Earning Your Turbine Waiver
by Jim Hiller [email protected]
Last year was an active year in my local club for jet flying, particularly for new jet modelers earning their turbine waivers. Helping new jet pilots through the waiver process is not only good for the new pilot, but also for the experienced jet modelers who are assisting. It puts us in a position to verbalize what makes jet models unique and to review the AMA regulations pertaining to them.
As our flying season starts, it is a good time for all of us to review the process—both for our own operations and in case we are called upon to assist an aspiring turbine applicant. The regulations have been unchanged for a while because they relate to fixed-wing models.
Let's start with the basic requirements. Before presenting yourself for a turbine waiver, you must have completed 50 flights on a high-performance model, defined as capable of sustained speeds of 100 mph or higher. Flying models capable of these speeds is impressive and helps develop the skills needed for turbine flying.
Many of our new, larger EDF models have this performance capability and help develop the skills for turbine flying. Many have the sophistication of flaps, retracts, and even brakes, which make the crossover to turbine-powered models a natural progression.
If you meet these requirements, you're eligible to progress to the turbine qualification flight. This is more than a single flight. It is a test process administered by two CDs (contest directors), one of whom must have a turbine waiver. Both need to agree that you are qualified when the test is complete. You can divide the test into parts:
- Verbal and qualification flight (administered by the CDs).
- Five solo flights supervised by an experienced turbine modeler.
The verbal "test" is more of a discussion with the CD to demonstrate your familiarity with the unique operating differences of turbine engines and how they relate to the model flying experience. I suggest downloading two documents from the AMA website document section:
- Safety Regulations for Model Aircraft Powered by Gas Turbines (Document 510-A)
- Fixed Wing - Turbine Waiver Application (Document 510-D)
These documents are thorough and concentrate on the differences you can expect with turbine modeling. Generally, expect what is covered in the Key Elements section of the Fixed Wing - Turbine Waiver Application form.
I like a discussion about turbine operations, fueling, startup, shutdown, and general flying differences. The turbine blows hot air out of the tailpipe, so think about where you point it.
When fueling a turbine model, most installations do not require disconnecting the kerosene line from the fuel pump, so fuel pressure is applied to the solenoid valve leading to the turbine. If this valve leaks you'll have a turbine full of kerosene and a hot start. This is why most models are equipped with a manual shutoff valve. Turn it off when fueling to prevent kerosene from leaking through the valve into the turbine.
This is most modelers' first experience with a power system controlled by an electronic control unit (ECU), in which many operations such as the start and shutdown sequences are computer controlled. It is important to understand what your turbine is doing during the start sequence so if something isn't right, you can recognize it and respond.
What can go wrong? Let's review a hot start with flames emitting from the tailpipe during start-up. You'll have to make a few quick decisions if this happens.
Modern tailpipes tend to be robust and can tolerate some flame, but only a small amount. Consider allowing the start sequence to continue to completion if it is minor; if larger, you should shut down the start sequence. It is better to know how. In many modern ECUs, moving the idle trim to the low position with the throttle at idle will stop the start sequence.
If flames remain behind the turbine with no air movement coming out to blow them away, you should act to remove the flames safely. I fly Jet Central and Wren turbines; both are kerosene-start versions. They offer the option of cycling the throttle to get the starter motor turning—blowing air out the back of the turbine to move the flames out without inducing more kerosene to the flames. Often this is sufficient, but if the turbine was overfilled or fuel puddled in the fuselage and is burning, do the next steps.
The AMA safety regulations state that a fire extinguisher should be handy. It is strongly recommended that a CO2 fire extinguisher be used. Dry-chemical fire extinguishers leave a residue that will bake onto metal surfaces, potentially causing expensive turbine repairs.
A quick, 1-second burst of CO2 into a confined space such as an inlet or fuselage hatch is enough to extinguish most flames. CO2 quickly replaces the oxygen and extinguishes the fire. Remember the fire triangle: fuel, oxygen, and heat. Remove the oxygen with CO2 and there is no fire.
Start-up issues with a turbine are unique but easily handled when you understand what is happening and are prepared to react. This is one of the primary reasons we still have a turbine waiver process—to educate modelers before that moment when knowledge is necessary. When everything performs normally, none of these exciting things happen; it's merely a simple 30- to 60-second sequence casually initiated by the modeler.
For experienced jet modelers, working with a new waiver applicant is a good review of what can happen, why it happens, how we can avoid common causes, and how to respond.
From here, the conversation usually leads to flying and how to respond when things go wrong and a crash occurs. The first reaction that must be trained into our heads is to shut down the turbine—not just pull the throttle to idle, but also pull the throttle trim to idle. Shutting down the turbine removes a heat source should a crash occur. This has proven effective in reducing post-crash fires in turbine aircraft.
Should a crash occur, be prepared with certain items to respond to a fire:
- A good CO2 fire extinguisher (preferred over dry-chemical).
- The local fire department's telephone number saved on your cell phone.
Neither may ever be required, but be prepared. Modelers should be prepared to contact the local fire department regardless of the power system utilized in their model. Post-crash fire potential exists with many power systems; it's not just a turbine issue.
That covers the verbal part. Let's fly.
Second Element
This is the second part of the key elements covered in the Fixed Wing - Turbine Waiver Application form: the flight skills demonstration. Many modelers expect fancy aerobatic flying to be required, but that's not what we are looking for; control is the main issue. Good, basic aerobatic flying skills are all that are required.
As someone who has been an event director, I know the most important parts of the flight are those near pilots, crew, and spectators. So the takeoff and landing requirements carry more weight. You had better know how to drive a model down the runway under control and stay near the centerline.
Lose control here and you're either going off the runway on the far side or off the runway toward people. This occurs not only on takeoff, but also on landing. At a major event a few years ago, a modeler actually lost control of his jet on landing. It came through the opening in the safety fence and stopped in one of the vacant startup boxes—definitely not under the pilot's full control. Moments such as this scare event directors.
Basic Flight Skills
You will be asked to perform some simple maneuvers, such as a Cuban 8, a horizontal figure eight, and a missed approach from the opposite direction as the takeoff. Why these maneuvers? They prove you have basic flying skills, are not limited to left-hand turns only, and can comfortably fly a model through a circuit in either direction. Turbine flying is not the place for pilots with limited skills.
Another basic requirement is a high-speed circuit—not flown at full throttle, but at an appropriately high speed. What the CDs are looking for is the ability to maintain a consistent altitude while flying the circuit. This requires precision turn control at higher speeds.
What is easy at 75 mph can become tough at speeds of more than 150 mph. Precision bank angles and smooth elevator input are key to performing a consistent, flat circuit.
If you take the flight test with a high-speed turbine aircraft, do not attempt full-throttle passes immediately. It typically takes pilots five to 20 flights to get comfortable at full speed on a jet model. Control in this case includes maintaining comfortable and safe speeds.
Landing
Land the airplane, control the landing roll, keep it safely on the runway, and shut down the turbine. That's it. If you've done it well, your turbine waiver will follow.
After qualification, you will be required to make your next five solo flights supervised by an experienced turbine pilot. This is a great way to develop friendships with fellow turbine modelers.
Jet models can be as straightforward, reliable, and enjoyable to fly as any other type of model, but they tend to be complex and fast and are unforgiving of mistakes. The turbine waiver process is in place to aid and educate you while developing new friends with similar interests in modeling and sharing experiences and information.
Now, let's get out and enjoy some turbine flying.
Sources
- AMA Turbine Waiver documents
www.modelaircraft.org/documents.aspx#Turbines
- Jet Pilot's Organization
Transcribed from original scans by AI. Minor OCR errors may remain.
