Editing Model aircraft (section)

====Propellers====
A large diameter and low-[[blade pitch|pitch]] propeller offers greater thrust and acceleration at low airspeed, while a small diameter and higher-pitch propeller sacrifices acceleration for higher maximum speeds. The builder can choose from a selection of propellers to match the model but a mismatched propeller can compromise performance, and if too heavy, cause undue wear on the powerplant. Model aircraft propellers are usually specified as diameter × pitch, in inches. For example, a 5 x 3 propeller has a diameter of {{convert|5|in}}, and a pitch of {{convert|3|in}}. The pitch is the distance that the propeller would advance if turned through one revolution in a solid medium. Two and three bladed propellers are the most common.

Three methods are used to transfer energy to the propeller:
*''Direct-drive'' systems have the propeller attached directly to the engine's [[crankshaft]] or driveshaft. This arrangement is preferred when the propeller and powerplant both operate near peak efficiency at similar [[revolutions per minute|rpms]]. Direct-drive is most common with fuel-powered engines. Rarely, some electric motors are designed with a sufficiently high ''torque'' and low enough speed and can utilize direct-drive as well. These motors are typically called ''outrunners''.
*''Reduction drive'' uses gears to reduce shaft rpm, so the motor can spin much faster. The higher the gear ratio, the slower the prop rotates, which also increases torque by roughly the same ratio. This is common on larger models and on those with unusually large propellers. The reduction drive matches the powerplant and propeller to their respective optimum operating speeds. Geared propellers are rare on internal combustion engines, but are common on electric motors because most electric motors spin extremely fast, but  lack torque.
*A built-in 2:1 gear reduction ratio can be obtained by attaching the propeller to the [[camshaft]] rather than the crankshaft of a four stroke engine, which runs at half the speed of the crankshaft.<ref>{{cite web|url=http://www.rcvengines.com/pdf_files/saepaper.pdf |title=The Rotating Cylinder Valve 4-stroke Engine (SAE Paper 2002-32-1828) |author=Keith Lawes |access-date=2012-01-03 |url-status=dead |archive-url=https://web.archive.org/web/20111112180807/http://www.rcvengines.com/pdf_files/saepaper.pdf |archive-date=12 November 2011 }}</ref>