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  #1  
Old 03-06-2018, 05:03 AM
KatanaPilot KatanaPilot is offline
 
Join Date: Feb 2015
Location: Locust Grove, GA
Posts: 356
Default Unusable fuel quantity

Just performed the FF tests for inspection, as well as calibration of the fuel senders/gauges (G3X through GEA).

We leveled the airplane for the calibrations and pumped all we could out of the tanks. From the fuel supply tank, we pumped out 1 gallon into a one gallon can and 5 gallons to a 5 gallon can (to their respective full lines) to "calibrate" the supply pump gauge.

Doing that, we found that we could only get about 39 gallons in to the tanks versus the specified 42 gallons. Either we have about 3 gallons of unusable
fuel or the supply tank gauge and our calibration of the gauge is way off.

The left tank has a flop tube which I assume could be a less effective pickup than the stock Van's.

I did search and what I found were most folks had ounces of unusable fuel and some got more than 42 gallons into their tanks. Anyone else have gallons unusable like it appears we do?
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Locust Grove, GA
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  #2  
Old 03-06-2018, 07:04 AM
rvsxer rvsxer is offline
 
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Location: Inver Grove Hgts, MN
Posts: 281
Default

The way I check unusable fuel is to drain and sump the tank (or do this the first time any fuel is put in the tank), level the plane, pour in a measured 5 gallons and pump it back out, through the fuel servo or carb supply line, using the boost pump just as the engine does. Measure what comes out, and the difference is the unusable fuel. I also time it so I get an idea of the max capable fuel flow of the pump. What you've done is measured the capacity of the tank, and I have no answer as to why it is different than Van's numbers. Your unusable fuel should be about .5 gallon per side.
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  #3  
Old 03-06-2018, 07:24 AM
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Bob Martin Bob Martin is offline
 
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Location: Richmond, Virginia
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Default

I hope someone else has a better answer,
but it sounds like you have RV-6 tanks.....
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RV-6, 0-360 Hartzell C/S, Tip up, 1150+TT
James extended cowl/plenum, induction, -8VS and Rudder. TSFlightline hoses. Oregon Aero leather seats.
D100-KMD150-660-TT ADI2- AS air/oil seperator. Vetterman exhaust with turndown tips.
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  #4  
Old 03-06-2018, 07:44 AM
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az_gila az_gila is offline
 
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 9,379
Exclamation

I initially tried calibration with 5 gallon fuel containers, and later re-did it with the airpark 100LL fuel pump system.

I found that the "full" marks on my 5 gallon and 2 gallon containers were way off.

Your problem is probably in the input system, not the tank.
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La Cholla Airpark (57AZ) Tucson AZ
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  #5  
Old 03-06-2018, 07:56 AM
KatanaPilot KatanaPilot is offline
 
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Location: Locust Grove, GA
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Default Thanks All

We have tried several methods of measuring unusable fuel and both have led to the same result - several gallons unusable. I still suspect the flop tube may be part of the problem.

The airplane was leveled and we used the electric fuel pump to drain each tank until we heard the pump start to run dry.

The first time we did this we only used the meter on the fuel supply tank and with completely dry tanks and fuel system - we pumped 41.2 gallons. We pumped them out and only drained 38 +- gallons.

Same approximate result yesterday.

Next time I will completely drain the tanks, weigh the airplane, fill the tanks and weigh again. Might be a little more accurate, but not convinced accuracy of scales is any better than that of the pump meter. Plus density of fuel changes with temperature, so weight/gallon comparisons might not work too well.

QB tanks from Van's, doubt they are for an RV-6. Made in Mexico I think, so I guess anything is possible.
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RV-10 under construction
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  #6  
Old 03-06-2018, 08:12 AM
az_gila's Avatar
az_gila az_gila is offline
 
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Location: 57AZ - NW Tucson area
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Question

So if I read it right, you measured the IN from a 100LL fuel dispenser, and measured the OUT with he "full" marks on 5 gallon containers?

If that is correct, it's an error in your OUT measurement.
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Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
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  #7  
Old 03-06-2018, 08:24 AM
rvsxer rvsxer is offline
 
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Location: Inver Grove Hgts, MN
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Before you start, you have to meter fuel from a pump into each container and mark them.
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RV-6 N207AM w/G3X, 1,500 hours +
South St. Paul, MN (KSGS)
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  #8  
Old 03-06-2018, 08:27 AM
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Bob Martin Bob Martin is offline
 
Join Date: Jan 2005
Location: Richmond, Virginia
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Default Flop tube

Ok, I hear you keep mentioning the Flop tube...
All your totals are for both tanks.
Do you have numbers for each tank?
That would show if one tank was different.
Remember the Vans SB about the fuel pickup coming loose?
Maybe you do have a problem internally....
While you have the tanks empty, you could stick a borescope up the drain hole and look around for issues.
A missing flop tube or pickup tube on one tank could cause your issue.

On the measuring topic, I bought a pitcher from a farm supply store that was 2 gallons, marked well up the side and used that to get accurate measurements.
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Bob Martin
RV-6, 0-360 Hartzell C/S, Tip up, 1150+TT
James extended cowl/plenum, induction, -8VS and Rudder. TSFlightline hoses. Oregon Aero leather seats.
D100-KMD150-660-TT ADI2- AS air/oil seperator. Vetterman exhaust with turndown tips.
Louisa, Virginia KLKU N94TB

Last edited by Bob Martin : 03-06-2018 at 08:30 AM.
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  #9  
Old 03-06-2018, 08:28 AM
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JonJay JonJay is offline
 
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Quote:
Originally Posted by az_gila View Post
So if I read it right, you measured the IN from a 100LL fuel dispenser, and measured the OUT with he "full" marks on 5 gallon containers?

If that is correct, it's an error in your OUT measurement.
I get your logic but when most of us can measure unusable fuel in ounces, it wouldn't matter what you used "out". It is going to be an obvious difference between a partial gallon and several gallons.
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  #10  
Old 03-06-2018, 08:30 AM
JonJay's Avatar
JonJay JonJay is offline
 
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Quote:
Originally Posted by Bob Martin View Post
Ok, I hear you keep mentioning the Flop tube...
All your totals are for both tanks.
Do you have numbers for each tank?
That would show if one tank was different.
Remember the Vans SB about the fuel pickup coming loose?
Maybe you do have a problem internally....
While you have the tanks empty, you could stick a borescope up the drain hole and look around for issues.
A missing flop tube or pickup tube on one tank could cause your issue.
To add to this, on my 6, the normal pick up can be seen without aid thru the drain hole. It should be laying right on top of it.
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RV1 - Proud Pilot.
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