underboost

English

Etymology

Pronunciation

Audio (US): (file)

Verb

underboost (third-person singular simple present underboosts, present participle underboosting, simple past and past participle underboosted)

To create too little pressure in an engine's combustion chamber.
- 1941, Bulletin - Issues 19-22, page 155:
  It enables you to properly time the automatic loading of the entire system so that the regulator will not overboost, which would cause a hunting action, or so that it will not underboost and cause a deficiency in the pressure.
- 1960, The Engineer's Digest, page 10:
  A pilot wishing to lose altitude rapidly and still not underboost could go to lower rpm, for example, 16 inches mp with 1600 rpm, rather than 16 inches mp with 2,000 rpm.
- 1973, United States. Naval Air Systems Command, United States. Office of the Chief of Naval Operations, Naval Historical Center (U.S.), Naval aviation news - Volume 55, page 84:
  The only significant problem encountered is that pilots must be particularly cautious about underboosting the engines during the drops.

Noun

underboost (countable and uncountable, plural underboosts)

(uncountable) The process of underboosting.
- 1970, Aerospace Safety - Volume 26:
  After much analysis and compromise of the variables such as RPM, altitude, carburetor air temperature, fuel/air ratio, that affect BMEP, a simple solution has been arrived at to prevent underboost.
- 1980, Scope and Impact of New Automotive Technology on the Inspection, Diagnosis and Repair Process.:
  This procedure requires a vacuum pump and a special compound gauge. (See Table 3-6.) Turbocharger problems lead to poor acceleration in the case of underboost, or poor fuel economy in the case of overboost.
- 1984, Fundamentals of fixed and rotary wing aerodynamics, page 130:
  It can be stated that while the time at high power outputs must be minimized by the correct operating techniques, the time at the underboost condition must be eliminated.
(countable) An instance of underboost.
- 1970, Aerospace Safety - Volume 26:
  So pilots, keep the pressure on to stop underboosts and watch the red lines to stop overboosts.
- 1995, Fly Like a Pro, →ISBN, page 72:
  An underboost can occur whenever an excessively high rpm setting is used with a very low MAP setting, such as when you pull the throttle nearly to idle while descending at high airspeed with a fixed-pitch prop or a constant-speed prop set at high rpm.
- 2011, Ken Babbs, Who Shot the Water Buffalo?: A Novel, →ISBN:
  We're walking along the flight line, heading toward the choppers, a clear morning with the sun's rays bouncing off the orange trees, Emmett giving us the straight skinny: “The underboost will tear up the engine as much as an overboost.

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