I recently visited with Wren Turbines USA’s Ron Ballard. He made the trek to England for the Wren Open Day at the main factory, where the action never stops. Ron was anxious to tell me about exciting product improvements and new merchandise coming to the Wren turbine line. Some new products were introduced at Open Day. The upcoming Wren 140 turbine engine is a highly competitive, 140-kilogram, 31-pound-thrust turbine with smaller case diameters of approximately 4 inches. The powerful, lightweight turbine weighs 47 ounces (approximately 3 pounds).
Like many Wren products, the 140 is available in propane-start and kerosene-start versions. The plan is to have the Wren 140 up to full production volumes for the spring of 2013. Expect this to be another popular turbine.
Also premiered was the Wren 75 Jubilee for the cost-conscience consumer. An 18-pound thrust turbine for less than $2,000 is impressive. The 75 Jubilee is the latest version of the original MW54 design. This turbine weighs only 35 ounces (less than 42 ounces with all ancillaries), and comes in the original 3.5-inch-diameter case.
Years ago, I paid more for my original MW54 kit motor, but that little devil ran for years with no trouble. I sold it to upgrade to the Wren 100, but the current owner is still happily flying that MW54.
This latest version, the Jubilee, should be a solid consideration for an entry-level jet modeler, but it would be perfect for me when I build that old Bob Violett Models T-33 kit collecting dust in the barn. This is the perfect excuse to start building a Scale model.
My reason for visiting Ron Ballard was to drop off my Wren 100 for its annual inspection. I fly often enough that my turbines need to be inspected each year.
Ron was excited to show me all of the improvements made to the 100, such as eliminating the kerosene-start external nozzle and replacing it with an internal start nozzle. This eliminates the original design, which was prone to clogging and sometimes required cleaning.
The neat part of visiting Ron is that he pulled the parts out of the bin and showed me the new design of the kerosene-start nozzle and how it is orientated to the combustion chamber and igniter, which is why it is a better system.
Other subtle changes to the Wren 100 include a retention ring machined into the case to prevent the turbine from moving forward if the mounting straps slip. Wren continues to tweak all of the details to improve its products.
The company also announced development of a Wren 180. That’s 180 kilograms, or 40 pounds of thrust. This motor will complete the Wren turbine line, which ranges from the smallest—the Wren 44 at only 21 ounces of weight, putting out 10 pounds of thrust—to this bad boy. Talk about a solid product line from a company with a great reputation!
Air Leaks
My old CAI Razor began leaking retract air during a flying session this year. This brings up the issue of how to pinpoint air leaks.
When I got home, pulled the hatches off, and filled it up with air, I immediately heard the leak coming from underneath the main fuel tank. I pulled out the fuel tank, which was not an easy task on this model but had to be done. Underneath the fuel tank I found that the air line had been worn through due to the weight of the fuel tank resting on a section of air tubing. This was an easy find.
I replaced the worn air tubing, along with some other runs of tubing that were dry-rotted. This model is 10 to 15 years old. I’m only fixing it once, the right way.
Throughout most of the summer, the Razor lost air pressure in less than 20 minutes. While I had the systems apart, I decided to find the leak. I began with a bowl of water with a couple of drops of dishwater soap to make good air bubbles.
The first part tested was the air-fill valve. This can accumulate dirt, causing it to improperly seal and fill the air system. I submerged the air-fill valve in the water. There were no air bubbles, so this was not the source.
I tested the retract control valve by pulling and observing it under pressure. There were many air bubbles when I tested it under the soapy water—but why was it leaking? What could be the source of the air bubbles coming from the air retract valve?
I first considered the valve. Air was leaking past the retract control-valve seals, but that’s not the only potential source of air bubbles. When the valve moves to cycle the retracts, it not only sends pressurized air to the cylinders, but also exhausts air from the opposite side of the air cylinders. Should an air cylinder have an internal leak past the piston seals, air will bubble out of the exhaust side of the retract control valve.
I tested for piston-seal leaks by using a pair of forceps to pinch off the air to each of the air cylinders, retract units, and gear door cylinders on the Razor—all while the air-control valve was submerged in water. Sure enough, when I pinched off the nose gear’s air line, the leak stopped.
It doesn’t matter whether you pinch off the pressurized air line or the exhausting air line, the air bubbles will stop. It takes slightly longer for the air bubbles to stop if you pinch off the pressurized air line.
I dug through my parts bin of old retract units from crashed models and found a replacement air cylinder. I pulled the nose gear retract, removed the air lines, temporarily put them on the replacement cylinder, and rechecked the system for air leaks by submerging both the air control valve and the replacement cylinder. The replacement air cylinder was checked for an air leak near the piston rod seals. It is a good idea to check old seals for leaks.
It held air with no leaks. A check of the air system showed that it held pressure for an hour, so it was time to finish installing the replacement nose gear cylinder and get back to flying.
Time to Fly
It’s a warm, winter day outside, at least for northeast Ohio. The wind is calm, so I’m going flying. See you at the field.
The Wren 100 kerosene-start turbine has been improved with features such as an internal start nozzle and a retention ring machined into the case to stop the turbine from sliding forward in its mounts.
Terry Holston with his Wren-powered Baby Boomerang: a wonderful combination for the sport modeler. Wren’s new 75 Jubilee turbine engine is based on the original MW54 design, but now puts out 18 pounds of thrust for less than $2,000.
