Sight Glass + Fuel Tank in cockpit = Bad Mix?

[WingedFrog]

Yesterday I had the visit of a neighbor pilot, just back from Sun'nFun. While I was telling him about my mulling about the Gas Tank option and that I was concern about getting a good seal around the sight glass, he told me the following scare he had in his aerobatic Christen Eagle a few years ago:

He was flying with a passenger in the front seat about 13 miles from RDU. His passenger told him suddenly that he was smelling gas and, shortly after, he too started smelling gas. Then the passenger told him he was seeing gas dripping at his feet just under where the gas tank is located in the Eagle. He called an emergency, cut all power leaving only ignition and started climbing, waiting for the engine to starve at any time and trying to get enough altitude to glide to RDU. He managed to land on runway 23 with the fire trucks waiting... very, very soft landing! By this time 6 gallons of gas had dumped on the floor of the cockpit. There was a crack in the sight glass of the gas tank. He later found out that there was an AD for the Pitts which is the certified version of the Eagle. This AD required to change the sight glass every 4 years - his was 20 years old and as the Eagle is Experimental this AD had been missed by the previous owner!

This enlightening story put a close to my own pondering and led me to decide to build the tank rather than buy the pre-built tank. Although this might seem counter intuitive, here is what I think:

- There is no way to predict if a problem similar to the Pitts' AD will happen on the RV-12. Likely VANs was careful choosing the plastic used for the sight glass as well as the way it is fastened. However, the oldest -12s have only 2 years of flying and are not that many.
- In case problems arise in the future I will be in better shape taking care of the fix if I built the tank myself.
- I might well, as several -12 builders have already done, decide not to wait for a problem to close the sight glass window and put a mechanical level sensor. Here again having built the tank will make things easier.

Conclusion: I will order my finishing kit without the prebuilt tank option.

 

[Geico266]

Some of us early builders installed a fuel gage in the top of the fuel tank and closed off the site gage.

Use the search function.

 

[GDS]

I like the sight glass, there are a lot of graduation marks to go by when calculating fuel remaining.

The problem is when filling the tank. I'm reluctant to fill it all the way to the top of the filler tube, prefer to go just above the highest window in the sight glass. So I have to go back and forth, fill a little, then go look at the sight glass. The modification suggested by Geico266 is a great mod; it is a marine float gauge that goes in the top of the tank and you can see it while you're fueling. I plan to install one of these at the next annual inspection, but keep the sight glass.

 

[DonFromTX]

Someone told me the sight glass was worthless if you burn Mogas, since it has no coloring, you cannot see the level. Also, can you actually see the level when flying by looking over your shoulder?

 

[N520TX]

Grumman

Someone told me the sight glass was worthless if you burn Mogas, since it has no coloring, you cannot see the level.

My Grumman AA1A uses the glass site gauges also - there was an AD some time ago that required the insertion of a red float ball in the glass so that the level is easier to spot. I still fly that Grumman, and with avgas, without those floats, it would be real tough to spot the fill line.

 

[Peterk]

Seal it up...fill it up every time you fly and fly by time, not "remaining fuel". I consistently fill mine to right below the cap where I can see fuel in the tunnel. Like a car, you can hear it coming up the tunnel. Holds just over 20 gallons.

Pete

 

[jrs14855]

sight gauge

The material used in the Pitts is hard to find. Most use hardware store plastic tube. This was a well know problem 30 years ago. I always changed the tubing at annual and never had a problem.
The Christen Eagle copies most of the structure of the Pitts S2A. Frank Christen tried to buy Pitts, was unsucessful, and "designed" the Eagle. Much later he was sucessful in buying Pitts.

 

[Gagarin737]

Moeller marine gauge

 

[Geico266]

Perfect Gagarin!!

The engineering and prototype building team of Marty Santic & John Bender came up with that fix. Works great, you can see the gage when fueling and from the pilot's seat in the air. It is amazingly accurate also, every 1/4 of a tank is 5 gallons. It takes an addition 2 gallons when it hits full. The last 1/4 is a little iffy due to the shape of the tank so when I see alittle less than 1/4 it is time to land.

Perfect!

 

[Gagarin737]

Thanks Larry
I copied the measurements from master John Bender. The distance is measured from the edge not from the blue plastic! More info: mykitlog

Joeri.

 

[GDS]

While on the fuel tank subject, it's not in the plans, but it's a good idea to run a ground wire to the mounting plate for the kit-supplied sensor. Looking at the picture posted by Gagarin737, attach a ring terminal and wire to one of those mounting screws and connect the other end to the airframe. Otherwise, the fuel tank sealant may insulate the sensor from ground and give you intermittent fuel level readings.

 

[Gagarin737]

it's a good idea to run a ground wire to the mounting plate for the kit-supplied sensor.

I have seen that done by other builders and I keep it in mind but when testing in the plane with an ohm meter I had good ground between the mounting plate and the airframe.