PA-44 Seminole fuel cap with ruler?

[RussR]

I have started teaching in a PA-44-180, Seminole, that has unusual (to me) fuel caps. The fuel caps have a ruler sticking out from the bottom that has both inches and centimeters marked on it. You can see how much fuel is in the tank by looking at where it's wet on the ruler when you pull it out. I imagine this is to measure the amount of fuel on board. However, I can't find anything in the POH or STCs that talks about this.

Since the measurements are in inches and centimeters, I suspect there must be a conversion chart - something like "5 inches of fuel = 40 gallons".

My Google skills have failed me. All I can find is information about dip sticks, the type you put your thumb over (which the POH talks about), nothing about these fuel caps.

Anybody know what I'm talking about? Ultimately I'm hoping to find a conversion chart.

 

[TrueCourse]

Sounds like a home brewed gauge, but I hope I’m proven wrong. How is the ruler portion attached to the cap itself?

 

[RussR]

Sounds like a home brewed gauge, but I hope I’m proven wrong. How is the ruler portion attached to the cap itself?

I'll be out there tomorrow and will take a closer look (and hopefully remember to get a picture). This is a 2002 model and has been through several flight schools in its hard life...

 

[Bs4304]

I think this is what you are looking for.

 

[RussR]

I think this is what you are looking for.

I agree, I think that is exactly what I'm looking for. Where did you find it?

Here are pictures of the fuel caps. The ruler just looks like one you could get at any hardware store, though it is nicely safety-wired on.

 

[Bs4304]

That is much different than I remember. The photo I posted is from a checklist used by UND Aerospace for the Seminole. The PA44-180s I flew there were manufactured 2014-2016. I assumed the ruler/dipstick was a factory mounted item. It looked much more an integrated part of the fuel cap than the photo you posted.

 

[RussR]

Perhaps they got fancier as the years went on - maybe they went from being an aftermarket item to OEM. It is interesting though - using "inches" seems more like a prototype design to me. If you're making enough to make them nicer, wouldn't you just go to labeling the gallons right on the dipstick?

 

[Bs4304]

I thought the same thing. Every other fuel dipstick I’ve used has shown the measurement in gallons. I thought maybe this was a Piper thing, being an inexperienced pilot. It only makes sense to go to gallons and remove the chance of an error with the extra step of conversion from inches to gallons. I wonder if it was a UND addition, or a Piper design.