Actual Flying Rotax Installs

[13brv3]

I won't be in the "actual flying" category for another couple months probably, but first run was yesterday and there were no surprises. There should be a big asterisk by the "first run", because this engine had 670 hours on it when I bought it a few years ago, and I had it on a previous plane that I hated, so we already have some history. I guess it's just first run on this plane. My first pitch guess was 13 degrees, and it hit 5540 rpm on full power static.

W&B came out great. 618 lbs minus wheel pants, and the CG is such that anyone from 100-300 lbs could fly it from full to empty fuel and stay in balance.

Rusty

[Skippydiesel]

I like it!

[CaseyCooper]

I have not been on this page in a while so I’m doing my best to catch up!

Kai,
I’m just not particularly fond of heel brakes. If I had a choice I’d either have a handle on the stick or toe brakes before I had heel brakes. The coordination between heel brakes and rudder pedals can be tricky and a pain (in my opinion). But like all things, with practice, comes proficiency. You might be able to design a great heel brake mod that works! But I just went with toes. On one of my other planes I made dual handles on the stick and they work awesome.

Zack,
I’m going to try and offer as much information to you as I can, which hopefully other people will learn from as well. As stated previously in the forum I finished my install last year almost 200 hours ago. I destroyed the original Sonex mounts in just hours. I then designed the new bed mount they’re using (the aluminum bracket system) to adapt to the chromoly structure to solve issues at that time. The problem I experienced am experiencing now is a motor mount flex or sag if you will in the chromoly structure. Really the proper mount to have is a ring mount. It would allow for better room for components, it would be lighter, and discourage certain characteristics of a bed mount. Plus a ring mount would allow for turbo charged models, like the 915, which requires the exhaust/turbo system to remain standardized so it would not work with the current bed mount.
With all that being said, my left side parallel bar that the aluminum mount bars attach to (your left side when sitting in the plane), has slightly sagged due to a lack of support. Only about a 1/16” but that translates to a bit at the propeller flange. In talking with Mark, I’m going to do a field upgrade to my motor mount to remove the sag, increase support strength, and hopefully solve the issue. Being that my plane is the only one flying with this mount system and the steady accumulation of hours, it has kind of been turned into a test monkey fortunately/unfortunately. So I will be doing some further modification and I will let everyone know how it goes. With your current set up, your propeller flange WILL NOT, and I’m not saying this to be a Debby downer, stay centered in your cowl and you will end up with an off center spinner. (Low and left if sitting in the plane) and it will look more pronounced with your set up. Your cowl setup is gorgeous. I just don’t want to see it potentially be damaged or have problems. My original cowl for my plane was made with the intention of seeing what worked and what doesn’t, and I’m now in the process of refining the cowling.
I work on Rotax’s everyday and have many hours behind and in front of them. My friend who overhauled my engine before I put it in is a performance Rotax builder, iRmt instructor, mans the Rotax booth at Airventure and one the go to (if not the go to) guys in the U.S.
We’ve talked a lot about Rotax “do’s and don’t s.” The 912uls/ul (carbureted) lends itself well to dual exhaust set ups, or 4 into 1 set ups. As long as you have proper tuning (as you’ve stated) you’ll be fine. You just don’t want any pulses canceling or a surplus of back pressure to keep the engine from breathing properly. After all, an engine is an air pump. It only pulls in as much air as it can push out, it is an exchange for energy. You ideally want a pulse to be accompanied by the next pulse at the proper rate to help cycle air through the engine properly.
However, on the 912is you absolutely have to use their stock exhaust (muffler). Being that it’s computer controlled the exhaust plays a big roll in its operating parameters (o2). So in modification to the exhaust system, it must be “tricked” into thinking its stock but just simply tuning it to stock parameters. Which you are attempting to do so kudos. The problem with your current setup is that the way to do that is to fit a muffler under the mounting truss but now you have radiators in the way. (Which I do also, my radiators are in the exact spot yours are). So that’s a factor to account for. I know at Sonex they’re mounting their radiators to the side allowing for the side ducts on the cowling to provide cooling, then using the under space for the exhaust. Your current exhaust work is a thing of beauty. The only thing I worry about is on hard starts or killing the engine, a Rotax bucks a bit because of its high compression and usually a large propeller up front. So I worry about your exhaust slapping the support it’s directed around. I’m not saying it will, but it’s possible.
Again, I offer my experience just as that. I have no intention of belittling anyones project. Yours definitely is being built with some care. Keep it up!

13brv3,
I’m eager to see you fly that thing! Looks awesome! You may want to dial your pitch in a little more. At WOT at straight and level flight you want to be as close to 5,600 rpm as you can. With your current pitch setting you’ll blow passed that, likely passed the max recommended. Static of 5,300 will get you right where you want to be and give you some more top end.

Someone also asked about the Rotax exhaust growl. My plane I intentionally made it LOUD. I wanted a hot rod and one that sounded like it. I get complements all the time on it’s noise. But in the cockpit it’s no louder than a 3300 or VW. But, you can sure make a 912 whisper which is wonderful in a completely separate way.
I’ll copy the link to an old video but at 11:38 in the video I do a low pass during testing and it gives a good indication of what it sounds like.
https://youtu.be/5lCcuGX2KLc

I’m going to try to keep up to date on my current cowling crusade. I’m switching from the dreaded vertical split cowl to horizontal split with a new look and new exhaust and radiator placement. As well as some aerodynamic devices to be added to the plane to clean it up a bit.

I’m so excited for all these builds! They’re all looking awesome. I can’t wait to sit back and see what comes out. I’ll be flying my plane to Airventure again next year, maybe we’ll get one or two more Rotax powered Sonex’s to show up

[13brv3]

13brv3,
I’m eager to see you fly that thing! Looks awesome! You may want to dial your pitch in a little more. At WOT at straight and level flight you want to be as close to 5,600 rpm as you can. With your current pitch setting you’ll blow passed that, likely passed the max recommended. Static of 5,300 will get you right where you want to be and give you some more top end.

Thanks for the comments. My target RPM is 5200-5300 for static, and 13 degrees was just a first guess. I haven't settled on a spinner yet, and there's plenty of prop fiddling to do. I do worry that at some higher pitch the blades will be partially stalled, so that would give a false high RPM static reading.

I definitely recommend the ring mount. They're expensive, and not without their own challenges for routing hoses, but it frees the most space possible for everything else you need.

I definitely share your approach to cowling. I'm hesitant to show pictures of mine now :-)

Rusty

[CaseyCooper]

Rusty,
I know how it goes! It’s all the little odds and ends that add up. I particularly like your exhaust. I’m building a brand new Kolb M3xtra for a customer to take to Mexico and fly off the beaches and I installed that exhaust on his engine. It’s convenient because you can rotate those mufflers around the cylinder heads to position them exactly where you want. Plus the exit tubes can be trimmed and manipulated. The guys who make those really did a nice job.
On my plane I have a 64” Warp tapered 3 blade and I’m running 17 degrees of pitch. I tried a 64” 2 blade square tip and had 20 degrees in it to try and load the engine properly and that goes outside the realm of acceptable for me and had exactly that, stalling blades. I have a 68” 2 blade I’m going to give a try but that means 3 point take offs and landings. I should theoretically have the space for it. Props are an interesting science.

[Skippydiesel]

Herraripower;

The engine "sagging" you referred to; are you using the first Sonex ( 2 piece parallel rails) Rotax adaptor or have you moved to the second (4 piece angle)?

[13brv3]

Herraripower,

The Toucan exhaust is certainly a convenient package. The guy who makes them now is not the original guy who came up with it. He bought the business some time back. People worry about the comments in the Rotax manual about not using dual mufflers, but the original Toucan exhaust was developed to satisfy all of the Rotax requirements at the time. It was designed for the 80 HP engine, so maybe all bets are off when you go over that.

As for props, I'm starting with a 60" 3 blade Warp Drive. This is for 80 HP with the lower numerical 2.27 ratio gearbox. I'm thinking you're running 100 HP from the diameters and pitches you mentioned. 60" gives me 5.5 " of clearance at level attitude, but with no pilot or fuel. I never wheel land, and I won't be starting now :-) Warp said we can go lower than 60" and stay with 3 blade, but we decided to carefully try the 60" with full square tips, then use the flight data to decide if they should be tapered, or if they can be shortened.

Everything is an experiment, and that's the part I like. I tend to get rid of planes after I get done tinkering, so it's best to build planes that will require long term tinkering :-)

Rusty

[CaseyCooper]

Skippy,
I’m not using the original attach bars. I only used them for about 10 hours before the failed. I designed the new mounts and have put almost 200 hours on them since. I’ve done pretty extensive measuring and found the flexing in the chromoly structure. So hopefully the field upgrade will prove fruitful. The Rotax is just a powerhouse of torque so it works on materials a little differently than the Jabirus and Aerovees like Sonex is used to.

Rusty,
Well one thing is for sure, it’s easier to say don’t do something and have people comply than it is to leave people the option to tinker and potentially cause issues. Kolb exclusively uses the toucan on all their 912uls installations and I’ve seen them on other planes. I’m sure they work just as great.
When I had my 912 gone through I actually had the 2.27:1 gears installed. I wanted a little more speed if I could get it. I know the uls comes with 2:43:1 but they do offer the option for 2.27:1. I actually know a few people who have changed from the 2.27:1 in the ul to a 2.43:1 with a slipper clutch and they love it.
But I wish you luck with your testing! I’m sure that Onex will be a ball of fun. Kelly at Warp is a great guy and he always goes the extra mile to take care of his customers.
I hear ya! Experimentals keep the mind working and ideas original. But sometimes that isn’t always a good/bad thing, but I always find they keep everybody learning.
How close are you to flying?

[13brv3]

How close are you to flying?

A year ago I would have told you "just a few months" :-) Winter will be my biggest delay now, since I hate trying to work in the cold. There really isn't that much left to be done though. I'll be shooting for the first warm days of early spring. I figure that gives the pilot a chance to not be cold, and gives the engine the best chance of not being hot.

Rusty

[Skippydiesel]

Herraripower

"Skippy,
I’m not using the original attach bars. I only used them for about 10 hours before the failed. I designed the new mounts and have put almost 200 hours on them since. I’ve done pretty extensive measuring and found the flexing in the chromoly structure. So hopefully the field upgrade will prove fruitful. The Rotax is just a powerhouse of torque so it works on materials a little differently than the Jabirus and Aerovees like Sonex is used to."

I hope I am in the final months of building - partial build aircraft came to me fitted with the original two piece Sonex / Rotax adapter.
Previous owner reluctant to action the Sonex offered swap to the newer design 4 piece design (no idea why).
I dont much like the look of rubber isolator's "in shear" - the new design where they are in compression, makes much mores sense.
I am about to start on the engine cowling installation, so will have to purchase the new design ASAP, so as to accommodate any small changes in engine & prop alignment .
Its a bit of concern that the Sonex chromoly engine frame is flexing - any changes since the new mounts were installed ?