The Pazmany Efficiency Contest... Make It Work For You! By Philip B. Groelz (EAA 32604) 4925 William Omaha, Neb. 68106

W HERE CAN YOUR airplane be improved? Could your piloting technique be refined? How do you stack up among your peers? How does your jewel of an airplane perform, compared to other airplanes of its class? We can get answers to some of these questions by taking another, closer look at the information developed from the past few years of flying the Pazmany Efficiency Contest. The data can be recomputed as an aerodynamic handicapping factor multiplied by the speed achieved during the timed flight. From the aircraft data one handicap factor is computed for the low speed flight and another handicapping factor is used for the high speed flight. This handicapping is very similar in nature to the handicapping used in other competitive sports and allows the minimum speed performance of a Taylorcraft to be compared with a Taylor Titch, for example. Let's examine the low speed portion of the efficiency equation first. Stall speed for a given airfoil varies in direct relation to the square root of the wing loading, so the low speed handicap factor becomes the inverse of that expression or H Slow = W_ S

Beginning here, we can begin to compare Cubs against Sidewinders and Taylorcrafts against T-18's. Flaps lower the stall speed of an airfoil — right? How do you explain, then, the fact that the handicapped low speed performance of the Cubs and Taylorcrafts is as good or better than the T-18's and Sidewinders? It is here that we can start to ask about our own piloting technique. How well do you stack up when riding the stall? Do you really know your airplane, or do you just ride in it? All T-18's, for example, should be able to achieve the same handicapped stall speed as the airfoils and flap

systems are virtually identical. Yet,

the handicapped minimum speed figures show a surprising variation. Actually, T-18's, Tailwinds, Turner T-40's, Davis DA-2A's, Sidewinder's, Mustang IPs and BD-4's should be able to acheive nearly identical handicapped low speeds. The fact that they don't may show a need for refinement on the wings of some of these aircraft. I suspect pilot technique is a far greater variable, however. In trying for the all-out efficiency coefficient, the low-speed performance of the airplane-aviator combination cannot be over emphasized. Reducing the m i n i m u m speed by three mph has about the same influence on the overall points score as a nine mph increase in the maximum speed! If you don't believe it, try the numbers on a high scoring airplane and see for yourself. "Power required goes up as the cube of the airspeed." That's a pretty common statement. By reworking this expression we arrive at an equivalent expression that says the maximum speed is proportional to the cube root of the ratio of power to drag producing area — the wing, in this contest. If you can figure out how to eliminate the fuselage, you are ahead of the game. From this discussion, we can see why the maximum speed handicap factor is "Fast =

Comparing the handicapped high speed of your homebuilt against the handicapped high speed for others of its class or type tells how your airplane measures up aerodynamically. Compare your bird against the top performer of its type. What is different? Do your wheel pants fit as tight? Did he work out a better solution with his antennas? Are your gap seals as good as his? If these visible details are very similar, perhaps you could get him to show you his cowling and cooling system details. On a clean homebuilt, 10% of the net power is required for cooling, and this figure can be doubled or tripled. Perhaps your own cooling system can be improved to give you both extra speed and improved cooling. Another nearly invisible area to

explore is engine operation and the engine/propeller combination. Many builders are now observing that their own cars cruise all day at 3000-3500 rpm. Yet, the more carefully built

aircraft engine is operated at 25002700 rpm, apparently due to engine balance tolerances and propeller tip speed limitations while-swinging a six foot club. Consequently, since

many of the faster homebuilts are limited to smaller propellers, the builders are balancing the engines and using 3000+ rpm as their maximum. K... the coefficient of performance, then, is determined by dividing the handicapped maximum speed by the handicapped m i n i m u m speed. Interestingly, after breaking down the Pazmany Efficiency Equation to this more useable form, the K... is identical to the value computed directly from the formula. The timers are there for you and me to use in refining our own airplanes! Let's use them! Judging from the articles that have appeared in SPORT AVIATION many people had been searching for a method of comparing the performance of airplanes that are very different. Pazmany has done all ol us an outstanding service by providing his Efficiency Equation! Men like Noel Becar, Ray Borst and Art Froelich and all the men who built the equipment, and helped run the contest, as well as the owners and pilots who made the effort to fly the contest, deserved our appreciation for developing the data we now have available. I became interested in the Pazmany Efficiency Equation first from a designers' viewpoint because it allows a builder to compare a Fournier RF-4 against a Comanche, for example. Now, as a builder, it will allow me to compare my Tailwind against other Tailwinds, the T-18's, and the BD-4's. How effective will my streamlining approaches be when compared to some of the best? I can hardly wait to get my bird off the ground and through the traps! (Continued on Next Page)

ABOUT THE AUTHOR — Philip Groelz is a registered professional engineer in the state of Nebraska and graduated from the University of Nebraska with a B.S. degree in electrical engineering. Philip is the current president of EAA Chapter 80 which serves Eastern Nebraska and Western Iowa. He is shown attaching fabric to the belly of his Tailwind.

SLOW SPEED RUN

HIGH SPEED RUN Aircraft

Pilot

Vans RV-3 Sidewinder Taylor Mono KR-1 Mustang II

Van Grunsven Smyth Crossland Rand Bushby

Sonerai II Daphne T-18 Mustang II Piper Arrow Swift

Cessna 170A Skeeter Bellanca VS-1 Zenith Tailwind T-18

Mustang II Tailwind Jodel D-11 Tailwind Cliff Mooney Mite Cessna 150 Skyhopper Taylor El Chuparosa Jodel F-11

Monnett Darmstadt Zimmerman Chard Vonheeder Kingry Williams

Eaves De Franco Vidervol Heintz Tileston Giller Bushby Stanton Hodktnson Korngold Smith Willingham

Jania Shinn Ladd

MacDonald S-20 Pazmany PL-1 T-18 Jodel D-1 1

Fleet Canuck Lark

Tee Voto

Turbulent T-18 T-18 PJ-260 Pipit Taylorcraft Luscombe Taylor PL-2

Weishaar Wallace Neunteufel

Stinson 108

Playboy Playmate Maranda R A- 14 Jodel D-11 or F-11 Aeronca Tailwind

Skyscooter Tailwind Commonwealth Sky Ranger Jeanie's Teeny

Playmate Pietenpol Sky coupe Mod -Cub Skycoupe Fly-Baby Jodel D-11 or F-11 Miniplane Baby Ace Miniplane J-3 Cub Miniplane Fly-Baby Skycoupe

207.6 180.1 146.3 140.8

186.0 180.5 169.7 169.0 165.9 164.9 162.2 161.8 161.5 159.1 158.5 158.2 154.8 154.7

71 •71 '73

'73 '71 •73 '71 '73

71 '73 •70 '73 '71 '71 '73 '70 '71 71 '73 '71 '71

'73 '73 73

Hawley

T-Craft Davis

73 •71 •73 •73 '73 '73

Carlson Darst Carter MacDonald Brewer Hamlyn Zimmerman

Fly Baby T-18 Honey Bee

HFast

'71

Playboy

Starduster

Mph

Hegy

Turner T-40

Tailwind

Year

Pfouts Sisler Hall Reid Linn Pio

Bookwalter Mezharsic Gonzales Mooney

Olsen Lange

Royal Pulliam Balcer Boudeau Callahan Lamb

Johnson Thorp McAdams Barnard Parker Balcer

Lovley Carrithers Brown Hall Ingram

Putney Martin

Jania Schuster McKinney Janson

Campbell Reel y

'71 '73 '73 '70 '73 '73 '71 '73 '71 '71 '71 '71 '73 '70 '70 '71 '71 '73 '73 •70 '71 '71 73

'70 •73 '73 '70 70 '71 '70 '71 T3 '71

'71 '71 70 '71 '71 •71 '70 '70 •73 '70 '70 •70 '73 '70

198.0 147.4 139.8 187.0 194.8 168.0 154.5

158.8 168.8 174.0 128.0 150.9 174.2 184.0 179.9 150.0 125.7 151.2 125.7 122.0 125.1 115.8 115.2 139.2 122.6 155.7 152.7 147.6 111.5 155.1 154.5 106.2 105.9 129.0 100.6 161.0 170.8 141.7 121.8 95.5 114.0 122.3 135.8 138.2 107.3 148.9 113.4 91.7 131.7 136.4 128.3 135.5 112.7 101.6 99.1 142.7 105.5 132.0 96.8 108.8 120.2 77.4 97.6 90.5 116.0 95.2 88.2 122.8 90.3 101.5 82.8 99.5 82.9 91.6

153.3 153.2 152.2 149.6 149.5 149.1 146.8 146.7

146.6 145.4 145.4

145.0 144.8 144.6 144.1 144.0 143.8 141.3

140.5 137.1 136.4 136.1 136.1 135.6 135.3 134.8 134.2 134.0 134.0 133.7 133.5 133.1 132.8 132.4 132.0 131.6 131.3 131.0 130.6 129.9 127.8 127.1 125.7 125.0 124.4 124.3 123.5 123.2 120.8 120.7

120.3 118.9 117.5 117.5 117.4 117.1 113.8 113.6 110.0 106.1 105.5 104.5 102.0 96.5

Aircraft

Pilot

Aeronca Stinson 108 Cessna 150 T-Craft

Lamb Royal

Pietenpol

Lovley

Vans RV-3 Cessna 170A

Van Grunsven Williams Reid Wallace Heintz Johnson Rand

Luscombe T-18 Zenith

Tailwind KR-1 J-3 Cub Davis DA-2A Playboy Skyscooter T-18 Tailwind Mod -Cub Jodel F-11 Lark

Taylor Tailwind VS-1 PL-1

Bellanca Mooney Mite Daphne Tailwind T-18

Skeeter Skycoupe PL-2 Miniplane Turbulent Commonwealth Sky Ranger PJ-260 Cliff Jodel D-11 or F-11 Mustang II Jodel D-11 or F-11 Tailwind Taylor Baby Ace T-18 Miniplane Pipit Swift Fly Baby Jodel D-11 Fly Baby Skycoupe MacDonald S-20 Mustang II

Jania Olsen

McKinney Lange Pulliam Thorp Zimmerman Carter Brown

Carlson Voto Linn Korngold

Vidervol Brewer DeFranco Willingham Darmstadt Tileston Giller

Eaves Hall Pio Schuster

Weishaar Barnard Pfouts Smith

Putney Bushby Callahan McAdams Ladd Jania Neunteufel Martin Sisler Kingry

Campbell Zimmerman Mezharsic

Reel y MacDonald Bushby

Playmate

Balcer

Taylor Mono Starduster Maranda RA-14 Fly Baby Jeanie's Teeny Playmate Skyhopper Fleet Canuck T-18 Miniplane Turner T-40

Crossland Bookwalter Boudeau Ingram

Parker Balcer Shinn Tee

73 71 71 71 70 73

73 71 71 '70 71 70 71 71 73 71 70 71 71 '73 '73 '73 70 73 71 73 73 71 73 71 71 71 71 73

Gonzales

73 70 73 73 70 73 71 70 73 71 70 70 73 73 71 73

Hawley

Taylorcraft Tailwind

Hall

Honey Bee Jodel D-11

Mooney Hodkinson

Lance Stanton Hegy Hamlyn

Carrithers Vonheeder Monnett Smyth

Chard

'70 data from July 1970, SPORT AVIATION. '71 data from July 1971, SPORT AVIATION. '73 data from October 1973, SPORT AVIATION.

60 JULY 1974

'70 73 73 71 71 '73 73 70 71 73 71 '73 '70 71 70 70 71 71 71 73 71 70 70 71 73 '73 71 71 70

Janson Darst

Playboy Starduster

El Chuparosa T-18 Skycoupe Piper Arrow Sonerai II Sidewinder Mustang II

Year

Mph 36.9 47.3

43.7

36.6 38.0 53.9 52.2 48.7 60.0 52.2 57.7 46.8 40.1 56.5 54.6 48.7 61.2

56.1 43.3 45.6 53.5 52.5 65.0 48.9 62.6 67.4 45.2 48.7 68.2 68.0 62.2 54.9 62.0 54.6 51.6

50.9 55.5 53.7 50.3 72.0 47.6 70.0 56.9 50.8 70.5 55.3 56.8 61.1 52.9 52.9 54.3 56.3 52.8 69.3 64.9 63.2 59.4 52.5 54.1

61.2 64.4

55.5 58.8 79.3 62.5 79.2 69.4 65.5 49.4 72.0 62.4 65.6 64.7 80.0 63.5 81.0 65.9

72.8 87.5

H

Slow 14.04 14.20 14.97 15.41 15.51

15.63 15.68

15.84 15.92 15.96 16.03 16.19 16.20 16.21 16.32 16.40 16.42 16.45 16.62 16.76 16.82 16.85 16.88 17.01 17.10 17.11 17.12 17.39 17.45 17.53 17.54 17.60 17.61 17.68 17.79 17.92 18.08 18.10 18.22

18.29 18.31 18.35 18.47

18.47 18.55 18.62 18,75 19.09 19.10

19.10 19.12 19.15 19.20 19.36 19.42 19.51 19.58 19.58 19.67 19.69 20.00 20.07 20.21 20.23 20.23 20.26 20.72 20.73 20.83 21.02 21.08 21.59 21.86 22.04 22.28 22.31 22.57 23.37 23.72