P.Bowers Curtiss Aircraft 1907-1947 (Putnam)
Model 18 Series (Model 15)
In March 1918, the Navy authorized Curtiss to build two two-seat fighter triplanes designed at Garden City by Curtiss engineer Charles Kirkham, Navy serial numbers A3325 and A3326. Unit prices were $55,400 less GFE. Although these were identified in service as Model 18T (for triplane) and were also known as Curtiss-Kirkhams, they carried the Curtiss engineering designation of Experimental 502.
The 18 was designed specifically for the 400 hp Curtiss-Kirkham K-12 engine, a water-cooled geared V-12 type of somewhat unorthodox construction developed late in 1917. The K-12 gave the Model 18 world-record performance in 1918 and evolved into the C-12 and eventually into the D-12 and the Conqueror.
The fuselage was a well-streamlined structure featuring a combination of previous Curtiss flying-boat practice and German laminated wood veneer construction in a new process called Curtiss ply. The nose was kept as streamlined as possible by mounting the radiators on the sides of the fuselage. Armament was a pair of .30-calibre Marlin machine-guns on the nose, a pair of .30-calibre Lewis guns on the rear cockpit Scarff ring, and a single Lewis firing out of the belly.
18T-1 Wasp - Kirkham chose the triplane configuration for his new fighter because the shorter span would enhance the manoeuvrability. The -1 was added to the designation after alternate wings of longer span became available on a -2 version. In all configurations, the 18T was known as the Wasp but, because of the sound of its wires during landing approaches, it was known around Garden City as Whistling Benny.
For its first flight, on 5 July, 1918, the 18T had straight wings; tail heaviness was soon corrected by sweeping the wings back five degrees. The Army became interested in the design and arranged to borrow the first one from the Navy. Tests with full military load in August 1915 produced a top speed of 163 mph (262,3 km/h), making the 18T the world's fastest aeroplane at the time even though the record was not recognized. The Army then ordered two 18Ts of its own with Army serial numbers 40054 and 40059.
No Navy production orders were received for the 18T; its hand-built engine was more experimental than the aeroplane itself and the end of the war killed any requirement for it as a Service type.
The speed of the 18T-1 was put to good use, however, since the Navy entered both examples in postwar air races. Both were flown in the 1920 Pulitzer Trophy Race but dropped out because of engine trouble. As single-float seaplanes, both were entered in the 1922 Curtiss Marine Trophy Race. A3325 (painted green, Race No.5) dropped out with engine trouble and A3326 (painted yellow, Race No.4) was in the lead when it ran out of fuel just short of the finishing line. As landplanes again, both were entered in the 1923 Liberty Engine Builder's Trophy Race for Service two-seaters. A3325 crashed during a trial flight and A3326 (Race No.3) broke its crankshaft during the race and was destroyed.
The first of the two Army 18T-1s was delivered to McCook Field for static test in February 1919.
18T-2 - Since the Navy had no urgent need for both 18s after the Armistice, A3325 was left at Garden City for further testing. A longer set of wings, with two bays of struts and a span of 40 ft 7 1/2 in (12,25 m), was fitted, creating the 18T-2 designation. On 18 September, 1919, Curtiss test pilot Roland Rholfs set a new world's altitude record of 34,910 ft (10,640 m) with this aircraft. Fitted with floats, A3325 also set a world's seaplane altitude record.
In 1919, Curtiss built a fifth 18T as a civil aeroplane. Fitted with long wings, it was sold to Bolivia, where it became the first aeroplane to fly from the capital city of La Paz at an elevation of 13,500 ft (4,115 m). After consistent performance there it crashed on 19 May, 1921.
18B Hornet (Model 15A) - After introducing the 18T, Curtiss offered the same design with more conventional two-bay biplane wings and designated it 19B. This was known as Experimental 510 but was publicized as the Hornet. The Army ordered two in August 1915, with Army serial numbers 40058 and 40064. The first was delivered for static test in June 1919; the flight test aircraft crashed soon after delivery.
Model 18T-1 - Fighter/Observation landplane. Pilot and gunner/observer. 400 hp Curtiss K-12.
Span 32 ft (9,75 m); length 23 ft 4 in (7,11 m); height 10 ft 2 in (3,09 m); wing area 288 sq ft (26,75 sq m).
Empty weight 1,980 lb (898 kg); gross weight 3,050 lb (1,383 kg).
Maximum speed 163 mph (262,31 km/h); climb in 10 min - 12,500 ft (3,810 m): service ceiling 23,000 ft (7,010 m); endurance 5,9 hr.
Armament - two fixed Marlin and three flexible Lewis machine-guns.
Model 18T-2 - Fighter/Observation seaplane. Pilot and gunner/observer. 400 hp Curtiss K-12.
Span 40 ft 7 1/2 in (12,25 m); length 28 ft 3 7/8 in (8,63 m); height 12 ft (3,65 m); wing area 400 sq ft (37,16 sq m).
Empty weight 2,417 lb (1,096 kg); gross weight 3,572 lb (1,620 kg).
Maximum speed 139 mph (223,69 km/h); climb in 10 min - 10,400 ft (3,170 m); service ceiling 21,000 ft (6,400 m).
Armament - one fixed Marlin and one flexible Lewis machine-gun.
Model 18B - Fighter/Observation landplane. Pilot and observer/gunner. 400 hp Curtiss K-12.
Span 37 ft 6 in (11,43 m); length 23 ft 4 in (7,11 m); wing area 306 sq ft (28,42 sq m).
Empty weight 1,690 lb (766 kg); gross weight 2,867 lb (1,300 kg).
Armament - two fixed Marlin and two flexible Lewis machine-guns.
G.Swanborough, P.Bowers United States Navy Aircraft Since 1911 (Putnam)
Although the Navy had only two Curtiss 18-Ts, which the manufacturer named Wasp, they set numerous records and had a significant effect on subsequent designs. The two were ordered on March 30, 1918, and were intended as two-seat fighters. Unusually clean design was achieved in spite of triplane configuration by the fact that the fuselage was a beautifully streamlined structure built up of cross-laminated strips of wood veneer formed over a mould and then attached to the inner structure of longerons and formers. This method was well-established in Germany during the World War I years by such manufacturers as Roland and Pfalz, but had been used only on a limited scale in the United States, most notably by Lowe, Willard and Fowler (L.W.F.). Curtiss had previous experience with similar construction in the hulls of the Model F flying-boats and the early H-boats, and this feature was to reappear in several subsequent Curtiss designs, most notably the Pulitzer and Schneider racers of the early 1920s.
At a time when equivalent American military designs were being planned round the Liberty engine, the 18-T used an entirely new power plant, the Curtiss K-12, developed for Curtiss by the well-known engine designer Charles Kirkham. The aircraft and the engine were designed for each other, and because of this, the 18-T and its equivalent biplane version, the 18-B Hornet for the Army, were often referred to as Curtiss-Kirkhams. The compact power plant, which produced 400 hp, developed into the famous Curtiss D-12 (V-1150) of the 1920s and the larger V-1570 Conqueror of the 1930s, some examples of which remained in use until World War II. The K-12 enabled the 18-T to set an official world's speed record of 163 mph with full military load on August 19, 1918. On July 25, 1919, Curtiss test pilot Roland Rholfs established an American altitude record of 30,100ft, later raising it to an official world record of 34,610ft on September 19.
In its original form the 18-T, which first flew on July 5, 1918, had single-bay unswept wings of 31 ft 11 in span. Because of tail heaviness resulting from the heavy wood construction, five degrees of sweepback were built in to move the centre of lift aft. The Navy loaned the first modified 18-T, A3325, to the Army for test, after which the Army ordered two examples of its own for comparison with the biplane version then under construction. In order to improve the altitude capability of the design and accommodate the additional weight of floats, longer two-bay wings were built and installed, the short-wing version becoming 18-T1 and the long-wing 18-T2.
While never ordered into production as a service type, the 18-Ts' performance was such that they were both kept on hand by the Navy as racers. In the short-wing landplane configuration, both were entered in the 1920 Pulitzer Race, but dropped out before the finish with engine trouble. They were inactive as racers in 1921 because the Navy withdrew from racing that year, but reappeared as short-wing seaplanes for the 1922 Curtiss Marine Trophy Race, one of the events in the 1922 National Air Races held at Detroit, Michigan. Lt R. Irvine, flying A3325, which had been painted bright green for identification purposes, dropped out in the fifth lap. Lt L. H. Sanderson, flying the yellow-painted A3326, was leading the field in the last lap with an average speed of 125.3 mph round the 20-mile triangular course when he ran out of fuel and was forced to land short of the finishing line, damaging the plane in the process. A3326 was returned to the Naval Aircraft Factory for repair, along with its sister ship. Both were reconverted to landplanes and appeared at the 1923 National Air Races held in St Louis, Missouri. A3325 crashed during a preliminary trial flight. A3326 piloted by Lt L. G. Hughes, broke a crankshaft during the Liberty Engine Builders Trophy race and was destroyed in the resulting crash.
TECHNICAL DATA (Curtiss 18-T1)
Manufacturer: Curtiss Aeroplane and Motor Co, Inc, Garden City, LI, NY
Accommodation: Crew of two.
Power plant: One 400 hp Curtiss K-12.
Dimensions: Span, 31ft 10 in; length, 23ft 4in; height 9ft lO 3/4 in; wing area, 309 sq ft.
Weights: Empty, 1,980 lb; gross, 3,050 lb.
Performance: Max speed, 160mph at sea level; initial climb, 10 min to 12500ft; service ceiling, 23,000 ft; endurance, 5.9 hrs.
Armament: Two fixed forward-firing 0.30-in Marlin guns; two 0,30-in Lewis guns on flexible mount in rear cockpit.
Serial numbers: A3325-A3326.
Jane's All The World Aircraft 1919
CURTISS TYPE 18T. TRIPLANE.
Wing span, upper plane 31 ft. 11 in.
Wing span, middle plane 31 ft. 11 in.
Wing span, lower plane 31 ft. 11 in.
Depth of wing chord
(upper, middle and lower) 42 in.
Gap between wings
(between upper and middle) 42 in.
Gap between wings
(between middle and lower) 35 9/16. in.
Length of machine overall 23 ft. 3 3/16 in.
Height of machine overall 9 ft. 10 3/8 in.
Angle of incidence 2 1/2 degrees.
Dihedral angle None.
Sweepback 5 degrees.
Wing curve Sloane.
angle of incidence 0.5 degrees.
Wings, upper 112.0 sq.ft.
Wings, middle 87.71 sq. ft.
Wings, lower 87.71 sq. ft.
Ailerons (middle 10.79, lower 10.79) 21.58 sq.ft.
Horizontal stabilizer 14.3 sq. ft.
Vertical stabiliser 5.2 sq. ft.
Elevators (each 6.51) 13.02 sq. ft.
Rudder 8.66 sq. ft.
Total supporting surface 309.0 sq. ft.
Loading (weight carried per sq. ft.
of supporting surface) 9.4 lbs.
Loading (per r.h.p.) 7.25 lbs.
Net weight, machine empty 1.825 lbs.
Gross weight, machine and load 2,901 lbs.
Useful load 1,076 lbs.
Fuel 400 lbs.
Oil 45 lbs.
Pilot and passenger 330 lbs.
Useful load 301 lbs.
Total 1076 lbs.
Speed, max. (horizontal flight) 163 m ph.
Speed, mm. (horizontal flight) 58 m.p.h.
Climbing speed 15.000 ft. in 10 mins.
Model K.12, 12 cylinder, Vee, four-stroke cycle
Horse power (rated) at 2500 r.p.m. 400
Wright per rated h.p. 1.70
Bore and stroke 4 1/2 x 6.
Fuel consumption per hour 36.7 galls.
Fuel tank capacity 67 galls.
Oil capacity provided, crankcase 6 galls.
Fuel consumption per b.h.p. .55 lbs. per hour.
Oil consumption per b.h.p. .030 lbs. per hour.
Material. - Wood.
Pitch. - According to requirements of performance.
Diameter. - According to requirements of performance.
Direction of rotation, as viewed from pilot a seat. - Clockwise.
One pressure and one gravity gasoline tank located in fuselage.
Tail skid independent of tail post; landing gear wheel, also 26 in. x 4 in.
Standard Equipment. - Tachometer, oil gauge, gasoline gauge, complete set of tools; other equipment on special order.
At economic speed, about 880 miles.
W.Green, G.Swanborough The Complete Book of Fighters
CURTISS 18-T USA
Designed by Charles B Kirkham, the Curtiss 18-T two-seat fighter triplane was ordered by the US Navy on 30 March 1918 when a contract was placed for two prototypes. The first of these was flown on 7 May 1918. Designed around the Curtiss-Kirkham K-12 water-cooled 12-cylinder engine of 400 hp, the 18-T was of extremely clean aerodynamic design by contemporary standards and featured a monocoque three-ply fuselage and side radiators positioned between the lower wings. The proposed armament comprised two forward-firing synchronized 0.3-in (7,62-mm) Marlin machine guns and two 0.3-in (7,62-mm) Lewis guns on a Scarff mounting in the rear cockpit. Known unofficially as the "Wasp” (an allusion to the sound emitted by the K-12 engine during landing approach), the 18-T initially suffered some tail heaviness which was corrected by applying five degrees of sweepback to the wings for further trials. A max speed of 163 mph (262 km/h) was achieved with full military load in August 1918, the 18-T being acclaimed as the world's fastest aeroplane as a result. The US Navy promptly ordered two examples, the first of which was delivered in February 1919. In the summer of 1919, the first prototype was fitted with longer-span two-bay wings, these having a span and area of 40 ft 7 1/2 in (12,38 m) and 400 sq ft (37,16 m2) respectively, and in this form the aircraft became the 18T-2, the short-span version becoming the 18T-1. The 18T-2 established a world altitude record of 34,910 ft (10 640 m) on 18 September 1919, and a second 18T-2 was built by Curtiss for export to Bolivia, where it arrived in 1920. The following data relate to the 18T-1.
Max speed, 165 mph (265 km/h).
Time to 12,500 ft (3810 m), 10 min.
Endurance, 5.9 hrs.
Empty weight, 1,980 lb (898 kg).
Loaded weight, 3,050 lb (1 383 kg).
Span, 31ft 10 in (9,70 m).
Length, 23 ft 4 in (7,11m).
Height, 9 ft 10 3/4 in (3,02 m).
Wing area, 288 sqft (26,76 m2).
CURTISS 18-B USA
US Army interest in the 18-T prompted Curtiss to offer the same basic design in two-bay biplane configuration, and an order was placed by the US Army for two examples in August 1918. Known unofficially as the "Hornet”, the 18-B two-seat fighter employed an identical fuselage to that of the 18-T and a similar Curtiss-Kirkham K-12 engine. The proposed armament comprised two forward-firing Marlin guns and two Lewis guns on a flexible mount. The two prototypes were delivered to the US Army during the summer of 1919, one being confined to static testing and the other crashing shortly after the commencement of flight trials, and further development was then abandoned.
Max speed, 160 mph (257 km/h).
Empty weight, 1,690 lb (767 kg).
Loaded weight, 2,867 lb (1300 kg).
Span, 37 ft 5 3/4 in (11,41 m).
Length, 23 ft 4 in (7,11 m).
Wing area, 306 sq ft (28,43 m2).
Flight, May 29, 1919.
THE CURTISS MODEL 18-T TRIPLANE
WE are able to give this week further particulars, with scale drawings (for which we are indebted to our American contemporary, Aerial Age), of the Curtiss 18-T triplane. Special attention to streamlining has resulted in the production of a machine which is not only pleasing to the eye, but is, at the same time, mechanically and aerodynamically efficient. The fuselage presents an almost continuous contour, whilst the tail units are so formed that they appear as natural and expected extensions of the body, the engine cowling and exhaust manifolds completing the unity of the design. The machine is designed around the Curtiss K-12 400 h.p. engine (12-cyl. "V"), and the tractor screw is practically centred on the engine and fuselage by the location of the reduction gears integral with the engine. The tractor screw is either two or four-bladed, and is supplied according to requirements of performance. Standard instrument equipment includes a tachometer, oil gauge, petrol gauge, and complete set of tools.
The main planes of this machine are of equal span and chord, but it will be noticed that gap between the middle and lower planes is slightly less than that between the middle and upper ones. They are braced by one pair of interplane struts a side, and the usual flying, landing, and incidence wires. The top plane is attached to a small centre section supported on the fuselage by four struts sloping outwards, whilst the middle and lower planes are attached to the top and bottom longerons of the fuselage respectively. The following are the main characteristics of the Curtiss 18-T :-
Wing span (all three planes) 31 ft. 11 in.
Chord (all three planes) 3 ft. 6 in.
Gap between upper and middle 3 ft. 6 in.
Gap between lower and middle 2 ft. 11 9/16 in.
Overall length 23 ft. 3 3/16 in.
Overall height 9 ft. 10 3/8 in.
Angle of incidence, mainplanes 2 1/2 deg.
Angle of incidence, tail plane 5 deg.
Wing section Sloan.
Areas (sq. ft.)
Upper plane 112
(minus ailerons) 87.71
(minus ailerons) 87.71
Ailerons (four) 21.58
Tail plane 14.3
Elevators (two) 5
Total supporting 8.66
Loading and Weights (lbs.)
Weight per sq. ft. 9.4
Weight per rated
Weight of machine, empty 1,825
Weight of machine, loaded 2,901
Weight of fuel (67 gals.) 400
Weight of oil (6 gals.) 45
Weight of pilot and passenger 330
Useful load 301
Total useful load 1,076
Speed range (m.p.h.) 58-163
Climb 15,000 ft. 10 mins.
Maximum range at economic
speed 550 miles.
Curtiss (K-12) 12-cyl. "V" watercooled,
4 1/2 in. by 6 in.
H.P. at 2,500 r.p.m. 400
Weight without fuel and oil 680 lbs.
Weight per h.p. 1.7 lb.
Fuel consumption per hour 36.7 gals.
Fuel consumption per b.h.p. 0.55 lb.
Oil consumption per b.h.p. 0.03 lb.
Flight, July 10, 1919.
THE CURTISS MODEL 18-B BIPLANE
AFTER the successful trials of the Curtiss Model 18-T Triplane (described in FLIGHT, May 29 last), the two-seater 18-B Biplane was brought out by the Curtiss Engineering Corp. This machine is built around the same fuselage and power plant as the triplane, but having a lesser overall height the gunner has a wider arc of fire. The housing of the engine is particularly neat, it being entirely encased by cowling with the streamlined exhaust stacks projecting upwards. The cowling around the engine is removable, giving access or adjustment and repair.
As in the triplane, all interplane bracing cables are of true streamline section, and where cables cross one another they are clamped by streamlined blocks.
A peculiarity of this machine is in the employment of ailerons on the lower plane only. These ailerons are operated by steel tubes running through the lower plane and directly connected to the control column. This arrangement eliminates entirely all outside control cables and rigging. Rudders and elevators are operated by levers enclosed in the fuselage termination, thereby doing away with all outside control cables. There are no external braces for the stabilizer or fin.
The main planes are rectangular in plan form, and have no dihedral or sweepback. They are built up in five sections, three for the top and two for the lower. The centre section over the body is 2 ft. 6 ins. wide, and the outer sections of both top and bottom planes are 17 ft. 5 7/8 ins. span. As indicated in the accompanying scale drawings, the ribs are spaced about 6 ins. apart, and instead of the usual two main spars, the Curtiss 18-B employs five - the idea being to more evenly distribute the loading on them.
The chord of the upper plane is 4 ft. 6 ins., and the front main wing spar is located 9 ins. from the leading edge, the fourth spar, which carries the rear body and interplane struts, being 2 ft. 9 ins, from the leading edge. The chord of the lower plane is 4 it., and its forward main spar is similarly placed 9 ins. from the leading edge, the other spars being spaced 7 5/16 ins. apart.
The ailerons on the lower plane have a very high aspect ratio, being 13 ft. 5 1/16 ins. in length and 10 3/4 ins. chord. The intermediate interplane struts are centred 6 ft. 1 1/2 ins. from the body struts, the outer interplane struts being 7 ft . 8 1/2 ins. from former, leaving an overhang of 3 ft. 7 7/8 ins.
The fuselage is of monocoque construction, finely streamlined, and 21 ft. in length. The pilot's cockpit is just below the trailing edge of the top plane, and aft of the pilot is the gunner's compartment so arranged that a wide range of fire is provided for the two Lewis machine guns, one of which is located on a rotatable scarff ring surrounding the cockpit, and the other fires through an opening in the underside of the fuselage.
The landing gear is of the V-type, and is similar to that on the 18-T Triplane. The track of the wheels is 4 ft. 11 1/8 ins., the wheels themselves being 2 ft. 2 ins. diameter. The axle is located 3 ft. 8 3/4 ins. from the nose of the fuselage, and 4 ft. 1 1/2 ins. below the line of thrust. With the machine in flying position, the centre of gravity of the machine occurs at a point 1 ft. 4.6 ins. behind the axle. When at rest on the ground, a straight line from the wheels to the tail skid makes an angle of 11° 15' with the centre line.
The tail consists of a small divided horizontal stabilizer with elevator flaps hinged to the trailing edges, a triangular vertical fin (3 ft. by 3 ft. 6 ins.) and an unbalanced rudder (3 ft. 10 ins. by 2 ft. 7 11/16 ins.).
The engine is a Curtiss model K-12 12-cylinder V-type, with cylinders cast en bloc. Aluminium is used extensively in its construction. The bore and stroke is 4 1/2 ins. and 6 ins. respectively, and the rated horse power at 2,500 r.p.m. is 400. Ignition is by two high-tension double spark "six-cylinder" magnetos, located at the forward end of the engine, and driven through flexible couplings by beveled gears from a vertical shaft. Two Duplex carburettors are used, located between the groups of cylinders. They are supplied with an auxiliary altitude hand-controlled air valve, and also with non-back-firing screen.
Without oil or water, the engine weighs 680 lbs.; the deadweight per rated horse power being 1.7 lbs. The petrol consumption is at the rate of .55 lbs. per brake horse power per hour, and the oil, .03 lbs. per brake horse power per hour.
The tractor screw is 9 ft. in diameter, and when the machine is in flying position, the tips clear the ground by 8 1/2 ins.
The general specifications of the 18-B biplane are as follows :-
Span, top and bottom planes 37 ft. 5 3/4 ins
Overall length 23 ft. 4 ins.
Overall height 8 ft. 10 1/2 ins
Chord, top plane 4 ft. 6 ins.
Chord, bottom plane 4 ft.
Gap 5 ft .
Stagger 1 ft. 4 1/2 ins
Weight, fully loaded 3,001 lbs.
Useful load 1,013 lbs.
Service ceiling 22,000 ft.
Maximum ceiling 23,000 ft.
Climb in 10 minutes 12,500 ft.
Climb in 10 minutes
(light load) 16,000 ft.
Sea 5,000 10,000 15,000 20,000
Level. ft. ft. ft. ft.
High speed (m.p.h.) 160.5 158.5 157.5 155 152
Low speed (m.p.h.) 59 68.2 73.6 79.8 86
Economical (m.p.h.) 80 85 92 100 118
Rate of climb
(ft. per minute) 2,390 1,690 1,040 580 210
Time of climb 0 2.5 6.3 12.9 27
Endurance (high speed) 283 miles 1.75 hours
Endurance (economical speed) 536 '' 6.7 ''