fuel system
fuel system
Note- This post will seem boring to everyone except some Helicycle builders who have asked me questions that I am trying to cover here in one place.
So at the threat of being bored.....read at your own risk.
I am trying to minimize the chances of my turbine going silent because of fuel delivery...or my electrical system failing. I have recently been asked by e-mail and I responded I would answer it here...as other Helicycle guys will see it.
My fuel system has a few modifications to it that like any rotorcraft, are unique to itself.
My fuel is delivered out of a port about 1.5 inches above the wedge shaped bottom of both the left and right tank. I am a nut about sumps, so here was an opportunity to have a sump for each outlet. I installed a fitting at the bottom of each sump and installed a petccock for drainage. I can actually dump in a half pint of water in each tank, and it will go down to these wedge shaped sumps where they can be drained, along with any debris.
The main fuel outlets also have drain petcocks on them, and the fuel goes on to a shutoff valve, then on to a gascolator. The gascolator has a 70 micron filter, and has a metal bowl that screws off for dumping the fuel and cleaning the screen. I installed the shutoff valve ahead of this gascolator so that I could service it without dumping fuel everywhere. The valve is safety wired of course.
The gascolator has a port where I can insert a probe from my sample cup and draw fuel out...checking for water.
After the gascolator...the fuel goes to the electric boost pump. This pump is not needed after the turbine starts as the mechanical pump takes over. This electric boost pump is a flow through type so that the mechanical pump can draw fuel through it with it turned off. Some guys leave this boost pump on, and some dont. I will leave mine on. I like the idea of constant fuel pressure keeping the mechanical fuel pump primed under pressure.
The fuel leaves the boost pump and goes to a fuel control valve...which from the cabin I can shut it off....send it to the turbine...or turn it to aux and fill the aux tank on the ground either by gravity feed, or by pumping it in. The aux tank is just a transfer tank...it holds 5 gallons...and I will use it to top off the main tanks after 10 minutes of flight. The transfer takes about 12 minutes...and it basically will top off the aft fuel tank. I have an in cabin sight tube to monitor so that I know I am not over filling this tank! This burning off the aft fuel while transferring the aux fuel minimizes the cg shift, rather than burning off 5 gallons first, then tranferring the 5 gallons from the aux tank. I did a weight and balance on it and came up with only a 7/16 inch cg shift transferring the fuel after about 2 gallons has been burned off.
Its too complicated to explain here without a drawing..but most that run this aux tank have it all plumbed in with the other tanks. The problem with that is the top tank burns off first...and its aft of the rotorshaft, while this aux tank is in front of it. The standard way sees all of this aft fuel being completely burned off first, thus causing the forward aux fuel to have its full weight effecting the cg. It will cause a cg shift around 7/8 of an inch if memory serves me correctly.
The fuel ends up running through a final 25 micron filter just before entering the mechanical fuel pump on the turbine.
I have checked the flow rates of my boost pump....both pumping and free flow, and the flow rates through my filters. All comfortably exceed the fuel consumption of the turbine by 2 to 1.
On to my electrical system:
I have a Keywest regulator that will continue to supply power to the governor and main fuel solenoid, and basic electrical needs, should I completely lose all battery voltage.
The fuel goes through a main fuel solenoid that automatically closes if the 12 volts is lost to it. I am going to convert it after the factory checkout to a fail safe mode...where it takes voltage to shut the fuel off...instead of turning the fuel on. There has to be a way for the overspeed circuitry to intervene and supply voltage to the main fuel solenoid should an overspeed occur.
The factory is going to offer a modification that not only makes the main fuel solenoid fail safe....but also have a small backup battery that will be charged by the system, but if the electrical system fails, this back up battery is diode protected from losing its voltage to the failed system, yet supply voltage to keep the governor and the main fuel solenoid open. They wont be offering this until after my checkout as they are still working on this kit upgrade.
One cant cover every scenario.. but I feel this covers the basics and is better than the stock setup. Again,,,this mod is by the factory so they are behind this change.
Stan