The B-36 took shape as an aircraft of immense proportions. It was two-thirds longer than the previous "superbomber", the B-29. The wingspan and tail height of the B-36 exceeded those of the Antonov An-22, the largest ever mass-produced propeller-driven aircraft. Only with the advent of the Boeing 747 and the Lockheed C-5 Galaxy, both designed two decades later, did aircraft capable of lifting a heavier payload become commonplace.
The wings of the B-36 were large even when compared with present-day aircraft, exceeding, for example, those of the C-5 Galaxy, and enabled the B-36 to carry enough fuel to fly very long missions without refueling. The widest point around the chord of the wing was seven and a half feet thick containing a crawlspace that allowed crew access to the engines. The wing area permitted cruising altitudes well above the operating ceiling of any 1940s-era piston and jet-turbine fighters. All versions of the B-36 could cruise at over 40,000 ft (12,000 m). B-36 mission logs commonly recorded mock attacks against U.S. cities while flying at 49,000 ft. In 1954, the turrets and other nonessential equipment were removed, resulting in a "featherweight" configuration believed to have resulted in a top speed of 423 mph (700 km/h), and cruise at 50,000 ft (15,000 m) and dash at over 55,000 ft (16,800 m), perhaps even higher.
The large wing area and the option of starting the four jet engines gave the B-36 a wide margin between stall speed (VS) and maximum speed (Vmax) at these altitudes. This made the B-36 more maneuverable at high altitude than the USAF jet interceptors of the day, which either could not fly above 40,000 ft (12,000 m), or if they did, were likely to stall out when trying to maneuver or fire their guns. However, the Navy argued that their McDonnell F2H Banshee fighter could intercept the B-36, thanks to its ability to operate at more than 50,000 ft (15,000 m). The Air Force declined the Navy's invitation to a fly-off between the Banshee and the B-36. Later, the new Secretary of Defense, Louis A. Johnson, who considered the U.S. Navy and Naval Aviation essentially obsolete in favor of the U.S. Air Force and Strategic Air Command, forbade putting the Navy's claim to the test.
The propulsion system alone made the B-36 a very unusual aircraft. All B-36s featured six 28-cylinder Pratt & Whitney R-4360 'Wasp Major' radial engines. Even though the prototype R-4360s delivered a total of 18,000 hp (13 MW), early B-36s were slow and required long takeoff runs. The situation improved with later versions delivering 3,800 hp (2.8 MW) apiece. Each engine drove an immense three-bladed propeller, 19 ft (5.8 m) in diameter, mounted in the pusher configuration. This unusual configuration prevented propeller turbulence from interfering with airflow over the wing, but also led to chronic engine-overheating due to insufficient airflow around the engines, resulting in numerous in-flight engine fires.
Beginning with the B-36D, Convair added a pair of General Electric J47-19 jet engines suspended near the end of each wing; these were also retrofitted to all extant B-36Bs. Thus the B-36 came to have 10 engines ("six turnin' and four burnin' ", as said by American airmen), more than any other mass-produced aircraft. The jet pods greatly improved takeoff performance and dash speed over the target. In normal cruising flight, the jet engines were shut down to conserve fuel. The two pods with four turbojets and the six piston engines combined gave the B-36 a total of 40,000 hp for short periods of time.
The B-36 had a crew of 15. As in the B-29, the pressurized flight deck and crew compartment were linked to the rear compartment by a pressurized tunnel through the bomb bay. In the B-36, one rode through the tunnel on a wheeled trolley, by pulling oneself on a rope. The rear compartment featured six bunks and a dining galley, and led to the tail turret. The B-36 also tested the experimental Boston Camera.
The XB-36 featured a single-wheel landing gear whose tires were the largest ever manufactured up to that time, 9 ft 2 in (2.7 m) tall, 3 ft (1 m) wide, and weighing 1,320 lb (600 kg), with enough rubber for 60 automobile tires. These tires placed so much weight per unit area on runways, the XB-36 was restricted to the Fort Worth airfield adjacent to the plant of manufacture, and to a mere two USAF bases beyond that. At the suggestion of General Henry H. Arnold, the single-wheel gear was soon replaced by a four-wheel bogie. At one point a tank-like tracked landing gear was also tried on the XB-36, but proved heavy and noisy and was quickly abandoned.
The four bomb bays could carry up to 86,000 lb (39 metric tons) of bombs, more than 10 times the load carried by the World War II workhorse, the Boeing B-17 Flying Fortress, and substantially more than the entire B-17's gross weight. The B-36 was not designed with nuclear weaponry in mind, because the mere existence of such weapons was top secret during the period when the B-36 was conceived and designed (1941–46). Nevertheless, the B-36 stepped into its nuclear delivery role immediately upon becoming operational. In all respects except speed, the B-36 could match what was arguably its approximate Soviet counterpart, the Tu-95, which began production in January 1956 and at the time of this writing is still in service. Until the B-52 came on line, the B-36 was the only means of delivering the first generation Mark-17 hydrogen bomb, 25 ft (7.5 m) long, 5 ft (1.5 m) in diameter, and weighing 42,000 lb (19,000 kg), the heaviest and bulkiest American aerial nuclear bomb ever. Carrying this massive weapon required merging two adjacent bomb bays.
The defensive armament consisted of six remote-controlled retractable gun turrets, and fixed tail and nose turrets. Each turret was fitted with two 20 mm cannons, for a total of 16 cannons. Recoil vibration from gunnery practice often caused the airplane's electrical wiring to jar loose or the vacuum tube electronics to malfunction, leading to failure of the aircraft controls and navigation equipment. This contributed to the crash of B-36B 44-92035 on 22 November 1950.
The Convair B-36 was the only aircraft designed to carry the T-12 Cloudmaker, a gravity bomb weighing 43,600 lb (19,800 kg) and designed to produce an earthquake bomb effect.
The first prototype XB-36 flew on 8 August 1946. The speed and range of the prototype failed to meet the standards set out by the Army Air Corps in 1941. This was expected, as the engines required (Pratt & Whitney R-4360s) were not yet available, and the lack of qualified workers and materials needed to install them prevented Convair from achieving its goals.
A second aircraft, the YB-36, flew on 4 December 1947. It featured a redesigned high visibility bubble canopy, which was later adopted for production. Altogether, the YB-36 was much closer to the production aircraft. Additionally, the engines used on the YB-36 were a good deal more powerful and more efficient.
The first of 21 B-36As were delivered in 1948. They were admittedly interim airframes, intended for crew training and later conversion. No defensive armament was fitted as none was ready. Once later models were available, all B-36As were converted to RB-36E reconnaissance models. The first B-36 variant meant for normal operation was the B-36B, delivered beginning in November 1948. This aircraft met all the 1941 requirements, but had serious problems with engine reliability and maintenance (changing the 336 spark plugs was a task dreaded by ground crews), and with the availability of armaments and spare parts. Later models featured more powerful variants of the R-4360 engine, improved radar, and redesigned crew compartments.
The four jet engines raised fuel consumption, thus reducing range. Meanwhile, the advent of air-to-air missiles rendered conventional gun turrets obsolete. In February 1954, the USAF awarded Convair a contract reducing the weight of the entire B-36 fleet by implementing a new "Featherweight" design program in three configurations:
- Featherweight I removed the six movable gun turrets and other defensive hardware.
- Featherweight II removed the rear compartment crew comfort features, and all hardware accommodating the XF-85 parasite fighter.
- Featherweight III incorporated both configurations I and II.
- Crew: 13
- Length: 162 ft 1 in (49.42 m)
- Wingspan: 230 ft 0 in (70.12 m)
- Height: 46 ft 9 in (14.25 m)
- Wing area: 4,772 ft² (443.5 m²)
- Airfoil: NACA 63(420)-422 root, NACA 63(420)-517 tip
- Empty weight: 166,165 lb (75,530 kg)
- Loaded weight: 262,500 lb (119,318 kg) (combat weight)
- Max takeoff weight: 410,000 lb (186,000 kg)
- 4 × General Electric J47 turbojets, 5,200 lbf (23.2 kN) each
- 6 × Pratt & Whitney R-4360-53 "Wasp Major" radials, 3,800 hp (2,835 kW) each
- Maximum speed: 418 mph (363 knots, 672 km/h)
- Cruise speed: 230 mph (200 knots, 370 km/h)
- Combat radius: 3,985 mi (3,465 nmi, 6,415 km)
- Ferry range: 10,000 mi (8,700 nmi, 16,000 km)
- Service ceiling: 43,600 ft (13,300 m)
- Rate of climb: 1,995 ft/min (10.1m/s)
- Guns: 1 remotely operated tail turret with 2× 20 mm (0.787 in) M24A1 autocannons
- Bombs: 86,000 lb (39,000 kg) with weight restrictions, 72,000 lb (32,700 kg) normal