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Fuel Tank Q's

Jamie Aust

Jamie Aust

Well Known Member
Im about to order my wing and fuse kit very soon.
I plan to have an 0-360 , FP, Trigear, slider. for cross country navs. day vfr.
only +G Acros ( dont like oil on the fuse ). No Flop tube, standard fuel caps.

I know that float type senders, are mostly used, I would like to hear from Cap sender people that have installed them and if they have failed ?
Some posters have said that the Cap BNC leaks, the plastic shims are not suitable for use with fuel, etc. I will build my own Cap to Res converter for each tank.

So what have you used ?
 
My capacitance senders are unreliable. I've tried two different converters (Princeton & Blue Mountain) and neither has worked. They calibrate just fine on the ground. I'm at the point where I believe it may be due to static buildup. Who knows.

I'd go floats next time. And no flop tubes either.
 
Some people say they work great others like Dan have had nothing but fits.

I have never rented a spam can were the float type ever worked so I guess there is no such thing as a reliable fuel guage on an airplane.

I think most of us these days are convinced that the fuel computer is the way to go and use the fuel guages to meet the FAR's and as a backup to the computer.
 
Jamie,

Properly installed float senders are highly reliable and easily repair/replaceable if ever the need arises. Not so with capacitive units, and there are reports of significant error when dealing with different fuel densities.

Fuel computers are only as good as the garbage in. If you stuff up fueling, number punching, or fuel leaks upstream of it, well... there's nothing like a gauge to tell you what remains.

John Siebold
Boise, ID
 
I installed the capacitance senders available from Vans and have an EI FL-2C fuel guage. I may be easily impressed, but this combo is really working slick for me. I have been diligent about checking my actual fuel amount using a calibrated dipstick with the amount that is reading on the fuel guage. Spot on each time.

I'd recommend this combination, so long as you stay with the same type of fuel. As was mentioned, the calibration for 100LL will not be accurate when using Mogas.

Regards,
 
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RV7ator said:
Jamie,

Properly installed float senders are highly reliable and easily repair/replaceable if ever the need arises. Not so with capacitive units, and there are reports of significant error when dealing with different fuel densities.

Fuel computers are only as good as the garbage in. If you stuff up fueling, number punching, or fuel leaks upstream of it, well... there's nothing like a gauge to tell you what remains.

John Siebold
Boise, ID
Click to expand...

I had a wise instructor tell me one day "If you trust that fuel gauge, it will kill you!" That was Evelyn Johnson, 58,000+ flying hours. I trust her judgement in this regard.
 
Floats

I have the float style in my 7. It took a couple of hours to calibrate the AF2500 but they seem relatively accurate.

I do not have any flop tubes either. I've done lots of aerobatics with only momentary neg G stuff. (Like a little push on the bottom half of a 4 point roll).

I think the simple logic would be, if you're not doing an inverted oil system, why go through the BS of putting in the flop tubes? You just aren't going to be negative that long.
 
cjensen said:
Why no flops Dan? I have floats and one flop. Are there problems with the flop tubes? :confused:
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IMHO, the problem with the flop tube is it forces you to put the float sender in a different location and swing direction. Add to that lack of care iin installation (as in the case of my store bought RV) and you have tank sensors that measure differently & incorrectly; one cannot measure the high end of the range, the other cannot measure the low end of the range (more critical). I hope to correct mine back to identical location & orientation, now that the flop tube has been removed.
 
cjensen said:
Why no flops Dan? I have floats and one flop. Are there problems with the flop tubes? :confused:
Click to expand...
Flop tubes are hoses, and hoses don't last forever. Theoretically they'll last longer than most people keep their RVs before selling 'em...

Ditto Darwin's response about acro. And ditto my reply to AX-O the other day about builders (myself included) tending to overestimate some of their upcoming "needs" as RV flyers, specifically on the topic of inverted systems.
 
I am convinced that the problem with the capacitive senders and different types of fuel can be solved. I have the capacitive senders, and expect to run MOGAS, so I am motivated to fix this. It does not look that difficult to solve. Unfortunately, it'll be a few years before I can prove this.

Now, if there is a problem with inaccuracies using the same fuel that was used to calibrate the gauges, then that is another problem. If it is due to changes in the dielectric constant of the fuel, that is easily solved. But, if there are unknown external influences, then this might be more difficult to solve (unless, it is temperature related, which can be dealt with). Might be a little more work than I anticipated. Not to worry, none of this time is logged.

On the other hand, the engine monitor that I am using will measure fuel flow, so the capacitive gauges will just be another reference point.

Cheers,
Tracy.
 
This is probably a dumb question since we all know that good pilots never make mistakes, but why not put a (small) switchable reserve fuel tank in line, like many motorcycles have, to add a gallon or two of fuel for emergency use?
 
rtry9a said:
This is probably a dumb question since we all know that good pilots never make mistakes, but why not put a (small) switchable reserve fuel tank in line, like many motorcycles have, to add a gallon or two of fuel for emergency use?
Click to expand...

We have that already - its called the other tank! Might be a good idea for those high wing Cessna's that have the luxury of feeding off of both tanks at the same time.
 
Not a dumb question, but you already have two tanks. Anyone dumb enough to run two tanks dry is probably dumb enough to run three tanks dry. At 8 GPH, a 1 gallon extra reserve will only get you 7.5 more minutes.


Tracy.
 
but 7 minutes at RV speed will get you to an airport or safe landing spot (at least in FL). That being said, my RV won't have an emergency tank.
 
Cap fuel sender

Thought I would pass along my experience with the captaincy fuels sensors. First they are simple to build and easy to calibrate. They give readings all the way from empty to full. The floats can?t do that because they are fully submerged at ? full. I also remember the problems with an old car and the mechanical sender. The coil resistance pot? wore out. The cork float in the lawnmower sank and sat on the bottom. I thought I would try something else this time around.

I ran into problems while calibrating the capacitance sender for the tanks. The battery ran low while pumping fuel between tanks. The low voltage threw the readings off and I had to recalibrate. I am not sure I fully trust readings knowing they can be off when the battery is not fully charged. I will take a second look at the voltage every time I look at the fuel level. Maybe that is a good thing; maybe I am just more paranoid as I learn more. The other thread where you just buy a plane not knowing how it works has a somewhat blissful appeal to me at this point.
 
TOAD said:
Thought I would pass along my experience with the captaincy fuels sensors. First they are simple to build and easy to calibrate. They give readings all the way from empty to full. The floats can?t do that because they are fully submerged at ? full. I also remember the problems with an old car and the mechanical sender. The coil resistance pot? wore out. The cork float in the lawnmower sank and sat on the bottom. I thought I would try something else this time around.
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Exactly what I want, full range, accurate measurement. Now tell me details of "simple to build & easy to calibrate", but for my already existing plane.... I know, build new tanks!
 
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GrayHawk said:
Exactly what I want, full range, accurate measurement. Now tell me details of "simple to build & easy to calibrate", but for my already existing plane.... I know, build new tanks!
Click to expand...

There are some capacitive "Probe" type sensors out there. I have seen them somewhere but don't remember where. These can be installed in a finished tank in the existing float type hole.
 
Capacitive Probes

Brantel said:
There are some capacitive "Probe" type sensors out there. I have seen them somewhere but don't remember where. These can be installed in a finished tank in the existing float type hole.
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Try SkySports Capacitive Fuel Senders. Very simple design & they'll build them to your specifications. We're putting them in our -10 tanks. Got a long way to go though before we can provide any real world feedback on them. In order to retrofit them you'd have to get a bendable probe so it could be routed from the existing float hole to the top of the tank, and then back down to the bottom of the tank. There are other mounting suggestions on their website. We ordered the probes only (no gauges since we're using an EFIS) and I think the cost was ~$80 for each probe.
 
Brantel said:
There are some capacitive "Probe" type sensors out there. I have seen them somewhere but don't remember where. These can be installed in a finished tank in the existing float type hole.
Click to expand...
I'll look into these; but in order to meet the "full range" measurement critera mentioned, the bendable probe would need to pass through the lowest spot in the tank (near pickup tube) and also the highest spot in the tank (near the filler cap). I was more or less challenging 'TOAD' to explain how he was getting full range measurement with his system. The other thing mentioned was "easy to build". I've looked at the installation of the Van's plate type sensors on rvproject.com and Dan has some very descriptive language on the installation of these; plus I don't believe they are able to sense full range.

Probably good enough though is accrurate measurement below 85% or so and you could achieve that with a bendable probe in the 1st bay, mounted through the existing float hole.
 
GrayHawk said:
I was more or less challenging 'TOAD' to explain how he was getting full range measurement with his system. The other thing mentioned was "easy to build". I've looked at the installation of the Van's plate type sensors on rvproject.com and Dan has some very descriptive language on the installation of these; plus I don't believe they are able to sense full range.
Click to expand...

Well, The outboard plate is just a few inches from the fill hole so maybe not to 100% full but maybe 98% full. I would consider this close enough to full range. I would be much more concerned with the lower level reading capability than the top.

As far as the install goes, it is a pain to get the wires crimped but other than that, the install is easy as pie.
 
GrayHawk said:
I'll look into these; but in order to meet the "full range" measurement critera mentioned, the bendable probe would need to pass through the lowest spot in the tank (near pickup tube) and also the highest spot in the tank (near the filler cap).
Click to expand...
Very true. Since I'm installing mine during the initial build my plan is to get about as close to this as reasonably possible by having the probe start near the pickup and traverse diagonally across 2 bays, terminating near the third rib and the upper skin. It's based on this installation by Chris Johnston (although his installation starts high near the inboard rib, and gets lower as it traverses outboard).
Anyway, just a datapoint...
 
Brantel said:
Well, The outboard plate is just a few inches from the fill hole so maybe not to 100% full but maybe 98% full. I would consider this close enough to full range. I would be much more concerned with the lower level reading capability than the top.
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98% sounds good. Any data on the low end? I would give on the high end for good accurate reading on the low end.
 
Low level indicator...

rtry9a said:
This is probably a dumb question since we all know that good pilots never make mistakes, but why not put a (small) switchable reserve fuel tank in line, like many motorcycles have, to add a gallon or two of fuel for emergency use?
Click to expand...

Or you could add a big red light and use this float/switch....

It is still for sale.... no-one wanted it.... :)

http://www.vansairforce.com/community/showthread.php?t=13777

gil in Tucson
 
Has anyone had any problems using capacitive sensors with a Dynon engine monitor? That is my current plan and was wondering if any other builders out there have had good or bad luck with that setup???
 
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