Prop sync question

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nozmoking

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Nozmo King
This is a procedural question that's bugging the heck out of me. I've not flown for quite a few years but my curiosity and love of flying still gets the better of me.
Someone departs an executive (GA) airport at about midnight 3-4 nights a week.
It's a Cessna 402C and when it passes overhead, they are about 25 miles from departure, roughly 160 knots and at about 3000 feet. What gets my attention is not just the sound of full throttles but the props are obviously not yet synced. And it bugs me! Is it too early in the flight (roughly 1100 miles total) to sync the props?
I know it's not a huge deal and I may be just over-thinking. But I'm really curious.
 
I usually synch the props on initial climb out. Its a small tweak.
I'm surprised a 402C doesn't have prop synchrophasers.
 
I would have had them synced on initial climb too. But I’ve observed that many pilots either aren’t bothered by a slight mismatch or they can’t hear it. Perhaps this person is one of those people.
 
mondtster said:
I would have had them synced on initial climb too. But I’ve observed that many pilots either aren’t bothered by a slight mismatch or they can’t hear it. Perhaps this person is one of those people.
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Evidently they aren't a musician.
 
Kenny Phillips said:
Evidently they aren't a musician.
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Having grown up with music I always thought syncing props by ear was easy. But I’ve given enough multiengine instruction over the years to realize that many people don’t have that gift. People can usually get them close but they’ll still be out of sync and apparently can’t hear it.

It drives me crazy.
 
nozmoking said:
This is a procedural question that's bugging the heck out of me. I've not flown for quite a few years but my curiosity and love of flying still gets the better of me.
Someone departs an executive (GA) airport at about midnight 3-4 nights a week.
It's a Cessna 402C and when it passes overhead, they are about 25 miles from departure, roughly 160 knots and at about 3000 feet. What gets my attention is not just the sound of full throttles but the props are obviously not yet synced. And it bugs me! Is it too early in the flight (roughly 1100 miles total) to sync the props?
I know it's not a huge deal and I may be just over-thinking. But I'm really curious.
Click to expand...

Some of these details really make me raise an eyebrow.

Presumably you are getting this information from one of the flight tracking websites.

So the pilot is on an 1100 nm flight (which is a really long way for a 402), but is still at 3,000 ft 25 nm from takeoff. That implies they're cruising at 3000, which seems unlikely, especially for a flight of that length. And of course, if they are then they wouldn't be at full power any longer.

But yes, I usually do my prop syncing during initial climb once above 1000 AGL or so.
 
After reading this, I have the Dolby Sound music chord crescendo you hear before they start a movie stuck in my head now.
 
GRG55 said:
I usually synch the props on initial climb out. Its a small tweak.
I'm surprised a 402C doesn't have prop synchrophasers.
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It was apparently an option or aftermarket retrofit. Cessna released a TSB about an issue with the system so it must have been OEM.
 
Maybe they’re turning the switch on, assuming that it’s working but it’s not.
 
MauleSkinner said:
Maybe they’re turning the switch on, assuming that it’s working but it’s not.
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You can hear the beat frequency oscillation if it isn't.

mondtster said:
Having grown up with music I always thought syncing props by ear was easy. But I’ve given enough multiengine instruction over the years to realize that many people don’t have that gift. People can usually get them close but they’ll still be out of sync and apparently can’t hear it.

It drives me crazy.
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Then again, maybe not?
I have zero musical talent whatsoever, but I still find it incredibly irritating if I don't have the props absolutely in synch.
It never occurred to me there are some people that can't hear it.
 
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GRG55 said:
You can hear the beat frequency oscillation if it isn't.
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Maybe they’re not listening or feeling for that. Wouldnt be the first pilot to habitually flip a switch with absolutely no verification that it’s doing what it’s supposed to.
 
sourdough44 said:
Maybe you have to track him(her) down & State your concerns?
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I did capture the ADSB data a few nights ago when they flew over and drafted text to send off an FAA hotline report. I just haven't decided if I want to go that far because it's not really a safety issue per se and apparently most 402's require manual prop sync if they don't have the kit installed. And, it's true that not all pilots have the ear to manually sync props.
But thanks to everyone my question's been answered. Ain't perfectionism grand?
 
MauleSkinner said:
Maybe they’re not listening or feeling for that. Wouldnt be the first pilot to habitually flip a switch with absolutely no verification that it’s doing what it’s supposed to.
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If they aren't paying attention to this sort of thing, what other subtle things are they ignoring that are potentially more important?
 
nozmoking said:
I did capture the ADSB data a few nights ago when they flew over and drafted text to send off an FAA hotline report. I just haven't decided if I want to go that far because it's not really a safety issue per se and apparently most 402's require manual prop sync if they don't have the kit installed. And, it's true that not all pilots have the ear to manually sync props.
But thanks to everyone my question's been answered. Ain't perfectionism grand?
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What exactly is there to report to the FAA? And why would they care if a pilot synchs the props?

Never mind, I figured it out. OP joined yesterday. No way is he a pilot - he’s just a know-it-all never-been.
 
I think some of the whole ‘sync thing’ is how the individuals ear is tuned. Time in type factors in. What’s right for one, could be slightly off for the next.

I wouldn’t involve the FAA over such matters. Most don’t care to receive that call, ‘this is the FAA, here to help’.
 
Here's my theory.

Have you seen how far apart the props are on a 402C?

The props could be perfectly synced from the cockpit, but because of the effects of the slightly different off-center path of the sonic pulses from the blades caused by interference with the airframe and wing, there is a phase shift. Anyone listening from outside cannot possibly hear both sonic paths at the same time for more than a second or a fraction of a second with an airplane going that fast, IMHO.

Some people are able to hear a dissonance of only a couple of Cents, and to them, props are never synced.
 
I used to sync the props during the takeoff roll — not only because outta sync props bug me, but because I wanted to recognize a poor-running engine immediately. Even did that during the runup,...sync them and check the mags on both engines simultaneously; if one engine has an excessive RPM drop it’s easy to tell.
 
Maybe it’s the awesome noise cancelling headsets.

How does the auto sync switch do its thing? What’s it do to sync them up?

Also, at some RPM differential, you get on average less sound due to cancellation, no? And no louder when they’re in phase. So theoretically, a twin pilot’s hearing only has half the loud hours than a single engine pilot...if they don’t sync. I’m playing here.
 
RussR said:
I've never noticed any difference between types of aircraft as far as being able to notice un-synced props. It's one of the few things that, to me, is identical across all types.
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In my experience, how noticeable it is depends far more on the individual airframe is rigged and maintained than aircraft type.

Some twins are naturally better synced without operator intervention than others.

My Beech 18 at fairly well synced on its own with takeoff power applied. Not perfect, but close enough that I don’t intentionally sync the props until after I make the first power reduction around 500’ AGL.

The props on my Baron, on the other hand, were so noticeably out of sync that I was adjusting them on the takeoff roll.

So, take the variations between two different twins of the same type and add in the effect of pilots who have better or worse hearing than others and you get some pretty big variations in practice.
 
Fearless Tower said:
In my experience, how noticeable it is depends far more on the individual airframe is rigged and maintained than aircraft type.

Some twins are naturally better synced without operator intervention than others.

My Beech 18 at fairly well synced on its own with takeoff power applied. Not perfect, but close enough that I don’t intentionally sync the props until after I make the first power reduction around 500’ AGL.

The props on my Baron, on the other hand, were so noticeably out of sync that I was adjusting them on the takeoff roll.

So, take the variations between two different twins of the same type and add in the effect of pilots who have better or worse hearing than others and you get some pretty big variations in practice.
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Okay, but how closely the engines are synced for takeoff would really just depend on how closely and accurately the governors are set for max rpm. I don't see that as having anything to do with the particular airframe or engine. More to do with the mechanic.

And the OP's question was (presumably) about cruise flight anyway, which is what I was referring to. I've never seen any difference in the process of manually syncing engines from one airframe to the other.

So, as far as I can tell, the difference is entirely in the pilot's hearing, ability, and desire to sync it.
 
Fearless Tower said:
In my experience, how noticeable it is depends far more on the individual airframe is rigged and maintained than aircraft type.

Some twins are naturally better synced without operator intervention than others.

My Beech 18 at fairly well synced on its own with takeoff power applied. Not perfect, but close enough that I don’t intentionally sync the props until after I make the first power reduction around 500’ AGL.

The props on my Baron, on the other hand, were so noticeably out of sync that I was adjusting them on the takeoff roll.

So, take the variations between two different twins of the same type and add in the effect of pilots who have better or worse hearing than others and you get some pretty big variations in practice.
Click to expand...


While poorly rigged twins are annoying on takeoff, I don’t think it is important in this discussion because it sounds like the plane in question is well beyond that point.

Either the pilot can hear that the props are out of sync or they can’t. Many pilots seem to be tone deaf or not bothered by the warble. Some of the problem may be that the pilot doesn’t understand what they’re hearing or how to fix it as well. I had one student who got their multi in a newer Seminole with the little wheel on the dash to indicate which engine is turning faster and they had no idea how to sync the props without it. Others would just line up the tach needles and call it good even though there was a very noticeable audible difference.

At the end of the day, I just view it as being annoying. There doesn’t seem to be enough difference in yaw with the props synced vs. without to talk about, as long as the power settings are reasonably close to the same.
 
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