Fuel system in my training 152

[energie]

with all the preflight check, start up check blahblah checks, I am really doing a whole bunch of things which I don't currently understand. i would call up my instructor but he's probably drunk (that's a whole different story :( )
With so many instructors in here, I couldn't think of a better place to ask!
I understand vaguely why I have to do certain items on the check list, but I feel that I am lacking a cohesive understanding on how the whole fuel system work on the 152. (i.e. test-drain the fuel to see if there are any sediments and water since it's gravity fed, prime the engine on cold starts etc)
I really want to know how fuel travels from the tank (i know it's gravity fed, but what's next? reservoir? carburetor?), how it gets into the engine? where does the fuel gauge measure from? why do i have to prime on cold starts? etc
does anyone mind taking me through the end to end process of the fuel system on a 152? I have tried googling this but haven't found anything useful :(


thanks in advance!
E

[barrow]

It starts with 13 gallons in each wing, with fuel pipes that run from each tank down the door posts behind front seats, over to an on/off valve between the seats, from there it runs to a strainer in the engine compartment where it's filtered thru a screen, from there to the carburetor where it fills the float bowl, it will stay in float bowl until it is drawn out thru the idle jet, for idle or the main jet for partial to full throttle. This will happen when the pistons are on the downward stroke causing a sucking force, helped by the curved restriction in the carb called a venturi to draw atomized fuel/air up thru the intake manifold into the cylinders.


The primer works by drawing fuel out of the strainer and forcing it into the intake manifold directly behind the intake valve, however stock 152's only had one pipe from the strainer to one cylinder, so in some cases when you over prime, you will flood this cylinder, and the 3 others have no fuel for starting. The reason you need the primer is cos during cold starting crank the engine needs a richer mix and lower temps are not good for atomizing fuel, plus their isn't enough sucking by the engine to get extra fuel from the main jet.

You can start in very cold temps by, setting throttle to 1/2 inch, mixture rich, pull primer to fill chamber, then crank with right hand while pushing primer with left hand, the harder you push primer the better the atomization to aid the start, do this as required, once it starts, don't be in a hurry to in and lock the primer if it's out, let it stabilize first or you could flood it.


The fuel quantity indicators, are float type in each tank, as the fuel is consumed the float descends with the fuel level, changing resistance in the circuit and the quantity on the gauges

[BroomstickPilot]

Hi energie,
First of all, may I suggest you borrow or buy and read a copy, either of the user manual for any aeroplane you fly, or a copy of one of the not-bad third party manuals, when you commence to convert onto it. That will enable you to ensure that you are fully acquainted with the details of the aeroplane at an early stage and make your familiarisation on type much quicker. The manual should be available to users at your club or FTO.

There is definitely quite a good third party manual for the C152 and it's cheap and currently in print and easy to get. The fuel system is fully described.
Metal parts of fuel systems are prone to internal corrosion, hence the sediment.

Fuel is hygroscopic, so it absorbs moisture out of the air in the tank. Fuel filler caps both on the storage bowser and on the aeroplane can be an imperfect fit and there is the potential for rain to get in, admittedly in small quantities, but these build up.

It takes some time for water to settle to the bottom, so if you refuel from a recently recharged bowser with water in suspension it will take perhaps 30 minutes to settle out, hence the need to check the fuel at the various bleed points before you fly.

If you have an instructor whose drinking interfers with his/her job, dump him/her NOW!.

I don't know much about the details of the pipe runs in the C152: you can look these up in the manual. As I recall, its a gravity feed to dual fuel pumps.

You have to prime your engine for the same reason you use a choke in your car. A cold engine starts much more easily on an extra-rich mixture, but you don't need the extra-rich mixture once the engine is running.

Anything I haven't dealt with here is in the manual; 'hope this helps.

Broomstick.

[barrow]

Their are no fuel pumps in a 152!

[the dean]

energie,

you do'nt say what stage you're at...but i assume only a few hours done.

i would'nt worry greatly at this stage about the plumbing...more important to get the checks right and understand what you are doing and why you are doing ithem..you can look at the plumbing later...the diagram is in the aircraft manual..

i also assume you are talking about calling your instructor after hours ...if so he's perfectly entitled to have a few drinks...

since i am assuming you are at an early atage i am therefore also assuming that you are not yet solo as you should certainly understand the checks and why you are doing them by then...but up to then it is a process of learning a little with each lesson...and that goes for the checks also but such things normally are introduced at an early stage under supervision...and with the later lessons you would normally be expected to do them yourself being monitored...

we used to do a more elaborate walk round even on days when the weather was bad and we could'nt fly...that gave plenty of time for questions...try that...go in on a bad day and spend time with the instructor on duty...

not knowing the full details of your relationship with your normal instructor i would'nt want to jump to conclusions...but if you are not getting good instruction or not clicking with a particular instructor...get another...or go to another school...

good luck.:ok:

the dean.

[S-Works]

Their are no fuel pumps in a 152!

Oh yes there are...........

[barrow]

oh no their friggin aint!

[S-Works]

Ok I stand corrected, not all 150/152 have fuel pumps. On most of the them the mechanical fuel pump drive has a blanking plate. However there are a few kicking around that do have a mechanical fuel pump on them. We have a 152 in for service at the moment with a fuel pump. Generally fitted when aux tanks have been used.

[smarthawke]

C150s are powered by Continental O-200s (or the FRA150L/M with the RR O-240) and there is no where to fit a fuel pump.

C152s are fitted with Lycoming O-235 L2C or the later ones, the N2C (basically the same, the N2C having a different combustion chamber design to help prevent lead fouling of the spark plugs - doesn't work and it's slightly less powerful - 108 against 112hp).

The L2C is also used in the Tomahawk. Tomahawks have low wings (and tanks) and have electric and mechanical fuel pumps. The mechanical fuel pump is mounted on the engine accessory casing at the back of the engine. I stand to be corrected, but I've never seen a mechanical pump on the back of a 152 engine in the 152 Parts Manual so it would not be a legit fit unless there was some form of mod in place courtesy of EASA or the CAA for a UK reg aircraft. It certainly isn't mentioned in the Service Manual. Many 152s don't even have the accessory casing fuel pump pad milled out so there isn't hole there to blank!

It may be part of a removed ferry/aux fuel system (in a 152?!) or perhaps someone not very bright has bolted a PA38 engine into a C152! Any pictures bose-x or a registration?

[energie]

Thanks very much. i appreciate the answers