Wednesday, 29 August 2018 16:01

Big-airplane Features for a Small-airplane Price: The Cessna 175 Featured

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Cessna introduced the 175 hp, four-seat Cessna 175 in 1958; with the goal of filling the gap between the 172’s price and the 182’s performance. The 175 garnered positive initial reviews. Yet only six years later, the model was discontinued. So, what went wrong? 

Just over 60 years ago, on March 22, 1958, Cessna offered its first Cessna 175 for sale. Then, as now, marketing departments used flowery language to sell the dream of “the family airplane.” 

A big and beautiful two-page ad in the April 1958 issue of Flying offered readers the “big, beautiful” new “Power-Geared” Cessna 175. The 175 promised “big-airplane stability, big-airplane comfort, big-airplane speeds”—but for a small-airplane price.

On the surface, the 175 seemed to fit perfectly in the Cessna lineup. 

At the time the 175 debuted, the 172 was Cessna’s entry-level model (the two-seat 150 wasn’t introduced until late 1958). The 182, though quite capable and roomy, was a significant step up from the 172 in both price and performance.

In 1958, a 172 cost $8,995. A standard 182 was $14,350. The deluxe 182 Skylane was $16,850. The 175, priced at only $10,995 while offering “big-airplane” features, seemed to be what General Aviation buyers desired. Flying reviewed the 175 in July 1958 and deemed it to be “an answer to a market requirement—a constructive answer.”

However, after only a few short years, the market soured on the Cessna 175. The last aircraft carrying the 175 name were produced in 1962. 

A close relative of the 172

At a distance, it’s difficult to distinguish a Cessna 175 from a Cessna 172 of the same era. This is especially true for earlier 175 models, before the 175A adopted a noticeably “humped” cowl. The 175 and 172 airframes were developed concurrently, with extensive parts commonality. 

Delays with the Cessna 175’s newly-developed Continental GO-300A powerplant meant that the 175 debuted two years later than the Cessna 172 and 182, which were both first sold in 1956. 

The 175 prototype took to the skies over Wichita April 26, 1956. The Cessna 175 received type certification on January 14, 1958. An aggressive schedule brought the aircraft to market by late March 1958. 

 

Model evolution

The 175 and 172, though extremely similar when viewed from across the tarmac, do exhibit differences, especially under the cowl and in the cabin. 

Early straight-tail 175s and 172s (pre-A models) have the same fuselage dimensions. However, the firewall position and firewall structures differ. 

The 175’s firewall is a stepped design, rather than the flat firewall of the early 172. The 175’s firewall is further rearward on the fuselage than that of the 172, allowing for a longer, more gradually-tapered cowl with larger inlets for cooling air. The cowls of early 175s appear more like those found on Cessna 182s.

The position of the 175’s firewall affects the position of other internal fuselage components. The instrument panel is correspondingly further rearward, in a wider area of the fuselage. Cessna engineers took advantage of this increased panel width and designed a new instrument panel exclusive to the 175; the early 172’s “shotgun panel” layout was not used. 

The 175’s instruments are clustered on the left side of the cabin, in clear view of the pilot. Though not a quite a linear six-pack arrangement, the 175 has a modern-looking instrument panel. The instrument panel layout was “easy-to-work, easy-to-read,” according to Cessna’s marketing. 

In 1960, the Cessna 175A—as well as the 172A—received Cessna’s new swept-tail design, paired with the “fastback” fuselage. The 175A and later models are fitted with a distinctive “humped” cowl. 

The 172B borrowed from the 175’s design: Cessna adopted the stepped firewall of the 175, a longer engine mount and cowl, and also changed the instrument panel layout to match the 175’s. 

The 172B and 175B fuselages—and in fact, the entire airplanes—are dimensionally nearly identical.

The 175’s wing structure is very similar to that of the 172, with differences in the internal inboard third of the wing to account for the fuel tanks. 

 

Fuel

The 175 has two tanks, one in each wing, that hold a total of 52 gallons of fuel; an upgrade from the 42 gallons of the 172.

Due to the location of the fuel pickups in the tanks, only 42 of the 52 gallons is usable in all flight conditions. The 175’s POH states that an additional nine gallons are usable in “level flight.” However, the 175’s TCDS carries a rather ominous warning: “The Models 175A and 175B fuel system does not comply with CAR 3.433 and 3.434 for horsepower greater than 167 at the best angle of climb which is the most critical attitude.”

 

Options

The deluxe trim model offered from late 1959 onward was called the “Skylark”—all Skylarks are 175s, but not all 175s are Skylarks. Some were fitted with Levelair T-2 or Tactair T-3 autopilots. 

The 175 could be ordered as a seaplane, also. This option boosted gross weight by 100 pounds for the 175A and 175B.

In addition, an 18-gallon auxiliary tank was available for the 175 as a factory-installed option. The tank was installed on the baggage compartment floor with a filler neck on the right side of the fuselage. An electric pump connected the tank to the right wing tank.

Powerplant

As the 175 was being developed, Continental Motors offered Cessna the exclusive use of a new high-rpm 175 hp variant of the O-300. This new powerplant, which would become the Continental GO-300, promised increased performance with a negligible weight penalty. 

According to a July 1958 Flying review of the 175, Cessna engineers debated whether the high-rpm engine design would be better served by connecting a smaller-diameter propeller directly to the crankshaft or by gearing down to a larger prop. Connecting the propeller directly to the crankshaft in a standard arrangement would be no doubt simpler mechanically, but the geared reduction drive offered the lure of more efficient operation, especially at takeoff and climb speeds. They chose to use a geared drive. 

Cessna Flyer contributing editor and A&P/IA Steve Ells explains how it works:

“The reduction gear assembly consisted of spur-type gears with the propeller shaft located above the engine crankshaft centerline. The propeller’s center was approximately nine inches above the center of the crankshaft. This arrangement enabled the installation of a much longer propeller than was possible in any direct-drive engine. The Cessna 175 landplane swung an 84-inch McCauley prop that produced more thrust than the 172’s 76-inch propeller. 

The offset of the reduction drive still provided the required flat nose tire and flat strut prop-to-ground clearance distance mandated by airplane certification regulations. An enormous 90-inch prop was approved on the 175A and 175B when on floats.

A propeller-to-engine reduction ratio of 0.75 provided 2,400 prop rpm at the takeoff power setting of 3,200 crankshaft rpm. At the recommended cruise rpm of 3,000 on the tachometer, the prop settled down to 2,250 rpm. This slower prop speed resulted in lower prop-generated noise at both takeoff and cruise power settings.”

The 175 hp GO-300A spun at a maximum of 3,200 rpm; noticeably faster than the non-geared O-300 which redlined at 2,700 rpm. The difference in engine rotational speed had a price. While the O-300 had a TBO of 1,800 hours, the GO-300s found in 175s had a TBO of 1,200 hours. 

The GO-300A of the early 175 was replaced by the GO-300C and -300D in 1959. The last 175s used the GO-300E and swung a constant-speed propeller. 

The decision to use the high-rpm GO-300 engine and geared reduction drive would ultimately determine the success of the 175 and Skylark names. 

Performance

The most noticeable difference between the 175 and 172, aside from the engine, reduction drive and panel layout, is their relative performance. 

Steve Ells found this to be the case several decades ago: 

“In 1985, I was dropped off with a box of tools at an unimproved strip across from Kenai, Alaska, on the west side of the Cook Inlet to troubleshoot engine problems in a customer’s Cessna 175. I loosened up a draggy exhaust valve with a liberal dosing of Kroil penetrating oil before flying back. 

Although the inlet is less than 30 nm across at that point, I knew if I had to ditch in the cold waters I was a goner, so I climbed up to 8,500 feet before turning toward home and the other shore. 

The GO-300 never missed a lick and I was very impressed with how much more power it seemed to have versus the 172s I have flown previously.” 

Pilots with time in unmodified straight-tail 172s know that they’re sweet-handling aircraft; they also realize that the 145 hp Continental O-300 gives merely adequate performance. Cruise speeds are typically around 120 mph tas (104 ktas). Though early 172s are light airframes (over 300 pounds lighter than today’s 172s), their low MTOW of 2,200 pounds limits payload. After filling the tanks, about 640 pounds are left for passengers and luggage. 

A stock 175 weighs about 100 pounds more than its 172 counterpart, but that is offset by a 150-pound increase in MTOW from 2,200 to 2,350 pounds. Useful load is best on the standard model (just over 1,000 pounds) and lower on the deluxe Skylark, at approximately 950 pounds. After the tanks are filled, the 175 Skylark has a slightly lower payload than the 172; in the 630-pound range. 

Cessna claims the 175 cruises in the 135–140 mph tas range (117–122 ktas), and with larger tanks than the 172, the 175 can go about 100 miles further nonstop. 

According to book numbers, the 175 also sports much-improved short-field and climb performance, nearly on par with the 182. The 175 Owner’s Manual states the aircraft can climb at 850 fpm at sea level at its full 2,350-pound mtow, while the takeoff ground roll consumes only 735 feet of runway. At lighter weights, climb rate approaches 1,400 fpm, and the 175 needs just 345 feet to get off the ground. 

 

Engine issues

The 175, at least on the surface, offered a great value proposition for buyers. The 1958 and 1959 models of the Cessna 175 sold well: 1,239 left the factory in the first two years of production.

Cessna’s 1959 ads claimed that the 175 could provide “8 cents-per-mile operation,” including fuel, maintenance, storage, insurance and depreciation. 

However, issues with the GO-300 engine soon challenged Cessna’s assertion. Many GO-300s never made it to the promised 1,000-hour TBO, and those that did often required cylinder work to get there.

Steve Ells shares his thoughts on the engine: 

“It’s often thought that the 175 lost favor with buyers because the engine was rumored to be unreliable. The GO-300 initially had a 1,000-hour TBO (amended to 1,200 in 1968), which was not uncommon for that era. One very experienced engine builder described the GO-300 to me as a powerful smooth-running engine, but cylinder problems seemed to head the list of issues. 

One plausible theory is that pilots that had been flying Cessna single-engine airplanes at cruise rpm of 2,350 to 2,500 were very reluctant to cruise at the GO-300’s preferred 3,000 rpm, so they pulled the throttle back to what they thought was the “correct” rpm. 

I believe that if the tachometer had shown propeller rpm instead of crankshaft engine rpm, the engine reputation would not have suffered as much as it did.”

The lower power settings may have “sounded” right to pilots used to standard engines, but at low rpm, the GO-300 didn’t develop sufficient oil pressure to provide lubrication and cooling. 

A 1972 Flying article entitled “Cessna’s Neglected 175” concurred: “People ran the 175s as they would have a 172… the engines warped their valves, broke rings, scored cylinders, cracked pistons. The bad-mouthing began as engines started to fold in 500 hours of a promised 1,000 [hour] TBO.”

Airflow for cooling also likely suffered at low speeds in early tightly-cowled 175s, contributing to premature cylinder issues. Later 175s suffered the opposite problem. The redesigned cowl of the A and later models brought plenty of air to the cylinders. Shock cooling became an issue in low- or idle-power descents.

The Cessna 175’s POH listed cruise speeds and fuel burns down to 36 percent power and 2,400 engine rpm, which may have exacerbated these issues by giving pilots the impression that this was a “safe” power setting.

In addition to the engine problems, the GO-300’s gearbox was prone to issues if operated incorrectly. Numerous posts on today’s Cessna 175 type forums warn pilots to always keep a load on the engine; and under no circumstances to let the propeller “drive” the engine at idle. Gradual, constant-power descents are advised.

 

Declining production

By 1960 and the 175A model, sales had slowed: 540 175As were produced in 1960. Only 225 175B aircraft were sold in 1961.

The 1962 175C model, sporting a Continental GO-300E driving a constant-speed propeller, offered performance and payload improvements. Despite better climb numbers and a greater MTOW of 2,450 pounds, the 175C didn’t sell any better. Only 117 175Cs were produced.

When a 175 isn’t a 175 any longer

In 1963, with a marketing sleight-of-hand, the model that would have been the Cessna 175D morphed into the “Powermatic P172D Skyhawk.” Ostensibly, Cessna calculated that the 172 brand was stronger and the change would help dissociate the airframe from the troubled 175/Skylark name. 

Cessna upped the MTOW to 2,500 pounds, which gave the P172D an impressive 1,100 pounds of useful load. The P172D dropped the fastback fuselage and received the “OmniVision” rear window. It also was fitted with cowl flaps for better engine cooling. 

However, the market didn’t bend. Only 72 of the Powermatics were built; 69 in the United States and three which were assembled under license by Reims Aviation in France as FP172Ds. (The “F” prefix was for “French-produced.”) 

The 175 lives on

Cessna 175 and P172D  production ceased in 1963, after a total production run of 2,118 aircraft. The Skylark was abandoned—almost. 

In addition to the three FP172Ds which had been delivered to European buyers by Reims Aviation, a fourth airframe had been shipped to France.

In mid-1963, Reims engineers converted this airframe into a prototype military liaison aircraft. It featured a 210 hp Continental IO-360-D powerplant matched with a constant-speed propeller.

This proof-of-concept would inspire a number of variants—several of which Cessna eventually certified under the 175 Type Certificate, including the US Air Force T-41B through D (and non-USAF versions, the R172E through J) and the R172K Hawk XP (profiled in the April 2018 issue of Cessna Flyer). 

Cessna produced 2,080 of these IO-360-powered “172s” which were, at least from a certification basis standpoint, 175s.

Though the Reims Rocket is nearly equivalent to the T-41B and shares a common ancestry, it is not included on the 175’s Type Certificate, nor was the French-produced FR172K Hawk XP.

In late 1978, Cessna created a version of the airframe with a retractable undercarriage, a 180 hp Lycoming O-360-F1A6 engine and a three-bladed constant-speed prop. This aircraft, the 172RG Cutlass RG, though a 172 in name, is also on the 175 Type Certificate. 1,191 172RGs were produced between 1980 and 1985.

In total, some 3,271 of these “175 derivatives” left the Cessna factory.

The early positive reception for the 175, the later success of “souped-up 172s” like the R172K Hawk XP, and the number of STC’d 180 hp conversions of legacy 172 airframes demonstrated that there was, and still is, a market for an airplane that is a step up from a standard 172. 

However, the Cessna 175’s reliance on a new, unproven engine to achieve “big-airplane performance” was its ultimate undoing.

As a further testament to the “172-plus” concept and the 175 airframe itself, many of today’s still-flying 175s have been upgraded with one of several STC’d engine conversions. 

Next month: Cessna 175 STCs and modifications, and a flight test of an O-360-powered Skylark.

 

Scott Kinney is a self-described aviation geek (#avgeek), private pilot and instructor (CFI-Sport, AGI). He is associate editor for Cessna Flyer. Scott and his partner Julia are based in Eugene, Oregon. They are often found buzzing around the West in their vintage airplane. Send questions or comments to .

SOURCES (ONLINE)
Type Certificate Data Sheet No. 3A17 Rev. 46, May 14, 2007; Skylark Associ-ation International Forums, cessna175.org; Flying, Apr. 1958, Jul. 1958, Sep. 1958, Mar. 1959, Jun. 1959, Nov. 1961, Aug. 1972, Sep. 2008. [Note: many back issues of Flying, including all cited here, are available free on Google Books: books.google.com.]
 
SOURCES (PRINT)
“Airlife’s General Aviation: A Guide to Postwar General Aviation Manufacturers and Their Aircraft” 
R.W. Simpson. Shrewsbury (UK): Airlife Publishing, 2000. 
 
“Cessna 172: A Pocket History”
Ron Smith. Stroud (UK): Amberley, 2010. 
 
“Cessna: Wings for the World”
William D. Thompson. Bend, Oregon: Maverick Publications, 1991.
 
“The General Aviation Handbook”
Rod Simpson. Hinckley, Minnesota: Midland, 2005. 
 
Jane’s All the World’s Aircraft 
New York, NY: McGraw-Hill, 1967. 
 
“The Planes of Wichita: The People and the Aircraft of the Air Capital”
Daryl Murphy. Bloomington, Indiana: iUniverse, 2008. 
 
“T-41 Mescalero: The Military Cessna 172” Walt Shiel, Jan Forsgren and Michael R. Little. Lake Linden, Michigan: Slipdown Mountain Publications, 2006.
 
Resources
FURTHER READING
“Cessna’s In-between Single: The R172K Hawk XP” 
by Steve Ells. Cessna Flyer, April 2018.

Available at https://www.cessnaflyer.org/magazines/item/1036-april-2018-cessna-flyer-magazine.html

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