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Rotax 912 TBO (15 years) and On Condition


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Hey all,

 

So my bird has a Rotax 912ULS with only 320 odd hours on it. The problem is, it will be 15 years old (TBO) in 3 very short years. So I have a few questions I would love your opinion on.

 

1) - Would you try to offload it now, and put that coin towards a new one?

 

OR

 

2) - Would you wait for the 3 years and try and offload at TBO and do as above?

 

OR

 

3) - Would you keep it and run it "On Condition" as allowable under RAAus? (Private use only)

 

I would love to hear your thoughts. The engine has meticulously maintained, with all SBs etc completed.

 

Just scratching my head on how to proceed. I want to keep the airframe (also only 320 hours in) as it's immaculate, and I love it.

 

Anyways... Fire away.

 

Cheers

 

J

 

 

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I have had enough crap jobs on cars by qualified tradesmen to understand that there could be the same possibilities hopefully rare, on aircraft.  This is WHY I do all my own car repairs including engi

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I thought Rotax stopped any "on condition" authorisation and the RAA backed that up?

 

Personally, I would still run it but obviously for private use only. You couldn't "hire & reward" or use for any training.

 

If your engine is a 2007 build, it probably has the upgraded crankcase which make it a 2000 hr tbo also.

 

Which makes it more of a reason to keep running it.

 

 

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I thought Rotax stopped any "on condition" authorisation and the RAA backed that up?

 

Personally, I would still run it but obviously for private use only. You couldn't "hire & reward" or use for any training.

 

If your engine is a 2007 build, it probably has the upgraded crankcase which make it a 2000 hr tbo also.

 

Which makes it more of a reason to keep running it.

Hmm.. The manual states On Condition is OK - No mention of exception s to Rotax etc. And yes, it's the latter with 2000 TBO. Hence why I think there is still a lot of life left in it yet.

 

 

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What the engine maker says has a lot of effect on the legality of the situation if that's the issue. If you can get around that in a practical sense, I don't see why the engine shouldn't keep on running for many hours yet. Lot's of things have a shelf life so even if they never went into service they are time expired at some stage. Nev

 

 

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May be my story will put your mind at rest -

 

My 19 aircraft was commissioned in 2000, with a new Rotax 912 ULS. It is just about to receive its 900 hr service.

 

Apart from replacing the Sprag Clutch, the engine has been trouble free, still uses so little oil, that top ups, between 50 hr oil change services, are unnecessary. Oil pressure is excellent and compression & leak down tests (last 100 hr) are well within acceptable parameters.

 

The Sprag Clutch issue was probably caused (at least in part) by hanging on to poorly performing batteries, long after they should have been replaced. A shortsighted and costly "saving" which I will never repeat again.

 

My servicing is "by the book" using Rotax recommended coolant & oils, Rotax plugs & oil filters and for 5 year "Rubber" Rotax OM/supplied parts where appropriate and good quality automotive on the remainder..

 

I prefer to use ULP 98 Ron but will accept 95 and have once or twice, topped up with AvGas.

 

My 912 starts very well, delivers the expected power and runs effortlessly/smoothly hour after hour.

 

I warm my engine befor rolling, usually, climb out @ 5200-5400 rpm for 1-1500 ft/min, economy cruise at 100 knots indicated, 4800-5000 rpm, ground adjustable prop set for "advantage climb", for a fuel burn of under 13 L/hr one pilot and 13.5 L/hr two persons. My standard flight planning @ 14L/hr is very conservative. We can achieve 120 knots @ about 17L/hr, 5400 rpm, in level flight, but why?

 

In short I am very happy with my engines performance, even at 19 years of age and intend to go on running it until it shows signs that it may be nearing the end of its effective life.

 

 

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Thanks Skippy. That's great info.

 

98 Ron. Hmm. All of my manuals state 95. Very interesting. Your fuel burn is amazing. I have an in flight adjustable and I do similar to you. I have it pitched at full fine to climb out on takeoff at about 5500. Then cruise at about 5200 at WOT with the prop pitched up. That usually has me on about 110.

 

 

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I got 14.7 litres/hour on a long flight recently with the 100hp turbo rotax. It was throttled back a bit. We did the flight plan on the lot higher figure of 20 l/hr, which I now think was excessively conservative.

 

 

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Thanks Skippy. That's great info.

 

98 Ron. Hmm. All of my manuals state 95. Very interesting. Your fuel burn is amazing. I have an in flight adjustable and I do similar to you. I have it pitched at full fine to climb out on takeoff at about 5500. Then cruise at about 5200 at WOT with the prop pitched up. That usually has me on about 110.

The Rotax manual advises 95 RON however I work on the principal that fuel from an automotive supplier (your local servo) may have been contaminated, by other fuels, at variose points along its delivery journey to your aircraft. Its probably just a "piece of mind" thing but I figure that the 98 RON I purchase, will definitely be 95 or better, whereas if I purchase 95 it may have a lower RON. Anyhow 98 RON does no harm, except to my wallet.

 

People are often surprised by my fuel consumption - I think the combination of a relatively low drag compost, light weight, air-frame, meticulous carbi balance and efficient two bladed prop must be the answer to my consistently (well over 10 years recording) low consumption figures.

 

 

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People are often surprised by my fuel consumption - I think the combination of a relatively low drag compost, light weight, air-frame, meticulous carbi balance and efficient two bladed prop must be the answer to my consistently (well over 10 years recording) low consumption figures.

That is a very efficient airframe Skippy, to get 100kts while the engine is only producing about 50hp is amazing

 

 

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The airframe, propeller choice and pitch plus your personal input have a lot to do with fuel consumption. The manufacturer of my engine says 24 - 26 litres/hour at the cruise RPM I run at but I actually only burn 18-19 lph at those settings.

 

 

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These older (in time not usage hours) motors would probably only need seals gaskets etc replaced. Pretty much ALL motors would need that after 10 years if we were serious about oil leaks etc The neoprene goes hard moreso with certain oils. Some plastic parts are suss also as they go brittle with time and lose a lot of their strength.. Skills at dismantling and reassembly outside of assembly lines situations are not very efficient compared with what's done at a mass production factory where they just assemble new stuff.. Throw away is/will be the order of things in most circumstances in the future. Older aero engines could be rebuilt up to say 2 nd rebuild say 4,000 hours total but many were cracking and running out of metal to remachine at about that time. so they weren't the same Quality.. Don't forget the cost of inspecting and tolerance checking is very individual part time consuming. and the whole lot has to be scrupulously cleaned and assembled in clean areas using a lot of space if you take the time it's there into account. . Labor is now the cost area to reduce. Hi volume is materials cost plus not much.. Nev

 

 

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That is a very efficient airframe Skippy, to get 100kts while the engine is only producing about 50hp is amazing

There is one other factor which I havent got an answer for & that engine hours. What I mean by this is all my actual (refuelling to same level) fuel usage is calculated against engine hours and the assumption that this is both consist ant & meaningful.

 

In support of this my figures are planned fuel burn when away on a trip - I use 14 L/hr and it works out to be conservative.

 

Oh! and factory (POH) fuel burn figures are comparable with mine.

 

Cant comment on the 50 hp but you may be correct - dont forget my 13L/hr is the actual fuel used for the trip against the engine hours (includes climb & decent power) - not fuel used in cruise only.

 

 

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Sorry for thread drift but FYI my trike has mtow of 415kg and a 80hp R912 with fixed pitch 3 blade

 

60knt cruise

 

4,100rpm

 

11lph for 3hr legs incl climb and descents etc. with start at mtow.

 

So I get pretty much 10l per 100km. Much worse than my car but I do enjoy it more.

 

And for the masochists I have the same wing on a 447 powered trike with mtow of 367kg that burns 15lph for 50knts. It’s saving grace is it only cost me $2000 to buy complete.

 

 

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Possibly do some further reading on 98 fuel, it has light aromatics to give it the extra rating and these evaporate quickly and yes it can end up lower than 98- theres info on RAA website indicating very short life

 

Also these aromatics can pass through some rubber hoses.

 

 

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When BP did some testing of 98 being left in vehicle tanks for 5 weeks they found that the lighter components like Toluene did evaporate off but as it did the RON octane rating climbed to over 99 in that time. The problem identified was cold start acceleration resulting in detonation and pre-ignition resulting in piston damage. After evaporation the remaining components are high octane which can increase over time but it is not available for high revving conditions.

 

 

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Possibly do some further reading on 98 fuel, it has light aromatics to give it the extra rating and these evaporate quickly and yes it can end up lower than 98- theres info on RAA website indicating very short life

 

Also these aromatics can pass through some rubber hoses.

 

Check out KGWILSONS comments - I have read the BP study and accordingly I have been reassured. Further important points are:

 

  • The aromatics are lost when the fuel is open to atmosphere - this will be true for most vented aircraft tanks.
     
  • The full will maintain its specifications (for at least 9 months) if sealed in an air-tight container where the fuel makes up 75% or better than the volume ie nearly full.
     

 

Soooooo -

 

  • I top up, with fresh fuel, immediately befor most flights, as this will restore almost all of the fuel elements lost over the proceeding days, since the last flight.
     
  • Keep my fuel in airtight 20 L plastic Jerry cans ($20 from Bunnings aerospace). Having exactly 20 L per Jerry also helps with refuelling calculations.
     

 

 

Plastic Jerry's are good because you get a visual check on air/gas tight - they "balloon" when warmed but only if air tight.

 

"Also these aromatics can pass through some rubber hoses" - this is true of almost all volatile liquids/gas. However using higher quality fuel hoses such as "Gates - Barricade Fuel Injection Hose" (their speck sheet will give you all the data you might need) will minimise the losses (& smell)

 

 

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I have always run mine on 95 (last 3 years) and it runs like a dream! The Rotax manual states 95, and it's even on a sticker at the fuel tanks, so I will certainly stick with that.

 

Back on track though, a lot of what I am reading and the research I am doing is stating that the engine should be fine to run past the 15 year TBO. With good maintenance, and rubber replacements etc, it should be good to go!

 

 

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I thought Rotax stopped any "on condition" authorisation and the RAA backed that up?

 

Personally, I would still run it but obviously for private use only. You couldn't "hire & reward" or use for any training.

 

If your engine is a 2007 build, it probably has the upgraded crankcase which make it a 2000 hr tbo also.

 

Which makes it more of a reason to keep running it.

 

For what it is worth;

 

The issue is LSA aircraft with ASTM engines.   The airworthiness requirements are that the manufacturers maintenance instructions are followed - there is *almost* no scope for "on condition" extensions in this regime if not permitted by the relevant maintenance manuals or explicit manufacturer authorisation.  I would argue that with the mechanically identical certified forms of the engine (912A and 912F), there is a reasonable legal basis to run them on condition.  But the certification basis for the ASTM version of the engine (912UL) does not allow 'on condition' operation contra to manufacturer instructions.  For what it is worth, Rotax had a competition in 2016 to find their oldest certified engine still in service, it was won by a certified 912A, ESN36351, which had successfully run over 5,500 hours and 25 years without overhaul, on condition, (for this ESN, the Rotax TBO is 600 hours/10 years) - this engine remained in service at that time and has presumably gained hours and time since.  Rotax have discretely buried that information now....   The price of the certified versions of the 912 runs between 50% and 100% more (dependant on certification basis), whilst EASA certified versions of the later 914 and 915 are in the order of less than 10% more expensive than ASTM versions.

 

For the Rotax 91x series ASTM engines in an LSA, you are permitted by the AMM  a 5% over run on TBO and a 6 month extension on calendar life, which is better than nothing, I guess.

 

regards,

 

Paul

 

 

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Interesting Paul, as that contradicts the info I have now from a number of sources.

 

Can I ask where this information you have provided can be sourced?

 

Cheers

 

J

 

 

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Interesting Paul, as that contradicts the info I have now from a number of sources.

 

Can I ask where this information you have provided can be sourced?

 

Could you perhaps narrow the scope of what it is that contradicts your info?  It would make it easier for me to tell you the source.

 

regards,

 

Paul

 

 

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I thought the "10 years in service" caught all  912 engines . That's the one most (private use) engines would be affected by.  You can't zero time a Rotax.  as far as the maker is concerned. I don't find that difficult as a concept. I'd never run past the 2nd rebuild in any aero engine and many develop cracks inside the first TBO. Plenty of 912's especially the 80 HP engines which seem to be the most reliabl;e of all, do high hours, but nothing's magic. Old planes present great challenges to restorers. Some metals just don't like aging and some get brittle.  While we all like old time things, with a plane, NEW is best especially near a salty environment . Nev

 

 

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The calendar life specified in part 5 of the Rotax AMM gives 10, 12 or 15 years in the 912 series dependant on ESN, certification and model, with a 6 month extension permitted in all cases.

 

The mandatory part of the AMM (in the certified environment) is the Airworthiness limitations section.  If you read this, it states that there are no limitations, but it does give a note about the lifed components, TBO, calendar life etc...  required in part 5.   A note is not a limitation.

 

Therefore running on condition is not prohibited by the AMM in the certified environment.   LSA rules are different., 

 

With regard to "you can't zero time a Rotax", that is completely untrue.  However, there are few facilities authorised by Rotax to do overhauls and Rotax will not supply some of the mandatory components to non-authorised facilities.  A zero time 912 always requires a new crankshaft, exhaust valves, rings, seals and gaskets.  Cylinders are not reworked (they are nikasil) but may usually be reused just as they are.  Heads are reused.  Dependant on serial number, a new crankcase may be mandatory to get a 2,000 hour TBO, but if serviceable, it may also be reused even if will give a shorter TBO.  Intake valves are changed on condition, as are camshafts.  Pistons are on condition.  Gearboxes are on condition and usually require no replacement items other than seals - unless run on 100LL or 100/130, in which case the slipper clutch disks may need to be replaced due to lead fouling.  The ignition system is on condition.  The carburetors have to be overhauled.   I haven't caught up with the requirements for fuel injection.  

 

An overhaul is expensive, many elect to buy a new engine instead, a certified 912A costs $33,000 new, a zero time overhaul can be expected to be around $17,000, whilst you should be able to get at least $3,500 for the old core when buying new.  The mechanically identical uncertified 912UL only costs $22,500 new.

 

There are some good reasons for mandatory crankshaft replacement on hours run, with the design of the 91x series crankshafts.  I can think of no technical argument to support a blanket calendar life for them...

 

With regard to "new is best", in my experience this is not the case.  'Newish" to middle aged is best.  With regard to cracks etc...   this is exactly dealt with by "on condition" inspection.  Many engines will not reach their TBO, but we hope to find them 'on condition' before they have a chance to fail.   On condition inspections are our best defence, not arbitary TBO or calender life.   But there are good reasons for calendar life - however, they certainly don't require a bulk strip and mandatory crankshaft replacement to ensure continued airworthiness.  The possibility of a minor oil leak that will not cause a hazard and will be picked up and rectified on a recurrent inspection is not a reason to, in effect, throw away an engine.  No matter how much this might suit a manufacturer.  By and large, a new engine is much more likely to fail than one that has reached or exceeded TBO with proper maintenance and operation.

 

In the certified, commercial world, there are ways to deal with the calendar life issue for piston engines - in private ops of certified aircraft these are not available, but 'on condition' operation is available, and it does seem a darned sight more practical.  Before the latest amendment of AD/ENG/4, there was an explicit authorisation to exceed TBO in private ops if using schedule 5 - now there is not.However, this can be problematical on the regulatory front for many Rotax operators who have uncertified aircraft with uncertified engines. 

 

The crying shame is, the 912 series do have a demonstrated potential to greatly exceed TBO if looked after, but due to the method of crankshaft construction, if incidents such as prop strikes, or even engine backfires have been concealed from the logbook, they can also fail catastrophically even before half TBO.  This is probably one of the major factors in BRP having such a conservative approach.   Anyone who tries to save money by buying the uncertified versions without the slipper clutch has got rocks in their head if you ask me.

 

regards,

 

Paul

 

 

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I DID Qualify the zero time statement with the difficulties with the manufacturers conditions which you elaborate on. New is the only FIX with the crankshaft assy and any" required"  parts. The new is best applies to the entire plane at some stage unless the thing is of historical significance and you don't have to consider the "real" economics. Retiring  a plane (Putting it permanently out of service) is practiced extensively in aviation on high lifed airframes. Everything  made well has a "design life". or it's not economic or properly assessed. project/ design..

 

 Yes some new stuff has gremlins in it  till its done a shakedown period, but this only reflects a shoddy quality control situation. IF you are going to recondition/ remanufacture there needs to be a good  standard insisted upon at that point not backyard type shows usually. One of the reasons the 912 series performs Ok is that generally they don't get fiddled with and the bores aren't subject to corrosion to the usual extent. Nev

 

 

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