Hobbs meter is a

genericized trademark A generic trademark, also known as a genericized trademark or proprietary eponym, is a trademark or brand name that, because of its popularity or significance, has become the generic term for, or synonymous with, a general class of products or ...

for devices used in

aviation Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air craft such as hot air ...

to measure the time that an aircraft is in use. The meters typically display hours and tenths of an hour, but there are several ways in which the meter may be activated: # It can measure the time that the electrical system is on. This maximizes the recorded time. # It can be activated by oil pressure running into a pressure switch, and therefore runs while the engine is running. Many rental aircraft use this method to remove the incentive to fly with the master electrical switch off. # It can be activated by another switch, either an airspeed sensing vane under a wing (as in the

Cessna Caravan The Cessna 208 Caravan is a utility aircraft produced by Cessna. The project was commenced on November 20, 1981, and the prototype first flew on December 9, 1982. The production model was certified by the FAA in October 1984 and its Cargoma ...

) or a pressure switch attached to the landing gear (as in many twin engine planes). In these cases, the meter only measures the time the aircraft is actually flying. Metrics such as Time In Service and Turbine Actual Runtime are kept to monitor overhaul cycles, and are usually used by commercial operators under

Federal Aviation Regulations The Federal Aviation Regulations (FARs) are rules prescribed by the Federal Aviation Administration (FAA) governing all aviation activities in the United States. The FARs comprise Title 14 of the Code of Federal Regulations (CFR). A wide variety ...

Parts 135, 121, or 125. # It can be activated when the engine alternators are online (as in the

Cirrus Cirrus may refer to: Science *Cirrus (biology), any of various thin, thread-like structures on the body of an animal *Cirrus (botany), a tendril * Infrared cirrus, in astronomy, filamentary structures seen in infrared light *Cirrus cloud, a typ ...

SR series).

General aviation use

For general aviation, Hobbs time is usually recorded in the pilot's log book, and many

fixed-base operator A fixed-base operator (FBO) is an organization granted the right by an airport to operate at the airport and provide aeronautical services such as fueling, hangaring, tie-down and parking, aircraft rental, aircraft maintenance, flight instruction, ...

s that rent airplanes charge an hourly rate based on Hobbs Time. Tach Time is recorded in the engine's log books and is used, for example, to determine when the oil should be changed and the

time between overhaul Time between overhauls (abbreviated as TBO or TBOH) is the manufacturer's recommended number of running hours or calendar time before an aircraft engine or other component requires overhaul. On rotorcraft, many components have recommended or ma ...

s. Tach (tachometer) time differs from Hobbs Time in that it is linked to engine

revolutions per minute Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...

(RPM). Tach Time records the time at some specific RPM. It is most accurate at cruise RPM, and least accurate while taxiing or stationary with the engine running. At these times, the clock runs slower. Depending on the type of flight, Tach Time can be 10–20% less than Hobbs Time. Many organizations such as flying clubs charge by Tach Time so as to differentiate themselves from fixed-base operators by the fact that 10-20% less time recorded makes it 10-20% cheaper to fly (if the hourly rate is the same). In the case where flying clubs use Tach Time, many will charge a dry rate, thus requiring the renter to pay for fuel on top of the hourly Tach Time rate.

History

The Hobbs Meter is named after John Weston Hobbs (1889–1968), who in 1938 founded the company named after him in Springfield, Illinois which manufactured the first electrically wound clocks for vehicle use. World War II created the demand for aviation hour meters which led to the development of the original Hobbs Meter. The company was eventually renamed Honeywell Hobbs after being acquired by

Honeywell International Honeywell International Inc. is an American publicly traded, multinational conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four areas of business: aerospace, building technologies, performance m ...

, who in 2009 announced plans to move manufacturing to Mexico.

References

{{DEFAULTSORT:Hobbs Meter Timers Aircraft instruments Avionics