Firewall Forward details of Legal Eagle XL-58

10/28/2010; fabricating the throttle quadrant

After a lot of sitting in the Eagle making engine noises, the location of the throttle quadrant was finalized. Priorities were insuring the throttle was easy to reach without strain and making sure it wouldn't be in the way of entering/exiting the plane. The location that won the polling is the lower left fuse longeron below seat level. This is an easy and logical reach and completely protected from flailing arms and legs as I articulate myself into the seat.

Shown are the components of the quadrant. The base of the control is a piece of 4130 sheet with a bushing welded to it and a 1/4" x 20 nut welded to the outboard end of the bushing. The nut captures the friction knob and the bushing means the throttle arm will not be eroded by the knob threads. Two washers and a short length of rubber fuel line complete the adjustable friction control. Turning the large black knob compresses the hose and applies friction to the lever.

The lever terminates the barrel end of the cable via a 0.090" spacer and the aluminum fork which is slotted to allow the cable to be installed. The whole deal is very secure with no chance of the cable coming loose. The cable is a heavy-duty go-kart brake cable with the barrel on one end and naked cable on the other. The cable and housing will be cut to final length when the carb is installed. The aluminum angle captures the cable outer housing.

The throttle control being mocked up and all the geometry checked. Adel clamps secure the control to the fuse without the need for welded tabs. Tabs may come later after test flights confirm this is the finished iteration of the control. I didn't want to drill holes in the fuse members in order to avoid the possibility of fatigue cracks in these highly-stressed tubes.

Right side of the throttle quadrant showing the friction knob and how the cable is secured. The entire arrangement is very rigid and smooth and allows quick cable replacement. The cable makes a straight shot up the lower longeron under the floorboard to the firewall without any bends.

Update: Flight testing revealed it was not possible to tighten the friction knob enough to prevent throttle creep. The knob was replaced with a bolt, and nylon washers replaced the steel washers. The bolt can now be tightened sufficiently for the throttle to hold position correctly.

This seems like a good place for the magneto switch. It is guarded from inadvertent contact but readily accessible for starting the engine or emergency shutdown. The grounding lead will be easily routed to the firewall along the lower longeron.

This photo shows the quadrant in relationship to the control stick. The grip is identical to the one on the control stick. A 1" wood dowel was split and glued to the throttle arm to make the grip fit properly.

3/15/2011; instruments

The Eagle by necessity and desire has minimal instrumentation. The only engine gauges are oil pressure and tach. The fuel level is monitored by the float gauge in the tank cap. Flight instruments are a slip ball and LRI angle of attack indicator. A Hall wind meter on the right main wing strut provides airspeed and a GPS displays altitude and flight timer..

The cowl tank occupies space that is usually used for the panel, so alternatives had to be found for the oil pressure gauge  I decided on the floor location in order to simplify routing of the pressure hose. 

Also visible is the Vertex radio mounted on a simple tray and attached to an external antenna beneath the cabin.

The slip indicator is located at the rear of the fuel tank in the primary line of sight with rubber mounts.

I feel strongly that every aircraft needs a slip indicator for spin prevention and the pilot must know how to fly with the ball centered, especially while maneuvering for landing. Aviation indicators cost $60 and up, but leveling gauges for boats and RVs can be had for well under $20. This one is popular in the marine community and I verified its operation by flying it in my RV-6. It is lightweight, and the tube is shatterproof plastic. The slip indicator was attached with double-back tape.

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