Jabiru experience

[jetjr]

Id love to see some evidence that the 45kt stall and 600kg was developed from some data, of any kind. Even CASA proposed 760kg for a while.

 

I agree re the technology and materials are improving

 

The hard reality is most of our accidents are result of poor descisions not tecnical issues BUT old rules not based on evidence dont help

 

 

[Ada Elle]

The point here is that the MTOW limitation is not structural but related to stall speed and therefore has little to do with safety as being implied.Without doubt its the rules we operate under and breaking them is illegal. Thats a different debate to it being unsafe.

The details discussed provides basis for the push for altering stall/MTOW limitation currently in place to something more appropriate.

Well, no - if the MTOW limitation was not structural, then they could have tested/certificated to greater than +3.8/-1.9. You don't actually know what the limitation on MTOW is.

 

I'm now very confused about the Jabiru speeds.

 

Vs1 is 53KCAS; Va is 102KIAS (or 97-98 KCAS according to Jabiru's tables). They mention that stall speed is reduced with aft CoG (supporting Oscar's statement about elevator authority) but not by how much. 97KCAS/sqrt(3.8) is 50KCAS, which sounds pretty reasonable for Vs at full aft CoG.

 

However, I thought that the reason that Va is related to Vs is so that the aircraft will stall before it breaks. If Vs is not an aerodynamic stall speed in this instance, does this calculation for Va still apply?

 

Also, we had the discussion that higher weight == higher stall speed == more chance of stall/spin on turn final == less safety.

 

 

[jetjr]

Why would they test to higher limits than required.

 

Most of my comments relate to larger version where you have several wings and MTOW to compare inc speeds. They all have wider elevator

 

The point re stall ned spin is appreciated but its just 3kts kias from 544 to 700kg.

 

 

[Bruce Tuncks]

My experience is in line with Nobody's post #12. After suffering a prematurely-worn exhaust valve seat at 50 hours, I reckoned that the factory setup needed some improvement and so I replaced the rear 2 heads with the then new bigger-finned ones and worked on the cooling system . Bigger cowl-holes with a better transition to the ducts, better sealing of the ducts, smaller hole to the lower-cowl and better directing of the air to the oil-cooler. The idea was to increase the pressure-differential between the ducts and the lower-cowl, and to ensure that all of the air entering the ducts went close enough to the cooling-fins to pick up some heat.

 

Added CHT senders so all 4 cylinders were monitored. It ran about 15 degrees cooler and went 13 years and 450 hours with no problems until I got it too hot some weeks ago when ground-running while using a dynamic balancer. The exhaust-valve seat of No.4 came loose. It's flying again now and I'll be even more careful of those cylinder-head temperatures than before.

 

I don't regret buying the Jabiru engine for a moment.

 

 

[Oscar]

Bruce:

 

Was chatting to (and looking at his aircraft) a bloke down at Camden about two weeks ago, who has been patiently and very, very thoroughly working on his J160 C cooling. He's an engineer so he's fully instrumented everything, records his results and flight-tests every change (often in a range of ambient temps.) The word 'meticulous' for his work is probably selling him short - he's even put borescope cameras into the back of the ram ducts so he can observe the behaviour of the baffles ( I assume, though he didn't mention it, that he tufts the baffles so he can observe and record the airflow patterns).

 

He got 1000 hours out of his first engine and changed to a new engine only because he's by nature conservative and reckoned it a better investment than a full top overhaul ( it had given him nothing but excellent service). He now has about 450 hours on the second engine - but here's where the story starts!

 

He had only one cht on the first engine - on No. #4 He'd never seen seriously high temps on it - but with the new engine, he put full cht and egt monitoring and was quite shocked to see that some pots were up to 40C hotter than no.#4 in certain flight conditions (75 kt climb-out, 32C ambient day - i.e. getting around 180C when he'd never really seen much more than about 140 on the single cht.) He's been modifying the baffles inside the ram ducts - with advice from Jabiru, I must add - and also with extended lips on the outlet ducts either side of the front leg. He's now getting no more than about 5C difference across all pots and a pretty-much constant 140C average - climb-out at 75 kts in up to 32C ambient, but he commented that it really takes quite careful work to get there - and the baffles differ in size and shape from left to right hand side, which makes sense due to the rising prop on the lhs and falling on the rhs.

 

He is seeing better than 6" of water in the p-delta between the ram-ducts and the exhaust to the lower cowl virtually throughout the flight range, though he feels that his extension lips on the bottom cowl are a wee bit too long and starting to cause a back-eddy on climb, and will trim them back slightly.

 

His next step will be to isolate the oil cooler air circuit from exiting into the lower cowl and reducing the low-pressure scavenging effect of the lower cowl air exits; something I've been working on myself. This is what I've come up with (though that only fits an entirely new cowl design that I've made):

 

 

This isn't the finished version; it plugs onto the oil cooler intake and exits through the bottom of the cowl ahead of the nose leg, and is totally supported by the cowl rather than being shaken by engine vibration. The intake and exit duct dimensions aren't quite optimal for pressure recovery through the cooler matrix, but reasonably close. I'm using a 7-row Aero Classics cooler ( pretty much line-ball for performance with the any of the 7-row Stewart-Warner type coolers, and PMA'd) and feeding it using a CAMit TOCA. It'll be some time before we can do flight tests and see if it works as expected..

 

The guy I was talking to is very enthusiastic about Jab's basic cooling set-up when fettled for optimal performance. ( now, how often have you heard THAT! - it's a first for me. ) I've seen exactly what he has done, and it's all subtle changes - a wee bit of a cut here, a wee bit of additional area/change of shape there..

 

What I get from all of that, is that getting optimal performance from Jab's basic set-up ( for the 160; like you, I have an earlier model that is really rather ugly in the basics) is a matter of fine-tuning to the individual aircraft. Once again, as has been discussed on a number of threads here, it requires attention to detail and it is NOT something that can be looked at and intuitively determined - real, accurate testing is required. And, ABSOLUTELY, full engine monitoring with recording capability is the key: Jab engines are killed from overtemp.

 

This guy's aircraft is only flown by him - no school use, no circuit-bashing come whatever the day throws at you. He does a lot of travelling - always happily, he's never had a moment's worry in around 1500 hours.

 

 

[jetjr]

totally agree and share your Camden mates experience. These are not engine problems but installation.

 

Other interesting things Ive learnt about CHT measurements - 500hrs ago fitted full EMS system, scared myself with variation. Thought I had it well sorted after hours of baffles and deflectors mods, with ring CHT terminals. Fiddly to seal and odd crazy readings so then fitted down hole adapters, bit hotter but OK, fitted rubber hose to insulate brass plug (inspired by Camit heat shield)... instant 10-20 deg rise in readings

 

200hrs passed and new engine inc CAE CHT fitted, importantly longer with cold junction in cockpit.....another 30 deg rise.

 

Now thats around 40-50 degrees hotter than indicated and probably had some heads well over 180 C at times before I started addressing it. Its no wonder there is issues in non optimized setups.

 

So now another round of effort duct sealing, deflector adjusting and playing with oil cooler intake. End result is very stable 130-140 deg C. For a tight engine pretty good.

 

Used to use cooler blocking plate to regulate oil temp, with TOCA no longer needed but too much air bypasses heads without it. Your duct looks excellent - want to make another of the rear half?

 

Under barrel deflectors help stablize temps well. Some discussion that roughening and painting heads helps temps too.

 

I do feel for factory built purchasers led to believe all this is sorted out before delivery.

 

 

[Oscar]

JJ - all SO true.

 

When we were setting up the Test cell, we calibrated the (CAMit-supplied) cht's back to the mgl recording instrument inside the cell control room. The cold junctionsare in the engine running room.. The apparatus was basically a brass rod of about 100 mm diameter x 250mm length, heated by a domestic stove hotplate, with both Laboratory mercury thermometers ( two, for redundancy) and an IR temp. indicating non-contact probe. Aggregate accuracy: +/- 1.5 C at all temps from about 18C to 220C.

 

We calibrated at 5C intervals from ambient ( about 18C ) through to 220C and back again: nearly four hours elapsed in total, because the thermal mass of the brass block was enough to do a roast for four, with crispy potato chips on the side.. The cht probes tested were CAMit probes, screwed down to the brass block. The MGL Strato instrument was within 2C of the calibration block temp. throughout.

 

As you have basically indicated if the cht instrument is a simple device and the cold junction is not ambient compensated, the apparent chts can be way, way out. This leads to the oft-repeated experiences of Jab. operators believing that they have never operated the engine over-temp. - on the evidence they have had - and Jabiru saying that the physical evidence shows that the engine HAS been operated over-temp. BOTH assertions are true, from the information available to each party.

 

I would concur that factory-built Jabs. have inadequate calibration of cooling performance ex-factory. I believe that it would have saved a great deal of pain all around, if Rod Stiff had added a couple of $K to the factory price and ensured that each aircraft delivered, performed to spec.

 

The phrase 'for the sake of a ha'penny worth of tar' springs to mind. The flip side - I believe - is that there is a very, very good aircraft available PROVIDED it is 'final-finished'. I personally will fly in ANY jabiru, but not some of the competition - for instance Stings, RV6's, Lancair 3x series, Cirrus anythings, Gazelle's, at any offer of reward.

 

 

[DrZoos]

This guy's aircraft is only flown by him - no school use, no circuit-bashing come whatever the day throws at you. He does a lot of travelling - always happily, he's never had a moment's worry in around 1500 hours.

That is the problem in a nutshell......any pilot or flight school with multiple pilots (many of who have limited knowledge of the intimacies and idiosyncrasies) should be able to buy and fly by maintaining it to a maintenance manual, flying it to a POH and not have to nurse and monitor the thing like its in intensive care unit.

 

 

[facthunter]

Yes it really is difficult, and it's the same with every aero motor, in principle. If it's getting too hot, increase climb speed. Some engines weren't installed properly. That is obvious. You have to install ALL motors properly. If this is done, I can't see that you need an array of CHT readings on the panel, once the installation is proven. Nev

 

 

[Oscar]

Fine, good point Dr. Z.. Will you put your own airplane on the line?

 

 

[DrZoos]

I believe - is that there is a very, very good aircraft available PROVIDED it is 'final-finished'.

Absolutely it is and still can be, but it needs a few mods to bring it back to decent for the ordinary man...most pilots are not as inteliigent or well informed as you and

 

Fine, good point Dr. Z.. Will you put your own airplane on the line?

No i wont because of hard landings, but if I was a club executive or wasn't flying my aircraft as much as I currently do, I would have every faith in my rotax to survive...we currently have 2 aircraft in our club both with Rotax and they are accumulating around 1500hrs per year and 800 per year with no problems. One aircraft is at 3000 hours on its second engine and not a single issue with temps or engine

Our previous foxbat went through 3 Rotax engines to TBO no issues, then it was written off from a front wheel collapse...

 

 

[Happyflyer]

I personally will fly in ANY jabiru, but not some of the competition - for instance Stings, RV6's, Lancair 3x series, Cirrus anythings, Gazelle's, at any offer of reward.

Of those, I have flown a Jabiru, RV6s and a couple of Cirrus aircraft. You are missing a wonderful flying experience by not flying an RV. Beautiful, light on the controls, responsive, fast. RV's are, in my opinion, the worlds best designed home build aircraft. Cirrus aircraft also are a joy to fly.

 

 

[Oscar]

Absolutely it is and still can be, but it needs a few mods to bring it back to decent for the ordinary man...most pilots are not as inteliigent or well informed as you andNo i wont because of hard landings, but if I was a club executive or wasn't flying my aircraft as much as I currently do, I would have every faith in my rotax to survive...we currently have 2 aircraft in our club both with Rotax and they are accumulating around 1500hrs per year and 800 per year with no problems. One aircraft is at 3000 hours on its second engine and not a single issue with temps or engine

 

Our previous foxbat went through 3 Rotax engines to TBO no issues, then it was written off from a front wheel collapse...

Which is, somwhat, the point that Jab. operators tend to make: there are always trade-offs, nothing is perfect nor bullet-proof. I believe that there are sites (and operations) for which a Jab. engine just is not a good choice, and certainly, Rotax will take far more 'punishment' than a Jab. engine. However, there are quite a few sites that have very successfully operated Jabs in their training fleet for years, and perhaps if we had better information about what it is they do differently to other sites that have had a bad time with them, we could assemble a better picture of the tricks and tweaks that make the difference.

 

 

[jetjr]

Looking at it from another viewpoint

 

What IF Jabiru/Camit/Bex/Oscar/Me .........comes up with engineering solutions which allows Jab engine to run to TBO reliably.

 

Or perhaps the new 2210 version turns out to be a great step forward.

 

You'd have whats agreed is a great training airframe with engine nearly half the price. Both locally supported.

 

Link in the issue that many other training aircraft are imported and your looking at major business cost impacts for a flight school

 

Relying on big companies located overseas for small volume products means high prices or high risk.

 

 

[Icarus]

A few things.

 

Jabirus now come standard with Dynon 7" Flight DEK D 180 glass panel with full EGT CHT temp monitoring for all cylinders.

 

The 750kg MTOW {South Africa and some here} in the 230/430 at least is due to the Fact that the aircraft was designed with an extra 10% safety Buffer built in. on top of the normal ultimate load factor.

 

This info was from Rod Stiff himself.

 

My TIF was at Lismore on a 30* day.

 

We landed downwind aprox 3 knots over hot tarmac in a J170 . I now understand what F L O A T I N G a landing means. That long runway got shorter ,,,and shorter .........

 

 

[bexrbetter]

come up with engineering solutions which allows Jab engine to run to TBO reliably.

I would make one piece heads for them, spread the stud loads and spread the heat more evenly.

 

I would also work on getting rid of the spaghetti underneath.

 

 

 

[jetjr]

You gotta have all that spaghetti somewhere

 

Having left and right heads would simplify 3300 maybe?

 

 

[facthunter]

The way that is done is the most common. At least the carburetter is under the motor.(where it can gravity feed in some installations and fuel won't run all over the motor if it floods). I don't like float carburetters on aircraft. A mechanical fuel injection would be OK (to six points). The carb would only be a throttle body with air cleaner. No carb heat required..Nev

 

 

[bexrbetter]

You gotta have all that spaghetti somewhere

Can be done a lot better, I got a complete 2200 3D last night to play with actually, just converting it from 54 megabytes to a usable Sketchup size, if anyone wants it let me know.

 

 

The way that is done is the most common.

I used to smash my feet with a hammer until someone pointed out that it was what was causing my feet to hurt, doesn't hurt anymore since I stopped.

 

A mechanical fuel injection would be OK

By "mechanical" you must mean the part now in 2015 where you mechanically turn the key to start the engine and then all the electronics inside the EFI's computer do the rest.

 

 

[Oscar]

The problem with mechanical FI ( or single-point EFI, for that matter, e.g. megasquirt Mk 1 or SDS) is that it does not correct for mixture difference at each cylinder and thus take out the varying difference with fuel/air ratio at different revs. The basic Jab. set up is extremely badly affected by swirl from the induction system feeding different air/fuel ratios to different inlet tracts through a very small plenum at different inlet airspeeds.

 

It is possible - by tiresome experimentation - to get reasonably even mixture throughout the normal rev. range, but add power load in and it's still pretty arbitrary.

 

Multi-point EFI would solve a huge amount of the fuel/air ratio problems for Jab engines - and they are ALREADY built - for Drone use - with individual injectors in the inlet tracts - but the regs. won't allow that to be used on normal aircraft. That is a hang-over from electronics reliability perceptions of about 20 years ago, and nobody - including the FAA - is prepared to undertake a sensible risk assessment of using readily-available EFI solutions vs. the problems of 'conventional' systems. The actual lowering of fuel quality for other than 100LL adds to this situation - whereas modern EFI systems can cope extremely well.

 

Frankly, it's a wonder that we have been able to progress - given the extreme conservatism of the relevant authorities - beyond flint-and tinder for ignition and drip-feed for fuel. Don't blame Jabiru for the state of the regs. under which they have to operate.

 

 

[DrZoos]

Sack the entire FFA with the entire CASA and lets move on!

 

 

[jetjr]

SDS is multiport injection setup

 

Bing is a single point mechanical system :) buggered up by swirling air

 

Have to say my newest one is pretty good distribution.

 

 

[Oscar]

Ah, yes, apologies: SDS is multiport injectors BUT not individual inlet tract control. The 'squirt' is multiport, but the control is ( unless I am now out of date), mass.

 

 

[jetjr]

Yep, correct

 

but seeing as its even distribution and injected near head it should be a big improvement.

 

Maybe not as good as Id hoped though, still 80-100 deg spread, see EMS pictures on this page.

 

http://www.avcom.co.za/phpBB3/viewtopic.php?f=59&t=137074&start=495

 

 

[Old Koreelah]

...J160 C cooling...isolate the oil cooler air circuit from exiting into the lower cowl and reducing the low-pressure scavenging effect of the lower cowl air exits; something I've been working on myself.

[ATTACH=full]38850[/ATTACH]...

Very interested in how that works, Oscar. My installation works okey but I reckon it can be improved. I'm about to remove my ram-air ducts and replace them with a simple fence that seals against the cowl. If I can get the sealing right it should cool better, but I need to get as much suction below the engine as possible. Best way might be to totally separate air flow to the oil cooler and the engine, and have a cowl flap for each.

 

I have heard from a source at the factory that someone put a lot of work into a similar setup but went back to standard ram-air ducts.

 

Would be nice to know more before I start cutting.