For many of us, this is the time of year when we prepare for our next flying season. For those of you who live in the South, I don’t know how you do it. I don’t understand how you can make yourself stop flying to build new airplanes.
Here in the North, we are deep into the construction of next season’s airplanes. We do have some relief from the workshop. Indoor flying season is underway and with the new UMX Habu 180 from E-flite, we have an EDF to fly in tight spaces. It’s a cool little airplane.
2013 Jet Modeling Recap
Jet modeling is growing fast, not only in the number of aeromodelers, but also in products and events. The growth of Jets Over Kentucky, one of our premier jet events, is a reflection of the growth of jet modeling.
With 199 registered pilots at the Lebanon, Kentucky, event, there was enough interest for RCKen (also known as Ken Isaac of RCUniverse) to create a two-disk DVD set. One DVD is a video, and the other is a photo slideshow.
Ken thought he knew what he was getting into, but when the action started, he lived on the flightline. He convinced pilots to strap his camera onto their jets and capture everything needed for this DVD set.
This set is well worth the cost. I love the dual-screen action from the onboard camera that is synched with the ground shots of the jets. You’ll feel the action. Thanks for your hard work, Ken. It is a great project. Learn more about it at the website listed in “Sources.”
There are now more local jet meets. Most of the events include wonderful flying and social activities. What a blast! You can fly as often as you like with your friends, and the skies are typically not crowded. At many of the meets, pilots wait for each other to allow for solo flights for special models. I attended a fly-in nearly every other weekend last summer.
Some trends in the jet hobby include improved performance of the new turbines in the 100-class size. Many modelers enjoy using turbines such as the Wren 100K, Jet Central Rabbit, and the JetCat P100 for performance improvements in a smaller size. These turbines are popular engines for new jet pilots and work great in smaller models.
I put together a 1.7-meter Jet-Teng Viper and flew it with my Jet Central Rabbit and my Wren 100K. It’s a 171/2-pound aerobatic airplane with 22 pounds of thrust and is fun for constant-speed aerobatic flying.
The smaller, 72-inch wingspan makes the aircraft easy to transport to the field, and it’s small and light enough to assemble without assistance. I love this package for everyday flying. Typical flights burn approximately a half gallon of fuel per flight, so a 5-gallon jug keeps you flying all day.
At the other end of the power range, large jets have gotten bigger. It is common to see jets that are more than 8 feet long, with turbines exceeding the 160 size. That’s 36 pounds of thrust and more. The weight of these aircraft has also increased.
The experimental-class rules were modified throughout the years to simplify the certification process. The advent of the Large Turbine Model Aircraft (LTMA-1) class allows takeoff weights of more than 55 pounds, so more jets are certified. I can’t stress enough the importance of certifying your heavy models that fall into this class.
You no longer have to leave off options, run limited fuel, forgo smoke systems, or have redundant safety features such as dual batteries to make weight. The process has been simplified, so use the LTMA-1 class in the experimental program for all models.
Propeller-powered airplanes can use the Large Model Aircraft (LMA-1) class. It allows airplanes to be flown at AMA events and flying fields and comply with the rules.
Nose-Gear Spring Problems
I had to relearn an old lesson with my FeiBao Hawk. I had a nasty landing and it began to bounce. Each successive bounce increased until the nose gear failed.
The hops got worse with each bounce because the nose-gear spring was too stiff. When it collapsed, it launched the nose higher than before. I should have installed a soft spring in the nose gear before I began flying. Manufacturers don’t always bring that type of setup experience to the table. We fly their airplanes more then they test them, so it pays to second guess everything.
What would the spring rate be for an effective landing gear system? That’s a matter of preference. I prefer slightly softer springs. For main gear springs, my rule is that I should be able to push down on the wing and compress the springs, but they should be strong enough to be fully extended with the airplane fully loaded and ready for takeoff. If you do this check, you’ll find that on some models, you can’t compress the springs without excessive force. You could damage the model before the springs compress.
Stiff springs such as these will not make the ride smooth, but they will protect the airplane from excessive force on a hard landing, reducing airframe stress. Soft springs create a soft ride, but will bottom out on hard landings, transferring the shock load to the airframe.
The nose gear supports roughly 10% of an airplane’s weight, so how hard does a nose gear spring need to be? A stiffer spring will absorb a greater hit before it bottoms out. When it compresses, that spring will extend with all its force. A stiff spring launches 10% of the airframe’s weight. The main gear springs will launch the back of the airplane, sending the nose higher than the wing on successive bounces.
I prefer a nose gear spring’s stiffness to be light so that when I apply the brakes I can see the airplane’s nose dip and partially collapse the nose gear. With a soft spring such as this, the model’s nose will not launch higher with each bounce.
If you fly off of a rough field you may find that a stiffer spring is needed to protect the airframe. Give it some thought. A landing gear system is supposed to absorb a hard landing without creating new problems.
