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Old 02-01-2020, 09:10 PM
seagull seagull is offline
Join Date: Dec 2019
Location: San Bernardino
Posts: 11
Default 912ULS air duct, keep or remove?

I am wondering if anyone has removed the fiberglass shroud / duct from the 912ULS . The one that funnels the air from the front left opening to the cylinders? I understand the shroud is not being used on current kits. Does anyone have experience with and without? I am trying to decide if I should remove mine.
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Old 02-02-2020, 02:06 AM
Handclutch Handclutch is offline
Join Date: Feb 2015
Location: Bendigo, Australia
Posts: 100

Took mine off early last year when doing the 5 year hose replacement. Thought it was then or never. Absolutely no change in temps - or anything else.

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Old 02-02-2020, 04:18 AM
mike newall's Avatar
mike newall mike newall is offline
Join Date: Jan 2005
Location: Yorkshire, England
Posts: 1,882

Never put the shroud on either of our 12's with later voltage regulator location within the cabin, under the instrument tray.

No issues apart from low temps on coolant and oil on flight testing.

OAT in the 60's, couldn't get heat in at all, so we made up some blanks for the oil cooler and radiator out of .032 with large holes unibit cut in. That allowed us to experiment easily with snips.

Around 50% of coolant radiator now blocked and 30% of oil cooler blocked.

On a 5 minute timed climb at gross for the flight test, the oil temp nearly got into the amber, but in normal flight at say 4900 rpm, all temps are bang in the middle.
"I add a little excitement, a little spice to your lives, and all you do is complain!" - Q

Donated in 2019
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Old 02-03-2020, 08:08 PM
alexe alexe is offline
Join Date: May 2013
Location: Temecula, CA
Posts: 290

Iím sure you guys did some testing on this prior to deciding to drop the shroud. Is there any benefit/penalty without the shroud?
Alex Erdelyi
RV-9A Purchased
RV-12 Built and Sold
Paid through December, 2020
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Old 02-03-2020, 09:35 PM
rvbuilder2002 rvbuilder2002 is offline
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 8,643

Originally Posted by alexe View Post
Iím sure you guys did some testing on this prior to deciding to drop the shroud. Is there any benefit/penalty without the shroud?
Yes, some detailed testing was done in conjunction with some other testing that was happening and the data indicated that benefit from the use of the shroud was net neutral.
No negative impact, but no benefit either. Considering the additional cost of using the part, the amount of labor/build time to install it, and the added risk of something going wrong with the disassembly/ reassembly that was involved, the decision to delete it from the design was an easy one.

Because of these factors, I also wouldnít advocate for anyone doing the delete unless they were already disassembling for a 5 year hose replacement or other work.

Having said this, a lot of people may wonder why it was even used in the first place......
Being totally transparent and straight up.....
It was plain and simply a conservative engineering decision out of ignorance and lack of experience with the Rotax 912.
When the RV-12 developement program was started, we were venturing into enough new territory as it was. Reinventing the wheel with the engine installation was not something we were trying to avoid if possible.
We new we would have about as tightly of a cowled engine as there was at the time, and Rotax had a factory cooling shroud available for use on tightly cowl engines. The natural assumption was that Rotax has years of experience with the engine and if they have this part available, it must be needed. Problem was it was hugely expensive, so we designed our own.

It was only after getting a lot of experience with the engine ourself that we discovered it is not always necessary.
Any opinions expressed in this message are my own and not necessarily those of my employer.

Scott McDaniels
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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Old 02-03-2020, 09:49 PM
RFSchaller RFSchaller is offline
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,639

Iím with Scott on this one: why remove it if itís a no never mind. Every maintenance activity carries a risk of screwing up something, so why remove one?
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