hopper theory & practice

[RC Steve Sterling]

Yes-- I have used a bladder tank (AKA bubbleless) from the get-go and had no
troubles with my Webra 1.45 (after getting the pipe length right and the
mixture right). Gordon Anderson, who has had real trouble with his Webra, is
switching to the bladder and planning to test today. I'm sure he will give
us a report.

  -----Original Message-----
  From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]On
Behalf Of Randy
  Sent: Friday, August 13, 2004 8:07 AM
  To: discussion at nsrca.org
  Subject: Re: hopper theory & practice


  Any one using a bladder tank with their Webra 145 or 160?  Some poeple at
the local fuel has started using them in sports plane for fuel related
problems.  Seems to sovle thier problems.

  Randy
    ----- Original Message -----
    From: Wayne Galligan
    To: discussion at nsrca.org
    Sent: Friday, August 13, 2004 10:43 AM
    Subject: Re: hopper theory & practice


    There has to be more pressure(muffler tap) to the main tank then there
is draw from the carb in order for this system to work properly.  Inertia
can effect this as I stated in one of my other posts.  I proved this in my
Prophecy that had the tank higher then the needle valve and when I pressed a
hard negative "g" load it would go lean.  At all other attitudes it ran
fine, i.e, uplines, downlines, snaps, positive maneuvers.  All up it has its
merits but the best is that it reduces the possibility of picking up air in
the main feed line and reducing the possible lean run or lean burp,
something you don't want happening on a turbine or helo engine.  The hopper
will reduce the amount of air that enters the hopper when the main pickup
encounters bubbles of foaming.   The hopper pickup will still be in
bubbleless fuel (fairly fuel tank) if the tank is isolated well enough. Jet
and helo guys use then for this reason.  The other is if you are trying to
move weight forward for a tail heavy airplane. This makes good use of the
fuel transfer and extra tank instead of adding lead ballast.  I think the
bladder tank(like the Tettra) is the best alternative to bubbleless feed and
I am seriously considering using it.

    Wayne Galligan

    - Original Message -----
      From: Jim_Woodward at beaerospace.com
      To: discussion at nsrca.org
      Sent: Friday, August 13, 2004 7:54 AM
      Subject: Re: hopper theory & practice



      I'll take a stab as why the hopper tanks work.  Liquid may be
incompressible, but it is "movable".  The hopper tank has a fuel entry and
exit point.  Exit point being the clunk line that goes to the engine, entry
point being the vent line.  The hopper tank becomes a reservoir of fuel.
Although I think you can argue that the entry and exit point fuel velocity
(or suction force) is the same, this cannot be said for the middle of the
tank were the suction force is diffused over a larger volumetric cross
section.  The image in my mind is a wind tunnel's stilling chamber.  I think
an interesting question would be this:  How small can a hopper tank be to
still provide the ease of fuel draw we are looking for?  Can the hopper tank
be reduced to a section of fuel tubing that is "bubbled"?  Would the
"bubble" work is there was a separate entry and exit point like the ven t
and clunk lines of the hopper tank?  If the bubble was 5 times larger than
the ID of fuel tubing would it work?
      Thanks,
      Jim W.



           ronlock at comcast.net
            Sent by: discussion-request at nsrca.org
            08/13/2004 08:34 AM
            Please respond to discussion


                    To:        discussion at nsrca.org, discussion at nsrca.org
                    cc:        Jerry Budd <jbudd at QNET.COM>
                    Subject:        Re: hopper theory & practice



      Ive been a hopper tank diss-believer for years.  I also wonder why
many continue to report benefits.  What's responsible for the benefit?
      I'm in agreement with Nat, and what "I think" Jerry has said regarding
the fuel system with a FULL hopper tank being a column of fluid, and the
hopper would have no benefit.

      Maybe hopper serves to eliminate foaming and bubbles?  Do I understand
heli pilots use hoppers for that reason?

      In practice do we usually have some air in the hopper?   Or do we
usually have a hopper tank that is flexible?   Might we be drawing from the
hopper without replenishing from the main tank during a vertical?    Then
the hopper gets replenished during level lines?

      Still wondering, Ron Lockhart

      -------------- Original message --------------

      > >Matt,
      > >With or without the hopper tank we still have a solid column of
      > >incompressible fluid for gravity and G's to play its tricks on. I
      > >contend if it runs ok with the hopper it will run just as well
      > >without. Nat
      >
      > Nat,
      >
      > While not exactly accurate as stated, your point is well taken. Your
      > hypothesis has some merit when the tank is full, but it falls short
      > anytime else (which is most of the flight). Adding just a small
      > amount of air causes the system to become compressible (just like
the
      > brakes on your car).
      >
      > Jerry
      > --
      > ___________
      > Jerry Budd
      > mailto:jbudd at qnet.com
      > =====================================
      > # To be removed from this list, go to
http://www.nsrca.org/discussionA.htm
      > and follow the instructions.
      >


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