Timeline for Cause of Drag From Windmilling
Current License: CC BY-SA 4.0
9 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Aug 13, 2023 at 1:59 | comment | added | Aditya Sharma | @MichaelHall I invite you to this chat room to continue this discussion | |
| Aug 12, 2023 at 21:14 | comment | added | sophit | @AdityaSharma: you should write it in an answer | |
| Aug 12, 2023 at 15:28 | comment | added | Michael Hall | @AdityaSharma, "Virtually all of the work that goes into compressing the air should be recovered back during the power stroke". That sounds good in theory, but if it were actually true engines wouldn't be so difficult to turn over by hand. There is a huge difference in the effort needed to turn an engine over when you remove the spark plugs to take away the compression. | |
| Aug 12, 2023 at 8:55 | comment | added | Aditya Sharma | Secondly, exhaust stroke: This loss results from the back pressure in the exhaust manifold, and the piston trying to force the exhaust gases against it. For example, a muffler alone can cause around 10 kPa (1.5psi) of back pressure. Apart from the pumping losses, the second biggest power absorber is the internal friction of the engine. | |
| Aug 12, 2023 at 8:55 | comment | added | Aditya Sharma | @BowlOfRed Virtually all of the work that goes into compressing the air should be recovered back during the power stroke (even when there is no combustion); so there shouldn't be a net energy loss. What actually absorb the energy (from the windmilling prop) are the pumping losses, i.e. Induction and exhaust stroke. Induction stroke: This is because the engine is essentially pulling a vaccum through the induction manifold (a volumetric efficiency of less than 10% would be typical with the throttle fully closed). This effect can be greatly reduced by fully opening the throttle valve. | |
| Aug 11, 2023 at 18:59 | comment | added | BowlOfRed | @Bergi, "friction" is probably the wrong word. Most of the work goes into compressive heating of the air in the cylinders. | |
| Aug 11, 2023 at 14:07 | comment | added | sophit | @Bergi: plus the aerodynamic drag of the blades | |
| Aug 11, 2023 at 13:02 | comment | added | Bergi | So it's only the friction in the engine? | |
| Aug 11, 2023 at 4:09 | history | answered | niels nielsen | CC BY-SA 4.0 |