Flying the Wren
Last year, I had a friend ask me to find him an airplane. That's always a loaded and open-ended task. Another friend told him "You ought to buy a Super Cub." Most aircraft dealers would be happy to find just the kind of airplane the customer asked for - but this man is a friend - and I knew a Super Cub was not the airplane for him. I asked him to better define his intended mission - and his budget.
The prospective airplane owner is an avid hunter. To support his hunting habit, he owns several farms within a 500 mile radius - both for the hunting and as working farms. He also has a circle of friends with similar interests. He wanted to be able to fly to his farms for business and for hunting.
Super Cubs are revered for back-country flying and operation from short or unimproved airstrips. The shortcoming of the Super Cub is that they have little interior room for all of the "stuff" that hunters carry with them - shotguns, rifles, decoys, ammo, hunting apparel for every contingency, blinds, perhaps a dog or two ... he needed a larger airplane.
I showed him a Maule - an airplane that offered far more interior room, cargo doors, speed, and range - all while retaining good short-field capabilities. I explained that it addressed all of his needs, but for some reason, he just wasn't excited about it. He asked about tricycle gear - I explained that tri-gear airplanes have been used by Flying Farmers for decades, but there were some attributes of "conventional gear" that he might need. I asked him if outfitting the airplane for floats or skis was important to him - "not really." He was more interested in being able to operate from unimproved airstrips.
I showed him my Cessna 206 - he liked it, but thought that "I don't need all that room." (I tried to explain to him that for a hunter and a pilot, there was no such thing as "too much room.") I showed him a Cessna 182 - it was more to his liking. I explained that the 182 could be outfitted with oversized tires, and that for uses similar to his anticipated use, many aircraft had been modified with Robertson Short Takeoff and Landing (STOL) modifications. Without ever seeing one, he said "that's our airplane - find me one."
I started out looking for Robertson STOL-modified airplanes - and found a few. To demonstrate the capabilities of the breed, I also showed him a video of a Katmai-modified 182. It's pretty impressive - and so is the price--$299,500 for a freshly-converted airplane - especially for someone that had yet to take his first flight lesson. He was interested, though. In the trade we call this "mission creep" - buyers constantly expand their perceived missions for the airplane, causing them to buy more airplane than they really need. While it is a great airplane, it was simply more money than I thought he should spend. Back to a R/STOL modified 182.
While researching the market, I found another airplane for sale - something of a rarity. It was a 1968 WREN-460 conversion on a Cessna 182. It was low time - IFR equipped with modern avionics (including a $15,000 Garmin 530 WAAS and JPI engine analyzer). It had heavy-duty landing gear and speed mods. Obviously, somebody had been taking care of the airplane. Best of all, it was priced under $100,000. I made the call - the owner had tried to sell it but died only the week before - so I talked with his wife. Because of the owner's illness, the aircraft had only been flown a few times in the last six months. I called an aircraft dealer friend in the area to have him look at it. The airplane was as advertised - so we bought it. The only disappointment - the owner had sold the 29" Alaska Bushwheels just before he died.
The Wren was the brainchild of master aircraft modifier Jim Robertson, who went on to develop the R/STOL system, and the "Blended Winglets" seen on Boeing jets and numerous bizjets. Robertson saw the need for a relatively simple off-the-shelf airplane for civil and military use from unprepared fields. (There are some that say that he was urged by the government--military and "clandestine ops"--to develop cheaper and easier-to-fly aircraft that could match the performance of the Helio Courier). He wanted tricycle landing gear and a big engine for performance carrying heavy loads, so he chose the proven Cessna 182 as the base airplane. To get the short-field performance, he not only installed the recontoured wing leading edge and the drooping ailerons that he would later adopt for the R/STOL system, but he made both the ailerons and flaps double-slotted as well. To give more pitch authority for operating out of soft or rough fields, he made the entire horizontal stabilizer moveable (much like the Cessna 180/185) moveable with flap extension. This coupling had the added bonus of not requiring big pitch changes with flap extension or retraction.
He also utilized the forward canard elevator. Located in the propeller slip stream, the forward canard helps lift the nose off the ground right away with full power. By requiring less "down force" on the tailplane, the aircraft becomes a "three-surface" airplane like the Piaggio Avanti business turboprop. As a result - the airplane is capable of flying at low speeds in an almost-level attitude. To maintain aileron effectiveness at low speed and to keep the stall from progressing from the wing root to the tips, he installed the trademark "Wren's Teeth" - 5 moveable devices on the top of each wing. The Wren's Teeth are normally streamlined into the wind. At low speeds, they act like a wing fence to prevent spanwise stalling.
They improve handling at slow speed by angling outboard with aileron deflection - causing drag on the "down" wing and pivoting the aircraft into the turn - eliminating adverse aileron yaw. The result is an airplane that can fly as slow as an advertised 26 statute miles per hour at an almost level attitude, with complete control!
I had seen the aircraft in action while based in San Antonio while serving in the Army in 1967. A local TV station had one instead of a helicopter for traffic reporting and getting to news scenes away from the City. It was regularly featured in their advertising, but it wasn't long until several worriers became afraid - "What would happen if the engine quit above the city? Where would it land?" (Never mind that the same question was not asked about news helicopters). Rather than shy from the possible negative publicity, the TV station met the issue head-on - explaining the superior glide capability of the aircraft, then marking out a regulation heliport on the airport and operating the Wren from it - featuring it on their TV promotions. It was the end of the opposition - it has been said to "never argue with a publisher that buys ink by the barrel" - DOUBLE that for television!
The Wren folks also engaged in some surprising publicity stunts. They landed the aircraft on a football field - stopping at the 50 yard line. They then took off from the same 50 yard line, spiraling up out of the field-never leaving the dimensions of the field. The aircraft was advertised as having a radius of turn of only 150 to 200 feet! On another occasion, Wren applied for FAA approval of IFR minimums applicable to helicopters for the Wren due to its helicopter-like approach speeds. The FAA denied them the special certification at the time, but the point was made - most light helicopters at the time were incapable of IFR certification anyway. (Side note: Today, the Wren COULD be certified for CAT II IFR single-pilot approaches for non-revenue flights, as the approach speed is less than 91 knots.) The Wren provided most of the capability of a helicopter, at a fraction of the cost.
Here are the advertised performance numbers for the airplane:
Cruise speed 148 mph
Optimum range 84 gallons 1150 miles
Rate of climb 1080 fpm
Takeoff run gross 300 feet. 605' over 50' obstacle
Landing 300'. 612' over 50' obstacle
Useful load 936 Lb.
FLYING THE WREN
When we took delivery, we embarked on a careful checkout of the capabilities of the aircraft. Some observations:
• One of the biggest changes-because of the huge flaps, extension speed is limited to 90 mph. The 40 degree position of extension is eliminated. Unlike unmodified Cessnas, there is no pitch change with flap extension or retraction.
• Normal takeoffs are conducted with 10 degrees, 20 degrees, or zero flaps (though 20 degrees is more fun!) STOL takeoffs are done with 30 degrees of flaps.
• The nose can be raised off the ground by the time the power comes up, minimizing any concern about soft or rough fields.
• Like almost all aircraft with drooped ailerons, roll control is diminished with flap extension - HOWEVER-roll control is better than a Robertson-only system-probably due to the "Wren's Teeth."
• The aircraft rolls much faster when you use the rudder aggressively into the turn.
• For steeper landing over an obstacle, there is no prohibition on slipping with flaps extended.
• Stalls are straightforward, with lots of warning. The stall breaks straight ahead, even in a turn or when aggravated by rudder (the aircraft is placarded against intentional spins). The nose attitude is not nearly as high with power-on as a normal 182 - no feeling of "hanging it on the prop."
• Pilots of big-engine Cessna singles are used to dragging the aircraft in with power in a nose-high attitude. The Wren approaches in a more or less level attitude. Couple that with the very low approach speeds (50 mph indicated is comfortable with an experienced pilot and typical landing weights) usually results in some float until you get used to it.
• I can't quite match the book stall speeds, but they are close. Using the GPS ground speed on the 4 compass headings averaged 29 statute mph power-on (the book says 26-still impressive!). I can't quite match the short-field numbers claimed as well, but takeoff and landing runs of around 300' on a no-wind evening are easily obtainable. The difference might be due to the derring-do difference between the test pilot and me-but if you REALLY need the 50 feet between the listed distance and what I am able to get, perhaps you would be better off with that helicopter!
• Cruise speeds. The Robertson handbook is quite forthright - it says that the modifications will cost you 9 statute miles per hour at max cruise. That's not a bad tradeoff for the safety and utility gained by the STOL mods - it still gives you a max cruise in the 145-150 mph range. The differences can be mitigated by selecting lower power for cruise, installing the speed fairings, or going high where the drag is less.
• If you don't have the big Bushwheels installed, the Maple Leaf speed wheel fairing mods are available for the 6:00X6 wheels or the optional 8:50X6 tires. Operators of Cessna 206s I've talked to with the Maple Leaf fairings are complimentary about the results. If you want to re-install the Bushwheels, the drag will cost you 5-8 mph over the cruise speed of the normal un-faired wheels.
• The airplane was never certified on floats. Skis and wheel-skis can be fitted.
• Parts are not a problem. Most of the airframe is Cessna. Petersen Aviation of El Dorado, KS. holds the STC, and can supply most parts.
• Engine mods-the 230 h.p. Continental can be swapped for a 260 h.p. IO-470, a 300 h.p. IO-520, or an IO-550 if you need even more performance.
Why was the Wren not successful? There are several reasons:
• The airframes were purchased new from Cessna, then flown to the Wren modification center where they were disassembled and modified - adding to cost.
• There was (and continues to be) a bias against tri-gear airplanes as "not really bush planes." That's understandable, but an aircraft like the Wren shows that it IS up to matching taildraggers in performance.
• Lack of a dealer network. In the 60s, Cessna dealers were selling all of the 182s they could get their hands on anyway - no need to sell the mod.
• Helicopters with turbine engines became available, offering much of the speed and lifting capability of an airplane - though at much higher cost.
• With the exception of Alaska, the FAA seems to consider operating from anything other than a licensed airport as potentially "careless and reckless," with any incident subject to investigation.
• The Wren was expensive to modify, with all of the high-lift devices. Jim Robertson himself developed the Robertson STOL kits - utilizing the drooped leading edge and drooped ailerons. Todd Petersen - builder of the Katmai - acquired the STC for the Wren. To save manufacturing costs, he eliminated the double-slotted ailerons and flaps, the Wren's teeth, and the synchronized stabilizer - retaining the drooped ailerons, the drooped leading edge, and the canard. To recapture some of the lost short-field performance, he added wingtip extensions and made bigger engines available - up to the IO-550 Continental. The result (called the Katmai) was an aircraft that did much of what the Wren did, at a lower cost to manufacture. These airplanes offer marked improvement to the performance on the 182 - but if you REALLY NEED the extra performance, nothing less than the full Wren mods will do.
STOL flying is fun. One of the great things about helicopter flying is indulging the pilot's wish to land almost anywhere - and STOL airplanes are a much cheaper way to accomplish that wish. They are safer than standard airplanes - almost any patch of ground that is over 300' long and able to be driven upon by a pickup or ATV is an emergency field. In the event that there is NOT a suitable landing field, the very slow stall speed of a STOL airplane means much less dire consequences for the occupants.
At a local airport, the cross runways diverge by 60 degrees. During a demo, the wind split the difference between the two runways. The paved intersection at the ends of the runways is 400' wide - more than enough for the Wren - and either runway is available only 30 degrees from the takeoff heading in case of an emergency. First time passengers are amazed and slightly nervous when we line up with only 400' of runway ahead. It's fun to visit friends with farm strips - including a former ultralight strip only 1000' long with trees on the ends. Yes - Super Cub pilots may still have an edge in STOL performance - but let's see them do that with two hunters and a quarter-ton of gear on board!
Unfortunately, the aircraft is for sale again. The owner developed a medical condition that may or may not be waivered. Even if a "driver's license medical" is eventually adopted, he will not feel comfortable flying passengers. If you have the need or desire for a well-equipped STOL airplane please give me a call. It would be even BETTER if you lived close to Albert Lea and would let me continue to fly it!
Jim Hanson has been the operator at Albert Lea Airport for 33 years. He has owned 547 airplanes, and the Wren marks 318 unique types of airplanes he has flown. Jim loves "working" airplanes - those that earn their keep instead of being "Hangar Queens." He especially likes all STOL airplanes - he even has a T-shirt that says "Fly it like you STOL it! Jim can be reached at his airport office at 507.373.0608, or firstname.lastname@example.org