Zoom climb
A zoom climb or an unrestricted climb is a maneuver in which the rate of climb is greater than the maximum climb rate using only the thrust of the aircraft's engines. The additional climb rate is attained by reduction of horizontal speed. Before a zoom climb, the aircraft accelerates to a high airspeed at an altitude at which it can operate in sustained level flight. The pilot then pulls steeply upward, trading the kinetic energy of forward motion for altitude. This is different from a steady climb, where the increase in potential energy comes from mechanical work done by the engines.
Zoom climbs are somewhat commonly performed by modern fighter aircraft and are typically referred to as "unrestricted climbs" in this context. Pilots will take off, accelerate to high speed at low altitude, and then pull the aircraft vertical or nearly vertical to quickly climb to the aircraft's cruising altitude.
Performance history
Zoom climbs have been used to test new aircraft designs and conduct research in different flight regimes.An NF-104A fitted with an additional rocket engine was regularly used in zoom-climb research for future spaceflight. On 7 May 1958, the aircraft reached an altitude of in a zoom climb at Edwards Air Force Base, setting a new altitude record. The Mach 2 mission took the airplane so high that the standard F-104's engine routinely exceeded its temperature limit and had to be shut down. Sometimes the engine simply flamed out for lack of air. Then the pilot steered the aircraft like a returning spaceship to a lower altitude, where he would restart the engine. An NF-104 set an unofficial altitude record of on 6 December 1963.
NASA tested a reaction control system on the JF-104, derived from a YF-104A, to give the jet maneuverability over in the thin air where normal control surfaces have little effect.
On 4 September 1959, a specially modified Sukhoi Su-9 set a record of using a zoom climb.
On 6 December 1959, during the proving phase of the McDonnell Douglas F-4 Phantom II, an early version of the aircraft performed a zoom climb to as part of Operation "Top Flight". Commander Lawrence E. Flint Jr. accelerated his aircraft to at Mach 2.5 and climbed to at a 45-degree angle. He then shut down the engines and glided to the peak altitude. As the aircraft fell through, Flint restarted the engines and resumed normal flight.
On 10 December 1963, flight test pilot Chuck Yeager was nearly killed flying a heavily modified F-104.
On 25 July 1973, Aleksandr Fedotov reached in a Mikoyan-Gurevich MiG-25M with a payload, and with no load. In the thin air, the engines flamed out and the aircraft coasted in a ballistic trajectory by inertia alone. At the apex, the indicated airspeed had dropped to. On 31 August 1977, Fedotov broke his own record by reaching, which remains the record for highest crewed jet aircraft and highest self-launched planes as of 2023.
Without engine power, the cockpit would depressurize on these missions. Above, the standard oxygen system cannot provide blood oxygen saturation enough for the pilot to function, so a full-body pressure suit must be used.
In a 1984 demonstration of their performance, an English Electric Lightning fighter aircraft used a zoom climb to intercept a Lockheed U-2 cruising at, above the Lightning's service ceiling of. Shortly before this, it had even reached.