Chicken Hopper uniflow..what's the difference?

[DanielGelinas]

Hi,

I just added a 3 oz. chicken hopper uniflow to my super clown stunter with fox .35.
Is this a good tank setup for stunt?

What is the difference between the chicken hopper tanks and regular uniflow tanks?

Why are they called chicken hopper?

Thanks,

-Daniel

[Jim Thomerson]

Most chicken hopper tanks are not really chicken hoppers; but, if they are, they do not need uniflow.  A true chicken hopper tank has two tubes into the small tank.  One allows fuel in from the large tank.  The other goes a short way into the small tank, and allows air in when the fuel in the small tank drains down to uncover its end.  This maintains the level of fuel in the small tank in a steady state.  So uniflow is not needed.  I have not personally opened a uniflowed chicken hopper to see what is what.  But I have been told that the uniflow may be not where I would expect it to be, and that is why people sometimes have to set the tank high or low to get a good run.  The only chicken hopper I've ever set up was on a Slow Rat with an inboard big tank, and an outboard hopper.   

[Dave_Trible]

Jim was spot on with his description but I'll put in my two cents.  Haven't heard much about chicken hoppers in years.  They are usually associated with racing and carrier more than stunt.  They can look like a small tank mounted on a larger one or as a blister on the outside (could be inside) a tank acting in a way to prevent surges of head pressure from causing the engine to change RPM during the run.  A uniflow operates in much the same way by capturing and holding a positive head pressure on the fuel flow.  In our approach the benefit is more about maintaining a constant lap speed throughout the flight.  Open or suction-vented tanks tend to allow the engine to go leaner as fuel weight diminishes, pushing with less force up the feed line to the engine.  To combine the two designs will work I guess but I'm not sure what is to be gained by it.  For sure the chicken hopper has to add unwanted weight.

[Paul Smith]

I always made & used chicken hoppers for Slow Combat.

They consisted of a 1/4 ounce triangular uniflow tank, replenished from a 3-4 ounce main tank.

At 100 MPH, the decline in fuel mass causes a change in fuel pressure that not even the best uniflow can mitigate.  With this setup, the tank that feeds the engine has the same fuel level throughout the flight and the declining level in the big tank has no effect. 

In my setup it is essential that the small tank be a true, functional uniflow.

[Dennis Moritz]

Eric Rule, RSM Distribution, and Brodak sell chicken hoppers. I have used them successfully on Profiles for years. Useful on profiles with short noses, because they are comparatively short. The feed tube comes out of the small tank, outside edge. The fill tube is on the main tank, along with the overflow tube. The outer tube on the main tank is labeled unifo in the directions on the package. The inner tube labeled overflow. On profiles without major vibration issues I have run muffler pressure to the uniflo tube and gotten excellent results. A uniform run, beginning to end of flight, except for the lap of two lean, signalling end of run. If the engine breaks lean and runs away, I have solved the issue at times, by running the muffler pressure to the overflow tube and capping the uniflo. It's also possible to leave the uniflow (or overflow vent) uncapped open to the atmosphere. I prefer not to do this, because it can lead to leaning out and speeding up down wind and richening and slowing down into the wind. Profile tanks, same as tanks within the fues, need to be adjusted at times to provide similar engine run upright and inverted. Tank style has not been issue for me, far as that is concerned.

Whether the commercial chicken hoppers are true uniflo tanks or not. I don't know. Having never taken one apart. Also, "true uniflo" is kind of an enigmatic statement to me. Since I have read a number of descriptions of how uniflo tanks theoretical work. These theories differ.

[Jim Thomerson]

Just a side comment, on open uniflow vents, I use a one way valve to prevent siphoning, and buffer the tank from outside pressure changes in maneuvers. 

[Garf]

Every chicken hopper tank I have tested has has one or more pinhole leaks in it. There must be NO leaks in the tank for it to work the way it is supposed to.

[Tim Wescott]

On a different note, while I don't have a lot of mileage with the Fox 35, everything I've read here seems to indicate that 3oz isn't enough -- I'm pretty sure you want more like a 4oz tank into which you load 3.5oz of fuel for a full pattern.

Others with more real knowledge should jump in and correct me if I am wrong.

[DanielGelinas]

You are correct Tim.
The fox drinks a lot of fuel...and 3 oz is a very short fly with the fox 35.
However, I have the oriental to learn the pattern.
After looking the tank over, I've realized it isn't even a chicken hopper. It is what Brodak's call a profile tank.
Sorry to everyone for the confusion.
-Daniel