Challenger Builder’s Notes and Construction Tips

Here are some notes that I made to myself during my first build as lessons learned and reminders if I should ever build another plane. When I started my 2nd Challenger, these came in handy and I must say that things went smoother the 2nd time around as a result of applying these. The third plane was a breeze!

1. Using Glue. Use less glue and clean up any excess. Smear out any drops. A messy glue job will show through on the final paint job. Don’t expect the primer to fill it in and smooth it out. It will not. Wick up the extra glue with a damp cloth before it gets tacky or hardens. If you discover some drips later after its dried, take the iron set at 200F and smear them out. The setting at 200 degrees will soften the glue but not shrink the fabric. If you are using the Polyspray system, a cloth soaked in MEK will smear out drops and excess glue.
2. Painting. Use an HVLP paint sprayer. When I switched to HVLP, the finish was nicer, I used less paint, had less over spray, and the air compressor ran less often. For more tips on painting go to the section Tips on Painting a Challenger Ultralight.
3. Wing Stands. I really recommend building a pair of stands to support your wings when you paint them. When I painted my first Challenger, I just suspended the wings from the ceiling and painted them as they hung there. The wings have a chord of about 6 feet. So with even an 8 foot ceiling, it left very little room to paint the leading and trailing edges. So on the second Challenger, I resolved to build a pair of simple wing stands from lumber so that I could pivot the wings during the painting process and thus easily get at all the hard to reach places. These wing stands were easy and cheap to build. I used about 6 lengths of 8 foot 2×4 lumber. I purchased some metal L brackets from the hardware store to support the vertical post. I drilled a 1/2″ hole through the post and inserted bolts 1/2″ diameter x 6″ long. I took some 1/8″ thick aluminum sheet left over from the instrument panel and formed 4 brackets with a 1/2″ pivot hole in the center of each. These brackets I installed in the wing boxes at the end of each wing. (I opted for the Hoerner fiberglass wing tips.) The bolts acted as pivot rods when inserted into the flanges. Total cost was about $30. It really made painting the wings much easier.
4. Flip-Up Nose Cone. Install the Flip-Up Nose Cone option. It makes accessing all the stuff in the nose section a lot easier, such as the back of the instrument panel, the electronics, the rudder pedals, and so on. See the Challenger Ultralight Modifications section for more on this subject.
5. Ignition Switch. Install the Ignition switch off center in the instrument panel. Off to the left side is best. The Start push button too. This makes it easier when starting up the aircraft. Your right hand will be on the control stick holding the brakes on. Your left hand will be working the start button, throttle and primer. I sometimes get a bit of interference between my brake handle and the ignition key because I put the ignition right in the center of the panel near the bottom. See the separate page on Challenger Instrument Panels for more tips on logical instrument panel layout.
6. Engine Instrumentation. Add lots of engine instruments to fully monitor your engine. The kit only comes with a CHT and an analogue Tach. That’s not enough. The Rotax engine guys recommend a full suite of engine gauges. You need to monitor the CHT and EGT on both cylinders to watch the health of your engine. Label these gauges so that you know which temperature reading applies to which cylinder. This will help diagnose any problems. The analogue Tach is not accurate. Use the digital Tiny Tach in the kit. It may look hokey but it works great. Add a voltmeter and an ammeter to keep an eye on your battery and alternator. Of course, the other option is to install an electronic engine instrumentation system (EIS) or Electronic Flight Information System (EFIS) which will have quite a comprehensive set of gauges all in one nifty package. I have done instrument panels both ways but I’m old fashioned and love the look of a beautifully laid out panel of “steam” gauges. Call me a Luddite. See the separate page on Challenger Instrument Panels for more information.
7. Instrument Panel Layout. Carefully lay out the instruments on your panel. The gauge layout should follow a logical format that reflects the importance of the gauges in flight and will enable the pilot to keep his eyes looking up and out of the aircraft . That means that important gauges like Airspeed and Altitude should be at the top of the panel easily read with a quick glance. Other gauges like CHT, EGT, Tachometer, Fuel, Volts, Amps, Clock, Hobbs meter, along with switches and fuses, should be located further down on the panel. They are important, of course, but not as important as a quick look at your airspeed when you are on short final on a short field. Many instrument panels that I have seen look like they have been put together with little forethought to safety and flight priority. Some appear to have been arranged using a shotgun style method. The panel on the Challenger needs to be mounted on a slight angle so that the gauges, especially those located lower on the panel, are readable to the pilot. A tall pilot will need more of an angle. Also, take care that the big ASI and Altimeter gauges do not interfere with the rounded horizontal structural tube in front of the panel. It is best to install the gauges on cardboard or plywood and check for fit, angle and interference, before cutting an expensive plate of aluminum and mounting it for keeps only to run into a problem with fit or readability. It takes a long time to cut out an aluminum panel. The electrical gauges should be kept as far away from the compass as possible to prevent their magnetic fields from affecting its accuracy. See the Photo Gallery on this site, fuselage pics 5 to 8, for an idea of a good panel layout. See the separate page on Challenger Instrument Panels for more information.



8. Storage Space. Make more storage spaces. You will need little places to store things in your plane ie maps, water bottles, snacks, spares, oil, sunglasses, and so on. See the Challenger Ultralight Modifications section for more on this subject.
9. Door Edging. Buy more of the door edge guard for installing around the edges of the lexan windshie
   ld and doors. The kit does not come with enough. You can buy this at an automotive supply store. It will save you from cutting yourself on the sharp edges of the lexan and save your paint from chafing where the lexan meets the fuselage.
10. LPS Lubricant. Buy some LPS3 lubricant at an auto supply or aircraft supply store and spray it inside the rod eyes on the control rods. Yes inside the rod eyes where the male thread goes into the female thread. When Bruce inspected my plane, he removed the threads and corrosion had already begun to form! LPS3 will form a waxy coating on the metal surface to prevent corrosion. Use it on your hinges, and wheel shafts and bearings too.
11. Throttle Placement. Install your throttle levers carefully in a place where they will not be accidentally nudged by the foot or elbow of your passenger. Bruce would not give my plane a passing grade on its inspection for Advanced Ultralight until I moved the front throttle to a safer 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. I ordered the nice throttle quadrant from Aerocontrols and placed the levers such that there was no chance of accidental throttle inputs. See the Challenger Ultralight Modifications section for more on this subject.



12. Mark the Engine Shaft Bolt. Take a black permanent marker and put a line on the head of the bolt holding the small cog wheel to the output shaft of the engine. Put another mark in line with it on the metal of the shaft. This will make it obvious if your bolt is coming loose as the two lines will move apart. Mine moved during the first few hours of use! I noticed and tightened it. It has not moved since.