Reduction gear vs direct drive

[danny_galaga]

Seems to me the two big contenders for LSA are the Rotax 912 and the Jabiru 2200. What are peoples thoughts on the two? My own thoughts are these:

 

Rotax 912 seems to have a great reputation for reliability and have quite a few years up their sleeves for fine tuning the design. Jabiru have had some hiccups not long ago but hopefully reliability issues ironed out .

 

Gear drive apparently adds quite a bit to the cost of the Rotax 912 and I suppose means more parts to wear out. Direct drive on the Jabiru might mean higher fuel consumption inherent in slow-revving design?

 

Again with simplicity the Rotax seems to have more parts associated with oil and water cooling. But then that seems to me the partial water cooling would reduce the amount of shock cooling on long descents.

 

Jabiru I imagine should be a fair bit cheaper, being of local manufacture. And it would certainly be nice to buy local.

 

I think if all things were equal I would prefer a direct drive engine, but of course all things aren't equal. Cost, reliability, simplicity. Different amounts of each in those two motors.

 

Discuss!

 

 

[bexrbetter]

Discuss!

In the case of these 2 that you are comparing directly here, I feel you get what you pay for.

Depending on plane, I think the Aeromomentum is a valid choice too, especially if you are hedging over money, and especially long term costs.

 

 

[Guest nicephotog]

You would want to see this PDF produced by the ATSB (Australian Transport Safety Bureau)

 

It mentions engine failures p/10,000 in four manufacturers including Rotax and Jabiru.

 

ATSB intro page URL:

 

Investigation: AR-2013-107 - Engine failures and malfunctions in light aeroplanes 2009 - 2014

 

report URL:

 

https://www.atsb.gov.au/media/5769864/ar-2013-107-final-report.pdf

 

 

[bexrbetter]

I see the Aeromomentum had no failures at all so the choice is clear - that's the sort of twist you can do with statistics you know.

 

There's a couple of brands there I know for fact there has been more failures than listed, so the actual number's validity worries me a bit.

 

But at the end of the day, all those reports tell me is get a BRS parachute.

 

 

[cscotthendry]

Seems to me the two big contenders for LSA are the Rotax 912 and the Jabiru 2200. What are peoples thoughts on the two? My own thoughts are these:Rotax 912 seems to have a great reputation for reliability and have quite a few years up their sleeves for fine tuning the design. Jabiru have had some hiccups not long ago but hopefully reliability issues ironed out .

Gear drive apparently adds quite a bit to the cost of the Rotax 912 and I suppose means more parts to wear out. Direct drive on the Jabiru might mean higher fuel consumption inherent in slow-revving design?

 

Again with simplicity the Rotax seems to have more parts associated with oil and water cooling. But then that seems to me the partial water cooling would reduce the amount of shock cooling on long descents.

 

Jabiru I imagine should be a fair bit cheaper, being of local manufacture. And it would certainly be nice to buy local.

 

I think if all things were equal I would prefer a direct drive engine, but of course all things aren't equal. Cost, reliability, simplicity. Different amounts of each in those two motors.

 

Discuss!

I think you summed it up pretty well there.For me, reliability is the most important factor in an aircraft engine choice.

 

The purchase price of the engine is a one off cost.

 

I've heard a lot of Jab owners say "Rotax spares are so expensive" which is true, but apart from consumables, the Rotax engines mostly don't require spares.

 

As for the complexity of having a gearbox, that is also true and as the saying goes "more things to go wrong" but the Rotax gearbox has a lot of history of reliable operation. That's saying something because with a lot of other types of engines (particularly converted car engines) the PSRU is the part that seems most prone to failure regardless whether it's gears or belts.

 

One of the side benefits of the gearbox in the Rotax (particularly the 100HP) is that it protects the crankshaft somewhat in the case of a prop strike. In a direct drive engine, a prop strike will most likely bend or possibly break the crank.

 

 

[Guest nicephotog]

bexrbetter..."But at the end of the day, all those reports tell me is get a BRS parachute."...

 

Either personal or aircraft parachutes are not the answer to it in Australia,

 

Just arguing in another thread,

 

it's modern STOL systems since 2010 to 2013 experimental license kit builds have some excellent systems of which one of the most important features is the undercarriage in 4 seat STOL not merely runway roll . along with it however is also stall speeds and glide.

 

The video again for the same purpose of attempting find what people see in this point, Australia is too vast geographically and the tax department is too vast to have engine failure and lose the investment to non appropriate equipment !

 

 

 

[danny_galaga]

Some good points there guys! Another thing I hadn’t thought to list is I guess the jab 2200 only comes as 85 hp whereas you have a 100 hp option with the rotax. I hadn’t thought about the traditional guys but I am guessing the cost and maintenance on a continental would be quite high. Also hadn’t considered the safety feature of a gearbox in regards a prop strike.

 

Looking at that engine failure report it would be interesting to see what the failure rates of the new jab engines are. But that will take time for the data. I’m not waiting around THAT long to find out

 

 

[Guest nicephotog]

The ATSB report dates 2014

 

This link in that document is for Jabiru dates 2015 (update into it)

 

http://jabiru.net.au/images/JSB031-3_Through_Bolt_Replacement_and_Upgrade.pdf

 

Of Jabiru, it makes an 80 HP and a 120 HP , It's a great pity it does not understand 0-350 Lycoming is quite common

 

and hence make a 160 HP and a 220 HP (thereabout), along with perhaps other aircraft mounts for it .

 

(Also part of the technical spec of STOL is the HP for takeoff climb - a "sort of" overpowered aircraft for safety performance purpose on takeoff)

 

 

[Camel]

Some good points there guys! Another thing I hadn’t thought to list is I guess the jab 2200 only comes as 85 hp whereas you have a 100 hp option with the rotax. I hadn’t thought about the traditional guys but I am guessing the cost and maintenance on a continental would be quite high. Also hadn’t considered the safety feature of a gearbox in regards a prop strike. Looking at that engine failure report it would be interesting to see what the failure rates of the new jab engines are. But that will take time for the data. I’m not waiting around THAT long to find out

You seem to have the right idea about the differences but one more very important thing is what sort of plane, you said LSA so that means it's designed by the manufacturer, if it was kit and you could use any engine then another consideration is if it is stol you may have cooling problem with an air cooled motor also an engine with a gearbox is able to develope power quicker than a direct drive, my preference is air cooled and direct drive , I like the Jabiru 3300 and have a Jabiru 230, but I would still like more power, I had a Rotax ULS 100 with an in flight adjustable prop and it was perfect for short field work and steep climb, I would not dare attempt that in a Jab as the cooling is critical.

 

 

[danny_galaga]

Ah you have to forgive this noobs loose use of terms! I am talking kits. I don’t think I would go for anything too experimental (I have never been an early adopter). That Suzuki jobbie sounds like a good option for other people. A lot of kits seem to have mounts for jabiru and rotax so although I’d like to hear about what’s out there (for instance D motor) in all likelihood it will boil down to those two. I am doing my RA-aus conversation from GFPT at the moment so already familiar with the 912 in the tecnam the school uses but I haven’t even looked at a jabiru engine let alone flown with one.

 

 

[Guest nicephotog]

Sorry to reprint , the engine version seems to get around common in many aircraft , and would possibly make some sort of complete range if they ever developed them.

 

..."Of Jabiru, it makes an 80 HP and a 120 HP , It's a great pity it does not understand 0-360 Lycoming is quite common

 

and hence make a 160 HP and a 220 HP (thereabout), along with perhaps other aircraft mounts for it .

 

(Also part of the technical spec of STOL is the HP for takeoff climb - a "sort of" overpowered aircraft for safety performance purpose on takeoff)"...

 

 

[cscotthendry]

Ah you have to forgive this noobs loose use of terms! I am talking kits. I don’t think I would go for anything too experimental (I have never been an early adopter). That Suzuki jobbie sounds like a good option for other people. A lot of kits seem to have mounts for jabiru and rotax so although I’d like to hear about what’s out there (for instance D motor) in all likelihood it will boil down to those two. I am doing my RA-aus conversation from GFPT at the moment so already familiar with the 912 in the tecnam the school uses but I haven’t even looked at a jabiru engine let alone flown with one.

The D motor is an interesting one. Liquid cooled and very ancient, but proven side valve technology coupled to electronic ignition (and fuel injection I think). Slow revving and if other side valve engines are anything to go by, nearly bulletproof. Unfortunately they haven't been in use for very long and there's not a lot of planes about that have them, so the reliability is still a little unknown.

[SDQDI]

Personally I think it depends a lot on what sort of pilot you are, inasmuch as if you are meticulous about scanning gauges every few minutes and are perfect at watching temps on climb then you would be fine with a jab, but if you are like me and operate gear a bit rougher then the rotax with its water cooling is a lot more forgiving!

 

 

[bexrbetter]

That's saying something because with a lot of other types of engines (particularly converted car engines) the PSRU is the part that seems most prone to failure regardless whether it's gears or belts..

Could you back that statement up with some facts please?

 

The D motor is an interesting one. so the reliability is still a little unknown.

Well, no, they have had known failures, enough for them to go back and redesign them again, and you are starting all over again with the unknown on the second design release.

I've actually grown to like the concept after initial shock of, and laughing at someone releasing a sidevalve, but why on earth would you take one over a Rotax 912 at the similar price.

 

 

[danny_galaga]

Personally I think it depends a lot on what sort of pilot you are, inasmuch as if you are meticulous about scanning gauges every few minutes and are perfect at watching temps on climb then you would be fine with a jab, but if you are like me and operate gear a bit rougher then the rotax with its water cooling is a lot more forgiving!

Hmm, in that one sentence you may have just narrowed it down for me

 

 

[pmccarthy]

The time it matters will be when you are caught on the edge of bad weather and have to climb quickly while manoeuvring around a lot of low cloud. Ask me how I know, it happens even though it shouldn't! Then five minutes later you remember you haven't looked at the engine instruments and the temp is way up. You may be good at managing a normal climb but other things can get your attention.

 

 

[Geoff13]

Ah you have to forgive this noobs loose use of terms! I am talking kits. I don’t think I would go for anything too experimental (I have never been an early adopter). That Suzuki jobbie sounds like a good option for other people. A lot of kits seem to have mounts for jabiru and rotax so although I’d like to hear about what’s out there (for instance D motor) in all likelihood it will boil down to those two. I am doing my RA-aus conversation from GFPT at the moment so already familiar with the 912 in the tecnam the school uses but I haven’t even looked at a jabiru engine let alone flown with one.

The D Motor uses the Jab engine mount so no problems there.

But as you said you are not normally an early adopter so that probably cuts you out from both DMotor and Jabiru.

 

Lets not be under and false assumtions about the new Jab motor, It is still totally unproven and in fact has had some issues.

 

 

[Yenn]

Geoff 13. Would you care to enlighten us on the new Jab motor issues?

 

 

[SDQDI]

Geoff 13. Would you care to enlighten us on the new Jab motor issues?

Bruce did mention some hassles in post 187 I think, but bear in mind these are the first of the first.Question - Latest Jabiru 2200 - reliability

 

 

[Ian West]

Seems to me the two big contenders for LSA are the Rotax 912 and the Jabiru 2200. What are peoples thoughts on the two? My own thoughts are these:Rotax 912 seems to have a great reputation for reliability and have quite a few years up their sleeves for fine tuning the design. Jabiru have had some hiccups not long ago but hopefully reliability issues ironed out .

Gear drive apparently adds quite a bit to the cost of the Rotax 912 and I suppose means more parts to wear out. Direct drive on the Jabiru might mean higher fuel consumption inherent in slow-revving design?

 

Again with simplicity the Rotax seems to have more parts associated with oil and water cooling. But then that seems to me the partial water cooling would reduce the amount of shock cooling on long descents.

 

Jabiru I imagine should be a fair bit cheaper, being of local manufacture. And it would certainly be nice to buy local.

 

I think if all things were equal I would prefer a direct drive engine, but of course all things aren't equal. Cost, reliability, simplicity. Different amounts of each in those two motors.

 

Discuss!

Hi allI have always been a fan of slower revving engines - less wear at 2800 RPM than at 5500RPM and do like a direct drive as stated there are less moving parts and of course the weight consideration. I have a Jabiru early LSA that has the generation 1 engine which has never given me any trouble or cause for concern. This engine has the solid lifters and there has never been any through bolt issues with this generation 1 type. I am not sure whether the later 2.2 engines had a higher compression rate that might have been causing the older sized through bolts breaking. Any way I have had over 500 hours of trouble free operation on this engine.

 

Regards

 

Westy - 3261

 

 

[bexrbetter]

Hi allI have always been a fan of slower revving engines - less wear at 2800 RPM than at 5500RPM

Not true.

 

there are less moving parts and of course the weight consideration.

Why don't you guys buy 2 strokes then, you can't get "less moving parts" count and lower weight.

Aircraft engines will stay being sub-standard as long as the market continues to make it's demands based on nonsensical myths and lore.

 

 

[Guest Guest]

It's always an interesting subject, the reliability of aero engines, I enjoy reading people's opinions etc. To me it boils down to one thing, risk, what price do you put on risk yourself? The "price" is foremost your life, second consideration is the loss of an airframe, the rest is academic.