Wednesday, December 23, 2009

Chapter 21 : Improving on Perfection

Photo of N88EW via Neil Bilodeau

In many fields, excellence is represented by a single name which needs to further explanation. In music it is a Stradivarius, in automobiles it is a Rolls-Royce. In aerobatics it is the Pitts Special.

I had first flown the Pitts Special when taking an advanced aerobatic course just after I arrived in southern California. It was hard work but it was fun. At the end of the course I was left with a lasting impression of the exhilarating performance of this diminutive biplane. The controls were light and the roll rate was phenomenal, equaling that of many high-performance military jets. It excelled in inverted flight. I was captivated. Since that time I had flown aerobatics in a variety of military and civil aircraft and found nothing to approach the handling of the Pitts S-2A. I had flown a number of S-2As and had fun in all of them. However, the S-2A did have one shortcoming. With two on board the 200HP S-2A would inexorably lose altitude during a training sequence. After a few minutes of aerobatics it was standard practice to break off and climb back to altitude. It was an inconvenience at best for my type of flying, but a distinct handicap in serious aerobatic competition.

So the Pitts Aircraft company of Afton, Wyoming, shoe-horned the 260HP Avco Lycoming AEIO-540-D4A5 six-cylinder engine into the Pitts airframe to give improved vertical performance. The resulting two-seater S-2B had the capability to complete an unlimited aerobatic sequence two-up without losing altitude. The single-seat S-2T with the same engine would outfly just about anything.
But was the S-2B much different to fly that the S-2A? I had the opportunity to fly Bill Hare’s S-2B N88EW from Hawthorne Airport in Southern California.

ChristenAircraft built this aircraft.

During the walk-round Bill pointed out the differences from the S-2A. The engine of course was much bigger and heavier. Consequently the wings and main landing gear had been moved forward five inches to compensate for the c.g shift. The wings remained the same two-spar spruce construction, the top wing of NACA 6400 section and the lower wing of 00 series. The wings were of symmetrical section to make inverted flight easier.

I marveled at the attention to detail. One example could be seen on the inboard side of the airfoil-section strut linking the upper and lower ailerons. A wire was doped along the length of the inboard side of the strut. Bill explained: ” The older S-2A had round –section struts. This new airfoil-section strut on the S-2B reduced drag, but sideslip caused the strut to produce lift and could cause it to vibrate. The wire effectively spoils the lift and prevents any vibration.”
Bill/s S-2B stood noticeably higher off the ground than the regular S-2A, with the pointed spinner almost at eye-level. The propeller was an eighty-inch constant speed Hartzell two-blade metal prop. Tightly re-cowled, the engine compartment was all new. The characteristic cheek air outlets at the back of the engine bay were deleted and there was now a controllable cowl-flap in the bottom of the engine compartment for cooling.

Naturally enough, a full inverted fuel and oil system was standard. Minor changes to the center fuselage included provision for a smoke system tank and plumbing. The fuselage framework was constructed of welded 4130 steel tube with wooden stringers, together with aluminum top decking and side panels. The fuselage sides were now metal –covered, extending back to the rear cockpit and replacing the fabric- and-stringer cockpit walls of the earlier models. On the S-2B the two-seat bubble canopy introduced on later S-2As was now standard. The four ailerons were of symmetrical section with aerodynamic “spades” on the lower pair.

Digressing for a moment, I’ll explain. As if the roll rate was not fast enough on the regular Pitts to make your eyes water, aerobatic aces had started fitting spades to further increase the roll rate. The spades were basically rectangular metal plates cantilevered forward from the bottom of the lower ailerons. Their function was to provide a degree of aerodynamic balance. As the aileron was deflected up, the spades were forced down into the airstream and this in turn helped push the aileron further up. In effect this felt rather like power steering on a car, as the aileron forces in flight were reduced dramatically.

N88EW still had that new plane smell, having only fifty hours on the Hobbs meter at the time of our flight. Resplendent in an eye-catching red, white and blue sunburst paint scheme on the upper surfaces, with the undersides a red and white checkerboard design, it squatted pugnaciously on the ramp. Every line was purposeful. This airplane was made for serious fun.

Strapping into the rear cockpit I found that even with a back-type parachute I was not unduly constricted. This Pitts was flown solo from the rear cockpit and the front office was less comprehensively equipped, although full dual controls were fitted. Squeezing my six feet plus frame into small aircraft is sometimes accomplished only with some effort, but the S-2B’s rear cockpit was entirely adequate.

The cockpit layout was familiar, being mainly as I remembered from the S-2A. A hefty throttle lever was mounted on the left hand wall. Mixture and prop plungers protruded from the left side of the panel. The panel had normal VFR instruments with room for the obligatory Aresti aerobatic sequence card on the rear panel. One prominent addition was the cowl flap control plunger down on the left hand side of the bucket seat. My rudder and brake pedals were now enclosed in fiberglass tunnels, a precaution to stop them from becoming entangled with the loose strap ends from the front seat. A clear plexiglass floor in the cockpit was an aid to orientation over the ground markers during competition. Before Bill climbed into the front seat we carefully checked the operation of the sideways-opening canopy. I swung it shut and slid it forward an inch or two before it locked home. Bill warned that on the S-2B the canopy had to be positively locked before engine start. An unlocked canopy could be lifted open by the slipstream and slammed into the top wing. At $1,500 for a new canopy, it seemed prudent to follow Bill’s bidding.

The engine started easily on the first turn of the key. With the oil pressure in the green I listened to ATIS, switched to ground to obtain taxi clearance, and taxied out. We had a five knot wind from the west. As we taxied to the runup area for Runway 25 I realized that forward view was of course minimal, so I had to weave to clear the blind spot ahead where the oversized engine blanked out most of the forward view. Another problem turned out to be trying to keep the speed down without riding the brakes. Even throttled back the S-2B kept accelerating. I kept the cowl flap closed during taxiing to raise engine temperature as quickly as possible.

Under the bubble canopy the temperature was rising rapidly as the sun blazed down on us. I wasted no time in finishing my pre-takeoff control checks, then ran the engine up for the normal magneto and propeller checks. Checks complete, I checked that there was no other traffic, and requested takeoff clearance.

Hawthorne is a historic field. The Northrop Flying Wings and F-89 jet fighters originally flew from here before civilization encroached upon the field. Now the area around the field is completely built-up, causing Northrop to switch their flight test activities some ninety miles away to Palmdale. These days Hawthorne is normally restricted to general aviation aircraft with the occasional visiting Warbird or executive jet to enliven the proceedings.

Cleared for takeoff I swung out onto the runway, with a last visual check that there was no traffic on finals. I appreciated the good view around given by the bubble canopy. Rolling forward a couple of feet to straighten the tailwheel , I checked that the brakes were off and smoothly advanced the throttle.

The S-2B leaped forward. My headset cut down the racket of the six-cylinder engine to a throaty growl, but the acceleration was awesome. I needed right rudder to keep straight and barely had time to raise the tail before the Pitts flew itself off the runway. When we had briefed for the flight, Bill had told me to climb at 100mph. I pulled the stick back, only to find that the airspeed was still increasing. I pulled further and finally got us stabilized at 100mph but in a very steep nose-high attitude. In the absence of other visual cues the transparent floor panel already was proving useful in maintaining reference eith the centerline of the runway as it receded rapidly below. Abeam the tower, half-way down the five-thousand foot runway, we were already passing through 900 feet and by the end of the runway the Pitts was at 1,500 feet.

This rocket-like climb gave one unusual operational advantage. With the Los Angeles Class B airspace extending to the boundary of Hawthorne airport on its northern side, aircraft leaving Hawthorne usually had to circle the field to the south, climbing to 2,500 feet over the field before entering the VFR corridor which traversed the Class B heading north. The S-2B, as Bill pointed out to me, could reach this point in a straight climb from takeoff.

Levelling from this initial climb at 2,500 feet in less than a minute from brake release, I started breathing again and banked south towards the local aerobatic area over the Pacific, south of the Palos Verdes Pensinsula. Setting up for cruise with cowl flap one-third open and prop pulled back to 2,400rpm gave us a comfortable 140mph witht eh mixture leaned to give a fuel flow of fifteen gallons per hour. Manifold pressure was back to twenty inches. I gently weaved every few seconds to clear the airspace ahead of us. An intercom switch on the panel enabled us to talk without the embarrassment of transmitting inadvertently to the world at large. A boon for training.

I gingerly retrimmed in pitch with the lever on the left-hand cockpit wall, reminding myself that in a Pitts a sensitive hand was required. Even during that steep climb-out I had been aware that I was over-controlling with the light ailerons. Now I tried a few exploratory control inputs. It took a few minutes to reacquaint myself with the lightness of control of the Pitts. Rudder response seemed even more sensitive than I remembered from the S-2A. Inputs of a quarter on an inch banged the nose to either side, while lateral control was such that merely thinking of applying aileron gave a thirty-degree bank almost instantaneously. With this sort of response, the days of thought control didn’t seem far away at all.

Arriving at the aerobatic area, I checked for other traffic before setting up for our first maneuver. Aerobatic practice in California has its own set of problems. Ideally for this assessment we would fly over the desert, using straight roads as markers. Here over the ocean occasionally the wakes of yachts or boats could be utilized, but today the pacific was an unrelenting blue beneath us from horizon to horizon.

Initially I set up for a loop using the mountains of Catalina Island, some twenty miles offshore, as a reference in lieu of any conventional markers. After making sure that everything was ship-shape on board, I jiggled the prop control forward to 2,600rpm and pushed the mixture control to RICH. Today I would use 3,500 feet as my reference altitude. With the TCA airspace extending down to 5000 feet over us at this point, this give me a buffer zone to stay underneath this ceiling.
After a last look around to check for stray Cessnas, I dived slightly to 160mph, pulled back to level flight momentarily and eased back on the stick. My initial effort at a loop proved embarrassingly untidy, as the light elevator forces caused me to oscillate above and below the perfect arc and the g-meter needle jiggled either side of 3g.

Bill chortled. A subsequent loop proved easier, and I even remembered to open out the loop the correct amount at the top as the speed dropped off. This time we bounced in our own propwash at the bottom of the loop. As we came back into level flight, the altimeter read exactly at our reference altitude of 3,500 feet.
I progressed to maneuvers in the rolling plane. Half-rolls proved as precise as in the S-2A. With these magic ailerons it was easy to flip to inverted flight and just play about until you were tired of seeing the world upside down. I tried a number of full rolls with various amount of stick. Full stick gave a mind-blowing roll rate of 240 degrees per second and the roll happened so quickly that little co-ordination could be achieved. I slowed things down by trying a conventional slow roll, giving me more time to observe what was going on. I found that the controls were well harmonized, with little adverse yaw from the ailerons.

The Pitts flew perfectly, any bobbles in our flight path being due entirely to my rusty technique. The spades on the ailerons certainly made a difference. Roll rate was even higher than the S-2A and rolling was no effort at all compared to the sedate Great Lakes Biplane which I had recently been flying. Inverted flight proved to be simple and comfortable, with the five-point aerobatic harness and back-up lap belt giving confidence-inspiring support to my lower body. It made a change to fly prolonged inverted maneuvers without the necessity of having the straps so tight that the circulation to my legs was cut off altogether.

Rolling upright once more, I progressed to Cuban Eights. I initiated the maneuver from 170mph, pulling round the loop and floating over the top, waiting until we were inverted in a forty-five degree dive before rolling upright. No problems here and I repeated the maneuver to complete the Cuban Eight. I tried it again, refining my timing on the roll-out to equalize the inverted and upright segments of the dive. It all felt very natural and for variety I tried a couple of reverse Cuban Eights, pulling up to a forty-five degree climb before rolling inverted and pulling through.

“Look at the altitude,” said Bill. Sure enough, at the end of this sequence, our altitude was still at 3,500 feet and at fifty-five percent power the AEIO-540 was not even breathing hard. This was all rather fun. I spent a few minutes trying to perfect my stall turns, managing to do a reasonably tidy maneuver but finding a consistent vertical line on the exit somewhat elusive. However it eventually came together. Once back in level flight I even remembered how to do the odd inverted turn without disgracing myself. The Pitts did it all without hesitation.

Bill remarked from the front cockpit that time was getting on and we had better check the fuel remaining. I reluctantly rolled the Pitts upright and checked the fuel. The S-2B is limited to fifteen gallons of fuel with two on board to keep away from the aft c.g. limit. Aerobatic sorties are limited to somewhat less than an hour. As our maneuvering had consumed a fair amount of gasoline, it was time to head back to Hawthorne. With the blunt nose of the Pitts pointed north, the whole of the LA basin was spread out on this clear morning, with Mount Wilson visible through the shimmer of the prop and the whole of the San Gabriel mountain range athwart our path. We coasted inland over the Palos Verdes Peninsula, past the white golf balls of the LAX radar on the hill below. Once past the traffic pattern at Torrance airport, we started downhill towards Hawthorne over the urban sprawl of the South Bay.

I was impressed by this machine. When Curtis Pitts first came out with his diminutive 90HP single-seater in 1944, little could he imagine that forty years down the road his design would still be in production. But the basic Pitts Special had been constantly refined to produce a stable of factory-built and home-built variants of progressively greater power and performance, culminating in the potent machine I was flying. First appearing in September 1982, the S-2B took first place in the Advanced Category as the US Nationals held at Sherman, Texas that same year. The pilot was Clint McHenry and the unusual part of this story was that McHenry carried a passenger, having had his first-class medical pulled by the FAA and getting permission from the authorities to compete only on the condition that he flew with a safety pilot. It was an impressive performance for both plane and pilot.

As the white strip of the Hawthorne runway came into view, I checked ATIS, then switched to tower frequency to obtain clearance to land. Down to 1,100 feet I set up a downwind leg at 100mph for runway 25, turning tightly round onto finals. When flying a Pitts, approach involves either a tight continuous turn to finals, or a sideslip in order to keep the runway in sight for the longest possible time. We were cleared #2 to land, with traffic in front of us, so I set up a straight-in approach, cross-controlling with stick and rudder to give some sideslip. With more headroom under the big bubble canopy than in the S-2A I could see further along the side of the nose. Even so, the runway disappeared under the nose as I scooted in over the fence and I killed the sideslip. As the nose swung to track down the runway I eased the stick back to flare. The Pitts adopted a three-point attitude. But I had not got the stick back quite far enough asnd we touched prematurely on the main wheels, causing them to skip an instant before the tailwheel hit the ground and then we were running down the rather rough runway. Keeping straight required some dexterous footwork. Just the same as the S-2A, I remembered, and one of the penalties of attaining the superlative aerobatic performance of the Pitts aircraft.

This was a short flight and one in which I did not explore the furthest reaches of the flight envelope of this aircraft. The G-meter after flight gave evidence of only +4.6g and -1.5g, well within the +6 and -3g placarded limits of the Pitts. Flying a Pitts well requires constant practice. A single flight could do no more than scratch the surface. In the hands of an expert a Pitts could still dazzle an airshow audience or hold its own against the latest aerobatic competition monoplanes. The S-2A had been fun. The S-2B was improving on perfection.

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