PL. 4. RUBBER-MOTOR MODEL AERODROME NO. 26 [◊]
OBSERVATION OF NOVEMBER 20, 1891. | ||||||||
| OBSERVER, S.P.L. | LOCALITY, UPPERHALL, SMITHSONIANBUILDING. | |||||||
| No. 30. Single wings. | No. 31. Superposed wings. | |||||||
|---|---|---|---|---|---|---|---|---|
| CPm | 1516.5 | cm. | ||||||
| CG1 | 1515 | 1517 | cm. | |||||
| CFw | 1528 | cm. | ||||||
| Length (without fender) | 120 | cm. = | 3.94 | ft. | 120 | cm. = | 3.94 | ft. |
| Width over wing tips | 120 | cm. = | 3.94 | ft. | 120 | cm. = | 3.94 | ft. |
| Weight of rubber (72 grammes in each tube) | 144 | gr. = | 0.32 | lbs. | 144 | gr. = | 0.32 | lbs. |
| Total flying weight (including tail) | 432 | gr. = | 0.95 | lbs. | 506 | gr. = | 1.11 | lbs. |
| Turns of rubber | 30 | 30 | ||||||
| Diameter of propellers | 37 | cm. = | 1.21 | ft. | 37 | cm. = | 1.21 | ft. |
| Width of propellers | 7 | cm. = | 0.23 | ft. | 7 | cm. = | 0.23 | ft. |
| Pitch of propellers | 50 | cm. = | 1.64 | ft. | 50 | cm. = | 1.64 | ft. |
| Area of wings (each 992 sq.cm.) | 1984 | sq.cm.= | 2.13 | sq.ft. | Each pair 1984 sq.cm.= 2.13 sq.ft. Total 3968 sq.cm.= 4.26 sq.ft. | |||
| Area of tail | 373 | sq.cm.= | 0.40 | sq.ft. | 373 | sq.cm.= | 0.40 | sq.ft. |
Area of wings and tail in No. 30, 2357 sq. cm. = 2.53 sq. ft. 2.53 sq. ft. ÷ .95 = 2.7. Therefore, there are 2.7 or nearly 3 square feet of sustaining area to the pound. | ||||||||
| Nov. 20, 1891. | ||
| Flight. | Aerodrome. | Results. |
|---|---|---|
| 1 | No. 30 | With 30 turns of the rubber, flew low through 10 metres. |
| 2 | No. 30 | Flew heavily through 12 metres. |
| 3 | No. 31 | Flew high and turned to left; distance not noted. |
| 4 | No. 31 | The right wing having been weighted (to depress it and correct the tendency to turn to the left), model flew high, but the rubber ran down when it had obtained a flight of 10 metres. |
| 5 | No. 31 | The wings were moved backward until the CP stood at 1493. The model still turned to the left; flight lasted three and a-half seconds; distance not noted. |
| 6 | No. 31 | Vertical tail was adjusted so as to further increase the tendency to go to the right. In spite of all this, the model turned sharply to the left, flying with a nearly horizontal motion; time of flight not noted; distance not noted. |
| 7 | No. 30 | Straight horizontal flight; time three and three-fifth seconds, when rubber ran down; distance 13 metres. |
| 8 | No. 30 | Straight flight as before; time two and four-fifth seconds; distance 13 metres. |
| 9 | No. 30 | With a curved wing in the same position as the flat wing had previously occupied, model flew up and struck the ceiling (nearly 30 feet high), turning to right, with a flight whose curtate length was 10 metres. |
| 10 | No. 30 | Wing having been carried back 5 centimetres, model still flew up, but not so high, and still turned to the right. |
| 11 | No. 30 | Wings carried back 5 centimetres more; model still flew high; time two and two-fifths seconds; distance 13 metres. |
| 12 | No. 30 | Wings carried back 4 centimetres more; model still flew high during a flight of 13 metres. |
The observations now ceased, owing to the breaking up of the model. | ||
The objects of these experiments, as of every other, were to find the practical conditions of equilibrium and of horizontal flight, and to compare the calculated with the observed positions of the center of pressure. They enable us to make a comparison of the performances given by earlier ones with a light rubber motor, with the relatively heavy motors used to-day, as well as a comparison of single flat, single curved, and superposed flat wings.
The average time of the running down of the rubber in flight was something like three seconds, while the average time of its running down when standing still was but one and a half seconds. It might have been expected from theory that it would take longer to run down when stationary, than in flight, and this was one of the many anomalies observed, whose explanation was found later in the inevitable defects of such apparatus.
The immediate inferences from the day’s work were:
1. That the calculated position of the CP at rest, as related to the CG, is trustworthy only in the case of the plane wing.
2. The formula altogether failed with the curved wing, for which the CP had to be carried indefinitely further backward.
On comparing the previous flights of November 14, with these, it seems that with the old rubber motor of 35 grammes and 50 turns, the single wing, either plane or curved, is altogether inferior to the double wing; while with the increased motor power of this day, the single wing, whether plane or curved, seems to be as good as the double wing. It also seems that the curved wing was rather more efficient than the plane one.