RADIO CONTROL JETS
Jim Hiller, 6090 Downs Rd., Champion OH 44481
THESE LAST FEW months have been an exciting time; I took a trip to Los Angeles CA to visit Tad and Christina Krzanowski of Golden West Models. I missed Florida Jets, but the reports were that most had a good time despite some soggy weather in the middle.
It has been quite some time since my last visit to Tad's place, so it was nice to visit again. Golden West Models has been known throughout the years as the source of some interesting jet-model projects.
The company started with the first commercial turbine engine produced in the United States: its PD3/67. This small engine of only 8½ pounds of thrust has been out of production for some years now but is still desirable among the turbine hobbyist. Try to find one on the used market; they go fast when they do show up there.
Since that time, the products and projects coming from Golden West Models have led the way in technology, reliability, and ingenuity. You can check the company out at www.goldenwestmodels.net.
My excuse for visiting Golden West Models came from an invite to test-fly Tad's latest scale model: a Giant Scale A-37B Dragonfly. This is the COIN (counterinsurgency) fighter version of the infamous Cessna T-37 Tweety Bird. This model's stats are unbelievable; I couldn't miss this opportunity to fly it myself.
The Dragonfly has a wingspan of 132 inches with tip tanks, a wing area of almost 18 square feet, is powered by two JetCat turbines, carries plenty of Jet-A fuel onboard, and has a fuselage wide enough for two people to work inside the model at the same time. The last statement is not an exaggeration; I was one of the two. However, the most incredible fact is that the Dragonfly is that big and has an empty weight of only 41 pounds.
How can that be true? It is just that light, although that figure doesn't include the final paint and cockpit detail. This model, fully detailed, can be built and flown at less than the 55-pound weight limit.
The construction methods are the key to this light weight. The wing panels are vacuum-bagged fiberglass and balsa composite with a full-depth composite spar. The fuselage is fiberglass, but it's only thick enough to do the job; there is no excess weight trying to make a stiff, crashproof model. Attention to detail in the weight department is the true success of this model. The all-up weight puts the wing loading at 48 ounces per square foot; that's a remarkably light figure by jet-modeling standards, especially on this size of model.
The airfoil is a thick, almost symmetrical shape that is intended to provide good aerobatic capability and soft stall characteristics.
The Dragonfly breaks down into parts of convenient lengths for shipping. The fuselage breaks into three sections, ahead of the canopy and aft of the wing. The wing panels outside the fuselage and the horizontal stabilizers come off in halves. A great deal of thought has gone into designing this model to be able to travel with it. Those of us who know Tad have always been amazed at how he can make a model break down into parts for transport.
The Dragonfly’s test flight was easy. Tad had me set the center of gravity for the flight, adding weight to compensate for the lack of cockpit detail, and we went to the field.
Tad flexed it up and we flew it. I slowly advanced the throttle to approximately half, and the model was accelerating well, so I waited for it to rotate. It was off the ground in less than 300 feet and climbing well, so I retracted the gear and left the throttles at half to avoid building up too much speed without first checking it out properly.
The flight characteristics could best be described as the same as any Y-scale to 40% aerobatic propeller model, but with turbines the airspeed could reach 110-120 mph. The Dragonfly is one big, stable, smooth-flying model. I resisted my true desires with this airplane and didn’t get into any serious aerobatics (promises made before takeoff), but the model’s potential is cool.
Landing the Dragonfly was easy. Flaps are used in setting up that perfect glide speed and angle, but I’m not used to those light loading. The Dragonfly on a long final is a test in patience; it glides as slow as I must admit. On one high approach, when the pilot decided I may have missed the center of gravity by a fraction, the elevator was so sensitive during the flare. He’ll use it once where it belongs for future flights.
Tad promises that kits will be made available for the A-37 Dragonfly; he’s not keeping this one to himself. Sung Su Kim has a second one under construction and should be flying by the time this is in print.
A couple new items to come from Golden West Models in the near future include nice small jet kits for 12- to 17-pound-thrust turbines, which include his famous MIG-17, an A-10 nose, and a new sport jet he calls the Blade.
Another great product is Tad’s new brake system with wheels and tires for sport models such as the HotSpot, which is a model he distributes. I saw two HotSpots under construction for customers while I was in the shop. The brakes are a true disk system with an actual pad applying pressure directly to the wheel. I will be trying a set of these on my next sport jet.
Also available are pneumatic solenoid valves for actuating retracts and brakes. These are sold as individual solenoid valves or as a block of two, and they include 3mm tubing with fast-fit connectors. They plug directly into your receiver, eliminating the need for a servo and associated linkages and valves, which greatly simplifies setup. The solenoids are programmable to match your radio, and they can be set up in pulse or continuous mode for use as proportional brakes. I’ll tell how well I like them once I have a set of these.
While in California I met Emald Schwet, who is an amazing hobbyist. He brought out his HotSpot model to show us. It is a miniature version of a HotSpot, complete with a miniature four-pound-thrust turbine of his own design and construction. The HotSpot has a fiberglass molded airframe with retractable landing gear, just like a full-size HotSpot.
I observed the running of Emald’s turbine, and it was impressive. Startup, acceleration, and deceleration were as good as that of any turbine on the market today. The engine was relatively quiet, without the high pitch which normally accentuates smaller turbine engines.
Emald machined his own turbine wheel from the hub of an approved X-ray inspected turbine wheel. I saw the EDM machine used to cut the wheel; it is also a home-built unit. I am sure we will see more of Emald and his creations in the turbine community. Don’t expect this turbine to come to market; he built it for himself as an educational experience.
The disappointing thing is that Emald’s turbine is outside the AMA home-built turbine definition. The AMA home-built turbine rules, basically written by home-built turbine modelers, were written around the concept of building from plans — not scratch-building a turbine of your own design. I hope we can find a solution to this dilemma and allow Emald to fly under the AMA guidelines.
While on the subject of AMA turbine issues, a new forum is available to aid the contest directors — particularly those who are unfamiliar with turbine operations and associated rules. Check the AMA website, in the Competition section for documents such as “AMA Sanctioned Event Participant’s Statement of Compliance Concerning Turbine Engine Operation.”
A lot of conversation has been on the Internet lately about the requirement of the AMA waiver and associated safety rules for turbine operation at AMA meets, or likewise for AMA insurance coverage.
Our designated Special Interest Group, the JetPilot’s Organization (JPO), acts as our voice to the AMA Safety Committee if change is desired or required. The committee does take our recommendations seriously, and rules have changed as a result of those recommendations. Further, in the case of the home-built turbine issue, the rules were developed from a multi-discussion process by dedicated home-builder modelers.
The original intent of the waiver appears to be working — that is, to have the aspiring turbine modeler recognize the complications of turbine operations prior to attempting to fly their first turbine-powered model. The JPO website (www.jetpilot.org) has an excellent article to aid the new turbine modeler in answering the AMA waiver application’s questionnaire. This education process is an important function that the JPO is carrying out.
Another organization — the US RC Jet Command (USRCJC) — is a web-based group that has developed in the process. It brings some different ideas to the table and provides a good crosscheck to the whole process. It is located at www.usjc.org.
JPO and USRCJC bring ideas forward on jet model operation. We will not always agree, but let’s continue to work together to improve our turbine-modeling experience. This hobby is, and always should be, fun.
Transcribed from original scans by AI. Minor OCR errors may remain.
