Low wing fuel system vrs high wing

[mtrv]

Whoa, not so fast there. It require less effort to feed from 2 tanks at once compared to one tank, assuming the tubing has the same diameter.

Take one of those little plastic coffee stirrers that's like a small straw. and suck some water through it. Now take two and suck water through both at the same time. Which will be easier and quicker to suck up a mouthful of water? one straw or two?

Now, take two seperate glasses to simulate two tanks, dump the water out of one, and see what happens. No flow at all.

Neither the Cessna high wing, nor the Piper low wing feeds fuel to the pump from two tank lines. Cessna feeds fuel from both tanks to the fuel selector valve, then a single header tank, then the pump,etc. Piper routes each tank supply to the selector valve, then one line to the aux. pump.

 

[mtrv]

I'm not about to get into a pissing match, but good ASSumption. Yeah, after restoring a car, working on tractors all the time growing up, and having an in-depth knowledge of aircraft systems I've been led to the conclusion of PFM. Riiiiight. Go back to turning some more nuts on your Polish Camel.

Fuel pumps for carbed engines as well as fuel injected engines are rated for output in psi. Less for the carburetor, and more psi for fuel injection. All rated on push and not pull.

Why not be an honest CFI, and admit that your explaination tends to suck.

 

[rfeathe1]

low wing fuel systems

The commander 112 is a low wing and has a "both" position on the fuel selector. At least the one that I flew did.

I've heard of Commanders having a "BOTH" position. One owner/pilot I talked to said most experienced AC pilots don't use the BOTH position, especially with a low tank.

Avbug--does the Dromader have a L&R position too?

 

[A Squared]

Now, take two seperate glasses to simulate two tanks, dump the water out of one, and see what happens. No flow at all.

Right. I wasn't commenting on running a tank dry. You apparently missed that.

Neither the Cessna high wing, nor the Piper low wing feeds fuel to the pump from two tank lines.

Didn't say that they did. They all feed the selector valve with 2 lines, though. It will be easier to pump fuel thru say 2-3 ft lines running to the selector valve, and one 4 ft line running from the valve to the pump than one line of the same diameter all the way. It will only be slightly easier, but my point is that it won't be harder, as has been suggested.

 

[DGdaPilot]

Fuel pumps for carbed engines as well as fuel injected engines are rated for output in psi. Less for the carburetor, and more psi for fuel injection. All rated on push and not pull.

Why not be an honest CFI, and admit that your explaination tends to suck.

And that push would not be there if there was not a pull to begin with. Ummm....waitress....check please. Now answer this one: Who came first, the chicken or the egg?

 

[VNugget]

And that pull wouldn't be there if there was not a push to begin with.

Everybody is making this so much more complicated than it needs to be... the bottom line is a pump moves fluid, by pulling it in one side and pushing it out the other. Easy cheesy.

 

[Bernoulli]

So any other comments on why low wings fuel selectors rarely ever have a BOTH selection while gravity fed high wings almost always have a "BOTH"...only two points made so far.
#1. Because if one tank get too low air could be pushed or pulled by the pump(your pick) into the system causing fuel starvation.
#2. a pump may not have enough power to draw from both tanks. (you'd think if this was the case though, a stronger pump would be used???)

 

[A Squared]

#2. a pump may not have enough power to draw from both tanks. (you'd think if this was the case though, a stronger pump would be used???)

No. Again (this is the second time), it takes *LESS* force to draw from two tanks than one, not *MORE*.

 

[Bernoulli]

OK... Then we're down to only one main reason... the emptier tank could have air drawn into the ignition syystem causing fuel starvation when you still actually have fuel. Is that the final answer?

 

[erj-145mech]

OK... Then we're down to only one main reason... the emptier tank could have air drawn into the ignition syystem causing fuel starvation when you still actually have fuel. Is that the final answer?

Ignition system doesn't play into this equasion. Unco-ordinated flight will also unport the tank.