Engine Specs
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[edit] Engine Specs
[edit] Description
to do... explain procedure for setting max throttle and maximum power output to simulate max continuous power versus take-off/emergency power.
See also: Turboprops
[edit] Location
[edit] Transmission
[edit] SFC/Sound
[edit] Limits 1 & 2
[edit] Arc Colors
[edit] Prop Plan
[edit] Tips & Comments on Piston Engines
[edit] Natural Aspiration vs. Superchargers
In X-Plane, all piston engines are treated as turbo-supercharged engines. They develop Maximum Power (as entered in the Plane Maker field) up to Critical Altitude.
- Turbo-supercharged engines can be simulated by entering the appropriate critical altitude. However, while X-Plane appears to model the demand of air by the engine so that boost pressure tends to drop when RPMs are increased, the increased amount of exhaust gases that would normally increase pressure seems not to be simulated.
- Normally aspirated engines can be simulated by entering a critical altitude of 0 ft.
- Engines with mechanically-driven centrifugal superchargers (as used in most Warbirds) have to be approximated by selecting a critical altitude and maximum power combination the real engine was capable of. Below critical altitude, the simulated engine will develop a bit too much power since the power loss due to throttling back is not considered.
- Single-speed superchargers can be simulated relatively accurately.
- Two-speed (or three-speed) superchargers are difficult to simulate correctly because they have two (or three) different combinations of critical altitude and maximum power. Select the high critical altitude/low maximum power combination to get the top speed at best altitude correct, or select the low critical altitude/high maximum power combination to get speed at sea level and take-off performance correct. Or select anything between for a compromise.
[edit] Tuning for realistic speed
When tuning for realistic speed, make sure
- If Max Forwards Throttle is set to 1.0, Redline should be equal to Top of Green Arc, or the engine will not develop full power.
- Transmission Losses for most engines that are built with a gearbox as default are 0. That's the way they are rated.
- Make sure the propeller tip speed is in the correct range and you get a propeller efficiency of at least 80% in level flight.
- Check if the Gear Ratio is correct. Some engines have different versions with different ratios, and if the propeller tips go supersonic, efficiency will drop.
- Check if the Prop Radius is correct. It affects propeller tip speed just like the gear ratio.
- Make sure that Propeller Design Speed is in the desired top speed range.
- Make sure that Propeller Design RPM is top of green arc divided by gear ratio.
