Columnist Mark R. Twombly is the co-owner of a Piper Twin Comanche.
I was brought up believing there are three airspeeds you could use to answer the question, "How fast is that airplane?" The first is indicated airspeed; the second is calibrated airspeed; and the third, which usually provides the best answer because it's the highest of the three, is true airspeed. You could use a fourth, groundspeed, but groundspeed is at the mercy of the winds. Besides, cars and trucks use groundspeed. Airplanes use airspeed.
Now I discover there is another speed — one that isn't in the official aviation lexicon, but one that many pilots seem to use in their conversations and calculations. Like indicated airspeed, it goes by the initials IAS, except that the I stands for inflationary. You calculate inflationary airspeed by taking historical true airspeed and correcting for the expense of adding performance modifications.
Here's an example: Harry's aging, dowdy Mooney trued out at a shade over 145 knots before he bought and had installed numerous aerodynamic mods. Following the five-figure-plus makeover, Harry's Mooney now routinely achieves an inflationary speed of 160 knots, according to his expense calculations.
Time was when the airplane manufacturer was the guilty party in terms of overstating performance figures. Today it's the owner who is more apt to practice hyperbole; specifically, the owner who has purchased and had installed expensive go-fast modifications. And why not? If you've just dropped a bundle on a bunch of mods, you'll convince yourself the airplane is faster whether it actually is or not.
When I owned a Cessna 172 I was only peripherally aware of the extent to which airplane owners inflate cruise speeds. A 172 pilot can't fool anyone with high-speed braggadocio. It's a great all-around airplane that does a remarkable job of doing a lot of things very well. Going fast isn't one of them. Cessna tried retracting the wheels — with the 172RG — and others offer 180-hp engine upgrades, but even these major mods have only marginal effect on cruise speeds. So, 172 owners concentrate more on utilitarian and cosmetic upgrades than performance enhancements.
After I sold my 172, I entered a partnership in a Piper Twin Comanche. I soon discovered a basic truth about the PA-30 that applies equally to any performance-oriented airplane. Stock performance is pretty good, but it doesn't take long for performance-enhancing thoughts to start creeping into the subconscious. Performance truly is an addiction: Once enjoyed, you've just got to have more.
As with any human craving, the desire for more performance generates commerce. The aftermarket modifications industry has prospered as pilots have sought to eke more performance from GA aircraft of every vintage. Higher-horsepower engines, radical props, raked and one-piece windshields, lower-drag cowls, fillets, fairings, and seals — the list of hot-rod mods is creative, extensive, and growing.
The popularity of performance modifications has spawned a spirited debate about the cost-benefit ratio of such mods. The debaters fall into two camps: those who have — modified, that is — and those who haven't. One side talks up the performance benefits, while the other tends to dwell on the cost side of the equation, which can be considerable.
My partner and I are among the haves. Our airplane has a one-piece windshield, wing-root leading- and trailing-edge fillets, flap-gap seals, fairings behind the retracted main wheels (which protrude slightly from the wheel wells), and sexy new lower-drag nose cowls that feature smaller cooling air inlets. We haven't yet gone the extra mile to buy and install fairings over the flap hinges, add an extended dorsal fin where we could hide antennas, or switch the brake assembly from the outside of each main wheel to the inside so they retract out of the slipstream. For now we're content with what we've done. We also need to nurse the airplane bank account back to good health.
All of our check writing has not yielded the performance others say they now enjoy — cruise speeds approaching three nautical miles a minute on fuel flows that redefine the stoichiometric laws governing acceptable fuel-air ratios. Sure, we picked up a few knots of true airspeed, but nothing like what others say we should be seeing. We have more work to do on our airplane to allow the mods to perform to their full potential. For example, the paint surface is chalky and rough, some fiberglass parts are chipped and peeling, and the airplane is slightly out of trim; it needs to be rerigged.
We could be accused of putting the cart before the horse by installing mods before the rest of the airframe is brought up to standards, but we had our reasons. The most extensive and expensive modification — replacing the standard nose cowls on each engine with new LoPresti Wow! cowls — was undertaken because the stock cowls were worn out from 34 years of removing and reinstalling them every time the oil was changed or the engines examined. We had to have new cowls; why not go for something new and different that might just bump performance up a notch?
Modifications add to the overall enjoyment of ownership. We think our airplane is closer to state of the art than before the first mod was installed, and that affects its value to us and in the market. The mods also add to the airplane's ramp appeal — we're frequently asked about the neat cowls — and that's always fun. Oh, by the way, did I mention what we're seeing now for IAS?
