GREAT LAKES . . . (Continued from page 33)

Questions about the "Baby Great Lakes" tend to standardize into several patterns, and the following is a condensation of several hundred inquiries and their answers: 1. What are flight performance characteristics? See specifications.

2. How are control responses? Light, but not overly sensitive. 3. What is it stressed for in Gs? 9G, normal or inverted flight.

Increasing The

4. What are its ground handling characteristics? Very

good, even with a locked tailwheel. 5. What are its landing and take-off distances? See specifications. 6. What are the power ranges and types of engines? 50

By Capt. Luther M. Nail ALO — HQ YD Corps. APO, New York, N.Y. 09107

to 100 hp. 7. Is it easy to build? Yes, as construction is straightforward.

8. What are the construction materials and are they easy

to obtain? Construction details follow the same general methods used on the Great Lakes sport trainer, and

both aircraft have: N-type interplane struts; double landing and flying wires, N-type center-section supporting struts; ailerons on bottom wings only; spruce spars and ribs, fabric covered; welded steel tube fuselage, fabric covered; single open cockpit on the "Baby" with two open tandem cockpits on the trainer; and welded steel tail structure, fabric covered. In addition, the landing gear can be of the oleo main-leg type with alternate bungee, spring steel, or rigid versions available. Material kits are available from several sources, including Great Lakes Aircraft Co. 9. How old is the design? Fourteen years old, and it has been constantly updated to conform with the contemporary state of the art. 10. Who can advise about construction difficulties that

may arise? Harvey Swack, Coordinator of Great Lakes Aircraft Co. 11. Is there an information service available concerning

the design? The plans seller has an information packet and sends periodic newsletters to builders. 12. What is the average construction cost, less engine?

$750.00 to $1,000.00.

13. Are any being built outside of the United States? Yes, construction is known in Canada, Australia, and Italy —probably others. 14. Is it easy to fly? Yes, gentle as a lamb, and out-glides a "Cub." 15. Does it have any faults, either in the air or on the ground? None that are known. 16. What is the safety record of the design? Perfect.

17. How many are under construction and now flying?

Over 140 are under construction and at least eight are now flying regularly. "BABY GREAT LAKES" SPECIFICATIONS

Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 ft. 8 in. Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 ft. 9 in. Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 ft. 6 in. Wheel track . . . . . . . . . . . . . . . . . . . . . . . . . 4 ft. 6 in. Total wing area . . . . . . . . . . . . . . . . . . . . . . 86 sq. ft.

Empty weight (varies with engine) . . . . . . 475 Ibs.

Gross weight . . . . . . . . . . . . . . . . . . . . . . . . . 850 Ibs. Maximum speed . . . . . . . . . . 135 mph at sea level

Cruise speed . . . . . . . . . . . . . . . . . . . . . . . . . 118 mph Stall speed . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 mph Rate of climb . . . . . . . . . . . . . . . . . . . . . . . 2,000 fpm Service ceiling . . . . . . . . . . . . . . . . . . . . . . 17,000 ft. Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 miles Take-off run . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 ft. Landing run (less brakes) . . . . . . . . . . . . . . . 400 ft. PAGE 36

NOVEMBER 1989

(EDITOR'S NOTE: The following piece has been adapted from a letter originally written to Gus Limbach by Capt. Nail. We have extracted those parts of the letter of general interest, and are pleased to offer this material. It gives an insight to how small, well-thought-out changes can be made to overcome an airplane's flight deficiencies).

It was with interest that I read the article about Gus Limbach's fine little "Gusty" aerobatic monoplane in the April, 1968 issue of SPORT AVIATION. It sounds and

looks great, and I would not be surprised to see duplicates of it being constructed. Of particular interest to me was the part about the ailerons. A while ago I was researching some NASA reports for my own project, an original delta with, as it just happens, a symmetrical airfoil in its wing. As I read about "Gusty", I remembered some things I had come upon about how to increase aileron effectiveness. As this information may be of help not only to Gus and his "Gusty" but to other experimenters as well, I am putting it on paper as follows. Referring to the aileron problem described by Gus, the first thing that might be done is to attach short strips of yarn to the upper surface of the wing and flight-check the ship for airflow characteristics. The symmetrical airfoil is efficient at cruising speeds, but at lower speeds higher angles of attack are required to produce the necessary lift as compared to a positive-cambered airfoil section. Thus, the air must negotiate a greater change in flow direction and consequently more energy is lost. It should not be necessary to tuft the wing forward of approximately the mid-chord point or inboard of the aileron. In the speed range where a lack of lateral responsiveness has been noted in the ailerons, some whipping of the tufts will probably be noticed. However, it will appear to be "lazy" rather than violent. Fig. 1 shows what is probably happening; a lazy whipping would indicate reduced energy flow or aerodynamically dead air in the boundary layer which is quite thick. Since the aileron is in this area, response will be proportional to the loss or gain in the energy of the air in which the surface operates. This is not meant to suggest that the symmetrical airfoil is not good; it just depends on what characteristics are desired. The symmetrical airfoil is very desirable for an aircraft like "Gusty", producing excellent inverted flight characteristics with minimum effort on the part of the plane and its pilot. But along with this advantage comes

Effectiveness Of Ailerons

CAMBERED WING FIG. 1 AERODYNAMICALLY DEAD AIR

SYMMETRICAL WING

B.UL. SLAKE

4" TO 6" APART ~— ALTERNATE DIRECTION OF S\ DEFLECTION WITH AIRFLOW * DEFLECTION ANGLE 1 TO 3'

Vl" TO

3

/i" ABOVE WING SURFACE

the problem of aileron control due to the air-flow characteristics. The solution to the aileron problem lies either in reenergizing the airflow or redesigning the ailerons. The latter approach can be time consuming and expensive. It is much quicker and cheaper to attach vortex generators to the top surface of the wing ahead of the ailerons. These are small vanes set at a slight angle to the airflow and are a familiar detail on jet aircraft. By checking the airflow pattern as indicated by the tufts, it should be easy to decide where to locate them. Place them where lateral or bouncing movement of the tufts is first noted, following the pattern shown in Fig. 2. It would be proper to start out by putting some vortex generators ahead of a small section of the inboard portion of each aileron for the first flight test, and add more of them outboard of the first ones if some improvement in aileron control is noted and more seems desirable. But before adding more generators, make stall tests and highG roll response tests as a precaution against making the ailerons too effective under severe maneuvering conditions. Another approach might be to change the aileron section. Fig. 3 shows ways in which ailerons hinged in various popular ways can be so treated. Modification in this manner can be accomplished easily on fabric-covered ailerons, while all-metal ailerons could be "double-covered" with aluminum sheet bent to the shape shown by the dotted lines and temporarily although securely attached for flight tests. Flutter should not be a problem but, just in case, it would be well to be watchful for it when making tests. High-speed and cruising-speed feel, and behavior of the ailerons, should not be too much different — perhaps a little more sensitive. But low-speed responsiveness should definitely improve! If none of these modifications gives the desired amount of aileron responsiveness, then an increase in aileron chord might be considered. I have flown several military aircraft having short-span, very-long-chord ailerons, including the F-104, T-38, and F-4. They, too, had symmetrical or modified symmetrical airfoils of very thin section, requiring very high angles of attack when flying at low speeds. As aileron chord is increased, more of the aileron's surface area is put ahead of the area of aerodynamically dead air operating farther back on the chord. And for a given angular upward displacement, the trailing edge of a long-chord aileron will move up farther, in effect moving its surface up out of the stagnant area with resulting increased responsiveness. The foregoing suggestions are based on practical experience and observation; I don't claim to be an authority on aerodynamics. So in the interest of safety please take these suggestions with certain reservations and ease into modifications carefully and gradually. But done prudently, the modifications I have suggested can be the simple

answers to seemingly baffling aileron behavior.

SPORT AVIATION

®

37