News in the turbine world
by Jim Hiller [email protected]
Eric Clapp has retired as Jet Central's managing director after working for the company for more than 10 years. Although he no longer works for Jet Central, Eric has not walked away from the hobby. He will continue to grow his own business, Jet Central USA. In addition to selling Jet Central turbines, he will offer FeiBao Jets. Jose Melendez is Eric's replacement at Jet Central, so change your contact information to what is listed in the "Sources" when looking for Jet Central service and support.
Xtreme Repairs
I have a maintenance program for my jet models, and I conduct a thorough inspection roughly once a year. My most recent inspection was on my Xtreme A.R.F. SH-Discus 2A. This large, 6-meter fiberglass composite sailplane is powered with a Wren 100 turbine on a power-pod setup. I put this model together last year and rushed to have it ready to fly before winter set in. Now, with approximately 25 flights on it, I have a list of improvements and minor repairs to make.
First, the pesky landing-gear doors broke off, snapping the glue joints because of excessive mechanical force during operation. The Discus has a single-wheel retract with two gear doors that are pushed open by the tire, then the landing gear pushes the doors the rest of the way open. The gear doors are pulled closed by a spring on each door, again rubbing on the landing gear and then the tire, as the landing gear closes. After determining why the doors broke off, I found a tight spot when opening them. The wheel no longer contacts the doors and the doors continue to open while being pushed by the extending landing-gear structure. The geometry of the system puts an unusual angle between the landing gear and the doors, aggravated by strong gear-door springs.
The solution is softer springs and a slight geometry cleanup with a bumper to aid in the operation. Now, I look forward to many flights with full gear-door operation. One maintenance project down!
The next task I wanted to complete was simplifying the model's refueling, which is a clumsy process on this glider. The hatch is hinged in the front, tilts forward for scale canopy operation, and cannot be removed. Removing the cockpit/seat assembly includes turning four twist locks while holding the canopy open. With the seat removed, I can finally access the fuel system. It's a hassle because the hatch has to be held open the entire time.
I chose a simple fix for this: a fuel-filler dot. The device plugs the fuel-fill line. When the fuel tubing is pushed back inside the airplane, it is secured by an aluminum receiver. The unit I used is slightly larger and fancier than a typical fuel dot, but it also adds a bit of bling to the model. Now fueling will be a simple matter of pulling out the fuel dot, removing the plug, and filling the tanks. When fueling is complete, I can reinsert the plug and push the tubing back into the fuselage. I now also have an external fuel overflow extending outside of the fuselage, allowing a ground tank to be connected during a long wait for takeoff clearance.
These types of issues are usually resolved during the initial build, but because it is a sailplane, I concentrated on aerodynamic cleanliness and kept external systems to a minimum. Never again! When it comes to being able to enjoy a day of flying, convenience is more important than a clean appearance.
On the subject of fuel systems, watch your fuel fitting and hose sizes. For the 100-newton, 22-pound-thrust turbine I am using on the Discus, I added large Tygon tubing to assure plenty of kerosene would be supplied to the turbine fuel pump. Large-diameter Tygon tubing has a 1/8-inch inside diameter (ID) (approximately 3 mm ID), and the fuel is sucked through all of those tank fittings and the tubing on its way to the fuel pump. I have used this setup for years with no problems. My philosophy on fuel tubing, clunks, and fittings is to switch to larger sizes as the turbine power goes up. On my Jet Central Cheetah, a 147-newton turbine uses even larger-diameter tubing.
Transcribed from original scans by AI. Minor OCR errors may remain.
