One of the few Cessnas with a geared engine, the 175 may have been ahead of its time – or maybe not.
I almost expected the gauge to jump out of the panel and land in my lap. Too many years of watching tachometers redlined at 2500 to 2800 rpm had conditioned me to assume any higher indication was obviously the work of the devil or a runaway prop. The last time I’d seen 3200 rpm was on a Twin Comanche I was flying in tight photo formation when the right prop governor ran away.
In this case, I was flying a fully restored Cessna 175 out of Jackson, California, and there was no cause for concern. The engine was running normally, and the noise level was no higher than I might have expected from a garden-variety Skyhawk.
The engine out front was a Continental GO-300C, and the G stood for Geared. Yes, it was turning 3200 rpm, but the gearing reduced the revs to a more sedate 2400 propeller rpm with a .75 reduction gear. Owners of older 172s may recognize the engine designation as similar to that used on the original 145-hp Skyhawk. Adding the gearing mechanism allowed the same engine to develop 175 hp.
Still, 3200 rpm seemed all wrong from a pilot’s perspective. Owner Jack Purdue smiled from the right seat and noted that there’s always a difference between the reaction of pilots and non-pilots in evaluating the indicated rpm. “Pilots are sometimes uncomfortable or even downright concerned about the high rev count. Non-pilots don’t mind it a bit, as they’ve been looking at rpm limits in their cars for years that far exceed that figure, often by double or more.”
The Skylark was Cessna’s attempt to inject more speed and performance into a basically stock Skyhawk without adding significant weight. Cessna reasoned that a geared engine was a logical method of increasing power and thrust that wouldn’t demand a third prop blade or turning the existing prop faster.
The math is inescapable. Turn a standard, 76-inch prop at 2800 rpm on an airplane at rest on the ramp, and the tip speed is a rapid 550 knots, or about Mach .83 (at sea level). Just as the engines on jet fighters must slow inlet air to well below the speed of sound in order to provide proper burning of fuel, propellers have progressively more difficulty dealing with air moving faster than about Mach .86. Even at slightly reduced Mach numbers, the tips are turning much too fast to generate any significant thrust, though the slower inboard sections of the blades closer to the hub are progressively more efficient.
Cessna produced Skylarks relatively unchanged through 1960 and delivered some 1800 units in the first three years of production. After that, it was all downhill. The geared engine gained a perhaps-undeserved reputation as problematical. TBO was only 1200 hours compared to 1800 hours on the non-geared version that powered the standard Skyhawk, and prospective Skylark buyers began to question whether the geared airplane offered enough performance improvement to justify the higher purchase price, increased fuel burn, and lower TBO.
In 1961, Cessna added a constant speed prop and cowl flaps to try to shore up sales, but demand was winding down to a precious few. Finally, in 1963, Cessna changed the name to the Powermatic in an attempt to disassociate it from the Skylark and save the model, but the damage had been done. The Wichita company built only a little over 100 of the geared airplanes that year. Cessna quietly retired the model altogether in 1963 after a total of 2119 geared Skyhawks had been produced.
Jack Purdue’s Skylark is a 1960 model 175A; built halfway through the airplane’s five-year production run and therefore blessed with the “modern” swept tail bestowed upon all Cessna singles that year, plus a more efficient streamlined cowling. Purdue’s Skylark was one of the last to fly behind the simple, fixed-pitch McCauley prop.
Parked on the ramp, it’s hard to tell the Skylark’s basic contour from that of an equivalent Skyhawk. One giveaway is the bump at top-center on the cowling. The reduction gearing is mounted on top of the engine and creates a pronounced hump in the cowl. The higher thrust line lets the Skylark use an 84-inch diameter McCauley prop in place of the 172’s 76-inch blades; yet, still preserves nearly the same 21-inch ground clearance.
Purdue has become something of a student of the type, with an impressive library of material on the airplane’s design and execution. “I’m convinced it was a better design than Cessna thought,” he says. “The airplane’s maintenance problems were primarily a result of pilots who simply refused to run the airplane by the book rather than any inherent mechanical flaw.
“The geared engine was intended to be run at 3200 rpm for takeoff and as high as 3000 revs for cruise,” Purdue comments. “The cruise setting is only equivalent to 2250 prop rpm, but pilots insisted on running it slower because of their own preconceptions. Naturally, performance suffered at the lower power and cooling was poor at the reduced speed, and that led to many of the mechanical problems. Cessna might have solved the problem by simply rerouting the tach to display prop rpm rather than engine rpm, but that might have caused certification questions.”
For pilots willing to fly the airplane by the book, the Skylark provided a few notable advantages over the standard Skyhawk. One common complaint against the 172 was that despite Cessna’s famous high-lift wing, the airplane’s climb was fairly anemic with a full load. The POH called for 660 fpm at sea level on the early 172s, but many pilots agree even that may have been a little optimistic. Cessna knew the ‘Hawk would rarely be called on to lift four folks, and 650 to 700 fpm was well within reach with only two up front.
In contrast, a healthy Skylark could manage more like 850 fpm, granting reasonable off and up performance with a 2+2 full house. Reduce the load to a more typical two pilots in the front seats, and you could record a consistent 900 fpm from sea level. Purdue reports he’s seen an occasional 1000 fpm from his airplane—all the more impressive since his airport is located 1700 feet up in the western foothills of the Sierra Nevada.
Cruise was also more generous in the Skylark. A typical 172 cruise number in those early days was about 113 knots under optimum conditions at 8,000 feet. Purdue’s airplane trued more like 122 knots between 6000 and 8000 feet with the power set for a maximum 3000 rpm (75 percent). That may not exactly be blistering the sky, but it’s not too shabby for a piston single with fixed gear, wing struts hanging in the wind and a fixed-pitch prop out front.
In keeping with the universal law of TINSTAAFL (There Is No Such Thing As A Free Lunch), fuel burn increased proportionally to the horsepower used and fuel capacity didn’t – two factors that conspired to limit range and endurance. The Skylark was fitted with the same 43-gallon tanks mounted on the Skyhawk, and at 10 gph, that meant you needed to look for a place to perch about every three hours to avoid burning into your fuel reserve. That’s not exactly outstanding endurance.
“Things aren’t really that bad,” says Purdue. “Actual capacity was 52 gallons, but usable was limited to 43 gallons, presumably because of the location of the fuel pickup – in the middle of the tank. This meant any major attitude change with fairly low fuel could result in unporting and possibly induce a power loss. If you flew the airplane within moderate pitch and roll limits, you could get four hours out of it and still have a reasonable reserve.”
Considering that weight is relatively unchanged and the fuselage and wing are identical to the ‘Hawks, it shouldn’t come as any big surprise that the Skylark flies very much like a 172. In flying Purdue’s airplane for several hours, I couldn’t tell any difference at all between its handling and that of a 1961 Skyhawk I’d flown a few days before. Performance obviously benefitted from the extra 30 hp, but the airplane handled and felt virtually identical in all modes of flight.
In contrast to what I might have expected, noise level actually seemed lower than that of a Skyhawk. That’s probably because the primary noisemaker, both inside and outside a typical general aviation aircraft, is the prop, and the Skylark’s reduction gearing reduced prop redline to a less frenetic, more neighborly 2400 rpm: That’s barely over .70 Mach at the tips—slow enough to minimize noise level for everyone.
Perhaps amazingly, I once saw a Skylark flying the bush country of Alaska for a Fairbanks charter company. The operator obviously had to be careful where he landed with the nosewheel, but he commented that 175s have such a low and predictable stall speed that the airplane allows a reasonably competent pilot to sneak into ridiculously short strips. The official number is less than 700 feet, but you can bet a competent bush pilot can subceed that number. No one will ever mistake a 175 for a legitimate, off-airport STOL-plane, but pilots willing to fly approaches at 1.1 Vso will probably find they can manage more like 500 feet from touchdown to full stop.
The problem is getting back off the ground. The Skylark’s manual suggests you can expect to use about 50 percent more horizontal space for takeoff. In Alaska, the saving grace is that, much of the time, the airplane lands, doesn’t refuel, offloads everything except the pilot, and goes out light.
Whatever your mission, the Cessna Skylark offers just a little more punch than the Skyhawk— enough to make a difference if the load is heavy, the runway is short, or the airport is above sea level. Just don’t let the reading on the tachometer psych you out.
Specifications & Performance – 1960 Cessna 175 Skylark
All specifications and performance figures are drawn from official sources, often the aircraft flight manual or the manufacturer’s web site. Another reliable source of information is Jane’s All-the-World’s Aircraft.
Specifications
Engine(s) – make/model: Continental GO-300C
Hp: 175
Fuel type: 100LL
Landing gear type: Tri/retr
Max TO weight (lbs): 2350
Std empty weight (lbs): 1325
Useful load–std (lbs): 1025
Usable fuel–std (gal/lbs): 43
Payload–full std fuel (lbs): 767
Wingspan: 36
Overall length: 25
Height: 8’ 5”
Wing area (sq ft): 174
Wing loading (lbs/sq ft): 13.5
Power loading (lbs/hp): 13.4
Seating capacity: 4
Cabin doors: 2
Cabin width (in): 40
Cabin height (in): 44
Performance
Cruise speed (kts–75%): 122
Cruise Fuel Burn (gph/lbs): 10
Best rate of climb, SL (fpm): 850
Service Ceiling (ft): 15,900
Stall (Vso – kts): 44
TO over 50 ft (ft): 1340
Ldg over 50 ft (ft): 1150
