Supercharging & Turbocharging
Restoring manifold pressure with altitude — engine-driven superchargers vs exhaust-driven turbochargers, wastegate and critical altitude.
Supercharging & turbocharging — summary notes
Free- Supercharging/turbocharging compresses the induction air to restore the manifold pressure (and hence power) lost as the aircraft climbs and the air thins — or to boost it above ambient at low level.
- A SUPERCHARGER is a compressor driven mechanically from the crankshaft (through gearing): instant response and no lag, but it consumes engine power to run.
- A TURBOCHARGER drives its compressor from a turbine spun by the otherwise-wasted EXHAUST gas: it takes no direct shaft power (better efficiency) but has some spool-up lag; a wastegate regulates boost by diverting exhaust around the turbine.
- 'Critical altitude' is the highest altitude at which the system can still maintain the rated manifold pressure; above it, MAP and power fall off. An intercooler cools the compressed charge to raise density and reduce detonation risk.
- 'Turbo-normalising' merely restores sea-level MAP at altitude; full 'turbo-charging' boosts MAP above ambient for extra power, demanding careful management to avoid detonation and overboost.
- ⚠ Exam trap: a supercharger is driven by the ENGINE (crankshaft), a turbocharger by the EXHAUST gas; the wastegate controls a turbocharger's boost by bypassing exhaust around the turbine — it does not drive a supercharger.
What is the fundamental difference in how a supercharger and a turbocharger are driven, and what practical trade-off does it create?
A supercharger is geared to the crankshaft and driven mechanically, so it responds instantly but consumes engine power. A turbocharger is driven by the exhaust-gas turbine, using energy that would otherwise be wasted, so it is more efficient and doesn't sap shaft power — but it has some lag before the turbine spools up and its boost must be regulated by a wastegate.
Boosting concept map
FreeSupercharging & Turbocharging
Supercharging & turbocharging quiz
ProThis quiz is part of Engineer
Upgrade to unlock every quiz, mock exam and advanced simulation across all modules. Notes and mind maps stay free.