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Opinion on topping off tanks! Before Flight or After?


wcb

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Taking off with full fuel is something we learn in primary training, but carrying more fuel than you need is not efficient.  The lighter your plane, the faster/higher/cheaper it flies; takeoff and landing performance is improved.  Airlines and commercial operators "fuel for the trip".

However, one off-airport landing due to fuel exhaustion will probably wipe out all that efficiency.  :o

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I fuel for each trip specifically just prior to taking off. I never fill the tanks after landing. Here's why... In no particular order...

  • I taxi to and from my hangar on grass... so lighter is better.
  • With 76 gal useable, I rarely need full tanks and with absolutely accurate CiES fuel senders and JPI EDM900 fuel gauges, I don't believe in tankering fuel.
  • From the research I've done, the theory of water condensing in half full tanks or gasoline somehow protecting the sealant, are both old wives tales and therefore don't subscribe to either.
    • I've never once sump'ed water out of my tanks
    • The harm of taxiing over rough ground with full tanks greatly out weighs any benefit gasoline might have on the sealant.

Just my $0.02

 

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Only time I might fuel on a previous day is if we need to make an early start and that usually means we are going to need full fuel. Otherwise why carry 324 pounds when for a given flight much less is still more than enough. As such we fuel before departing and it really adds up to the same amount of time doing before or after.

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Summary:  I think I see a trend forming...

- large or extended fuel tanks have a big option to weigh... no need to fill 100 gallons when 30 is enough for the flight and reserves...

- having a fuel totalizer, and fuel level gauges... the exact amount of fuel burned is known and the other gauges work as a qualified back-up.

- having Ceis fuel gauges, calibrated FF, and a totalizer connected to a GPS that knows distance to the destination... the only known unknown left is effects of the headwind.  The unknown unknown would be a leak before the FF sensor... where Ceis accuracy can indicate something leaving the tank isn’t going to the FF sensor...

- Starting with the right amount of fuel is still a big PIC decision... Two MSers have gambled on flying to a fueling airport and had off-field landings prior to reaching that destination...

- When you get to really know your plane... the excess fuel is seen as extra weight that is unusually flammable...

- When you get to know your filling procedures... you know exactly how much fuel you are starting with... whether you use a stick, or wing mounted analog gauges, or Cies gauges calibrated for filling...

Parts of really getting to know your plane...

- Knowing your true un-useable fuel is really important. 

- Knowing when the low fuel warning comes on the anuncuator panel, how much is really in the tank...

- knowing how to activate the low fuel warning system before each flight... this one surprised me, because I forgot it over time...

 

Reminder to ask... how do Ceis gauges calibrate FL for filling while on the ground?  @fuellevel

Mooney’s have a significant nose up attitude while sitting on their wheels. This positions the surface of the fuel where the floats are, differently than when level in flight...

The more you know... Before the flight And During the flight, ...the closer your prediction is to what happens at the End of the flight...

Get to the destination safely, all the time...

For me... carrying excess weight messes with my 0 - 65 kias time... and slows the VS...

There is a lot of flexibility generated by a calibrated stick, and a calibrated FF/totalizer sensor... and excess fuel capacity...

PP thoughts only... not a cfi...

Best regards,

-a-

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7 hours ago, carusoam said:

 

Reminder to ask... how do Ceis gauges calibrate FL for filling while on the ground?  @fuellevel

 

I wondered that myself.  So after I finished calibrating the gauge I took the airplane off the jacks, drained a tank, and started putting in a gallon at a time while the airplane was sitting in the hangar.  I would then compare the known quantity with the gauge reading.  The idea was to create a conversion table.  Read the gauge then check the table to see how much I really have.  I gave up after about 15 gallons or so because the gauge was never more than .5 gallons different than actual.

What does make a difference is turns on the ground that make fuel slide from side to side.  That will make a difference of several gallons and will take a couple minutes to return to normal.

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 @carusoam

Well the ground filling component is a function of the smartphone APP I showed - tongue in cheek - for fuel level on the ground to replace a stick.    With an accelerometer onboard the integral  phone modem - aircraft attitude and ramp angle can be considered.    This APP is being developed for several of our commercial customers where this is a critical issue.  Equally hauling out a stick - does not inspire customer confidence.   

Kenmore - DeHavilland Beaver - Floats or Gear      

Cape Air - Tecnam P2012 - Commercial Application 

We are quite popular in Alaska for the reasons you stated in your post  - weight performance is critical for several missions and commercial operators are utilizing the combined fuel information & GPS  allow operators to put customers safely in places, that a lack of precise aircraft loading knowledge would have carried too much risk and liability.  As the season is over we have this month,   approx. 90 orders for Cessna 180, 185 headed in that direction.   Our acceptance rate in Alaska is staggering.   

So the intention of this APP takes care of Tundra Tires, Floats or Conventional Gear without cluttering up the cockpit with unnecessary flight information.    Once this portal is in place there are a lot of things that could be added in the future  - tire pressure, oil level, De-ice fluid, oleo pressure,  strain gauges for critical structure (not a Mooney Issue) - the list goes on ......

So yes - I think we are on to something.   

 

 

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Don't underestimate the importance of your taxi to and from the pumps if you use self service.

Fueling after a flight means you'll need to hot start.  Depending on your engine, you may or may not engage the starter more than once (wear item).  You'll have a short taxi to parking / hangar when you may shut down without having your battery reach a full charge on ship power (another wear item). 

I typically fuel prior to flight unless I'm using a significant proportion of fuel or I need a fuel receipt that day.

 

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Joining this discussion a little late, but I also have a different fueling procedure. I am fortunate to live ~5 minutes from my plane, so I will go out the night before any flight of significant length (2+ hrs.) to fuel to my planned level and do a thorough pre-flight (oil level, tire pressure, clean windscreen, etc.). Then in the morning, the fuel has settled for a good sumping and the final pre-flight.

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