Cessna adds muscle to a proven performer and brings some unexpected benefits to the 172Dave Higdon/Wichita

Preconceptions can be risky when you are experiencing something new and different. You may think you have "been there, done that" - but then you realise you have never been there at all. Such was almost the case during Flight International's evaluation of the 172S Skyhawk SP (Special Performance), the newest product from Cessna's piston-single factory at Independence, Kansas, USA.

As the main difference from the standard 172R Skyhawk was the engine's extra 15kW (20hp) power output, I thought the 135kW 172S would be fairly similar aloft to the basic 120kW aircraft .

The reality was demonstrated even before my first flight in Cessna's prototype 172S. It happened during the aerial photography session to obtain the pictures that accompany this report. Flight International had hired a commercial pilot and a late-1970s standard 172R powered by a 120kW Textron Lycoming.

The same aircraft had been used 18 months earlier to take photographs of the then-new 172R. On that cold December day, little difference in performance was discernible between the two, manufactured two decades apart.

So I was taken by surpise when the new 172S, or Skyhawk SP, nimbly outpaced the older Skyhawk on this hot June morning. The proof came at the end of our photography session and about 55km (30nm) downwind of our airport operations base. The 172R pilot put the throttle to the panel a few seconds ahead of the photo-aircraft pilot doing the same, but the SP crew was already walking into the terminal at Wichita's Jabara Airport when we turned off the taxiway and on to the ramp.

In a little under 15min, the SP had gained about a 2min advantage on the photo-aircraft. Where we squeezed out about 120kt (225km/h), the Skyhawk achieved a maximum cruising speed of around 130kt.

As my own flight later confirmed, the $149,500 172S proved a more spirited aircraft than its standard-power stablemate. In other areas, however, the 172S proved almost indistinguishable from the basic 172R, which costs more than $16,000 less.

That 15kW extra, however, deliver just enough added power to make the humble 172 Skyhawk seem, well, more fun and certainly more enthusiastic in SP form.

Overall, the shared traits can be nothing less than a major marketing asset when you acknowledge the well-rounded flying characteristics that made the Skyhawk the world's all-time best-selling aircraft, a position the 172 has held on to despite being out of production for more than a decade.

If there is one item people seem to question most, it is the price difference between the two Skyhawks. Despite this scepticism, Cessna executives expect one in three Skyhawks sold this year to be an SP.

The new SP is far from being the first Skyhawk to be given a power boost, either straight from the Cessna factory or from an aftermarket shop. Skyhawk XPs sported bigger engines and constant-speed propellers, and there were retractable-gear versions with higher horsepower. Compared with past engine-power increases, however, making the 120kW 172R into a 135kW 172S required almost nothing to accomplish.

The credit goes entirely to Cessna's decision to use Textron Lycoming's IO-360-L2A four-cylinder engine for the standard Skyhawk instead of the traditional O-320 Lycoming long used on the standard aircraft. Cessna wanted 120kW out of a larger engine running at lower RPM; in this case, a 135kW, 2,700RPM engine limited to a 2,400RPM redline.

The derated arrangement brought two distinct advantages: lower sound levels and enhanced durability, both important to Cessna in view of regulatory and marketing concerns in Europe and North America.

Even as the first new-production 172 emerged from the Independence plant, the signs were that Cessna had also banked a third benefit from its engine choice - the ability to get 135kW from those 5.9 litres by raising the powerplant redline to 2,700RPM.

The difference between the 172R and the 172S boils down to that difference in redline. Cessna achieves the enhanced power by installing a McCauley fixed-pitch propeller 25mm larger in diameter than that used on the 172R, within blades pitched to absorb 135kW at 2,700RPM.

minor changes

Of course, other minor powerplant changes must accompany the higher redline: a larger-volume induction system intake box is installed, and the fuel-injection controller is adjusted for higher fuel flows. In the only difference obvious to the casual observer, Cessna has revised the engine tachometer to reflect the 2,700RPM redline and a different green range.

Beyond the under-cowling and instrument changes, Cessna has also attended to the marketing considerations leading from asking customers to pay thousands of dollars more for an aircraft that seems little different.

Cessna's team designed a new, sweeping paint scheme to go over the basic white, added a pretty Skyhawk SP logo on the tail, and created a tasteful leather interior and trim instead of the cloth upholstery and trim which features in the 172R. The customer can opt out of the leather and have the same cloth upholstery used on the stock Skyhawk; but, cloth or leather, you pay the same difference.

Otherwise, the standard-equipment lists match, item by item, including the AlliedSignal Bendix/King avionics. The same applies to the two avionics-upgrade packages: Nav I - $13,700 for a second navigation/communication radio with glideslope, an automatic direction finder and a visual flight rules global positioning system and Nav II - $19,300, which adds to the Nav I package a single-axis autopilot and substitutes an instrument flight rules global positioning system and associated hardware.

What's so 'Special'?

Back-to-back flying in both aircraft, the 172R and the 172S, would have provided the best basis for comparing the modest performance differences between the two Skyhawks. Such was not to be the case. Thanks to my notes from December 1996, however, when Cessna put me in the first 172R, describing those differences is still relatively painless.

There is virtually nothing to differentiate between how the two Skyhawks handle. The performance differences, while neither dramatic nor startling, are worth noting. Payload may be the most attractive improvement an SP buyer gets over an owner of a straight 172R - a 45kg (100lb) increase to 430kg. This is because the more powerful Skyhawk SP's improved climb performance lets the 172S carry 45kg more and still meets the US Federal Aviation Administration standard for climb gradient during a rejected landing.

My first take-off in the SP is a useful point of reference when looking at the difference in performance. When Cessna put me in the left seat of a new 172R for a flight test on a cold (-4íC) December day in 1996, it took just under 800ft (245m) to reach rotation speed with two aboard and three-quarters-full fuel tanks - about 975kg, 135kg below maximum gross weight.

In mid-June 1998, a day about 15íC warmer, the SP took all of 900ft to rotate at about 1,000kg - around 28kg heavier than in the 172R and 160kg below maximum take-off weight for the 172S. With the temperature at about 29íC and with moderate humidity, however, the 172S posted climb rates more than 100ft/min (0.5m/s) better than the 600ft/min rate the 172R delivered at 100kt (185km/h).

Even better, trimming to a 500ft/min climb rate brought the SP to a speed of about 105kt, a good 5kt faster than the standard Skyhawk on that cooler day. In addition, during a full-power speed run at 4,500ft, the 135kW SP provided about 132kt true airspeed, nearly 10kt faster than the maximum-power sea-level speed of the standard 120kW Skyhawk.

My guess is that the SP will cruise at about 126-127kt at 75% power and 8,000ft. So, overall, it enjoys incremental gains in launch, climb and cruise. Instead of consuming fuel at a rate of about 30 litres/h, however, the SP uses fuel at 38 litres/h. This higher consumption cuts 190km off the stock Skyhawk's 1,070km book cruise range, leaving the SP with a quoted range of 880km. The 172R and 172S airframes are virtually identical, including their 210 litre fuel tanks providing 200 litres of useable fuel.

It is my belief that an SP owner could enjoy the best of both versions - the higher payload of the 172S and the range of the 172R by adjusting the 135kW Lycoming to a lower power setting in cruise. In other words, by flying the 172S at 65% power, about the equivalent of 75% power in the 120kW 172R, the SP will cruise happily at speeds and fuel consumptions comparable to those of the standard Skyhawk. That is not a bad combination of utility, most pilots would agree.

Same Skyhawk handling

As noted, a Skyhawk buyer can count on that reliable, venerable 172 handling, regardless of horsepower preference. Unlike previous higher-power Skyhawks, the identical engines mean no weight difference, so there is a smaller difference in handling than there is, say, with a 110kW (O-320-powered) Piper Cherokee compared with a 135kW (O-360-powered) version of the same aircraft.

In fact, most of what there is to commend about the flying qualities of the 172S could come from Flight International's flight test (22-28 January, 1997), when "-it took only a few minutes into 2.2h of cross-country flying in the new 172R Skyhawk, followed by a couple of hours of photo-mission time in a late 1970s Skyhawk, to learn that the 1997 Skyhawk is a quieter, better equipped, more comfortable and more luxuriously appointed 172 than in the past. In a nutshell, the new version feels more solid, like a larger, heavier, more business-class aircraft than its 34,000-plus predecessors built over a span of three decades."

Those same comments also apply to the 172S. Skyhawks have the sort of handling traits that have made them the backbone of many a flight school's trainer fleet yet, with a cruise speed comfortably in the 120kt range and enough payload for two people and luggage, they bridge the gap easily as a first aircraft, family aircraft and, over reasonable distances, as a business tool that provides an attractive alternative to driving or airline travel.

Except, in the case of the 172S, the customer gets more power and the accompanying payload and climb-rate advantages with no difference in handling, stall speeds, control harmony, or the rest.

customers' needs

In the case of either Skyhawk, you get a 172 equipped like none of those built before 1986: the safety-driven dual-vacuum-pump system; standard strobes; a modern, well-illuminated panel; smart, accurate engine and fuel gauges; an annunciator panel to warn of low fuel, voltage or vacuum; 6mm-thick tinted glass; sound insulation; adjustable seats; four-place shoulder harnesses; and a six-point fresh-air system.

Whether customers' needs match the lower-priced, standard 172R or the higher power of the 172S depends on their perspectives and their wallets. Either way, most will not be disappointed by the SP - as long as their expectations do not outweigh their better judgements.o

The new Skyhawk owes its improved performance to engine-power increases

Length overall8.2m

Wing span overall10.29m

Height overall2.72m

Powerplant1 x Textron Lycoming IO-360-L2A

Power (each)135kW

Operating weight empty730kg

Maximum take-off weight1,160kg

Maximum payload430kg

Cruising speed at 75% power and 8,000ft126kt


Source: Flight International