What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Fuel velocity in AN6 tube

A5555

Well Known Member
I have often thought about how quickly fuel flows thru AN6 tubing at takeoff flow rates. At 12 gph the flow rate is 10.5 inches per second. Here's my numbers:

Fuel Flow Velocity in 3/8 tube
Flow - US gallon per hour 12.000 gph
Flow - cubic inch per second 0.770 in^3/s
3/8 dia tube ID (wall .035) 0.305 in
tube flow area 0.073 in^2
flow velocity in 3/8 tube 10.548 in/s (26.8 cm/s)

You really don't want to have too many sharp bends or 90 degree angles in the your fuel feel lines. Sharp bends reduce the flow flow capacity. Also, filters should be sized for the flow rate. More is better.
 
Last edited:
That's interesting to know. Thanks for doing the math. You say 12 gph at takeoff? My IO320 indicates 14.1 at takeoff. Is there that much difference between carb and FI?
 
That's interesting to know. Thanks for doing the math. You say 12 gph at takeoff? My IO320 indicates 14.1 at takeoff. Is there that much difference between carb and FI?

I used 12 gph for a reference point. you can scale the numbers for 14.1 gph. it's about a foot per second.
 
That's interesting to know. Thanks for doing the math. You say 12 gph at takeoff? My IO320 indicates 14.1 at takeoff. Is there that much difference between carb and FI?

Depends on prop. A CS turns more RPM, therefore more HP and therefore more fuel. TO flow is quite low for me with an FP, under 13 and I climb at 2500 and 13 ish GPH. I shoot for best power (approx. 100 ROP). 320 with Catto FP.

14 doesn't sound that excessive if you are spinning 2700.

Larry
 
...and

Don't forget the friction losses for flow within a pipe. If you really want to get a headache, look at the Darcy Weisbach Formula!:eek:
 
But that's only Mach .00077778 ;)

Actually, if my sources for data on gasoline are correct, that's about Mach .000202 in gasoline.

(The speed of sound in gasoline is almost four times faster than in air under usual standard atmosphere sea level temperatures...)


;)
 
Actually, if my sources for data on gasoline are correct, that's about Mach .000202 in gasoline.

(The speed of sound in gasoline is almost four times faster than in air under usual standard atmosphere sea level temperatures...);)

You got me!
 
Does the flow rate in an "open" tube need to be modified if there is a fuel flow transducer ( flowscan or red cube) in the path? The hole in the transducer is pretty small.
 
I had similar (but different) thoughts while sitting in an A10 cockpit. :D

Fuel, Gatling gun, ... what else?

Interesting though, is there a trade gouge or reference chart used by engine manufacturers that identifies correct fuel line size? Basically.

R
 
Line size

You look at the 1/4 line and fittings and wonder if they can flow enough, but Piper Saratoga with 300hp IO-540 from the factory has a -4 size hard line suppling the fuel flow transducer. They put it on top of the engine just before the flow divider.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
Back
Top