Giant-Scale Flying Engine Test Rig
WHAT DO YOU DO when you have a brand new still-in-the-box Moki 5-cylinder gas engine and you want to do a test run before you install it in your newly built scale masterpiece? Our good friend and flying buddy Whitney Philbrick of Nolensville, Tennessee, decided to come up with a stable and easy-to-fly test bed. Whitney started with a 12-footspan giant Telemaster ARF from Hobby Express and slightly modified the model so that he could attach the Moki. He notes that, overall, the combo was a pretty straightforward project. With his simple and easy-to-fly airplane, Whitney was able to accumulate a lot of run time on his new radial engine. This flight experience helped greatly as he learned the proper priming and starting sequence, and tested various propellers to get the most out of the engine. When everything was running perfectly, he installed the mighty Moki in his 1/3-scale Nieuport 28, which he built from a Balsa USA kit. We caught up with Whitney and asked him to tell us more about his flying engine test rig. Whitney Philbrick: The “Baby” 150cc 5-cylinder, four-stroke Moki gas engine is sold by Vogelsang Aeroscale, and “Doc,” the owner, spent a generous amount of time helping me better understand the engine. After several flights, we settled on a 50:1 fuel mixture using Red Line oil, with a small amount of Sea Foam added to reduce fouling. I removed the front cheeks to accommodate the engine cylinders. The modifications [involved] mostly adding internal reinforcements to better link firewall forces back to the first and second wing tubes/spars to better handle the vibration of the large gas engine. I also added support struts to the horizontal tail. It has a large hopper in the fuselage and a bomb-drop release for dropping candy and prizes, which the original airplane did for many years at the NEAT [Northeast Electric Aircraft Technology] Fair. It also has several attachment points for GoPro cameras. What radio gear do you use? I’m using an Airtronics radio with dual A123 2400mAh batteries from NoBS, and dual receivers split to the control on the left and right side of the plane—with the exception that one side runs the engine and rudder and one side runs the flaps. The tweaks we’ve made to the operation of the Moki 150 radial were an added fuel pump and a new ignition powered with a 6.6V 3-cell 2400mAh A123 pack. So was it all worth it? It has been a bit too successful, as we are reluctant now to remove the engine as the plane is relaxing and enjoyable to fly. I am planning on upgrading the landing gear to something with shock absorbers [because] during landings now, it tends to bounce no matter how smooth we bring it in; the straight music-wire gear just springs the plane back up. But other than that, it’s a fun plane, capable of mild aerobatics [like] lazy flights around the pattern. Its flight behavior is docile, and the engine can be set to putter along at 2,000rpm spinning a 28x14 or 28x12 prop. The best thing about the engine is the sound. It sounds like a loud sewing machine, with the rockers and valve noise—a deep exhaust note from the collector ring exhaust. It does make this MonoKote-covered ARF present in a very scale way. The only drawback is the level of maintenance with a Moki. This isn’t an industrial chain-saw conversion designed to run untouched for long periods. You have to do some oiling of the rockers and pushrods at the start of each flying day. And [you] also [need to] check that the valves are free and that the nuts on the exhaust are tight. I check valve lash every 10 flights but rarely have to adjust them.