Underboost

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.

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.

The only significant problem encountered is that pilots must be particularly cautious about underboosting the engines during the drops.

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.

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.

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.

So pilots, keep the pressure on to stop underboosts and watch the red lines to stop overboosts.

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.

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.