Partialling fueling 148 gallon tanks in later models

[JimC]

Hi all,

Is there an easy way to *accurately* partially fuel a late model 337 with long range (148 gal) tanks?

If I understand right, the early models with aux tanks have 4 tanks and 4 fillers - and fuel management issues aside, you can choose not to add fuel to some of the tanks and arrive at an accurate partial fuel load. Many Pipers have metal tabs attached to the filler necks of long range tanks that allow you to stop filling when you reach a particular level.

Does any such option exist for the P337s with 148 gallon tanks?

Thanks,

Jim

* One option, of course, is to use a fuel totalizer and give the fueler (no self-serve at my home base) specific instructions. But errors accumulate over time, and I have heard of a lineman making a mistake once or twice in the past.

[JeffAxel]

my '77 P model had only one filler port per side, but 3 interconnected fuel tanks in each wing. They functioned like one big tank though. I suppose you you could make a dipstick and fuel it in increments on level ground to determine how much fuel is on board. Even LOP, you only get 4:30 to 4:45 before you should be landing with an hours reserve. I burned 24gph LOP in the mid to high teens and saw 180-185KTAS.

[bjherron]

I only have the 128 gallon version. But I can tell you that a dipstick is only good for the top 20 gallons in each side. If I have run down each side more than 20 gallons, it looks dry when I look in the tank. I am not sure if the higher capacity version is any different.

My solution: a fuel totalizer and regularly topping off.

Brian

[hharney]

There are no dipsticks or tabs that work for fuel capacity on the skymaster. The original system with separate aux tanks did not allow a dipstick to be used either. Although on the original system I suppose you could make up something for the aux tanks because they are single units.

Fuel totalizer would be best option. The Shadin system is a good direct replacement for the original fuel flow from Cessna but if you want engine analyzer features it might be cheaper to go with JPI with fuel flow built in.

The fuel gauges need to read empty when tanks are empty. It's always good to know that the gauge is accurate. De-fuel the tanks and find out. Then as you add fuel back in you can verify the gauges.

[JimC]

I have yet to fly a Cessna with "accurate" gauges. Sure, they read empty when empty - but they also read empty at 10-15 gallons remaining. I have to remember to explain that to my passengers if they haven't been up with me before - the gauges are right in front of their face.

I use a JPI w/ totalizer and it's great. I suppose I'll use the same if/when I get a P337.

[Ernie Martin]

Allow me to be a contrarian and suggest a way that may come close to a solution. It is to accurately determine how much fuel is in the tank when you first see fuel under the filler hole. The determination may require you to drain a tank.

I'm on my second Skymaster (the first a 1969 337D with 4 filler caps, now a 337G with 2 filler caps), I know a bit about our fuel systems (see my "Fuel Supply Management" page at www.SkymasterUS.com), and because I fly mostly over water to a remote island where there is no 100LL, fuel is especially important.

In my 337G, I determined that at 30 gallons is when you first see fuel under the filler hole. You have to be on level ground, with the tank on the other wing at about the same fill, and allow a minute or two for the fuel to settle. Obviously, this method doesn't work for fills below that "just-see" amount, but it's great for greater fills: just add however many additional gallons (if any) you need.

Incidentally, I am critically dependent on this trick and use it on every trip to the island. You might deem me paranoid but I am concerned about falling out of the sky on the return trip, because someone stole fuel from the airplane over the days or weeks it sat on this island -- where automotive fuel is expensive, security is minimal and the people are poor. So, when I leave Miami, I first fill to the "just-see" mark and then I add the amount I need to get to the island plus a little more (note: can't add indiscriminately because we're typically at full load outbound.) Then, when I do the pre-flight check for the return trip, I climb on the wings and make sure I see fuel on both tanks.

Ernie

[JimC]

Ernie,

I was wondering if that would work, but I guessed that with the daisy chain of tanks that you'd have to be closer to 60 gallons/tank to see any fuel in the last outboard tank of a 148-gallon 337. It's nice to know that it's a relatively small amount. Do you have the 74 gallons-a-side tanks, or do you have the smaller tanks?

How critical is the level ground fore and aft? I'm fairly certain I can reliably park the plane so it's level side to side. My refueling site at my home base isn't level - it's very close, but I can tell you the plane comes out of the hangar a lot easier than it goes in.

Jim

[Ernie Martin]

My 1973 337G has extended-range tanks but of the 128-gallon variety. However, it's likely that the 148-gallon version has all or most of the added capacity outboard of the fill hole, in which case you're likely to find that the "just-see" amount is around 30 gallons.

If it looks level, it's good enough. Also, if you use a carpenter's level (with a bubble), there should be some park angle where the two main wheels are level. Perhaps more important is that both wings have similar amounts when you do the fills to the "just-see" amount. When I return from the island I have used about 14 of the 30 gallons I had on the island, so both tanks have about 16 gallons, and that's close enough. A situation where the opposite wing is entirely empty or completely full will, of course, change things.

Ernie

[cessnadriver]

Hello ALL.
I'm wondering has anyone tried (by Form 337) plumbing the AUX fuel tank into the mains on the earlier C337 (prior to Cessna doing it to the newer models)?
Thanks, BILLS