Aeroovee to Rotax mount conversion???

[xeriotti]

Lasercuts are here... I may drive to the hangar in a while i have a sheet metal bender there...



Started mocking up the 4 to 1 exhaust.. Equal lenght headers is the goal... Stainless steel tubing is on the way for the fabrication

[Kai]

Exhaust headers:

Maybe you could pick up some ideas from the exhaust system Rotax has developed for the R914.

Don´t let the turbine housing on this NA engine confuse you- it´s just there to provide a temporary anchor point for the R914 turbo muffler, which later on in the prosess was substituted with a specially manufactured elbow. This elbow is the only item in the system which is not standard Rotax, and which should be no problem at all for a welding virituoso like you to manufacture.

The resulting exhaust noise is very pleasing: a sort of dark, angry growl. The whining, clattering 912-sound is gone.

[xeriotti]

With a little bending my 3d file turned into a pretty decent oil reservoir mount... I will give it some magic and then to powdercoating.



This beauties arrived and after diner i started fabricating the exhaust headers.... I made 3 out of 4 before midnight (thats my deadline for using powertools like a maniac... Theres no problem, but i respect my neighbors after that specific hour jajaja)

[13brv3]

That some seriously impressive fabrication skill. At the rate you're going, you'll be flying in a couple weeks :-)
Rusty

[xeriotti]

That some seriously impressive fabrication skill. At the rate you're going, you'll be flying in a couple weeks :-)
Rusty

Thanks for your words! Its easy to stay motivated when you literally see the pile of random pieces turn into a plane! :)
I really enjoy flying. But the sensation of building something that flies... Thats really strong. A mix of sensations, when you go off plans and start finding solutions, when things click, when you receive a compliment about your craftmanship, creativity or ingenuity.... That my friend is what got me hooked into building planes... Im always building, repairing, upgrading or messing something up since i tried this drug called experimental aviation.

[Kai]

Yup!

I´m with you as far as the messing up things goes- high five!

From my days as an engine application engineer some exhaust system guidelines emerge:

Engines hate bends and elbows in the exhaust system-especially a tiny unit like the 912. They create back pressure which is highly undesireable. The rule of thumb is that one 90 degree 3D (the bending radius is three times the pipe diameter) creates back pressure 16 times the equivalent length of straight pipe (I am speculating you have 4D bends). Try to keep total pipe lengths and the total deviation in degrees as identical as possible for the four pipes; if the difference is too big, you are building a variation in egt´s into the system.

A roller coaster unit like a running 912 in its mounts is really jumping about all over the place. Somewhere very close to the exhaust ports you need something that can take up this movement. You also need something that can take up thermal expansion/contraction. If not you will face cracked piping.

And:
I have been leafing through my construction drawings (issues 2003!). They include building instructions for the Aerovee-, Jab 22A-, and Jab 33A engine mounts, and are intended for use if the builder wants to weld up his own truss. They are all dead straight in all axis- no deviation whatsoever.

[Zack]

Here is my custom Rotax exhaust. The factory bed mount drove much of my design choices, I really like how you integrated the ring mount! I think that's how it should have been done from the start. I had to take a 4-2-1 approach. From Sonex's webinar, they chose a similar setup but used a Toucan exhaust without a final merge, so it's really two 2-1 exhausts with a center line exit.

Regarding my design, I used PipePRO software application to try and determine ideal collector length, but between the assumptions I needed to make for the application and the compromises I needed to make working around the mount, I'm not sure what advantages I will see. I tried to keep the collectors all equal lengths, I used stainless steel also, and I used inline motorcycle style mufflers. In fact, I hired the job to a motorcycle shop used to working with the smaller diameter pipes and fabricating custom exhausts.

What diameter collectors are you using? Will you step up diameter after the collector? Will you use an in-line muffler? I'm enjoying following your progress. Thanks Kai for contributing also.

[Zack]

Here is the bottom view.

[xeriotti]

Yup!

I´m with you as far as the messing up things goes- high five!

From my days as an engine application engineer some exhaust system guidelines emerge:

Engines hate bends and elbows in the exhaust system-especially a tiny unit like the 912. They create back pressure which is highly undesireable. The rule of thumb is that one 90 degree 3D (the bending radius is three times the pipe diameter) creates back pressure 16 times the equivalent length of straight pipe (I am speculating you have 4D bends). Try to keep total pipe lengths and the total deviation in degrees as identical as possible for the four pipes; if the difference is too big, you are building a variation in egt´s into the system.

A roller coaster unit like a running 912 in its mounts is really jumping about all over the place. Somewhere very close to the exhaust ports you need something that can take up this movement. You also need something that can take up thermal expansion/contraction. If not you will face cracked piping.

And:
I have been leafing through my construction drawings (issues 2003!). They include building instructions for the Aerovee, Jab 22A, and Jab 33A, and are intended for use if the builder wants to weld up his own truss. They are all dead straight in all axis- no deviation whatsoever.

I tried to keep the lenghts/volumes as similar as possible... I will measure the CCs of each header maybe tomorrow to know how much its off one from each other. But im pretty confident on how it came out. its pretty close measuring the lenght, maybe +-1cm
If we consider that almost 95% of cars use unequal lenght exhaust systems and almost all of them are just logs... This will be a great upgrade.

Here is my custom Rotax exhaust. The factory bed mount drove much of my design choices, I really like how you integrated the ring mount! I think that's how it should have been done from the start. I had to take a 4-2-1 approach. From Sonex's webinar, they chose a similar setup but used a Toucan exhaust without a final merge, so it's really two 2-1 exhausts with a center line exit.

Regarding my design, I used PipePRO software application to try and determine ideal collector length, but between the assumptions I needed to make for the application and the compromises I needed to make working around the mount, I'm not sure what advantages I will see. I tried to keep the collectors all equal lengths, I used stainless steel also, and I used inline motorcycle style mufflers. In fact, I hired the job to a motorcycle shop used to working with the smaller diameter pipes and fabricating custom exhausts.

What diameter collectors are you using? Will you step up diameter after the collector? Will you use an in-line muffler? I'm enjoying following your progress. Thanks Kai for contributing also.

That Zack looks great!!!... Im using 29.8mm internal diameter headers, and as a rule of thumb i should be stepping up 1.9 times that for the collector. and 0.5 times the diameter.

I will make it slip on with springs...if it sounds horrible i will set up some kind of silencer. But i have real good expectations for sound and power levels.

[xeriotti]

Its almost done!... Tomorrow ill take care of that 4 to 1 collector, it will be fixated with springs (already bought them :) )
And I think im going for a 1.5 times diameter and 0.5 times lenght tube after the collector. I will try to make it slip on with 3 springs so i can try fun stuff later. The plane has aerobatic capabilities so a smoke system will e installed as soon as we become friends.







My exhaust building frenzy ended at 2AM... My neighbors wife was trying to sleep and the angle grinder had other plans for her XD