Conference vmszoo::rc

1544.0. "Chicken Hopper fuel tanks" by KAY::FISHER (The higher, the fewer) Wed Jul 28 1993 15:13

Some time back - maybe years ago I asked what a Chicken Hopper was.

At last the answer came in from the usenet - fyi.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

In article <[email protected]> [email protected] writes:
>
>
>---
>In article [email protected], [email protected] (Bill Lee) writes:
>>In article <[email protected]> [email protected] writes:
>>			(elided)
>>>
>>>My question is, can I place a small reservoir tank in the nose and
>>>feed it from a larger tank located at the C.G.  (feeble attempt
>>>at ascii illustration follows)
>>>
>>>
>>>-----------------------------------------------------
>>>        +------------------+         +-------+      |
>>>        | (10 oz tank)   / ===========(1 oz) ============> to carb
>>>        |   pick-up     /  |         |      /|      |
>>>        |   with clunk     ==\       |    /  |      |
>>>        |                  | ||      |  /    |      |
>>>        +------------------+ ||      +-------+      |
>>>-----------------------------||----------------------
>>>                             || pressure from mufler tap
>>>
>>>
>>>
>>>Is there any reason that this will not work in a plane, assuming 
>>>that the smaller tank is mounted for adequate fuel flow?
>>>
>>>We do this in boats regularly to insure that the carb is always
>>>drawing from a full tank and eliminates sucking air due to
>>>sloshing.
>>>
>>
>>Sure, you can do this, but I doubt it will accomplish anything.
>>After all, isn't the purpose of the "clunk" to keep the fuel pick-up
>>line in the fuel even when the model is in a maneuver? If it is,
>>why is there a "sloshing" problem?
>
>My main concerns were not fuel supply, but finding a work around for
>the fuel draw distance which occurs by not being able to mount the
>tank behind the firewall.
>
>In the boats, clunks and flex pick-up lines are replaced with solid pick-ups
>in the left,rear of the tank.  (Clockwise oval racing, right side up!)
>With a single tank, as it empties, sucking air becomes increasingly
>more posible.  A smaller "feed" tank solves this problem.
>
>>
>>Now if the two tanks were vented differently (e.g., the small tank
>>was "chicken hoppered" off of the main tank), you WOULD see a
>      ^^^^^^^ ^^^^^^^^
>
>Say What ???  Care to do an ASCII drawing of this?
>
>>difference. (I can see a thread coming on!)
>>

Oh, here comes the thread!  8-{)

We'll give it an ASCII try.

                +-----------------------+
      |         |..........||...........|
      |         |          ||           | <--- Primary Tank. Sealed airtight
      |         |          ||           |      after filling.
      V         |          ||           |
Direction of    |          ||           |
Dominant G      |          ||           |
                |          ||           |
                |          ||           |
                +----------||--||-------+
                           ||  ||
          Air feed ------> ||  ||<-------- Fuel feed
                           ||  ||
                      +----||--||----+
    Hopper tank --->  |    ||  ||  +====  <-- Air inlet, muffler pressure,
                      |....||..||..|.|         crankcase pressure, whatever...
                      |        ||  | |
		      +||------------+
    		       \ =============== --> feed to engine

O.k., here's the explanation.

The main (primary) tank is sealed once it is filled so that it will
hold a vacuum. The only way for air to enter the primary tank is
via the "Air Feed" line.

Now the "Hopper" tank is usually small and near the engine. As the
engine draws fuel from the "Hopper" tank, the fuel level drops (the
small dots represent the fuel level in each tank) and uncovers the
bottom of the "Air Feed" line. A bubble of air passes through the
"Air Feed" line and a corresponding amount of fuel moves the other
direction through the "Fuel Feed" line into the "Hopper", thus
raising the level of fuel in the "Hopper" and covering up the "Fuel
Feed" line. This cycle repeats over and over as the fuel is used
from the "Hopper" tank.

The net effect is that the level of the fuel in the hopper tank
oscillates back and forth over a very small distance, usually only
a few .01". The engine "sees" an essentially constant pressure
since there is no change in fuel level at all, that is, until the
primary tank is emptied and the hopper, too, is run dry.

The running characteristics of the "Chicken Hopper" tank is usually
a brief rich run right at the first as the dynamics of the hopper
get established, then a rock-solid run until the primary tank
empties. If the air inlet is placed in a uniflow location, the
engine will see no transition even after the primary tank empties:
it will just quit when the hopper empties.

The drawing and the explanation assume a dominant direction of
acceleration. As an example, this would be a top-view of a typical
Control Line speed or racing model where the dominant G is outward.
For a model that maneuvers, the hopper would likely have to have
the lines all attached together and clunked. I don't know if this
would work at all well. But a chicken hopper does work well for
those events where there is a dominant direction of acceleration.

The name comes from the farm! A "Chicken Hopper" is a means of
putting a water supply out for the chikens so that when they drink
some from the supply it is automatically replenished:

		+---------------+
		|             <-+--------Partial vacuum
		|...............|
		|               |
		|             <-+--------- Water Supply
		|               |
		|               |
		|               |
		|               |
		|               |
		|               |
           +-------------------------+
           |....|...............|... | <-- Pan where water is available
           \_________________________/

As the water supply is drawn down, a bubble of air bleeds past the
bottom of the can and lets a little water flow into the pan.

Oh, hell, you get the idea!


Regards,

Bill Lee


++++++++++++++++++++++ The full NEWS header follows +++++++++++++++++++++++++++
News Article 16292
Newsgroups: rec.models.rc
Path: nntpd.lkg.dec.com!pa.dec.com!decwrl!elroy.jpl.nasa.gov!swrinde!menudo.uh.edu!lobster!nuchat!leeweyr!bill
From: [email protected] (Bill Lee)
Subject: Re: Fuel Tank Question
Message-ID: <[email protected]>
Organization: Lee Aerie
References: <[email protected]> <[email protected]>
Date: Mon, 26 Jul 1993 04:26:17 GMT
Lines: 146