How big is the airplane?
The airplane has a wing span of 115 ft, a length of 30 ft, a height of 11 ft, and a weight of 90 lb. How much did the airplane cost?
This is a tough question to answer, because most of the material and labor was donated. However, Paul estimates (as of September 1997) that the material cost of the airplane is about $15,000. The control electronics are worth about $20,000. And the labor donated to the program is worth about $300,000.
How do you make an airplane so light?
We use advanced composite materials and careful design and construction.
How much does carbon weigh?
Carbon weighs between 95 and 115 lb. per cubic ft. The stiffer carbons are the heaviest.
How did you design the fuselage?
We defined the space required for the pilot, the pedals, and the landing gear. Once that space envelope was defined, three curves were created:
A crown line - extending from the nose of the fuselage, over the pedals and the pilot's head, and back to fuselage centerline
A keel line - extending from the nose of the fuselage, below the pedals and pilot, and aft below the crown line (allowing room for the retractable landing gear)
A mid line - on side, outside the pedals and pilot, and then up to the crown line (one for each side)
The crown, mid, and keel lines were used as guides to generate upper and lower ellipses which define the fuselage surface.
How much does the fuselage shell weigh?
We have allowed 4 lb. for the fuselage shell.
How much will your fuselage structure weigh?
We have allowed for a 5 lb. fuselage structure.
Why are you using a retractable landing gear?
The airplane has an overall drag restriction of 4.5 lb. By retracting the gear into the fuselage we can reduce airplane drag.
Why don't you use a releasable trolley to hold the airplane during take off?
We could use a trolley to hold the airplane during take off. It would offer reduced flight weight, greater ground stability, and lower drag. The only problem is that international rules specifically deny the use of trolleys.
Are you using a propeller to generate thrust?
Yes.
Why not use flapping wings?
While flapping wings are theoretically more efficient then a propeller, there are no materials available that are strong enough, stiff enough and light enough to make it possible.
Why did you place the propeller on the front of the fuselage?
Placing the propeller on the front of the fuselage makes sense for a lot of reasons:
It places the propeller in undisturbed air
It makes for a small drivetrain
It's lightweight
It moves the fuselage out of the propeller slipstream.
How fast will the propeller spin?
The current design has the propeller spinning at about 135 rpm.
What determines the how fast to spin the propeller?
The first factor is that the pilot will probably pedal at 90 rpm. This is the average pedal speed of a competition endurance bicyclist. (see the pilot FAQ)
Off the shelf gear sets will restrict propeller rpm to some standard multiple of 90 rpm.
Beyond that restriction, here are some rules of thumb for low speed propeller design. The slower the rotation speed, the better. The larger the diameter, the better and the smaller the chord, the better.
How will you move the control surfaces?
The will be two electro-mechanical servos in the aft section of the tail boom. One will control the vertical surface, the other will control the horizontal. Just like The Outer Limits.
What will happen to the airplane after it has flown?
After setting a new world record, the airplane will become the property of Seattle's Museum of Flight.
Why didn't the airplane fly in 1996?
It took us longer to build it than we had planned, mostly because we had trouble finding a place to build it.
What airfoils does the airplane use?
The RAVEN uses six different airfoils.
The main wing uses the DAE11, DAE21, DAE31, and DAE41 airfoils, all of which were invented by Professer Mark Drela of MIT for the Daedalus.
Each airfoil is designed to operated in a specific flow condition along the wing. Specificity, the airfoils are matched to the local Reynold's number (Re). At the wing root where the Re is highest, the DAE11 is used.
Airfoil Design Re Span Location
DAE11 750,000+ 0 - 25 ft
DAE21 500,000 40 ft
DAE31 250,000- 52 ft
DAE41 wing tip wing tip
The DAE41 is a special airfoil used at the wing tip. The airfoils are spaced along the span matching the local Re.
The airfoils are smoothly blended from one shape to another. That is, there is only one location on the wing that is actually DAE21, DAE31, or DAE41. At span location 32, the airfoil is half way between the DAE11 and DAE21 in shape.
The DAE51 is used for the propeller.
The tail surfaces use the WMF09 airfoil. The WMF09 is a reduced thickness WMF15. The WMF15 was designed by Winfried Feifel in support of one of the America's Cup yachts.
