Oil level check

You guys have to Stop just believing me!  

I made a major mistake in that explanation.  Oooops!!!

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51 is NOT a prime Number. 51=17x3.

51:21 = 17x3 : 7x3,  GCD =3

That means the 51:21 Gear-Set Re-Syncs every 7 Prop Revs (17 Crank Revs) and every tooth only mates with every 3rd. opposing tooth. Good.

The 50:22 Gear-Set Re-Syncs every 11 Prop Revs (25 Crank Revs) and each tooth mates with every 2nd. opposing tooth.  Better!

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A hypothetical 53:19 Gear-Set (2.79:1) would consist of 2 Prime Gears and only Re-Sync every 19 Prop Revs (53 Crank Revs) with every tooth mating with Every Single opposing tooth.  Best!!!

What did you mean in the earlier post by "co" prime numbers?  I knew 21 wasn't prime; I didn't think too hard about 51.

Now we are getting waaaay off the topic.

We were talking about Burping the engine and how close the compression points were.

And then the whole thing went sideways.

You can Google "Co-Primes" and get way more number theory explanations than you may want/need.

So let's put this to rest with this final explanation and If you want more on gear-train design, just open a new topic in the general section and we can pick it up there.

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I missed that also.  51 just feels like a prime number until you examine it closer.

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Co-Primes are numbers that do Not share the same Prime Factors.

They will make good gear sets even though they may or may not be prime numbers themselves.

An example:

17:23   Are obviously both primes.  And Technically, also Co-Prime by default.

35:66   Obvoiusly NOT primes but they are Co-Primes.

35 = 5x7  (Prime Factors)

66 = 2x3x11  (Yes, 2 is a prime number!)

They SHARE No common factors other than the number 1.  Co-Prime!  And would make an excellent 1.885671:1 gear set.

Not a nice even ratio but an ideal mesh/wear pattern.

The 66 tooth gear will resync only after 35 revolutions in which time the 35 Tooth gear will have made 66 revolutions.

Both Gears will have rotated the same (35x66=) 2310 teeth by default before the pattern would repeat with each tooth having meshed with each and every opposing tooth before repeating.

Bill Hertzel wrote:

You guys have to Stop just believing me!  

I made a major mistake in that explanation.  Oooops!!!

- - -

51 is NOT a prime Number. 51=17x3.

51:21 = 17x3 : 7x3,  GCD =3

That means the 51:21 Gear-Set Re-Syncs every 7 Prop Revs (17 Crank Revs) and every tooth only mates with every 3rd. opposing tooth. Good.

The 50:22 Gear-Set Re-Syncs every 11 Prop Revs (25 Crank Revs) and each tooth mates with every 2nd. opposing tooth.  Better!

- - -

A hypothetical 53:19 Gear-Set (2.79:1) would consist of 2 Prime Gears and only Re-Sync every 19 Prop Revs (53 Crank Revs) with every tooth mating with Every Single opposing tooth.  Best!!!

Why does Rotax not do this then if it would improve gearbox reliability?

I don't think it really affects reliabilty, as such.  The gearbox (if not the whole engine) will probably need replacing long before the tooth-meshing situation really affects anything.

But I am curious why Bill did not discuss a 50:21 ratio, as it's quite close to the 51:21, and seems to me that those numbers are co-prime. (factors of 2, 5, 10, 25, and 3, 7, respectively).