[Courtesy of Larry Brannan, lbrannan "at" yahoo.com, April 1999]
Notes on Bob Violett presentation April 9, 1999 at Toledo Show
There were about fifty modelers in attendance to hear Bob Violett's presentation on "Turbine Safety". Bob brought into the room his RAFALE twin RAM 750F turbine model that kind of majestically sat there on a table in front of the group. Bob used the wing to rest his note cards on. It's hard not to be impressed when you have this twosome in front of you.
He started his presentation by stating that the "advent of the turbine engine is the biggest single change in the last forty years of modeling". He pointed out that it took over 15 years to develop the piston engines and ducted fans to potential - yet turbines have jumped to 35lbs of thrust in two years. People had time to adjust as piston-driven engines and fans were refined. He feels people have not had time to adjust to the rapidly changing world of turbines. He is very concerned about the coming summer of jet meets where many new turbine jet flyers will be taking to the air, your author included.
Since the topic was turbine safety, Bob pointed out that a turbine carries three times as much fuel on board as does the ducted fan model. A crash for any reason gives the potential for fire since the fuel can be splattered out by the impact of the crash and a hot turbine passes through it and you instantly have a fire. The recent fire at Florida Jets was cited. He pointed out a very real concern that a single state politician could capitalize on the fire issue and propose a ban on turbines, especially in a dry state like Florida or California. A fire wagon or backpack sprayer should be on-site at every jet event where turbines are flown. This hit home to me since I am the CD of a Michigan jet event planned for the summer of 1999 (Jets Over Plainwell).
Bob also mentioned that every full-scale turbine manufacturer has had a blade come off at some time. He includes the kevlar safety band as a no option item when you buy his turbine installation kit. He mentioned that the kevlar band weighs only 2 oz. I learned that the kevlar is soft in the middle without resin so as to permit penetration of the blade without letting it through. He cited RAM standards where one of every ten turbine blades manufactured is destroyed to test the strength characteristics of the batch.
Nose gear steering is a key component in overall turbine safety. Bob cited in the past that if you lost control, it wasn't a big deal, but with 3x the fuel on board; a gyro for rudder/nosegear steering can correct thousands of times a second and should be considered. He wrapped up this section by commenting that the AMA rule of .5-. 9 thrust to weight ratio should not be violated. He offered food for thought in challenging us to consider what to do with the jet pilot who comes to an event with a turbine and fly's in an unsafe manner. He offered a potential solution that we may want to consider pulling the turbine waiver for such behavior just like losing your driving license if you drive reckless. Who's to turn in the violator? Other pilots? The CD? Bob did not offer specific recommendations; he only was trying to get us to think of what would we do? He feels and I agree that the person who owns and fly's the airplane is the one who is responsible.
He also spoke of the need to have knowledge of the difference between groundspeed and airspeed. He gave a good example using a crosswind landing pattern example showing how your actual airspeed may be much less due to wind coming aft over the model on the base leg. He mentioned that a lot of fliers think they "lost the radio" on the base leg when they actually have lost air speed due to wind coming aft. In such a crash, the ground speed still looks good, but the wind over the wing is diminished due to the crosswind condition. I had never really understood this before and it made my hour with Bob worthwhile. He ended this section with a statement that a power-on approach is the way we fly jets. He feels you have to have flaps and have to have an air brake.
Bob offered his peek into the future with a prediction that someone would invent a pitot sensor that will sense airspeed and then throttle back the engine if the Vne (Velocity to never exceed) is approaching. You would dial in your maximum airspeed and let technology do it's work. He mentioned that he had published the Vne for each of his jets in the latest issue of Inlet magazine. The Bandit for example is 260mph and all others are less. Bob also predicted someone will come up with a Halon on-board fire extinguisher system that will be activated by a severe overtemp condition or a high G impact.
Another thing I learned concerned slow flight characteristics. He mentioned that this is more demanding than flying fast. His suggestion was to practice your slow flight techniques thoroughly prior to attending a jet meet.
Kevlar tanks were also on the agenda as kevlar is very tear resistant. Bob stated that a pinhole leak of any kind in the header tank would cause you to pump air and cause your turbine to quit. Yet temperature decreases very quickly for a turbine that has "flamed out" due to ambient airflow around the turbine.
Finally Bob pointed out some final rules for turbines NEVER put your finger near the front of a running turbine to see if there is suction because you will not be able to stop your finger from going into it. This has happened twice on bench runs of turbines, something Bob does not recommend. He also said if you ever hear or feel any vibration in your turbine, shut it down and send it back to the manufacturer.
This was an hour well spent. The session was videotaped and I hope that the Toledo club will make the tape available. There was a lifetime of jet experiences and common sense suggestions that needs to be shared among all R/C jet pilots.
Let's all help to get the safety message out this summer to all jet pilots!!