Avid IV 912 engine conversion

[CGB3 1]

Hello all, I’m new to these forums so a bit of background. I fly trikes and also have an advanced ultralight called an Aerostar Festival R40 with a private license in Canada. I have some engineering background but it’s been 40 years since I was in school.

I recently purchased a badly ground looped Avid IV Heavy Hauler and am slowly straightening out the fuselage. While looking for info etc. I found a 912 Kitfox engine mount with the Rotax ring and I have a 80hp 912 from a trike. None of the mount points align so it needs to be modified. I have no idea how the 912 engine should be placed and if there are offsets and angles that need to be incorporated into the thrust line and where that line should be. 

I see the manuals that someone has downloaded here on the forum and have printed them up but there is no weight and balance section so I’m looking for a more complete builder’s manuals for the Avid. 

If anyone is willing to pass on some of their experience and has a manual I would be greatly appreciate it.

Thanks, Jeff 

Picton, Ontario 

 

[1avidflyer 2003]

Maybe you noticed this topic was discussed recently,  Not trying to sound negative in any way, just wondered if you saw it and were able to glean any info from it.  Avid empty weight and balance is about 11.2" to 16".   Avids do tend to be a bit on the nose heavy side even with a 582.  IN that other post, I did talk some about how I would modify my Avid firewall and the mount to make the Kitfox mount work in the Avid.  With the regular Kitfox 4 mount that uses 4 arms bolted to the engine, my prop flange face on a 912 is 24 1/2" from the firewall.  I have a Kitfox 5 ring mount style that was modified to fit the Kitfox 4, and with it the prop flange face on the 912 is 28 1/2".   I wonder if your ring mount is any different in distance out than mine is???   The 4 arm mount would be helpful for the nose heavy condition with the Avid if it keeps the engine further back.    JImChuk

[CGB3 1]

Thanks for the info. I am sorting through the posts.

Yes I am worried about the CofG. Where is the datum point (11.2-16”) measured from?

That is why I’m looking for the builder manual and weight and balance info. It is obvious to me that the mount I have will have to be modified. The thrust line of the engine is my biggest question as there should be an offset to the right which the mount has of 2.8deg but if I were to make attach points on the firewall as it came, the angle of the engine will point down 15.5deg?? So I bought a Kitfox mount hoping it would work with the Avid but…no.

So is there any known thrust line angles for the MK IV and a 912 and where is the CG supposed to be are what I’m looking for.

I also am changing the gear to Grove spring gear and moving them forward to complicate things further but hopefully help ground handling.

Thanks Jeff

[1avidflyer 2003]

Sorry,  I should have said, leading edge of the wing is the datum point.  I haven't checked for any offsets with the 912 Kitfox mount, but did on my Avid with a factory made Jabiru mount.  The Jabiru engine was not twisted to one side or the other.  Also, in checking for up or down offset, the prop was at 90 degrees to the underside of the wing spars.  I need just a small rudder trim tab as the plane tends to turn to the right just a little bit.  Here are a couple of pictures of crudely checking the up and down angles.  You did get me thinking, now I'll have to compare my Kitfox 4 and Avid MK IV projects to see if the firewalls are at the same angle in relation to the wing.  Can you post up a picture of your ring mount?

[1avidflyer 2003]

I finally got around to checking and comparing the Kitfox  and Avid firewall angles in relation to the wing carry throughs.  The Kitfox ends up being about 91 1/2 degrees, and the Avid is about 95 degrees.  The bottoms of the firewalls are further ahead then the tops of the firewalls.  The bottom of the Avid is further ahead than the Kitfox bottom.  Hope that makes sense.  I'm thinking I would still maybe use the Kitfox mount, and use the center bottom attachment point on the Kitfox mount as the starting point.  The center attachment points on the Avid are about 3/4" wider than the Kitfox mount so in modifying that, bushings could be turned enough to make up the different angle of the firewall.  Then the top two Kitfox attachment points are removed from the Kitfox mount, and new ones fabricated to fit the Avid mounting points.  This is how I see it at this point.  I think it would be way less work for me than building an entirely new mount, and I happen to have a spare Kitfox mount as well.  

[CGB3 1]

Here is the ring mount. I’ve talked to a few guys and generally the engine has a right angle of approximately 3 deg (2.8) on the Kitfox mount as is. Also there should be a similar angle downward to prevent abrupt nose up attitude when full power is applied in the air. So major mods to the Kitfox mount are required. I have made a template of the firewall mount points and will rework the engine mount from that for 912. In the mean time I’m going to reinstall the 582 and see if the plane is worth putting the 912 in. 
Jeff 

[Kitfoxy 0]