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Dynamic prop balance and Tips

 
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Roger Lee



Joined: 10 Jan 2006
Posts: 1461
Location: Tucson, Az.

PostPosted: Sun Feb 18, 2007 7:33 pm    Post subject: Dynamic prop balance and Tips Reply with quote

Hi All,
From Eric Tucker at Kodiak/Rotax.
The 912 came out in 1989 and the certified S came out in 1990. The original TBO was 600 hrs. Rotax currently produces 5k 912's a year. With a little more data they might go to 1800 hr. TBO. Business is booming worldwide for the Rotax.
I recommend evryone tha works on a Rotax engine take the class. Lots of good info.

1. If you built or changed your prop then you should get a Dynamic prop balance for the longevity of your gearbox.

2. The engine was set up to run better temps. and vibration smoothness at 4800-5200 rpm. 4700 and below usually run a little more temp, but more vibration, whether you feel it or not. I have heard of some guys that want to run the engine at 5500 rpm all the time, well yes it can, but pay more in excessive wear later.

3. Mufflers should have 5 liters volume for your Rotax 912uls/s to have a tuned exhaust.

4. You 912 was set up to fly for up to 30 minutes at 75% power if you lose oil pressure. Yes, btter to land, but not at the expense of crashing. Yes the engine will need some work if you go for the 75% at 30 min. Remember your cylinders are not water cooled, only the heads.

5. Water temp gauges are not needed if you are keeping you CHT's in limits.

6. Use only mineral spirits to clean you aluminum engine if it becomes necessary. If you use some types of cleaners and note that there are color changes then this is undesirable.

7. clean your carbs with only mineral spirits. No carb cleaners. They are too harsh.

8. No automotive wire connectors are supposed to be used.

9. Rotax would like to see an oil sample sent in to analysis lab once a year at annual.

10. Shock cooling a Rotax is not an issue while flying. Lots of data to support this.

Just some tips and issues disscused at the Rotax class. If you haven't been and heard something from a friend or other mechanic then it is just hearsay or some other logic or experience from a different engine type.
There have been quite a few items that have changed over the years and some of the old ideas do not apply to todays engines v.s. 10-15 year old 912's.


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Roger Lee
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JetPilot



Joined: 10 Jan 2006
Posts: 1246

PostPosted: Wed Feb 21, 2007 7:12 pm    Post subject: Re: Dynamic prop balance and Tips Reply with quote

Roger Lee wrote:
Hi All,

4. You 912 was set up to fly for up to 30 minutes at 75% power if you lose oil pressure. Yes, btter to land, but not at the expense of crashing. Yes the engine will need some work if you go for the 75% at 30 min. .



I am willing to bet that it would run only 30 seconds after losing oil pressure Wink Im betting you meant "if you lose the coolant ...
"
You talked about a minimum of vibration from 4800 to 5200 RPM. It makes perfect sense that you would get excessive wear running more than 5200 RPM, but What happens if you run 4500 RPM ? Mine engine and plane are very happy crusing at 4500 RPM, any problem with this ?

Mike


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PostPosted: Thu Feb 22, 2007 1:17 am    Post subject: Dynamic prop balance and Tips Reply with quote

<<I am willing to bet that it would run only 30 seconds after losing oil
pressure>>

It's been proven to run for more than 20 minutes, during an 80 mile sea
crossing where the oil pressure disappeared half way across!

Duncan McF.


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occom



Joined: 26 Aug 2006
Posts: 404

PostPosted: Thu Feb 22, 2007 12:34 pm    Post subject: Dynamic prop balance and Tips Reply with quote

I bet you could go 30 minutes. I once ran an industrial engine at full
throttle for 40 minutes before someone told me there was NO oil in it. I'm
sure there was damage but it's been years and that engine is still running
fine. I would have bet against it, but there ya go.
Do not archive
---


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Roger Lee



Joined: 10 Jan 2006
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Location: Tucson, Az.

PostPosted: Thu Feb 22, 2007 5:20 pm    Post subject: Re: Dynamic prop balance and Tips Reply with quote

Sorry, my mistake I did mean coolant. Not oil. Thanks for pointing it out.

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Roger Lee
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Roger Lee



Joined: 10 Jan 2006
Posts: 1461
Location: Tucson, Az.

PostPosted: Thu Feb 22, 2007 5:28 pm    Post subject: Re: Dynamic prop balance and Tips Reply with quote

Hi Guys,

In the class Eric stated that running under 4700 rpm and below has more vibration introduced to the gear box. Most engines tend to run better frquency vibration at certain rpm's. You should have better fuel burn with better distance covered at 4800-5200rpm. If you look at the torque chart for the 912/100hp the best torque v.s. hp happens at 4800 to 5200, after 5200 torque starts to fall off as hp slightly increases.

Sorry guys for the mistake on coolant v.s. oil loss. I have been typing so much lately my brain getting mushy. LOL


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daveaustin2(at)can.rogers
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PostPosted: Thu Feb 22, 2007 5:39 pm    Post subject: Dynamic prop balance and Tips Reply with quote

I'm inclined to believe this is a version of a story Chris Hientz told me.
On his way back from Oshkosh to Canada he flew across lake Michigan (45
miles) and had a coolant hose failure half way across. Throttled back to
75% and made an airport just beyond the Michigan shoreline. I think I agree
that without oil it would quit quite quickly.
Dave Austin 601HDS - 912, Spitfire Mk VIII
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JetPilot



Joined: 10 Jan 2006
Posts: 1246

PostPosted: Thu Feb 22, 2007 6:56 pm    Post subject: Re: Dynamic prop balance and Tips Reply with quote

Thanks for the good engine info as always Roger Lee Smile

Given that, I will keep it at least 4800 RPM for cruise.

Mike


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PostPosted: Fri Feb 23, 2007 12:42 pm    Post subject: Dynamic prop balance and Tips Reply with quote

No it isn't. It's a version of a UK 912-engined Europa on the 85 mile sea
crossing from Cherbourg to Isle of Wight. It was probably closer to 1/2 hour
that it ran without oil pressure, although a lot of the oil remained trapped
in the sump, so some splash lubrication and cooling would have been present.

DuncanMcF.
---


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