Warming up certain engines...

[River]

G’day team,

 

Now I’ve a reasonable working knowledge of engines, etc but this question has had me pondering as to why this happens.

 

I noted that the accident a month or some back involving a PT19 or maybe it was a PT22 trainer that crashed after losing its engine upon an unplanned take-off. Apparently the aircrafts engine model was known to either loose power or stop completely if the engine was not fully warmed up and at its standard operational temperature upon take-off. As was the case I understand with this accident, the engine was not at its operational temperature prior to take-off.

 

The same procedure of warming up the engine to its correct operational temperature before attempting a take-off with the Rotax 912’s is also a required SOP (Standard Operational Procedure) otherwise similar results may occur.

 

Of-course all engines require to be correctly brought up to their correct operating temperature but...

 

The question is why does the engine loose power? As in what exactly causes the engines lack of power or even totally stopping. It would appear that this would be caused by some form of carburettor malfunction or oil related cause?

 

I’d be interested in hearing from L2 mechanics or engineers as to the details why.

 

Cheers,

 

Rodger

 

 

[Student Pilot]

The engine manual with Lyc's says 2 minutes hot weather and 4 minutes cold weather. If you can advance engine revs without missing then Lycoming says take off.

 

Having said that, I usually get to 125C CHT and 40 oil temp before I do much. Remember those numbers from a 985 P+W.

 

There is such a thing as overdoing it though.

 

I think the problem of not warming up and seizing is to do with unequal expansion rates and the piston actually seizing onto the bore. Modern engines do not have this problem.

 

 

[Guest micgrace]

Hi guys

 

Thought I'd add a few points that apply to any engine.

 

1. Cold takeoff (why?)? Possibility fuel system may not supply sufficient fuel for richer mixture req. under full power Full power hot stochiometric mixture around 12 or so, cold? 8 or so. Need more fuel. If the carby can't supply required mix enginecuts out or misses.

 

And carby system very unlikely to be designed with this mistreatment in mind. But an EFI engine can be set up for this eventuality, not that anyone would, would they? (full power cold, that is)

 

2. Pistons. All pistons from the earliest engines (except the earliest, which were cast iron) had some form of expansion control. A "t" slot, cast in iron band etc. But all modern engine pistons are cam ground. What's that?

 

The piston is ground off a perfect circle so when cold doesn't fit the bore exactly, but when hot expands to fill the bore as a perfect circle.

 

Another point to note if piston is forged, must fit at looser clearence than cast. This gives a bit of a rattle when cold, but quickly balances out.

 

The point is warm up first.

 

Micgrace

 

 

[Guest marbrody]

I read the replies and all have good grounding, my limited experience is only with the humble 2 stroke, however the two stroke water cooled must be warmed up to operational temperature prior to applying take off power due to the probable problem of "cold seizure"

 

This relates to the water in the block reaching operational temperature and then and always then as take off power is applied generally at the worst possible moment the thermostat will open for the first time andflood the block with cold water causing an immediate engine failure and major rebuild.

 

Back in 2000/2001 this very same incident happened to a well known person amongst the RAA ranks @ Lismore and W.... was very lucky not to have been seriously hurt.

 

Since this incident I have also heard similiar stories from a chap @ Hernani (north eastern NSW) who has a 912 in his jyro copter and had a similiar incident with one of the first 912's that came out some years ago.

 

His problem may have been attributed to an old thermostat and may therefore have been maintenance related.

 

Still I hope this helps someone as did W....'s storey when he told me.