"Jaberoo" down (Mildura this time)

[rankamateur]

Dear Santa,Please may I have one of these for Christmas? I'll be ever so good.

Really another unproved, improvement on a proven design, made mine a standard one thanks.

 

 

[jetjr]

Theres an SDS kit being fitted and reported on Avcom currently, it is a full spec EFI with new TB and dual pumps.etc

 

Avocet is running SDS setup too I think

 

Agent in SA used Bing as throttle body and changes over seamlessly.

 

Re fuel distribution, i have two of those flow straightners in mine, both helped but still pretty bad, what really does help is carb heat.

 

Has been discussed using only in cowl air and jetting to suit, apparently "protected intakes" are permitted and understood even in GA world

 

Before someone says it, power output is hardly effected in 3300

 

 

[rankamateur]

Re fuel distribution, i have two of those flow straightners in mine, both helped but still pretty bad, what really does help is carb heat.

Are these straighteners like the Hyclones sold by a Queensland company to improve power and fuel economy in vehicle engines?

 

 

[dlegg]

Theres an SDS kit being fitted and reported on Avcom currently, it is a full spec EFI with new TB and dual pumps.etcAvocet is running SDS setup too I think

Agent in SA used Bing as throttle body and changes over seamlessly.

 

Re fuel distribution, i have two of those flow straightners in mine, both helped but still pretty bad, what really does help is carb heat.

 

Has been discussed using only in cowl air and jetting to suit, apparently "protected intakes" are permitted and understood even in GA world

 

Before someone says it, power output is hardly effected in 3300

I disconnected jab airbox inlet entirely and test flew without anything attached to carby inlet and could not believe watching CHT's all average 120c(normally 150c or above) and all EGT's nearly the same as well. I would like to try just a pod filter but lack of room prevents this. Is the standard Jab airbox too restrictive?

 

 

[bexrbetter]

Really another unproved, improvement on a proven design, made mine a standard one thanks.

If you have a look at the breadth and range of Bombadier/Rotax engine products you will find that the 912 is a very modest engine indeed by their standards.

 

They are a very competent engine company at the very highest levels and have world leading products using EFI and DI and sure, everyone can go through teething troubles, but I wouldn't hesitate in trusting there offerings/upgrades.

 

Of course the highlight of their product range is the BMW F650 engine made just up the road from me .

 

 

[Dafydd Llewellyn]

I disconnected jab airbox inlet entirely and test flew without anything attached to carby inlet and could not believe watching CHT's all average 120c(normally 150c or above) and all EGT's nearly the same as well. I would like to try just a pod filter but lack of room prevents this. Is the standard Jab airbox too restrictive?

Thank you; that's a most interesting piece of information; the engine in the test cell does not have the Jab airbox, at the moment it has a pod filter; I'm hoping to be able to run it early next week (still a lot of instrument wiring to install and test). After it's been run in, in the test cell, it goes into an aeroplane, so we'll be able to get a direct comparison similar to yours.

The question of restriction from the induction system can quickly be assessed by putting a manifold pressure gauge on it; at full throttle, you should not see more than about one inch of manifold pressure lower than what the gauge read before the engine was started.

 

I suspect - but do not yet know for certain - that the problem is mainly due to the "difficult" run to the carbie inlet, necessary to clear the corner of the firewall; the "tight clearance" cobra head is something to be avoided, I suspect - but we don't really know until it's been properly tested. That sort of thing has the potential to induce a virtual tornado running through the carbie and on into the plenum - but we don't yet know for sure whether it really does this. We may know that pretty soon; it's something that can be tried.

 

The induction system in the aircraft - tho not in the test cell - MUST be equipped to provide not less than 50 degrees C temperature rise in the air entering the carbie, when carburettor heat is fully ON. That is required at 75% power, and it has to be tested in flight. So any changes there must be tested and approved unless the aircraft is -19 or VH experimental; and if you make such a change in a -19 or VH EXP. after flying off your required hours, you'll have to do that all over again - so anybody wanting to try this needs to think before doing so.

 

 

[rick-p]

Thank you Rick for the feed back. And it is great to here that you are not having cooling issues, sounds like your airframe / engine combination is working well.

Dazza also the maximum revs I have on the prop and engine combination I get is 2650 revs and I cruise at 2150, 95 knts using about 11 to 12 litres per hour.

 

There seems to be enough fuel going through to keep things cool enough.

 

My motor runs pretty constantly about 145 CHT only on one occasion on a very long climb out did it get to 179 deg , the EGT 580 to 600 and oil temp 70, the highest it has ever been is 81 deg.

 

The airframe of my aircraft is quite slippery, very little drag and maybe the combination of it all is what suits the Jab motor best.

 

I do know that of the 6 Jab motors being used in my club in the Philippines apart from 2 problems I don't know of any others.

 

The 2 problems were explainable.

 

First, one of the operators went back to the States for 12 months it wasn't run and the motor ceased up with corrosion.

 

The other problem was chaffing of the crank case, this was caused by detonation through the use of inferior fuel and that's it.

 

Nearly all the motors have better than 500 to 600 hrs.

 

I wish someone could explain it all to me as in my experience the motors have worked well.

 

Thanks for listening.

 

 

[Dafydd Llewellyn]

Are these straighteners like the Hyclones sold by a Queensland company to improve power and fuel economy in vehicle engines?

Never seen of heard of them; Ian McPhee made those himself.

 

 

[Dafydd Llewellyn]

Are these straighteners like the Hyclones sold by a Queensland company to improve power and fuel economy in vehicle engines?

No, from the aerodynamic point of view, they're the exact opposite. And despite their crude appearance, they helped to even out the EGTs in the Motorfalke installation, which I approved under my CAR 35 authority in 2007. No snake oil involved, if that's what you mean; the plenum on the engine into which the carburettor delivers the fuel/air spray, is designed on the assumption that the air goes straight through the carburettor, i.e. the airflow is not moving in a spiral as it goes through the carbie. If that's not the case, the fuel spray will be off-centre in the plenum, which will mean the distribution pipes from it will not get an even share of the fuel spray. This is because the fuel is still largely in the form of droplets of liquid at that point; it hasn't had time to become vapour.

They are not a complete answer, but they can improve matters if the airbox is inadvertently generating a swirl in the air as it goes into the induction duct.

 

The Hiclones do look like snake oil to me.

 

 

[Dafydd Llewellyn]

Thanks, Deb.

 

 

[jetjr]

To add to the issue of induction swirl, it seems to change with rpm, which does make sense, egt go up and down as expected with needle position BUT it the spread of EGT thats alarmng. I have one which is hottest in climb, a different one (on the other side) in cruise and a different one again for power off descents

 

Regularly use carb heat to bring them into my limits

 

By installing under barrel deflectors, it has definitely helped stabilise CHT

 

I have seen some data from a Camit installation and egt were excellent spread, cht a little high and uneven though.

 

.

 

 

[Dafydd Llewellyn]

To add to the issue of induction swirl, it seems to change with rpm, which does make sense, egt go up and down as expected with needle position BUT it the spread of EGT thats alarmng. I have one which is hottest in climb, a different one (on the other side) in cruise and a different one again for power off descentsRegularly use carb heat to bring them into my limits

By installing under barrel deflectors, it has definitely helped stabilise CHT

 

I have seen some data from a Camit installation and egt were excellent spread, cht a little high and uneven though.

 

.

Thanks, JJ. The picture, thanks to Dlegg, JJ and Deb, is that there is a mixture mal-distribution issue; and it is significantly reduced if the induction air is warmer. Flow-straighteners in the duct upstream of the carbie help a bit, but are not a complete fix.

 

However, a note of caution: The result Dlegg had, in reduction of the average CHT and EGT, from disconnecting the carbie from the airbox, is almost certainly due to the change this makes in the carburettor bowl venting; the air pressure in the airspace above the fuel in the carburettor bowl has a major effect on the overall mixture; there were some bad experiences in the work-up of those engine installations until it was realised that the bowl vent location had to be chosen so that selecting cold or hot air did not alter it. The Skyfox Gazelle installation initially had an enormous problem with this; the RPM drop from selecting hot air was about 2000 RPM. Once the correct vent location was found, the RPM drop disappeared. The Jabiru carburettor jetting is set so that it works with the factory bowl vent setup; when you disconnect the carbie from the factory airbox, this jetting is not going to work the same; the carbie bowl vent line would need to be plumbed to a flush vent in the side of a smooth-walled piece of tube that supplies air to the carbie, downstream of any air intake filter - and even that may not give exactly the same effect as the original. Dlegg evidently got some enrichment, but not so much as to stop the engine.

 

I'm assuming, of course, that these experiments were done on -19 registered aircraft; it would be illegal to do that sort of thing on a -24 registration.

 

Here's what I am starting to see from this:

 

1. Since there is no change in the airflow ducting downstream of the airbox when carby heat is selected, the reduction in EGT spread due to carby heat can only be that much more of the fuel spray is being converted to vapour before it gets the the end of the plenum; vapour goes where the air goes , but liquid droplets do not follow the air around corners very well. It should follow that aircraft in cold climates have a worse mixture distribution than those in warm climates.

 

2. Some, but probably only a minor part of the mal-distribution is due to air swirl in the flow coming from the airbox. How much of the effect is due to the system upstream of the carbie, and how much of it is inherent in the plenum / carbie system, may be something that can be examined in the test cell, by varying the induction air temperature (this is measured in the cell) on an intake that does not use the normal Jabiru airbox system.

 

3. Some variation in the distribution due to power setting is to be expected due to the deflection of the flow coming out of the carburettor by the throttle butterfly, especially at part-power settings; the butterfly should have least effect at full throttle.

 

4. Carburettor lateral tilt is a known contributor to mal-distribution; however its effect should be to move the fuel spray from side to side. It should be possible to learn something about the shape of the carburettor spray pattern by observing which cylinders show a rise in EGT, and which show a fall as the carburettor tilt is altered. This is also something I can investigate in the test cell.

 

I'm very grateful for the information you have provided; it comes very timely, because I can add a few bits and pieces to the test cell setup, and maybe get some useful information as a result, which I will pass on. This is "wildcat" research; you never know what it will produce. There's never time for this in the commercial pressure of a certification exercise; I'm having a ball, doing this in my retirement.

 

In the meantime, it is very hazardous to fly with the carbie heat system disabled. The principle of the carbie heat system is to ALTER the air temperature in the region of the throttle butterfly, sufficiently to move the temperature out of the icing zone. That can be achieved, in principle, either by normally running on cold air, and selecting full hot air when necessary; or by normally running on full hot air, and selecting cold air when necessary. Some engines object to being fed hot air when it is not needed; you can induce detonation that way, in an extreme case. So whilst it's a most valuable piece of test data, I don't advise adopting it as standard practice. There's a problem; we need to find a proper answer to it.

 

 

[rankamateur]

http://www.hicloneqld.com/products.html could be just what they need! Magic.

[Oscar]

Magic indeed! Now, if you added the Brock Polariser and carefully tuned the turbo encabulator, with an IFA prop you could actually generate fuel by descending with the prop in reverse pitch and the fuel pump turned to suck instead of blow, thus making all your fuel-stops into touch-and-goes and avoiding call-out fees. Low-cost flying- at last!

 

 

[Dafydd Llewellyn]

http://www.hicloneqld.com/products.html could be just what they need! Magic.

I see you're based in Warialda; I'm near Clifton, QLD. If you're up this way, why not drop in and see what we're doing?

 

 

[Dafydd Llewellyn]

Magic indeed! Now, if you added the Brock Polariser and carefully tuned the turbo encabulator, with an IFA prop you could actually generate fuel by descending with the prop in reverse pitch and the fuel pump turned to suck instead of blow, thus making all your fuel-stops into touch-and-goes and avoiding call-out fees. Low-cost flying- at last!

Negative entropy, in fact!

 

 

[rankamateur]

I see you're based in Warialda; I'm near Clifton, QLD. If you're up this way, why not drop in and see what we're doing?

I've got a new 912s still in the box, when I get it all put together I hope Clifton will be one of my regular distractions. I almost bit on the hyclones for my irrigation pump, but I just wasn't convinced, 23% fuel saving was the bait.

 

 

[Oscar]

To add to the issue of induction swirl, it seems to change with rpm, which does make sense, egt go up and down as expected with needle position BUT it the spread of EGT thats alarmng. I have one which is hottest in climb, a different one (on the other side) in cruise and a different one again for power off descentsRegularly use carb heat to bring them into my limits

By installing under barrel deflectors, it has definitely helped stabilise CHT

 

I have seen some data from a Camit installation and egt were excellent spread, cht a little high and uneven though.

 

.

jj, as we've seen (and discussed, with really useful contributions from yourself and a lot of others, in the 'Jabiru cooling' thread), there is so much variation in installation effectiveness between different Jabs. that until there is a 'standard' test done comparing a CAMit install and a standard Jab install on a specific aircraft with no change to the installation details, we're not likely to get any 'authoritative' data re one vs the other in terms of cht performance - unfortunately. Since CAMit use (at least currently) standard-machined Jab heads, (but with a different alloy that has higher temp tolerance), about the only differences one would expect would come from changes to the exhaust-valve heat dissipation ability from any changes to the valve seat and guide material and improvements to the barrel cooling, and they may actually slightly increase the cht slightly if the head is 'working harder' in getting heat away from these two areas.

 

Provided such slightly higher chts aren't going anywhere near becoming of concern, that isn't necessarily a bad thing IF what is happening is that existing 'hot-spots' - and particularly those that cause exhaust-valve failure and top-ring lead deposit caking - are being managed better. If they are being managed better - and testing will determine that - then the next step along the yellow brick road is to improve the cooling installation so it becomes more effective: better distribution to and around the heads and barrels, better cowl extraction etc. Once again, it's the old 'everything is part of a set of interlinked systems' approach - and your experience with under-barrel deflectors I believe is a good example. Work is being done in that area to develop a set of deflectors based on NACA reports, that will be tested to see what benefits they might hold - watch this space, as they say...

 

 

[Old Koreelah]

Thank you; that's a most interesting piece of information; the engine in the test cell does not have the Jab airbox... I suspect - but do not yet know for certain - that the problem is mainly due to the "difficult" run to the carbie inlet, necessary to clear the corner of the firewall; the "tight clearance" cobra head is something to be avoided...

.

I learned a little bit about this when I first installed my 2.2 engine. Being a clever sort of bloke, my air intake was under the belly just behind the prop spinner. A scat hose ran up to an air cleaner box mounted in that wasted space on top of the engine in front of the starter. From there another scat hose took the filtered air down over the back of the engine to a home-made cobra head.

It didn't work. It would not rev beyond about 1800. Don at the factory looked at my pictures of the installation and pronounced that the air must come from the side, as far back from the prop as possible.

 

I ripped it all out and installed the inlet down behind the firewall feeding into a large box between the rudder pedals. A hole punched thru the firewall feeds filtered air in a straight line to the Bing. Works well.

 

 

[Dafydd Llewellyn]

I've got a new 912s still in the box, when I get it all put together I hope Clifton will be one of my regular distractions. I almost bit on the hyclones for my irrigation pump, but I just wasn't convinced, 23% fuel saving was the bait.

Well, I still don't know how to initiate a conversation on this thread; but I'm quite happy to collect you from Trevor Bange's strip. If you're flying a Savannah, you should be able to use my tiny strip, weather permitting (not advisable in a strong westerly). Right now, it's cluttered with building trusses, though.

 

 

[Dafydd Llewellyn]

we stopped at Warialda years back it was prety quietthere is proberbly a hat behind the hangar where I spewed my guts out because it was so bumpy

 

By the way we took off the hose from the duct on cowl and not the hot box

Yes, I got that - means you were running on air that is probably around 25C warmer than the outside air - so the benefit you saw was wholly from increased vapourisation of the fuel spray. The difference between what you saw and what Dlegg saw is valuable info.

 

 

[Dafydd Llewellyn]

I learned a little bit about this when I first installed my 2.2 engine. Being a clever sort of bloke, my air intake was under the belly just behind the prop spinner. A scat hose ran up to an air cleaner box mounted in that wasted space on top of the engine in front of the starter. From there another scat hose took the filtered air down over the back of the engine to a home-made cobra head.It didn't work. It would not rev beyond about 1800. Don at the factory looked at my pictures of the installation and pronounced that the air must come from the side, as far back from the prop as possible.

I ripped it all out and installed the inlet down behind the firewall feeding into a large box between the rudder pedals. A hole punched thru the firewall feeds filtered air in a straight line to the Bing. Works well.

Yep - that's another clue. Ta.

 

 

[geoffreywh]

Hmmm. In my quest for efficiency (0-200 - Ram air) I put the air intake just behind the prop with the filter first! Then a right angle turn into the(smallish) plenum, several more right angle turns into the cylinder, works a treat. I guess yours was just too long?.....AS far as the air having to come from the side, I would say balls to that!....

 

 

[Dafydd Llewellyn]

You're talking about a Marvel-Schebler (Facet) updraft carbie - an MA-3 I imagine - aren't you? With a typical nose-mounted Bracket filter, feeding a selector valve bolted directly to the carbie? And feeding directly into the normal 0-200 "spider" manifold? Yes, that setup is normal for them, and works fine. I'm not sure how even the spread of EGT is, for the 0-200, never had a chance to play with one. Quite a different arrangement than the one on the Jabiru, though. The Jab installation might well benefit from going to a selector valve right at the carbie, though; it's one of the things I'd like to try.

 

 

[dlegg]

This is a copy of a blog from a pilot in the USA who flys a lot and puts a lot of hrs on a Jab 3300. He is currently on his second 3300, 900 hrs on the first, 600 on the 2nd. He bought a FWF kit from Jab USA and this is his thoughts.

 

Having flown my Zodiac XL about 600 hours with my Jabiru 3300 and Bing carburetor I must say it has had it good points and bad.

 

The short story is that initially the performance I got was quite poor. With some minor changes, performance improved to the point where it seemed acceptable. However problems remain which are perhaps serious.

 

Now the longer story...

 

First, in defense of Jabiru and the Bing I will say that the firewall forward kit I got with the engine did not properly address installation in the Zodiac. Essentially the kit seemed to encourage installation techniques that produced bad results and were in direct conflict with the installation recommendations in the Jabiru engine installation manual. Note too that the manual itself has improved over time. The most recently released manual (dated August 2009) is the best yet.

 

To make matters worse, when I built my airplane I was new to the entire process, so I hired a certified A/P to install my engine. He did a mostly reasonable job but actually did not read the installation manual. I assumed he knew what he was doing. I have learned: hay, it’s your life, read the manual no matter who is on the job.

 

The firewall forward kit I got failed to address the following two issues mentioned in the installation manual:

 

1) Do not connect scat tube directly to the carburetor.

 

2) Avoid a 90 degree bend from the side in the intake tube coming into the carburetor.

 

In addition, I have learned though independent study and personal experience that scat tube in general offers significant turbulence and drag in the intake system, especially when bent. If you choose to use it, use as little as possible and avoid sharp turns.

 

I no longer have any scat tube in my cold air intake system. I almost never use my carburetor heat system so I am not worried about scat tube in that system. In your climate, perhaps you need carburetor heat, in my climate I don’t.

 

With my initial setup, which had scat tube everywhere, I found that the engine ran very rich at higher throttle settings. At full throttle the engine burned about 13 GPH – not exactly what I was expecting! Also at 10,000 feet the engine ran so rich that it shook the airplane badly at full throttle. I knew something was wrong so I started looking into it.

 

I learned that air does not like to turn corners. Because the air traveling along the outside of the bend has further to go than the air traveling along the inside of the bend, turbulence results. Scat tube is not smooth, especially when bent. The uneven walls of the scat tube create drag and turbulence. Inducing turbulence right at the carburetor intake creates problems, especially for the Bing carburetor which as sense ports at its opening.

 

I have read that A 90 degree bend in an intake system produce drag that is roughly equivalent to 3 feet of straight tube. Because of the way my intake system was put together, when I computed the total effective length of the tube in my cold air intake system it came out to about 12 feet! What a mess. No wonder the engine was performing badly.

 

My cold air intake system now uses only radiator hose. The hose is as short as possible with as few bends as I could manage without a complete re-work of the system.

 

 

 

Simply eliminating all scat tube and replacing it with radiator hose eliminated the high fuel consumption and added a very noticeable amount of power – it was not subtle. However a new problem showed up. At wide open throttle the EGTs were very uneven. To help reduce this problem I added a piece of aluminum inside the radiator hose running from the air box to the carburetor. The aluminum is centered in the hose, is vertical and is bent such that it runs down the center of the hose as it makes the 90 bend. This helps the air make the corner, reduces turbulence and has evened out the EGTs a bit.

 

 

All these modifications were made about 550 hours ago. EGT temperatures are still not as even as I would like and vary considerably with throttle and altitude. Different cylinders are hotter than others depending on throttle setting. On some days when I fly at about 1,800 feet MSL and have a certain throttle setting at least half of the EGTs get too hot. It is necessary to change altitude or throttle setting. About 150 hours ago I re-pitched my prop to make it steeper. That lowered my engine RPM by about 100 RPM. That has helped keep this annoyance to a minimum but it is still there.

 

I have noticed that on my engine it is the back cylinders which seem to have high EGTs. I have always suspected that this is because their intake runners connect to the intake manifold on the extreme left and right. The Bing’s main jet is in the middle and the Jabiru’s intake manifold is quite small so mixture is unevenly distributed to the cylinders. The two rear cylinders run lean as a result. Just a theory mind you…

 

About 80 hours ago I found a burned exhaust valve on my number 5 cylinder. It was easy to replace but got me to thinking. Perhaps that cylinder has been running too lean.

 

More recently oil consumption has been going way up. The engine now burns about a quart every 4 hours. When I replaced the burned valve I notice some scoring in the cylinder wall. I am not sure but at this point I am suspecting broken rings on #5 which might explain where the oil is going. In the next day or so I am going to run another compression check with the hope of learning what is wrong and where the oil might be going.

 

So, is it possible that in 600 hours with un-even EGTs with the tendency for the rear cylinders to run lean I have shortened the life of my engine? I don’t know – I am just wondering…

 

I have been considering one or more modifications.

 

1) Redesigning the air intake to eliminate the 90 degree bend from the side. This would be done with a custom air box intake system to replace the radiator hose.

 

2) Replacing the Bing carburetor with a Rotec TBI-40.

 

In summery one of the Bing’s strengths is also one of its weaknesses: the lack of a mixture control. I like the simplicity. I don’t like the lack of control.

 

I am attracted to the Rotec TBI-40 because of the claim that EGTs are more even. I am not looking forward to re-running my throttle cable, turning my coke cable into a primer cable and adding a mixture control.

 

On the other hand I can’t say I am thrilled at the prospect of an early engine overhaul either.

 

I wish I had more information…