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Rotax 915iS in RV9

mags591

Member
I know this was talked about a while ago, but I am wondering if there is anything more recent or if anyone has successfully made it happen?

Has anyone put a Rotax Engine (possibly the 915iS) in an RV9?

I have never used a Rotax engine but hear nothing but good things about them. Additionally, I love the idea of being able to use Mogas at several $$ less per gallon than 100LL. From what I have read, the 915iS is a powerful engine that could be a good power plant for the 9.

I am exploring options as I prepare my new RV9 build.

I appreciate all the comments.
 
I can run mogas in my 150HP O-320 no problem, and many others do as well. I'm sure the Rotax is a great engine but it's hard to beat the engine that the airframe was designed around. You may have issues with VNE as well with a turbocharged engine at altitude.

Chris
 
I can run mogas in my 150HP O-320 no problem, and many others do as well. I'm sure the Rotax is a great engine but it's hard to beat the engine that the airframe was designed around. You may have issues with VNE as well with a turbocharged engine at altitude.

Chris

That is awesome. I was not aware of this. I will have to do some more research. I am a newbie when in the aviation world.

Do you need any sort of aftermarket modifications to do this or is the engine capable of burning Mogas from the factory? What is your performance like with the mogas vs. 100LL in the O-320?
 
I'm running ethanol laced 91 in my IO-360, almost 800 hours in the last 5 years.
 
Are the fuel pump and fuel injector materials on the io- lycomings OK to use with ethanol laced fuel?
 
You will have no problems running mogas in the O-320/IO-320 Lycoming's as long as you have low compression pistons. I always kept a tank of 90 octane ethanol free "recreation gas" in my IO-540 powered RV-10 and never an issue. I'll be running it in my -9A also. I think the Rotax would be severely under-powering a -9.
 
Re: Mogas

The Rotax from what I’ve read will accept 91+ octane auto fuel. But to be clear Mogas is NOT your everyday automotive gas from your local gas station. It is Ethanol FREE. 87 octane is most readily available, the largest distributer here in Texas is Murphy Oil (Walmart). 91 + can be found near or at Marinas or Farm/Ranch stores.
Petersen Avation sell the Mogas STC for about $200 and Ethanol tester $15. EAA also offers?

On a new engine, after first 100 hrs of 100LL, we mix 87 Ethanol Free with 100 LL (80:20) on a C85. A Lycoming O320/150 will accept the 87+ per the STC.

Other than cost, you’ll realize reduced maintenance cost in spark plugs and dirty oil.

Hope this helps
Bill
A&P
 
Way too much for the RV9 airframe - and I'm a proponent of too much horsepower.
 
The new Rotax 918is at 231HP otta get the job done.

"Apparently word of the six-cylinder evolution of the long-running 912-series engines had not yet reached Austria in time for them to actually design and prototype one. We’ll get back to you when we know for sure."
 
I would jump on ordering a 9A if they factory supported the Rotax engine. Exceed VNE is not a problem. Like every other Green/Yellow/Red arc in a plane, limitations must be observed.

Plane going too fast? Pull power.
 
...currently busy with a 9 empennage and thinking about engine options (still plenty of time before I decide) and liking very much the 915.
Indeed if a FFW solution was offered I would go for it.
I understand this was evaluated but discarded because, in order to keep the CoG in the right range, the required FW elongation would be too much...
Maybe a combination of moving the engine FW and adding some mass in the engine area would work out (e.g. additional battery, a tool box? Oxygen system (maybe not a good idea close to the engine but not sure)? small luggage area?).
I am sure a solution that makes sense can be worked out by the smart engineering team at Vans...
Cheers
Diego
 
I think the 915 is a great engine. Rotax know this and are very proud of it; they want nearly $42k for it.
 
I think the Rotax would be severely under-powering a -9.

Have a look at a 4 seater Sling TSI with a Rotax 915iS at 141 HP... gross weight is greater than that of a RV-9A 2 seater @2094 #. https://en.wikipedia.org/wiki/Sling_Aircraft_Sling_TSi

So I guess I don't understand how it would be under powered, other than when you're maybe at or below 3000 to 4000 ft ft Density altitude? 3% loss per 1000 ft gain. .03 x 3000 = 0.09 or 9 % loss That's 136.5 HP available on a 320 150 hp engine at 3000 ft density altitude, while the 915 turbo will have the full 141 HP from sea level to well over 12 or 13000 ft of altitude.

Maybe my math needs to be corrected, but that does not sound underpowered, to me. Another aspect is the Rotax engine won't be burning oil at anywhere near the rate a taper bored O-320 will.

Another aspect is that Rotax motors, at least the 912 UL and 912 ULS NA motors, are known to go well, well past 2000 hrs on the motor, if properly serviced, by the books, with regular oil and filter changes on unleaded gas and fully synthetic motor oil. Need to add some weight to the nose? Get a constant speed prop for the 915iS
 
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Have a look at a 4 seater Sling TSI with a Rotax 915iS at 141 HP... gross weight is greater than that of a RV-9A 2 seater @2094 #. https://en.wikipedia.org/wiki/Sling_Aircraft_Sling_TSi

So I guess I don't understand how it would be under powered, other than when you're maybe at or below 3000 to 4000 ft ft Density altitude? 3% loss per 1000 ft gain. .03 x 3000 = 0.09 or 9 % loss That's 136.5 HP available on a 320 150 hp engine at 3000 ft density altitude, while the 915 turbo will have the full 141 HP from sea level to well over 12 or 13000 ft of altitude.

Maybe my math needs to be corrected, but that does not sound underpowered, to me. Another aspect is the Rotax engine won't be burning oil at anywhere near the rate a taper bored O-320 will.

Another aspect is that Rotax motors, at least the 912 UL and 912 ULS NA motors, are known to go well, well past 2000 hrs on the motor, if properly serviced, by the books, with regular oil and filter changes on unleaded gas and fully synthetic motor oil. Need to add some weight to the nose? Get a constant speed prop for the 915iS

I wish this forum softer had a “like button” I would pump it a few times for the above post.

Adding a constant speed prop and one or two batteries on the firewall along with slowly extending the engine mount forward would be interesting to look at. Since the overall package of the Rotax engines are smaller, there would be space on the firewall for a primary battery and a back up battery for the EFIS.

If we wind the clock back to the middle 90s the Rotax engines had a 600 hour TBO they are now at 2000 hours. Given the factory is finding no wear in the cylinders at 2000 hours, it won’t be long before TBO is lifted even further.

The fact the engine cost $10,000 more is almost no factor, given the overall acquisition cost of the aircraft and the greatly reduced operating cost over the arc of ownership.
 
The Rotax from what I’ve read will accept 91+ octane auto fuel. But to be clear Mogas is NOT your everyday automotive gas from your local gas station.

It depends on context and who you're talking to.. In the RV12, Rotax 912ULS world, Mogas is 91+ octane every day automotive gasoline, up to 10% ethanol, found at at any gas station and it burns just fine in a Rotax 912ULS..

Most, if not all of these "mogas" threads are talking about 91+ octane every day automotive gasoline with up to 10% ethanol. https://vansairforce.net/community/search.php?searchid=49661831
 
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"Apparently word of the six-cylinder evolution of the long-running 912-series engines had not yet reached Austria in time for them to actually design and prototype one. We’ll get back to you when we know for sure."

Mike Busch said in one of his EAA webinars Rotax had a 200hp engine, Lycoming bought the rights and buried it,
 
Rotax certified the 916iS last summer, 157hp for 5 mins then 134hp max continuous from sea level to 23,000ft. No fanfare... for a covert client.
 
The problem with the Rotax 915 from my perspective:
- weight and balance
- high cost
- could run mogas, but impractical due to on airport availability (or lack of)
- limited or expensive constant speed prop availability
- roll your own FWF package

If you can overcome these, or they are not an issue for you, then do it. Performance should be fine. My choice, though, is a Lycoming.

Tim
 
Need to add some weight to the nose? Get a constant speed prop for the 915iS

My understanding is that the 915is needs a constant-speed prop to operate properly. It has something to do with how the oil circulates through the crankshaft. At least that was what Rotax stipulated four years ago when the 915is was hitting the real production market. That was one of the "no go" items for USA-based by LSAs as constant speed props ae not allowed. Plus having one could easily have pushed the slicker LSAs past the maximum allowed. Perhaps there has been an accommodation like a crankshaft oil bypass valve for fixed-pitched propellers in the last 4 years.

Jim
 
That's an amazing development for the Cessna 150. A Rotax 915is with constant-speed prop STC. Add a tailwheel conversion to an early model and it would be a great bush plane.
 
The Rotax engines are a different breed. Might want to be sure you have a local “wrench” who is knowledgeable/experienced in their quirks.

Resale might be an issue, much smaller market for buying a used plane with what many consider, right or wrong, an oddball engine.

Carl
 
Rotax 915is upgrade for RV9 in the works

In a discussion with a reliable source at the end of Sun n Fun this past weekend I was told about an ongoing flight test program with a RV9 and a Rotax915is. The source said the upgraded RV9 can easily keep up with the RV fleet at 9k and above. The conversion package his company is working on will be complete with prop, cowling, and firewall forward and will be brought out soon when all the testing and details are complete.

On the other hand this might just be a Rotax POC working with Vans Aircraft developing the firewall forward design details for the RV15??

From my experience with the 915is I believe it's one, if not the most sophiscated reciprocating aircraft engine available today. It's fully computerized with redundant computer, fuel and ignition systems, turbo charged and inter cooled, gets full power to around 15k, computer will always work to get the most efficient fuel power combination with the single power lever. Burns mogas including ethanol mogas as well as avgas. And uses oil like a modern car engine does. Oil changes every 100 hours using unleaded fuel and 50 hours with leaded avgas. It's not cheap but it's operating costs will make it a good option for many folks.
 
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Updated 9 kit with final-size holes, more pre-fabed parts, updated plans, etc. and the option for a 915is? Sign me up.

That's the RV I'd build. Simplicity of the new kits with modern engine and kit would be amazing.
 
i think ''mogas'' is what is in the tank in the ground. it is 91 octane no lead for $3.99/gal at my airport now.
 
Has anyone reached out to the factory to see what modifications would need to be done to accommodate the different engine?
 
In a discussion with a reliable source at the end of Sun n Fun this past weekend I was told about an ongoing flight test program with a RV9 and a Rotax915is. The source said the upgraded RV9 can easily keep up with the RV fleet at 9k and above. The conversion package his company is working on will be complete with prop, cowling, and firewall forward and will be brought out soon when all the testing and details are complete.

On the other hand this might just be a Rotax POC working with Vans Aircraft developing the firewall forward design details for the RV15??

From my experience with the 915is I believe it's one, if not the most sophiscated reciprocating aircraft engine available today. It's fully computerized with redundant computer, fuel and ignition systems, turbo charged and inter cooled, gets full power to around 15k, computer will always work to get the most efficient fuel power combination with the single power lever. Burns mogas including ethanol mogas as well as avgas. And uses oil like a modern car engine does. Oil changes every 100 hours using unleaded fuel and 50 hours with leaded avgas. It's not cheap but it's operating costs will make it a good option for many folks.

Your source sounds very reliable indeed. Here's a flight out of Sebring with one of the Vans company RV-9s (N179RV) that is registered with a Rotax 915. There were a handful of flights the end of April. This particular flight went up to an altitude of 17k where it looks like the ground speed topped out at 190 kts!
 
Your source sounds very reliable indeed. Here's a flight out of Sebring with one of the Vans company RV-9s (N179RV) that is registered with a Rotax 915. There were a handful of flights the end of April. This particular flight went up to an altitude of 17k where it looks like the ground speed topped out at 190 kts!

Did you notice the 1,200-1,400fpm climb from 14k to 17k? WOW!

I hope they build a new cross-country airplane around that engine- the RV16 will be a great second plane for me to build. :)
 
That RV-9 might even be flying with the 161hp Rotax 916iS. Sebring would be a good place for development flying given Lockwood Aviation’s activities there

I heard the guys at Sling mention that the 916iS will be with GA consumers in the next 12 or so months. See this video from 44mins 40 onwards. https://youtu.be/lcFg7J5lIWw
 
If I were building a -9 now, I would install a 915 without hesitation. Slightly less HP down low, significantly more HP up high - and that's where the -9 shines in comparison to her short-winged brethren.

The ability to (mroe easily) run Mogas is a big plus, too. Yes, I know a lot of VAFer's run Mogas now - myself included - however, I've had several vapour lock issues depending on blend, the 915, or EFI on a Lycoming, would avoid those issues.
 
If Lockwood releases a FWF kit for this, I may just have a nice mid-time IO360 for sale. :cool:

That engine fits my mission profile perfectly.
 
That is awesome. I was not aware of this. I will have to do some more research. I am a newbie when in the aviation world.

Do you need any sort of aftermarket modifications to do this or is the engine capable of burning Mogas from the factory? What is your performance like with the mogas vs. 100LL in the O-320?

The biggest threat in your area will be vapor lock on a warm spring day. You may encounter winter-blend gas which vaporizes easier at lower temperatures. This may be mitigated several ways, but the easiest is to run on tank with 100LL (or 50/50) and takeoff and land on that tank.
 
Testing has shown that as little as 10% 100LL in a tank of mogas can significantly drop the vapor pressure and (help) prevent vapor lock. You get most of the benefit of reduced vapor pressure by the 25% mixture point.
 
Sure is fast

Impressive climb rates and speeds. Without knowing winds aloft I can only speculate speed is exceeding normal vne for rv9. Possible airframe or control surface construction mods? This is quite interesting to follow as I am still constructing fuselage and haven't ordered engine. Maybe we will see something at Oshkosh.
 

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Impressive climb rates and speeds. Without knowing winds aloft I can only speculate speed is exceeding normal vne for rv9.

Vne on the 9/9A is 210mph or 182knots, true air speed. The highest ground speed shown on the ADSB data was 198 knots at 15000', so only a 16 knot tailwind is required for that to be consistent with Vne.
 
I asked the guys at Vans about this at Sun n Fun and they would not admit to having an aircraft with a Rotax. They did say that they knew about a project with a 9A with a 915IS and that they were having yaw divergence issues. essentially when they put it into a full slip they did not have enough rudder authority to straighten back out due to the extended nose acting like a rudder and had to roll the aircraft to a high bank angle to get it back straight. They were having to modify the rudder to get controllability. I was asking because I was considering the new 916 for my 9A build but then i saw the 49,999 price tag for the 916 and no one with FWF support and changed my mind.
 
I asked the guys at Vans about this at Sun n Fun and they would not admit to having an aircraft with a Rotax. They did say that they knew about a project with a 9A with a 915IS and that they were having yaw divergence issues. essentially when they put it into a full slip they did not have enough rudder authority to straighten back out due to the extended nose acting like a rudder and had to roll the aircraft to a high bank angle to get it back straight. They were having to modify the rudder to get controllability. I was asking because I was considering the new 916 for my 9A build but then i saw the 49,999 price tag for the 916 and no one with FWF support and changed my mind.

Interesting. Not enough weight up front, opposite of the problem I was fighting with my 360 install. How does the 915is weight compare to the original Vans-designed O-235?
 
..........How does the 915is weight compare to the original Vans-designed O-235?

You can go to the Rotax configurator to get a good idea. I got 206 lbs with all engine accessories except prop governor, coolant radiator, coolant, and oil cooler. Put a heavy Hartzell on the front and you're not that far off of a parallel-valve Lyc installation.

Screenshot 2023-06-09 090815.jpg
 
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