Re: Rotax 912 prop indexing and dynamic balancing

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Induna
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Re: Rotax 912 prop indexing and dynamic balancing

Postby Induna » Tue Oct 07, 2014 7:19 pm

Hi all,

In my quest to get a super smooth engine I was wondering if indexing a 2 blade prop on a Rotax 912 makes a difference, and if so, what should the prop position be in relation to cyl1 TDC to get the best results?

Also, how effective is dynamic balancing of the prop?

I am sure there has been a lot of experimenting with this.

Regards

Jacques
Last edited by Induna on Wed Oct 08, 2014 8:06 pm, edited 2 times in total.
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Re: Rotax 912 ULS prop indexing

Postby Jean Crous » Tue Oct 07, 2014 7:36 pm

Induna, on a direct drive engine it is relatively easy, however on a geared engine it will prove a bit more of a headache . Try moving the prop one bolt hole at a time, go fly and record your figures and repeat till you find the sweet-spot.
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Re: Rotax 912 ULS prop indexing

Postby Boet » Wed Oct 08, 2014 7:51 pm

Do not waste your time. No "sweet spot" with the 2.43 gear ratio, ever. None needed. Go figure. :roll:
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Induna
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Re: Rotax 912 prop indexing and dynamic balancing

Postby Induna » Wed Oct 08, 2014 8:01 pm

Haha, ekt so gedink! Ek dink al wat nou nog kort is daai mooi spinner en n dynamic balance... Sal iemand naby die kaap moet kry om dit te doen... Moet nog net uitvind wie dit kan doen teen n bilikke prys.

Ek is baie beindruk hoe glad die prop van oom piet is (^^)

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Re: Rotax 912 prop indexing and dynamic balancing

Postby Goose » Wed Oct 08, 2014 9:49 pm

Induna wrote:. Moet nog net uitvind wie dit kan doen teen n bilikke prys.

J vhpy
Bring hom nylstroom tailwheel flyinn toe en ek doen dit vir jou verniet :twisted:
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Re: Rotax 912 prop indexing and dynamic balancing

Postby Induna » Wed Oct 08, 2014 9:57 pm

Dis baie gaaf!!! Maar nylstroom is dan nog lank in die toekoms...! :shock:
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Re: Rotax 912 prop indexing and dynamic balancing

Postby Boet » Thu Oct 09, 2014 8:09 pm

Boetman, die spinner is met sorg gemaak. Jy kan hom maar net aansit, en gaan vlieg lekker.
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Re: Rotax 912 prop indexing and dynamic balancing

Postby Dobbs » Sat Oct 11, 2014 5:09 pm

This is the first time I have heard of the position of a propellor blade relative to the piston position being of any relevance - or am I reading the question of Induna incorrectly?

Surely whether it is a direct drive or geared engine, the position of the blade relative to any piston position is totally immaterial and arbitary? :-o
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Re: Rotax 912 prop indexing and dynamic balancing

Postby justin.schoeman » Sat Oct 11, 2014 11:19 pm

Dobbs wrote:This is the first time I have heard of the position of a propellor blade relative to the piston position being of any relevance - or am I reading the question of Induna incorrectly?

Surely whether it is a direct drive or geared engine, the position of the blade relative to any piston position is totally immaterial and arbitary? :-o
The crank doesn't rotate at a constant rate. When a piston is on a power stroke, the crank is accelerating, and the prop is moving slightly faster. You generally want a prop blade to be near horizontal when it is turning fastest, as this is where most of the blade is exposed, and least interference with the slip stream.

The difference is slight, but it is there.

Once you have a geared prop - especially with an uneven ratio, the prop is in a different position for each power stroke, and then you are looking at averages - much more difficult to determine.
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Re: Rotax 912 prop indexing and dynamic balancing

Postby Dobbs » Sun Oct 12, 2014 3:53 pm

Thanks Justin - still doing research on the www to try and get a feel for the changes in rotational velocity of a typical 4 cyl engine.

I would think that with a composite prop, with their inherent flexibility, the tip speed of the prop does not vary much?

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