Prop sync

[Tigurius175]

Hi im new to fs9, especially twin engined props and i wanna know what prop sync is and how to use it. can anyone help me? thanks

[garymbuska]

Welcome to the sims.
Prop sync is used on any multiple propeller aircraft.
What it does is it keeps the propellers in sync with each other. Without this sync the air craft could literally vibrate apart. A good example is to think about what would happen if you were to take to 1 gallon buckets of sand then start to rotate them opposite of each other . By that I mean one bucket is going down while the other is going up. You can imagine how hard that would be to controll. But when the start coming down a few seconds apart from each other the vibation slows down. This is what prop sync does. The blades come down very close to one another. But not quite at the same time.

[Tigurius175]

so how do i use the prop sync buttons and the little black and white circley thing?

[RollerBall]

Prop sync is to do with engine revs.

If the revs of each engine aren't quite the same you get a resonnance. You know, sounds like

vooom   vooom   vooom

You must have heard it

The closer the engine revs are, the slower the waves of the resonnance become until when the revs are exactly equal, it disappears.

You can adjust the throttles manually but by hitting prop sysnc, it does it for you so you can avoid the at least annoying, but potentially damaging, resonnance

[garymbuska]

You can press the prop sync button before you start any engines or after you start one and before you start the other. But you do not want to start more than one engine with out this being pressed. The resonance created by the ofset props can damage the airframe.
The manual way is one way of doing this but since you are not actually in the plane you can not feel the effect and unless you have the stress causes damage slider set to on you really wont know any thing is wrong. But it can have adverse effects as to how the plane flys and taxi's. The idea is to have them pull together rather than independant of each other. One of the advantages of a twin engine is that you can actually use them to help offsett cross winds with out the rudder coming into play.

[Chris_F]

I thought (perhaps I learned it in the Learning Center) that you weren't supposed to use prop sync during takeoff.  I assume this is because you want to generate max power on takeoff and don't want to retard one engine for the sake of prop sinc.  Likewise if you loose an engine you don't want the other to throttle down in an attempt to sinc the prop.

The stress resulting from a non sinc'd prop shouldn't be that large.  Yes, having an un-sinc'd prop will put additional stress on the aircraft, but not so much that it causes damage quickly.  It's more of a way to get more useful life out of an airframe than a strict safety item.  Also it makes life more pleasant for the human occupants who don't have to listen to the resonance.

The example gary describes with the buckets would be true if the engines or props weren't ballanced.  But this would only be effective if the props and engines shared a common drive shaft.  Otherwise, prop sinc or no, the airframe would be succeptable to the vibration of an unbalanced prop or engine.  Imagine the following:  You're flying around and you loose a prop blade from each engine.  Now the props are in sinc but missing a prop blade.  Each prop/engine vibrates wildly.  The mounting points are stressed like crazy.  The plane's Center of Gravity may not vibrate because the props are sinc'd but everything else inside the plane (including you) gets shook up like a milkshake.