Challenger Throttle and Choke Controls

The throttle and choke control levers that come with the Challenger kit work fine. They are small and light weight and accomplish the job. They will not, however, win any awards for great looks. There are a couple of other issues that the discerning pilot/builder may find aggravating.

(Note: The two stroke engines on Challengers really do not use a true “choke” mechanism in the throat of the carburetor. The Rotax engines are equipped with carburetors that each have a cable operated valve that opens to allow additional fuel into the mixture. This is very useful for starting these engines. The proper term perhaps is “fuel enrichener” rather than choke. But hardly anyone uses the term “fuel enrichener”. It just does not flow off the tongue and is harder to spell. Most of us just call them chokes for simplicity.)

One issue is locating the two levers in the cockpit in a place that is convenient and easy to reach. The Challenger cockpit is small and places for levers is scarce. The throttle is usually located on the left side of the cockpit on the side rail. This should be far enough ahead that it will not be affected by the passengers foot resting on the rudder pedal.

Where, though, can we locate the choke control lever. Mounting it on the side rail in line with the throttle lever is not advisable because it will interfere with the passengers foot or where the pilot’s left arm will naturally rest. Other places along that side of the cockpit are cramped and difficult to reach. The right side of the cockpit is available but will interfere with climbing into the airplane or will require quickly switching hands on the brake and control stick right after engine start up. The throttle, choke, ignition key and start button control really should all be on the left side of the cockpit within quick and easy reach of the left hand. This leaves the right hand free to hold the control stick and the brake.

Some have placed the choke control in the ceiling. However the flaperon control handle is also in the ceiling. The radiator louver control for the Rotax 582 Challengers is also there. Some pilots mount their intercoms there also. Space in the ceiling is quite limited, as well as being awkward to reach. Mounting the choke lever would require fabricating a low profile bracket. Keep in mind, too, that the pilot’s head is usually mounted near the ceiling and gets even closer when flying in turbulence.

Another issue with the factory throttle lever is throttle creep. The carburetor pistons are spring loaded and, combined with engine vibration, the throttle wants to slowly return to the idle setting as you fly along. So if you want to take your left hand off the throttle for any length of time, the engine will slow down. There is no provision for a throttle friction control on the factory supplied levers.

The final issue a builder will have with the factory throttle and choke assemblies is running the cables in a nice gentle kink free arc into the cable receptacles on the carburetors. This involves changing the direction of the cables from horizontal to vertical if they pass through the firewall near the root tube. If they are brought through the opening below the firewall, the required arc in the cable is closer to 180 degrees. The cables run through stiff polyethylene plastic tubing and it is prone to kinking if it is bent too quickly. Once kinked it stays kinked.

So what is the solution to these issues? A nice easy to mount, one piece, two lever integral throttle and choke quadrant with an friction control knob and heavy duty armoured cables that resist kinking and have brass 90 degree elbows to guide the cables where they attach to the carburetors. Is that too much to ask?

This very thing is available pre-assembled and cut to length complete with mounting plates to fit Challengers. Bob Robertson at Light Engine Services (also called Aero Controls) in B.C. manufactures this throttle quadrant and provides it at a very reasonable price.

The mounting plate for the throttle quadrant attaches to the diagonal 2FB-3 fuselage brace tube in the front left cockpit. This puts both the throttle and choke control levers in a nice ergonomically friendly place in the cockpit. It can be ordered with a second throttle control lever for the rear cockpit on two place models. The second throttle control also comes with a mounting plate .

Rather than a daisy chain style of assembly as is provided with the QCU factory supplied throttles, the Light Engine Services model controls the carburetors directly from the front seat quadrant. The rear seat quadrant is just a slave of the front.

The quadrant also features a large adjustable friction control knob to reduce throttle creep. This is really handy on cross country flights.

The throttle and choke cables supplied from Light Engine Service have a metal casing that is coated in black plastic and have a plastic core. The cable itself is stainless steel wire. The carburetor ends of the cables pass through brass tubes bent into 90 degree elbows to prevent kinking and ease assembly onto the carburetor fittings. The ferrules on the carburetor ends of the cables are silver soldered for maximum strength.

The quadrants made for Challengers with Rotax 582 engines are slightly different than those with Rotax 503 engines. The carburetors on the 582’s are mounted slightly higher relative to the bottom of the Challenger wing. So the brass elbows for 582 equipped Challengers are supplied with a shorter height and a 110 degree bend on the throttle cables to help clear the bottom of the trailing edge of the wing.

The throttle lever on the Light Engine Services quadrant is fitted with a travel limiting screw. This allows the builder to limit the travel of the carburetor pistons. The carburetor pistons should not be allowed to be pulled all the way and strike the top of the carburetor. Doing this could enable the pilot to inadvertently apply very high pull forces on the ferrules attached to the ends of the control cables. These ferrules might break in such an instance. The throttle travel stop should be set so that the throttle lever is stopped just as the throttle pistons reach the top of the throat of the carburetor. Any further travel beyond this will not result in any extra power anyway.

The Light Engine Services throttle quadrant in made with a nice black finish. Another nice touch is to paint the delrin plastic knobs. It makes the quadrant really stand out.

The overall effect of this quadrant is to save space, as well as improve appearance, functionality and safety.