Fast Fill or Slow?.a Fueling puzzle

Ironflight · #1 08-13-2008, 07:36 PM

This may be news to those still building their first RV’s, but those flying will know what I am talking about. One of the great mathematical mysteries of RV flying is brought about by the baffles in the fuel tanks – they cause fuel to trickle from the outer bays to the inner at a rate slower than you can pour fuel into the tank neck. So if you fill the tank quickly to the top, then stop putting in gas, the level goes down, and you have to top it off. Got the picture?

OK, so here is the question before the floor - what is the quickest way to a full tank?

a) Fill quickly to the top, then trickle it in to match the flow through the baffles
b) Fill at a slow rate equal to the flow through the baffles
c) Fill at some rate in between that depends on how empty the tank is to start
d) None of the above – please tell us your method!

Mathematical, physical, and/or engineering proofs will be accepted, don’t look at anyone else’s paper, and no attempts to bribe the proctor – I have no idea what the answer is anyway!

Just what wanders through my mind as I stand in the evening sun at the fuel pump….

Kyle Boatright · #2 08-13-2008, 07:48 PM

I use one of two methods:

1) Fast fill till the tank is almost full, then continue at a slower rate until the tank is full. Switch tanks and repeat.

2) Fast fill until the fuel in the first tank is at the filler neck, then walk over to the second tank, fast fill it to the top and continue at a slower rate as the fuel moves into the inboard tank bays. I finish topping off the second tank, then walk back over and top off the first tank.

Sometimes I overfill a tank and watch liquid $$ pour across a wing. That makes me unhappy.

RyanM · #3 08-13-2008, 07:49 PM

Not being a engineer in the normal sense, but being through the rigors of a a few Microsoft interviews, I'd have to vote for A.

Once you reach fill up the inboard most bays, you'll be applying the most pressure to flood the other bays. Then keeping up with the flow, you top off until there is no more room for fuel.

I should go grab a fuel tank rib.. I wonder if you were to place "tooling holes" in the top of the ribs if that would allow for air to escape back to the fuel cap faster, and therefor letting you fill up even faster.

Okay, enough talk I have a plane to build.

mannanj · #4 08-13-2008, 07:50 PM

My choice is "C" for my RV. Seems to work best for me. It takes fuel fairly fast at first, then I slow it down as it fills. At todays fuel prices an ounce is worth $0.10, so don't waste it!

We old "retarded" f-rts have to be frugal ya know!

N941WR · #5 08-13-2008, 07:54 PM

OK, here is yet another way to do it.

Point the hose towards the inboard rib, not the outside baffle.

Fill the tank until it is full and and then go put fuel in the other tank.

When that tank is full, go back to the first tank and top it off and then return to the second tank and do the same.

jetjok · #6 08-13-2008, 07:55 PM

Paul,
Timewise, it is probably a wash to do a slow or fast fill. If you go slow, it will take longer to get the tank full, if you go fast it will get to the top sooner but then you have to wait.
My tanks hold 28 gal per side, and I think that it takes even longer to fill the additional bay. Therefore, I will fill one side, then go fill the other side and let the fuel settle. You end up making a few trips back and forth, but what the heck as my legs probably needed stretching anyway!
Anyone who has ever flown a Twin Commander (eeek! I just went OT) can tell you about having to wait for the fuel to settle from the one filler port! There are multiple tanks in each wing, plus the fuselage tank, so it took a while to get a full bag. And then, throw in a nice summer TSM adding pouring rain while you stand on a slippery ladder! Oh, the humanity!

Geico266 · #7 08-13-2008, 08:01 PM

While you guys are trying figure out how to fill the tanks, I'm taxing to the runway. I only fly 3.5 hour between fillups anyway. After that long I need to GO!

AlexPeterson · #8 08-13-2008, 08:01 PM

Hmmm. I don't seem to have that problem, at least with the various pumps I've used over the years. There are some pumps out there that really put out a ridiculous flow rate, but I tend to throttle those back to keep spray from coming back out in any case. Maybe the -6 is different with regard to venting.

With regard to your question, I vote for A.

captainron · #9 08-13-2008, 09:04 PM

Tell the line guy to "fill 'er up"!

Bryan Wood · #10 08-13-2008, 10:08 PM

Quote:

Originally Posted by Ironflight

Just what wanders through my mind as I stand in the evening sun at the fuel pump….

Paul, have you considered building another plane to keep your mind busy?

Here are a few questions that I got in an email today which might get you pondering other things in life as well if you need some relief from your fuel issue.

1. Why do croutons come in a sealed bag?
2. Do Lipton Tea employees take coffee breaks?
3. What hair color do they put on the drivers licenses of bald men?
4. If a cow laughs will milk come out of her nose?
5. What ever happened to Preparations A thru G?

So as you can see there are also deep thinkers walking around in the general public who Van has yet to reach with advertisements. From the way our hobby appears to be growing I'd say he is getting the attention of a great number of them.

When fueling have you ever used one of those pumps that has a trigger that is very hard to pull and when you finally are able to gently finesse and squeeze to get a trickle coming out the pump trys to dump several gallons into your tank in about 1/2 of a second? We have one locally and I don't even try to top off with it.