Visual determination of fuel on board
 

I have never owned a Cessna product before but I don't have any confidence in gauges no matter the bird. However, other than beginning every flight with full tanks how do you determine the fuel you have on board. For some of the singles I know there are "calibrated" dip tubes that are inserted into the fuel fill entry. And for my Seneca and Beech there were tabs that you could see.

But given the dihedral of the P337 and its single fill tube,it may be that the half full condition may not show up on the fill tube.

Can any of you give me a suggestion on what you do for this.

Dave Dillehay N84E

PS. Sorry if this has been answered before but the search function only shows gripes about gauges!

My first choice, like yours, is full tanks for each flight. I was taught to always fill the tanks when you return before you put the bird away. Having owned the current Skymaster for the last 33 years you sort of get to know all the characters of the particular aircraft. I too do not use the gauges as the only source of information. There are other stats that should be considered. First, my favorite TIME. Know your fuel burn and know how long you have been flying and how much time you have left. I also use the feature on the Garmin 530, essentially time again, that allows you to input the gallons and it calculates the fuel burn based on parameters that are user loaded given time flown. The other important stat is VISUAL. I still make a habit of visually looking in the tanks from the service port to make sure nothing funny has happened. This is especially important when parked outside on an unfamiliar ramp. Again when you have the FBO top the tanks you better make sure what tanks they topped and if they really did and if someone hasn't fooled with something. Just because it says 85 gallons on the ticket doesn't guarantee the tanks are full. Many times the FBO tops the inboards (normally the mains on a lot of aircraft) and not the outboards. This may be ok in the long run but if the mains are less than 1/2 I won't talk off. I will make them bring me a ladder and check the service port myself. Also because the mains are 2 separate tanks, interconnected by 3 couplings, if the tanks are filled with a high volume dispensing fuel valve the tanks will not have adequate time to equalize and your mains will not be full.

So in summery TIME is my gauge along with the instrument gauges (after 33 years I know what they read) and VISUAL check. Dipsticks will work in the inboards but you're not going to get a good reading with sticks in the mains.

I always like to use the upper half of the tanks instead of the lower half.

You use a dip tube which you calibrate per the instructions with the tube. It won't register below roughly 1/2 full, but it's quite accurate above that. In my 1973 normally aspirated 337E with long range tanks, a thin film visible under the fill port indicates you have 30 gallons in the tank (max 62). Greater fills can be accurately guaged with the tube.

Ernie

Hi Dave....

My model is a 1973 337G (no turbo and no pressure). Fuel determination can be a bit of a challenge for these planes. My plane has 4 tanks in each wing and one place to fuel all four way out towards the end of the wing and then the fuel SLOWLY feeds down to the inboard tanks. A calibrated dipstick would not work on my plane because I would only be dipping the outermost tank. I don't know if you have been reading about all my fuel gauge troubles lately but up until a few weeks ago I had very good luck with my gauges being very accurate and dependable. I do however never rely on them.

My methodology for determining fuel quantity is quite rudimentary but very dependable. When I top the tanks, making sure to take my time so the fuel has time to feed down to the inner tanks, I simply subtract 20 gallons for every hour I fly. Realistically the fuel burn is more like 16-18 gallons per hour but 20 makes a nice conservative round number guesstimate. You will most likely need to take the time to "get to know" your airplane and see precisely what it takes at the pump when you top it off. I find that I can usually be within 2 gallons when I fill her up. Just make sure your first few flights are with full tanks and learn what she uses and then add a little extra per hour for your flight planning and you will be fine. As I said, rudimentary but accurate enough.

I will reiterate once again, top her off SLOWLY and give the fuel time to feed down the line. The fuel pumps are ALWAYS faster than the plane can take the fuel. I personally will go back and fourth between each wing at least twice and occasionally 3 times if I was too impatient while SLOWLY feeding the tank the last several gallons.

My gauges always made a nice X-check with my math and I hope to have those back on line within a few days!

Hope this helps!

Ed Asmus

Oh yeah...

One more thing. Nobody fuels my airplane without my direct supervision. I prefer to do it myself but if the FBO must do it, then I am there period. Nobody secures my fuel caps except me!

Ed

I beg to differ with Ed, but I have exactly the same aircraft and you can indeed use a calibrated dipstick as long as you recognize the limitation, specifically that it won't measure below 30 gal per side. Above that, it's very accurate. Most of my flights are over water, adequate fuel is more critical to me than for most other Skymaster pilots, and I spent considerable time researching the system and making the information available in the Fuel Supply Management page at www.SKymasterUS.com

Other techniques, like supervising fueling and keeping close tabs on time, are critical, but for me the most important is climbing on the wings and using my dip tube.

Ernie

Ernie is correct. I was thinking in terms of the entire wing. One other thing I would like to add for Dave is to make certain you understand YOUR fuel system on YOUR particular model of Skymaster. These fuel systems vary greatly depending on the model!

Thanks for keeping me on my toes Ernie. I appreciate attention to detail!

Ed

Dear Ernie,

Just so I fully understand (given the model year differences) my 73 P337 with 128 gal capacity, should be the same as your 73 in fuel tankage. That is, if I can see fuel below the fuel tube, then I have at least 30 gallons. I will of course confirm this myself, but correct me if I am wrong.

Thanks,

Dave Dillehay

Yes, if the wing/tank arrangements are the same between your P model and my normally aspirated model, then if you see a thin film of fuel under the filler hole you have 30 gallons, and the tube (after you calibrate it) is used to determine quantity when you have more than just a film (1/4", 3/4", 1.5", etc.). The airplane must be on a level surface for accuracy, and, as mentioned by others, you need to wait until fuel has settled because the fuel SLOWLY feeds down to the inboard part of the tank system.

Filling is important, also. If you're starting from a very low fuel situation, use of the visual-and-tube technique on the first tank/side you fill will give you an inaccurately high reading, because the weight of the fuel on that side (unbalanced by the emptiness of the other side) will make the aircraft tilt in the direction of the tank you are filling, bringing more fuel under the fill port than there would be if the aircraft was level. So, when you just barely see fuel under the port (after waiting for fuel to settle, of course) you won't have 30 gallons, but 28 or 26 or perhaps less. Same with the tube. After calibration, if it shows you have 50 gal, you might have 45. The solution is to go fill the tank on the other wing and then return to the first tank to re-measure and refill as necessary. Generally, this iteration is not needed on the second tank/side, just the first.

Ernie

shadden, shadden digflo !!! unbelievably accurate all it takes is for the dumbass to reset the computer every time you get gas. on long fligths i would switch to mph. best mpg was 9+ gallons per mile

Agree, but.
 

You might want to lean it a little. (just kidding)

Regaardless the flowmeter, Ernie has a great point about fueling. An impatient line guy with a fast nozzle can leave you five gallons short per side.

Fuel Management
 

Hi Dave...congrats on the P337 purchase. Because of a past situation , I will never let a line guy fuel my airplane. I take my time and fuel slowly to the brim. Just remember, many a fine pilot have run a skymaster out of fuel. I have a shadden, and I love it, but time is always been my overriding factor. With 5 1/2 hours of fuel, I never push any legs past the 3 to 3 1/2 hour mark. Yes, when you are fat, dumb, and happy up in the upper teens in your pressurized beast (god, I love skymasters), it will be hard to let her back down. JIM

I also like to keep my legs to under 4 hours. But sometimes you can't (Miami to Boise RT, Virgin Islands to Miami) and these precautions pay off.

Ernie

if you look at the gas pump meter you know how much was put in, so if the line guy is impatient you will know

Getting old has its advantages
 

6 hour fuel range.

3 hour bladder range.

A pretty safe combination!

Yours or Jenny's?

Ernie

Fuel range - Jenny's.

Bladder Range - Mine.

This is an enjoyable thread. While all the techniques for the verification of fuel on board are fine for an aircraft either sitting on the ground or in flight with accurate gages, it is clear that the general consensus of pilots do not trust their fuel gauges and rightfully so. This begs yet another question. If an FAA examiner was administering a check ride in your aircraft what would you tell him about your fuel gauges. You would go and do all of the things you guys have talked about in the interest of verification, but the gauges had better indicate the same as you verify. If they did not, in the absence of an approved MEL, your aircraft would not be airworthy under FAR Part 91.205. The gauges must be installed and indicate the quantity of fuel in the tank. Timing the tanks is a great technique provided you do not have an inflight leak, which is the basis for the airworthiness issue regarding operable fuel gauges. If the aircraft was operated under a MEL then, if approved, you could use an alternate means like sticking the tank or operating with a known quantity prior to take-off to a specific limit. Without such approval, if you know your gauges to be inaccurate and you go fly, you would be operating in violation of 91.205. I understand that we all operate within the FAR's and that the gauges in every aircraft we have flown have been right on the money, all the time. But as aircraft owners we have an obligation to maintain the aircraft we fly in airworthy condition at all times. If their is doubt about the accuracy of your fuel quantity indicating system, it should be addressed in the same manner as a suspect crankshaft after a prop strike or engine ignition problem. You chase it down until you are confident that the system works the way it should. The 337 has a pretty straight forward fuel system yet we have all heard the stories of so many fuel related incidents.
Just my two cents.

Mark F
Atlanta

The only time that a fuel quantity gauge has to be dead nuts accurate is at EMPTY. This is spelled out in other OEM maintenance manuals. I don't care what it says at any other time, but I don't want to be running out when the gauge indicates 1/4 full.
They are all different at any other quantity, and I think that this is in FAR Part 23 (Certification).

Under Part 23 the gauge has to be calibrated to zero for the purposes of defining usable fuel from unusable fuel. And there are specifics for determining where usable fuel ends and unusable fuel begins. It has nothing to do whatsoever with gauge accuracy. The gauge is assumed accurate to determine the quantity of usable fuel in the tank at all levels. In order to maintain airworthiness the gauge must indicate the quantity in the tank. Having said this there is a bit of latitude as most light GA gauges are not graduated for dead nuts accuracy. But at half tanks indication you should have half of your usable fuel on board. If not and you decide to fill em up and go fly you would technically be operating an aircraft outside the parameters of airworthiness.

Mark F
Atlanta

engine gages
 

is there any stc engine gages out there for the 337 ??