Are there any Rotax 912 Engineers or owners here ?

[Phil Perry]

I fronted up at the airfield for my slot as voluntary radio operator a little late today, following  a punctured tyre on the batmobile. . . and for some reason, the spare was deflated too ( ? ) . . it was OK the last time I checked around 4 months back, but I digress.   A couple of lads had flown in for a first visit to our redoubtable site, in an Ikarus C-42, a German design with is very popular here.  It was fitted with the Rotax 912s, 100 hp engine.  They had arrived at 0800, one hour before we are legally allowed to operate on a Sunday due to local planning restrictions. ( Oops )     At around 11:30 AM, they had tried to depart, but the engine on the hired C-42 refused to start.    I admit that I did see them messing around with it, the cowl was off and they were scratching their heads. but the traffic was rather busy, and I couldn't talk to them about it for three hours, when things began to quieten down.

 

Up until then, I was having to maintain pressure on the PTT and use the term 'BreakBreak' at the end of each specific response call,  to differentiate the responses to various aircraft callsigns,  whose calls were coming in at a rapid rate.

 

Finally, the Airfield manager gave me a fag / coffee break, after warning me that some idiot had mixed the coffee in the canteen jar with 50/50 normal and DECAF coffee. . . .I said . . Oh crap,. . .that means I'll only stay awake for half the time. . .     I asked the lads from Manchester what the problem seemed to be and they had no idea at all.    I had to wonder why they had borrowed some tools and removed the engine cowlings, as they said that neither of them had ANY mechanical / technical knowledge of aircraft, engines. . . .?   well,. . .why bother taking off the . . . . .oh, never mind . . 

 

I suggested that they turned off the main fuel TAP,  ( mod censored for using the correct term. . . .) left the fuel booster pump off, and turned it over a few times,. . .it started, and ran until what bit of fuel there was in the line was exhausted.  Following this, with the <mod censored> back on, and the fuel pump activated, it started immediately and ran seemingly OK. . . .I had heard of this problem previously on other Rotax 912 powered types, but I admit, I know very litle about the Rotax 912 engine, never having owned one.

 

I wonder if the Brains Trust on RF can give me an inkling with regard to what was causing this problem ? ?  the local temperature was HOT ( 25 Deg C ! ! ! ) the crew said that they hired this aircraft on a weekly basis over the last 12 months,  and that they had never encountered this problem in the past.

 

Do any of you tecchies have an idea of the cause ? . . .I'd like to know so that I can sound knowledgeable the next time. . .   :-)

 

 

[pmccarthy]

As you well know, when it gets as hot as 25 degrees in Oz we crawl into under ground bunkers and wait for it to cool down.

 

 

[Kyle Communications]

If you have the throttle open too much on start the engine just will not start. You only just crack it off idle position

 

 

[Phil Perry]

If you have the throttle open too much on start the engine just will not start. You only just crack it off idle position

Oh don't get me wrong,. . I have FLOWN lots of aircraft which use this engine,. . .but I have not WORKED on the engines. . . .I try to apply logic to situations, and this time it seemed to work.. . .but I still don't know the WHY of it.

 

Had the engine been a Rotax 377, 462,  477, 503, 532, 582. . .  etc,. . .I HAVE experience in stripping / maintaining / rebuilding those old 'Deux Temp' 2 bangers, but none at all on the flat Four machines. 

 

( PS, subject alteration mate,. . .is there an AllStar node number that I could use to access your box ? . . .I should've emailed you about that really. . \.I still have not got access to the Brandmeister DMR network with my TYT MD 380. . .working on a DV mini / Mega to sort that out.  Nearest repeater on DMR is Birmingham, but that's bloody Phoenix. . .)

 

 

[Kyle Communications]

The MMDVM on VHF is up and running. So Dstar/DMR/Yeasu Fusion and P25 and also NXDN very soon. Works really well. The UHF will be up in about 2 weeks. I will see if there is something connecting Allstar with Brandmeister..I have a lot of link options on the list

 

 

[Phil Perry]

Sorry, I can't access a Brandmeister gateway or digital repeater from my home,. . .but I have instant access to the Analogue system running Hubnet.UK. . .I work into OZ regularly on that system, WA seems to have a lot of guys who call in regularly to Hubnework UK . . . .I have a 2 metre simplex gateway around 3 Km from home.  When I can organize things, I will set up a micro node so that I can access the internet with the Digital radio.  as using RF on UHF is impossible from my locality, my mate Rob, G0 DUQ has an node, but it's bloody Yaesu Fusion, and my radio won't do that ! ! ! 

 

Thanks for any advice mate,. . greatly appreciated.

 

Phil.

 

 

[BirdDog]

The only time so far I have had issues with my 912ULS is when I pulled choke to start and she was warm enough.  It cranked ok, but would not fire.  Choke back in, and it still took a really long time of attempting to start, and when she did, it was ugly for a few seconds and then settled down.

 

I am now very careful how I manage the choke.  Other than that, my birds starts very quickly usually.

 

 

[skippydiesel]

I run a Rotax 912 ULS (100 hp) - have often had hot start problems but not usually under 30C.

 

On my engine installation (with close fitting engine cowling) the main fuel line runs over the top of the engine to the mechanical fuel pump at the front. From there the pressurised fuel runs, back over the engine again, to a distributor that supplies the two carburetor float bowls. The whole set up encourages the fuel, in lines & carby float bowls, to boil - causing vapour lock.

 

In my case I have done the following to mitigate the effect

 

• Insulated the fuel lines as best as my budget will allow.
   
   
   
  
• Added a cool down (slightly fast idle)  period to my pre engine shut down routine (this may be met by taxi time).
   
   
   
  
• Open my oil inspection hatch after engine shut down to encourage hot air to escape & cool air to be drawn in to the engine cowling.
   
   
   
  
• I use my fuel boost/auxiliary pump befor start up, allowing it to bring fuel pressure up to "normal" (about 3-4 psi). On a hot day I will often see the pressure rise rapidly, only to plummet to zero, after continued pumping the pressure will usually rise again and stabilize, indicating vapour lock cleared. Once engine running I will turn the boost pump on again, remaining on until after TO.
   
   
   
  
• On rare occasions  when the fuel pump seems unable to "clear" the vapour lock I will start the engine with the boost pump running. Rotax 912 start procedure calls for boost pump to be turned off befor engaging engine start, so this is a  last ditch technique for me.
   
   
   
  

 

 

Note:

 

• I second Kyle Communications advice - the 912 is very sensitive to throttle position, it must be off or only cracked open the smallest hair for "proper" starting.
   
   
   
  
• Choke must be used with due regard to ambient temperatures - on hot days there is no reason not to try a start without choke or only partial choke - be quick to reduce choke, if not required, for continued running
   
   
   
  
• On my aircraft,  hot day departures (35C upwards) should always be conducted with the expectation of a momentary or complete loss of power due to vapour lock - no intersection departures and have a plan.
   
   
   
  

 

 

 

 

[Blueadventures]

Skippy do you have the return line / restricted fitted? It's not mentioned in your reply. They prevent fuel vapour lock. Cheers

 

 

[skippydiesel]

Skippy do you have the return line / restricted fitted? It's not mentioned in your reply. They prevent fuel vapour lock. Cheers

Short answer is no - I think my 18 year old engine/aircraft may predate the concept of the constant fuel/vapour bleed. My fuel system has a pressure adjustable regulator/ distributor (which has a tank return line) rather than the newer & much simpler constant bleed..

 

After  experiencing quite a few embarrassing hot weather "no starts"  and a couple of heart stopping power failures (usually at rotation), I learnt to manage my fuel system in hot weather. I now rarely have a problem but still stay alert to the possibility.

 

 

[Blueadventures]

Hi Skippy  I recommend all 912 drivers fit the return system easy enough to do either buy the manifold from Rotax or make up a manifold and fit the restriction in the respective return line nipple; hardest part is the return point into tank; if tank does not have one.  Mine returns to tank and I read some RV people return to the top of the gascalator (Not sure from experience the cons of that method.)  It's a pain when engine won't start when hot.  Best Regards.

 

 

[BirdDog]

Along with Skippy, I also allow a few minutes of run down time to let her cool and stabilise before I switch her off.  I also remove the cowl at the end of the days flying for a post flight inspection and to allow her to cool, before packing her away.

 

 

[corvairkr]

https://www.rotax-owner.com/en/flightsafety/476-ai476

 

jason 

 

 

[Blueadventures]

Hi Jason  I totally support this requirement for the 912's  as in reduces the consequence of fuel vapour locks.  I have seen RV setup's that return to the Gascolator but I believe this is not an equlivent fix as to me you are returning fuel and any fuel vapour back into the system just before the engine driven fuel pump; a sort of semi closed loop system.  The intended return to the tank is for flushing vapour out of the line so that you have 100% fuel liquid to the carbs.  Those who do not have this, IMHO, must get onto complying with Rotax's Mandatory instruction ASAP.  Regards 

 

 

[SSCBD]

the local temperature was HOT ( 25 Deg C ! ! ! )

Very funny! Phil.

 

 

[Phil Perry]

I just saw the weekend WX forecast mate,. . . ANOTHER HEATWAVE predicted with temperatures expected to 'Soar' to 23 DegC  Beachgoers are warned to make sure young children wear hats. . .

 

 

[bexrbetter]

 the local temperature was HOT ( 25 Deg C ! ! ! )

34 here at the moment at 7PM, must have been another 10 this afternoon inside my tin factory.

 

I died by the way.

 

 

[storchy neil]

ROTAX 912 HAVE HAD IN THEIR MANUAL RETURN LINE TO TANK SINCE 1997  neil 

 

 

[Phil Perry]

Thanks for that Neil,. . .but as I have never owned a 912 series,. . I don't have a manual either.

 

But THANK YOU ALL for your valuable input. 

 

 

[Guest langted]

In the original post, its sounds like it was resolved as flooding due to the particular carburetor setup.    But then the subject of vapor lock came up.   I'm not sure if this adds much to the conversation (perhaps you guys are already up on this) but I'm new here so....  related to vapor lock.... In the US, airports generally only sell 100LL AVgas, whereas a lot of light sport engines can run cheaper automobile fuel (Mogas).   If you run Mogas, it should be understood that its not just a matter of the octane, no lead content, and possibility of ethanol blends, but a whole different formulation.   Of significance to this thread is the vapor pressure of the fuel (Reid vapor pressure, or RVP).   In the US, RVP of AVgas is (I think), typically about 7 psi (48.3 kPa) year round.    Mogas vapor pressure is much higher:  typically up to 15 psi (103kPa) for "winter" fuel and regulated to be as low as 7.8 psi (54 kPa) in the summer, regionally dependent.   These are the absolute vapor pressures, measured at 100F (37.8C).    I took a quick look at Australian standards for Mogas, and it looks like there is a different summer/winter standard there as well, with a similar range.   

 

I first encountered this one early summer day in my small power boat on Lake Erie, in the US.   I was stranded on the lake 15 miles from shore and couldn't start until I figured out it was vapor lock and I got the carburetor and fuel lines cooled down.   It had never happened before in 10years of using that boat, but I had filled the tanks in November the prior year (that's late fall, here), when mogas stations were well into "winter" fuel.   I don't do that anymore.

 

Vapor lock is always inconvenient, but potentially lethal in an airplane, if it is susceptible by design.  The bottom line is that you are much more likely to encounter vapor lock if you use Mogas, and even more so if its a "winter" blend.