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"Usable" fuel capacity???

UnAnswerd

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In the PA28, if both tank were topped right up to the brim, the total fuel capacity would be 50 gallons. But what would be the "useable" capacity??? I couldn't find anything in the airplane manual.

Any information would be greatly appreciated.
 

viper548

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If I remember correctly, all the fuel in PA-28's is usable.
 

bigD

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It's been a long time since I've flown a Cherokee, but assuming you're talking about the PA28-140 you have listed in your profile, I remember it being 48 gallons.
 

FlyChicaga

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48 gallons. 2 gallons unusable fuel.
 

FOD

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now with that out the way, whats the purpose of having unusable fuel? just thought i would throw it out there, since i have had several DE's ask that.
 

gern_blanston

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It's like a guarantee. You can probably use the unusable fuel, but you WILL be able use the usable fuel. Just a little pad to include fuel that might get stuck in a wrinkle in the bladder, inaccessable due to a little slip or skid, etc. Way back when, one of our instructors taxied in in a '152 (WITH a student), shut down, and put 25.6 gallons of fuel in it after a cross-country. Usable is 24.5.
The good news, from my point of view, was that it happened a week before my CFI checkride, so I had a job waiting!
 
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NoPax

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I always thought it was the fuel left in the lines, pump etc, after the tank was dry - no pressure etc., to feed the engine.

I also thought it was a consideration in weight and balance, Standard or Licensed Empty Weight.

When I fuelled at the FBO I eventually got a job instructing at I put more than the capacity into a Cessna 152, and a Seneca II.

I see you got a 1 star rating UnAnswerd?...someone's at it again!
 

avbug

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now with that out the way, whats the purpose of having unusable fuel?

There is no purpose. That's why it's "unusable."

A certain amount of fuel remains which cannot be used due to fuel port positioning, and the inability of the lines to fully drain once the fuel pumps cavitate.

Fuel ports don't drain from the very bottom of the tank in order to prevent drafting any sediment or contaminants that may remain. What does remain is "ususable."
 

Kream926

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look in the daaammnn POH. thats usually where we find these things. dude, seriously.
 

Kream926

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shouldnt it though?????????????????
 

FN FAL

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NoPax said:
When I fuelled at the FBO I eventually got a job instructing at I put more than the capacity into a Cessna 152, and a Seneca II.
REALLY? Were the tanks dry because of mx?
 

avbug

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The Type Certificate Data Sheet (Cert #2A13, Revision 45) for the Cherokee 140 indicates a fuel capacity of 50 gallons at 95 degrees F. It also indicates in Note 1 of the same TCDS that an unuseable capacity of 2.2 lbs exists for the same, regardless of serial number. Therefore, the actual amount of unuseable fuel varies with temperature. The total volume in gallons for the tank remains constant due to physical dimensions, but the volume of a pound of fuel varies with it's temperature.

You can split hairs all you want wandering how much useable fuel you have, but from a practical point of view, if you never burn off the bottom half, as the saying goes, you won't run out of fuel. Never burn down that low, and you don't have to worry about how far you can push the airplane.
 

NoPax

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FN FAL said:
REALLY? Were the tanks dry because of mx?

No, just a couple of idiot pilots coming back from long cross countries. It wasn't much over the max fuel capacity, and I didn't spill any, nor did any leak out a vent...
 

Dr Pokenhiemer

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Maybe your pump needed to be calibrated. Maybe they paid for more than they actually got? I had an FBO try to tell me I bought more than my capacity once--turned out the fueler forgot to reset the meter before pumping my fuel.
 
T

TDTURBO

I had a guy put in 94 gallons in my 182, it only holds 92 with 88 useable. There is gouging going on at FBO's, needless to say I contacted the Department of weights and measures to investigate. Always watch what they put in, a lot of places will rip you off. I was told this was one of many calls they had on this guy, he advertises the lowest fuel prices in my area, now I know why.
 

avbug

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Fuel volume, and consequently gallonage, varies with fuel temperature. Rated capacity for a fuel cell occurs at a specific temperature...change the temperature, the actual amount of fuel that goes into that tank will vary from the published numbers.
 
T

TDTURBO

avbug said:
Fuel volume, and consequently gallonage, varies with fuel temperature. Rated capacity for a fuel cell occurs at a specific temperature...change the temperature, the actual amount of fuel that goes into that tank will vary from the published numbers.

I understand that, but by 10 gallons or approximately 10%?
 

avbug

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Ten gallons difference due to temperature, yes. Ten percent, I don't know...it may be possible, but that's for an intellectual type to sort out. However, in your case it was two gallons difference...you said 94 were put in, with a 92 gallon capacity. That's not ten gallons, but two, and it's only 2.2% of the total capacity, not ten percent.

When considering the ammount of fuel put into the tank, it's the total capacity, rather than the useable ammount that's relevant.

Why were your tanks that low to begin with?

A typical light aircraft fuel system is a float activated rheostat, and is purely volumetric in nature. A fuel gauge calibrated at zero degrees C will experience approximately a five percent error when going to fuel temp extremes of plus or minus 55 degrees, as suggested by AC 27.1337. Bear in mind that's strictly error on the fuel gauge. The variation by temperature is approximately 1% of fuel volume for each six degrees off the calibration temp, for some fuels.

You may have less useable fuel than you think if you've just flown at altitude or from a colder location, if you're reckoning fuel burn by gallons instead of pounds.

Also of note is the fact that virtually all gas pump calibration measurement is done using a Seraphin can, which measures strictly volume, and doesn't take into account temperature.
 
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