Performance Mods: Caveat Emptor

When a reader who recently bought a Piper Comanche 250 hit me up for ideas on how to make it go faster (a lot faster, unrealistically) I got to thinking about going down the rabbit hole of performance mods. I’ve seen plenty of success and failures. Some failed miserably enough to sell the airplane for a loss and simply buy one that went faster as stock—often the better idea from the start. I know one guy who went through three piston singles and one twin until he found the one that worked for him: A Cessna P210, which created a different set of woes, but he sure did increase his mission capability and test his tolerance for swapping cylinders. Life in the fast lane.

There’s no questioning that some performance mods are well worth the install effort and money, and these are the ones that are well proven. Vortex generators immediately come to mind, and in the case of lowering stall speeds and adding a safety net with slower touchdown speeds, I can’t think of many piston singles and twins that can’t benefit. If the mission includes going in and out of tight places, VGs increase slow-speed control and generally don’t knock anything off cruise speed. 

For some airframes, speedbrakes and spoilers make a world of difference for going down while slowing down without doing abusive things to the engine. But there might be limitations worth researching before pulling the trigger. Consider the STC for the PowerPac Spoilers allows for spoiler deployment and retraction in icing conditions, while Precise Flight’s speedbrakes might not be approved for use in visible ice. For the owner (often ones new to an airplane model) buying into speed mods in hopes of turning a mediocre performer at best into a speedster, it’s risky. It’s safe to say that there really is no guarantee that any performance mod will pay for itself in fuel savings or other gains over its useful life just because the FAA signed off on the STC. It’s more than that.

It’s Also About Support

No matter the claimed benefit of any mod, look beyond the STC and into your crystal ball. Before you do, have a look at the requirements for regular inspections and parts replacement. The good news is it shouldn’t be so difficult to figure out since newer STC’d mods will generally have approved ICA or Instructions for Continued Airworthiness. Lobby the help of a mechanic if you aren’t sure about what you’re reading in the ICA. Perhaps most important, consider how complex (expensive) it will be to put the plane back into its original configuration if support became an issue, whether it’s parts availability, a manufacturer going away, an FAA AD, or all of the above.

I was reminded of this frustration when I recently visited with the savvy owner of an AOG Cirrus that had a Forced Aeromotive supercharger-modded Continental engine. What a site to see this powerplant torn open as his mechanic worked to turn it back to normal aspiration after the frustrations getting critical replacement components because of a major manufacturing issue. Support aside, I’d flown with the mod for other reports and generally found it to be a decent performer. 

Healthy Dose of Realism

Face it, you’re not going to get 180 knots out of a Cherokee 180 and you aren’t going to throttle a Duke out of 1,000 feet. But if tacking on a few knots of speed is your plan, it’s almost always safe to stick with maintenance-free STC mods like gap seals, gear door mods, and non-structural fairings. Still, while nothing is a sure thing, sticking with suppliers who have been around a long time usually curtails the risk because for one thing, the modified fleet size will usually be large. I can’t come close to naming them all, but some respected names come to mind including Wisconsin-based Knots2U. What stands out is the late company founder Jim Bradshaw getting 20 more knots out of the Piper Twin Comanche. Bradshaw ultimately brought the mods to other models and acquired Met-Co Aire and the Hoerner wingtips—a huge success because they reduce the strength of wingtip vortices generated by high-pressure air under the wing moving outboard over the wingtip. They work so well some OEMs built them into their designs. 

Gear strut fairings (proven by Cirrus on the SR and from other makers on fixed-gear speedsters) can add nearly 3 to 5 knots to plain-vanilla Cherokees and Cessna singles, to name a couple. Better yet is that while the installation effort isn’t trivial, it isn’t exactly complicated. LoPresti Aviation (now Whelen Aerospace Technologies) has long been a household name in performance mods. The Whelan buy was one of those situations where sometimes a second company steps in and takes over the STCs because it was just too good not to keep the products going. The list of worthy performance mods at Whelan is long—everything from aero-efficient cowling kits, gap seals, fairings, and wheel covers.  

Buying a used airplane loaded up with aftermarket mods? There are plenty out there priced at a premium, but be extra careful during the prebuy evaluation and make sure all of it is properly documented in the aircraft logs and the appropriate flight manual supplements exist. I know buyers who got stuck with unairworthy aircraft because they were light on paperwork and didn’t do enough surveying of the records before making the deal.

Marketing Hype

When it comes to the STC (we wouldn’t buy any major modification that doesn’t have an STC that applies to the exact model and serial number aircraft) the FAA doesn’t really care if you see 1 or 100 knots of speed gain. It cares about the aircraft’s overall level of safety—and that means structural integrity and that modifying the airplane with the product doesn’t negatively affect stability and control. In reality, the daunting STC approval process does not require any demonstration or verification of new performance numbers, except maybe as it relates to safety margins. And you might notice that lots of mod suppliers advertise cruise speed gains in miles per hour rather than knots because, well, the numbers look bigger. Moreover, while it might be obvious to some, understand that it’s not about additive gains. Just because one mod is advertised to boost cruise speed by 8 knots, tacking another one on that’s advertised at 4 knots won’t give you 12 more knots.

Last, think in terms of simplicity before spending a boatload of dough on pricey speed mods. Start with a well-maintained airplane and that includes the proper rigging of flight controls, landing gear doors, and other areas that induce drag. Make certain that the instruments aren’t fooling you, either, and that includes gross errors in mechanical airspeed indicators, tachometers, and manifold pressure gauges. And when I look at all the stuff we carry around in our airplanes (plus upgraded interiors) it’s no wonder we always want more speed. Travel as lightly loaded as possible, while keeping the CG further back. If you have a need for a lot more speed, choose expensive speed mods carefully or face reality and simply get a faster, more efficient airplane.