The Cessna 310 was a radical departure and a solid advance in general aviation products when it was introduced late in 1954. The second airplane in the 300 series was the 320 Skyknight. Introduced in 1961 as a 62 model year product, the 320 was a big step up in performance. Featuring a larger cabin, it also represented one of many areas in which Cessna pioneered or at least persevered: turbocharging.
Turbocharging was not new, even to general aviation. But it was tricky, temperamental and not very reliable. Other manufacturers tried and gave up. Cessna and its vendors stuck with it, deciding that the performance gain was worth the difficulties.
For its time, the 320 was a big, sophisticated airplane-it had space for and could carry six adults. It could fly rings around quite a few airliners of the day.
(Today, many pilots think of the Skyknight as a version of the 310. It was licensed under a new certificate, however. The 310 TC is 3A10; the 320 TC is 3A25.)
History
The ABCs of the 320 are fairly straightforward. It was introduced with a larger cabin than the 310, having four side windows instead of two, and a higher gross weight than 310s of the same era. The biggest difference among the 320s themselves is the switch from the original 260-HP TSIO-470B Continental engines that powered the 320 through 320C to the 285-HP TSIO-520Bs on the 320D through F models.
The 1963 Model 320A did away with the slab-sided tuna tanks in favor of canted tip tanks. The 1964 320B received nacelle baggage lockers. And along with its bigger 285-HP engines, the 320-D in 1966 had three-bladed props and more cabin and baggage space.
The 1968 320F, the last of the line, received solid-state voltage regulators. A deluxe version, dubbed the Executive Skyknight was offered with creature comforts such as double-pane side windows and increased structural soundproofing.
Cessna officially suspended the 320 with the 1969 model year, but the Turbo 310 was introduced the same year to replace the Skyknight.
During its relatively brief production life, 575 320s were built, including an estimated 290 of the 260-HP versions, through the 320C, and 285 of the later 285-HP models.
Best of the line
For someone just looking for a relatively inexpensive (purchase price, that is, not operating/upkeep expense) high-performance twin, the 320F, the last of the line, is most desirable because it features all the factory improvements.
However, only 45 F versions were built. The careful shopper may find the same features in earlier models that have been upgraded to equal or even better state through aftermarket modifications.
The 320 initially was offered with 102 gallons of fuel capacity (100 gallons usable). Then auxiliary tanks in the wing became an option, then standard. They added 40 gallons of usable fuel. If there are any 320s with only 100 gallons available, it would be surprising. Nevertheless, it is something to watch for. A number of aftermarket aux. fuel systems have been offered, too.
Another early option was 66-amp generators to replace the standard 50-amp units. The biggest caveat for anyone attracted to the 320 is age. The last airframe was rolled out of the factory nearly thirty years ago. The effects of aging must be added to those from normal wear and tear, abuse, neglect and poor maintenance.
The biggest competition for the 320 probably is the turbo 310. Certainly within the roughly $60,000-$80,000 price range, there is nothing else to compare it with.
Marketplace
Average prices for 260-HP 320s range from $66,000 to $75,000. The 285-HP D through F models run from $86,000 to $92,000. The variations in price result from demand level, condition of the engines, airframe and accessories, and the amount of modification made to the airplane. The 320 continues to be a relative price bargain for its performance. But appearances can be deceiving, and money spent on an expert, exhaustive pre-purchase inspection is the best kind of insurance.
Most used airplanes of somewhat competitive performance are considerably more expensive. One reader said that if the 320 were being built today, it would probably cost well over $500,000. Well, a new Seneca V costs more than $560,000. The normally aspirated Beech 58 Baron costs more-a lot more: more than $750,000.
Performance
According to the operating manual for the 320D version, the Skyknight is a stormer. Initial rate of climb is 1,980 FPM and-the book says-the airplane will still climb at 1,190 FPM at FL200. Service ceiling is 29,300 feet (there was no maximum operating altitude in those days).
Critical altitude (the level at which the turbo wastegate closes fully and the engine is producing maximum continuous power) is 16,000 feet.
Book single-engine ROC is 500 FPM at sea level; single-engine ceiling is 19,200 feet.
At 5,200 pounds, the 320 can operate from a hard-surface strip of less than 2,000 feet (but 3,000 is more prudent; accelerate/stop distance under standard and ideal conditions is approximately 3,000 feet). Takeoff to clear a 50-foot barrier is listed as 1,360 feet; landing over the same obstacle requires 1,710 feet.
Claimed cruise performance is superior to that of some turboprops, but before you go out and try to duplicate the manufacturers numbers, remember that they are calculated figures based on hypothetical flights to dry tanks.
Owners who have written to The Aviation Consumer prefer cruising in the low to mid teens. Cruise performance improves with increased altitude-we prefer 12 to 16K where the air is usually cool and smooth. Fuel burn is 26-28 GPH at 190 knots TAS. We normally flew the airplane at 15,000-16,000 feet, and we would true out at 220-225 knots and 30-31 GPH. The Skyknight has the ability to cruise in the mid teens burning 30 gallons per hour at well over 200 knots.
With 140 gallons of fuel on board, a typically equipped 320 could lift almost six adults with no provision for baggage. If radar and other accessories are added, the payload is reduced, of course. But compared to many light twins, the range/payload capacity of the 320 is noteworthy.
However, before trusting book figures, any 320 owner-indeed, anyone who buys a used airplane of any kind, particularly if it is 15, 20 or more years old-is advised to have it weighed. There are many surprises-and needless weight-hidden behind the upholstery and bulkheads of most older aircraft.
Flight handling
Taken as a group, the 320s are better handling airplanes than most of their contemporary 310s. They are not quite as prone to Dutch roll as the shorter-coupled early versions of the 310. However, both the 310 and 320, as well as the 340 and any early 400 series Cessna-any with tip tanks-carry a great deal of weight and mass out at the ends of the wings.
Those tip tanks, which many people think are auxiliary tanks, are the mains. That means the pilot should plan the flight and manage fuel to assure there is enough out there to descend, land and divert. That is weight and mass out on the end of a lever, but that’s the way it works. (More about the fuel system later.) While the tendency is more pronounced in the shorter versions of the 310, any of the tip-tanked twin Cessnas can be encouraged to gyrate around an elusive point, particularly in approach configuration.
Generally speaking, the 320 shares similar handling characteristics with other Cessnas: fairly linear, smooth and comparably light aileron response, pretty good rudder response and heavy pitch forces. The latter have to be alleviated with trim input. It does come with training and some practice-and good anticipation.
Once the yaw instability characteristics are understood and controlled, the 320 is a solid airplane. In terms of handling, it is a comfortable instrument platform and it handles turbulence well.
While greasers are hard to achieve, good landings are not. Another advantageous characteristic, particularly in times of stress, is that the 320 can be planted on the runway without bounce or float, and it will stop flying.
Speed control is doubly important for the 300 series. Sample, practice and stick to the limiting speeds, and the 320 is very manageable. Ignore or abuse them, and trouble can ensue. When the 320 runs out of sufficient airspeed for directional control or for sustained flight, it quits-frequently with a bang. Like its stablemates, the 320 rewards good training and disciplined procedures. It can be very unforgiving of the unskilled and the careless.
Takeoff challenge
The period of greatest exposure is the takeoff. The gear is relatively slow to retract (and the pilot must remember to tap the brakes before selecting gear up to preclude possible rubbing or binding during retraction that can result in hung gear).
While a number of pilots think speed is the best goal after lift off, tests on a variety of 300 series twins shows that altitude is more important. Initial climb should be at best rate speed (105 KIAS) at least until the gear is fully up and locked. The key consideration governing departure and approach is engine failure.
The best procedure during approach is to maintain a higher than normal speed with only the first notch (15 deg) of flaps extended until landing is assured. This provides enough airspeed and a configuration to enable the competent pilot to execute a single-engine missed approach or balked landing.
For example, 320D book stall speeds are 75 KIAS clean and 66 KIAS in landing configuration. Vmc (minimum control speed) is 78 KIAS and Vsse (safe single engine stall) 91. Vy and Vyse (best single-engine rate of climb) are within less than one knot of each other (103.4 and 104.3). An approach speed of 120 KIAS, which seems hot, provides greater stability and, if an engine fails, should allow the pilot to recognize it and take action without getting below Vyse.
Speed control of the 320 is fairly easy. While 120 knots might seem excessive, extension of full flaps at the commitment point helps bleed that off quickly without jockeying the throttles or touching down at higher than recommended speed.
An approach speed at or below 105 KIAS, on the other hand, leaves the prudent pilot with one decision to make: where to put the airplane down.
Engine management from start to cool down and shut down is another important element.
Cabin comfort
Well soundproofed and well-maintained 320s can be very comfortable for both pilot and passengers. Passenger head, shoulder and leg room and visibility are more than ample.
My (significant other) loves the 320, but felt claustrophobic in the Baron, one owner writes.
Aside from considerations of weight and balance, with six seats filled, baggage space is limited. For later versions with the nacelle lockers, there are added loading options to carrying bags in your lap or under your legs. There is some room behind the fifth and sixth seats, but do not plan to carry much hard luggage with seats filled. However, compared to most other light twins, space for people and their belongings is generous.
CG range is good, but narrow. It pays to run a lot of exercises. Pilots new to the airplane should especially look for changes between full and low fuel loads. So CG should be calculated for beginning and end of flight.
Cockpit design
The 320 is a high workload airplane that rewards good operating procedures and technique. It can be quite intolerant of carelessness or ignorance. It is not a forgiving airplane.
The cockpits of many 320s are in the original, haphazard configuration. This taxes scan habits and raises pilot workload. Radios frequently are scattered across the panel, wherever there was space at the time, rather than neatly grouped in a stack. Pilots used to flying relatively modern airplanes with reasonably logical panel arrangement need to be particularly wary. The non-standard location of instruments, gauges and switches together with a variety of lighting results in a lot of potential traps for the unfamiliar pilot.
System management requires a lot of study, practice and thought, too. For instance, the fuel system requires planning and true management far beyond time, power setting and range calculations. Refueling has to be monitored for a couple of reasons. As was mentioned earlier, the tip tanks are frequently mistaken for auxiliary tanks and the aux. tanks in the wings for mains. At a high fill rate, fuel in the mains will swirl, leading line people to stop pumping before the tanks are full. Also, the aux. tanks are relatively shallow. Careless insertion of a fuel nozzle can damage the tank.
The fuel selector system is a bit of a Rube Goldberg design. Over time, pieces can wear and actuating rods and levers can bend. Careful inspection and preventive maintenance are very important. Fuel system plumbing also is quite complex, with aux. tank vent and return lines running to the mains.
The electric auxiliary fuel pumps are critical elements of the system both for proper operation but also as part of fuel system management from preflight through engine shut down. One element of the electric pump system is the engine primer system. Simultaneous use of primer and aux. pump can result in fuel pooling and engine fire.
Poor in-flight fuel management can lead to grief. A good rule of thumb is to run on the mains for at least one hour. Some pilots prefer to burn from the mains until one-half is consumed. (At high power settings, such as extended max. power climb, 25 gallons a side can be burned in less than an hour.) The quantity gauge needles will be pointing at each other. This procedure assures ample space in the mains for return fuel (otherwise, it can siphon overboard). Then aux. fuel is selected until it is time to descend, at which point mains must be selected since aux. fuel is to be used only in level flight.
Maintenance record
Nearly half of the service difficulty reports (SDRs) filed with FAA on the 320 series during the representative six-year period we examined concerned the landing gear-of which the nose gear is the most troublesome.
Somewhat surprisingly, there were none on cracked crankcases or cylinders, and only one on magnetos. There were three reports of corrosion, which also is low for this type of airplane. Two reported problems with the seat tracks.
The SDRs suggest that prospective owners should look for unauthorized repairs and modifications. Several reported unrecorded mods. One reported interference with elevator control that was traced to installation of a stereo system that obstructed the control column.
Another condition to watch for is accumulation of wiring and tubing from removed avionics and other accessories. Not only can this get in the way; it can add up to considerable weight.
Airworthiness Directives
Aside from the widely applicable Airworthiness Directives that affect accessories such as magnetos in many airplanes, relatively few ADs have been issued against the 320. Most of them are concerned with the fuel, turbo, exhaust (75-23-8 requires 50-hour repetitive inspections) and electrical systems.
Recent and notable ADs include: 97-18-2, repetitive inspection of the prop; 96-20-7, repetitive inspection of the Janitrol cabin heater; 96-12-22, repetitive inspection of the oil filter adapters; and 94-17-13, repetitive prop inspections.
The most recent type-specific AD, 90-02-13, covers the main landing gear barrel inner bearings. It applies to the 310, 340 and all piston-powered 400 series Cessnas except those with trailing link main gear. It requires inspections for cracks, including magnetic particle inspection every 1,000 hours or the replacement of the bearings with an improved part.
Focus on three areas
Three specific areas should be given special attention on C-320s. All elements of the turbo system, but particularly the exhaust, need to be regularly inspected and well maintained.
Related to the exhaust path of the 320, careful and repeated internal inspection of the wing structure beneath and aft of the exhaust system is needed to monitor for corrosion.
The entire landing gear system is showing the effects of poor design, age and abuse. The nose gear is most sensitive, but the entire system should be treated to careful and regular inspection, adjustment and rigging.
A lot of the gear system is hidden beneath floor boards and other skin. The actuating bell crank and torque tube are under the floor board in front of the pilot seat, for instance. There have been many instances of these bending or breaking.
The tenderness of the gear is in part a product of pilot technique. Too many fliers land nose-gear first or three-point them. Crosswind technique is not always what it ought to be, too, and higher than designed-for side loads are imposed.
Both the nose and main gear and their actuating and attach fittings need care. Larry A. Ball, president of the Twin Cessna Flyer, points out that there have been a number of cracked wing ribs at the main landing gear side brace attach point. Cessna issued a service bulletin (ME76-2) on the problem in January, 1976. A related service kit was developed. Ball, who says his organization has 1,500 owners of twin Cessnas, notes that very few 320s have had this kit installed. Depending on the model, the cost will run from three to eight thousand dollars.
Parts availability
The age of the 320 and its relatively low production run present some difficulties to owners and potential buyers. Legend has it that when the 310 line shut down for the last time in 1982, irreplaceable skills were lost. That legend says no two tip-tanked 300 series Cessnas were the same; each was form-fitted (or beaten into shape with stone hammers).
Whatever the case, the situation today is that thanks even more to availability than from price, a Cessna 320 owner in need of parts probably will find the best source to be the wreckers yards (look in Trade-a-Plane under parting out, for instance). This applies to accessories as well as airframe elements.
The owner who has to pay for a mechanic to learn the intricacies and tricks-and for the time to chase scarce parts-required to maintain a 320 and similar vintage aircraft is going to be faced with very high bills (to avoid excessive metaphor).
Now more than ever, the amount of time, effort and money spent before purchase of almost any airplane, but especially relics like the 320, will be rewarded. Unless you are truly rich, this is no place for impulse purchases.
Engines
People are being warned off the earlier versions with the 260-HP TSIO-470-B engines. One Aviation Consumer reader warns that parts for that engine series are very hard to find, especially pistons.
Other sources say this is not the case. Not all of the companies we contacted about engine questions responded by press time. This much is known: parts, including core components, can be obtained for the 470 series engines. However, Teledyne Continental does not offer it in that company’s factory remanufacture program, which indicates marginal factory support, at best.
A great many shops are experienced in overhauling and repairing this series of Continental engines. The most important consideration is not price. It is thoroughness and quality.
Both the 470 and 520 engines share the crankcase cracking and cylinder cracking problem so common to Continental powerplants. Some 320s have been converted to heavier cases.
But some later model 320s have the permamold case that is more susceptible to cracking than the sand cast cases. The permamold cases have an AD that requires inspection for cracks every 35 hours of operation.
Aside from the turbo system itself, the 320, like many turbocharged airplanes, has troublesome exhaust systems, particularly slip joints. Regular, thorough inspection is a must.
The higher temperatures within the nacelles takes a toll on accessories and other elements such as hoses, lines and baffles. These, too, need regular attention.
Mods, clubs
Mods include vortex generators from Robinson and Micro Aerodynamics and engine upgrades from RAM.
As far as owner support groups go, probably the best known is the Cessna Pilots Association (www.cessna.org, (805) 922-2580). Another that caters to Cessna twin owners is The Twin Cessna Flyer, (219) 749-2520. Both are well worth the price of admission.
Summary
If performance and two engines are among your requirements, the 320 looks like a bargain even if you take the steps and spend the bucks to make it nearly new. If your twin flying experience consists of 10 hours in a Seminole or even a Seneca, the 320 most definitely is not recommended.
A number of 320s look pretty good cosmetically, but are lacking in basics. Probably the best strategy for enjoying this bargain is to add $75,000 to $100,000 to the purchase kitty. Propulsion system upgrades, avionics replacement and detailed reconstruction of everything else would put a flight trustworthy 320 in your hangar for less than $200,000.
Owner Comments
We bought our 320D in 1988, and it has proved to be the right choice for us. It is used most for recreational travel, and an occasional business trip.
It is a family vehicle with ample room for me, my wife and two grown daughters and all the stuff they each insist on taking-plus skis, boots, poles or fishing gear, plus the inevitable treasures to bring home. The room and performance off high-altitude runways are a pleasure. Previously owned Bonanzas and a B-55 Baron were cramped by comparison.
Added benefits include large tires and good prop clearance for the many dirt runways we frequent in Baja and Canada. Prop filing was common after almost every trip in the Baron to an unpaved strip.
Handling is a plus with the 320. The long fuselage is a stabilizer, and it lands and takes off short for a high-speed twin. Slow flight is easy, and the split flaps do a good job of speed control on final. The early 310s reputation for yaw and Dutch rolls is not evident in our 320.
Maintenance is routine. I work with a freelance A&P/IA and we have avoided any big expenses. The TSIO-520B engines are great. The previous owner was good with them, and we have had good luck since we took over.
We recommend the 310 Owners Assn. for technical tips and assistance in addition to The Aviation Consumer and LightPlane Maintenance.
We paid $26,000 in 1988 when the twin market was low. We have upgraded and improved about $15,000 and the airplane is worth about $50,000, even with one high-time engine. Yes, we are happy with our 320D.
-George Saunder
San Jose, Calif.
I have owned two 1968 320F Skyknights. The first had very few problems, and we found the engines to be very dependable.
We normally flew the airplane at about 15,000-16,000 feet, truing out at approximately 220-225 knots, burning about 30-31 GPH. I loved the airplane because of the size. Its substantially larger than the 310.
Its just too bad that it doesn’t have an airstair door. We found parts to be fairly reasonable, and fairly easy to get hold of through the various parts facilities and wrecking yards.
In all, we’ve extremely satisfied with the Skyknight. As far as maintenance costs are concerned, I don’t find it any more expensive to operate than a turbo Cessna 310 would have been, even though the airframe is bigger.
-Harry B. Pravorne
San Diego, Calif.
If you want a machine that will handle six people, reasonable fuel loads and work well on hot days at high altitudes, the Skyknight is going to do the job for less than half the purchase cost of a comparable twin. The Skyknight has the ability to cruise along in the mid teens burning 30 GPH at well over 200 knots.
There are some snakes in the woodpile that are very worthy of mention. The 320 through 320C models (1962 through 1965) are powered by Cont. 260-HP TSIO-470-B engines, and parts are very hard to find, at best. We have been searching avidly for new pistons for the engine, and our efforts lead us to believe that there are no new pistons available anywhere at this time.
While parts for the 285-HP engines are more readily available, they have a rather long history of cylinder and case cracks that have been the subject of several SBs and ADs. When it comes time for engine overhaul, you are faced with the added cost of rebuilding turbochargers. The exhaust system must be watched carefully, as with all turbocharged engines.
As with any twin Cessna with electro-mechanical landing gear, a large share of the Skyknights have found themselves on their noses a the wrong time with the engines turning. The bellcrank (P/N 0842102-2) under the pilots feet that extends the nose gear has a high failure rate and should be carefully inspected each annual or 100 hours. The landing gear should be completely rigged at each annual or 200 hours.
The 320 has very few ADs compared to other light twins. We have seen incidents of cracks in the wing ribs where the main landing gear side braces attach. This was addressed by Cessna with Service Kit SK414-8E through SB ME76-2 in 1976.
Very few airframes have had this accomplished, and we are finding that as the aircraft get up in years and hours, this becomes necessary. The cost for installation of SK414-8E can set the owner back between $3,000 and $8,000, depending on the model.
If I were actively searching for a turbocharged twin, and my budget was limited, one of my first considerations would be a 320D through 320F. With a little well-thought-out maintenance and care, there is a tremendous amount of aircraft available for the dollar. We have a large number of 320 owners in our organization that are very satisfied with their airplane. We even have one owner who has a one-time approval for club seating.
Just remember, the newest Skyknight is 24 years old. If the same aircraft were available in todays market, the price would probably be well over $500,000
-Larry A. Ball, President
The Twin Cessna Flyer
New Haven, Ind.
Also With This Article
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