Complex Aircraft


Be able to transition safely to complex, high-performance aircraft. These include models with variable pitch propeller, retractable landing gear and turbocharged engines.


This is the required reading for this lesson. Numbers in [brackets] indicate the starting and ending page in the referenced reading material. Read all the pages and sections referenced.


The notes below highlight the important parts in the referenced material. Reading the notes without having read the actual referenced material is generally not sufficient to pass the written exam!

AFH Chapter 12


The wing lift is primarily determined by the camber and the surface area. But high camber and area deflection increases drag. Wing designs in order to increase efficiency on a broader range of speed either will compromise on the shape or introduce mechanism to change the shape on demand. At high speed the camber (and maybe surface) is smaller and at low speeds the pilot increases them with the use of flaps to maintain the similar amount of lift.


  1. Increase the camber of the wing
  2. Sometimes also increase the total surface.
  3. Introduce extra drag
  4. Do not change the critical AOA
  5. Usually affect the pitch
  6. Have specific range of speed for operation

Types of flaps

  1. Plain (hinge)
  2. Split
  3. Slotted
  4. Fowler

Flaps are controller mechanically, electrically or hydraulically.

Retractable Gear

Fixed landing gear introduce a permanent amount of drag. Retracting into the airplane structure removes that drag, streamlining the shape aerodynamically hence increasing the performance and speed. The mechanism to retract landing gear is a combination of shafts, gears, adapters, locks and actuators, powered either electrically or hydraulically (either from engine or electric pump). The complex system adds weight to the aircraft. On the other hand, and in comparison, a fixed landing gear is simple, low maintenance and lighter. Aircraft designers introduce retractable landing gears when the penalty of increased weight is justified by the benefit of increased performance.

Retractable landing gear

  1. Are either electronically or hydraulically operated.
  2. They are controlled by a level in the cockpit and annunciator lights display their position.
  3. It takes time from pilot input (using the lever) to actual extension or retraction and lock
  4. They induce drag and sometimes affect pitch.
  5. Have specific range of speed for operation

Usual pilot mistakes on retractable gear are omitting retracting or extending the gear, operating outside the speed range, retracting/retracting early/late during take-off, approach or landing. For that reason, it is imperative that the operation is coordinated by execution of the appropriate checklists (as normally) and memory items (in emergency).

Variable pitch propeller

Variable pitch propeller can have their blade pitch adjusted to be more efficient (blade AOA) in an extended range of power settings (RPM) and airspeeds contrary to fixed pitch propeller whose efficiency is maximized on specific RPM and airspeed.

At some older airplanes the pitch was manually adjusted, but after the initial period the constant speed propeller has dominated where the pitch is adjusted indirectly based on airspeed and the engine RPM, by the governor. The pilot controls the hydraulic pressure on the governor which adjusts pitch to equalise the hydraulic pressure with the pressure from the aerodynamic load on the blade hence maintaining contact RPM regardless of engine output and airspeed.

The RPM are controlled by a lever

  1. Forward position gives maximum RPM (minimum pitch)
  2. Moving backwards RPM decreases.

The potential power of the engine (load) is controlled by the throttle (manifold)

The total output of the engine is determined by the throttle and the RPM.

To decrease output first reduce throttle and then RPM. To increase, first increase RPM and then throttle.

An additional advantage of a constant pitch propeller is feathering where the blades can align with the wind (maximum pitch, zero RPM). That is very useful in case of an engine failure as the blades don’t induce any drag by the air hence increasing the gliding performance.


In modern aircraft and with the advancement of technology, automation systems are installed even in GA aircraft. One of them is FADEC (Full Authority Digital Engine Control). FADEC controls apart from basic functions of the engine, the mixture and the governor (when there is a constant speed propeller). There is no need for the pilot to manually control each parameter of the engine but instead just inputs the demand for power by single lever. FADEC calculates based on the environment and flight parameters, the best settings for the engine and applies them, constantly adjusting them for efficiency. Some even feature auto feather capability.

Tomas Hansson (This email address is being protected from spambots. You need JavaScript enabled to view it.)
Chief Flight Instructor, VATSTAR
DISCLAIMER: all information contained herein is for flight simulation purposes only.
July 2022

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