A2A programmers: primer lock

[Corkscrew196]

Is it possible to simulate the effects of an unlocked primer? In the aircraft I fly (Piper cadet/archer) it causes the engine running irregular. You don't want this to happen inflight! I know a couple of pilots who experienced this. One of the reasons this can happen is that to get the primer into the lock position (in these type of aircraft, I suspect all carburettor type aircraft as well) requires a rather subtle touch. Beware!
Maybe you brilliant A2A programmers can make this happen?? If so, you help me as a pilot.

regards,

Corkscrew

[AKar]

Hmm, interesting! Apparently this varies in between the airplanes. This is because someone who specifically tested this told that he noticed no effects whatsoever from unlocked primer. Of course by slight pumping action the engine immediately got unhappy. Not sure if I asked the aircraft type in question. Obviously, choosing from two possibilities, the one that causes issues would be more interesting!

In the simulation, the primer has no effect to the running engine even if pumped, so it would likely take quite some programming effort if created in a way other than scripted.

-Esa

[pjc747]

I second this request. If you leave it unlocked nothing may well happen, but it is a reality in the right alignment of conditions.

Hmm, interesting! Apparently this varies in between the airplanes. This is because someone who specifically tested this told that he noticed no effects whatsoever from unlocked primer. Of course by slight pumping action the engine immediately got unhappy. Not sure if I asked the aircraft type in question. Obviously, choosing from two possibilities, the one that causes issues would be more interesting!

If you leave it unlocked and it opens, it can allow enough fuel in the system to run excessively rich. I've seen it myself.

With that in mind, I'd also like to see an option to leave the primer in the full back position; when starting under very cold conditions, a trick that works quite effectively is to pull the primer out and leave it that way, deliberately allowing excess fuel into the system. When your engine is very cold, sub-40, often if you prime the engine the fuel will simply evaporate, extending the startup time. Pulling the primer out allows excess fuel to be drawn in throughout the cranking process, enough to overcome evaporation and allow quicker starting.

[n421nj]

Here's my take, if you take the time to model the primer locking and unlocking then why not add consequences to leaving it unlocked. With aircraft dna, vibrations are measured and captured. Perhaps the vibrations can effect if an unlocked primer opens during flight. Once opened maybe if effects the engine, maybe it doesn't. That's where the beauty of accusim comes into play.

[Bruce Hamilton]

Might be easier to change the animation and make the primer lock itself, pretty sure at least one plane already does that.

[AKar]

I second this request. If you leave it unlocked nothing may well happen, but it is a reality in the right alignment of conditions.

Hmm, interesting! Apparently this varies in between the airplanes. This is because someone who specifically tested this told that he noticed no effects whatsoever from unlocked primer. Of course by slight pumping action the engine immediately got unhappy. Not sure if I asked the aircraft type in question. Obviously, choosing from two possibilities, the one that causes issues would be more interesting!

If you leave it unlocked and it opens, it can allow enough fuel in the system to run excessively rich. I've seen it myself.

Yep, I'm aware of the mechanism, and at least some accounts of it coming open and causing some engine issues. As it often pops up, one guy had once specifically tested how unlocked primer pump affects the engine, and in his testing, it had no effect whatsoever, and that specific primer did not open on its own. Some other primer pump may shake open easier (there's a reason for the locking action of course!), but that one did not. I'm not sure if he tested how far you can pull it before (or if) any effect is noted. The pump is "sealed" by a pin-like thing that plugs a line from a check valve, it may allow some movement before the seal is broken.

Another 'failure mode', so to say, with primer pump are leaking O-rings. That may allow some fuel to leak into the cabin, which is not nice, but even worse, it may allow the air to get pulled into the primer line, leaning the mixture excessively.

-Esa

[stephan.cote.1]

Is it possible to simulate the effects of an unlocked primer? In the aircraft I fly (Piper cadet/archer) it causes the engine running irregular. You don't want this to happen inflight! I know a couple of pilots who experienced this. One of the reasons this can happen is that to get the primer into the lock position (in these type of aircraft, I suspect all carburettor type aircraft as well) requires a rather subtle touch. Beware!
Maybe you brilliant A2A programmers can make this happen?? If so, you help me as a pilot.

regards,

Corkscrew

Hey corckscrew, I think there are a few inaccuracies in your post, at least when applied to the R1340...

First, I do accept that leaving a primer pump opened probably let some fuel through to the engine. That being said, it is not the reason my dad would leave it opened or partially opened when he was starting his otter during cold winter days, it was because even with the mixture full rich, during the first seconds or minutes, the engine would tend to die... The way to keep it running was to pump some more fuel with the primer whenever the engine rpm would fall.

The reason why we have to prime fuel or more fuel is not because avgas tend to evaporate more when it's cold, it actually tends to remain in its liquid form longer.... I'm guessing it as more to do with the denser oxygen part in cold air and the fact that the fuel is more reluctant to vaporize and reach the Sparks of the spark plugs when introduced in a cold cylinder....

On a side note, IFFF I remember correctly, not all cylinders have priming lines on the 1340 to minimize risk of flooding the engine(I might be wrong on that one, maybe it primes in the carb?)

One more thing, although you might know it already, a R1340 would probably not start at -40 unless you warm it up with an engine tent and a heating pot which would take forever if you did not prewarm its oil first. Even if it would start, you would probably damage it badly from excessive oil pressure....There is no oil dilution so a common practice was to empty the oil after the last flight to keep it warm indoor over night....


Best regards
Steph

[AKar]

Yes, correct. With cold engine, the fuel doesn't want to evaporate and may even re-condense somewhat over the cylinder walls and induction system. The fuel that is in liquid form is not immediately available for combustion, and requires more fuel into the engine to 'replace' that portion. That's why most airplane piston engines have very rich idle mixtures. That's also why old cars used chokes to limit the airflow into the engine, and why many modern cars consume more fuel until the engine warms up. The larger oxygen content in the air won't help either, as both effectively lean the mixture.

On a side note, IFFF I remember correctly, not all cylinders have priming lines on the 1340 to minimize risk of flooding the engine(I might be wrong on that one, maybe it primes in the carb?)

The five top cylinders are primed.

-Esa