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Jeff Hinson
Joined: 03 Dec 2007
Posts: 5
Location: St. Louis, MO
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 Posted: Sat Dec 08, 2007 3:48 pm Post subject: 912S Ring Mount Warning |
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I'm building a 701 with the Rotax 912S Kit obtained from ZAC. I first had a problem with the ring; one of the bolts holes needed to be reamed out. I also noticed that the "forth" mount wasn't centered (with three engine mounts installed, the last one couldn't be installed). I called ZAC and they said to install the ring to the engine mount first, and then install the engine mount to the firewall.
This did work and I have been continuing assembly. Today I was fitting the formed cowl and it was looking strange. The engine looked out of line.
I measured the distance from firewall to ring mount attachment points and one of the top mounts was 14mm less than the others. The engine mount was manufactured by ZAC. I broke out my 'dusty' calculator, and determined that this 14mm would create a 53mm translation at the nose cone! (tan a = opp/adj)
A little more calculating and determined a thick washer at the mount ie 2mm, would cause a 7.5mm translation at the nose cone. I guess the bottom line is check your firewall to mount distance; if they're not all the same, the difference is amplified.
I'll be calling ZAC Monday morning.
Jeff
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n801bh(at)netzero.com
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| Posted: Sat Dec 08, 2007 4:47 pm Post subject: 912S Ring Mount Warning |
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Jeff. on most planes the mount locates the motor in a slightly cocked angle.Almost always it has the prop/spinner pointed down about 2-3 degrees. On Lyc's, Jabiru's and other clockwise turning engines the prop is aimed to the right as seen from the pilots seat. This offsets the P factor. I believe the Rotax rotates the opposite way so the prop might me aimed to the left. Either way the top tubes of the mount should be longer then the bottom ones. On average rotating motors the the pilot side tubes should be longer then the other side, The engine will sit in the front of the plane at an angle but the prop flange should end up at the specified centerline of the plane.
do not archive
Ben Haas
N801BH
www.haaspowerair.com
-- "N732JH" <jeffrey.w.hinson(at)boeing.com> wrote:
--> Zenith-List message posted by: "N732JH" <jeffrey.w.hinson(at)boeing.com>
I'm building a 701 with the Rotax 912S Kit obtained from ZAC. I first had a problem with the ring; one of the bolts holes needed to be reamed out. I also noticed that the "forth" mount wasn't centered (with three engine mounts installed, the last one couldn't be installed). I called ZAC and they said to install the ring to the engine mount first, and then install the engine mount to the firewall.
This did work and I have been continuing assembly. Today I was fitting the formed cowl and it was looking strange. The engine looked out of line.
I measured the distance from firewall to ring mount attachment points and one of the top mounts was 14mm less than the others. The engine mount was manufactured by ZAC. I broke out my 'dusty' calculator, and determined that this 14mm would create a 53mm translation at the nose cone! (tan a = opp/adj)
A little more calculating and determined a thick washer at the mount ie 2mm, would cause a 7.5mm translation at the nose cone. I guess the bottom line is check your firewall to mount distance; if they're not all the same, the difference is amplified.
I'll be calling ZAC Monday morning.
Jeff
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craig(at)craigandjean.com
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| Posted: Sat Dec 08, 2007 5:08 pm Post subject: 912S Ring Mount Warning |
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[quote]The plans for the old Rotax 912S bed mount show a left/right offset of 3 degrees (6-E-3, 4/2004). I don’t see any top/bottom offset. -- Craig [b]
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raymondj(at)frontiernet.n
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| Posted: Sat Dec 08, 2007 5:41 pm Post subject: 912S Ring Mount Warning |
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Ben,
Can you recommend any references for calculating the left/right and up/down thrust line angles for a particular airframe? I am designing my own airframe and want to center the vertical stab so I can use engines rotating either way. I plan to use thrustline alignment to minimize P-factor. I believe the prop affects the P-factor also. Any leads on either of these topics would be appreciated.
Thanks in advance,
Raymond Julian
Kettle River, MN
"Hope for the best,
but prepare for the worst."
do not archive
[quote] ---
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Jeff Hinson
Joined: 03 Dec 2007
Posts: 5
Location: St. Louis, MO
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| Posted: Sat Dec 08, 2007 8:30 pm Post subject: Re: 912S Ring Mount Warning |
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Thanks for the reply! I didn't notice the 3deg right deflection on my 7-E-2 drawing. I do have a 3.5deg deflection that a 2mm washer between the right upper engine mount/ring will reduce to 3.1deg--perhaps a thrust washer or two will get this perfect.
From the pilots point of view, from the firewall to the right ring is 266, and the left is 280mm. If I reduce this 14mm difference to 11.5 then:
tan(x)=11.5/220... x=2.99deg (220mm between mounting points).
I hope it's ok to add washers between the mount and ring.
Thanks again,
Jeff
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Tommy Walker
Joined: 12 Jan 2006
Posts: 442
Location: Anniston, AL 36207
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| Posted: Sun Dec 09, 2007 1:41 pm Post subject: 912S Ring Mount Warning |
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Hi Jeff,
In addition to Jon Croke’s 912 installation DVD, there is a very good series of articles in EAA’s Sport Pilot Magazine. The fourth part of this series deals with this issue. I think it is the December 2005 issue.
I’m going to post a link to it, but it’s kinda long so it may not format correctly in this email message:
http://www.sportpilot.org/magazine/feature/2005%20-%2012%20December%20-%20Tips%20and%20Tricks%20for%20Ideal%20Rotax%20912%20Installation.pdf
If you can’t get the link to work, go to http://www.sportpilot.org and look at the Sport Pilot Magazine link. There are four very good articles dealing with installation and setup of the 912.
Hopefully you are a member of EAA, but even if you are not, you can still read the magazine articles.
Tommy Walker in Alabama
N8701 18.5 hrs
Do Archive
[quote][b]
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Tommy Walker
N25A - Anniston, AL |
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