hopper theory & practice

[Jim_Woodward at beaerospace.com]

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 vent 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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