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Ellison Throttle Body Injector

Section 2 - Installation

2-1 Planning

Because of the many differences between the TBI and the aircraft's original fuel metering system, it is very important to carefully plan the routing of all linkages, plumbing, and ducting components before beginning the permanent installation.

Like other diaphragm fuel metering systems such as the Bendix PS-5 carburetor and the Bendix RSA-5 Fuel Injector, the TBI will experience momentary power loss when momentary interruptions in fuel flow occur. This can result from the formation of vapor or the ingestion of air from leaks in the fuel system.

Below is a list of potential vapor or air leak sources that should be considered during the planning phase of any TBI installation.

  1. Boost pump, gascolator, fuel filter, and fuel valve should preferably be located outside the engine compartment or mounted together and blast cooled.
  2. Boost pump should be located below the level of the fuel in the tanks.
  3. Engine driven fuel pump should be shrouded and blast cooled.
  4. Fuel lines in the engine compartment should be insulated by fire sleeve and protected from radiant heat sources (exhaust pipes) by reflecting baffles.
  5. Minimize the number of fuel line fittings, especially 90 degree elbows, and limit the length of the fuel line, especially in the engine compartment.
  6. Maintain constant upward slope of fuel line from the boost pump (i.e. avoid high points or loops where air bubbles can accumulate).
  7. On aircraft with improperly baffled fuel tanks, the fuel tank pick-up can become unported allowing air bubbles to enter the fuel line. In such cases, long slips and sharp taxi turns before takeoff should be avoided while operating with low fuel tank levels.
  8. Avoid the use of auto fuel.
  9. Avoid fuel system complications which invite errors in fuel management.
  10. Loose fittings, deffective O rings, split flares, or improperly installed components such as primer pumps and gascolator seals, can be a troublesome source of air leaks and are usually difficult to identify.

2-2 Installation Requirements

In order for the ELLISON TBI to perform satisfactorily and dependably, the finished installation must include the following features:

A. Inlet air filter
B. Induction air heat system
C. Cockpit throttle stops, open and closed
D. Cockpit mixture control stops, rich and lean
E. Fuel filter, 70 micron or finer
F. Fuel pressure requirements:

Models EFS-2, EFS-4-5, and EFS-5 require 2 to 6 psi

Model EFS-3A requires 0.5 to 6 psi

Model EFS-10 requires 6 to 12 psi.

Note
The Bendix RSA-5 fuel injection system and PS-5 pressure carburetor use fuel pumps with output pressures of 20 and 15 psi respectively. Such pressure may be incompatible with standard TBI configurations.
G. Induction system primer
H. The aircraft fuel system, up to the point of connection to the TBI, including lines, filters, pumps, valves, and fuel flow sensors, must demonstrate the capability of flowing 150% of the rated power fuel requirements of the engine when operating on the last gallon of fuel in the tank. This flow capacity must exist when the aircraft is at the pitch attitude yielding minimum fuel head and with the fuel boost pump operating.
I. Fuel tank vents in all tanks

2-3 Mounting

Because the ELLISON TBI uses a diaphragm in lieu of a float chamber, the unit may be mounted in nearly any position. There are a few positions which should be avoided if possible.

The TBI must be mounted in an orientation that places the metering tube in a horizontal plane. If the metering tube is not in a horizontal plane, positive or negative "G" forces acting on the diaphragm will alter fuel metering. Avoid orientations in which the throttle slide moves fore and aft (parallel to the crankshaft), especially in Lycoming engines. The best performance will be obtained when the throttle slide moves in a spanwise direction.

2-4 Fuel Inlet Fitting

On all TBI models the fuel inlet filter is a 150 mesh stainless steel finger screen which is quite fragile and must be handled with care when removed. Great care should also be exercised to avoid the introduction of contaminants when removing and replacing the inlet screen or the plug on the opposite end of the filter chamber. Because the fuel inlet screen is a "last chance" filter, the aircraft fuel system must include a primary filter of 70 micron rating or finer.

2-4.1 EFS-3A, -4, -4-5, -5, -10

The body castings of these models incorporate a double ended fuel inlet chamber which has a 9/16 - 18 female thread at each end. The fuel inlet filter may be installed in either end of this chamber. The opposite end contains an AN-814-6D plug. The TBI fuel inlet filter is compatible with standard 3/8 inch flared tube fittings found in most aircraft fuel systems. Installation of the inlet fitting requires the application of 75 to 120 in-lbs of torque.

2-4.2 EFS-2

The fuel inlet filter incorporates a 7/16 - 20 male thread which is compatible with 1/4 inch flared tube fittings. Installation of the fuel inlet filter requires the application of 40 to 65 in-lbs of torque.

Note
If contaminants are found inside the TBI inlet filter screen, then a failure of the main airframe filter has occurred and must be corrected.

 

Caution
Do not use thread sealing compounds or tape. All fitting joints use either an "O" ring seal or a flared tube seat and, if properly installed, require no additional sealing material.

Optional fuel inlet filters incorporating a 90 degree elbow are available on special order.

2-5 Throttle Linkage

During engine operation at less than full throttle, a substantial pressure difference exists between the two ends of the throttle slide. This pressure gradient causes a strong buoyancy force acting to close the throttle. This force is greatest at idle and diminishes at increased throttle openings.

Caution
In the event of any throttle linkage failure allowing unrestrained throttle movement, the engine will immediately and without hesitation, return to idle.

Because of the higher throttle friction associated with the TBI, linkage installations utilizing a pull cable in only one direction with spring return in the opposite direction are not satisfactory.

Throttle Body Injector models EFS-3A, EFS-4, EFS-4-5, EFS-5 and EFS-10 may be configured with their throttle control arms and fuel fittings located on either side of the body as illustrated in Fig. 2-5.1. Because throttle position cannot be changed in the field, customer preference for this option must be specified when ordering as either throttle configuration A or B.

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Fig. 2-5.1, View looking into the engine through the TBI inlet

Throttle linkage connection to the TBI throttle control arm must provide movement which is parallel to the throttle control arm within plus or minus 5 degrees. This requirement may be met using a bell crank arrangement such as the one illustrated in Figure 2-5.2 or a push-pull cable or rod as illustrated in Figure 2-5.3. The throttle control arm is supplied with a ball-swivel fitting containing a 10-32 female thread for connection to a pushrod or Morse cable end.

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Figure 2-5.2

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Figure 2-5.3

Throttle linkages which utilize a push-pull cable may have the cable housing secured to the TBI by an optional EFS cable clamp illustrated in figure 2-5.3. This optional cable clamp is not available for the EFS-2 or EFS-3A.

Note

Maximum throttle control arm extension at full throttle for the various models is as follows:

EFS-10 2.4 inches
EFS-5 2.0 inches
EFS-4-5 1.875 inches
EFS-4 1.750 inches
EFS-3A 1.562 inches
EFS-2 1.35 inches

Additional allowance must be made for engine movement on mounts to assure no interference with other parts of the engine or airframe components.

Following installation and hook up of the throttle linkage to the TBI throttle control arm, the cockpit mounted "open throttle" stop must be adjusted so that the cockpit throttle control contacts the stop concurrent with, or prior to, the slide reaching its full open position. This stop is required to prevent excessive pilot force being applied to the throttle control arm.

Adjustment of the "throttle closed" stop will be described in Section 3-4 of this manual.

2-6 Mixture Linkage

EFS-2:

The mixture control arm on the EFS-2 is a simple aluminum lever that can be positioned at any angle about the metering tube axis (Fig 2-6.1). Full travel of the mixture control requires that the arm be able to swing through 90 degrees of arc in going from full rich to full lean. The full rich mixture position occurs when the metering holes in the metering tube are oriented perpendicular to the airflow, and full lean occurs when the metering holes look directly into the the airflow. To avoid excessive overhang moments the control element connected to the mixture arm must be a lightweight bowden wire or the equivalent. Following the final full rich mixture adjustment procedure specified in Section 3-3 of this manual, the arm will be secured in place with a roll pin and lock wire.

EFS-3A, -4, -4-5, -5, -10:

The mixture control arm assembly located on the protruding end of the metering tube is permanently pinned in place limiting the tube rotation to a 90 degree angle. The mixture control is in the full rich position when the "R" arm contacts the stop pin (holes in the metering tube oriented perpendicular to the airflow). Full lean occurs when the opposite arm ("L") contacts the pin (metering holes looking directly into the the airflow). For installation flexibility, the outer portion of the control arm may be oriented at any angle for compatibility with the mixture control linkage.

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Figure 2-6.1

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Figure 2-6.2

2-7 Induction Heat

Contrary to common belief, the ELLISON TBI can accumulate ice! Additionally, engines with cold induction manifolds such as the four cylinder Continental engines, the Continental O-470, and all Volkswagen derivative engines are especially susceptible to the formation of manifold ice. FOR THESE REASONS, ALL TBI INSTALLATIONS MUST INCLUDE AN INDUCTION HEATING SYSTEM capable of providing an inlet air temperature rise of 90 degrees F. Follow engine or airframe manufacturer's recommendations for use of induction heat.

2-8 Protection from Engine Heat

Air temperatures in the engine compartment downstream of the cylinders are usually about the same as the engine's oil temperature. Fuel system components such as filters, gascolators, boost pumps etc, when located in this high temperature environment can easily heat the fuel to its boiling temperature. While float carburetors separate vapor and discharge it through the float bowl vent, the TBI, like other diaphragm controlled fuel metering devices, pass this vapor on to the engine, resulting in roughness, power loss or power instability.

Vapor problems can be avoided by:

  1. Locating filters, gascolators and boost pumps outside of the engine compartment,
  2. Insulating engine compartment fuel line with fire sleeve
  3. Blast cooling the engine driven fuel pump. If it is not possible to mount these components remotely, then they should be enclosed together in a box or shroud and blast cooled.

2-9 Induction Air Inlet

Fuel metering in the Ellison Throttle Body Injector is accomplished by sensing both the direction and velocity of air flowing past the metering tube. This means that engine performance can be adversely affected if air entering the Throttle Body Injector is extremely turbulent or is delivered from only one side of the inlet bell mouth.

In general, the efficiency of the induction air inlet can be judged by engine smoothness at full throttle and the extent to which the engine can be leaned at cruise power. An inlet with good flow characteristics will allow an engine equipped with a fixed pitch propeller to run smoothly with the mixture leaned 200 RPM below peak power when operating at or below 75% power. An engine equipped with a constant speed propeller should demonstrate smooth operation when leaned to peak exhaust gas temperature while operating at or below 75% power.

Caution

Severe engine damage can result from operation above 75% power with an excessively lean mixture. At a pressure altitude of 7000 feet, the engine produces only about 75% power at full throttle and can tolerate leaner mixtures. Consult the engine manufacturer's operating manual for proper leaning procedures for fuel injected engines.

Engines operating with poorly designed air inlets may demonstrate engine roughness at wide open throttle, inability to tolerate lean mixtures, and substantial variation in cylinder to cylinder head temperature or exhaust gas temperature.

2.9.1 Good Inlet Configurations

Fig. 6-1 through Fig. 6-3 of Appendix D, illustrate good inlet configurations. These promote good cylinder to cylinder fuel distribution because air enters the Throttle Body Injector inlet uniformly from 360 degrees around the inlet centerline.

2.9.2 Inlet Configurations to be Avoided

Inlet configurations such as shown in Fig. 6-4 and 6-5 of Appendix D, require intake air to undergo a sharp 90 degree bend while entering the Throttle Body Injector, causing some of the metered fuel to be deflected against the throat wall. Full throttle operation will be rough due to poor fuel distribution, and the engine will have little tolerance for operation on lean mixtures at cruise power settings.

Some configurations which do allow 360 degree air delivery like the one shown in Fig. 6-6 of Appendix D, may experience problems at full throttle due to the short vertical distance between the Throttle Body injector and the opposite air filter flange. This configuration promotes the formation of a standing vortex in the inlet bell mouth, reducing the airflow capacity of the Throttle Body Injector with resulting full throttle roughness and loss of power.

2.9.3 Improving The Performance of 90 Degree Inlets

The performance of engines with bending inlet flowpaths can be improved by increasing the bend radius or by providing a straight section of duct between the Throttle Body Injector and the bend. Alternatively, a 90 degree change in airflow direction can be accommodated by feeding the Throttle Body Injector from a relatively large volume plenum chamber as shown in Fig. 6-7 of Appendix D. Dimensions shown in this illustration should be considered minimum. Increasing any of the dimensions will result in improved fuel distribution.

If a Throttle Body Injector is to be installed utilizing intake ducting from an earlier carburetor installation, ground tests should be conducted to determine whether any performance deficiencies exist. If any adverse symptoms are noted, the information contained herein should be used as the basis for designing a new inlet configuration.

2-10 Fuel Drain Fitting

Following engine shutdown, approximately half of the fuel trapped in the regulator (about one teaspoon) will drain out through the metering tube and out the intake flange. Provision must be made in the engine compartment to allow this fuel to exit the cowling without creating a fire hazard.

2-11 Removal of Fuel Injection System

If the TBI will be used to replace a fuel injection system, all injector nozzles must be removed and replaced with plugs using a high temperature anti-seize thread lubricant. Consult Section 2-2 of this manual regarding TBI compatibility with fuel injection system pumps.

To Section 3

 

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