FYI Rotax Fuel Related Story

[skippydiesel]

 

[Thruster88]

Bit of a long video Skippy, perhaps you could summarise. I did see the bit when the engine was running rough over the mountain, no mention of fuel pressure or auxiliary pump operation which seemed a bit strange to me.  

[skippydiesel]

I concur - If possible, its even more long winded than myself some interesting tips on fuel plumbing but very much  focused on the Rotax 912iS.

 

I have not viewed the whole thing  & have skipped past a lot of "stuff"  Seems that he had a loss of power, on a hot day, over the Rockies  (+10,00ft) which he put down to fuel vaporisation.

Coupled with that he had to contend with turbulence  and mountain wave (he seems think fuel agitation was also a factor in vaporisation).

 

Don't know if he mentioned, that the fuel injection system will return hot fuel to the tank - not something that will help minimise fuel vaporization on a hot day. (30+C).

 

In addition the iS has significantly more complicated & extensive fuel supply system, than the carburettor variants,  just begging for heat load issues.

 

The focus is on the Vans (RV) 12  and US summer climatic conditions.  In Australia that's almost all the time, save for a few short months in winter - we just manage the possibility of fuel vaporisation, as one more factor in safe flying (just like carb ice) no hysteria required.

 

I have experienced (912ULS) fuel vaporization at rotation, on a near 40C takeoff (I don't usually fly when ambient exceeds 30C). Aborted TO. Returned to parking area, did as intensive eyeball engine/ fuel supply inspection as I could. Lined up and after extended run up/checks, took-off without further incident. Never had a vaporisation issue in the air.

 

 

Edited May 14, 2023 by skippydiesel

[Area-51]

The whole purpose of fuel injection is to atomise fuel into a mist from a high pressure spray nozzle... Bosch EFI systems run up to 60psi line pressure to mitigate any chance of vapour lock... and warm fuel vaporises more readily; especially if its Avgas... winter/summer mogas blend makes no difference at 30psi to 60psi working line pressure; vapour lock is left well behind with Dorothy and Toto in Kansas...

 

If a "hot day" with a 912is causes vapour lock then Joe Average's outback subaru or commodore in Longreach must be a real bad pig of a thing all through summer hey? ... So its  not a vapour lock issue.

 

Yes, you want that facet pump right at the tank exit point so the entire supply line can be pressurised and provide the best opportunity to mitigate vapour lock, especially if running carburettors... this is the whole reason automotive fuel pumps are immersed within fuel within the fuel tank itself; and the swirl pot prevents running dry during bumpy and low fuel level conditions.

 

Pressurising the tank might give you an explosive airframe; so don't think its a smart thing to do unless you want to bbq yourself and passenger; it can be a very probable outcome. That being said EFI fuel systems are commonly atmospherically sealed closed loop design holding 2psi to 3psi until the filler cap is removed... Why? to mitigate volatility losses to the atmosphere... Why the 912is system us not a sealed system is just beyond amazing... and thats the real cause of Mr Long-Story's situation... or its just a faulty check valve in the dual pump assembly; does happen, and the engine stops...

 

So the real issue here is not "Vapour Lock"... It's "Fuel Management"... Very poor human performance and quality of design thinking applied.. would of thought the people at Bombardier were smarter than this... If i was the project director i would hang my heard in shame...

 

[IBob]

I'd say that about covers it, Skippy.

I tried to listen to it, but the guy has such a pedestrian and meandering delivery, I'd had it after half an hour.
It seems he's trying to wander through every possible hole in the swiss cheese he encountered.

[skippydiesel]

12 hours ago, IBob said:

I'd say that about covers it, Skippy.

I tried to listen to it, but the guy has such a pedestrian and meandering delivery, I'd had it after half an hour.
It seems he's trying to wander through every possible hole in the swiss cheese he encountered.

Agreed!