[patowalker]

What are the main issues caused by running in the 4k's? I run the 912S in my CT at between 4300-4500, any more than that and it's screaming and I would be pulling the wings off.

See page 64 for the performance graph for the 912UL and page 67 for the 912ULS and draw your own conclusions. https://rotax-docs.secure.force.com/Doc ... sPdf=false

Are the aircraft manufacturers wrong in their setups?

viewtopic.php?p=1719403#p1719403

[leifarm]

I run my 912 UL at 25 in and about 4000 RPM in my Pipistrel Sinus. Seems to be ok according to the table on page 65 (5.3) in the linked manual (it's also cruise Pitch on the Pipisrel Vario propeller). Consumption slightly below 10 l/h

[jim harris]

Also with 912S, I cruise at 4000rpm giving 100 kts in the banbi (MCR01 ULS) and 10 litres per hour. 800 hrs so far and gearbox not broken - though it might tomorrow! Compressions are good too.
I too had increase in fuel consumption recently which was due to one faulty plug now fixed.
Lovely engine.

[mikehallam]

A little up-date:-

Having found out, -as pictured above somewhere - that the plugs didn't really show much difference in appearance between LH and RH cylinders mixture, today the floats were taken out & weighed.
The LH side pair were showing 12 or 13 gms !
The slightly sootier RH cylinders carb's floats were O.K. at 6 to 7 gms

Perhaps the LH ones were more susceptible & soaked up that French 98 Octane MoGas - with Ethanol - I'd uploaded in mid France ??

Either way they were seriously heavier today than when installed, which was back when the BMW float manufacurer changed spec's some three years ago causing a kerfuffle - at that time I did go for new floats
Today I put in a spare 'good' pair from stock with the correct <7gms mass into the LH carb..

[Admittedly the weighing m/c was only a set of electronic ngm kitchen scales, so was better as a comparator than absolute, I suspect.]

A short test flight & she still feels & runs well. Next longer flight might show a result.

[Miscellaneous]

Thanks @mikehallam I'll be interested to hear if a few grams on carb float is sufficient to increase the fuel consumption by 20%.

[T67M]

Interesting indeed that the first symptom you detected was increased fuel consumption - an aircraft I know with a Rotax first became increasingly hard to start until, a few flights later, the engine stopped (due to rich-cut) on the roll-out after landing and was impossible to re-start, leaving the aircraft stranded just off the side of the runway until the fire-crew could attach a tow-rope

I guess 7g to 13g does represent an 85% increase in weight, so the impact on the mixture ratio could be really quite significant.

[Charliesixtysix]

Thanks @mikehallam I'll be interested to hear if a few grams on carb float is sufficient to increase the fuel consumption by 20%.

It will indeed - which is probably why several early replies in this thread suggested checking the floats.

[Miscellaneous]

It will indeed - which is probably why several early replies in this thread suggested checking the floats.

The big learning point for me is the benefit of recording fuel burn. It would appear a symptom of dodgy floats may well be an increase in fuel consumption which is significant enough to be noticed before a complete failure of the floats, to float.

Time I paid closer attention to my fuel burn! Now if only I could get the weather...

[patowalker]

Mike,
Have you checked for fuel stains on the drip trays? I would expect sinking floats to cause more of the excess fuel out of carb bowl overflow pipe, rather than into the cylinders.

Donald

[mikehallam]

That's pretty difficult to check, but sounds an excellent possibility in my case.

The Rans supplied drip tray is very close fitting & not visible on its inside when the carb's are on, whilst when they were pulled off - intact and lumpily in the way of everything - I can't say i saw much of its inner/ upper face.
For safety they do have drain tubes leading down to below the firewall so it's highly plausible undetected overflowing in flight was the greater reason for observed over high 'consumption'.
In a way that would be the nicest answer to the conundrum, as it means the plugs didn't lie and the engine didn't suffer rich mix and lubrication wash off.

As for the fellow mentioning monitoring fuel use: why I do it virtually every filling:-
Wing tanks need dipping to see what's left, before it's toped up - with 20 litre gerry cans, funnel and measuring jug at the ready.
The tank side walls are fortunately translucent & the contents levels each side comfortingly visible in flight. China graph marks in 5 litre increments complete this crude 'instrumentation'.

[patowalker]

For safety they do have drain tubes leading down to below the firewall...

Then I would look under the fuselage to see if dripping fuel is leaving a clean streak.

[cockney steve]

Amazed that the float(s) could become so absorbent in such a short space of time.
It brings into question the quality-control and materials selection at Bing and the float sub-contractor. It also, of course, brings into question the whole ethos of Governments that try to force us to use a heavy dose of Ethanol in petrol.
I know someone who had the fuel-filters on the tank- taps totally disintegrate on all 3 vintage motorcycles he owned.
AIUI, some Esso refineries , covering a large part of mainland Britain, supply their premium fuel without added Ethanol. I'm surprised their PR department hasn't latched on to this and used it to their marketing-advantage.

[patowalker]

Nothing to do with ethanol and everything to do with a manufacturing fault. The 912 is approved for E10.