The History: Today, Wilbur Wright answered Octave Chanute's letter of August 27th. Wilbur and Orville have been working diligently on their motorized flying machine. Having made new calculations on the amount of power the machine would generate, the brothers have determined their machine will produce more power than they first predicted. Consequently, the brothers will strengthen particular components of their machine. For example, they are reconstructing the axles, which carry the propellers, to make the axles stronger. Wilbur estimates their new machine will weigh 675 pounds.

Their trip to Kitty Hawk to test the new machine has been delayed due to "outside matters". [Their father, Bishop Milton Wright was expelled from a church conference by a majority of the church elders.] However, the brothers hope to leave for Kitty Hawk within three weeks.

Wilbur addresses Chanute's first question on the area of the supporting [lifting] surfaces. At 18 miles per hour, Wilbur estimates that the supporting area of their machine is approximately 305 square feet. However, as the machine moves faster through the air the front rudder also contributes to the lifting capability of the machine [it acts like a wing]. Wilbur notes that at 30 miles per hour, a square foot of the front rudder lifts about twice as much as a square foot of the wing. At this speed, the front rudder is held at a higher angle of incidence than the wing.

Wilbur Wright Flying In the 1902 Glider

Chanute also had asked Wilbur, which 1901 wind tunnel airfoil shape data was used in the calculations of the 1902 glider. Wilbur related to Chanute that the brothers never wind tunnel tested a shape exactly like the one used on the 1902 glider's wings. Consequently, Wilbur used an average of the airfoil #9, #12 and # 35 data in his calculations.

Airfoils #9, #12 and #35.

At first glance, Wilbur's comments regarding the front rudder's lifting capabilities may be puzzling. Why would the front rudder be able to lift twice as much as an equivalent area of a wing? Today we know that aerodynamic lift (the lift force generated by an airplane) increases as:

• the speed increases;
• the area of the lifting surface increases;
• the angle of attack increases (the angle between the lifting surface (such as a wing) and the wind).

Wilbur states that the angle of incidence (now called the angle of attack) of the front rudder is greater than the angle of incidence of the wing. The higher angle of attack is one reason the front rudder would have a greater lifting capability.