NONPAREIL KR 2 PILOT
Articles and Photos
By Jack Cox
Unless someone who has been skulking around the airways unseen and therefore unheralded can step forward to claim otherwise, Dan Diehl of Tusla has to be the current high time KR-2 pilot. He has over 600 hours on his light blue N4DD and is a regular at the major fly ins around the country (Sun 'N Fun excepted -- he's been weathered out of that one for four years running!).
Dan's KR-2 was the third one to fly - preceded only by the prototype and Wicks Aircraft's N100W. It was started in November of 1974 and flew the following July.
Choosing a KR-2 as his project was based on Dan's previous hobby -- nearly 13 years of off-road racing in VW powered buggies. Whatever his plane was, it had to be powered by a VW. After graduation from Oklahoma State, he decided the time had come to fulfill his dream of owning an airplane, so a study was made of the various homebuilt offerings. A VP-2 seemed to be the ticket for a time, but then Ken Rand introduced his KR-2. A rundown of specs impressed Dan to the extent that he had his checkbook out in a flash to order plans.
This was Dan's first aircraft building project, so to stay on the conservative side he followed the plans faithfully ... until he came to the canopy. His father is 6' 2" and would want to fly some, so the cabin and canopy had to be enlarged somewhat to accommodate taller people. Gull wing doors similar to those on Emeraude plans were adapted and a windshield was formed to make the new hatch flow in to the KR's fuselage lines.
In anticipation of a lot of flying near gross weight, an inch was sawed off each end of the landing gear spring bar to make it a little stiffer. The only other change was to use fiber glass cloth on the wings rather than Dynel. The latter was used on the remainder of the airframe, however.
N4DD's engine is a 2200cc VW. Initially, Dan built it up as a normally aspirated job, but later decided to go with turbocharging to gain a little more umph on hot days at high airports. To do this it was necessary to reduce the compression ratio to 6.5 to 1 and to install a scavenge pump to keep oil out of the turbo. As the engine was being built up, Dan realized the sort of accessory section he wanted was not then available. He had worked between semesters in college in a machine shop, so decided to strike out on his own. He designed and carved out a wooden pattern and had his own accessory section cast. After machining, it was bolted on the VW -- providing a 20 amp alternator and electric starter. It was much admired at fly-ins he would attend in the seasons to follow, so after hard tooling was built, the unit was put into production. Over 100 have subsequently been sold.
Initially the engine was fitted with a two-blade Warnke, which performed quite well. It ultimately got to be chewed up from use on gravel strips and running in rain, so was replaced by a 3-blade beauty from Rand/Robinson. Virtually no difference in performance was noted between the two props, but the 3-blader certainly looked great on the airplane. Now, since Tullahoma '79 (where we took the pictures for this article), a third prop has been fitted ... with rather astounding results (see sidebar).
NIDD weighs 550 pounds empty and will carry its own weight in people, fuel and baggage. 168 pounds must be reserved for the 28 gallon fuel capacity - 14 in the fuselage ahead of the cockpit and 6.6 gallons in each wing. The wing aux tanks utilize little sports car boost pumps to transfer gasoline to the fuselage tank as it empties out in flight.
The airplane and its engine performed marvelously ... until it reached the 400 hour mark. As a result of his racing experience, Dan had installed a welded "stroker" crankshaft in his engine -- a stock model in which the outside of the throws had been welded and reground. It was not counterbalanced and was not stress relieved after the welding. This is a common practice in the hot rod world and the rationale was that if a stroker crank could stand up to the stresses of off-road racing, it ought to go on forever in the smooth-running environment of an airplane cowling. It didn't. On the way to Chino '79 it let go -- fortunately right over Albuququerque and within gliding distance of an airport.
Dan's engine is now fitted with a fully counterweighted, forged 4130 crankshaft built by SCAT. "They cost 400 bucks, but they won't break," he says ... and we might add that compared to the price of an 0-200 or 0-235 crank, that is the bargain of the decade!
N4DD stalls at about 50 mph and lands at 55. The VW burns 4.2 gph at 27-28 inches of manifold pressure. This used to produce a cruise speed of 160 or so, but as you see in the sidebar, the new Warnke prop has changed all that. Dan flies the turbocharged airplane pretty much by manifold pressure. He uses 35 inches for take-off, then comes back to 30 inches and locks the throttle there until he is ready to land. He will allow the m.p. to drop to about 25 inches if he climbs very high, but this still provides all the power he wants, so he doesn't fiddle with the throttle enroute.
Dan and his father operate a machine shop that makes oil field equipment. The accessory case that started out as a hobby has now become a significant part of the business and continues to grow. For the past year or so Dan has been building a new airplane -- an original design he has named the Scissortaiil. It is a twin boom, two-place, side-by-side retractable geared pusher. Very slick in profile, it is, of course, VW powered and will be of wood, foam and glass construction. It should fly this summer and might even show up at Oshkosh.
We'll keep you posted.
WARNKE'S "ALMOST CONSTANT SPEED" PROP
In April we received the following letter from Dan Diehl:
"N4DD now has over 600 hours flying time, with over 100 since installation of the turbocharger. With the high altitude capability of the engine, I realized the need for a more efficient propeller. I have tried several props, but was not fully satisfied with any of them. A call to Bernard Warnke revealed he had a prop of a new design -- one he calls an "almost constant speed." It involves the theories of scimitar blade design as well as the compressed air theory of an anhedral wing. The blades are flexible enough to let the pitch flatten out for climb, but as speed and altitude are gained, the blades tend to return to their natural setting. The result is a minimum spread in rpm between climb and cruise. I am also impressed with its super smooth and quiet operation -- a vibrationless feel I have never before experienced in an airplane. Following is a chart comparing my best previous prop with the new one:
KR-2 loaded to 900 Ibs. -- 2180 cc Turbo VW
Old New Static rpm at 30" mp 2750 2750 Rpm at 5000' at 30" mp 3500 2950 Rate of climb at sea level 1200 fpm 1800 fpm Ind. cruise speed at 5000' and 162 mph 172 mph 27" mp (@ 3250 rpm) (@2900 rpm)
The old ground adjustable prop had a diameter of 52 inches and pitch something over 50 inches. The new one is a fixed pitch prop 52 inches in diameter with a 56 inch pitch. It should be noted that my air speed reads slow, so indicated speeds are for comparison only and not for actual speed.
-- Dan Diehl