Synchronising is carried out to
- match engine rpm.
- match propeller tip speed.
- match blade phase angle difference.
Explanation
Synchronising adjusts the slave engine's governor so that all engines run at exactly the same rpm as the master, eliminating the slow beat caused by small rpm differences. Synchrophasing, by contrast, goes a step further and sets a fixed blade phase angle; plain synchronising only matches rpm.
obrien99 asking:
I was a bit unsure with this question, The props are synchronised by matching the engine RPM? but ultimatley this is to match the prop RPM. would you guys agree with this answer?
Community Comments (9)
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dimky Posts: 514 05.03.2012 / 21:12
I agree with you. Question is a bit complicated. Question bank refers to Jepperson Aircraft Propellers and Control page 132, but I don't have this book so can't check. If someone have it please be so kindly, send it to info@part66online.com
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obrien99 Posts: 17 06.03.2012 / 21:57
i have got this book i will check and get back to you
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dimky Posts: 514 06.03.2012 / 22:15
Okay, submit your research here. :)
If you have digital copy of this book, send it please to info@part66online.com
If you have digital copy of this book, send it please to info@part66online.com
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obrien99 Posts: 17 06.03.2012 / 23:29
"The synchronisation system is normally used for all flight operations except take off and landing. a master engine is used to establish the RPM to which all other engines(slave engines) will adjust"
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obrien99 Posts: 17 06.03.2012 / 23:32
Still not a clear answer the synchronisation system works by matching all engine RPM's. But by matching the engine RPM the prop RPM should also be matched and therefore tip speeds matched. if the answer was "match prop RPM" i would have gone for that but still not 100% sure.
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dimky Posts: 514 07.03.2012 / 22:41
Agree, matching engine RPM = matching prop RPM, because reduction ratio is fixed. :) Question is blurry...
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TURIN Posts: 4 16.03.2012 / 17:35
This sounds like a piston engine question. A gas turbine engine may have a free power turbine so matching engine speeds is a nonsense. Matching prop speed is correct (in a gas turbine).
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alberto Posts: 8 07.04.2013 / 13:58
your right dimky i agree with you. When synchronising engine rpm your synchronising the propeller automatically as the prop have an epicyclic gear system.
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aerorodder1 Posts: 20 23.12.2015 / 07:56
Obrien99 is correct the engine rpm is reduced or advanced to match the slave engine. On the MD-80 the switch is called "engine sync". If you didn't sync up,the passengers toward the rear of the plain right next to the engines would go crazy on a long flight. When we were kids, we would hum in front of a spinning fan mouths open,and move our noisy mouths until we could make these strange harmonies until would we found the one that would sync up perfectly. But in the interim there would be that specific warbling sound...well select an engine and sync and away goes the harmonics and vibrations. Don't care about props, sorry but if you want to advance in your carrer you'll have to work on turbojet or turbofan high bypass ratio engines.Small A/C has its place but the money is in the jets not props!
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