Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
davescj
Topic Author
Posts: 1287
Joined: Wed Jun 13, 2007 1:46 am

Propeller In Sync Meaning?

Sun Aug 07, 2011 1:04 pm

Pls move if I am in the wrong forum...

That said, I saw in another forum a flight on a turbo prop jet was delayed because the propellers were not in sync. By that, it RPM intended?

That said, why does the left side always start first?

Dave
Can I have a mojito on this flight?
 
EMBQA
Posts: 7858
Joined: Sat Oct 25, 2003 3:52 am

RE: Propeller In Sync Meaning?

Sun Aug 07, 2011 2:25 pm

Quoting davescj (Thread starter):

why does the left side always start first.?

I've almost always seen the right hand started first. Mainly because the pax air cooling comes from the right engine.. plus you can still board with the right engine running.

Quoting davescj (Thread starter):
I saw in another forum a flight on a turbo prop jet was delayed because the propellers were not in sync. By that, it RPM intended?

There is a system on multi engine turbo prop aircraft that keeps the props in sync to reduce vibration. The vibration is cause when the prop blades are not in phase and the uneven balance causes the vibration.
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
Dalmd88
Posts: 3131
Joined: Fri Jul 28, 2000 3:19 am

RE: Propeller In Sync Meaning?

Sun Aug 07, 2011 3:29 pm

Prop sync should be an MEL item. If it doesn't work it can either be slightly annoying or bad enough to make passengers sick.
The system uses magnetic targets and a sensor on each engine. These are fed into a small electronic box that compares the phase angles and then adjusts the rpm of the slave engine very slightly to align the angles. When the crew changes the engine settings the system takes a moment to catch up. It also only works if both engines are within a small relative rpm range to each other. Some turbofan aircraft also have a system like this. DC-9 and MD-80 have an engine sync system that adjusts N1.
 
futureualpilot
Posts: 2406
Joined: Thu May 25, 2000 10:52 am

RE: Propeller In Sync Meaning?

Sun Aug 07, 2011 4:11 pm

Our aircraft's prop sync system is MEL-able, meaning we have to manually sync the props rather than flip the switch that activates the system. It isn't difficult, we do it by adjusting the props to the desired RPM and then fine tuning them by sound. The sync system adjusts the props (at least on the aircraft I fly) so that only 1 blade crosses the wing root at a time, avoiding the "beating" or oscillating sound created when a prop blade from both engines crosses the wing root at the same time, producing a very noticeable sound throughout the aircraft.

We normally start the #2 (right) engine first, but there is at least 1 outstation in our system that requires us to start #1 (left) first because of the way the ground equipment is positioned. We can get air from either engine into the cabin, and as long as one engine is running and we reset the generator relay we have power to all of our electrical systems.
Life is better when you surf.
 
qslinger
Posts: 231
Joined: Fri Apr 07, 2006 5:14 pm

RE: Propeller In Sync Meaning?

Mon Aug 08, 2011 12:38 am

What about jet engines? Don;t they need to be in sync as well? do they have a system like this on jet engined planes?
Raj Koona
 
futureualpilot
Posts: 2406
Joined: Thu May 25, 2000 10:52 am

RE: Propeller In Sync Meaning?

Mon Aug 08, 2011 1:37 am

Dalmd88 said the DC9/MD88's have something of the sort. On most jets it isn't going to be as noticeable or as annoying, not to mention the vibrations aren't as bad as having a large prop assembly spinning at high RPM attached to the airframe.
Life is better when you surf.
 
KELPkid
Posts: 5247
Joined: Wed Nov 02, 2005 5:33 am

RE: Propeller In Sync Meaning?

Mon Aug 08, 2011 3:13 am

Quoting futureualpilot (Reply 5):
Dalmd88 said the DC9/MD88's have something of the sort. On most jets it isn't going to be as noticeable or as annoying,

It sure is on a Diesel-9 when you are seated between the engines. I have endured more than one DC-9 flight between the engines when the sync wasn't working quite right...it is very fatiguing, just as bad as it is in a GA twin   
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
baroque
Posts: 12302
Joined: Thu Apr 27, 2006 2:15 pm

RE: Propeller In Sync Meaning?

Mon Aug 08, 2011 6:21 am

For parts of WWII, bombers used to deliberately use unsynchronised engines because IIRC, it was supposed this made sound locators less effective. Not sure it did, but it must have made life inside the planes even more uncomfortable. There were some really wierd theories about this that and the other, mostly about radar and whether radar detectors could be detected.

A simple tip was that if you heard something going over at night, engines unsynch, enemy and likely to drop things that went bang, engines synch, probably a friend, you hoped!! While the radar folk had a better idea due to IFF and conveyed this to the AA, the general populace had to go on the engine sounds.

[By and large, the tonnage coming down in the UK from the AA was greater than that from the enemy, but not the case from large formations of heavy bombers. Also the stuff from the AA in theory had already gone bang, whereas that from the planes had yet to perform that "trick". But a 4.7" shell that exploded on its return made a heck of a big hole! And quite a few did just that.]

Not sure how all this went with large formations, we got mostly small numbers where I was.
 
futureualpilot
Posts: 2406
Joined: Thu May 25, 2000 10:52 am

RE: Propeller In Sync Meaning?

Mon Aug 08, 2011 2:16 pm

Quoting KELPkid (Reply 6):
It sure is on a Diesel-9 when you are seated between the engines. I have endured more than one DC-9 flight between the engines when the sync wasn't working quite right...it is very fatiguing, just as bad as it is in a GA twin

Agreed! I love the older jets and everything they are but wow.
Life is better when you surf.
 
kingairta
Posts: 454
Joined: Mon Feb 09, 2009 2:24 pm

RE: Propeller In Sync Meaning?

Tue Aug 09, 2011 3:26 pm

No prop sync on a C-130 is very very annoying. Nothing that would ground the airplane though. Just picture a loud low pitch waaaaaaa waaaaaa waaaaaaa for 8+ hours.
 
User avatar
Jetlagged
Posts: 2564
Joined: Sun Jan 23, 2005 3:00 pm

RE: Propeller In Sync Meaning?

Tue Aug 09, 2011 10:00 pm

The BAe 146 has an RPM synchronisation system which will align either N1 or N2 as selected on all four engines. The aircraft has no autothrottle and the system works by using variable length rods in the thrust lever to engine linkage. Either engine 1 or 2 can be selected as master. The same system is used to fine tune thrust settings for takeoff and climb. It only has limited authority so the thrust levers must be roughly aligned. In the later RJ versions of the 146 the synchronisation is done via the autothrottle.

VC10s and Comets had manual RPM synchronisation with an indicator which showed the relative speeds of each engine to the master engine. Each slave engine has a rotating pointer like a small compass needle which rotates in proportion to the RPM difference to the master. If all the pointers are stationary the engine RPMs are in sync.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
hercppmx
Posts: 159
Joined: Mon May 26, 2008 8:25 am

RE: Propeller In Sync Meaning?

Wed Aug 10, 2011 6:37 am

One the C-130, each prop has a magnet behind the Number 1 blade, the magnet is attached to the de-icer contact ring, which is bolted to the props rear spinner. Each time it passes it's pick up (right above the aux feather motor pump on the right side of the pump housing.) an electrical signal is sent to the synchrophaser. This lets the synchrophaser know where each number one blade is during their rotation. The magnets are gapped aprox .080 to .130 of an inch.

Each engines Tach Generator also provides the synchrophaser with the engines RPM. The synchrophaser can "correct" the RPM of each of the engine up to 3% I believe. You can select either engine 2 or 3 as your master engine (the leader) and the other 3 engines are the slave engines (the followers).

The goal is to prevent the propellers blades all hitting top dead center at once. If the blades were to hit TDC all at once it would create a very annoying vibration and sound through out the aircraft. Another by product of the synchrophaser is it helps maintain symmetrical thrust from all engines. On the older C-130's you can fly without a synchrophaser but the engines are a lot easier to over torque. (this leads to 6 weeks of 12 on 12 off and an embarrassed O-5)



Quoting KingairTA (Reply 9):
No prop sync on a C-130 is very very annoying. Nothing that would ground the airplane though. Just picture a loud low pitch waaaaaaa waaaaaa waaaaaaa for 8+ hours.

The same noise can be created from a prop flux, and yes it's very annoying.
C-130; it's a love-hate relationship
 
Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: Propeller In Sync Meaning?

Wed Aug 10, 2011 10:03 am

I may again look and sound old fashioned but prop synch is not such a big deal.
Most of the time, a manual adjustment is a lot more accurate than any synch-er I have seen.
What one needs is just a bit of attention :
It's exactly like tuning a guitar when - or if - one doesn't have the perfect pitch : One has to understand that when tuning has been achieved, there is no * beat sound* coming.
1/- adjust one propeller to the required value of RPM for your flight mode.
2/- Bring the second propeller RPM up toward the indicated value and listen : you'll hear the beat frequency - that's the sound interference between the two engines - like waahwaahwaah... move very slowly the second prop pitch lever and hear if the *beat* slows down like :
waahwaah...waaahwaaahwaaaahhwaaaahhwaaaaahhh...etc... when you only hear waaaaaaaaaaaaaaaaaaaaaahhhhhhhhh, you've synched your props and you can see your passengers smile.

3/- Synching a four-engined airplane goes the same. It's even easier if you can see the porps on one side : use the stroboscopic effect : by bringing the second engine to the first'RPM, you'll see the blades where they 're over the same area seem to slow down...and then stop... perfect synch again... Now align the engines on the other side to that original RPM... it's quite easy to differentiate the vibration sides.
Contrail designer
 
tdscanuck
Posts: 8573
Joined: Wed Jan 11, 2006 7:25 am

RE: Propeller In Sync Meaning?

Wed Aug 10, 2011 11:46 pm

Quoting qslinger (Reply 4):
What about jet engines? Don;t they need to be in sync as well?

Generally not for noise reasons. On a modern large turbofan the vibration from the spools is very benign, so there isn't much to interfere with each other. The N2 (and N3 on a RR engine) speed isn't directly controllable anyway so there's not much you can do with them. Fan interference is audible but the autothrottles will generally trim that out anyway on N1 controlled engines. On ETP/TPR controlled engines you don't want the fans to be in sync anyway.

Tom.
 
Arrow
Posts: 2325
Joined: Wed Jun 19, 2002 7:44 am

RE: Propeller In Sync Meaning?

Thu Aug 11, 2011 10:25 pm

Quoting Baroque (Reply 7):
A simple tip was that if you heard something going over at night, engines unsynch, enemy and likely to drop things that went bang, engines synch, probably a friend, you hoped!! While the radar folk had a better idea due to IFF and conveyed this to the AA, the general populace had to go on the engine sounds.

My grandmother always knew who was up there by the engine sounds. She called the bombers "Whirra-whirras" and immediately headed for the cellar. My father tried to explain why they sounded like that, but I don't think she cared much about the reasons.
Never let the facts get in the way of a good story.
 
kingairta
Posts: 454
Joined: Mon Feb 09, 2009 2:24 pm

RE: Propeller In Sync Meaning?

Fri Aug 12, 2011 1:59 pm

Quoting hercppmx (Reply 11):
The same noise can be created from a prop flux, and yes it's very annoying.

It's been a few years since I was a crewman on the Herc but iirc if we had a prop flux the motor would be shut down if it couldn't be corrected.

Going to mechanical on the prop sync loses throttle anticipation. That's why it's easier to over torque a motor.

Who is online

Users browsing this forum: No registered users and 32 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos