UH-1D/H/V Fuel System
The UH-1 D, E,H, V fuel system is not a simple system.
In this article I will explain how it works, identify components and how they function in the system. I will also identify problems, fixes, trouble shooting, and ways to keep it working properly. For maintenance and more detailed information use the TM 55-1520-210-23-2 Chapter 10.
Basic Fuel System
Figure 103 shows the fuel system in its entirety but it is difficult to see individual parts in some areas.
Starting with the fuel filler port on the upper right cell (figure 103 item 22 ). There are a couple of different ways to fuel the aircraft. Basic is open port Open the cap and there is an open port. Second is closed circuit. You open the cap and there is an adaptor in the inlet to connect to the closed circuit fueling hose. When filling the aircraft a float mechanism in the aircraft side will shut off the flow when full. Even though this is beneficial you should monitor this and shut it off manually if necessary.
I have seen aircraft after it doesn’t shutoff nominally. If it does not shut off the only way for the fuel is out is through the vent system with only the 1 inch line exiting the aircraft ( figure 103 item 2 ). In that case fuel was finding every weak point in the system it could find. The pressure practically detached and buckled panels surrounding the fuel cells.
The center cell is next, this is the largest of the cells, then the left cell. The right and left are the two smallest cells. If you look on the engine deck, on the right under the engine oil tank and on the left, below the main fuel filter, there are panels that go to the forward bulkhead. That is the area the right & left cells fit in.
The center cell fits between the inboard walls of two side cells. The center cell goes under the forward firewall to the front edge of the hell hole aft wall. Through the relatively large opening in the back of the center cell (figure 103 item 4) with access through the area under the engine deck. The two outside cells are bolted to the center cell at the bottom of the cells. They are connected by metal flanges with approximately 4 inch openings that are built into the cells near the bottom of the cell, this connects all three aft cells.
Breakaway fittings, in case of a crash, sever enough to pull the hoses away from their connections. The breakaway fittings will then break and seal off both ends keeping fuel in the cells reducing spilled fuel.
One hose, coming from the breakaway fitting on the bottom of the right cell, goes through a breakaway fitting connecting to the aft plate of the lower right cell. From the bottom front of the center cell a hose connects to the lower of the aft crossover hose assembly which connects to both lower cell aft plates.
From another breakaway fitting, a hose from the bottom of center cell, goes to a breakaway fitting (figure 103 item 6) on the bottom of the left cell. Another hose from that fitting goes forward, through a breakaway fitting, to the aft plate on the lower left cell. Notice that there is a forward crossover hose system (figure 103 item 15) and that connect at the front plates of the lower cells where the ejector pumps (figure 103 item 14) are internally mounted allowing fuel to transfer from one cell to another. If the boost pump on one side fails, the ejector pump on the good side can draw fuel from both cells.
The basics of the fuel system.
The items depicted are placed in relation to where they are in the system, not where they are actually located.
One example is the flapper valves, shown in the middle of the baffle of the lower cells. The flapper valves are at the bottom of the baffle, on the aft side, close to the inside wall of the cell. This places the flapper at the lowest point of the cell. They are positioned there in an attempt to keep fuel on the back side of the baffle, where the boost pump is located, when the fuel level is low.
In cruise flight the nose of the aircraft is low causing the fuel to flow forward away from the boost pump. The output from the boost pump has a T fitting one side to the flow (not pressure) switch (figure103 item11) then to the ejector pump. (figure 103 item 14)
The ejector uses pressure from the boost pump and runs it through a small orifice creating higher velocity causing lower pressure, creating suction picking up fuel from the front of the cell. You will notice there is a hose coming from the ejector pump that carries that fuel to an opening at the top inboard of the baffle and into the back side of the baffle.
This way, in a low fuel nose down condition, fuel is delivered from the ejector pump to behind the baffle to the boost pump. When the hose from the ejector to the baffle is tightened to the ejector pump output and clamped, the hose must be angled up if it has droop in the line otherwise it may not go all the way through the hole thus dumping fuel back into the front of the cell. The other half of the boost pump output goes to the engine out through the plate on the aft of each of the lower cells. From there the hoses connect to hoses that go up the aft wall and connect to hoses that run across the deck, under the tail rotor drive shaft, to the manifold/