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  #11  
Old 11-06-2019, 10:44 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Originally Posted by ALagonia View Post
What EFIS system are you referring to? I have dual AFS 4500’s. Calibrated my tanks two gallons at a time with the airplane in a level attitude and they are miserably inaccurate. So much that I don’t pay any attention to them. I use the gallons used from the red cube as my indication of fuel in the tanks. Finally tweaked that to where it is reliable.
Then you must have done something wrong, because that doesn't match the experience of most RV builders.

Maybe I need to qualify the accuracy statement since some people haven't fully developed a good understanding of how the standard float level sensors work in an RV...

When you have a wing tank on a wing with dihedral like we have on RV's, and have the fuel level sensor installed in the inboard most rib bay of the tank, it will never be possible to have the gauge measure the fuel level from 100% full to totally empty. That is because the dihedral angle makes some of the fuel in the tank, located at a higher level than the float on the sensor is. So until the fuel level reduces within the sloped tank to a point that the float just begins to drop from its highest possible point, there will be no indication of fuel usage and when doing the calibration process, the last few gallons will not register a change.

None of this matters in the grand scheme of operating the airplanes because knowing whether the fuel level has reduced 2 gallons or 3 gallons below a full tank doesn't matter.

What matters is accuracy from 1/2 full to empty. In general, RV's are very accurate from in the neighborhood of 3/4 to 4/5 ths, down to empty.

In the case of the 25 gallon tank in the RV-14, use of the first 4 gallons or so will not register as a change on the gauge, but from 21 gallons down to empty it will be very accurate.
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  #12  
Old 11-06-2019, 11:06 AM
j-red j-red is offline
 
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Location: Lewes, DE
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Originally Posted by HAL Pilot View Post
Really curious on how much extra fuel goes in after the fuel floats hit the top of the tank.
(

On my 8 with 21 gal tanks (leveled with a sawhorse under the tail to calibrate), the floats topped out at about 16 gallons. Once below that threshold, they're very accurate.
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  #13  
Old 11-06-2019, 11:16 AM
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mill2978 mill2978 is offline
 
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Location: Erie, CO (KEIK)
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I called the FBO and got a bored line guy to come out with the fuel truck. We added fuel two gallons at a time, calibrated in tail down attitude, then lifted the tail to flight attitude, took a calibration, dropped the tail, and repeated until the tanks were full.

I have what is likely one of the last capacitive fuel sender kits and dynon voltage converters feeding a garmin system. The setup is very accurate below 4/5th of a tank.

I wouldn't be too concerned about doing this calibration until you are on the gear, and even then it can wait until you are flying.
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  #14  
Old 11-06-2019, 04:18 PM
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emsvitil emsvitil is offline
 
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Location: SoCal
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Originally Posted by mill2978 View Post
I called the FBO and got a bored line guy to come out with the fuel truck. We added fuel two gallons at a time, calibrated in tail down attitude, then lifted the tail to flight attitude, took a calibration, dropped the tail, and repeated until the tanks were full.

I have what is likely one of the last capacitive fuel sender kits and dynon voltage converters feeding a garmin system. The setup is very accurate below 4/5th of a tank.

I wouldn't be too concerned about doing this calibration until you are on the gear, and even then it can wait until you are flying.

I hope he got a tip.........
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  #15  
Old 11-06-2019, 04:49 PM
BillL BillL is offline
 
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Location: Central IL
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Default +1 on dip stick

Quote:
Originally Posted by Discus2b View Post
Not sure if there is a reg. but I waited until after completion and had a few hours of flight time. I’m a bit old school and made a fuel tank dip stick the first time we filled her up, 5 gallon increments.
I don’t care for the saw horse idea as being too narrow even with a cushion. I would be one angry hombre if I put a crease in my new pony. So, small 300# step platform, some shotgun ammo cases and firm foam cushions under the bar attach point got me to level to do the fuel and attitudes calibration.
Hanger floor reasonably level for the lateral leveling, nothing was needed there.
Be careful.

R
Getting a dipstick calibrated drove me nuts. I found two things. The fuel wicks up a lot more than you think. 1/2 gal on my 7. The second is that a little roll knocks off the measurements. So - set the jacks under the wings to level them had hold the position as one tank is filled. A small glass or plastic tube worked best to measure the level. I tried wood, metal ruler and a tube. The tube worked best.

I made a strip of .025 X .3" from aluminum. It is marked by drilling 1/16" holes (maybe smaller) to catch the fuel in 1/2 gal increments. Wicking can easily show more than a 1/2 gal higher but the hole is not filled with fuel. Unlevel ground conditions yield less accurate levels on a single tank, but the combination is well within a gallon, mostly a half.

I only calibrated the stick with the tail on the ground.

But did both for the electronics.
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Last edited by BillL : 11-06-2019 at 04:59 PM.
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  #16  
Old 11-06-2019, 05:26 PM
ALagonia ALagonia is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
Then you must have done something wrong, because that doesn't match the experience of most RV builders.

Maybe I need to qualify the accuracy statement since some people haven't fully developed a good understanding of how the standard float level sensors work in an RV...

When you have a wing tank on a wing with dihedral like we have on RV's, and have the fuel level sensor installed in the inboard most rib bay of the tank, it will never be possible to have the gauge measure the fuel level from 100% full to totally empty. That is because the dihedral angle makes some of the fuel in the tank, located at a higher level than the float on the sensor is. So until the fuel level reduces within the sloped tank to a point that the float just begins to drop from its highest possible point, there will be no indication of fuel usage and when doing the calibration process, the last few gallons will not register a change.

None of this matters in the grand scheme of operating the airplanes because knowing whether the fuel level has reduced 2 gallons or 3 gallons below a full tank doesn't matter.

What matters is accuracy from 1/2 full to empty. In general, RV's are very accurate from in the neighborhood of 3/4 to 4/5 ths, down to empty.

In the case of the 25 gallon tank in the RV-14, use of the first 4 gallons or so will not register as a change on the gauge, but from 21 gallons down to empty it will be very accurate.
Maybe I should do the calibration again. But I did it carefully. Tail (I have a tailgragger) raised to level as checked with a level on the rails under the slider canopy. We put in 2 gallons at a time and calibrated accordingly. I understand about full doesn’t show full but will get accurate as fuel is burned. But my gauges are way off. The indications on the EFIS are no where close to what is actually in the tank.
Any thoughts on why this is so?
Thanks
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  #17  
Old 11-06-2019, 06:16 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by ALagonia View Post
Any thoughts on why this is so?
Thanks
A couple of possibilitys....

Some senders are a bit stiff and move with some friction when new. Others are always that way. This can effect calibration because with the engine running there is a lot of vibration that helps relieve the stickiness so that the float moves to its natural floating position. We don't normally do a fuel level calibration with the engine running, so it can result in different set point values.
To mitigate the possibility of induced error, you can vibrate the tank by smacking it with your hand repeatedly after adding fuel, until the set point value stops changing, and then save it.

The other possibility is that the grounding of the sender has changed since the calibration was done. The sender resistance range is only 30 (full) to 240 (empty) ohms. usually if the grounding gets some resistance in the path it is way over 240 ohms so the system usually quits working all together, but it is a possibility.
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  #18  
Old 11-06-2019, 07:32 PM
Discus2b Discus2b is offline
 
Join Date: Mar 2016
Location: Willis Gliderport
Posts: 143
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Quote:
Originally Posted by BillL View Post
Getting a dipstick calibrated drove me nuts. I found two things. The fuel wicks up a lot more than you think. 1/2 gal on my 7. The second is that a little roll knocks off the measurements. So - set the jacks under the wings to level them had hold the position as one tank is filled. A small glass or plastic tube worked best to measure the level. I tried wood, metal ruler and a tube. The tube worked best.

I made a strip of .025 X .3" from aluminum. It is marked by drilling 1/16" holes (maybe smaller) to catch the fuel in 1/2 gal increments. Wicking can easily show more than a 1/2 gal higher but the hole is not filled with fuel. Unlevel ground conditions yield less accurate levels on a single tank, but the combination is well within a gallon, mostly a half.

I only calibrated the stick with the tail on the ground.
But did both for the electronics.
I fueled the wings back and forth to keep even. The stick is to ‘ball park’. I’m not looking to loiter hoping for a lone MiG over Hanoi, with a 3 min bingo fuel.
A half gallon is within my acceptable margin of error. My Stick don’t Wick.
Sorry Scott, I just can’t relax getting on and off the wing, in and out of the cockpit multiple times with a ‘saw horse’ under the bar. Many do.

R
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  #19  
Old 11-06-2019, 08:47 PM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 1,170
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I have used dipsticks for some time and consider them to be quite reliable. I’ve used oak hardwood that I sanded to a very fine finish, so, not as much (or any) ‘wicking’. My latest dipstick is a plastic tube (see below). There is no wicking possible with this one, and when I topped off today, the stick was within 1/2 gallon total. Like all fuel dip sticks, or fuel level senders, requires calibration.

https://www.sportys.com/pilotshop/un....html?___SID=U
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  #20  
Old 11-07-2019, 05:06 AM
tgmillso tgmillso is offline
 
Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
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Another vote for the plastic tube style dipper. They are super accurate/repeatable. It would be great if someone would make a custom one for each RV type, but in the interim I'm using a C172 version, for the reason if I ever lose mine, you can generally get a C172 dipstick of some type most places. I just have a conversion table in my favourites on my phone and another in the back of my flight manual.
Regarding getting the aircraft up to level flight, I just lift the tail onto a 1" slab of particle board that sits on top of a 55gal drum (or 44 imp gal in this part of the world) and it gives me the perfect level flight attitude (for the RV-7) and a super stable platform.
Tom.
RV-7
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