flyboy1963

flyboy1963

Well Known Member
thought this must be specific to the -9, so wondering if anyone has calibrated their fuel levels.
I've drained my tank once, but haven't gotten a handle on measurement.
Assuming perfectly level ground, when the fuel level is just visible, how many gallons is that? Is it truly 'half tanks' or 8 gallons?
then, is the rest linear, ie' one inch is one gallon?

thanks to anyone with some numbers for me.
 
I don't have the answer for you, but I would love to have a calibrated dipstick for the fuel tanks on my 9A. Having a visual check prior to take off is very helpful. My 9A isn't flying yet, but the Gobosh 700S I have been renting at the airport has a dipstick on the fuel tank. Its a great addition.
 
On my RV-6A...

...measuring from the fuel filler...the fuel just becomes visible at the bottom of the tank at 4Gal.

Still measuring from the bottom of the tank, 1.25 inch up is 6 Gal total.

Measuring from the bottom of the tank, 2.5 inch up is 10 Gal total.

Measuring from the bottom of the tank, 4.0 inch up is 14 Gal total.

Measuring from the bottom of the tank, 5.5 inch up is 18 Gal total.

The overall length for the stick is 15 inches. This length ensures that if I slip and drop the stick in the tank, at least part of it will still be sticking out of the fuel filler and not floating in the fuel.

My measurements for each tank were not the same, but within 1/8 inch for the L and R tank. I split the difference and made a mark on the stick as my "APPROXIMATE" measured fuel quantity. I also put a mark on the stick to indicate the very top of the wing tank skin just to have a visible reference when "dipping" the tank.

I clip the Fuel Tester tube, the "fuel dip stick" and a stubby 3/8 open end wrench to the back of the pilots seat for easy pre-flight access. The wrench is used as my fuel-cap-lever-popper-tool.
 
See this thread for 9A calibration information Universal Fuelhawk Calibration

Note: The increments on the Universal Fuelhawk Aircraft Spruce item UNIV FUELHAWK FUEL GAUGE 11" Part No 13-00439 are 4/7" per increment.
 
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Fuel Stick Calibration

Don?t know where your airplane is but mine sits on sorta level ground in the hanger, in front of the gas pumps (on any field) or on a sorta level ramp in a tail down attitude. Doesn?t really matter cause you never know exactly where you may be. The ground is never perfectly level. The only time your plane is perfectly level is when you weight it.

I run a tank dry in the air, switch tanks and then land. That way un useable fuel is never on the dip stick. Taxi up to the gas pump, and start refuling. I use paint stick stirrers cause they?er cheap (free). I pump a in gas until I can see it in the tank where it will just touch the bottom of my stick when inserted perpendicular to the wing cord. I write that amount on the bottom of the stick. I then add incremental amounts of fuel and mark the stick appropriately for my specific needs to know until the tank is full. I repeat the entire process for the other tank but that stick usually becomes a back up since the tanks are within a couple of tenths of each other (and I tend to lose them). One I carry and one stays in the hanger.

I dip prior to every flight and maintain a running fuel burn average based on tach time. I find it very reliable. Never use the fuel gages. They are notoriously unreliable.
 
There was a thread here somewhere in the past that described an internal dipstick for fuel (thus I am not taking credit for what follows). For mine, I used a piece of 040 Al about 1/2 inch by 8 inches, which I bent at 90 degrees and drilled a hole in the short leg to fit onto the fuel cap nut (i.e., inside the tank). The bottom of the Al is just short of the tank bottom. I then filled the tank one gallon at a time and made a small notch on the edge of the Al at each gallon. If I can see fuel on the bottom of the tank, there are about 4.5 gallons in the tank. Filling is not linear, particularly near the top of the tank. Once I had the notches made, I put the Al in a drill press and drilled small holes (like, #55) at the appropriate level - I used two holes for even numbers of gallons and one hole for odd numbers. Finally, I used a marking tool (tungsten tip scriber) to mark the gallon numbers. I find that seeing the fuel level on the Al without the holes is difficult, but fuel will stay in the holes after you pull the dipstick out so it is relatively easy to tell how many gallons are in the tank by which holes are full of fuel and which are empty. And I never forget or lose the dipstick!

greg
 
RV-9A fuel calibration

here is a plot we did of usable fuel vs fuel depth. It done in Litres and millimeters, but I had to build a whole aeroplane using inches so i don't want to hear any whining ;-)

Dave



 
Jamie said:
If I look in and can't see any fuel, I know that I have less than 12 gallons left in that tank (I usually go with < 10 to provide a safety margin).
Click to expand...

I don't understand this statement.... If you look into the filler and see NO FUEL then you know that you have less then 12 gallons so you assume you have 10 gallons and go flying?

If you see NO FUEL, would not you assume that you have NO FUEL IN THAT TANK?

In my 6A tank, if I can just see the fuel, I have three gallons in that tank. So what you are saying is because the 7A tail is higher than the 6A, that you can get another 9 gallons in the tank before you see the fuel?? That would mean that the tank is over 1/2 full and it would only take 9 more gallons to fill the tank...... Something is wrong here!!!:eek:


BTW. I made my dip stick from a piece of OAK trim and marked it with a FINE LINE SHARPIE for each gallon that I added to an empty tank. It will start to fade after about a year, so just redo it before it is gone. Oak works good because it does not suck in the fuel like a soft wood would do.

I dip my tanks at every flight and enter remaining flight time based on fuel burn (with a good safety margin) into my count down timer. When I refuel based on the dip stick, I will be less than .5 of a gallon off total. You can't get that close by just looking into the tank......:eek:
 
Another thought...

...is to have a metal tab suspended from one of the rivets around the cap opening, like my Air Tractor comes with from the factory. The tank holds 117 gallons of Jet-A and the bottom of the tab is labelled 3/4.

Regards,
 
gasman said:
I don't understand this statement.... If you look into the filler and see NO FUEL then you know that you have less then 12 gallons so you assume you have 10 gallons and go flying?

If you see NO FUEL, would not you assume that you have NO FUEL IN THAT TANK?
Click to expand...

One thing I really hate about the Internet is how sometimes things get interpreted the wrong way. I am not an idiot, gasman. If I don't see fuel in the tank I don't depend on it and for planning purposes and I do assume that it is empty although it really isn't.

I re-read my previous posts and realized that they were sufficiently confusing so I deleted them. Also, I mentioned something incorrect. If I see a little fuel on the bottom of BOTH tanks then I know that I have 10 gallons remaining total (5 gallons per side). That is conservative. When I calibrated my float senders I watched each tank swallow a 5 gallon can of avgas and couldn't see any fuel in either tank after the fact.
 
Cheap Fuel Dipper

Just get some rigid clear plastic tubing (gas safe) at the hardware store, mark it with a sharpie. Use your thumb on the top when dipping. Same as the commercial product that you have to calibrate yourself, but cheaper by far. I don't remember which diameter I prefer, but I actually used two to see which was easier.

Note - because of dihedral you cannot measure the last 5 gallons or whatever it works out to on a -9.
 
Jamie said:
One thing I really hate about the Internet is how sometimes things get interpreted the wrong way. I am not an idiot, gasman. If I don't see fuel in the tank I don't depend on it and for planning purposes and I do assume that it is empty although it really isn't.

I re-read my previous posts and realized that they were sufficiently confusing so I deleted them. Also, I mentioned something incorrect. If I see a little fuel on the bottom of BOTH tanks then I know that I have 10 gallons remaining total (5 gallons per side). That is conservative. When I calibrated my float senders I watched each tank swallow a 5 gallon can of avgas and couldn't see any fuel in either tank after the fact.
Click to expand...

Never did I say you were an idiot..... All I did is read your post and DID NOT understand how that can be. I red it word for word and then made my comments based on the assumption that you red your own post and approved it for display.

As for your comment here about (If I see a little fuel on the bottom of BOTH tanks then I know that I have 10 gallons remaining total (5 gallons per side). Falls right into place with the higher tail on the 7A giving you about 2 gallons more in the lower end of the tank.

Some day I will probably write something that is way out of line and someone will challenge my statement............. But by then I probably will be an IDIOT!........:D
 
gasman said:
As for your comment here about (If I see a little fuel on the bottom of BOTH tanks then I know that I have 10 gallons remaining total (5 gallons per side). Falls right into place with the higher tail on the 7A giving you about 2 gallons more in the lower end of the tank.
Click to expand...

The -7 tanks are also bigger than the -6 tanks (by two gallons) so I would guess that has something to do with the difference.
 
Dip stick calibration

Question, does anyone know how much fuel is in the tank when it has been drained via the wing tank "push to drain" valve. RV-8. I drained what I thought was all the fuel from the wing tank. Using the push to drain valve on that tank. I then filled the tank two gal at a time, marking my dip stick with each two gal. However, the tank was full at 20 gal vs the spec capacity of 21 gal.

The spec also say that all the fuel is usable. So, am I to assume tha the wing drain valve does not drain the last gal ???

John L.
 
Less than 7oz. per tank. My 6A tanks are right on for volume. You might have an air pocket issue that is keeping you from filling your tanks. Try filling a tank then rock the wing and see if the level drops.

Mike is sleeping, so..... Welcome to VAF................:D
 
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