From the Cockpit — Later Model Cessna 172s

Cessna wanted a degree of commonality between the two aircraft – thus the new engine for the 172 – and believed the Cardinal would soon push the older design out of production. History shows it failed to do so and in fact the 1968 reengined 172I outsold its new stablemate by better than two to one in that year (1206 versus 601) and the margin was significantly greater in 1969 (1170 v 255) by which time a more powerful, 180hp (134kW) Cardinal had been introduced. The Cardinal remained in production only until 1980 while the venerable 172 carried on for several years after that and is set to return to production in the coming year in upgraded form.

Refinement of the Skyhawk continued. The 1969 172K had a slightly redesigned fin, optional increased fuel capacity and reshaped rear windows, while the 1970 version grew conical camber wingtips and a wider track undercarriage. The 172L of 1971-72 received an enlarged dorsal fin fillet.

The 1973-76 Model 172M was fitted with a wing with drooped leading edges for improved low speed handling and this model was also the first with the optional ‘II’ pack which indicated a further increase in standard equipment including an avionics fit. The ‘II’ package also applied to other aircraft in Cessna’s range, the extent of the installation depending on the aircraft type. Performance enhancements were also introduced during the 172M’s production life through improved aerodynamics. In 1976 the ‘172’ designation disappeared from Cessna’s sales literature, with the Skyhawk and its associated level of equipment now the basic model.

Production of the 172 by Reims Aviation in France continued during this period, although it stayed with the original Rolls-Royce/Continental O-300 powerplant until switching to the Lycoming O-320 in 1972.

The next major change to the Skyhawk’s specification came in 1977 with the introduction of the 172N. This differed from the previous models in having a 160hp (119kW) Lycoming O-320-H engine capable of running on 100 octane low lead fuel in place of the previously used 80/87 octane which was subject to increasingly limited supply in the USA. This aircraft was sometimes referred to as the Skyhawk/100 and also featured 28 rather than 14 volt electrics.

The O-320-H engine in the 172N caused Cessna and Lycoming some serious problems through difficulties with its valve train, oil pump, accessory drive gears and camshaft, all combining to produce expensive repair bills and inflight failures. Cessna even recalled all 1977 and 1978 172Ns for major engine repairs and although the oil pump and drive gear problems were quickly fixed, the others remained until Lycoming came up with a suitable modification program some time later.

Cessna eventually gave up on the 172N and its troublesome powerplant, replacing it with the 172P with the similarly rated Lycoming O-320-D and increased maximum takeoff weight in 1981. This model also featured a further increase in optional fuel capacity and remained in production until late 1985, at which point Cessna stopped manufacturing all its piston engined aircraft due to the effects of the general aviation recession of the 1980s and the USA’s ridiculous product liability laws.

The very low production rates achieved in the two or three years before Skyhawk production ceased compare most unfavourably with the extraordinary levels reached throughout the 1970s, especially the second half of the decade. Including production by Reims Aviation (but excluding developments such as the Hawk XP and Cutlass), the basic 172’s annual deliveries from 1968 (and the introduction of the first Lycoming powered model) were: 1968 – 1309; 1969 – 1254; 1970 – 822; 1971 – 910; 1972 – 1081; 1973 – 1689; 1974 – 1944; 1975 – 2028; 1976 – 2047; 1977 – 1862; 1978 – 1943; 1979 – 1765; 1980 – 1159; 1981 – 1022; 1982 – 389. After that, production was at a comparative trickle.

The Hawk XP

Cessna had previously developed more powerful versions of the 172, starting with the Model 175 Skylark with 175hp (130kW) Continental GO-300 in 1958 and developing the idea through the similarly powered P172D Powermatic in 1963 and the R172E (and Reims Rocket) with 210hp (156kW) Continental IO-360-D/H from 1967. These models were discussed in last month’s From the Cockpit.

The theme continued in 1976 with the introduction of the Model R172 Hawk XP, combining the latest 172 airframe specification with a 195hp (145kW) Continental IO-360-K engine, a constant speed propeller, extra optional fuel capacity and increased operating weights. The result was an aircraft about 10 knots (18km/h) faster in the cruise, a greater rate of climb, more range and the ability to carry a greater load.

Production continued in both the USA and France until 1982, by which time 1537 had been delivered. The peak year of production was 1977, during which 625 XPs were delivered including 27 by Reims Aviation.

New Generation Skyhawk

The passing of the General Aviation Revitalisation Act by the US Government in 1994 saw the introduction of much more reasonable product liability laws as they apply to aircraft manufacturers and gave Cessna the opportunity to announce it would resume production of some of its single piston engined aircraft from 1996. Among them was an upgraded 172 Skyhawk powered by a fuel injected Textron Lycoming IO-360 engine capable of running on low octane unleaded (82UL) fuel as well as the usual 100LL.

An engineering prototype ‘new generation’ Skyhawk (converted from a 1978 172N model) was flown in April 1995 and the first completely new aircraft took to the air a year later, in April 1996. New production aircraft are due to start rolling out of a new factory at Independence, Kansas, later this year.

Flying and Buying

The comments made about the early 172s last month apply equally to the later models – the aircraft provides average performance and safe, conservative handling which is unlikely to get any pilot into serious trouble unless he or she really makes a meal of it. The Skyhawk’s excellent behaviour at low speeds contributes to this and overall it has a lower accident rate than other types of aircraft in the same category.

There are, however, several potential problems worth looking at if you’re in the market for a used later model 172. The troubles with the 172N and its O-320-H engine have already been mentioned, but so many years have passed its unlikely that too many still have the unmodified engine installed.

Another area worthy of a look is the avionics installation. Just about all 172s built after 1974 had the factory listed ARC radios installed and these were subject to serious reliability and quality control problems, especially in aircraft built in the latter part of the 1970s. Again, sufficient time has passed to allow most of these installations to be replaced with more reliable brands such as King, Collins or Narco, so it may not be such a problem two decades on.

Most light aircraft of that age will have undergone a refurbishment at least once in the intervening years and that refurbishment will often include an avionics upgrade. The same applies to another potential problem identified in the USA, that of filiform corrosion resulting from Cessna’s improper application of the polyurethane paints it used on about 8000 Skyhawks between 1977 and 1982. The corrosion has been noted mainly in warm, humid coastal areas.

The higher performance R172 Hawk XP is powered by a six cylinder Continental IO-360 and cruises at 130kt (240km/h). (Bill Lines)

How Much?

The following prices reflect a selection of Skyhawks advertised for sale in Australia during the preparation of this article. As always, higher prices for a given model usually reflect more engine and propeller hours to run before overhaul, lower total hours and perhaps a recent refurbish of the aircraft inside and out, or an avionics refit. There is a near infinite number of variables, but it is safe to assume an aircraft at the lower end of the scale won’t have too many engine and/or propeller hours remaining. Prices are in Australian dollars and a single price indicates just one aircraft was noted for sale.

172K – $39-45,000; 172M – $59-75,000; 172N – $55-85,000; 172P – $69-99,000; Hawk XP – $69-98,000. Next month: Piper Cherokee early models, don’t miss it.