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3/8-inch or 1/2-inch at carb?

K

King Brown

Registered User
Nova Scotia
Noted on PA12 1/2-inch fuel line to carb on 180hp Lycoming BUT 3/8 from the wing tanks to the selector, and buddy said there's measured increased fuel flow from the 1/2 inch compared to the 3/8 to the carb. This doesn't make sense to me.

We've plumbed 3/8 all the way from Smith wings to the carb on our 180hp Bushmaster, headerless, and understand 180hp SC is the same. Appreciate comment on why 1/2-inch to PA12 180hp, experimental or otherwise---as a sort of header with more fuel for climb or unusual attitude or both? Beats me.
 
most all stc's (penn yan, crosswinds,??)I can think of for 180 horse on cub use the 3/8.... jensen used 1/2..... from selector?? or was it all the way?

I could see maybe a difference with both tanks selected????

but all those others got certified decades ago with a flow test with the 3/8"...... so....... but some do require the gas caps with the thing sticking up to blow into tank (penn yan)....
 
.....and buddy said there's measured increased fuel flow from the 1/2 inch compared to the 3/8 to the carb. This doesn't make sense to me.

Why not? (I'm not quite sure from the sentence above, what your line of thought is)
JimC
 
3/8 or 1/2-inch at carb

The 1/2-inch fuel line was from the PA12 selector to carb, 3/8 to the selector from tanks. The smaller line should govern the fuel flow. I'm sticking to 3/8 all the way; enough fuel flow for me!
 
As a final check of the fuel system after an extensive rebuilding of our Super Cub, our IA, Bob Eckstein, had us disconnect the 3/8 fuel line from the carb. With minimal fuel in the tanks, we recorded the time to flow 2 gallons into a container. The fuel flow rate was about 20 gph as I recall. This was a simple way of assuring that there were no restrictions and that the engine would get plenty of fuel to make full power with adequate reserve. I recommend this simple test just to set your mind at ease.
Darrel
 
Darrel
I would add , put the main wheels up on blocks to get the plane in a high
AOA.
This was a "must" do back when homebuilts were really homebuilts
Doug
 
Doug, good idea -- basically set it up so the gravity feed is the minimum you will experience in flight.
Darrel
 
.....The smaller line should govern the fuel flow.

Depends upon whether it is in inlet or outlet control. Have you compared the orifice equation against the Hazen-Williams equation to see which is controlling?
JimC
 
3/8inch or 1/2inch at Carb

This from the Cessna 175 TCDS 3A17
The 175A and 175B fuel system does not comply with CAR3.433 and 3.434 for horsepower greater than 167 at the best angle of climb which is the most critical attitude.
The A and B models had 3/8 lines.C model thru Hawk XP 1/2" lines.They went to the big lines and constant speed prop at the same time.

Bill
 
JimC said:
Depends upon whether it is in inlet or outlet control.[/quote

Jim,

Hmm, it's been a few months since I messed with those equations - - well ok, a few years. Alright, alright - a few decades.

However - - I don't think it makes any difference which tube comes first, as long as the flow through the little tube is sufficient to fill the big tube and the little tube doesn't make excessive turbulence. Here's why I think that - -

There will be a certain pressure drop across each of the tubes for any given flow rate, and those pressure drops are additive, right? So - - the volumetric flow will be such that the total pressure drop across the entire tube -fitting-valve system equals the static head at the inlet, minus the sum of the dynamic head plus static head at the outlet.

For that given flow, the pressure drop across each element of the system is independent of the pressure drop across other elements, because the pressure drop is only dependent on flow rate, size of the tube, roughness, viscosity, and so on. No order is implied for the addition of the pressure drops across the elements of the system. I would suppose that might not be true if substantial turbulence is initiated upstream or something. But for this low flow rate I doubt if that is the case?

Is this stuff correct or am I missing something? I'm ready to duck - - -
Click to expand...
 
12 Geezer said:
JimC said:
Depends upon whether it is in inlet or outlet control.[/quote

Jim,

Hmm, it's been a few months since I messed with those equations - - well ok, a few years. Alright, alright - a few decades.

However - - I don't think it makes any difference which tube comes first, as long as the flow through the little tube is sufficient to fill the big tube and the little tube doesn't make excessive turbulence. Here's why I think that - -

There will be a certain pressure drop across each of the tubes for any given flow rate, and those pressure drops are additive, right? So - - the volumetric flow will be such that the total pressure drop across the entire tube -fitting-valve system equals the static head at the inlet, minus the sum of the dynamic head plus static head at the outlet.

For that given flow, the pressure drop across each element of the system is independent of the pressure drop across other elements, because the pressure drop is only dependent on flow rate, size of the tube, roughness, viscosity, and so on. No order is implied for the addition of the pressure drops across the elements of the system. I would suppose that might not be true if substantial turbulence is initiated upstream or something. But for this low flow rate I doubt if that is the case?

Is this stuff correct or am I missing something? I'm ready to duck - - -
Click to expand...

that wasn't confusing and technical enough, so I took it and feed it to http://babelfish.yahoo.com/... to japanese.... and then back to english.... much better now..


babelfish said:
Gym, Hmm and it' Because I died those same equalizations - - the healthy ok stand, small-numbered month, s which is several years. Without something to say, without something to say - small-numbered ten years.

However - - I don' The tube and small tube doesn' where the flow which passes by the small tube where you think t is large; Filling up, if it is sufficient, causing the difference where the tube first comes; t makes the excessive disorder. Here' I think that why, s - -

there is pressure drop of a certain specification which crosses each one of the tube for fluidity the specification which is, is those pressure drop the additive and right? Therefore - - the flow of capacity measurement is decrease of the total pressure which crosses kind of thing thing the tube of the whole that - as for the accessory valve system in the exit total of the static head and the dynamic head it is a match to the static head, with the entrance which is pulled.

Because as for the pressure drop which crosses each element of the system for flowing the specification which is that, pressure drop depends on just fluidity the independent person of the pressure drop which crosses the other element, size of the tube, it is rough, stickiness, and so on is. Order is not meant addition for the pressure drop which crosses the element of the system. If it is begun high-level, I perhaps the suitable disorder or what it is not true, suppose. But if because of this am low flux ratio I that fact, it doubts?
Click to expand...

hmmmmmm :drinking:
Click to expand...
 
[quote="mike mcs repair
that wasn't confusing and technical enough, so I took it and feed it to http://babelfish.yahoo.com/... to japanese.... and then back to english.... much better now..


babelfish said:
Gym, Hmm and it' Because I died those same equalizations - - the healthy ok stand, small-numbered month, s which is several years. Without something to say, without something to say - small-numbered ten years.

However - - I don' The tube and small tube doesn' where the flow which passes by the small tube where you think t is large; Filling up, if it is sufficient, causing the difference where the tube first comes; t makes the excessive disorder. Here' I think that why, s - -

there is pressure drop of a certain specification which crosses each one of the tube for fluidity the specification which is, is those pressure drop the additive and right? Therefore - - the flow of capacity measurement is decrease of the total pressure which crosses kind of thing thing the tube of the whole that - as for the accessory valve system in the exit total of the static head and the dynamic head it is a match to the static head, with the entrance which is pulled.

Because as for the pressure drop which crosses each element of the system for flowing the specification which is that, pressure drop depends on just fluidity the independent person of the pressure drop which crosses the other element, size of the tube, it is rough, stickiness, and so on is. Order is not meant addition for the pressure drop which crosses the element of the system. If it is begun high-level, I perhaps the suitable disorder or what it is not true, suppose. But if because of this am low flux ratio I that fact, it doubts?
Click to expand...

hmmmmmm :drinking:[/quote]

You keep that up and the FAA as well as TSA will be wanting to hire you!! :eek:

JH
 
I think Mike got it right..... :)

Gordon, with the addition of a few fitting losses, so did you.
JimC
 
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