The final production PW-9D (the 16th) was retained by Boeing for the experimental installation of a 600hp water-cooled Curtiss Conqueror V-1570 engine and, as the XP-7 (Model 93), was eventually delivered to the USAAC on 4 September 1928. Distinguished from the PW-9D by a shorter, deeper nose with a larger radiator, the XP-7 enjoyed some success during trials, proving the suitability of the Conqueror for fighter installation. Proposals to build four service evaluation P-7s were abandoned when it was concluded that the basic PW-9 airframe had reached the limit of its development. The XP-7, the last Boeing fighter biplane to employ a liquid-cooled engine, was reconverted to PW-9D standards.
Engine: 600hp water-cooled Curtiss Conqueror V-1570 Take-off weight: 1479 kg / 3261 lb Empty weight: 1 053 kg Wingspan: 9.75 m / 31 ft 12 in Length: 7.31 m / 23 ft 12 in Height: 2.74 m / 8 ft 12 in Wing area: 22.39 sq.m / 241.00 sq ft Max. speed: 269 km/h / 167 mph
Both Models 83 and 89 were Navy designated Boeing XF4B-1 fighters. The difference was the Model 83 had a spreader-bar axle landing gear, and an arrester hook. The Boeing Model 89 had a split-axle landing gear so that a 500 lb bomb could be carried beneath the fuselage.
A private venture built at Boeing’s expense, the XF4B-1 first flew on 7 August 1928. It was placed in production as the Boeing 99 for the Navy F4B-1 series and Model 102 for Army P-12 series, 27 were ordered as F4B-1, and was first delivered in July 1928.
The P-12 was constructed of dural tubing, fabric covered and having wooden wings with corrugated metal control surfaces. Powered by a Pratt & Whitney R-1340 Wasp of 450 hp, the top speed was 171 mph and ceiling 29,000 ft fully loaded.
Model 102 P-12
One XP-12A was built as a test vehicle for the newly NACA cowl. The fuselage was flared to conform to the enlarged nose and shorter landing gear was installed. The XP-12A was a modification of the 10th production P-12. It was later destroyed in a crash. The original P-12 and P-12B were the only two P-12 models that were not equipped with a speed-ring cowl.
XP-12A
The USAAC ordered ten aircraft similar to the F4B-1 in late 1928, accepting the naval evaluation as being correct. Designated P-12, these differed only by having the arrester hook and other specifically naval equipment deleted. P-12B, of which 90 were built with 317kW Wasp engines, differed very slightly with Frise balanced ailerons and internal improvements and were followed by 96 P-12C, which were similar to the Navy’s F4B-2. P-12D, of which 35 were built, had a more powerful 391kW Wasp engine.
The P-12C and P-12D models were improved models and utilised improved and heavier constructed cross-axle landing gear and a speed ring cowl around a Pratt & Whitney Wasp of 550 hp. Many P-12C and D models were fitted later with P-12E type vertical tail surfaces to give better control. The P-12E introduced an all metal monocopue fuselage with greater greater structural rigidity of the fuselage for higher G loads. Most extensively built of the Army versions was the P-12E. This had a pilot’s headrest faired by a turtleback and the more powerful engine of the P-12D. A total of 135 were ordered in 1931, many remaining in service until replaced by P-26A in 1935. The last few of the order were given 447kW / 550 hp Pratt & Whitney R-1340-19 Wasp engines and the designation P-12F. The P-12F had a top speed of 195 mph and ceiling of 32,000 ft. The P-12F had a swivel tail wheel in place of a skid. All P-12s in service were later fitted with tail wheels.
Model 218 c/n 1260
The Boeing Model 218 (XP-925H) was the prototype of the P-12E/F4B-3 series. With a 500 hp Pratt & Whitney Wasp engine the P-12E had a top speed of over 190 mph and a service ceiling of 27,000 ft fully loaded. One P-12E was fitted with a special cockpit enclosure and others had “Panama Conversion Kits” installed. Experimental test models included; XP-12G – turbo-supercharged Wasp engine and 3 blade propeller. XP-12H – basic P-12D with a geared Wasp engine instead of the usual direct drive. P-12L – engine test model. P-12J – engine test model. P-12K – P-12Es modified for fuel injection.
Forty-six F4B-2, delivered in early 1931, had the spreader-bar axle, a tailwheel, Frise ailerons and a neat ring cowling for the engine. They were followed by 21 F4B-3 with a semi-monocoque metal fuselage and 92 F4B-4 which differed by having a larger fin and rudder.
F4B-2 USN
The F4B-3 and P-12E were identical except for the carrier hook, cabane wire, and double row of rivets, and a tall radio mast on the F4B-3. The F4B-4 served the US Navy and US Marines.
F4B-3 Marines
The Navy bought 94 F4B-4s, 21 going to the Marine Corp to operate from land bases.
The Boeing 100 of 1929 was an ATC’d civil version of the P-12 built as a sport plane and for export. They were lighter in weight and the early models resembled the P-12B in appearance. Seven were built and owners included Howard Hughes, Art Goebel, Tex Rankin and Paul Mantz, as well as several foreign governments. Howard Hughes one was delivered as a two-seater as Model 100-A. Hughes soon had it reconverted to one seat, and it survived as such until 1958.
Model 100-A
It was reported in September 1956 that the sole Boeing 100-A, N247K, crashed at Dallas, USA, killing the owner -pilot, Robert Hallbeck. Hallbeck was rolling the machine at about 3000 ft when one of the wings collapsed, and although he was wearing a parachute he was unable to jump clear.
The Japanese imported a civil Boeing 100 and two Boeing 100Es were exported to Siam in September 1931.
Boeing 100E
One Boeing 100E survives on display at the Kings Museum, Bangkok, Thailand. Fourteen F4B-4s were exported to Brazil before World War 2. A total of 554 in the P-12 – F4B series were built, 110 of which were P-12Es. The one surviving P-12E is on display in “The Air Museum”, Ontario International Airport, Ontario, Canada.
Boeing 100E
P-12/F4Bs saw service in Panama, Hawaii and the Phillipines. A few went to China and one of them was the first American made plane to shoot down a Japanese plane in combat prior to World War 2. Two F4B-4 Navy aircraft were released to the CAA Air Safety Board during the early 1930s. Later sold to private buyers, they were used in many pre-war and post-war airshows. One was owned by Hyland Flying Service, Rochester, New York, was later acquired by the Smithsonian Institute and placed on loan to the Navy Museum, fully restored.
75% replica: Reid Boeing P-12E Aero-Tech Boeing F4B-2/P-12C
Boeing F4B / P-12 Engine: 1 x Pratt & Whitney R-1340-D Wasp Length: 20.08ft (6.12m) Width: 29.99ft (9.14m) Height: 9.32ft (2.84m) Empty Weight: 2,355lbs (1,068kg) Maximum Take-Off Weight: 3,611lbs (1,638kg) Maximum Speed: 188mph (303kmh; 164kts) Maximum Range: 370miles (595km) Rate-of-Climb: 1,666ft/min (508m/min) Service Ceiling: 26,903ft (8,200m) Armament: 2 x 7.62mm machine guns Accommodation: 1
Variants:
Boeing 83 / XF4B-1 Number built: 1 Serial number / Registration: 8129 First flight: 25 June 1928 Bought by Navy 19 June 1929.
Boeing 89 / XF4B-1 Number built: 1 Serial number / Registration: 8128 First flight: 7 August 1928 Bought by Navy 19 June 1929.
Armament: 500 lb bomb
Boeing 99 / F4B-1 Number built: 27 Serial number / Registration: 8130-8156 First flight: 6 May 1929 Production version of 89. Navy sn8133 converted to executive model.
Boeing 100 Number built: 4 Serial number / Registration: NS-21, NC872H, C873H, NC874H First flight: 18 October 1929 Civil version of 83/89.
Boeing 100A Number built: 1 Serial number / Registration: 247K First flight: 26 July 1929 Howard Hughes 2 seat version.
Boeing 100E Number built: 2 Serial number / Registration: First flight: Siam P-12E export version.
Boeing 100F Number built: 1 Serial number / Registration: X10696 First flight: 20 June 1932 Civil P-12F testbed for Pratt & Whitney.
Boeing 101 / XP-12A Number built: 1 Serial number / Registration: 29-362 First flight: 10 May 1929 Destroyed in mid-air collision.
Boeing 102 / P-12 Number built: 9 Serial number / Registration: 29-353 – 29-361 First flight: 11 April 1929 83, 89 Army version.
Engine: Pratt & Whitney R-1340 Wasp, 450 hp Top speed: 171 mph Ceiling at MAUW: 29,000 ft
Boeing 102B / P-12B Number built: 90 Serial number / Registration: 29-329 – 29-341, 29-433 – 29-450, 30-29 – 30-87 First flight: 12 May 1930
Engine: Pratt & Whitney R-1340 Wasp, 317kW
Boeing 218 / XP-925 Number built: 1 Serial number / Registration: X66W First flight: 29 September 1930 Army revised P-12B, prototype P-12E & F4B-3.
Engine: Pratt & Whitney R-1340 Wasp, 500 hp Top speed: 190+ mph Service ceiling at MAUW: 27,000 ft
Boeing 222 / P-12C Number built: 96 Serial number / Registration: 31-147 – 31-229, 31-230 – 31-242 First flight: 31 January 1931 131 ordered, last 35 built as P-12D.
Engine: Pratt & Whitney R-1340 Wasp, 391kW / 550 hp
Boeing 223 / F4B-2 Number built: 46 Serial number / Registration: 8806, 8613-8639, 8791-8809
Engine: Pratt & Whitney R-1340 Wasp, 391kW / 550 hp
Boeing 227 / P-12D Number built: 35 Serial number / Registration: 31-243 – 31-277 First flight: 2 March 1931 Improved P-12C, last 35 P-12C built as P-12D.
Engine: Pratt & Whitney R-1340 Wasp, 391kW / 550 hp Top speed: 188mph
Boeing 234 / P-12E Number built: 110 Serial number / Registration: 31-553 – 31-586, 32-1 – 32-76 First flight: 15 October 1931 Production 218 models, 1 converted to P-12J, 7 to P-12K.
Engine: Pratt & Whitney R-1340E Wasp, 391kW / 550 hp, 500 hp at 6000 ft Engine compression ration: 6:1 Overall span (Upper): 30 ft Length: 20 ft 4 11/16 in Height: 8 ft 9 in Airfoil section: Boeing 106 Total wing area: 227.5 sq.ft Upper wing span: 30 ft Upper wing chord: 60 in Upper wing diherdral: 0 degs Upper wing area: 141.4 sq. ft Lower wing span: 26 ft 4 in Lower wing chord: 45 in Lower wing diherdral: 2 degs Lower wing area: 86.1 sq. ft Empty weight: 1981.5 lb Fuel: 300 lb Wing loading: 11.75 lb/sq.ft Loaded weight: 2674.3 lb Landing speed; 59 mph Cruise speed: 167 mph Max speed: 190 mph Range at cruise: 475 miles Armament: 2 x .30 Browning 30M mg or 1 x .30 mg and 1 x .50 mg, and 2 x M-3 bombs
Boeing 235 / F4B-3 Number built: 21 Serial number / Registration: 8891-8911 Production 218 models.
Engine: Pratt & Whitney R-1340D Wasp, 391kW / 550 hp Speed: 187 mph at 6000 ft Empty weight: 2200 lb Armament: 2 x .30 Browing mg or 1 x .30 and 1 x .50 cal mg
Boeing 235 / F4B-4 Number built: 92 Serial number / Registration: 8912-8920, 9009-9053, 9226-9263 Improved F4B-3, larger tail. 14 to Brazil.
Engine: Pratt & Whitney R-1340D Wasp, 500 hp Speed: 187 mph at 6000 ft Empty weight: 2312 lb Armament: 2 x .30 Browing mg or 1 x .30 and 1 x .50 cal mg
Boeing 251 / P-12F Number built: 25 Serial number / Registration: 31-77 – 31-101 Improved P-12E.
Engine: Pratt & Whitney R-1340-19 Wasp, 447kW / 550 hp Top speed: 195 mph Ceiling: 32,000 ft
Boeing 256 / “1932” Number built: 14 Export F4B-4s from Navy order to Brazil.
Boeing 267 / F4B-3 / P-12E Number built: 9 F4B-3 fuselage, P-12E wings. Light export model to Brazil.
XP-12G turbo-supercharged Wasp engine and 3 blade propeller.
XP-12H basic P-12D with a geared Wasp engine instead of the usual direct drive.
The growth of operations on Boeing Air Transport’s San Francisco-Chicago route resulted in the design and development of a purpose-designed passenger transport, the Boeing Model 80, first flown during August 1928. A large unequal-span biplane, with the lower wing of reduced chord, the Model 80 had a wing structure of wood, fabric-covered, and a fuselage and tail unit of welded steel tube, also fabric-covered. Landing gear was of fixed tailwheel type, and power was provided by three 306kW Pratt & Whitney Wasp radial engines. These were mounted in tri-motor configuration, one in the fuselage nose, and one each side of the fuselage, between the biplane wings. The main cabin of the Model 80 accommodated 12 passengers, plus a flight stewardess. Boeing stewardesses were all registered nurses. The Model 80 provided a separate enclosed flight deck for the pilot and co-pilot/navigator. Four of these aircraft were built, entering service with Boeing Air Transport in the late summer of 1928.
The Model 80s were followed by 10 of the improved Model 80A, this type having more powerful Pratt & Whitney Hornet engines, refinements to the wing, improved streamlining and, because of the increased power available, a cabin layout to accommodate a maximum of 18 passengers.
80A
Some pilots insisted on an open cockpit. One Model 80 was re-designed as the Model 80B with open cockpit and raised seats.
80B
The 80B was rebuilt to 80A configuration at the insistence of the majority.
Boeing 80 Engines: 3 x Pratt & Whitney Wasp, 306 kW Passengers: 12
Boeing 80A-1 Engines: 3 x 391kW Pratt & Whitney Hornet radial piston Take-off weight: 7938 kg / 17500 lb Empty weight: 4800 kg / 10582 lb Wingspan: 24.38 m / 79 ft 12 in Length: 17.22 m / 56 ft 6 in Height: 4.65 m / 15 ft 3 in Wing area: 113.34 sq.m / 1219.98 sq ft Max. speed: 222 km/h / 138 mph Cruise speed: 201 km/h / 125 mph Ceiling: 4265 m / 14000 ft Range: 740 km / 460 miles Passengers: 18
In May 1928, the USAAC issued a single-seat fighter specification to which Boeing responded with a shoulder-wing all-metal monoplane, the Model 96, which was assigned the official designation XP-9. Low development priority and production problems delayed the planned delivery date of the XP-9 from April 1929 until September 1930, the aircraft eventually flying for the first time on 18 November of that year. Powered by a Curtiss V-1570-15 liquid-cooled engine rated at 600hp, but actually delivering 583hp, the XP-9 featured a semi-monocoque fuselage of sheet Dural over metal formers. Performance proved disappointing, the poor vision from the rear-positioned cockpit and the unpleasant handling characteristics resulting in the test pilot referring to the XP-9 as “a menace”. After initial tests, the original vertical tail surfaces were replaced by larger P-12 surfaces, but little improvement resulted and the USAAC did not exercise its option on five Y1P-9s.
Engine: Curtiss V-1570-15 liquid-cooled, 583hp Take-off weight: 1643 kg / 3622 lb Empty weight: 1210 kg / 2668 lb Wingspan: 11.13 m / 36 ft 6 in Length: 7.66 m / 25 ft 2 in Height: 2.36 m / 7 ft 9 in Max. speed: 343 km/h / 213 mph
The XF3B-1 (Model 74) was built by Boeing as a private venture and externally resembled closely the F2B-1, but had provision for a single central float with outboard stabilising floats. Powered by a 425hp Pratt & Whitney R-1340 Wasp, it was flown for the first time on 2 March 1927 as a float seaplane. Showing no significant advance over the F2B-1, the XF3B-1 was returned to Boeing by the US Navy and completely rebuilt (as the Model 77), a redesigned undercarriage, wing and tail being introduced. In this new form the fighter proved successful and was the basis of an order from the US Navy for 73 production examples as F3B-1s. The F3B-1 was of mixed construction with wooden wings, a steel-tube fuselage and fabric skinning, but the ailerons and tail surfaces were of semi-monocoque all-metal construction with corrugated covering. Armament comprised two synchronised 7.62mm machine guns and provision was made for five 11kg bombs to be carried. The first flight of the rebuilt XF3B-1 took place on 3 February 1928, and the first production F3B-1, powered by an R-1340-B Wasp, was delivered to the US Navy on 23 November 1928.
F3B-1 Engine: Pratt & Whitney R-1340-B Wasp Take-off weight: 1336 kg / 2945 lb Empty weight: 988 kg / 2178 lb Wingspan 10.06 m / 33 ft 0 in Length: 7.56 m / 24 ft 10 in Height: 2.79 m / 9 ft 2 in Wing area: 25.55 sq.m / 275.02 sq ft Max. speed: 253 km/h / 157 mph Range: 547 km / 340 miles
US Navy evaluation of the FB-4 with a Wright P-1 radial engine led to this aircraft being re-engined with a Pratt & Whitney Wasp and redesignated FB-6. It was flight-tested and demonstrated the clear superiority of the Wasp, leading to a decision to combine this engine with an airframe based on the Model 66. From this marriage of airframe and powerplant came the Boeing Model 69, designated XF2B-1 by the US Navy, and first flown in prototype form on 3 November 1926. It differed mainly in having the span of upper and lower wings more nearly equal, and by the propeller having a large spinner.
74 / XF3B-1
Satisfactory testing of the prototype resulted in an order for 32 production aircraft under the designation F2B-1, with deliveries beginning on 30 January 1928, and these served with US Navy Squadrons VF-1B (fighter) and VB-2B (bomber) on board USS Saratoga. The F2B-1s differed from the prototype by deletion of the spinner, and introduction of a balanced rudder.
Three F2B-1s were flown by the “Three Sea Hawks” Navy precision stunt flying team of the late 1920s.
Model 69 / F2B-1 Engine: 1 x 317kW Pratt & Whitney R-1340-B Wasp radial Take-Off Weight: 1272 kg / 2804 lb Empty Weight: 902 kg / 1989 lb Wingspan: 9.17 m / 30 ft 1 in Length: 6.98 m / 22 ft 11 in Height: 2.81 m / 9 ft 3 in Wing Area: 22.57 sq.m / 242.94 sq ft Max. Speed: 254 km/h / 158 mph Cruise Speed: 212 km/h / 132 mph Ceiling: 6555 m / 21500 ft Range: 507 km / 315 miles Armament: 1 x 12.7mm + 1 x 7.62mm machine-guns, 5 x 11kg bombs
To meet the requirements of the Air Mail Department of the US Post Office, which needed a new mailplane to replace its ageing DH-4s, Boeing designed in 1925 a large biplane transport under the designation Boeing Model 40. It was required to compete against other manufacturers, and the Post Office specification had stipulated the use of a Liberty engine, plus an ability to carry 454kg of airmail. A conventional biplane with tailskid landing gear and a Liberty engine, the Model 40 had a mail compartment in the forward fuselage, with the pilot seated well aft in an open cockpit. First flown on 7 July 1925, the Model 40 was unsuccessful in the competition, the Douglas entry being declared winner. This was to result in Boeing’s design gathering factory dust for some 18 months until, in early 1927, the US Post Office began the process of turning the government air mail service over to private enterprise.
Requiring an aircraft to operate on any of the routes for which it might bid, Boeing began a redesign and conversion of the Model 40 to make it suitable for the sort of operation the company had in mind. The resulting Model 40A had three major changes by comparison with the original Model 40 prototype: the Liberty engine was replaced by a Pratt & Whitney Wasp radial, the composite structure fuselage was replaced with steel tube with fabric covering, and better use was made of fuselage capacity. The pilot’s position remained unchanged, but an enclosed cabin for two passengers was provided more or less directly over the lower wing, with cargo/mail compartments between the pilot’s cockpit and the cabin, and between the cabin and the engine firewall. Boeing was successful in its bid for the San Francisco-Chicago route, and was equally successful in gaining approval for its new aircraft. Following tests for certification, the Model 40A gained Approved Type Certificate No. 2, issued by the US Department of Commerce. Boeing built a fleet of 25 Model 40A mail planes in five months and their enclosed cabins and heated cockpits made possible the first regular transcontinental air passenger service by Boeing Air Transport which, like Varney Air Lines and National Air Transport, later hecame part of United Air Lines’ 13,250-mile network. One model 40A was utilised as an engine test-bed for Pratt & Whitney. The first example of the Model 40A was flown initially on 20 May 1927, and all 24 for Boeing Air Transport had been delivered in time for inauguration of the company’s first airmail service on 1 July 1927.
Boeing 40B-4 of Pacific Air Transport
40 Engine: Liberty
40A Engine: 1 x 313kW Pratt & Whitney Wasp radial piston Take-off weight: 2722 kg / 6001 lb Empty weight: 1602 kg / 3532 lb Wingspan: 13.47 m / 44 ft 2 in Length: 10.12 m / 33 ft 2 in Height: 3.73 m / 12 ft 3 in Wing area: 50.82 sq.m / 547.02 sq ft Max. speed: 206 km/h / 128 mph Cruise speed: 169 km/h / 105 mph Ceiling: 4420 m / 14500 ft Range: 1046 km / 650 miles
Having become recognised as a designer of military aircraft, following the supply of Model 15 to both the US Army (PW-9) and US Navy (FB-1), the company designed the Boeing Model 21 to meet a US Navy requirement for a primary trainer. This was an equal-span biplane, incorporating an unusually wide wing centre-section, and introduced N-type interplane struts to eliminate wing incidence-bracing wires. The divided-axle main units of the tail-skid landing gear had rubber bungee shock absorbers, plus provision for easy conversion to operation with floats. The pilot and pupil were accommodated in tandem open cockpits. Power was provided by a Lawrance J-1 radial engine. US Navy testing of the Model 21 was carried out with the prototype aircraft, under the designation VNB-1. From the potential operator’s point of view, however, the type was unsuitable for the required role, being unspinnable and too easy to fly. On the understanding that modifications would be introduced to make the aircraft a little more demanding, and spinnable, 41 production aircraft were ordered under the designation NB-1. The first of these was delivered on 5 December 1924, and it was soon discovered that Boeing’s spin modifications were too effective, since it was possible to get into a flat spin from which recovery was virtually impossible.
Further modifications produced an acceptable compromise. Some NB-1s had Lawrance J-2 or J-4 engines, and several aircraft had 164kW Wright J-5 engines installed at a later date. Following delivery of the NB-1s an additional 30 were ordered of the NB-2 variant, this differing only by having war-surplus 134kW Wright-Hispano E-4 engines, installed at the US Navy’s request to utilise some of the very large number of these licence-built engines held in naval stores.
Boeing Model 21 / NB-1 Engine: 1 x 149kW Lawrance J-1 radial piston engine Take-Off Weight: 1287 kg / 2837 lb Empty Weight: 969 kg / 2136 lb Wingspan: 11.23 m / 36 ft 10 in Length: 8.76 m / 28 ft 9 in Height: 3.56 m / 11 ft 8 in Wing Area: 31.96 sq.m / 344.01 sq ft Max. Speed: 160 km/h / 99 mph Cruise Speed: 145 km/h / 90 mph Ceiling: 3110 m / 10200 ft Range: 483 km / 300 miles Armament: 1 x 7.62mm machine-gun
NB-2 Engine: 1 x 134kW Wright-Hispano E-4 Wingspan: 11.23 m / 36 ft 10 in Length: 8.76 m / 28 ft 9 in Height: 3.56 m / 11 ft 8 in Wing Area: 31.96 sq.m / 344.01 sq ft Armament: 1 x 7.62mm machine-gun
In April 1925 the USAAC issued a specification for a single-seat fighter to be powered by a new 447kW Packard engine of inverted layout. Boeing’s airframe for this requirement was generally similar to that of the Model 15 family, but incorporated a coolant radiator in the centre-section of the lower wing. Designated XP-8 (Boeing Model 66), this model preceded the XP-7, delivered in July 1927, having been launched as a private venture late in the previous year. Powered by a 600hp Packard 2A-1500 water-cooled engine, the XP-8 utilised an airframe essentially similar to that of the US Navy XF2B-1, but performance failed to meet the requirements of the 1925 USAAC specification which it had been designed to meet, and the aircraft was finally scrapped in June 1929. Armament comprised one 7.62mm and one 12.7mm machine gun.
Engine: 600hp Packard 2A-1500 water-cooled Take-off weight: 1552 kg / 3422 lb Empty weight: 1084 kg / 2390 lb Wingspan: 9.16 m / 30 ft 1 in Length: 6.95 m / 22 ft 10 in Height: 3.27 m / 10 ft 9 in Wing area: 22.57 sq.m / 242.94 sq ft Max. speed: 278 km/h / 173 mph
The last aircraft built by Boeing against an order for 30 PW-9 single-seat fighters was retained by the company at the request of the USAAC for trials with a turbo-supercharged version of the 510hp Packard 1A-1500 water-cooled engine (utilised by the FB-2). The USAAC also requested an increase in wing area, because of the higher weights involved, and while the standard PW-9 upper wing was retained, an enlarged lower wing was introduced, resulting in an equi-span biplane with vertical N-type interplane struts. The standard PW-9 armament of two 7.62mm synchronised machine guns was augmented by a pair of similar-calibre weapons mounted beneath the lower wing outside the propeller arc. With these changes the aircraft was designated XP-4 (Model 58), and delivered on 27 July 1926, but the 6.32sq.m increase in gross wing area by comparison with the PW-9 failed to compensate for the 370kg increase in loaded weight. The XP-4 proved to possess extremely unsatisfactory handling characteristics and after a few hours flying the test programme was abandoned.
Engine: turbo-supercharged Packard 1A-1500, 510hp Take-off weight: 1656 kg / 3651 lb Empty weight: 1262 kg / 2782 lb Wingspan: 9.75 m / 31 ft 12 in Length: 7.29 m / 23 ft 11 in Height: 2.69 m / 8 ft 10 in Wing area: 28.71 sq.m / 309.03 sq ft Max. speed: 259 km/h / 161 mph Range: 603 km / 375 miles
All Aero 