What's too Much Weight?

[markb5900]

Late to the party on this one.
Interesting discussion to read.

Back to the OP though. As a relatively "young" pilot with 55 hours, when you are going to operate up near that Max Gross number it takes a little more planning than just jump in an go.
The easiest way to get down to where you need to be when you know you are taking all those peeps in the plane with you is to lower your fuel load. Since I rent, I usually tell the FBO a day or two before that I am only going to want xx gallons in it for my trip and they have always been good about helping out with the fuel on the prior flight or two.
Also, please do your take off roll calculations. Even though it will fly 30 pounds under weight, it may not fly off that 2,000 foot strip that you plan on taking your friends to that day. (Just an example)
Not necessarily talking about THIS trip, but in the future, if you are needing to only have xxx amount of fuel on board, and you plan on getting fuel somewhere. Either go to a self serve pump or make sure you stand there when it is fueled. The line guy you told to only go to the tabs may get called away and now no. 2 line guy comes out and tops it, not knowing. Then the fun starts with who is paying for the extra fuel and who is going to get it out of the plane.

Hope you have a fun trip!!!

 

[Ted]

With the understanding that the weight of the fuel changes with temperature.

I've found that, provided you operate the engine the same, it ends up amounting to the same number of hours worth of fuel just about every time. So, I try to record time.

What I've done on the planes I fly is purposely take an appropriate mission to fly each tank dry to get an appropriate time. Obviously this gets more difficult if you can only take off and land on particular tanks.

 

[jesse]

I've found that, provided you operate the engine the same, it ends up amounting to the same number of hours worth of fuel just about every time. So, I try to record time.

What I've done on the planes I fly is purposely take an appropriate mission to fly each tank dry to get an appropriate time. Obviously this gets more difficult if you can only take off and land on particular tanks.

Sure. The actual fuel weight differences with varying temperatures rather negligible for the quantities of fuel we generally operate with. I only stated it as the word "precision" was used

 

[poadeleted20]

On the third hand, if you empty the tanks before weighing and then fill them, you know not only what the empty weight is, but, since you know how much fuel you just added, you also know the weight with full fuel and precisely how much fuel it will actually hold!

That would be the best of all possible worlds.

 

[poadeleted20]

With the understanding that the weight of the fuel changes with temperature.

Technically, the weight of a given mass of fuel doesn't change, but the volume that weight of fuel occupies does, and the weight of fuel which will fit in the tanks will change. So, if it warms up after you fill the tanks, some will spill out. If it cools off, you'll be able to stuff more in.

That said, I doubt the difference will be particularly significant unless you do the weighing at Lat 90S in July and then refuel two days later in Central Africa.

 

[jesse]

Technically, the weight of a given mass of fuel doesn't change, but the volume that weight of fuel occupies does, and the weight of fuel which will fit in the tanks will change. So, if it warms up after you fill the tanks, some will spill out. If it cools off, you'll be able to stuff more in.

That said, I doubt the difference will be particularly significant unless you do the weighing at Lat 90S in July and then refuel two days later in Central Africa.

Ron, you were talking about the differences in fuel tank capacity based on the allowed tolerances of the design. That's pretty negligible. Since the word "precision" was used I added another variable that would be required for the level of precision you were referring to.

I also didn't say that the weight of fuel magically changes with temperature - I was saying that the weight of your tanks with "full fuel" will change with temperature.

It's all negligible at the quantities of fuel we carry.

Anyone who is worried about the quantity of fuel to the above precision is operating way too damn close to the margins and will get screwed by many other variables that will play a larger role.

 

[TMetzinger]

Anyone who is worried about the quantity of fuel to the above precision is operating way too damn close to the margins and will get screwed by many other variables that will play a larger role.

Yep. Sort of like calculating runway length required to the foot or tens of feet. If the runway has to be 2510 feet because 2500 is too short - I really shouldn't be operating on it.

 

[Ted]

That would be the best of all possible worlds.

It would end up providing you less useful information than just running the tank dry and refilling it, since if you completely drained the tank you would then be refilling it with unusable fuel. By running it dry, you know how much usable fuel you have. As you know, a lot of older aircraft, especially with bladders, can have some discrepancies from what they ought to.