Unicom

August 2005 Issue




Unicom: 08/05

Turbines, Plus Cirrus
I disagree with many of the points in “Are Turbines Safer?” (June 2005). To start, the argument that turbines are prohibitively expensive to fabricate is no longer true. Widely available and relatively inexpensive CNC machining equipment is easily capable of the necessary precision. When/if small (200-300 hp) turbines are built in the same numbers as piston engines, the manufacturing costs will end up being very similar (greater precision, but fewer parts).

The author says replacing piston engines with turbines wouldn’t help safety. The assertion is that a higher-performance engine will cause people to be in more accidents (weather, loss of control). As advocates for aviation safety, it seems it would be better to argue for adequate training rather than argue that we should all fly less-powerful aircraft to keep us safe. The less-power-is-better position would be right at home arguing against the transition from steam engines to internal combustion. It’s also worth pondering how many accidents would be avoided in turbine (lighter, more powerful) aircraft that take off shorter, climb faster, stall slower and recover quicker.

The author presupposes that fuel exhaustion would be more common because turbines use fuel more quickly. Again, in the interest of aviation safety, I’d recommend we pilots take a glance at our fuel gauges every once in a while whether we’re flying a piston or a turbine. Fuel management is no more complicated in a turbine—look at your fuel gauge to see how much you have, look at your fuel flow to see how fast you’re using it, and land before either gauge gets too close to zero. Pilot buffoonery (running out of gas for example) is not a rationale for one engine over another—it’s a rationale for training pilots to not be buffoons.

The author also uses a statement from Robinson Helicopter Company to argue that turbines aren’t more reliable. They wouldn’t appear to be an objective source of data since they only sell piston-powered helicopters.

Finally, if turbines aren’t more reliable, then why would the military uniformly use turbine engines for aircraft regardless of the altitude or speed required?

The article explores a worthwhile topic, but I believe unjustifiably maligns turbines. We shouldn’t miss the opportunity to encourage in GA a technology that has enabled such a dramatic increase in safety in every other category of aviation.

Randy Trosper
Via e-mail

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Turbine Economics...
While the premise of the article “Are Turbines Safer?” is that engine failures rarely account for fatal accidents, and that reducing perceived risk may lead to more accidents may be correct, the author’s comparison to the hourly maintenance costs of an airliner jet engine are not borne out. These new-design, small turbine engines are vastly simpler and cheaper than what has come before.

A look a the Innodyn Turbine’s Web site shows their 165-255 hp engines with retail prices of $26,500 to $34,500. At an estimated seven gallons per 100 hp per hour, the cost of fuel may be twice as high as for a piston engine. However, with a TBO for the 255 hp engine estimated at 5000 hours, and a factory assertion that the rebuild will cost less than one-third the engine’s price, the rebuild comes in a little under $11,500, or $2.29/hr, far from the $100 per hour asserted by the author. That is actually quite a bit lower than the hourly rebuilding cost of a comparable reciprocating engine. Even if a certified version of this engine cost twice as much as the experimental version, the economics of these small, relatively simple turbines appear to be quite favorable. I have no connection with any engine manufacturer, by the way.

Dan Sternglass
Via e-mail

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...And Reliability
Mr. Travis’ article “Are Turbines Safer?” is disappointing as it never fulfills the implied promise of the title. While the article provides a very basic description of how turbine and piston engines work, it skirts around the issue of reliability. The argument that turbines would not be safer because they are associated with higher performance aircraft could be applied to any of several comparisons, e.g., by Mr. Travis’ logic, Cessna 210 engines are less “safe” than Cessna 152 engines, or Piper Tomahawk engines are more safe than Piper Arrow engines. Really?

The only discussion of actual reliability is a short recitation of Robinson Helicopter’s claim that their reciprocating engines have fewer failures than the competition’s turbine engines. Perhaps, but if so, is that a valid comparison? Given the very large number of turbine engines in operation in many different configurations, certainly statistics on engine failure must be available. Too bad the article didn’t bother to bring those to bear on the issue implied by the title.

I recollect one pilot, transitioning to jets, whose comment at the time (some 40 years ago) was that jet engines are so much simpler in operation—they either work or they don’t; none of that in-between stuff. If still true today, that could be an interesting discussion on its own. If the engine never fails once it starts, then having an all-or-nothing power plant may be great. If it does fail in flight, would a pilot prefer something that coughs and wheezes but puts out some modicum of power for a period of time, or something which has suddenly become the proverbial brick in the sky?

I’m not turbine-qualified, but I recall various turbine failure modes involved in accidents, anything from disintegration of the turbine to flame outs and compressor stalls. A comparison of the incidence (or probability) of such events compared to failure modes in reciprocating engines would have been helpful. While the article did point out the much higher cost of purchasing and operating a turbine, its bottom line seems to be that higher performance and thus higher expectations (e.g., IFR flight, night flight, cross-country flight, over-water flight) diminish safety and thus turbines will not be used because they decrease safety indirectly. That is the reason the airlines avoid turbines, right?

R. T. Wojciechowski
Via e-mail

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“The Problem With Cirrus”
The problem with Cirrus is clear to me. What Cirrus did “wrong” was to do an excellent job of creating an aircraft attractive to a huge amount of people. When I considered upgrading aircraft, I discussed each possibility with my wife. “Buy the one with the parachute,” she said. Cirrus SR20s and later SR22s were the subject of many extremely enthusiastic cover stories in all of the magazines in this country and most foreign publications as well. The drumbeat was clear: This plane was a great example of brand-new technology done almost exactly right.

When I ordered an SR20, I was a 150-hr pilot. I stayed current with all the news updates and later changed my SR20 order to an SR22. As delivery approached, I signed up for the training program offered by Cirrus/UND. After delivery I was going to fly it to Wisconsin for custom graphics, then home to the East Coast.

There are a lot of us low-time pilots with the money to consider the Cirrus. I hope that personally I would have chosen to “grow into” the plane (I am Instrument-rated now, but won’t yet venture out into IMC until I do some clag time with an instructor).

My guess is that buyers of new Cessnas, Beeches and Mooneys have been around the block a few more times and therefore may have more inherent judgment about just how much a plane can be expected to do. As time goes by and the training and expectations for these planes reach the right levels, the SR20 and -22 will live up to all the accolades while eventually achieving a safety record more consistent with their originally high expectations.

Eric Hall
Via e-mail