Actual Flying Rotax Installs

[Kai]

Bett,

Hm- I have the same reflections.

The prop flange face of my R912/EP (without any spacer) is 35mm forward of the Jab 33 face with the shortest flange. Because of the lighter R912/EP compared to the Jab33, I did not dare move it further back. I am still a bit away from the session with scales and CG calculations, but I have an additional 10USG seat back fuel tank so my inital stomach feeling is presently calm.

An interesting aside turned up in the latest edition of Light Aviation, the publication of LAA: they were actually fight testing a Sonex Legacy with a Jab 33. In a few hours the test pilot found out the same as I with my 560 hrs in my Sonex (!). The LAA has a mandatory requirement to put 10 kilo’s of ballast in the luggage compartment should the single pilot weight in with less than 80 kg’s. As far as I can understand this means that they feel the plane is on the nose heavy side with the J33? Maybe this is why Sonex moves the Rotax backwards? I have never noticed anything of this nose heavy thing myself, however with my 5’9 I passed 80 kgs 25 years ago.......

For 25 years I have been chairing the Tech. Dept. of the SLA section in our national airsports federation. The carb and fuel pump issues with the R912 have aged me prematurely, so I went EFI.

Thanks
Kai
Sonex Legacy #0525, SG, DS
Formerly Jab 120HP
560 hrs

[CaseyCooper]

As far as CG calculations go, and feel of the aircraft in the real world instead of on paper, my Sonex is very well balanced. My cg calculations full forward, and aft, fall right in FAA standards, and within Sonex limits. Solo with full fuel I’m actually just aft of the forward limit by .20”. In flight when solo and full fuel I have to barely apply nose up trim to maintain straight and level flight. I weigh 180 lbs.
I know you might think, well how can that be? A lighter power plant all the way up there and still on the edge of the forward limit?
It really pretty simple. I’m running one of the heavier props you can get, and a three blade at that. As well as a 2” billet spacer. So it may be a lighter power plant, but my moment arm with a considerable amount of weight compared to a Sensenich like most people run on Aerovees and Jabirus, makes a difference. It’s an easy way to move your CG without just adding weight to the front. In the pre-flight stages I was actually considering using a 4 blade prop, with shorter blades, to move my cg even further forward. But with some calculations prior to choosing my propeller I found out that wouldn’t be necessary.
In my opinion spacers are nothing to be afraid of. People use them for good reason and they allow for assistance in these instances where we might need a little more clearance or help elsewhere.

Brett,
I wouldn’t worry about issues during spins or wing overs with your Rotax. As long as you are coordinated and keep positive G’s you won’t have an issue. It’s only a problem if you’re negative for more than a few seconds which is the same with most aircraft without an inverted fuel system. I’ve seen plenty of people do spins, I’ve seen 7 full rotations, and not have an issue. The 3300’s use just a larger version of the 912’s and they perform just fine as well. Although I do recommend operating with an electronic fuel pump as back up, or ON prior to any “aerobatic” maneuvers.

Rotax’s are pretty easy when you get down to the peas and carrots of them. The carbs are nothing to be afraid of, as long as you know how to properly tune them, or have someone who does, they’re wonderful. As most of us know, in the experimental category we can do whatever we want with our aircraft (almost) which means we can run stuff indefinitely if we so choose. But replacing the mechanical pump every 5 years per Rotax specifications will keep things happy.

[Kai]

Well,

As far as the Bings on the R912 go, Europe has been fighting the float issue for at least the last 7-8 years. I am out of count as to how many float SB’s Rotax have issued.

Part of the problem is undoubtedly the universal authority imposed bioethanol (10-15%) content in our 95 octane (RON) mogas. It dissolves the plastic in the floats and they loose buoyancy. The result is that the engines start running rich. Add to that carbs out of synch, props out of ballance, ignition issues, and leaking fuel pumps. It is not a very short list, and a considerable number of running engines shake like wet dogs: easily felt in the airframe.

The operation of a factory standard R912 over here require that you are very much on the ball when it comes to inspection and maintnance, with a much increased frequency.

Thanks
Kai

[CaseyCooper]

Kai,
Floats can definitely be an issue but not unmanageable. On each condition inspection you should be taking down the float bowls and inspecting at a minimum as it is. Allow the floats to dry, and weigh them to make sure they’re within spec and give them a shake by your ear and make sure you don’t hear any liquid inside. Also a misaligned float arm can cause issues, as well as old float needles not sealing from old age. Which most the time I’ve found it’s a misaligned float arm or needle causing the issue. I find most people tend to run their carb parts too long and don’t take them down and take the time to maintain them. One, because it’s not cheap to kit both carburetors, and two, people are afraid of them. Then put them back together and re sync them.
I find it VERY rare to find a prop imbalance, leaking fuel pump, or ignition issues. A lot of these come through our doors and it’s not a common issue. But one in a while, we’ll have an ignition issue with a module or stator. But like you say, you have ethanol fuels, and here in Arizona that’s all we can get also unfortunately. Which means more attention to the fuel system and rubbers that may come in contact with the fuel. But it’s a better evil than running avgas in my opinion. As long as you’re flying often, circulating the fuel, and not flying fuel more than a month old, it helps keep things conditioned. Fortunately, and unfortunately, we put on close to 2,000 hours just on our trainer in 3 years which means lots of maintenance, love and care.

[Kai]

So- all is well, then?

It has struck me that there always seems to be some genereic fault with our engines.

The R912 issues have already been mentioned. The Jab gen 1-3 brand has been fighting its top end issues since conception. We have had our fair share of broken cranks on VW type 1 aeroderivatives. And so further, and so forth.

Fairly new on the market is UL-Power; too new for anything to chrystalize. Let’s hope it fares better.

I have a 2007 year 100HP Yamaha 4-stroke outboard on my boat, close to 900 hours TT. It is run much like an aircraft engine: a fairly hard pull to get the boat up on plane (t/o and climb), and then a long stint with a little reduced rpm on cruise. So far I have replaced the oil each fall, the timing belt once, and the plugs twice. No one touches it during the winter months lay-up. First start up each spring is a non event, and it runs happily all summer.

Why can’t they engineer and build our engines to a standard like this??

Tailwinds
Kai

[Scott Todd]

I agree Kai. My dad ran a marina for 20 years in the 90's and 00's. I serviced lots of outboards that were totally abused and usually kept running. I was always impressed with them. I've been flying a Rotax 912 for the last 25 years. While its a nice engine, I think it has too many maintenance issues and the prices have gone crazy. Modern technology should be able to make an affordable engine that lasts 1000 hours with oil changes and basic maintenance. Oh wait, we already do for cars and boats, like yours. I know every few years someone comes out with a car engine conversion that is supposed to be the next best thing since sliced bead but I really have my eye on the Aeromomentum guys. They have run their engines for thousands of hours in air boat operations building data and confidence. As my Rotax nears overhaul time, I might seriously consider one.

[cj1711]

I have the sonex 912 engine mount also, the engine has just been fitted. After reading some of the posts about the rubber bushings I am concerned that they are not strong enough. I have chrome moly penny washers (home made) on the outside of the bushings and inserted a close fitting chrome moly bush an 1/8" narrower through the rubber bushings, so that there is some pressure on the rubber when the nut and bolt are tightened. Would like to know how long they are lasting in installations that are flying.

cj1711.

[CaseyCooper]

Cj,
As far as I know I’m the only one on this thread that’s flown them. Jake has done some ground testing. As mentioned earlier in the thread there has been a few issues with a both of us and a lot of discussion into it. I’ve been working with Mark at Sonex to find a solution and they’re working very diligently to solve the issues at hand.

[cj1711]

Herraripower
I like the the mounts you have made, I'm sure that would fix the issue because the engine is mounted in a bed, which is well supported by the Barry mounts. Are you not happy with mounts?

[CaseyCooper]

Cj,
I’m very happy with the mounts I made! More vibration isolation and more support. I’ve been flying them a few times a week since I made them with no issues. I think a mount system like that is the way to go in combination with the current Rotax mount from Sonex