Thursday, 02 August 2018 16:48

Cessna’s In-between Single – The R172K Hawk XP Featured

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The final result of a three-decades-long quest to fill the gap between the 172 and 182, Cessna’s R172K Hawk XP is a stellar performer in a 172-sized package.

When it’s boiled down to basics, the Cessna Hawk XP (XP for Extra Performance) is a four-place Cessna 172 Skyhawk airframe, sporting a six-cylinder fuel-injected 195 hp Continental IO-360-K engine and a McCauley constant-speed prop. 

It’s a 172 on steroids. In exchange for over 30 percent more power, an XP pilot will also need to pay attention to three more items: the constant-speed prop, rudder trim and cowl flap controls.

Although the airframes of the 172 and 172XP are almost identical, Cessna certified the Hawk XP (R172K) under Type Certificate No. 3A17; a different Type Certificate than the 172. Other airplanes on the 3A17 certificate include the Cessna 175 and the 172RG. The R172 E, F, G, H and J on Type Certificate No. 3A17 were sold to the U. S. and foreign armed forces and were designated the T-41B, C and D models. 

Fill the gap

The Cessna Hawk XP was Cessna’s final iteration in its nearly 30-year-long quest to build an airplane to fill the gap between the 160 hp, four-door sedan-like Cessna 172 and the big-hauling, pickup truck-like 230 hp Cessna 182. 

1,454 Hawk XPs were built over a five-year period from 1977 to 1981. It’s considered one of the most successful of the gap airplanes.

The first iteration of the more powerful 172-like models was introduced in 1958 as the Cessna 175. The exterior of the 175 looks almost exactly like the 172, except for a distinctive hump in the upper cowling. The hump in the cowling was required to accommodate the propeller reduction gear housing. The 175 had the geared Continental GO-300 series engines which produced 175 hp at 3,200 engine rpm (but only 2,400 prop rpm). Serial numbers indicate that 2,118 Cessna 175s were built.

Army and Air Force 172s

In 1964, the U. S. Army bought a version of the Cessna 172 equipped with six-cylinder, 210 hp fuel-injected Continental IO-360-D and -DB engines as the T-41B and C. The Army purchased both fixed-pitch and constant-speed propeller aircraft, and later a 28-volt version (T-41D) developed for the U. S. Military Air Program. 

The Air Force ordered Cessna 172Fs in 1964 under the T-41A designation, and would eventually shift to the 210 hp IO-360-powered versions.

U. S. forces bought 518 T-41s. FAA TCDS listings indicate that the T-41s were produced from 1964 until 1981. 

Hawk XP production

Cessna airplane production and the number of active pilots soared in the 1970s to levels that had never been seen before and likely will never be seen again. In 1975, Cessna shipped more than 15,000 airplanes; the number topped 18,000 in 1978. That equates to nearly 50 airplanes a day, every day of the year. The number of active pilots peaked at over 825,000 in 1980. 

In 1977, just before the crest of this exhilarating ride, Cessna introduced the 195 hp Hawk XP, or to be precise, a modern derated version of the T-41D. 

By the late 1970s, Cessna’s 177 Cardinal and 177RG Cardinal RG production numbers had fallen. 1978 was the last year for these “nonstandard configuration” beauties; fewer than 100 units were produced. My supposition is that Cessna’s management concluded that the Hawk XP would be an easy-to-produce and reliable 200-ish hp replacement for the Cardinals.

Cessna gauged the market correctly. The Hawk XP was a hit. Buyers bought over 700 XPs the first year on the market. The following year, an additional 204 were shipped. 

Unfortunately for the XP, for Cessna and for all other General Aviation manufacturers, the bottom was beginning to fall out of the market. The decline in U.S. gross domestic product numbers tell the tale. GDP growth was at 5.3 percent in the third quarter of 1978; by the second quarter of 1980, the GDP number had belly-flopped to a negative 1.6 percent. The recession of 1980 settled in around the world. 

Hawk XP production numbers continued to drop; just 54 airplanes left the factory at the end of production in 1981.

Hawk XP features and faults

An Aviation Consumer side-by-side comparison of the 177 and the Hawk XP reported, “The XP was, objectively, inferior to the Cardinal. The Cardinal had better handling and visibility, much more cabin room, lower cabin noise, lower maintenance costs and virtually identical performance and load-carrying ability.” The article concluded that the six-cylinder Continental engine and constant-speed prop extracted a price in reliability, maintenance and economy. 

The Hawk XP’s fuel capacity is only 52 gallons, with 49 useable. The R172K pilot operating handbook cites a fuel burn of 10.2 gph while cruising at 6,000 feet msl and 72 percent power. This setting results in 124 ktas. The result—with a one-hour fuel reserve—is a still-air range of 471 miles in 3.8 hours flight time. 

Some references cite optional fuel tanks that increase the capacity an extra 14 gallons to 66 gallons, but I haven’t been able to find any printed data confirming this option. The 172RG, which Cessna produced from 1980 until 1985, did have a 66-gallon fuel capacity—and it’s on the same TCDS. I’ve heard of owners who have installed a set of 172RG wings on their Hawk XPs, but any other method of upping the capacity to 66 gallons seems to be impossible to find. (CFA supporter Flint Aero offers STC-approved tiptanks for the R172K. The tanks add 24 gallons of capacity; 23 gallons are usable. —Ed.)

All the Hawk XPs had a 2,550-pound mtow, which yielded a useful load with average equipment of around 950 pounds. 

The POH cites ground runs of 830 feet using “short field” techniques at 2,550 pounds and temperatures of 20 C (68 F) at sea level. The book numbers show it takes nine minutes to climb to 6,000 feet msl from sea level. Climb rate is cited at 860 fpm at sea level and 540 fpm at 6,000 feet msl. 

Another place the XP shined was as a floatplane. The TCDS provides for the installation of an 80-inch propeller—instead of the 76-inch one on the XP landplane—when floats are installed. 

Corrosion: an insidious blight 

Buyers and owners should know that Cessna only applied paint to the interior skins of its single-engine airplanes that were sold with a float kit. Therefore, always be aware of the strong possibility of airframe corrosion. One of the best and easiest ways to determine if airframe corrosion is an issue is to look at the skin surface above the headliner. 

Cessna Service Newsletter (SNL) 93-3 covers what I consider to be another must-inspect airframe item. SNL 93-3 cites the possibility of sometimes extensive corrosion that may be found under the lead-vinyl sound-deadening pads glued to the inside skins of the fuselage. The best place to start inspecting for this common problem is at the skin panels forward of the forward door post and below the windshield. 

Airframe ADs

While there are 22 airframe-specific ADs for the Hawk XP, most are easy to comply with. The most important is the latest seat rail and seat inspection and replacement information in AD 2011-10-09. Worn seat rails and worn parts in the seat rail mechanism on Cessna seats need to be in excellent condition to prevent seat slippage during flight. Seats that don’t lock securely are (often fatal) accidents waiting to happen.

AD 2001-23-03 calls for repetitive inspections of the fuel line and map light wiring and switch located in and behind the left forward upper door post for burning and evidence of fuel line chafing. 

A new AD will likely be issued in the near future which calls for the inspection of the left and right lower forward door post area of Hawk XP (and many other Cessna) airframes, especially where the wing strut and built-up door post join, for corrosion and cracks. 

Engine ADs

In mid-1978, and in all Hawk XPs beginning with Serial No. 2930 in 1979, the IO-360-K engine was replaced with an IO-360-KB engine. Both engines develop 195 hp at 2,600 rpm. 

The -K engine was certified in April 1976; the -KB in March 1978. Both engines featured oil-cooled pistons and counterweight-tuned crankshafts. 

Note 10 in the engine TCDS approves the installation of any engine with a B in the suffix in place of an engine without the B suffix.

The engine Type Certificate says that the -KB is similar to the -K except for a “modified crankshaft.” This seemingly minor difference is very important.

A clue to the crankshaft modification is contained in Continental Critical Service Bulletin (CSB) 96-8 in the following sentence: “In 1978 TCM began using VAR process steel in the forging of crankshafts for use in a number of its engines. The VAR process material produces a forging with fewer impurities providing the greatest reliability and resistance to unusual operating circumstances.” 

VAR is an acronym for Vacuum Arc Remelt. Earlier crankshafts were manufactured using a process called “Airmelt.” 

The Continental CSB was followed by AD 97-26-17 titled “To prevent crankshaft failure and subsequent engine failure.” The AD required replacement of all Airmelt crankshafts with VAR crankshafts whenever the engine case halves were split for any reason at all. 

The bulletin also says that any new Continental engines built after Jan. 1, 1981, are factory-equipped with VAR crankshafts. All Continental factory-rebuilt engines after Serial No. 210114-R for -K engines and 288506-R for -KB engines had VAR crankshafts installed by the factory. 

Today, Continental sells both -K and -KB engines, and both have VAR crankshafts. According to a Continental sales person, the TBO for a -K is 1,500 hours while the -KB has a TBO of 2,000 hours. The -KB TBO can be extended out to 2,200 hours if the engine is flown 40 hours a month, according to Continental Service Information Letter SIL 98-9. There is no additional upcharge from Continental when an engine with an Airmelt crankshaft is returned as a core. Factory new and rebuilt engines sell for around $40,000.

One thing to watch out for when shopping for a Hawk XP are airplanes that have flown little in recent years because the owner wants to sell without incurring the cost to buy a new VAR crankshaft. Remember, if the engine’s case is opened for any reason (not just in case of overhaul), the crankshaft must be replaced. Though Continental won’t upcharge to swap the crankshaft as a part of a factory overhaul, third-party shops will likely charge a hefty fee. 

Another crankshaft AD was issued as emergency AD 2000-8-51 in 2000. It was shortly thereafter superseded by AD 2000-23-21. Due to manufacturing defects that may have been introduced to crankshafts built between April 1, 1998, and March 31, 2000, certain engines defined by serial number must have a core plug removed from the crankshaft prop flange to determine if the correct metallurgy exists in the crankshaft forging. Further details are in TCM Mandatory Service Bulletin (MSB) 00-5C, dated Oct. 10, 2000. Modifications

One of the most significant FAA-approved modifications for the R172K ups the engine horsepower rating from 195 hp at 2,600 rpm to 210 hp at 2,800 rpm. This STC consists of replacing the colored arcs and redline on the tachometer, changing the internal stops in the propeller and modifying the prop governor settings. This mod is sometimes referred to as the Isham mod, after Brad Isham. The upgrade is sold by Plane Tools. The website claims that the mod results in “Near Cessna Skylane performance at a fraction of the cost.”

Other notable mods include the Sportsman STOL kit for improved STOL performance. The kit contains a drooped wing leading edge, aileron gap covers and replacement wingtips. It is available from Stene Aviation in Polson, Montana. Improved cowling fastener conversion kits are available from Skybolt and from MilSpec Products.

Dollars and sense

A search at Vref, the aircraft valuation company, showed an average retail price of $61,000 for a 1979 R172K Hawk XP with 4,650 airframe hours and 1,000 hours since overhaul. A 1981 version with 4,410 airframe hours was valued at $65,000. 

Add-ons, such as the Isham mod; a WAAS-compliant navigator such as a Garmin 530W; an engine monitor such as the JPI EDM 700; and an autopilot such as the Genesys (S-TEC) 30 with altitude hold would boost the price by another $15,000 to $20,000. 

The Barnstormers aviation classifieds website listed a 1979 XP with 692 airframe hours and the Isham engine modification for $149,000. A Canadian-registered XP with a set of floats and 5,600 airframe hours is priced at $135,000 Canadian or $109,900 USD.

For comparison, Vref figures for a 1979 Cessna 172N Skyhawk show a base value of $44,000. However, this lower valuation is offset by the average airframe time of 6,200 hours. The valuation for a 1979 Cessna 182Q Skylane shows a base valuation of $85,000 with 4,150 airframe hours. 

So, there it is. The Hawk XP fits just where Cessna intended it. It hauls more, goes faster and is more powerful than the 172 of the same year, and with the Isham engine modification STC it almost does what a 182 can do (but costs less). To top it off, it’s a good floatplane. 

Sources: Aviation Consumer Used Aircraft Guide (aviationconsumer.com/issues/1_1/); FAA TCDS No. 3A17, Rev. 46; Federal Reserve Bank of St. Louis (https://fred.stlouisfed.org/series/A191RO1Q156NBEA); Cessna175.org. Steve Ells has been an A&P/IA for 44 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and lives in Templeton, California with his wife Audrey. Send questions and comments to .

Resources

AIRWORTHINESS DIRECTIVES

AD 2011-10-09, seat rails

AD 2001-23-03, Repetitive inspection of fuel line and map light wiring and switch

AD 2000-23-21 (supersedes AD 2000-23-21), Manufacturing defect in crankshaft

AD 97-26-17 “To prevent crankshaft failure and subsequent engine failure.”

 

Proposed Cessna doorpost AD

The ADs and proposed AD referenced in this article are available under “Magazine Extras” in the Cessna Flyer forums at CessnaFlyer.org/forums.

 

For more Airworthiness Directives, 

visit CessnaFlyer.org and go to “Aviation Alerts” under the Knowledge Base menu. 

 

SERVICE BULLETINS Cessna Service Newsletter (SNL) 93-3

support.cessna.com

 

Continental Critical Service Bulletin (CSB) 96-8; Continental Service Information Letter SIL 98-9 and TCM Mandatory Service Bulletin (MSB) 00-5C

continentalmotors.aero/support/service-bulletins.aspx

 

MODIFICATIONS – CFA SUPPORTERS

Sportsman STOL kit Knots2U, Ltd.

knots2u.net/sportsman-stol-kit-cessna-170b-172-175/

 

Stene Aviation steneaviation.com/pages/sportsman-stol

 

Tiptanks

Flint Aero Inc.

flintaero.com/kits/internal-tip-tanks/165-2/

 

Additional Cessna R172K modifications & STCs cessnaflyer.org/cessna-yellow-pages/modifications-and-stc-s.html

 

MODIFICATIONS – OTHER

210 hp “Isham” STC Plane Tools planetools.com

 

Cowl fastener upgrades Skybolt skybolt.com

 

MilSpec Products milspecproducts.com

 

AIRCRAFT VALUE REFERENCE Barnstormers barnstormers.com

 

Vref vrefonline.com

Read 9179 times Last modified on Wednesday, 12 September 2018 12:36
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