Engine outs/fuel related

[cloud 10]

Hi all, I have always wondered why our modern Rotax (and other) engines are so prone to fail whilst in flight due to dirt/filters/water/blocked jets/cracked hoses etc. even though they are regularly inspected. This is to compare with modern motor cars, I mean how often do you see a car that had an engine out on the Ben Schoeman ? There are many thousands more cars on the roads than microlights flying and they don't have pre flight inspections, your petrol hoses last forever, there is never water in the fuel , things don't get blocked easily etc. Surely the operating conditions can't be that different ? In fact it should be the other way round. Just wondering......

[RV4ker (RIP)]

Cars drive every day and thus the fuel is changed regularly and the moving parts are lubricated and "working" all the time. Engines hate to stand...

[Big-D]

Bearing in mind that I am probably the most non-technical guy alive:

I think the reason cars keep going and engines don't quit like potentialy in Microlights is the fact that the wheels are in constant contact with the ground, if the engine in a car does quit for a microsecond due to a little dirt or water in the fuel then the movement on the wheels due to moving on the tar will keep the cars gears and ultimately the engine going untill it fires again - Thus, no engine out - in the air however, there is nothing keeping the prop going - Except the engine.

So, if me theory is true, most "engine outs" on a car will only happen at stop street or robot when idling

I could be, and probably am completely wrong, and would like to hear some opinions


D

[Tailspin]

A car has multiple methods of making sure no water junk etc makes it way to the injectors / Carbs.
It has a huge filter in the Fuel tank or close to it, it has another HUGE filter inline and then it is sprayed into one of at least 4 chambers (Compared to our two) so it will not loose 50% of it's drive if one chamber does not fire fully yet on our little motors one chamber does not deliver power and we have an Immediate 50% power loss then the next chamber does not fire and OH CRAP a distinct Sponge taste in the mouth. The there is that Flywheel to hold momentum and yes the car traveling alone the road will also keep the motor turning. In the car we feel a bit of a lag then the motor go's again as it has had chance to clear it's throat and get going again but well in an aircraft, unless you can keep that motor spinning till all the water or gunk is gone. Sorry for you.

[MADDOG]

We are spoilt with modern cars, so lets go back and compare out Rotax problem with older carb fitted cars pre-dating the current electronics.

On these cars the fuel pump was mechanically operated from the engine. It had to suck the fuel from the tank to the pump and them it could push it to the carb. Any deteriation of the fuel pipe/hoses or filters would cause an air lock and the car splutters and dies. Our vacuum fuel pump also has to first suck the fuel out of the tank through the filter. Any deteriation of the hose, clamps or filter has the same effect. Only difference is for the sake of lightness, our fuel delivery system is 10 times smaller and has to deliver twice the fuel. All filters/hoses/clamps have to good condition - there is no margin for error. The filter is around half to a quarter the size, but has to deal with twice the fuel (if not more)

The car has a single carb with a fuel bowel of around 100cc capacity feeding all 4 cylinders and is not designed for any significant tilt or G loading. For water to collect under just the jet feed area to cause the engine to stop is near impossible. (Poor starting maybe) In our carbs the fuel is directed into a tiny bowl area surrounding the jet. This is around 1cc in volume
and only supplies one cylinder. It only takes a tiny amount of water trapped here to stop that cylinder.

Cars run at more or less constant altitude and being 4 stroke, can and do run rich of peak without any real fear of fouling the plugs. Our engines - and especially 2 strokes - run very rich. They cannot be lean because they have to produce max power on the ground for take off, and then steadily richen up as the altitude increases. 2 strokes are doubly effected in that as the mixture gets richer, so the plugs get more oil that they have to deal with, but the richer mixer means cooler plug which is harder to burn the oil off. The bottom line is oil/oil mixture/fuel mixture and plugs have to be perfect or else you will foul plugs.(Car change plugs 10 to 15 000 km, plane 25 hours or you fall out the sky).

Car has an airfilter the size of a cake tin to deal with half the air our rotax has to deal with through 2 tiny filters. As the filter clogs up, it reduces the amount of air the engine gets causing a richer mixure which greatly adds to all the problems the plugs have to deal with as above. So keep filters clean and change plugs regularly.

I drive a few old cars, and believe me they require constant attention and I have stopped on the side of the road a few times.
Your Rotax requires all the attention it deserves and the maintance schedule is far more important most people think.

[Tumbleweed]

And we dont arrive at our garage with multiple old petrol drums, stained from old oil premixes, dust off the old hoze hanging on a hook and give a quick wank either.

[MADDOG]

And we dont arrive at our garage with multiple old petrol drums, stained from old oil premixes, dust off the old hoze hanging on a hook and give a quick wank either.

Lets not go down this road. Next will be a regulation that only AP's can refuel using a sterile environment with surgical use once only drum hose gloves condom and whatever. Cost R225.67 per litre - sign logbook in triplicate and keep three copies.

[cloud 10]

Thanks guys, you have given me much more insight into the differences and it all makes sense , especially the point mentioned that the momentum of the wheels keep the engine of a car going until the obstruction is cleared and it fires again, a prop has no momentum.( or wind to turn it at our speeds)