In the tradition of the 21st century Volksplane thread, I have been kicking around a concept for a wood geodetic light aircraft in the same weight class as the Evans VP-2, so about 1050 lb gross weight, but with far better performance thanks to lighter construction and cleaner design.
The nature of wood geodetic construction lends itself to a rounded cross section fuselage but I could see going with a Reuleaux polygon shape (odd number of sides, each side an arc of a circle like a Wankel rotor) instead. The triangle could work well for a low-wing design with bulged left and right canopy sections or the pentagon for a low-wing or shoulder-wing cabin design.
The idea would be to use short sections of geodetic diagonals rather than the continuous spirals like the Thalman designs to make more efficient use of materials and create a kit that could fit within ordinary package delivery size limits. Standard UPS limits are 150 lb/68 kg max weight, 108 in/274 cm max length, and 165 in/419 cm max length + girth. That could be managed with the short geodetic elements, longerons and wing spars in graduated sizes assembled by the builder, and large bulkheads/formers in left/right or top/bottom halves.
Performance-wise, here are the numbers I am getting with a 64 hp Suzuki G10 3-cylinder auto engine and redrive. Probably a bit optimistic, but it's a place to start.
PRELIMINARY PERFORMANCE ESTIMATE FOR PROPELLER DRIVEN AIRCRAFT
Crew weight 400 lbs
Fuel + baggage weight 100 lbs
A/C empty weight 550 lbs
Total weight 1050 lbs
Stall speed (flaps up) Vs1 45 mph
Climb airspeed 58.5 mph (climb speed = 1.3 x stall speed)
Climb airspeed 85.8 ft/sec
CLmax 1.5 (flaps up)
CL at 1.3 Vs 0.89 (at 1.3 Vs, CL = CLmax x (1/1.3²))
Wing area required 135.0 ft² (L=1/2 rho V² S CL)
Propeller efficiency at take-off 70 70%
Propeller efficiency in the climb 75 75%
Propeller efficiency in the cruise 85 85%
Cd (profile) 0.01 0.01
Cd (parasite) 0.015 0.015 (Speeds between 1.1 Vs and 2.7 Vs)
Aspect ratio 5.8
Induced drag factor K 1.2 (Cd (induced) = K CL²/π A)
(K = 1.0 elliptical wing, 1.1 moderately tapered, 1.2 rectangular)
Wing span 28.0 feet
Mean wing chord 4.83 feet
ESTIMATED PERFORMANCE WITH AN ENGINE OF YOUR PROPOSED RATED POWER
Selected rated shaft power 64.0 BHP
Effective flat plate area 3.75 ft²
Take off run 530 feet
Rate of climb at 1.3 Vs 1062 feet per minute
Max level speed 128 mph
Cruise speed at 75% power 116 mph
Flaps up stall speed 45 mph
Glide descent rate at 1.3 Vs 446 feet per minute
Just notions at this point, but I'd welcome some feedback. See also the attached Powell articles on wood geodetic design, which have been posted before but are always worth a second look.
Cheers,
Matthew
The nature of wood geodetic construction lends itself to a rounded cross section fuselage but I could see going with a Reuleaux polygon shape (odd number of sides, each side an arc of a circle like a Wankel rotor) instead. The triangle could work well for a low-wing design with bulged left and right canopy sections or the pentagon for a low-wing or shoulder-wing cabin design.
The idea would be to use short sections of geodetic diagonals rather than the continuous spirals like the Thalman designs to make more efficient use of materials and create a kit that could fit within ordinary package delivery size limits. Standard UPS limits are 150 lb/68 kg max weight, 108 in/274 cm max length, and 165 in/419 cm max length + girth. That could be managed with the short geodetic elements, longerons and wing spars in graduated sizes assembled by the builder, and large bulkheads/formers in left/right or top/bottom halves.
Performance-wise, here are the numbers I am getting with a 64 hp Suzuki G10 3-cylinder auto engine and redrive. Probably a bit optimistic, but it's a place to start.
PRELIMINARY PERFORMANCE ESTIMATE FOR PROPELLER DRIVEN AIRCRAFT
Crew weight 400 lbs
Fuel + baggage weight 100 lbs
A/C empty weight 550 lbs
Total weight 1050 lbs
Stall speed (flaps up) Vs1 45 mph
Climb airspeed 58.5 mph (climb speed = 1.3 x stall speed)
Climb airspeed 85.8 ft/sec
CLmax 1.5 (flaps up)
CL at 1.3 Vs 0.89 (at 1.3 Vs, CL = CLmax x (1/1.3²))
Wing area required 135.0 ft² (L=1/2 rho V² S CL)
Propeller efficiency at take-off 70 70%
Propeller efficiency in the climb 75 75%
Propeller efficiency in the cruise 85 85%
Cd (profile) 0.01 0.01
Cd (parasite) 0.015 0.015 (Speeds between 1.1 Vs and 2.7 Vs)
Aspect ratio 5.8
Induced drag factor K 1.2 (Cd (induced) = K CL²/π A)
(K = 1.0 elliptical wing, 1.1 moderately tapered, 1.2 rectangular)
Wing span 28.0 feet
Mean wing chord 4.83 feet
ESTIMATED PERFORMANCE WITH AN ENGINE OF YOUR PROPOSED RATED POWER
Selected rated shaft power 64.0 BHP
Effective flat plate area 3.75 ft²
Take off run 530 feet
Rate of climb at 1.3 Vs 1062 feet per minute
Max level speed 128 mph
Cruise speed at 75% power 116 mph
Flaps up stall speed 45 mph
Glide descent rate at 1.3 Vs 446 feet per minute
Just notions at this point, but I'd welcome some feedback. See also the attached Powell articles on wood geodetic design, which have been posted before but are always worth a second look.
Cheers,
Matthew
