Rotax 912 (all) series SB

[Freizeitpilot]

SB-912-079.pdf In the latest broad ranging Service Bulletin from Rotax, they make a strong case to preference 98 octane fuel to minimise the risk of piston damage.
 

This has particular relevance to CSU operators and the need to manage MAP vs fuel type.

 

Interesting reading.

 

[skippydiesel]

As most (in Au) Rotax 912 UL & S powered aircraft are using ground/fixed pitch props, the question of 95 or 98 RON is bordering on academic😈

[FlyBoy1960]

Where i am in SEQ, most are constant speed or IFA props.

[aro]

1 hour ago, skippydiesel said:

As most (in Au) Rotax 912 UL & S powered aircraft are using ground/fixed pitch props, the question of 95 or 98 RON is bordering on academic

Not necessarily. 912ULS specify minimum of 5200 rpm at WOT, which can be a problem at climb speed for aircraft with higher cruise speeds. Some manufacturers fudge it a bit so 98 would give some extra margin.

That's one area where variable pitch would actually be useful for the Rotax.

[skippydiesel]

55 minutes ago, FlyBoy1960 said:

Where i am in SEQ, most are constant speed or IFA props.

If any of them use an Airmaster CS, I would very much like to make contact to discuss pilot (me) operating shortcomings/observations. Initial contact through this Forums person to person service.

[skippydiesel]

55 minutes ago, aro said:

Not necessarily. 912ULS specify minimum of 5200 rpm at WOT, which can be a problem at climb speed for aircraft with higher cruise speeds. - The 5200 rpm @WOT static setting, is a hotly debated topic in the USA - not so much in AU. Some manufacturers fudge it a bit  -  by fudge it, do you mean huger/lower RPM at static or as seems to be quite common in the USA, adjust for Max Cruise 5500 rpm @WOT? so 98 would give some extra margin. I agree with the 98 RON - I use it almost exclusively.

That's one area where variable pitch would actually be useful for the Rotax. If its a CS but if its an In Flight Adjust it can be set as per a ground/fixed pitch

 

[BurnieM]

Am I the only one finding this SB a bit wierd ?

 

Seems to be "If you do all these things you probably won't have fuel vaporization issues, maybe".

[Underwood]

Its standard practice to have a few Lawyers proof read everything before it goes out, do they still have the disclaimer on uncertified (UL/ULS)  engine's manuals saying something like 'this engine can stop at any time'?

 

[Freizeitpilot]

Ahhh yes - lawyers.
I particularly liked the requirement for a retained fuel sample in the event you cook a piston and want to make a claim.  
 

How many operators would duck down to the servo after the engine strip, fill up a jar and then announce “here’s one I prepared earlier !”

[facthunter]

Mogas is not a quality controlled produce like avtur and avgas are.  The liquid cooled heads should make the 912's more tolerant. High boost at low(er) revs is like being stuck in top gear up a hill..  Nev

[Blueadventures]

Like the info about MAP gauge min and max. I’ll mark mine for 95 grade.(I have a fixed pitch E-prop on 912 ULS)

Edited November 30 by Blueadventures

[skippydiesel]

"I have a fixed pitch E-prop on 912 ULS"

Speculation:

The 95/98 RON debate is about detonation/load.

You the pilot have an influence on the likelihood of this occurring.

What prop pitch you set, the climb angle you aim for and rpm you select, will be the significant factors - all pilot controlled.

Rotax used to specify 5200 rpm @ WOT aircraft tied down (static). This recommendation seems to have been dropped in favour of MAP & the pilot/engineer deciding from a range of RPM/MAP possibilities. 

I think the 5200 rpm static is still a good SAFE starting point for anyone selecting a prop pitch. Once the aircraft has been tested with this setting the pilot may opt for something a little diffrent/applicable to their "mission" objectives. Mission in this context includes aircraft TO weight, strip type (grass/gravel/sealed) & usable length (accounting for terrain/obstructions), etc

Keep in mind that selecting a courser pitch (lower static rpm @ WOT) may impact negatively on your aircrafts take off role & climb out and visa versa.

I would be concerned about a prop pitch that did not allow 5200 - 5500 rpm on a significan climb angle (load).

 

In my area 95 RON has become quite scarce - most servos rationalising their offering to 91 or 98 RON.

 

[Blueadventures]

In my area 95 RON has become quite scarce - most servos rationalising their offering to 91 or 98 RON.

 

not in my town Mackay, 90% have 95 even the new ones ( I use Mobil locally and have choice of BP, Caltex, Shell.) After 7pm 5 cents off per litre.
 

 

[Moneybox]

Cue doesn't have fuel at the airport but in town we have 91 and 98. My friend turned up the other day in the Bristell with an inflight adjustable prop with instructions to use 95. He flew the extra 115km to Meekatharra for Avgas adding 230km to his trip. I'd already filled the jerry can with 98 but he wouldn't accept it. I guess if you know no better you go with what you're told.

[facthunter]

Avgas OCTANE ratings are different to Mogas, and give two figures one for Lean and the other for rich.   Nev

[BurnieM]

21 hours ago, Moneybox said:

Cue doesn't have fuel at the airport but in town we have 91 and 98. My friend turned up the other day in the Bristell with an inflight adjustable prop with instructions to use 95. He flew the extra 115km to Meekatharra for Avgas adding 230km to his trip. I'd already filled the jerry can with 98 but he wouldn't accept it. I guess if you know no better you go with what you're told.

This is scary.

Not having a basic mechanical understanding exposes you to risk.

 

What else is he exercising bad judgement over ?

Edited December 1 by BurnieM

[skippydiesel]

1 hour ago, BurnieM said:

This is scary.

Not having a basic mechanical understanding exposes you to risk.

 

What else is he exercising bad judgement over ?

Some may say "......having a basic mechanical understanding exposes you to GREATER risk."

[BurnieM]

Every trip we take, whether by car, rail, boat or plane, exposes us to risk.

 

Not accepting 98 octane mogas because you were told to only use 95 octane makes no sense and I suggest using the 98 would add zero extra risk.

However, travelling 230 km extra distance to get another fuel has a definite extra risk.

 

I am not a mechanical or aviation expert but this is/or should be risk assessment 101.

 

Edited December 1 by BurnieM

[Moneybox]

1 hour ago, BurnieM said:

Every trip we take, whether by car, rail, boat or plane, exposes us to risk.

 

Not accepting 98 octane mogas because you were told to only use 95 octane makes no sense and I suggest using the 98 would add zero extra risk.

However, travelling 230 km extra distance to get another fuel has a definite extra risk.

 

I am not a mechanical or aviation expert but this is/or should be risk assessment 101.

 

He hired the training school plane so was determined to do the right thing even though ignorance may have cost him a little more. I said "That would add quite a bit to the cost of your journey". His reply was "No I hired it wet so I'm not paying for the fuel just the hire per hour" and he intended to spend all day with us anyway returning to Jandakot before dark so it didn't cost him anything at all.

[facthunter]

If you are counting extra Miles as a risk, why fly at all? THAT will lower the risk.  Nev

[Underwood]

Does anyone know if you can connect a MAP sensor to an MGL RDAC VD?

 

[Garfly]

This guy makes the point that there can be more to premium fuels than octane ratings.

He reckons that premium additives like friction-modifiers can make a big difference to engine wear.

 

(with Octane ratings measured differently in the US, their label numbers don't line up with ours)

 

 

 

Edited December 1 by Garfly

[skippydiesel]

If this guy didnt oversell every point, the video would be 75% shorter.  A real endurance effort to get through it - I failed.😈

[facthunter]

Friction modifiers in fuels?? Nev

[Garfly]

21 minutes ago, facthunter said:

Friction modifiers in fuels?? Nev

 

Yes, apparently.

 

Improving sustainability by enhanced engine component lifetime through friction modifier additives in fuels - ScienceDirect

WWW.SCIENCEDIRECT.COM

---

Engine test rig runs with a standard and a friction modifier containing premium fuel using an artificially altered close to end-of-life oil were...

 

"All 3 independent methods for wear measurement confirmed that the premium fuel containing friction modifier results in an overall superior wear protection compared to standard fuel. Mass spectrometry of oil aliquots from the engine test rig runs showed an accumulation of friction modifier in the end-of-life engine oil, which explains the better tribological characteristics observed in this case. Accordingly, application of friction modifier in fuels can lead to increased oil change intervals since the wear protection is acceptable even in case of an end-of-life oil condition and potentially improved engine component lifetime. Both factors offer economic and environmental benefits."