fat avid 912 engine mount

[akflyer 1427]

The mount is under way.  making the cups that all tubes to mount to the firewall is 16 pieces welded together to make the cups.  i think i know why kitfox and rotax charge what they do for these.  next one i will have the discs cut on the water jet and save some shop time by getting a whole bunch done at once.  The firewall jig is based off the pattern that Randy Tyler made of his firewall.  This will locate the mount flanges and basic tube lay out.  I still have to fabricate the stand offs to hold the cups for welding the tubes.  Our plan is to move the 912 forwards about 5 inches to keep the cg the same as it was with the subaru engine.  Its a fair bit of work to get the first one perfected but future mounts will be easy to weld.  I will use hardened all thread to locate the cups so it will be easy in the future to make the prop flange fall where ever the builder desires to make the cg so engine swaps wont require a bunch of battery moving etc.

[EDMO 1078]

Any offset to engine?  EDMO

[akflyer 1427]

Any offset to engine?  EDMO

straight ahead and 2 deg down.  Pics will follow later, its not letting me upload from my phone.

Edited 7 Dec 2017 by akflyer

[EDMO 1078]

Any offset to engine?  EDMO

straight ahead and 2 deg down.  Pics will follow later, its not letting me upload from my phone.

The 2 degrees down - Was that just to line up prop flange with cowl, or other reasons?   EDMO

[SuberAvid 617]

Ed,

When we got to measuring my Subaru mount we discovered that Airdale made it at a 6.5 degree down angle.  The only thing I can figure is that they had their jig set up wrong or the welder screwed up.  Anyway, it explains why Jack's plane and my plane fly so different when everything else is pretty identical.  The reason we are going back to (1.5 degree down Leni) is to get it more standard, better takeoff performance and less drag in cruise.  (Jack's is 1.6 degrees down).  Many of the cub guys are going to in line mounts now.

I swore I would never go back to a Rotax because I hate the way they treat their customers with their pricing but I wanted more horsepower and less weight and could not figure out how to get it with my Subaru without adding even more weight of a supercharger and probably would cost more in the end with custom heads, etc; so I bit the bullet and bought a used 912 ULS and just ordered a high HP Zipper kit from Hal last weekend. 

I really like the Yamaha idea but it is still a bit in the development stage for me to make it a quick swap project that I wanted.

Hope to have the new extended wings with 3/4" washout, much stiffer spars/inserts, lengthened lift struts, extended flaperons and engine swap done by end of summer next year (although that may be a bit ambitious).  I sure appreciate the Magnum wing build info you sent, these wings will be identical to the magnum wings dimensionally but with the flaperon hangar spacing of the heavy hauler wings. 

Still plan to use the great Subie motor again though, want to extend the new MKIV fuselage I have and put it together with the Subie and current wings.  You can't beat the ease of operation and reliability of the Subie!

Having Leni building the mount for me is awesome; Many thanks Leni!

Randy

 

Edited 7 Dec 2017 by SuberAvid

[Av8r3400 1179]

I hope your Rotax project works well for you, Randy, and doesn't make a liar of me. 

We (as 912 operators) are finding more and more aftermarket and non-traditional sources for parts for the 912 engines all the time. We are also coming up with new and better tuning tricks to make them run better.  Please don't be shy to ask if it gets funny with you. 

[TJay 1041]

 

 

 I sure appreciate the Magnum wing build info you sent, these wings will be identical to the magnum wings dimensionally but with the flaperon hangar spacing of the heavy hauler wings. 

 

 

 

 

where can a guy get a hold of this info?

[EDMO 1078]

 

 

 I sure appreciate the Magnum wing build info you sent, these wings will be identical to the magnum wings dimensionally but with the flaperon hangar spacing of the heavy hauler wings. 

 

 

 

 

where can a guy get a hold of this info?

TJay,  I don't know if this is in Files and Forms, and I sold my Magnum book.  I think I helped Randy decide to get the Just inserts, like you have.  Moving struts outward more than Avid might be a benefit too.  Magnum wings are comparable to Kitfox, except 4 feet longer span and 083 spars.  Larger flaperons should help him too, but not as much as my flaps and ailerons, IMO.   HH rib spacing would be good.  That's about all I can remember.   I don't know if he is going to use Kitfox 4 ribs like Leni plans to do on the Coyote.   Maybe Randy can tell you more?   EDMO

Edited 7 Dec 2017 by EDMO

[marshawk 82]

Randy, thats interesting to hear your soob mount was angle down 6 degrees , I had the same problem with mind ,same guy must of built them. It caused alot of head scatching trying to get it to fly level,good luck with the new projects

[Guest]

Hi Randy,

My fat Avid with 912 weighs under 700 empty if it were not for the larger tires I have on it, so it is pretty much as light as it can easily be made. In other words not a lot of extra weight in any location that would mess with basic weight and balance.

I do not know where the subaru mount placed the engine, but I can tell you that the "stock" (whatever that means :-) Avid 912 mount places the prop in the right place (front to back) to allow the motor to fit a stock mkiv airframe and cowl without modifying the cowl.

With that mount on my Fat Avid the plane sits about an inch in back of the front CG limit when empty. So, it's much better with regard to CG than putting a 912 on a stock MKIV that is not stretched because the empty CG will fall in front of the forward limit.

Anyway the reason I am posting is that if I had put my engine 5 inches forward of where it is located on my plane the CG would be super too far forward. As it is, I have temporarily placed 10lb of lead the in the Fat Avid tail until I can move the battery back because it flys so much nicer than it does an inch back of the forward limit..... and I can still load it up with a lot of shit and not go aft.

If you haven't completed the mount yet I would highly recommend placing the engine in the same place as Avid placed it with their various 912 mounts. I've seen three and they are all different, but they did all place the prop in the same position in very close to the same place as the 582 mount place the prop for that engine.

Chris

 

[dholly 718]

Leni - I think Chris is correct, 5 in. forward sounds like way too much. Lowell Fitt built a 912 ring mount for his KF4-1200 where he added 2.2" forward and later claimed it was probably 1" too much. He was trying to compensate for added tail weight calculated to be just under 7lbs. at an 11' arm after installing speed rib Intercoastals and trim etc. There's obviously more length and weight in the A+ empennage than KF4-1200 but surely not >15lbs.?

[EDMO 1078]

Leni - I think Chris is correct, 5 in. forward sounds like way too much. Lowell Fitt built a 912 ring mount for his KF4-1200 where he added 2.2" forward and later claimed it was probably 1" too much. He was trying to compensate for added tail weight calculated to be just under 7lbs. at an 11' arm after installing speed rib Intercoastals and trim etc. There's obviously more length and weight in the A+ empennage than KF4-1200 but surely not >15lbs.?

Randy hauls huge Moose and Caribou parts and camping gear out of the Bush - Maybe that's why he needs forward engine weight?  Evidently he is trying to keep the same CG that the Subaru engine had because he has been flying it that way and it works for him.   EDMO

Edited 8 Dec 2017 by EDMO

[SuberAvid 617]

Thank you all for the info, it will likely save Me from positioning the engine in the wrong place (and Leni from a lot of work and rework).  I was trying to keep the CG pretty close to where it is currently with the Subie motor since as Ed says, I tend to load my plane pretty heavy at times and it has a baggage area that extends back 6' behind the truss that the bungees wrap around.  I also keep my tool box at the very back of the baggage area right now but moved the battery to the cabin side of the firewall when I went to the EarthX battery.  My Subie motor is about 195 lbs dry without exhaust and I think the 912 is around 130 lbs dry, but is quite a bit longer motor and the redrive sticks out a lot farther, so my position estimation may be off.  Leni was going to take some more measurements of the motor and CG length of it before we made any final decisions but this is great help!.

Chris, can you give me a length from your firewall to the redrive prop flange?  My plane is still going to be quite a bit heavier than yours, likely in the 770 lb range but that will still give me the best known starting position.

Larry, you can bet I will be hitting you up for help as I try to learn the care and operation of the 912.  I also had Hal send me the parts to convert to the 1" manifold crossover tube.  He says between that and the lighter pistons of the Zipper kit the engine will run smother and idle down to 1000 rpm without chattering everything.  I am used to pulling my Subie down to 600 rpm when landing and find it a bit difficult to land short while trying to keep the engine at 1400 rpm like Rotax says.  Hopefully this will help in that regard.

Willis, look forward to hearing about how your Yamaha conversion performs as well.

Edited 8 Dec 2017 by SuberAvid

[Guest]

Sorry....just saw this...I am on it!

Will measure firewall to prop flange on my Flat Avid and report back. I know the firewall to prop flange distance is the same on all 4 "Avid 912 mounts" I have seen.

I do not think you want to mount the engine further forward than this or you will never get the plane to fly right unless you put a moose in the back and then it would be way over gross :-)

Chris

[EDMO 1078]

Sorry....just saw this...I am on it!

Will measure firewall to prop flange on my Flat Avid and report back. I know the firewall to prop flange distance is the same on all 4 "Avid 912 mounts" I have seen.

I do not think you want to mount the engine further forward than this or you will never get the plane to fly right unless you put a moose in the back and then it would be way over gross :-)

Chris

Gross Weight in Alaska is measured by whether you can get any space between the tires and the Earth!  Getting out of ground effect is a challenge sometimes until you burn off enough fuel, or find colder air.   ;<)  EDMO

Edited 12 Dec 2017 by EDMO

[Guest]

Front of prop flange / back of spinner to firewall measures 25 1/2 inches on my avid 912 mount.

[Guest]

I was able to make up the firewall to not have any doghouses or indents by bending 45s for the footwell which totally cleared the pedals. More foot room than I need and fits big people well.

[SuberAvid 617]

Thanks Chris, that is just what I needed.  Leni was able to weigh the engine and get the CG of it yesterday and because of it's longer length and especially the added length of the redrive, my calculations to keep the CG about where it is currently with my Subie is only slightly forward of this.  Yours being a nosewheel plane would put a bit more weight forward than mine so that would put them pretty close overall.

Your FW looks like it gives you a huge amount of foot room.  I have plenty with mine even as a flat FW but I have my seat at the back of it's adjustment range.  You can probably run yours forward a bit?  It looks like everything fits really well on your install.

Thanks again for the measurement, it is a real help.

Ed, so far I haven't packed out a moose with mine, only sheep, caribou and bear; but don't think I would attempt a moose all in one load.  Ground affect is great but those pesky trees eventually seem to get in the way, Lol.  Sure hope I can get one of those bison tags one of these days though; now that will take a few trips!

I got a box of Zipper parts in the mail yesterday too but will be a while before I get it all assembled and installed.  Poor Leni has to put up with me calling and texting him constantly now.

[akflyer 1427]

Chris,

Do both of your air filters clear the firewall no problem?  How much clearance from the back of the starter to the firewall do you have?  Can you measure the down thrust on the engine?

I have seen numbers all over the place that lead me to believe the factory jigs were shit at best as no two mounts seem to be the same.  My goal is to make the best of all the mounts taking cues from various ones with the builder in mind as well as the guy that has to try and service / work on the planes.  It seems previous attempts to stuff 20 pounds of crap into a 5 pound bag left lots to be desired.

I am pretty sure I know why the numbers vary so much on the different mounts.  My first jig that allowed me to locate all the tubes and get everything in place did not adequately hold all the main fixtures rigid after tacking all the tubes in place during weld out.  This lets the cups and tubes walk all over the place during finish welding.  I made a second jig to hold all mount points and cups 100% rigid in place during welding so nothing could move.

 

Randy,

I welcome the calls and texts.  As you know the last couple of years have been a bit strained for various reasons.  I welcome the challenge of making the best mount we can through collaborated efforts.   Now to get to a point where I can build one of these mounts for my own plane one day

 

 

[wypaul 448]

Hey Randy what do you have for a serial number on the 912.  The cases were beefed up in 2006 because there were issues of stretching with the 912S.  I have the serial number some where and will take a look for it. That said, my engine is an early 90,s engine and so far so good.  The other fellow that sells the kits won't put them on the older engines.  I have 300 and some hours on my Zipper so far. 

[Av8r3400 1179]

Is that why Dallas’s engine failed?

[akflyer 1427]

here are a few of the pics.  The basic parts I am using to make the mount cups for the rubber isolators.  Also pictured are some holding jigs I have made that I got the idea from Fireballtools.com  If you are into fabrication, check out the videos on youtube, look up fireball tools and see the how and why that he came up with these squares etc for welders.  Pretty cool designs and they work AWESOME to be able to hold parts / tubes in place.  I made some in miniature for holding the 1/2" tubes and I just can't get enough of them.. they are the cats ass for positioning and holding parts.

Using the adjustable fixture to hold the landing gear of an unspecified aircraft while I fit and weld in reinforcement tubes on the gear.

 

[Guest]

One of my air cleaners is pretty tight but I can get it off. I would definitely not want the CG more forward than it is. But it prolly wouldn’t have too much effect to move the engine forward a half inch for air cleaner clearance if you wanted to do that.

My friend Jeromie sure is happy with his zipper. He did the lowest level upgrade and his engine puts out 5 more hp than mine and his can still run ethanol free regular where I have to run premium. He’s come to the conclusion to run it up higher in rpm than Rotax recommends for the stock 912. Its serving him well.

[Guest]

Answers to the questions I can answer right now:

Your FW looks like it gives you a huge amount of foot room.  I have plenty with mine even as a flat FW but I have my seat at the back of it's adjustment range.  You can probably run yours forward a bit? Yes I have rny my seat forward and with decent padding on the seat back for comfort. If I run the seat all the way back with minimal padding on the back rest I can't  reach the pedals. I'm 5'10".

Do both of your air filters clear the firewall no problem? I have to work the pilot air cleaner around and flex the rubber flange on the air cleaner a bit to get it off. I do not consider it a problem. Would it be nicer with another half inch? Yes, but I would not want to move the empty CG forward of where it is now personally.

How much clearance from the back of the starter to the firewall do you have? Plenty of clearance to the starter motor. I will try and measure and report back.

Can you measure the down thrust on the engine? How would you like me to measure down thrust? Against what? Leveled plane for measuring W&B? This might tale me some time to do but I will try and make time. Also my mount has some side offset to compensate for p factor so it will fly without rudder trim. Not exactly sure how to measure that.

Everyone I know (except me) and that is 3 other 912 mounts, have had to cut and weld in bent tubing where avid put straight pieces in between the firewall and the mount "ring" My mount seems to be an early one when they were still made by Avid proper and has bends to clear hoses and exhaust in appropriate places. I would strongly recommend that you start with an exhaust from kitfox or another "high volume" kit producer and fabricate the mount to work around that. That way when your exhaust rots out you can buy another and just bolt it on, rather than having to create a custom exhaust every time. just a thought.

 

 

Edited 13 Dec 2017 by Chris Bolkan

[akflyer 1427]

down thrust of prop flange versus the firewall.  A straight edge on the back of the prop flange and a measurement to the firewall at the edges, or mount points or some place on the firewall will give the numbers to figure the angles to get degrees or thrust offset.