A COMPARISON OF A STOCK
J3 WITH A CLIPPED-WING "CUB"
By Giles Henderson (EAA 53234/1AC 159) and
Amos Townley (EAA 53090)
ED. NOTE: The following article was unearthed from the December, 1970 issue of SPORT AVIATION Magazine. Considering that date, some of the names and/or owners of aircraft etc. may be presently incorrect. The technical information, however, should still be relevant.
The J3 "CUB" has been a long-time sentimental favorite of the aviation buff. Many articles, books, and even poems have been written about this aircraft. In its stock configuration it has gained an almost legendary reputation in the roles of a trainer, bush plane, ranch hand, float plane, duster, and all-around sport plane. It has probably won more spot-landing and flour-bombing contests than any other type of aircraft. To top it off, it has frequently been the star of the air show. The Stolen Cub'," "Drunk Pilot," and other comedy acts flown by the late Dick Schram, Marion Cole, Bill Lumley, Dale Cites, and many others have always been real air show crowd pleasers. The stock "Cub" has been used by National Air Shows, Henry Mallet, Cole Brothers, Bill Adams, and many other professional performers for car to plane transfers, car-top landings, etc.
The “clipped-wing Cub" has also been a long-time air show performer. Many of the best-known aerobatic pilots in the country including Duane Cole, Harold Krier, Bevo Howard, Pappy Spinks, Charlie Hillard, Bill and John Lumley, Pete Myers, and Mary Gaffaney started their aerobatic careers in "clipped-wing" "Cubs".
A few ultra-high-performance "clipped-wings" have been built up for exhibition and unlimited competition. Probably the best known are N-42963 owned, built, and flown to an EAA international unlimited championship in 1966, by Pete Myers of Oak Lawn, Illinois; and N-10135, built by Howard Dutton of Haverill, Massachusetts and presently owned by Bill Lacy of Chandler, Arizona. Both of these all-out machines have had their fuselages shortened, vertical fins modified, been converted to single place, and had 150-hp or better engines installed. The wings on N-42963 have undergone an evolution of changes. At this time they are Taylorcraft wings shortened to a 24-ft. span. This nearly symmetrical airfoil improves the outside capabilities of the aircraft tremendously. However, the Taylorcraft wing does not produce as fast a roll rate as the "Cub" wing of equivalent span. Also well known in both competition and air show exhibition is N-38333 built by the Piper factory for Bevo Howard, later owned by Charlie Hillard, and presently owned by Bob Copeland, also of Chandler, Arizona, Bob has converted to Taylorcraft wings also.
In the last couple of years, both experimental "Cubs" and standard category Reed "clipped-wing Cubs" have been active in primary competition. Table 1 lists some of the more-active competition pilots and their "Cubs".
Because of the popularity and interest in the "Cub" as both a sport plane and as a competition/air show plane, we felt it would be of interest to compare the character- istics and performance of a stock "Cub" and "clipped-wing" with equivalent power. Amos Townley, owner of N-2041M, is a newspaper writer and photographer for the "Coles County Times" of Charleston, Illinois. N-2041M has been used by Bill Lumley for air show comedy acts. Giles Henderson is a chemist and member of the faculty at Eastern Illinois University at Charleston. He is a co-owner with Dan Foote, also a chemistry professor at EIU, of the "clipped-wing", N-6620H. Henderson and Foote modified the aircraf~ in 1968 and it has been active in both competition and air shows since.
COMPETITION "CUBS" AND PILOTS
Name Base Engine
Harold Tapley, Shaw, MS 0-200
Dot Etheridge, Greenville, MS 0-200*
Gary Wilson, Kaneoke, HI C-85
Joe Molinary, New Orleans, LA A-75
Jim Guzman, Dallas, TX C-85
Gene Olson, Crystal Lake, IL C-75
Dan McGarry, Riverdale, IL C-90'
Jerry Spear, St. Louis, MO C-85
Giles Henderson, Charleston, IL A-65'
Don DeWitt, Worth, IL C-85'
Jay Harowitz, Shreveport, LA C-90
*Air show smoke system
Aircraft Stock J3 Clipped-Wing
Engine A-65 A-65
Propeller Metal Metal
Empty Weight 728 Ibs. 696 Ibs.
Useful load 501 Ibs. 404 Ibs.
Wing span 35 ft. 28 ft.
Wing area 178.5 sq. ft. 143.0 sq. ft.
Wing area .107 .134
Power loading 15.2 Ibs./hp 14.7 Ibs./hp
Wing loading 5.53 Ibs./sq. ft. 6.69 Ibs./sq. ft.
(Power off) 38 mph 46 mph
(75 percent power) 70 mph 75 mph
Maximum speed 82 mph 86 mph
Take-off ground run 230 ft. 344 ft.
Normal rate of climb 560 fpm 473 fpm
Maximum glide ratiob 10:1 6.8:1
Roll rate 33 deg./sec. 86 deg./sec.
Snap-roll rate 150 deg./sec.
NOTE: Above data measured with one pilot (160 Ibs.), 12 gals. of fuel, and air temperature 94-100 degrees F.
In order to obtain a meaningful comparison of performance, the test flights were made with identical loads in both "Cubs" and were flown on the same day under identical weather conditions. The data used in this report represents an average of at least three trials. The air-speed indicators were calibrated relative to each other using a pressure manometer. All altitude measurements were made with the same calibrated sensitive altimeter in both aircraft. Rates of climb and descent were measured with a sensitive altimeter and stopwatch beginning each test 300 ft. above or below the starting altitude and timing point to take up the lag in the altimeter. In a climb test, for example, full power was applied and the attitude of the aircrafL adjusted for the desired air speed at 1700 ft. At 2000 ft. the stopwatch was initiated. The rate of climb for that particular trial could be obtained by dividing the change in altitude by the corresponding elapsed time. Table 2 compares the characteristics of the "Cubs".
Note that the take-off ground-roll requirements for the "clipped-wing" is approximately 50 percent higher than for the stock "Cub". The shorter wing raises the stall speed by 21 percent and only increases the cruise speed by seven percent. A very significant point is the tremendous loss in useful load. In fact, with a full load of fuel, the "clipped-wing" can only carry a 120 lb. passenger (with parachutes and a 150 lb. pilot).
Fig. 1 compares the rate of climb as a function of indicated air speed. At normal climb configuration (full power and 56 mph IAS) the stock "Cub" has a substantially better climb rate. The difference is much more dramatic when both aircraft are at gross weight. It is interesting to note that at extreme pitch attitudes, right on the verge of stall, the "clipped-wing's" performance is better. Naturally climbs in this range are normally considered abusive to the engine and potentially Unsafe.
Fig. 2 and 3 clearly reveal that without power the "clipped-wing" "falls out of the sky" in contrast to the stock "Cub". Shortening the wings does not improve the air speed very much. Fig. 4 plots air speed as a function of horsepower and engine rpm.
By conventional standards, the stock "Cub" clearly has higher all-around performance and is a far safer airplane than the "clipped-wing" with an equivalent engine. However, this very significant sacrifice in performance (particularly useful load) is compensated by a large increase in structural integrity due to the larger struts, fittings, and shorter coupling. From an aerobatic standpoint, the "clipped-wing" has far better aileron and rudder response resulting in a high increase in roll rate (See Table 2). Practically the entire trailing edge of the "clipped-wing" is aileron. Barrel rolls and slow rolls can be completed with only a fraction of available aileron travel. In experienced hands, the "Cub" can hold its own in Primary competition, even with the little 65-hp engine· There is no question that it is handicapped with the small powerplant, but contest records speak for themselves.
Many of the performance deficiencies can be greatly improved with larger engines. However, this invariably raises the modification costs substantially. In fact it is not at all uncommon that the powerplant, inverted system, propeller, cowl, and engine mount will cost considerably more than the rest of the entire airplane.
The clipped-wing Cub" offers a compromise between aerobatic capability and a more general sport aircraft. Certainly the "clipped-wing" Taylorcraft is a far more efficient aircraft with considerably more aerobatic potential. However, the “Cub" offers a two-place configuration.
In conclusion, we hope we have pointed out the rather severe sacrifices in clipping the wings of the "Cub". The consistent appearance of clipped-wing" Cubs" in "Trade-A-Plane" vouches for the dissatisfaction of many owners. Typically the air show buff goes home from the fly-in with a great deal of enthusiasm and determination to saw the wings off his "Cub". After the modification, he discovers that he doesn't really enjoy aerobatics and that the loss in performance was far greater than expected. He can either go to a larger engine or sell. If he has lost his enthusiasm for aerobatics he probably elects the latter.
Our advice is either to buy an already modified "Cub" (which is almost always far cheaper than modifying one yourself) or, if you insist on cutting up your own stock "Cub", at least be certain that you know what you will wind up with. As scarce as good "Cubs" are becoming, it seems a shame to cut the wings off and then decide that's not what you want after all.
The authors would like to express their gratitude to Co-Air, Inc. of Coles County Airport at Mattoon, Illinois for the use of a calibrated sensitive altimeter and, in particular to Earl Adkisson, EAA 1476, owner and operator of Tuscola Flying Service at Tuscola, .Illinois for his, encouragement, and technical advice. Earl, well
known in the Midwest for his 1908 French "Demoiselle" replica and an original gull-wing design, supervised and assisted in the modification of N-6620H.
6 APRIL 1979