Control Line Navy Carrier
Dick Perry [<REDACTED>]
The CL Carrier world mourns the loss of Marion Sawicki
NAVY CARRIER lost another pioneer and comrade in February. Marion Sawicki was extremely active and successful in Navy Carrier flying in the 1960s and 1970s. He placed in the top three in Class I or Class II at each Nats from 1968 to 1974. I had the pleasure of competing with Marion at the 1973 Nats. He will be missed.
Also included in this column:
- Using uniflow and chicken-hopper tanks in Carrier applications
This month I will continue the topic of engine necessities with the subject switching to fuel tanks. With suction fuel systems dictated for Profile Carrier and usable in Class I and Class II, I'll start with a discussion of uniflow fuel tanks.
The uniflow principle is used in a wide variety of events that require suction fuel systems. By immersing the single vent-line outlet below the surface of the fuel, the fuel pressure seen by the engine as it draws fuel to the carburetor remains more constant. If the vent line is located near the fuel pickup in the tank, the fuel pressure will remain constant throughout most of the engine run.
The purpose of the uniflow tank in most CL events is to counteract centripetal forces caused by flying a circle. In the Carrier classes, we also have to deal with acceleration forces during takeoff.
Engine sag on takeoff can have effects ranging from reducing high speed by a couple miles per hour (for a half-second reduction in power) to the loss of a flight if the aircraft is unable to get airborne before the end of the deck. Larger carburetors result in less suction and greater sensitivity to fuel pressure, but even standard RC carburetors sized for the engine
CL Navy Carrier
Dick Perry
can be affected by acceleration.
I prefer to set the needle valve for optimum reliability during the low-speed portion of the flight. In Nostalgia Carrier that is done predominantly with the idle mixture setting, and the high-speed needle can be used for fine-tuning the high-speed engine run.
At the higher low-speed power setting required for prop-hanging, the high-speed needle is more dominant, and some of the high-speed mixture must be managed by controlling fuel pressure. A richer ground setting to accommodate the nose-high, low-speed attitude may not produce an optimum high speed. That's where the uniflow tank comes in.
If the wet end of the vent tube is aligned (inboard/outboard position) with the carburetor, the fuel pressure in flight should be similar to that on the ground. In Carrier that condition may result in engine sag during initial acceleration.
If the wet end of the vent line is outboard of the carburetor, fuel pressure will decrease as the model gains speed, allowing the needle valve to be set richer on the ground. That also has the advantage of allowing the engine to lean out to an optimum mixture during takeoff (rather than an overlean setting, which causes loss of power), resulting in faster acceleration and a better high-speed score.
Some modelers build their fuel tanks and then adjust their lateral positions to fine-tune the high-speed mixture. That method works fine. I find it easier to build an adjustable vent line using telescoping tubing sizes (1/8 inch inside/3/32 inch) with silicone fuel line over both to seal the joint and keep the adjustable vent in position.
The adjustable vent is shown in the photograph with the tank installed on a Profile Carrier model. In practice the adjustable vent is moved outboard to lean the high-speed mixture and inboard to richen it.
A variation of the uniflow tank is the chicken-hopper type, shown in the photograph of Bob Frogner's Sea Vampire. The small tank contains the uniflow vent. It can be adjustable as I described, although Bob adjusts the tank position for optimum high speed.
The large inboard tank has filler and vent lines for filling the tank, but they are sealed after fueling, and the only way for fuel or air to move between the tanks is through two lines connecting the small tank and the large tank — one for fuel and the other for air.
The fuel-transfer line runs from the aft, lower, outboard corner of the large (hopper) tank and goes to the outboard, aft, lower side of the small (feed) tank. The air-transfer line runs from the high, forward portion of the feed tank — usually slightly outboard from the inboard edge of the tank — to a position in the hopper tank that is higher, more forward, and more inboard than the intake end of the fuel-transfer line.
The objective is to ensure that the fuel pressure on the output end of the air-transfer line is always lower than the fuel pressure on the intake end of the fuel-transfer line, whether the model is running on the deck, accelerating, or flying.
In practice the engine draws fuel from the feed tank, reducing the pressure in the tank, thus drawing air into the feed tank through the uniflow vent. Air bubbles to the top, inboard side of the feed tank (in flight).
As the level of fuel in the feed tank drops below the end of the air-transfer line, air escapes through the line to the hopper tank, allowing an equal amount of fuel to flow from the hopper tank to the feed tank through the fuel-transfer line.
When the fuel level rises in the feed tank and covers the end of the air-transfer line, air and fuel transfer stops until the cycle repeats.
Pressure fuel systems react similarly to suction fuel systems but are less sensitive to vent/pressure-line location because of the higher pressure. A significant difference between Carrier pressure systems and those in other events is that our engines' pressure output varies significantly with engine speed. If the pressure line is immersed in fuel when the engine slows, pressure in the tank will force fuel back through the pressure line with the potential to flood the engine.
One can solve the problem by trying to ensure that the pressure line is always dry, but maneuvers, turbulence, and other factors can make that difficult to do under all flight conditions. Next time I'll write about an effective method of solving the problem. MA
Transcribed from original scans by AI. Minor OCR errors may remain.
