Sport Pilot Talk

Yesterday I FINALLY got around to replacing the original fuel pump on the ROTAX 912 in my 2007 Sky Arrow.

I had bought the pump some time ago, but fell into the "if it ain't broke..." mentality. But it was time to start on my second rubber parts replacement and I figured with the fuel lines it would make sense to do the new pump at the same time. Also installed the drain line as required.

I just finished with the fuel lines today, and have not done a runup yet. But something in the SB is just a tad unclear...



My POH shows the acceptable fuel pressure range to be from 2.2 to 5.8 psi. Here's how my gauge is marked:



In the latest ROTAX 912 Owners Manual I can find, it still says 2.2-5.8 psi, but then parenthetically says the high end is 7.26 psi "Applicable only for fuel pump from s/n 11.0036".

Am I correct in assuming that includes my new style fuel pump? I don't have the s/n here to check. If so, rather than try to remark the fuel pressure gauge, I'll just add a small placard with the new max psi.

Tomorrow when I do the runup I'll check the fuel pressure for any change and get the s/n of my pump.

Yes Eddie, although I’m not a mechanic if it’s the new Corona style pump then the high end is 7.2. My gauge range was easy to change since it’s Dynon glass.

I was of the same mentality as you several years ago when the SB came out. I was reluctant to change it as my old pump was working beautifully but Rotax offered a free pump and I had to send my old one back. I figured, what the heck, it’s free.

Thanks! I’ll get to work on the placard.

As an off-topic aside, I thought it was quite a coincidence that this diagram came across my Twitter feed this morning:



On the lower right, I discovered that “If it ain’t broke - don’t fix it” it actually has a name: Status Quo Bias!

I'm not convinced all cognitive bias is a bad thing. Some of them have developed as survival strategies, after all...

MrMorden wrote:I'm not convinced all cognitive bias is a bad thing. Some of them have developed as survival strategies, after all...

Of course.

A rustling in the bushes was historically probably not a saber-toothed tiger.

But assuming that it wasn't could end up culling the gene pool for that tendency to assume. Whereas assuming it was a saber-toothed tiger when it wasn't had little downside.

Still, I think its generally good to be aware of these biases, along with other errors in reasoning, i.e. logical fallacies. Which are EVERYWHERE!

Unless that's a hasty generalization, of course!

FastEddieB wrote:
Unless that's a hasty generalization, of course!

Of course, all generalizations are untrue!

I think the "if it ain't broke, don't fix it" can *sometimes* be valid. You are using your personal experience to color your decision of that of others to arrive at a decision. Of course, the "others" might have more info than you do, and you could always be a moment away from disaster, but all maintenance carries risks.

I agree that understanding bias is critical, even if you allow yourself to indulge in it occasionally! The key is to know why you are making decisions, and not to just let apathy make them for you

MrMorden wrote:I think the "if it ain't broke, don't fix it" can *sometimes* be valid.

I prefer the Mechanic's Corollary: if it ain't broke, break it. Then, fix it.

I guess most ROTAX 912's already have the new style fuel pump in place, but here it is installed on mine:



Fuel pressure solidly in the green:



Finally, placarded the fuel pressure gauge with the new upper limit:



Working on the logbook entry now, will test fly for return to service in the next couple of days.

drseti wrote:

MrMorden wrote:I think the "if it ain't broke, don't fix it" can *sometimes* be valid.

I prefer the Mechanic's Corollary: if it ain't broke, break it. Then, fix it.

And don’t forget corollary 2: “If force doesn’t fix it, apply more of it.”

MrMorden wrote:

drseti wrote:

MrMorden wrote:I think the "if it ain't broke, don't fix it" can *sometimes* be valid.

I prefer the Mechanic's Corollary: if it ain't broke, break it. Then, fix it.

And don’t forget corollary 2: “If force doesn’t fix it, apply more of it.”

Or...get a bigger hammer!

So what was in the bushes

I didn't know the guy but do know the author who tells of a solder on point in VN. He heard a rustle in the bushes and it was indeed a tiger!
It lunged, clamped down on his head and commenced to drag him off. He managed a long burst and the tiger let him go...

How many have a tale like that to tell

FastEddieB wrote:Or...get a bigger hammer!

Is this what you had in mind, Eddie?

Flew the plane today as a test flight.

Fuel pressures are definitely higher throughout. At the lower left, you can see it just touching the top of the old green, 6 psi, at what might be a normal cruise altitude and power setting.



Bear in mind, more is not necessarily better. Same carbs on a motorcycle get enough fuel from just gravity feed, and too much can overpower the needle and seat. But even the new limit of 7.2 psi is not a whole lot of pressure.

I had one airplane that the new fuel pump was to much for the carb. It would overpower the needle at idle and the engine would run rough. After trying a few things myself I removed the carb and sent it to Leading Edge Airfoils and they worked some magic on it and the problem went away.