The pilots sacred trinity: Higher, faster, farther. Not to be vulgar, but to that precious list, its our duty to add one more item: More money. Lots of it.
In single-engine airplanes, think of the money-to-speed ratio as a predictably gentle curve out to about 160 knots. Beyond that, it rockets upward steeply such that every additional knot costs at least a grand or two. (The general rule of thumb that speed mods deliver 1 knot per $1000 spent is remarkably reliable.)
While speed mods trickle on added knots by nibbling away at drag, the big gains come from turbocharging, which allows an engine to deliver rated power up into the thin air, where true airspeeds inch upward.
Every major manufacturer has offered turbocharged models of some sort, occasionally across most of the product line. In parallel, aftermarketers have offered retrofit turbo systems to a handful of engines, a business that seems to run according to its own unpredictable cycle.
With the recent introduction of a new turbonormalizer for the popular Mooney M-20 series and the re-invigoration of the system formerly marketed by FliteCraft for Bonanzas and recently taken over by the group producing GAMIjector balanced fuel nozzles, the cycle is back on the upswing. The former FliteCraft system is now being pitched as the Whirlwind Bonanza under a new company name, Tornado Alley Turbo, Inc.
First, a clarification of terms: Turbocharging has traditionally been done in one of two ways: ground boosting or turbonormalizing, which is sometimes called altitude turbocharging.
As the term implies, ground boost turbocharging is capable of driving manifold pressures above 30 inches of mercury at sea level, often to values well above 40 inches. Ground boost systems have generally remained the province of the engine and airframe manufacturers, since adding ground boosting after the fact opens up a tangle of certification issues related to an engines maximum certified power.
Traditionally, most ground-boosted engines have been designed for that purpose from the outset, with low-compression pistons, more durable valves and guides, beefier crankshafts and additional lubrication for cooling.
Turbonormalizing systems, on the other hand, limit boost to 30 inches or so, virtually the same value a normally aspirated engine can manage at sea level. But boost is regulated to maintain the engines MP at 29 to 30 inches all the way to a defined or critical altitude, above which power declines below 100 percent, just as in a normally aspirated engine.
The beauty of turbonormalizing is that it can deliver high altitude and performance on about the same fuel as the equivalent non-turbocharged engine would burn. Thus the fuel specifics are better than the typical ground-boost system can claim.
Further, with lower peak cylinder pressures and potentially lower temperatures, turbonormalized engines are theoretically less prone to high cylinder, valve and guide wear that plague some turbocharged engines. Loss of cooling efficiency at high altitude is still a concern, but intercoolers address that issue. (And so does aggressive leaning.)
Engine and airframe makers have generally stuck to ground boost systems (although not universally) and some of these have earned good service histories. Still, others have driven their owners screaming into the night with high maintenance bills and downtime. An owner can reasonably expect slightly higher operating costs with turbocharged engines, but most are put off by top overhauls at 500 hours and a mid-run turbocharger overhaul.
Does turbonormalizing avoid all that? No guarantees, but its logical that limiting boost exacts less wear and tear and heat-related stress on an engine, especially with intercooling, which both of these systems have. Whether that impacts reaching TBO is an open question.
A Faster Mooney
Mooneys popular M-20 line-the C, E, F and J-models, specifically-have a reputation for speed and efficiency. But the truth is, with cruise speeds in the 140 to 160-knot range, theyre more economical than blistering fast. Mooneys answer was to re-engine the M-20 long-body with a Continental TSIO-360-GB, yielding the 231, a ground-boost design with a fixed wastegate. At high altitude, the 231 was fast enough but it earned a checkered service history, leaving thousands of Lycoming-powered M-20s ripe for an aftermarket turbo system.
When Bill Sandman, a retired industrialist and principle in M-20 Turbos, set out to turbonorm alize his own 201 a couple of years ago, he initially intended it only for his own and his partners use. However, Sandman told us his project generated so much interest that he formed M-20 Turbos and pursued the STC, which was awarded last summer.
The M-20 system, which sells for $23,389 for the kit plus another $2500 to $3500 for installation, is about as simple as turbocharging gets. It uses a Rayjay/Consolidated turbo with a fixed wastegate but no turbo controller. Boost is fixed at 30 inches, controlled entirely by a pressure relieve or pop-off valve on the outlet side of the turbocharger. (Lycoming developed a similar design for the Seminole and Comanche.) The designs chief advantage is simplicity; there are fewer parts to install and maintain and, especially, no turbo controller to fuss with.
On the other hand, the system depends entirely on a single mechanical valve to regulate and prevent overboosting and at low altitude, the fixed wastegate can constipate exhaust flow, sapping performance.
Heat is a problem, too, since the turbocharger is whirring away pumping up the manifold pressure and increasing the induction inlet temperature and, theoretically at least, reducing the engines detonation margins, especially if it has high-compression pistons, which the IO-360 does. The M-20 Turbo kit addresses this problem with intercooling, essentially a radiator that cools the turbochargers compressed air before its pumped into the induction system. Over the years, weve heard tall claims of dramatic power and speed increases attributed to aftermarket intercoolers but the undeniable best reason for having them is to reduce operating temperatures and prolong engine life.
The Mooney M-20 Turbo kit is all-inclusive, providing the turbo and all related hardware, a new exhaust system, intercooler and induction airbox, plus new oil lines for the turbocharger plumbing. The fuel system retains the Bendix/RSA servo, but the kit includes an altitude-compensating fuel pump and injectors with upper deck air reference fittings.
The 201 cowling is hardly expansive but the turbo and intercooler fit comfortably without introducing any maintenance access nightmares. The turbo is attached not to the engine but to the motor mounts, which should reduce vibration-related cracking in the mount hardware.
Bruce Jaeger of Willmar Air Service, a respected Mooney shop, inspected and flew one of M-20 Turbos initial conversions and found only one beef: The stock exhaust system muffler is removed and with it goes the airplanes generous heat muff. The new muff delivers insufficient warm air, making for a chilly cabin. Sandman told us hes aware of the problem and is working on fixes, which might include a supplemental electric heater of some sort.
The M-20 Turbo mod subjects the cowling to major surgery: To improve cooling-what Sandman calls after cooling-the lower cowling gets a fixed center cowl flap and cheek louvers to improve air flow. The left cowl flap is also trimmed in length for the same reason.
Last, for intercooler inlet air, a new opening is cut on the left side of the cowling, opposite the landing light. The stock ram air door goes away and the control cable is converted to set an adjustable oil cooler shutter. If you own a pre-201 Mooney, by the way, youll have to convert to a 201-style cowling, which will add significantly to the bottom line.
Cool in the Climb
All that attention to cooling evidently paid off, at least in the climb. For takeoff and climb through the low altitudes, the turbonormalized M-20 behaves like the stock airplane. On a warmish Florida day during peak performance, low speed climbs, we noted that the CHTs remained in the 350- to 380-degree range, noticeably warmer than our stock 201 but hardly cause for concern. Above 3000 feet, where the full-power MP would normally have started its decline, the turbonormalized engine continues to deliver full power so the speed increases and climb rate remains at a brisk 700 to 1000 FPM.
We leveled at various altitudes and let the airplane gather itself to cruise speed. At 12,500 feet, we recorded 170 knots TAS at 11.5 gallons per hour, leaned to 100 degrees F rich-of-peak, as per Lycoming best power recommendations. (Not that we necessarily agree with that.)
Continuing the climb, we leveled at 16,500 feet and noted a TAS of 177 knots, also at 11.5 gallons with the same leaning. Ron Saeger, a North Dakota J-model owner who bought one of M-20 Turbos first conversions, told us he has seen airspeeds of 186 knots at 10.1 gallons at 21,000 feet; an impressive number if youre willing to suck oxygen to go that fast.
Sandman says M-20 Turbo recommendsLycomings best economy leaning advice, which is 25 degrees rich of peak. We experimented only briefly with lean-of-peak TIT operation and this engine seems to do it without complaint. Saeger told us he found that the engine operated smoothly as lean as 30 degrees lean of peak TIT. Frankly, we think with some tweaking of the fuel/air ratios, this engine can and should be operated in that regime.
That would solve one minor problem we noted: In the thinner air at 16,500 feet, we noted the number 3 CHT at just over 400 degrees F. Although Lycoming sets the redline at 475 degrees (500 degrees on some engines), anything over 400 degrees is cause for concern, in our view, based on General Aviation Modifications research that shows cylinder out of roundness and piston scuffing occurs at CHTs above 400 degrees, especially if the cylinder is unevenly cooled. We would like to see it 20 degrees cooler, at least.
The most expedient way of doing this is lean-of-peak operation, as Tornado Alley recommends for its Whirlwind Bonanza conversion. Failing that, perhaps some work on the baffling might suffice.
As it is now, 185-plus knots on 10 gallons per hour puts this conversion into a league of its own as far as raw efficiency. The Mooney 231 will do that kind of speed but on two to three gallons more fuel and at the expense of poorer climb and low-altitude performance.
In the low oxygen altitudes, say 16,500 feet, the M-20 conversions additional speed extends the stock airplanes range by a solid 10 percent at 65 percent power; more if youre willing to throttle back.
The M-20 Turbo system adds 23 pounds to the stock Mooney airframe, a modest hit in our view. Theres little or no impact on center of gravity. The system has a pass-through warranty based on coverage provided by the manufacturers of each individual component.
Extended range and efficiency-plus speed, of course-is undeniably the selling point of Tornado Alleys Whirlwind Bonanza. A little history here: This is the very same Bonanza conversion formerly marketed by FliteCraft of Pagosa Springs, Colorado, a company well respected for solid engineering and good customer service.
Last year, General Aviation Modifications, Inc. (of GAMIjector fame) formed Tornado Alley Turbo and bought the FliteCraft STCs. Theyre now marketing the system as the Tornado Alley Whirlwind Bonanza, a twist of marketing hype that actually has a discernible philosophy.
Tornado Alleys George Braly told us that turbocharging in general and specifically the sort of aftermarket systems sold by FliteCraft and others have traditionally been pitched toward pilots flying in mountainous areas.
Braly says the Whirlwind package certainly applies to mountain flying but its also aimed as a speed enhancer for flat land pilots lusting for 180-knot or higher speeds, with the added attraction of not having to climb into the oxygen altitudes to go that fast.
Heres the idea: In a TCM IO-520 equipped Bonanza, a Tornado Alley turbonormalizer delivers 30 inches of manifold pressure to its critical altitude of 20,000 feet. For a Bonanza that means it will true in the mid-180s on just less than 15 gallons per hour, if leaned aggressively.
Thats about 14 to 16 knots faster than the normally aspirated version will fly at its best altitude, normally between 7000 and 8000 feet. Since the fuel flows are the same, the turbonormalizing effectively extends the Bonanzas range by 10 to as much as 20 percent.
Climbing into the high teens and low 20s will yield yet higher airspeeds, again at the same fuel flows. Weve flown the GAMI/TAT turbonormalized IO-550 Bonanza on several occasions and noted true airspeeds just shy of 200-knots at 20,000, aggressively leaned and burning 13 to 14 gallons per hour. At higher altitudes and fuel flows, it will true in the 210-knot range.
Aggressive leaning, according to Braly and company translates to lean-of-peak TIT operation at any power settings up to 75 percent. To achieve that, Tornado Alley equips all of its conversions with turboGAMIjectors, improved fuel injection nozzles that balance the poor fuel/air ratios in most TCM engines.
The TAT System
Tornado Alley bought the FliteCraft system lock, stock and turbo controller and other than some tweaking of the upper deck cooling and the turboGAMIjectors, the system remains unchanged. Cost: $34,500 installed, plus minor additional charges for air conditioned models and relocation of components on some airframes. (For now, installations are done only at TATs Ada, Oklahoma shop.)
The Tornado Alley conversion applies to all IO-520/550 models found in Beechcraft 33, 35 and 36 series airframes. In addition, TAT took over the STC that FliteCraft developed for the Cessna 185.
Although its a turbonormalizer, the Tornado Alley system is a bit different than the M-20 Turbo design. It has a Garrett turbocharger, an automatic variable waste gate and an absolute pressure controller. In addition to those components, the kit also includes a new exhaust system with greater wall thickness, a Teflon hose package, an altitude-compensating fuel pump and an intercooler which lives below the right side cylinder bank.
Having been through several iterations, the TAT install is one of the most organized weve seen, with easy access to both the turbo and the intercooler and related hardware. Cosmetically, its nicely gussied up with enameled piping to and from the turbocharger and eye-catching silicon rubber baffling gaskets to replace the factory stuff, which becomes an eyesore after a few years of service.
The TAT system adds 67 pounds to the airframe and although that reduces payload a bit, it all but eliminates the aft-tending CG problem that 33 and 35-series Bonanzas suffer. TATs warranty is a generous two years and 250 hours on the turbo components and four years/1000 hours on exhaust and induction air components. TAT says it will continue to support FliteCraft systems still in the field, of which there are some 250.
What to Do?
In our view, both of these conversions are well-engineered and well supported and we dont see any significant red flags against either, including M-20 Turbos anemic heater. Both appear to be as good as if not better than factory turbo set-ups. The Tornado Alley system was well-proven in the FliteCraft iteration and amassed a good service history and happy customers. If anything, TAT has improved it.
The M-20 Turbo system is a relative newcomer with little service history in the field. Although Sandman reports that the company plans to continue improving it, he was also upfront with us about his future plans: The M-20 Turbo partners never intended to make a full-blown business of their project and will eventually sell the STC to another company. Sandman says he doesnt know when that sale will occur but we think a buyer ought to be aware of it.
In lumping these two systems together, were not implying a side-by-side choice where none exists. If you have a Bonanza, the choice is Tornado Alley; if a Mooney, M-20 Turbo is it. If you have neither and want to buy a step-up airframe and then convert it, some careful shopping is in order.
Lets talk money and whether you want any of it back after investing in a high-dollar mod. Figure on recovering half to two-thirds the cost of a major mod at resale. If youre in toys-for-boys mode, dont give this a second thought. Pay the money, fly high, be happy.
Otherwise, shop some. Given the nature of the airframe and costs involved, we think the M-20 Turbos system is best applied to the J-model. If you own one, adding this conversion will cost about $27,000, bringing the total investment in a clean 201 to some $112,000, about 25 percent above market value for an unmodified airplane.
Before springing for the conversion, its worth considering what else $112,000 will buy in high-flying turbocharged performance in a single. There are other picks: An early 1980s 231, Cessna T210 or turbo 182 are possibilities. These may seem out-of-class comparisons but if you dont care about seats, speed is speed.
All airplanes have warts, of course: The 231 is a poor low-altitude performer and, compared to the turbonormalized 201, all the other picks are gas hogs. Further, our bet is that even a turbonormalized IO-360 will require less engine maintenance than the TSIO-520 in a Cessna 210. On fuel economy alone the M-20 conversion shines. Our view is add up the numbers and make your choice.
The same considerations apply to the Tornado Alley conversion, although theres more price variability in the used Bonanza market due to the range of models and large numbers of airframes. Figuring a mid-$70,000 to $90,000 as an S- to V-35 starting place, youll still have $105,000 to $125,000 invested. The same shop-around advice applies, but expand the list to include an early A36TC, if you can tickle a little more money out of the bank.
Buying an airplane already equipped with what you want-including a turbocharger-will usually yield the better deal valuewise and the airframe will doubtless continue to appreciate. The same cant be said of a high-dollar mod.
But you have a nice V-tail or Mooney 201 that you plan to keep for awhile, these two mods will indeed make it go higher, faster and farther and at a fair buck.
Also With This Article
Click here to view the Turbo Retrofit Checklists.
Click here to view the Turbo Performance Comparisons.
Click here to view “Demon Detonation: Missing in Action.”
Click here to view Turbo Retrofit Addresses.
-by Paul Bertorelli