hopper theory & practice

[Wayne Galligan]

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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