P.Bowers Boeing Aircraft since 1916 (Putnam)

MODEL 2 (C-4) - The C-4 was so named because it was the third aeroplane design used and the fourth aeroplane owned by Boeing, including the Martin seaplane. It was the second Boeing design, even though the firm was still known as Pacific Aero Products at the time it was built, and carried Serial Number 3 because it was the third aeroplane built. It was an entirely original design and differed considerably from the B & W both in basic aerodynamic characteristics and general appearance. The wings had an unusual degree of stagger and dihedral angle compared to other aircraft of the period for the purpose of providing inherent stability. This was considered by the Boeing engineers as the most desirable characteristic for a training aeroplane. The tail surfaces differed from the B & W in that the horizontal stabilizer was deleted and a vertical fin added. The C-4 was dismantled after testing but was rebuilt and flown in August 1918. See Model 3 for specifications.

MODEL 3 (C-5,6,11) - Slightly revised versions of the Model 2 (C-4), the major outward difference being rearrangement of the centre section struts to join at the centre line of the upper wing. C-5 and C-6 were sold to the US Navy for evaluation as trainers after the United States entered WW-I and C-11, rebuilt from the C-4, was delivered to a private owner in July 1918.

TECHNICAL DATA - C-5
   Type: Trainer
   Accommodation: 2 in tandem
   Power plant: Hall-Scott A-7A, 100 hp
   Span: 43 ft 10 in
   Length: 27 ft overall
   Height: 12 ft 7 in
   Wing area: 495 sq ft
   Empty weight: 1,898 lb
   Gross weight: 2,395 lb
   Max speed: 72.7 mph
   Cruising speed: 65 mph
   Service ceiling: 6,500 ft
   Range: 200 miles
   C/ns: 6,7,8
   Navy serial numbers: 147, 148 (for 6 and 7)
  

MODEL 5 (C-650-700, C-1F, CL-4S) - Fifty Model 5s were ordered by the Navy as primary trainers following evaluation of the two Model 3s (C-5 and C-6) which can be considered the military prototypes. Since the production models were practically identical, Boeing retained the designation of Model C, supplementing it with the Navy-assigned serial number 650 to 699 for each individual aeroplane. The Navy ordered one additional aircraft (A-4347) for test with a single main float installation and a Curtiss OXX-6 engine. This was identified by Boeing as the C-1F (meaning Model C with one float). Before the C-1F was completed, the single float installation was tested on the rebuilt Model 2 (C-4), that became the C-11.
   One additional Model C was built for William E Boeing, and since it followed the last Navy trainer, C-699, through the shop, it was logically called C-700. The C-700 was modified slightly in December 1918, and redesignated CL-4S, indicating a Model C with the new four-cylinder Hall-Scott L-4 engine. This aeroplane was used by William Boeing and Edward Hubbard on March 3, 1919, to make a demonstration international air mail flight from Vancouver to Seattle in connection with a Canadian exposition. This flight inspired the later inauguration of the Seattle - Victoria Contract International Air Mail route, where transpacific mail was delivered to and picked up from ships a day out of Seattle. Since it was operating in Canada at a time when Canadian aircraft had to carry registrations but US aircraft did not, it was registered as G-CADR (G for Great Britain, CA for Canada) for the initial part of its mail service. The G-prefix was soon changed to the assigned N for the United States to show its true ownership.
   The Navy declared all the Model Cs surplus after WW-I, taking full-page ads in the aviation magazines to advertise them and quote the original price of $ 10,250 each. About the first thing the private owners did was to replace the highly unreliable Hall-Scott engines with either 90 hp Curtiss OX-5s or 150 hp Wright-Hispano surplus engines. Several Cs were still flying when US registration became mandatory in January 1927, and at least two were painted in German WW-I markings and crashed for the film 'Dawn Patrol' in 1931.

TECHNICAL DATA - C-650/C-700
   Accommodation: 2 in tandem
   Power plant: Hall-Scott A-7A, 100 hp
   Span: 43 ft 10 in
   Length: 27 ft overall
   Height: 12 ft 7 in
   Wing area: 495 sq ft
   Empty weight: 1,898 lb
   Gross weight: 2,395 lb
   Max speed: 72.7 mph
   Cruising speed: 65 mph
   Service ceiling: 6,500 ft
   Range: 200 miles
   C/ns: 9/60
   Navy serial numbers: 650/699 for c/n 10/59, 4347 for c/n 9

G.Swanborough, P.Bowers United States Navy Aircraft Since 1911 (Putnam)

Boeing C, C-1F

   The sixth and seventh Boeing aeroplanes built, designated C-5 and C-6 by the manufacturer, were submitted to the Navy early in 1917 for test as primary trainers. The design was a slight modification of the C-4, incorporating an unusual degree of stagger and dihedral on the wings to achieve inherent stability. On the basis of the tests, the Navy ordered 50 production models that established the tiny Boeing Airplane Company as a 'major' manufacturer. The production versions were still called Model C by Boeing, and individual machines were identified by appending the Navy serial number to the designation, the whole lot thus being identified as C-650 through C-699. Although not a naval aircraft, an additional Model C built for Mr William E. Boeing in 1918 was called C-700 simply because it followed the last of the Navy machines through the factory.
   An unusual feature of the Model C, apart from the amount of stagger to the wings, was the absence of a fixed horizontal tail plane. This last feature became a point of controversy between the pilots, who insisted there should be one, and the designer, who maintained that because of the stability imparted by the stagger, a stabilizer was not necessary and performance was increased by the weight saving.
   Otherwise a conventional twin-float seaplane, the Model C was not used at Naval training schools after delivery because of the extremely poor performance of the Hall-Scott A-7A engine. Most of the Cs were sold as surplus after the war, still in their original packing crates. The Army had similar experience with the Hall-Scott, and grounded its Standard Model J primary trainers, which used the same engine.
   Recognizing the deficiencies of the Hall-Scott, the Navy ordered an additional Model C, powered with the 100 hp Curtiss OXX-6 engine, under the designation of C-1F, meamng a C with one main float instead of the usual two.

TECHNICAL DATA (Boeing Model C)
   Manufacturer: Boeing Airplane Company, Seattle, Washington.
   Type: Training seaplane.
   Accommodation: Two pilots.
   Power plant: One 100 hp Hall-Scott A-7A.
   Dimensions: Span, 43 ft 10 in; length, 27 ft; height, 12 ft 7 in; wing area, 495 sq ft.
   Weights: Empty, 1,898 lb; gross, 2,395 lb.
   Performance: Max speed, 72.7 mph at sea level; cruising speed, 65 mph at sea level; climb, 23.5 min to 5,000 ft; service ceiling, 6,500 ft; range, 200 st miles.
   Serial numbers: C: A147-A148, A650-A699. C-1F: A4347.

Jane's All The World Aircraft 1919

General Description of Model C.L. 4 S.
  
   The model C.L. 4 S is a modification of the model " ? " seaplane. Although the general appearance and characteristics remain the same, the new engine installation together with a few minor changes have added to the performance of this machine.
   The wing structure with its center cabane of steel simplifies assembly and clears the approach to, and vision from, the cockpits.
   The tail unit, consisting of balanced elevators, rudder and fin, is independently complete, readily assembled and firmly fixed in place by steel tuning, forming a compact structure in keeping with the wind surfaces.
   The body, although short in appearance, is wholly in keeping with the aero and hydro conditions met with in this type of seaplane.
  
  
Specification.
  
Power Plant.
   (Hall-Scott Liberty Four) 125 h.p.
  
Wing and Control Surface Areas.
   Main planes (including ailerons) 475 sq. ft.
   Upper planes (including ailerons) 246 sq. ft.
   Lower planes 229 sq.ft.
   Ailerons 36.0 sq.ft.
   Number of ailerons 2.
   Elevators 30.0 sq. ft.
   Rudder 12.0 sq.ft.
   Vertical fin 6.0 sq.ft.
  
Overall Dimensions.
   Span, upper 43 ft. 6 in.
   Span, lower 43 ft. 2 in.
   Chord, upper and lower 69 in.
   Gap 72 in.
   Length overall 27 ft.
  
Incidence of Wings with Propeller Axis.
   Upper 6 1/2 degrees.
   Lower 4 degrees.
   Dihedral 2 3/4 degrees.
   Stagger 29 1/2 in.
  
Performance.
   Get away 11 sec
   Climb in 10 mm. (full load) 3.600 ft.
   High speed 75 m.p.h.
   Landing speed 38 m.p.h.
   Endurance at full speed 3 hours.
   Gasoline consumption
   (during altitude climb) 10.5 gallons per hour.
   Oil consumption
   (during altitude climb) 1.0 gallon per hour.
  
Weight
   Fully loaded 2,430 lbs.