Radio Control Jets
Jim Hiller [[email protected]]
Small turbines and examples
BIG, POWERFUL aircraft tend to get the most attention at any model meet, yet most of the sport airplanes are smaller. The same holds true in jet modeling. Big jets draw the most interest, so guess what? We don't hear a lot about small turbine-powered jets.
The smallest turbine on the popular market is the Wren 44. I have seen it power quite a few nice jets. Gary Arthur and Marc Thomson attended the fall Winamac, Indiana, event with some fine-flying Wren 44–powered machines: a pair of scale Savex L-39 Albatroses and a Yellow Aircraft Stingray. Their performance is as impressive as that of any turbine model. They are neat machines.
The Savex L-39 Albatros is 1/8 scale and typically weighs less than 10 pounds. Powered by the 10-pound-thrust Wren 44, the roughly 1:1 power-to-weight ratio makes for impressive performance.
The L-39's wingspan is 48 inches, and it is only 59 inches long. Its convenient size makes it easy to transport, yet it's powerful enough to handle windy weather conditions. Check out the Savex Web site, shown in the source listing, for additional information.
The full-scale L-39 Albatros has become a popular sport aircraft. It can be modeled in a wide variety of paint schemes ranging from military themes to some wild civilian paint designs. You can have fun building and flying this model.
The sharp Yellow Aircraft Stingray is rarely seen at jet meets. Powered by a Wren 44, it boasts a great combination of power and airframe. The small turbine helps keep the weight down to 10.5 pounds, and the Stingray looked right flying at this weight.
This model's performance is as good as that of any delta-wing sport jet. Its high-speed flight is impressive; it looks fast because it is.
The landing speed is the main advantage of using the lightweight Wren 44 on the Stingray. Its landing-approach speed matched that of any sport jet. As a small model, the Stingray is unforgiving to weight gains. Many are powered with heavy, more powerful turbines, and the associated high landing speeds have been an issue.
Yellow Aircraft has been selling the 52-inch-wingspan Stingray. It is intended to introduce modelers to turbine flying. The engine is mounted aft and above the wing for easy access. See the source listing for additional information.
Homebuilt turbines and a test flight
Jeff Minotti is doing some exciting things up here in northeast Ohio. He has been building a selection of homebuilt turbines for a few years. He has had success running them, and as a Gas Turbine Builders Association (GTBA) member he has shared his experiences with others throughout the world. The Internet makes communication worldwide a practical and educational experience.
Jeff has been developing his flying skills with a variety of ducted-fan and performance sport aircraft in preparation for his first turbine-powered model and has joined the jet-modeling community. He got his turbine waiver, had his first homebuilt turbine approved by AMA for flight, and then went out and flew it.
Jeff allowed me to test-fly his modified Balsa USA Enforcer powered by a 10-pound-thrust turbine. His previous experience with the Enforcer as a ducted-fan jet proved itself on the test flight. The control throws, CG, and general setup were perfect. It required no changes, and the flight was sweet. Jeff took the second flight.
I was impressed by how smoothly his turbine ran. It had one of the most even fuel burns I have seen or heard in one of these engines. It made me realize how much of a difference in sound there is when a turbine is "right." Not many commercial turbines sound as smooth as his. Great job, Jeff!
The low pass (Flyby)
Let's discuss a flying skill: the art of the low pass. I am not referring to those descents that finish with a hard pull up before hitting the ground. I have in mind that level photo pass down the runway for a couple hundred feet. The altitude might be 20 or merely 2 feet above the ground, but the airplane is under perfect control in level flight. It is a wonderful display of precision flying. In Scale competition the low pass is recognized as a precision maneuver called the "Flyby." It's judged at cruise speed and as a slow pass displaying the airplane in the down-and-dirty configuration with landing gear and flaps extended.
How do you make such a pretty pass? It takes setup and developed skill.
You have to trim your aircraft well; pitch and roll trim must be dead-on. The ground is like a straightedge, measuring how accurately you draw a straight line with your model. Most people who have trouble with a low pass are fighting an out-of-trim condition with their aircraft.
Take your time to accurately trim for pitch and roll. At altitude set the jet level and remove your hand from the stick. It should fly a couple hundred feet without varying in either roll or pitch. If your model is not trimmed this precisely, you will fight it all the time.
Once you have the trims set up, you have to learn to position and point your jet accurately. What do I mean by this?
Do you trim your aircraft for a slight dive so you correct regularly with up-elevator? This is a typical trim setup that compensates for inaccurate level flight when rolling out of turns. You pull up out of the turn and allow the down-elevator trim to lower the model's nose until you achieve the flight level you want, and then you tap some up-elevator to level off.
This is a sloppy technique. When you make a low pass, that pitch correction will be obvious. The ground makes an accurate gauge, and the lower your pass, the more visible your careless technique will be.
After your jet is trimmed for level flight, concentrate on rolling out of turns without climbing. Criteria that must be met as you roll out of a turn are position relative to the runway, altitude above the ground, heading parallel to the runway, and climbing or diving.
Normally you want to nail your jet's position and heading as it rolls out of a turn, yet have it come out of the turn in a slight descent. A perfectly trimmed model will continue that descent until you stop it with a breath of up-elevator as you reach the altitude you want. This is similar to that down-elevator trim philosophy of flight, only you consciously point the model in a slight descent as you roll out of the turn.
If you have completed rolling out of the turn, all you have to do is stop the descent at the right altitude and position to start the low pass. When you pull on the elevator, the goal is to achieve level flight relative to the ground and then release the controls and enjoy the view of your jet as it flies by.
That is where the time spent accurately trimming it for level flight will be appreciated. No more corrections should be required.
It may seem simple as you read this, but applying the theory in flight is difficult. Every turn you make while flying a model is an opportunity to practice positioning it accurately—not only its position in the sky, but its heading parallel to the flightline, altitude, and angle of descent.
The better you are at using the turn maneuver to position your jet, the better and easier your flying will be. Just as you use the turn on final to land your model on the runway heading, every turn is used to similarly align the aircraft and set up for something else such as a pass or maneuver.
The supposedly simple low pass, or Flyby, is a result of proper aircraft setup and trim followed by precision flying skills that begin with a turn that properly aligns the model. The low pass itself is merely the reward for the previous hard work.
Practicing these flying techniques will greatly improve your flying skills, which will in turn reduce the pilot workload, particularly when flying jets at higher speeds. Poor heading and pointing of your aircraft when coming out of turns makes flying high-speed aircraft difficult. You end up following behind the model, trying to keep it within a reasonable distance from yourself rather than enjoying the thrill of high-speed flight.
Closing
It is time to get back to the building board. My T-33 is getting an upgrade to its landing gear, and who knows what else I will build this winter? See you at the jet meets.
MA
Sources
- Savex
(+420) 377240464 www.savex.cz
- Yellow Aircraft
(781) 935-9868 www.yellowaircraft.com
Transcribed from original scans by AI. Minor OCR errors may remain.
