Text and Photos by Budd Davisson
Air Progress, November, 1971
Yellow Jacket: Son of Shoestring
Like to daydream? How about a yellow, 175mph, glass daydream that you pull on like a pair of pants? You sit there, with the bubble canopy fitting so close you feel more like a scuba diver than a pilot, while the 100hp Continental perched above your outstretched feet forces noise in past your headset, letting you know how fast it's dragging you through the air. Ahead, a V-tailed outline forms and solidifies into a Bonanza. You pull up alongside and the pilot looks over at you and grins. As your eyes meet, you return the grin, your left hand moves the throttle forward, and the Bonanza falls quickly behind. That's what it's like to be flying a 200 cubic inch Formula One racer-more specifically, that's what it's like to be flying Yellow Jacket, the first offspring of the famous Shoestring Formula One winner.
These days (Ed, things have changed since 1971), when you talk about Formula One racing, forget about all but two airplanes--Rivets and Shoestring. Rivets is the tubing-and-fabric invention of one man, Bill Falck, and as Falck's imagination changes, so does the airplane. On the other hand, Shoestring, the only airplane to consistently beat Rivets on equal footing, was the result of a 1949 team effort, and has seen very few major modifications. It was fast and beautiful in 1949, and today it is still very much the same, only more so.
The original Shoestring was designed by Rod Kriemendahl and was built in Van Nuys, California, by Carl and Vince Ast, with the help of anyone willing to wield a wrench. Shoestring is a fairly big airplane, for a Formula One. Its 19-foot wing has an aspect ratio of over five, which is one reason it can keep ahead of the slightly smaller Rivets in the high, thin air of Reno. All Formula One racers are required to have a minimum of 66 square feet of wing area, but most of them have used a short, wide wing to get the area. Rivets and Shoestring stand alone with their tapered, longish wings. Apparently, the better overall efficiency of the higher aspect ratio wings is well worth the slight increase in drag because these two airplanes consistently bring home all the trophies.
The canopy lifts up and back and fits so tightly there are no edges exposed to the wind.
Yellow Jacket, the first reproduction of Shoestring, was built by Jim Strode of Melbourne, Florida. Jim lives just up the coast from Vero Beach, which is the reason his Shoestring was the first to fly. The plans for the airplane are produced by Landis Ketner, a Piper engineering draftsman at Vero Beach, and Jim was building parts as fast as Landis could make the drawings.
The original drawings and engineering studies done by Kriemendahl in 1949 were lost or destroyed, a fact that worried John Anderson, one of the several past owners of the original Shoestring. Before Anderson sold the airplane to its present owner, Ray Cote, he commissioned Ketner to go through the airplane with a tape measure and dividers and come up with a set of drawings he could use for repair work in case he ever dinged it. Ketner measured and miked until he had enough dimensions to make up a complete set of working drawings. He had an engineering study run on the main spar and it was increased in thickness to bring it up to a 10-G strength. He has proof loaded the fuselage structure to 9 Gs with no deformation.
When Jim Strode decided to build a replica of Shoestring, he was ahead of the game because he had already finished an immaculate Pitts Special and had a well-equipped shop ready for another project. When Jim builds airplanes, he gets fanatical about it. He built the Pitts in 10 months, and Yellow jacket took just over a year. Ketner told me he once walked into Strode's shop with a drawing for the motor mount, and Strode had it tack welded before Ketner left, four hours later!
Strode is not only fast, but thorough. Yellow jacket is a fantastic study in drag reduction and attention to the tiniest detail. Jim made four different cowlings before he got the shape and weight he wanted. This one, which is a far cry from the original shape of Shoestring, weighs only 11 pounds. His tinted canopy is as optically perfect as any I've looked through. There is not a lap joint anywhere on the airplane; every single joint is a butt joint. The cowling, wing fairings, landing gear fairings, and the canopy fit into their own little recesses, making everything flush. It's possibly the finest piece of streamlining I've ever seen.
The wing is completely wooden construction, with plywood skins that make it easy to produce a smooth surface. Not wanting to cause even the slightest ripple in the airflow, Strode even "flushmounted" his paint trim! That impossibly complex paint scheme isn't the usual paint-it-yellow-then-trim-it-with-black approach. Strode masked off the areas that were to be black, painted the air-plane yellow, then masked off the yellow and painted the black, making the black layer the same thickness as the yellow. Nowhere can you find a masking line or ridge. He says it took between 40 and 50 rolls of masking tape. Talk about dedication!
The airplane is smooth and quick with not a hint of stability on any axis. It requires a hand on the controls all the time.
When Jim offered to let me fly his airplane, I looked at Yellow Jacket and saw the thousands of hours of welding, sanding, and painting, and thought that this man was either crazy for letting me fly it, or he knew something about the airplane I didn't. Jim thinks the airplane is so easy to fly that any average taildragger pilot could do it. As I prepared to board, I hoped he was right.
Boarding a waist-high aircraft that has the cockpit right in the middle of the wing presents something of a problem. I considered taking a flying, feet-first leap over the trailing edge. Then, I thought about jumping up on the wing tip and walking in, but Jim vetoed that. The correct method of entry involves first emptying your back pockets. Then you hoist your fanny up on the leading edge, just outboard of the wing fairing. Once you're sitting on the wing, you pivot gently and you place your feet in the cockpit. At this point, things get very complicated, because it's like trying to get into a skin diver's wetsuit. If you bend your legs at all trying to get them under the spar, you'll never make it because they'll jam tight. You must keep your legs perfectly straight, supporting yourself with a hand on each side of the cockpit. It's a real test of your shoulder muscles, letting yourself slowly down, inching your legs down under the spar/panel. Once in place, your feet are gone forever, as you can't see them. I tried several times to look under and locate the brake pedals, but they were too far forward to see.
The canopy is on an overcenter tubing arrangement that lifts up and back at the same time, rather than employ the usual hinge on one side. This system allows Jim to jettison the canopy easily and immediately. I ducked my head a little as Jim slammed the canopy shut and the two G. M. hood latches captured the appropriate pins. The hood latches still have their safety positions allowing you to taxi with the canopy open a few inches.
The cockpit is complete with a navcom unit and most of the other gadgets you need to fly an airplane anywhere--they're just a little closer together than usual. The only gauges that really matter-airspeed and tachometer-are mounted directly in front of your face, which is fortunate for racing. The rest of the cockpit feels as if you're sitting in somebody's ballerina slipper. The fuselage sides come up on both sides of your legs and seat, leaving just enough room to squirm a little. It's not uncomfortable, but it's tidy. The stick is a short metal stub in the normal position between your knees, which places it a sizable distance forward under the panel and spar. The knob on the quadrant-type mixture control had to be removed, making it a straight lever, to allow more leg room. The trim tab is a converted vernier throttle control mounted on the lower right side of the spar. Since Yellow Jacket was built as much for sport flying as for racing, it's equipped with a starter and battery, and everything else needed to make life livable for the sport pilot. Jim figures it has about 100 pounds that can be unbolted for racing.
I had started the 100-hp 0-200 Con-tinental and taxied for some distance when the people watching from the sidelines saw something that must have left them talking for days. I came to a halt on the taxiway, shut down the engine, popped the canopy, and sat up on the wing waiting for Jim to catch up. When he got out of his car and asked what was wrong, I pulled off my boots and handed them to him. I couldn't taxi with cowboy boots on. Every time I reached for the rudder, I got some toe brake, too, so I figured it was safer to fly it in my stocking feet. Jim shook his head, and I strapped in again and taxied away.
Yellow Jacket's ground handling is as much like a Cherokee as anything else, but the seating position and proximity to the ground made things seem strange. The airplane sits in a very flat attitude, making your angle of vision equally flat. Also, the wing is shoulder high and the canopy edges come up to about your chin, making you feel a bit like a prairie dog peering out of his burrow. Visibility is entirely adequate, but I'm used to looking down at the runway, rather than parallel to it, and there were so many things (like wings) protruding into my peripheral vision, that it was an entirely new situation for me. I had to taxi nearly a mile across the field, and I used that time to try to accustom myself to the unusual attitude references.
During my runup and pretakeoff check, I exercised the controls and found, to my dismay, that the ailerons were very stiff. Jim had commented on the problems of lining up five hinges per aileron, and I could feel them binding. I was sorry to see such stiff controls on such a pretty little airplane, but I was soon to be thankful for them.
I lined up for takeoff and gingerly fed the power in. Even the headset couldn't keep out all the noise, but it didn't bother me because I was too entranced by the acceleration of the tiny 100-hp mill. It was hard to believe this was the same engine I'd flown in Cessna 150s. The airplane tracked straight as a chalkline, requiring practically no rudder, and I was careful about bringing the tail up. I figured I wouldn't have to do much pushing with the stick to get the tail up because we were already sitting nearly level. I let it accelerate to about 100 mph indicated before I allowed it to fly off. Once in the air, even the slightest stick movement fore and aft produced a tremendous attitude change and the airspeed changed accordingly. It was a few minutes before I could hold 110 mph on the gauge.
Even though the airplane had neither a racing nor a climb prop on it, it was winding up the altimeter like crazy. I timed it and found the climb to be approaching 2,000 fpm even though I didn't have the vaguest idea what best rate-of-climb speed was. I just held 110 mph and let it roar.
As I leveled out, I found I welcomed the heavy ailerons. They weren't hard to move, just a little stiff, but if they'd been as free as the elevators, the only time I would have been level would have been in the middle of a bank-to-bank oscillation. While doing tight banks, 1 could barely see the ailerons moving. Later on, during the slow rolls, they didn't appear to be moving much more than a quarter of an inch. Because the wing has practically no dihedral at all, the airplane has almost no stability in roll, so you have to fly it every second. It would be very busy and sensitive with light ailerons.
It seems as if the first question anybody asks about anything is, "...how fast'll she go, mister?" In this airplane, a racer, the question is particularly pertinent, and the answer to can only be, "Very fast." At a more or less normal cruise setting, I was indicating 175 mph, as verified by flying formation on the camera plane. At that altitude, this is about 185 to 190 mph TAS. Full bore, it jumped up to about 190 IAS, or about 210 mph TAS. With the prop Jim had on it, I was a good solid 300 rpm short of what it would turn up with a racing prop, which should make 200 mph IAS a cinch. How about that for a C-150 powerplant?
This image is why it took so long to load this file. I couldn't see squashing it down, it is so well done. It was done by Design Maru and is acyrlic and airbrush. No computer art here.
I dropped the nose a little in one turn, and when I rolled out I had so much extra airspeed that I just had to do something with it. So, I pulled the nose up and started doing rolls right and left. Since the aircraft has so little adverse yaw, you can almost roll it with your feet flat on the floor. It does a very solid, silky roll and is about as good as any airplane I've ever had on its back. The aileron friction proved to be no hindrance because I didn't need to move the stick very far anyway.
I tried some loops and chandelles and found it loops like a fighter. You can open them up on top and make them great big lazy ones, or you can try to maintain a constant G force all the way around and make them small. It looks as if it would take only a small mistake to come out at a near supersonic speed because Yellow Jacket accelerates downhill like a bullet.
I scared hell out of myself when I did a four-point roll coming out of a loop. I was trying to keep the nose on a cloud, so I went negative on the second point and suddenly I had a clear liquid running all over me and the inside of the canopy. I racked it around right side up. The second I saw the liquid I remembered the gas tank over my legs and the engine at my feet and the words gasoline and fire flashed across my mind at the same time. I quickly smelled my shirt sleeve and tasted my hand -- it was nothing but water. Jim had neglected to tell me he'd just washed the airplane, and water had pooled in the bottom.
In most ways, Yellow Jacket handled like the high-performance airplane she is. This is also true of stalls. As you near the stall, a slight amount of instability sets in. It buffets just a little, and then drops a wing and the nose at the same time. The break is fairly sharp, and the nose must be dropped and a fair amount of power added to get it flying. I wouldn't consider the stall dangerous, as it's what you'd expect with a wing this thin and an airplane this small.
I looped and rolled around a little more and then checked the gas gauge. The petrol is measured about as accurately as you can get without poking a stick in the gas tank. A clear plastic tube comes out of the bottom of the tank and connects with the tank vent, so the fuel level is read directly from the tube that goes over the spar and up the panel face. When it got down to half, I headed back.
Feeling like a fighter pilot, I thumbed the mike button on the top of the stick and spoke into the boom mike, telling Melbourne tower I was coming in. As I entered the pattern, I found myself working fairly hard to maintain my speed exactly. It was easy to stay within a 5-mph bracket, but it took real work to keep it right on the money. The turbulence was making a plowed field out of final, so I finally established what looked like a good glide attitude and ignored the airspeed. At about 90 mph on final, the rate of sink felt very much like that of a Cherokee.
Apparently I was too fast when I broke the glide, about 85 mph, because I floated, and floated. Considering the amount of wind I was fighting and the size of the airplane, I was frankly amazed. I had expected it to fall out of the air as soon as I killed the power. I was really embarrassed. When it finally quit floating, I found I had been holding it in a three-point attitude about two or three feet up. I had flared at an altitude that would put my head a normal amount above the runway, which put the rest of the airplane too high. I came down with a small thud.
Roll-out was only a little more eventful than takeoff. It took minimum rudder to keep it straight. Jim has said its roll-out was like a Cub's, but I found it to be a little easier. Jim had warned me about using too much brake, so I just let it roll.
My overall impression of the airplane is that it is a great sport plane as well as racer. It's also fairly docile when you consider its operating envelope. It's particularly easy to operate in the critical takeoff/landing regime. I was operating in a gusty, sometimes crosswind, and the airplane was much easier to handle than something like a Citabria or a Cub because it didn't have so much wing for the wind to get under. Once in the air, it's a simple matter of getting used to an airplane that goes like crazy and reacts to your every move.
The airplane is not a very simple one to build, and Ketner, who sells the plans, makes no bones about that. But, it's not impossibly difficult either. The plans are very complete and readable--more like production drawings than the usual homebuilt type. Whoever takes the time to build one is going to be very happy with its performance and is going to own one of the prettiest airplanes ever built. And, just think, it can all be done on a "shoestring." BD
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