jabirus, carb heat is very effective at richening mix and there is no problems running full time with this on.

 

People have tried both Rotec tbi and aerocarb carb units with mixture control and although with good results mixture spread variations still a problem

 

My maybe uneducated view on failure modes is that right now we see detonation and early wear being the main failure points in the engine.

 

MFI would be great, there is a mob in US who make one and were working to make a kit for Jabiru but hvent heard much for a while

 

Im understanding but seeing complexity in Oscars dual ystem, getting CV carb to deliver only a portion of fuel would see same problems as currently seen with varying distribution with RPM and the EFI having to automatically sort it out. This will need a range of fairly critical sensors inc egt into ECU.

 

The basic concept of the multipoint EFI is to evenly inject fuel as a separate isue to air and in flight can adjust flow to each cylinder and develop map which should remain constant egt over different duties. Use of AFR should help even further get mixtures correct

 

My understanding is the EFI injectors fail to closed, the ECU, despite being reliable can be isolated and shut down. Similar for HP pump. Cant see how it could ever fail rich, Main source of failure is likely to be the electrical generation on the engine.

 

Overall if you use the old CV carb as full redundant system then you are the same as running currently.

 

South Africans have developed their own EFI setup using twin throttle body injectors, i believe they may have moved to multipoint now but all news has stopped. They are also changing ignition to ECU control too.

 

SDS can handle this too in thier unit but our focus is on fuel. If we are to spend the cash should we be upgrading ign too?

 

At this point no body can fix the current system, and whilst I agree the CV carb is the prefered option it simply doesnt work adequately and no amount of money or effort seems able to get it to work correctly on the Jab engines. If someone could develop a $2K widget which made EGT even throughout the range I would take it very seriously.

 

 

[Bob Llewellyn]

Solid lot of opinions there, all validA few points

I have two flow straightners in my Jab engine, small improvement, still have 100 deg C variation in EGT

 

EGT spread is undoubtedly caused by swirl etc in the intake but fixing it is not easy. Plenty of people including me have been trying for many years. Discussions with older Jab people say its been an issue sinc ethe engine was first concieved.

 

I have tried three factory jet and needle kits, and maybe 10-15 different jetting arrangements, NONE deliver a good even mixture for all conditions and the best can be hoped is a "safe" range of operation, which invariable means running rich.

 

There is mixture control in Jabirus, carb heat is very effective at richening mix and there is no problems running full time with this on.

 

People have tried both Rotec tbi and aerocarb carb units with mixture control and although with good results mixture spread variations still a problem

 

My maybe uneducated view on failure modes is that right now we see detonation and early wear being the main failure points in the engine.

 

MFI would be great, there is a mob in US who make one and were working to make a kit for Jabiru but hvent heard much for a while

 

Im understanding but seeing complexity in Oscars dual ystem, getting CV carb to deliver only a portion of fuel would see same problems as currently seen with varying distribution with RPM and the EFI having to automatically sort it out. This will need a range of fairly critical sensors inc egt into ECU.

 

The basic concept of the multipoint EFI is to evenly inject fuel as a separate isue to air and in flight can adjust flow to each cylinder and develop map which should remain constant egt over different duties. Use of AFR should help even further get mixtures correct

 

My understanding is the EFI injectors fail to closed, the ECU, despite being reliable can be isolated and shut down. Similar for HP pump. Cant see how it could ever fail rich, Main source of failure is likely to be the electrical generation on the engine.

 

Overall if you use the old CV carb as full redundant system then you are the same as running currently.

 

South Africans have developed their own EFI setup using twin throttle body injectors, i believe they may have moved to multipoint now but all news has stopped. They are also changing ignition to ECU control too.

 

SDS can handle this too in thier unit but our focus is on fuel. If we are to spend the cash should we be upgrading ign too?

 

At this point no body can fix the current system, and whilst I agree the CV carb is the prefered option it simply doesnt work adequately and no amount of money or effort seems able to get it to work correctly on the Jab engines. If someone could develop a $2K widget which made EGT even throughout the range I would take it very seriously.

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.

 

 

[Bob Llewellyn]

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

 

 

[Dafydd Llewellyn]

Flow straightening can't fix the up & down movement of the fuel spray stream with varying butterfly position; it can affect the side - to- side distribution. The vertical movement would probably have minimal effect if the carbie fed no more than two cylinders, and the manifold divider was vertical. One might need to take advantage of the flexible carbie mounting to adjust the side-to-side balance, but once set, it should stay OK over a range of throttle settings - if the flow is de-swirled. All this is hypothetical; it needs testing on a bench. I may be able to do that later this year. If it works, then using two carburettors for a four cylinder engine should allow a considerable improvement in mixture distribution.

 

With a single carbie, on a four cylinder engine, part of the problem is almost certainly the form of the intake end of the induction manifold. Presumably, if the outlets are arranged in stacked pairs for a four-cylinder engine, the vertical movement due to butterfly position will bias the mixture distribution between the upper and lower pairs of outlets. Offhand, I cannot visualise a form of fixed-geometry flow divider that would correct that; however perhaps one could put an adjustable vane - somewhat in the nature of a second butterfly, moving in reverse to the throttle butterfly - in the passage between the carbie and the manifold; this would introduce an additional icing problem (though maybe not much worse than for the butterfly - for which the existing carbie hot-air system is sufficient). Experimentation needed; it may be possible to simply gear it to the main butterfly. This would require an STC approval for any certificated engine.

 

The other question is, just how important is a small split in EGT? I suspect 25 degrees C is not worth chasing, or that one could realistically expect to do much better, unless you have a full closed-loop feedback setup for each cylinder - and no automotive EFI that I've come across goes to that length.

 

 

[jetjr]

Yes 25 deg would be probably good enough, possibly getting within instrument limits anyway.

 

Problem is greater on a 6 cyl no doubt

 

There are two factory intake manifolds, older one uses vane in front of 6 outlets pipes, they are just one beside the other at an angle to flow.

 

Some have found replacement of vane with round rod has improvement, morw turbulence?

 

Newer version has more longer plenum it is better but not sufficient to justify cost of upgrade -$1k

 

Phots are around in manuals and on the web

 

Guy in US has centre mount updraft on 4 cyl which again is better.

 

By turning carb a few degrees, mix left and right is influenced, just that cant move it much in one direction and even less the other

 

My straightening vanes upstream of carb are 25mm long each and in cross config. One at air cleaner outlet, other just before carb. Smoothing out air cleaner housing had improvement too.

 

Thrown in to confuse is air leaks in carb mount rubber and joining hoses in intake tubes.

 

 

[facthunter]

We all agree that designing an adequately branching manifold from a single throat carb is near impossible. My experience tuning "one throat, one cylinder" layouts is that they are very simple to get good running from. Also a backfire from one will not affect the others, as I think may be a cause of a lot of the failures here. A 4 or 6 throat carb is not hard to engineer and it has to go under the engine. All the work that went into the manifold on the six could have been put into a diaphragm carb with six throats if that was the way you decided to go. The 2 carb layout on the Rotax 912 is suss too. It's just that the engine runs so much cooler that the problem doesn't become so critical. A MECHANICAL drip system fed to each port would do the job too. An aero engine doesn't change power settings like a road vehicle does. Nev

 

 

[Dafydd Llewellyn]

Thanks, Nev - this is the sort of thing I meant, when I said that we have not pursued the CD carburettor far enough as yet, to justify dropping it. We need to delve into these sorts of options; what has been done so far is to take the least-cost option - one carbie - and fiddle with the manifold to get it to work after a fashion. We need to go one better.

 

I'll shortly be trying a single Bing 64 carbie on a 582, with a heated Y-branch manifold; the carbie will be mounted under the engine, not on the engine, and I'll have provision to adjust the aim from side to side to balance the mixture distribution. This requires that the elastic centre of the engine mount system is at the powerplant centre of gravity, otherwise the motion will likely be too much for the rubber connections at either end of the manifold to accommodate; but it will greatly reduce the vibration level to which the carbie is subjected. If this works, it could provide some data for a multi-cylinder adaption.

 

If one wanted to adapt such a setup to provide some detonation protection, it would be not too difficult to use a standard knock-sensor plus EGT to switch a small solenoid valve to slightly alter the pressure above the fuel in the carbie bowl, to richen the mixture somewhat. Again, this needs a test bench. One could arrange the setup so it failed rich, which would greatly simplify approval. It needs some smarts, to prevent the system from hunting; a PID controller may be necessary. However the hardware is all off-the-shelf, and not stupidly costly.

 

If anything needs to be closed-loop automated with a carburettor setup, it is the use of induction air preheat to keep the induction air temp above the icing range (i.e. above around 15C); the manual carbie heat control would be the reversion option. I'm not against such applications, provided each one of them is independent and can be made to fail - safe - that way, the system will not stop the noise - and it will be vastly easier to trouble-shoot.

 

 

[facthunter]

The trouble with heating the carb all the time is that you are down on power over what you could have had without the heat applied. Injecting further downstream near the port the heat of the engine covers it. Nev

 

 

[Dafydd Llewellyn]

True - that's one of the real advantages of a multi-point FI system. But you still require an alternate air source with some pre-heat - see FAR 23. The practical difference between the MFI and the carbie only becomes noticable if the outside air temp is below 15 C. Above that, no carbie heat is necessary. A "smart" closed-loop carbie heat system would supply only that amount of heat actually required, whereas the normal manual setup must supply at least 50C temperature rise upstream of the carbie. If the outside temp is below -5C, no carbie heat is required. So one does not need to heat the carbie all the time.

 

 

[jetjr]

If electric heat is acceptable there are simple options?

 

Another problem with Jabiru engines is the lack of space underneath, not sure a six throat carby would fit

 

This would require new intake runners and possibly new exhaust

 

Dollars ticking away

 

 

[facthunter]

Nothing will happen unless someone makes it happen. the intakes can go through the sump. That cools the oil. All ports face down. Not a big deal. You could have a bit more radical valve timing also with individual ports and more power as a result and still a steady idle. Nev

 

 

[Dafydd Llewellyn]

If electric heat is acceptable there are simple options?Another problem with Jabiru engines is the lack of space underneath, not sure a six throat carby would fit

This would require new intake runners and possibly new exhaust

 

Dollars ticking away

Quite right. We've been amusing ourselves hypothesizing about a possible next step beyond the current CAMIT engine. The sort of mod. needed to do all this to an existing Jabiru installation as a minimum-cost change to an existing aircraft, may well be impractical; we won't know one way or the other without a lot of experimentation, to see what can be done without radical alteration to the engine installation. We also don't know whether the benefits would justify the cost. But it's entertaining to look for a glimmer of pie in the sky, at least in a forum such as this. Call it brainstorming.

Returning to what is practical here and now, the current CAMIT engine is essentially a greatly-improved drop-in replacement for the original engine, and it has to fit within the same constraints - so the sort of idealistic answers we've been discussing may not be feasible; any improvement in mixture distribution - if indeed one were really necessary - may have to come from an EFI approach, because perhaps that's all that would fit. However, burning a little more fuel than the theoretical optimum - probably a little less than for an original Jab. engine, tho this is yet to be seen - will allow it to achieve the reliability and durability targets with the existing carburettor; so that's the first step; and it's a big one. That will get the aircraft flying the way they were originally intended to; further refinements - if any - must wait to be developed and proven. It's taken Ian Bent a decade to do the research for the existing CAMIT engine; let's be realistic.

 

This does not mean we should stop at that point; the discussion has been about what options might be worth further research. However, it would unquestionably be pursuing diminishing returns. One can develop a product for ever, but it does not necessarily make economic sense to do so.

 

The requirement for carburettor air preheat is a temperature rise of 50 C minimum in the air entering the carburettor. Normally one gets about half that from the heat coming off the engine cooling fins, and the other half from an exhaust muff. The amount of heat needed to do that would be around five kilowatts, I'd guess. At least an order of magnitude more than the alternator output. Electric preheaters are a bad joke.

 

 

[Powerin]

Nothing will happen unless someone makes it happen. the intakes can go through the sump. That cools the oil. All ports face down. Not a big deal. You could have a bit more radical valve timing also with individual ports and more power as a result and still a steady idle. Nev

Wouldn't this also warm the air, lowering the density and therefore engine power (in the same way that carby heat does)?

 

 

[Bob Llewellyn]

Wouldn't this also warm the air, lowering the density and therefore engine power (in the same way that carby heat does)?

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...

 

 

[Powerin]

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...

True I guess. But if you started from that design parameter you would be behind the eight ball as far as power/weight was concerned wouldn't you? You *usually* don't need rated power at 5000 with carb heat on do you? You would be compromising on power/weight ratio in an attempt to get 100% power in a situation where it is rarely needed.

I remember early in my training being shocked to find (coming from a farming background) that the wheel bearings of the plane I was flying were unsealed....until I realised that wheel bearings are one of the least used items on an aircraft.

 

Please note I know very little about aero engines and design and this thread is great for learning despite the black magic that often seems to be invoked

 

 

[Oscar]

Trying to make myself heard above the static of a certain engineer who loves to twiddle with his femur - sorry, FMEA - can I just drag us back to the boring regime of practicality here?

 

This thread is about the use of CAMit engines - primarily in Jabirus. Short of major re-engineering, that per se imposes a whole set of parameters on what can in fact be done and multi-carby inlet tracts, major changes to the inlet arrangement, whippy-doo automated carby heat boxes etc. is at the very least pushing the envelope.

 

The major attraction of the CAMit engine is that it can be plugged in to the front of a Jabiru with essentially NO difficult changes and offers better reliability at a highly competitive cost. It's a bloody bolt-on better option.

 

There are, without doubt, a considerable number of changes that COULD be introduced to enhance the performance, reliability etc. of CAMit or indeed basic Jabiru engines. Killjoy that I am, I'm going to suggest certain limits in the interests of practicality.

 

Those limits include: NO changes to the engine mount, cowlings, and only minor tweaks to the W&B situation. NO increased PIC workload. Potential cost of changes to be amortised over one rebuild at 400 hours vs. one rebuild at 1000 hours. NO insurmountable problems with meeting regulatory requirements. NO nett loss of utility of the aircraft. Plus - preferably - the ability to remove whatever changes have been done and revert to standard if experience finds they don't work, or worse. Also, preferably, no (or very little) double-expenditure for reverting to standard (beyond the initial cost of the bits, at least)

 

Let us assume that the CAMit engine addresses the 'internal' problems: things like through-bolt issues, oil pressure and temperature control, crankcase movement, exhaust valve heat dissipation, rocker gear loading, rocker lubrication, shaft harmonic balancing. To me, that leaves really only airflow cooling and fuel mixture as the known problem areas. We KNOW that these areas can cause serious damage to any Jab engine, and in a very short time - if it were not a serious problem then it wouldn't be worth chasing solutions. We KNOW that a perfectly happily performing Jab. engine that is inadvertently operated too far beyond limits can go from fine at opening the throttle at the start of take-off to BANG by 1,000 feet as a result of detonation. You don't have to be an engine-molesting monster to have that happen: with a tankful of dud fuel, someone who has a perfectly reasonable climb-out regime instilled in her or his mind, that 'always' works fine, can be caught out.

 

Seriously: how many reports have we seen of people stating (and I am sure, absolutely genuinely) that they have had a failure of a Jab engine that was being operated 'absolutely normally', has not been previously abused etc., let go? I've seen plenty, and in not ONE case have I heard of anybody subsequently having the fuel in the tank analysed. Of course, fuel quality isn't the ONLY cause; if 'normal' operation has the cht's routinely near the top of the green, even (and if only one cht is installed, the likelihood is very high that some of the pots have been running in the red at times) - that engine is being degraded quickly.

 

The supplementary EFI idea will fit a standard installation, it's a matter of changing the intake runner tubes for ones with injector holders. Everything else can be located around the existing engine mount etc. and reversion to standard is simply putting the old runners back on. I suspect that smarter people than I can readily work out a ratio of 'basic fuel delivery' from the carby and 'fine tuning' fuel to be delivered via the EFI system so that even instantaneous EFI failure at a critical moment doesn't result in total loss of power.

 

That there are better solutions possible than the sort of hybrid I'm suggesting, is certain - but at what cost of far more major changes to the basic aircraft? That can be accomplished without major journeys into testing and approval? Nothing comes for nothing, but if we were to put our collective heads together and work through a smorgasbord of ideas to some depth for each, my personal feeling is that the 'suppplementary EFI' idea will remain as a potentially reasonably attractive and 'do-able' option.

 

 

[Oscar]

Incidentally - a basic MOTEC EFI controller with I think all the capability required is around $2200, injectors about $100 each, new intake runners shouldn't be more than about $100 each, a high-pressure fuel pump what - around $200? Add ilnes etc, total hardware, maybe around $3.5k.

 

Then, it would need testing, fiddling etc. - but if someone were to develop a complete, programmed package it'd be possible to amortise the cost over a number of installations, surely?

 

 

[David Isaac]

It is difficult to disagree with that logic Oscar. The only remaining discussion is how you would practically and cost effectively achieve redundancy of the systems and the electrical supply.

 

This is a very interesting discussion and I do particularly enjoy the humour of the parties involved.

 

I also have a particular interest in this area of engine science, most of my lessons building and destroying race boat engines were costly. LOL

 

 

[facthunter]

Powerin, the cooling of the intake air is mainly from evaporation of the of the fuel and any adiabatic expansion (pressure drop) as it goes through the carburettor. The ice is formed from moisture already present in water vapour in the ambient air. Some Lycomings have the inlet tracts passing through the sump casting. This has two effects mainly that it allows a larger sump, and some cooling of the sump itself which is related to engine power at the time. Jet engines use fuel (unvaporised) to cool things in the same way with the same logic. ie higher flow when more heat outputted.

 

Any heating of the inlet charge is going to cause power reduction, (as you state). Injecting fuel will cause a lowering of the charge temperature, but there is no expansion of air in the inlet ducts as there is in a carburettor (or throttle body) and ice forming in a carburettor does a lot of complex things, besides impeding airflow. injection engines experience much less intake icing problems than carbs. Mainly impact ice (rhime) which occurs at much lower temps and usually in cloud. Nev

 

 

[jetjr]

Oscar, Thats exactly what SDS have done

 

The injector bosses weld to your existing intake runners

 

Comes with single pump, reg, fuel manifold and plumbing

 

Mount ECU and then controller in std instrument hole

 

Fit up hall effct sensor on front inc mount, MAP inc manifold.

 

It has base fuel map and you can fiddle to hearts content even in flight using in panel controller

 

From your egt you can dial in more or less fuel each injector AND theres a basic rotary knob for leaning overall if required

 

Cost around $3500k

 

Jabiru can supply a 1 into 2 fuel tap, one path feeds old carb setup, other to EFI. If the EFI fails for any reason, swap taps, restart on carb and can run at 100% power

 

With Camits new altenator theres plenty of power, if your concerned on redundancy fit a second pump for $200, thats the most common failure after electrical generation.

 

I believe some fit second isolated battery, which gives around 1 hr flight wih efi running

 

There are guys in SA running Motec setups for some time. Have nozzle in TBI for redundancy.

 

 

[Oscar]

It is difficult to disagree with that logic Oscar. The only remaining discussion is how you would practically and cost effectively achieve redundancy of the systems and the electrical supply.This is a very interesting discussion and I do particularly enjoy the humour of the parties involved.

 

I also have a particular interest in this area of engine science, most of my lessons building and destroying race boat engines were costly. LOL

David, I actually think that most of those problems have been - at least partially - addressed in this rambling discussion!. I don't have the knowledge or skills to know the numbers, but conceptually, I'd go about it this way:

 

By test, find out the fuel delivery profile using the cd carby only that delivers more or less reliably about, say 90% of the fuel required on average to keep the engine reasonably happy at say 75% power. Set the carby up to do that; needle, jetting. Then add Dafydd's idea of an auto-rich solenoid that simply fools the carby into delivering more than required if in abnormal situation i.e. EFI failure. Perhaps also modify the existing 'choke' function on the carby to provide 'climb-rich' condition, that one simply pulls on at the start of the take-off run and leaves alone until throttling back to cruise climb.

 

Then size the injectors adequately to provide all the additional individual pot supply in normal circumstances so that when everything is running happily, the added injector droplet size is an efficient fuel-air mixture. That is intended to mainly provide even fuel distribution to all pots at the best economy rate..

 

For electrical supply redundancy, I'd think a fairly small LiFePo4 battery could be plumbed in, utilising the more reliable charging functionality of the CAMit standard-type alternator that has much better protection from dangerous voltage spikes than the Jab style alternator. In fact, I don't think I'd be happy even running the EFI box from anything other than a well-regulated supply, for safety reasons, and certainly NOT any LiFePo4 type battery. Even quite a small (say around 1 kg, 8300 mh-hour HobbyKing battery) should, I'd think, give a decent amount of EFI-running capability - enough to get well along the way to a bug-out destination and set up a get-there height profile that assumes you may need to go back to carby-only power settings.

 

It would take some intelligent system design for both the fuel and electrical supply, but the beauty of the EFI supplementary is that once the EFI is programmed, it should be possible to apply the entire package to any Jab engine and the EFI will handle the different individual engine / operation characteristics.

 

Well, that's my theory... cue the dance of the effema angels-on-a-pinhead philosophers..

 

 

[Oscar]

JJ - the SDS kit is very impressive - but I think it doesn't have the capability to change distribution to each pot individually, or have I missed something? I think it's kind of one-step-further-removed from being an add-on idea, more a replacement.. and for those interested in taking that step, certainly worthy of major consideration.