WHAT MODIFICATIONS CAN YOU AND SHOULD YOU USE ON A CHALLENGER?

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 addition, in Canada, many of these modifications are illegal for an “Advanced Ultralight”.

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.

These extra modifications also add significantly to the total assembly time for the aircraft. Often I have met builders who are discouraged with the little progress that they have made over time. When I look at their project, it is often littered with unnecessary and time consuming modifications. If they had simply followed the factory instructions, they probably would have completed the aircraft before they hit the wall of discouragement.

Some add modifications because they expect and want the Challenger to look like a Cessna or Piper on the inside. This expectation is wrong. The purpose, design and characteristics of the Challenger are completely different from GA (General Aviation) aircraft.

Tail stands, heavy shock absorbing landing gear, extremely complex instrument panels, storage compartments under the engine, and many more mods 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. Avoid the commonly voiced sentiment: “it only added a few pounds”. Multiply this “few pounds” by a “few mods” and you have a significant weight penalty on an airplane intended to be ultra light.

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

Challenger Third Door Challenger Modification

It is a simple fact that it is a challenge to get into a Challenger. The older we get the more challenging it seems. The taller we are the more challenging it is as well.

Although the entrance to the front seat is not impeded by the struts, the front wind screen supplied when you have the doors option is quite large. It wraps further around than the original wind screen. This leaves a smaller gap for the pilot to climb through.

One solution to this problem is the thrid door mod. The second solution involves a strict diet and a gym membership. Let’s look at the first solution.

The third door modification involves cutting the wind screen in a straight line from top to bottom in front of the right hand 2DT-1 down tube (the vertical posts that go up to the square root tube at the top of the cockpit). Then a 26” long section of hinge is installed on the inside of the wind screen along the cut in the lexan. 1/2” diameter aluminum tubes back up both sides of the hinge to provide rigidity. A 3/16” channel must be cut to accommodate the barrel of the hinge.

Challenger Third Door Modification

The section of wind screen to the rear of this cut in the lexan becomes a third door. More 1/2” tubes have to be riveted to the new door section to give it some rigidity. These tubes have to be bent to conform to the required curve of the door. Aluminumrivets must be used or the lexan will be damaged. This door section will need a couple of nylon D-005 door latches or another bungie style door latch to hold it closed.

The result is a much larger opening for the pilot to enter the front seat. Climbing in to the Challenger will no longer be a challenge.

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 o

wner 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:

Challenger 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 f

uel 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.

Challenger Flip Up Nose Cone

This is one of the handiest modifications for a Challenger. The flip up nose modification enables quick and easy access to the front of the aircraft without the hassle of removing the nose cone. Thus the owner is able to access the back of the instrument panel, the avionics shelf, the front rudder pedals and any other equipment located in the nose area. This is great for trouble shooting, maintenance or inspections.

This mod 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.

The key component is a really nicely machined hinge bracket that is rivetted to the two sides of the nose cone. It also includes two rubber straps and posts to hold the two halves together (like is used on the cowling of a snow mobile). This modification is available in kit form from Lake Aviation for $185.00 Cdn . Send us an email to order it. The part number is “Flip-Up-Nose-Cone-Kit”. It includes instructions.

Click on the images below for a larger picture:

Challenger 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.

Challenger 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.

Larger Challenger Fuel Tank

The original standard Challenger ultralight comes with a 5 gallon fuel tank. This makes it conform to the FAA rules for ultralights in the USA. It also only gives you about one hour of flight time and a very short range. The factory later added an optional 10 gallon tank. Then came after market 15 and 17 gallon tanks. Now the LSA version can even be equipped with 2 ten gallon tanks in the wings for a whopping 20 gallon total capacity.

The large fuel tank options really open up the ability for cross country trips with long legs and fewer refueling stops. Keep in mind though that the true range of a small aircraft is really measured by the size of the pilot’s bladder not the fuel tank.

The larger fuel tanks also enable the frugal pilot to load up a cheap mogas from home rather than spending big bucks on high priced 100LL at airports.

There is a downside or a word of caution with the large tanks and it has to do with the additional weight of all that fuel. A Challenger with 15 gallons of gas and two averaged sized people on board (185 lbs each) will be carrying 460 lbs of payload. Many of us weigh more than that. On a hot summer day all this weight will severely affect the aircraft performance. If the aircraft is mounted on floats, the effect is even worse. The aircraft will likely be over gross weight. Unless equipped wih the larger Rotax 582 engine, the plane may not want to fly at all. So larger fuel tanks require the pilot to use discretion when flight planning. That discretion may at times determine that it is a “no fly day” due to high density altitude and a heavy aircraft.

The large after-market fuel tanks fully loaded will weigh over 100 pounds. This requires that they be mounted so that, in the event of turbulence or an upset, the tank will stay in place and not break free and start roving about in the cabin. These tanks should be well restrained with an aluminum tube or angle fastened to the aircraft frame and passing across the top of the tank. Bungie cords and plastic straps are simply not enough to hold down this amount of weight.

Having larger fuel tanks means that fuel will often remain in the tank for weeks. As 2 stroke fuel ages it loses its octane rating. The octane rating of aged fuel may fall below the minimum rating that the engine requires to run. An engine stoppage may occur. If the fuel will remain standing in the tank for more than a couple of weeks, octane booster and fuel preserving additive should be added. Motor cycle shops often carry this item. Klotz is a popular and effective octane booster that prevents mixed two stroke fuel from aging.

The smaller 5 and 10 gallon tanks were made of plastic. Plastic and fibreglass fuel tanks have the advantage of not sweating like metal fuel tanks when the temperature changes. As we all learned in aviation ground school, when air cools the moisture entrained in the air condenses. This happens in large after-market aluminum fuel tanks supplied for Challengers. Condensed water left in the tank may be drawn into the fuel system and cause an engine stoppage. It could freeze and cause fuel starvation. It may combine with any alcohol in the fuel, form a gel and clog the fuel filter.

To prevent this, a fuel drain valve should be installed in the bottom of the aluminum fuel tanks. These tanks are usually manufactured with a 1/8NPT female pipe thread port in the bottom of the tank. A matching 1/8NPT male threaded drain valve can be purchased through an aviation supply house like Aircraft Spruce (part # CAV-110H4). Keep in mind that 1/8NPT (National Pipe Thread) actually has nothing to do with the measurement 1/8”. It will actually measure closer to 3/8” across the opening. Do not be fooled and order a larger thread size.

The CAV-110H4 from Aircraft Spruce has a barb connection that will fit the 3/8×1/4 fuel line. Push about 6” of fuel line onto the barb and it will extend through the belly skin of the plane. Pushing up on this hose will open the valve and allow you to drain off a sample of fuel and check for water. This should be done before every flight.

Challenger Aircraft Lighting

Additional lighting such as strobes and a landing light are a highly recommended modification. This is especially true if you are flying at a busy airport or will be mixing with faster general aviation aircraft in the landing pattern.

Strobe lights and landing lights increase the ability of other pilots to see your aircraft. They are an anti-collision safety feature. Any pilot quickly learns how difficult it is to see other aircraft in flight especially aircraft that are painted white. Remember the old saying: “One mid-air collision can ruin your whole day”.

The electrical current draw of most strobe systems is well within the capacity of the Rotax engines. A couple of manufacturers make aircraft strobe systems that are made specifically for ultralight aircraft and are well priced. Kuntszleman Electronics is one such company. They have a strobe light package that can be mounted top and bottom or on the wing tips. Another higher end unit is made to fit on the wing tips and combines strobes and all three navigation lights.

Lake Aviation offers a small light weight 12 volt landing light that includes the mounting bracket and fasteners. The light is streamlined and low profile to minimize drag. It draws about 4 – 5 Amps.

Challenger Ultralight Upholstery

Many Challenger pilots like to line the sides of the cockpit with some fabric to hide all the cables, wires and tubes. With some extra effort some pockets can be sewn into this fabric to provide some handy extra storage for car keys, cereal bars, spare batteries and fuses, pens and pencils, and so on. This is a very good idea as long as the fabric is not too heavy and does not interfere with the free movement of any of the controls such as the rudder pedals.

The fabric should be kept light in weight but also in colour. Black is beautiful but if you drop something in a Challenger cockpit lined with black upholstery, it is as if it fell into a cosmic black hole. Things seldom emerge from this chasm. Odd for such a small aircraft but true never the less.

The floor should also be covered with some upholstery. This floor fabric will collect the sand and other debris that we carry into the aircraft on our shoes. Otherwise the little bits of sand will get wedged in between the fabric and aluminum tubes. Over time and with the vibration and flexing of the airframe, the microscopic sharp edges on these grains of sand will cut away at the fabric and holes will form. Some fabric upholstery laying along the floor will catch these nasty grains of sand before they reach the aircraft fabric. The result will be a longer service life for the aircraft fabric skin.

A good idea is to Velcro the fabric upholstery into place. This will prevent the upholstery fabric from moving in flight and perhaps getting caught in any of the controls such as the rudder pedals, the aileron cables or the elevator torque tube. This obviously would be very dangerous.

Velcro can be purchased with adhesive on the back side of the Velcro strips. The best brand is 3M. The 3M adhesive is very strong. Cheaper brands generally peel of very easy. For extra strength you can also rivet the Velcro in place with same kind of wide head aluminum fabric rivets such as those used on the Challenger wing ribs.

Apply the strips of Velcro hooks to the aluminum tubes on the plane where the fabric will be placed. Sew the matching strips of Velcro loops to the back of your upholstery fabric. Then press your upholstery into place. It can thus be easily removed in the future for cleaning or getting at the airframe for maintenance or inspections.

Avoid using carpeting for the floor of the plane. It is too heavy. It absorbs and retains water. It is also very stiff which makes it difficult to install and remove. Also if a stiff piece of carpeting ever got caught in the controls, it would be very hard to overpower it.

Some good ideas for upholstery materials are denim, light weight vinyl fabrics and the fuzzy seat cover type materials. These can be purchased at dress making supply stores. You will need about 3 yards of material (that’s 3 meters in Canada).

If you do not want to make your own upholstery, Jean Claude Lachance and his wife Pauline at Turbulence Aviation make upholstery specifically for Challenger ultralights. It is really well made and features handy storage pockets. Upon request they will also supply matching vinyl to cover the floor.

Challenger Seat Cushions

The factory seat cushions work fine but after a few hours in the plane on a cross country trip, your rear end may demand some more padding. You may want to sit a little higher or a little further forward on the seat. You may want some seat cushions that look a little nicer.

If you decide to make your own cushions, be sure to include straps and/or Velcro to hold the cushions in place. Otherwise they will tend to slide to the side when you get into the aircraft. The rear seat cushion must be well fastened in place so that when you are flying solo, it will not come loose and perhaps interfere with the controls. If you are flying solo without doors, the rear seat cushion has to be well restrained or it will be blown out of the cockpit and pass through the propeller.

Turbulence Aviation manufactures a nice series of after market seat cushions made specifically for Challenger ultralights. They are not cheap but they look great and they are much more comfortable than the factory supplied cushions.