Ready For Action . . .
A Much Modified KR-1 With A British Accent
By Richard Kunc, EAA 146954
1434 W. Fairbanks Ave.
Winter Park, FL. 32789
"Dogsbody, Dogsbody, Beetle calling, Beetle calling."
"Hallo Beetle, Dogsbody answering. Over.
"Hallo Douglas, vector one-three-five. Bandits ahead of you, angels one-five. Over.
"Hallo Woodie. Tally-ho! Am attacking now! Out!"
Outnumbered six to one, quickly patched battle-wary Spitfires rose from a country aerodrome to beat back the avaricious Hun. It was routine. It was barbarous, unhinging, aging, addictive to some, but routine nonetheless. It was a long war.
One of those gallant Englishmen was Douglas Bader, the legless Spitfire wing commander shot down over France in August '41. "Dogsbody", as he was dubbed by Group Captain Woodhall, his alterego ground controller, personified the dash, courage, and calm resolve of the outnumbered pilots who fought the Battle of Britain. It is in his honor that my little airplane is marked.
I'm a soliary aviator. When I leave the ground, I like to leave the world behind, so a single-seater was for me. I don't ever want to grow all the way up, and sometimes the Waiter Mitty in me likes to leave 1990 behind, too. So needed an airplane with the guts and romance of a World War II fighter, something with some zip and personality. But who can afford a REAL Spit or Mustang?
I started with some design goals and some economic realities. Single seat. Proven design. Fast. Simple. Adaptable. Versatile. Garage buildable. Inexpensive, whatever that means. In 1982, the Volkswagen-powered KR-1 was the only design I liked that hit all these targets.
For you history students, the KRs were early adventures in "composite" construction. Even today, they are a lot of great flying for very few dollars. The basic KR airframe is traditional in design, easy to build, and very strong. It has a spruce and plywood fuselage, spruce and plywood box spars in the wings, and spruce spars and ribs in the empennage. Designer Ken Rand used the foam, glass, and resin primarily to form airfoils and contours, not as structural materials. The KR-1 is stressed to plus and minus 9 Gs, and the KR-2 for 7. I'm only stressed to about 2, so I guess I'm pretty safe. The KRs have excellent safety records, and builders have customized the stuffing out of it without creating problems. There are ZERO prefab KR-1 pieces, unless you count one particularly ugly cowling and the standard teardrop canopy. This is no airplane you take out of a box in so many premolded, prefinished pieces and glue together. You make EVERYTHING. This is REAL homebuilding. Remember?
The idea of VW power was attractive, too. I'd built up some special VW engines for the street, and had a healthy respect for the plucky little four-banger. At that time, a lot of "experts" were saying that the VW had no business turning a propeller, and that only certified engines were safe. My guess was that most of the people who were maligning it had no experience with it as an aircraft engine. Seems to me that any engine is only as good as the last guy who worked on it. I've seen plenty of certified engines that unravelled after lots of high-priced official service. And the 3.5 gallons an hour a VW burns is hard to beat.
The keys to safe, successful "personalization" are realistic expectations, careful planning, and lots of homework. You can't get 300 mph out of 60 hp, and a KR-1 wasn't meant to carry a full IFR panel. So, starting with the basic KR-1 plans, I began my customization program. Some of the modifications were deliberate, planned out way ahead, like the sliding canopy, the redesigned gear latch system, and the improved control system. Others came along as the results of problem solving and discovery of alternative approaches and materials. All modifications were made to improve performance; none for purely cosmetic reasons. All were thought out on computer and paper long before picking up a hammer or a chainsaw, and all perform beautifully. This dreaming and designing and building and trying is what homebuilding is really all about.
The only major performance problem was caused by an error in the plans, an error I didn't discover until it was too late. The wing's angle of incidence was mistakenly given as 5 degrees instead of 3.5. This gave the airplane a strong nose-up tendency that intensified with speed. That first flight was very interesting.
Resetting the wing was impossible, so the only answer was to reset the horizontal stabilizer's angle of incidence to compensate. One little problem. The stabilizer was now permanently webbed and epoxied in place. But with great care and the invention of some special "shade tree" tools, I finally cut it loose. The proper new angle was calculated, but calculatin' ain't flyin'. So I designed an aluminum bracket that would hold the stabilizer very securely, yet permit adjustments until the ideal angle was found. It took about three tries. Incidentally, the fairings where the tail feathers join the fuselage were made removable. I didn't like the idea of sealing up so many important nuts, bolts, brackets and things.
The KR is notorious for its touchy elevator and annoying porpoising tendency at low speeds. Many a rookie KR driver has nearly lost it when approaching at low speed or when ducking down to work that unfriendly gear lever. It seemed to me that the sensitivity was the result of (1) high-ratio linkage between the stick and the elevator, (2) long unsupported cables running the length of the fuselage, and (3) very little stick feel. So, I designed a new elevator control system. The front portion starts with an elevator/mixer connected through a push-pull tube to a cable bellcrank aft of the seat. A choice of tube attach points on the bellcrank lets me vary the sensitivity of the elevator without distorting the parallelogram of the cables that follow. The aft section is still cables, but now they're much shorter. The resulting system is tight, precise and adjustable.
I wanted internal elevator trim, so a balanced elevator was in order. The plans don't call for balancing anything but the ailerons, but it's a good idea, especially at the high Mach numbers I'd be hitting. The computer came in handy here working out shapes and arcs and stuff. The molded lead weight is entirely internal and hidden from view.
The trim system is basically a bungee (surgical rubber tubing) running parallel to the push-pull tube and linked center-to-center to it. Adjusting the position of the bungee in relation to the tube applies fore or aft "influence", and also gives the stick a nice firm feel, something the average KR lacks.
The first five versions of the system had a center stick. Then I flew the Dragonfly prototype with Rex Taylor, and fell in love with the sidearm stick ... even though it wasn't classic WW-II fighter stuff. The next two versions were sidearm, and the final system is a joy to use.
The aileron and rudder controls are pretty standard, but I added similar bungee trim systems to them, too. Few KRs will fly straight and level, hands off. I like to fly formation with my hangarmate's KR-2, and the three-axis trim helps a lot. To give me a little more climb and a little lower landing speed, I added 11" to each wing, ending in handcarved tips. The ailerons, by the way, are solid rather than hollow.
After hearing all the horror stories about KR gear collapses, I redesigned the gear latching system. The original setup used Mickey Mousetrap coil springs to hold one chunk of aluminum in notches cut in another. One good runway rut and it's bye-bye prop. My system uses heavy-gauge moving tabs locked with hardened steel pins to heavy-gauge stationary plates at the gearup and gear-down positions. It's extremely positive and completely unaffected by vibration. The actuating handle is shaped to provide easy one-hand operation without crawling under the instrument panel. It works like a charm and it's very easy to use.
At the aft end, I junked the usual spring steel KR tailwheel business. Instead, I adapted the pultruded glass spring and sheet steel fork of the Dragonfly. The wheel came from a company that makes shopping carts. "Would a red wheel be at all right?" the guy asked. It's taken some pretty brutal landings without any problems.
Rather than glassing everything together permanently, I made the front deck removable, with the windscreen and fuel tank attached. This lets me get at the rudder pedals, the engine mount hardware, the back of the instrument panel, and so forth. It makes maintenance and inspections MUCH easier, and does a lot for my peace of mind, too.
The usual side-hinged teardrop KR-1 canopy is awful. Waiting for the runway under one of those things in hot Florida summer weather is pure torture. Besides, Captain Mitty wanted a sliding canopy so his white scarf could flap in the breeze as he taxied back after a mission. My canopy was cut down from (I think) an imperfect Starduster canopy, and mounted backwards on disappearing slides made from heavy-duty aluminum drawer slides, U. S. Government surplus. It took four months of tedious work and more special shade tree tools to get it right.
If you make the rear deck according to the plans, gluing soft foam strips together and glassing the outside only, you end up with an irregular surface with little strength. More Dragonfly technology here. I pressed cross-scored half-inch Clark Foam into a female wooden mold and then glassed the inside. After popping it out, I glassed the other side and wound up with a VERY strong and graceful rear deck, ready to bond onto the fuselage longerons. The same light, strong sandwich structure makes up the turnover bracing just behind my head.
I didn't like the lines of the only available cowling, so I built one. But first I did lots of homework about inlet areas and outlet areas and internal air flow. Very important stuff. Hot engines die young.
The suggested method of gluing blocks of foam around the engine and then carving yourself a cowling is messy and laborious. It's nearly impossible to produce a cowling of uniform thickness, so they tend to be quite heavy when glassed.
I started with the graceful Dragonfly spinner and worked aft toward the firewall. My cowling was built in several sections from a wonderful quarter-inch-thick foam called Divinycell. At room temperature, Divinycell is rigid. But at about 200 degrees it becomes about as pliable as toast. You can bend it and shape it any way you want. Then, when it cools, it holds its new shape. I shaped the canopy in sections, right over the engine. The shaped sections were then sewn together (that's what I said) and the assembled cowling glassed inside and out. The result is a light, strong cowling that looks great.
The canvas sling seat shown in the plans is a real backbreaker. Anything over five minutes in it is cruel and unusual punishment. My seat is patterned after the orthopaedically designed seats in those high-priced jacuzzi whirlpool deals. The foam seat and backrest were sculpted to fit my personal anatomy, then covered with glass and resin. So far, I've felt no need to add any padding.
The venerable VW engine is a monument to simplicity and reliability. The one in my airplane follows that philosophy, with no "hot redding" whatsoever. It may put out only 65 horsepower, but it'll crank out those horses all day long without working up a sweat. I used Hex Taylor's engine building book, the very best parts I could buy, and put it all together myself. It's an 1835 with single-port heads, a HAPI UltraCarb, and single electronic ignition. That means I use regular auto-type plugs and auto-type plug wires, and have no radio noise. Since this ignition must have an external source of voltage, I carry two batteries, just in case.
How does it fly? It lifts off at about 70, climbs easily at 1000 feet a minute, cruises at 150, tops out at 160, and comes over the fence comfortably at 75. But those are just numbers ...
Climbing up onto the port wing and sliding down into the snug, all-business cockpit, my hands fall naturally to stick and throttle. A quick pre-start check, and then the prop begins to swing. One turn, two turns, three turns, and then she catches. The sound of caged excitement blocks out everything else. She warms from rough to smooth, and we taxi out. Check the carb heat, scan the gauges, and we're ready. Canopy latched, throttle coming open, tail up. She breaks ground and the gear snaps up over the end of the runway. Climbing steeply, we're on our way into the spanking blue.
"Hallo Dogsbody, Beetle calling. Hawks in the sun. Hawks in the sun. Closing rapidly from the Southwest. Vector one-nine-zero. Seventy plus bandits approaching Tangmere. Buster. Out."