Challenger Ultralight Modifications

It is important to be very careful and judicious in adding extra features and modifications to the Challenger. The weight of these extras adds up quickly. They therefore reduce the payload and performance of the finished plane. In Canada, many modifications are illegal.

A builder should be very careful and selective with modifications to any aircraft. The Challenger is no exception. There are many modifications for Challengers published on the internet. Many are unnecessary and simply add weight and complexity to the aircraft. They add significantly to the total assembly time for the aircraft. Tail stands, heavy shock absorbing landing gear, leading edge sheet metal wraps, storage compartments under the engine, elevator trim tabs, and many more like them will add weight and are not recommended or approved by the factory. Many of these add weight to the tail end of the aircraft resulting in dangerous center of gravity issues.

In Canada, these modifications may prevent your aircraft from receiving its certificate of conformance for “advanced ultralight”. They are not factory approved. They adversely affect the safety of the plane. So builder beware.

With all of this in mind, there are some mods that I have found useful on my Challengers. They add minimal weight. They do not affect the aircraft airworthiness. They will not snag on the aircraft certificate of conformance inspection.

Other mods are actually tools and fixtures used to build the Challenger. I have found a number of simple and easy tricks to make the job simple. Sometimes I needed to make something so I could work on the plane without having to have a second pair of hands.

USEFUL AND LEGAL CHALLENGER MODIFICATIONS

Locking Doors:

With the flaperon option, the factory supplied trim tabs sent with the kit are no longer required. The “L” shaped brackets used for the trim tabs (and are the same bracket used to make the tail surface hinges) are also useful in making an assembly that enables the aircraft owner to lock the aircraft doors using small padlocks. It’s not a bulletproof lock. A really determined thief will get into any ultralight. This mod will simply dissuade a casual thief. It gives me a bit of piece of mind when I am away from my plane. It enables me to leave the plane behind with my radio, GPS and headsets locked safe inside.

Simply rivet the L brackets in matching pairs, one to the lexan door, the other to the vertical bracket on the fuselage frame below the door. Be really, really careful when drilling the holes for the rivets, that you do not slip with your drill and poke a hole through the fabric. Center punch the holes to hold the drill bit in place. See the picture below:

Storage Compartments:

Challengers, like most small aircraft, have very little storage space. In fact, the stock kit from the factory makes absolutely no provision for storage! And yet, some storage is required for spares, oil, tie downs, small tools, water bottles, snacks, the Flight Supplement book, charts, and the list goes on. So it is left up to the builder to incorporate some storage spaces in the design. Here are some that I found to be effective.

The rear seat tower storage is built above the fuel tank using just some aluminum sheet metal, a length of hinge, and some velcro to keep the door closed. Be sure to leave enough clearance above the fuel tank for ease of access to service the fuel filter and lines.

The nose cone storage compartment is a little more complicated. It involved cutting a piece out of the nose cone, reinforcing the edges with aluminum strips, and building a frame inside. I made this box with a removable bottom and large enough that the battery could be removed through the hatch. Be sure to use only aluminum rivets so as not to damage the fiberglass nose cone. The other challenge is to place the hatch so as not to interfere with any of the other things inside the nose cone. A keyed lock from the hardware store finished of the installation.

Another place to easily add some storage area is alongside the nosecone and the nose frame beside the rudder pedals. Simply cut some aluminum sheet to fit the frame tubes above the main 2″ fuselage tubes as shown in the pictures here below. I find this space is great for storing my tie down ropes, water bottles, and my Canadian Flight Supplement manual.

Click on an image to see a larger picture.

Flip Up Nose Cone:

One of the handiest modifications is supplied by Steve Buzby of Aero Lite in Brockville, Ontario. (www.aeroliteflight.ca) The flip up nose modification enables quick and easy access to the front of the aircraft without the hassle of removing the nose cone. It requires you to cut the nose cone about a foot from the cockpit edge. Leave 4 corners uncut for about 2″. Buy a fiberglass repair kit at a hardware store or automotive supply company. On the nose side of the cone, apply mold release compound. (I found it at West Marine) Then use the fiberglass kit to make a flange that will stick to the cockpit side but not the nose side of the two halves of the nose cone. It makes a flange for the flip up side to fit over. Steve has made a really nicely machined hinge bracket that is rivetted to the two sides. And he includes two rubber straps and posts to hold the two halves together (like is used on the cowling of a snow mobile). Click on the images below for a larger picture:

Avionics Shelf:

The standard Challenger kit does not give a builder much room to install the electrical equipment such as the voltage regulator, wiring busses and any other avionics equipment associated with the instrument panel. The builder must find a way to make room for this.

One solution is to build a small avionics platform in the nose just in front of the panel and above the foot pedals. This panel can easily be about 14 inches wide and as much as 10 inches deep. Make sure it allows enough room for the instruments that extend well beyond the front panel face and also for your legs and feet. It must also allow clearance for the nose cone and, if you install the flip up nose cone option, room for the hinge assembly.

The platform framework can be built using 1/16″ thick x 1/2″ or 3/4″ aluminum angle from the hardware store. The shelf itself is .025 sheet aluminum. Small sheet metal pieces along the sides give the platform more rigidity.

After Market Throttle Quadrant

There is a nice after market throttle quadrant from a company in western Canada called Aero Controls. They make one specifically for Challenger Ultralights (Model AC-CTP). This quadrant puts both the throttle and the choke levers together in a single unit. The throttle lever is taller and larger than the choke lever so that there is no confusion. It also has a nice friction adjustment knob on the side. It is beefier and more professional looking than the standard throttle levers that are sent in the Challenger kit. It also includes mounting brackets to fit the frame tubes in the Challenger cockpit. The cables and connections for the carburetors are also included and sized to the right length for a Challenger 2. A nice touch is to paint the control knobs on the quadrant, maybe green for the throttle and yellow for the choke.

Install your throttle levers carefully in a place where they will not be accidentally nudged by the foot or elbow of your passenger. The front throttle must be located in a safe position where there was no chance that the rear passenger could inadvertently move it with his leg or foot. Similarly, the rear throttle must be located where the rear passenger will not be able to accidentally push it with either his knee or elbow.