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How Much Fuel Can You Siphon from an RV-8 Tank?

Ironflight

VAF Moderator / Line Boy
Mentor
Well, I’ll tell you!

I had the need to drain one fuel tank on the Val, and decided to see if I could make some of the process easier by not having to duck under the wing and shuffle four different gas cans around. I had succumbed to that carnival barker at SnF last year and bought one of those handy-dandy siphon hoses with the valve on the bottom (I use it to fuel the jet without hoisting cans high in the air), and it worked great!

However, of course, it can only go as far into the tank as the first rib in from the tip. Seems like a long way out from the root, and taking dihedral into account, I figured I’d still have quite a bit to drain.

Well the answer is that I managed to get 16 gallons of the 21 gallon capacity out through the full valve...way more than I thought I’d get.

Didn’t leave much to drain, and I only had to duck under the wing with one can.

Just a data point for the trivia experts (i.e., other engineers) out there.....

Paul
 
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Good job.

I would have expected 1/2.

I have always drained my -6 by removing the drain at the sump and swapping gas cans. Yes I purchased enough 5-gallon containers to hold all the fuel on one side.
 
Was this what you used?

2610539new.jpg


We bought one at OSH for transferring water in our camper and it works amazingly well!
 
Was this what you used?

2610539new.jpg


We bought one at OSH for transferring water in our camper and it works amazingly well!

Yup - that?s the one! Felt kind of silly buying from what seems to be a very typical carnival barker....but hey, it does work! And no mouthful of Avgas (or Kerosene).
 
Yup - that?s the one! Felt kind of silly buying from what seems to be a very typical carnival barker....but hey, it does work! And no mouthful of Avgas (or Kerosene).

I felt the same way about my purchase. Then I tried it on my own and was stunned at how well it worked.
 
Turbo advised me on that sucking thingy. Works great. I am able to recover 10 gallons out of 18. RV9A.
 
How Much Fuel Can You Siphon from an RV-8 Tank?


I got about 12 Gallons........ and then the owner showed up.
 
:D

Bought one of those some 20 years ago @ OSH, and I?m sure it is stashed safely away somewhere in my garage...
Assuming I find it, how does one get the device started?

Thanks 🙏
 
:D

Bought one of those some 20 years ago @ OSH, and I?m sure it is stashed safely away somewhere in my garage...
Assuming I find it, how does one get the device started?

Thanks 🙏

The ball acts like a check valve. You just jiggle it up and down. When the fuel or whatever starts flowing, you stop juggling. It really doesn't take long to get it to start flowing.
 
Why is everyone siphoning fuel from their tanks in the first place? Haven’t had a need to yet, but I’m wondering what I have to look forward to. :eek:
 
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Why is everyone siphoning fuel from their tanks in the first place? Haven?t had a need to yet, but I?m wondering what I have to look forward to. :eek:

I've done it a couple of times. Once to bring the plane home after a prop strike, once to fix a leak, and to recalibrate the capacitance fuel senders (Which are now spot on!).
 
Well, I?ll tell you!

I had the need to drain one fuel tank on the Val, and decided to see if I could make some of the process easier by not having to duck under the wing and shuffle four different gas cans around. I had succumbed to that carnival barker at SnF last year and bought one of those handy-dandy siphon hoses with the valve on the bottom (I use it to fuel the jet without hoisting cans high in the air), and it worked great!

However, of course, it can only go as far into the tank as the first rib in from the tip. Seems like a long way out from the root, and taking dihedral into account, I figured I?d still have quite a bit to drain.

Well the answer is that I managed to get 16 gallons of the 21 gallon capacity out through the full valve...way more than I thought I?d get.

Didn?t leave much to drain, and I only had to duck under the wing with one can.

Just a data point for the trivia experts (i.e., other engineers) out there.....

Paul

That sounds about right. I used one of these battery operated pumps and was able to fill 3 5-gal buckets with the pump in just a few minutes and then trained one more 5 gal bucket by removeing the drain under the wing. Using the pump to put it all back in was really simple and fast.
 
Why is everyone siphoning fuel from their tanks in the first place? Haven’t had a need to yet, but I’m wondering what I have to look forward to. :eek:

Every time I did a W & B for somebody.
Every time I did a tank re-seal for someone.
Every time the partners didn't refill the gas Gerry can for the lawn mower.
 
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Good point on the W&B. After 8 years flying I should probably do a new one to account for mods/additions done over the years.

Rather than siphoning out, is there any problem with just disconnecting the fuel line at the carburetor and turning on the auxiliary fuel pump just like we did when we tested fuel flow prior to Phase I? That seems lot easier, at least if the cowl is already off.
 
Too slow, too much bother. Siphoning off the top 3/4 of the tank & unscrewing the drain valve for the remainder of the tank much faster.

Besides, unscrewing fuel lines to pump gas into the lawn mower way too messy.
 
i have been using this type of hose for years mostly going into the tank with car gas. beware the cheap knock off brand that has a cheap valve. the vendor at snf sells the good ones in many sizes. :)
 
Has anyone considered grounding the can or bucket to the plane? Surprised that topic not coming up since it is one that is used as an argument against filling the plane from cans......
 
Has anyone considered grounding the can or bucket to the plane? Surprised that topic not coming up since it is one that is used as an argument against filling the plane from cans......

Well....that really had nothing to do with the the original intent of the post, which was to point that you can siphon 16 gallons out of the tank before you have to drain the rest out the drain valve.

We can start a whole new thread on how to safely drain tanks if you?d like!

(BTW, yes - I had everything grounded with alligator-clip jumper wires, both when siphoning and when draining)
 
Well....that really had nothing to do with the the original intent of the post, which was to point that you can siphon 16 gallons out of the tank before you have to drain the rest out the drain valve.

We can start a whole new thread on how to safely drain tanks if you’d like!

(BTW, yes - I had everything grounded with alligator-clip jumper wires, both when siphoning and when draining)

I just found it interesting that most any time there is a thread about fueling from a can that only 3-4 posts into the thread there are those saying we are about to blow ourselves up.......yet 18 posts into this thread and nobody had mentioned gasoline explosions with all the siphonin' and buckets and cans goin' on....... :)
 
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Good point on the W&B. After 8 years flying I should probably do a new one to account for mods/additions done over the years.

Rather than siphoning out, is there any problem with just disconnecting the fuel line at the carburetor and turning on the auxiliary fuel pump just like we did when we tested fuel flow prior to Phase I? That seems lot easier, at least if the cowl is already off.

It is a LOT less work to fill the tanks for the re-weighing, weigh the airplane with max fuel, and then subtract the weight of fuel out from the calculations.
 
It is a LOT less work to fill the tanks for the re-weighing, weigh the airplane with max fuel, and then subtract the weight of fuel out from the calculations.

1. Do you know the *exact* arm of the fuel?
2. Do you know the *exact* density of fuel and its corresponding weight at the weighed temperature?

Without these two pieces of data, a significant error can occur.

Normally when emptying an airplane of fuel I use clean 5 gal. buckets with lids that I only use for this purpose.
 
1. Do you know the *exact* arm of the fuel?
2. Do you know the *exact* density of fuel and its corresponding weight at the weighed temperature?

Without these two pieces of data, a significant error can occur.

Normally when emptying an airplane of fuel I use clean 5 gal. buckets with lids that I only use for this purpose.

1. Yes. I measured / calculated it when I weighed the airplane the first time. Airplane was weighed empty with unusable fuel, fuel truck called while still on scales, airplane fuel to max capacity while still on the scales, additional scale readings taken and recorded.
2. Yes. They test the fuel at the local fuel farm every day and include the specific gravity. It is easy to borrow their equipment and test what is in the tank of the airplane. In actual experience, I have found the difference to be so small that it is irrelevant for calculations on an RV.
 
1. Do you know the *exact* arm of the fuel?
2. Do you know the *exact* density of fuel and its corresponding weight at the weighed temperature?

Without these two pieces of data, a significant error can occur.

Normally when emptying an airplane of fuel I use clean 5 gal. buckets with lids that I only use for this purpose.

I would also add, do you know the exact amount of fuel in the tanks?

Van's lists the fuel capacity of the -9 as 18 gallons a side. However, since my -9 is a taildragger, it holds more like 19 gallons a side. The reason is the fuel cap is perfectly horizontal when the tail is down. When I raise the tail to level the plane, the fuel cap position moves relative to the horizon and it won't hold that extra gallon of fuel.
 
about the same for a -7

I've done the same thing with my -7 several times. (for fixing a leak, and calibrating capacitive sensors)

The results were about the same.... Can siphon all but about 4 gallons.
 
I would also add, do you know the exact amount of fuel in the tanks?

Van's lists the fuel capacity of the -9 as 18 gallons a side. However, since my -9 is a taildragger, it holds more like 19 gallons a side. The reason is the fuel cap is perfectly horizontal when the tail is down. When I raise the tail to level the plane, the fuel cap position moves relative to the horizon and it won't hold that extra gallon of fuel.

That was part of the process of building the airplane. Airplane was assembled and fuel measured as it was added to one tank. System was then primed, hose removed from carb, airplane placed in level flight attitude, and fuel pump ran till it started sucking air. Fuel measured was then subtracted from the fuel added to the tank to determine unusable fuel in one tank. Repeat for other tank.
 
Fly is an option

I had a leaky rivet in my tank one time...took it up and flew it until there was only about 2 gallons in the tank, took out drain and ran it into a gas can...and yep, I grounded it while draining.
 
I would also add, do you know the exact amount of fuel in the tanks?

Van's lists the fuel capacity of the -9 as 18 gallons a side. However, since my -9 is a taildragger, it holds more like 19 gallons a side. The reason is the fuel cap is perfectly horizontal when the tail is down. When I raise the tail to level the plane, the fuel cap position moves relative to the horizon and it won't hold that extra gallon of fuel.

That was part of the process of building the airplane. Airplane was assembled and fuel measured as it was added to one tank. System was then primed, hose removed from carb, airplane placed in level flight attitude, and fuel pump ran till it started sucking air. Fuel measured was then subtracted from the fuel added to the tank to determine unusable fuel in one tank. Repeat for other tank.
What I was commenting on is that the -9 can hold more fuel than the -9A because with the tail down, the cap is truly at the top of the tank in that position. With the nose gear, there is still air in the top of thank due to the curvature of the wing.

This was in response to "filling the tanks" and then weighing the plane and remove the weight of the fuel. Thus my comment that you don't really know how much fuel is in the plane when it is "full".

As for testing unusable fuel, you are correct, that test should be done prior to the first flight and the amount of unusable fuel is negligible in all the RV's, which I consider a great feature!
 
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