RV-9 with Rotax 915

Adam Weiss

Adam Weiss

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I’ve always thought this would be THE killer combination.
135hp up to 15,000 ft.
Cruising WOT (almost) at 6,000, I only get 75%, or 120 hp.
I often cruise higher and only get 60-65% (96-104hp).

I already plan 155KTAS at 8gph, and with tip tanks, I have 46.5 gal useable.
Seems like that extra HP and 100lbs lighter would yield a serious beast of an XC machine!

Others have commented how W&B would be an issue, and I agree.
But now it looks like Vans might actually be testing this out!
Looks like an RV-9 with a 915 registered to Vans Aircraft flew in March of this year.

https://flightaware.com/live/flight/N179RV

Love to hear everyone’s thoughts.
 
It is all about tradeoffs, right? With the 915 you would give up initial acceleration and climb performance and low(er) altitude performance and begin to gain performance above ~8,000'. You would probably burn less fuel - about 10% less at equivalent altitudes and airspeeds.

Then, there's the cost. The price difference between the 915 and an O-320 the engines is pushing $10K, and I dunno about all of the other stuff - prop, etc. Every mechanic in North America can work on your O-320, not so with the -915.

Choose the engine for the mission you wanna fly and be happy...
 
I saw a pic on one, they get around the ballance issue with a motor mount that is a over a foot longer and matching long cowl
 
The 915 is technically 145hp to 15,000ft and can produce just about 130hp to FL290. It’s an amazing engine and would a great replacement for an O-320. Apparently a Lycoming engineer said the 915 is more comparable in power to an O-320. The 916 will be even better. Here’s a screenshot of the VL3 with a 915 and hydraulic constant speed prop.
 

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kyleb said:
It is all about tradeoffs, right? With the 915 you would give up initial acceleration and climb performance and low(er) altitude performance and begin to gain performance above ~8,000'. You would probably burn less fuel - about 10% less at equivalent altitudes and airspeeds.

Then, there's the cost. The price difference between the 915 and an O-320 the engines is pushing $10K, and I dunno about all of the other stuff - prop, etc. Every mechanic in North America can work on your O-320, not so with the -915.

Choose the engine for the mission you wanna fly and be happy...
Click to expand...

Well, as in my original post, with my O-320 I'm only getting 75% (120hp) power at 6,000ft, and at 1200-1500fpm climb, I'm there in 4-5 min.
I rarely fly lower, unless it's just to fart around the area or grab a nearby $100 burger.
The 141hp of the 915 at takeoff is 88% of an O-320, so I assume, I'd be at 6,000ft in roughly the same time.
Performance-wise, I only see upside.
It's a fair point about the cost and maintenance though.
 
The 915 iS dyno’s at 145/146hp with 45” and 5800 RPM. They are just very conservatively listing it at 141hp. That would put it on equal ground (assuming 3.5% per 1,000ft) with an O-320 at 2,500ft MSL and at an installed weight of around 200 pounds.

The 916 will be 165hp at 50” of manifold and weigh the exact same.
 
Andrew Morris said:
The 915 iS dyno’s at 145/146hp with 45” and 5800 RPM. They are just very conservatively listing it at 141hp. That would put it on equal ground (assuming 3.5% per 1,000ft) with an O-320 at 2,500ft MSL and at an installed weight of around 200 pounds.

The 916 will be 165hp at 50” of manifold and weigh the exact same.
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Actual MSL at my home field is 1000ft, and density altitude at my field is around 2000ft a good portion of the year.
Seems like I'd be starting off on equal ground, and only getting better.

A real concern though...at lower altitudes, like 6000ft, I see IAS of 143kts in cruise.
At 8000, it's more like 135.
With Vno at 157kts, I suspect I'd be pushing right up against that very easily, and for sure slipping right by it in descent.
I'd probably have to keep an eye on Vne in descent as well.
With the 916, I think it'd fall into the IO-360 kind of power, which Vans does not recommend for a 9A due to the reasons above.

Very, very interesting options for experimental!
 
Adam Weiss said:
Well, as in my original post, with my O-320 I'm only getting 75% (120hp) power at 6,000ft.
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The engine is capable of 75% power to about 8,000’. If you don’t choose to use all of it or the airplane is configured where you can’t use all of the engine’s available power, that isn’t an engine issue.
 
kyleb said:
The engine is capable of 75% power to about 8,000’. If you don’t choose to use all of it or the airplane is configured where you can’t use all of the engine’s available power, that isn’t an engine issue.
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There must be something else going on then.
I have an EDM-900 reading manifold pressure, and (almost) WOT, rich of peak at 6000ft I see 75%.
At 8000ft, I'm fully WOT, and I never see anywhere near 75%.
 
Several possibilities.

Compare the % power from the EIS to lycoming’s power charts. For the same conditions do they agree?

Are you achieving rated RPM (probably 2700)? If not, you won’t be able to maintain 75% as high.

Is the engine leaned for full power at that altitude?

Etc.
 
Adding any of the larger turbo Rotax engines to the RV-9A would be an exciting development. Fantastic engine. Would be nice to fly behind something invented in the modern era.

One could view the RV-9A with turbo Rotax as the LSA everyone wants but regs won’t allow.

(Next post is a guy saying the RV-9 is not an LSA)
 
steingar said:
I really don't understand this discussion at all. An RV9 is an experimental airplane. You can put whatever engine in it you want.
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It's all about whether the ROTAX be a better option than the Lycoming based upon price vs performance (and the fact you'd have to roll your own FWF package). IOW its not about "can you" (we all get that you can), it's about whether the juice is worth the squeeze.
 
There's a thread on Vansairforce, in which somebody claims that Van's tried this combination but abandoned it as they had to move the engine so far forward, to stay within CG limits, that they deemed it impractical. Supposedly the program has then been abandoned.

Now, while there is probably truth to this, I would still take it with a grain of salt: Van's is (very) fat and happy and they haven't launched anything new in years. I would therefore be very surprised if they would pursue the integration of a new engine type, for an airframe that isn't their hottest seller anyway, if any amount of development is needed to make it work.

The other thing is that probably relatively few customers would even opt for this engine, since it is around $10k more than an O-320 and mandates a CS prop.

Personally, I would love this combination, but I'm into travelling. The vast majority of RVs (with the exception of the 10) is only flown locally - no need to spend the extra money for an engine that primarily shines up high.
 
Supposedly, the RV9 was designed around the O-235, which I understand is around 245 lbs dry. The 915 is about 60 lbs less. However, the 915 requires a (heavy) constant speed prop. The 3-blade airmaster is 26.6 lbs, while a fixed pitch Catto prop is only about half of that.

I would therefore think that the 915 would indeed have to be installed further forward than an O-235 or O-320 but probably not by a crazy amount.
 
German guy said:
There's a thread on Vansairforce, in which somebody claims that Van's tried this combination but abandoned it as they had to move the engine so far forward, to stay within CG limits, that they deemed it impractical. Supposedly the program has then been abandoned.

Now, while there is probably truth to this, I would still take it with a grain of salt: Van's is (very) fat and happy and they haven't launched anything new in years. I would therefore be very surprised if they would pursue the integration of a new engine type, for an airframe that isn't their hottest seller anyway, if any amount of development is needed to make it work.

The other thing is that probably relatively few customers would even opt for this engine, since it is around $10k more than an O-320 and mandates a CS prop.

Personally, I would love this combination, but I'm into travelling. The vast majority of RVs (with the exception of the 10) is only flown locally - no need to spend the extra money for an engine that primarily shines up high.
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I'm in the same boat.
I primarily fly long XC and lots of IFR.
I'd love this combo.

German guy said:
Supposedly, the RV9 was designed around the O-235, which I understand is around 245 lbs dry. The 915 is about 60 lbs less. However, the 915 requires a (heavy) constant speed prop. The 3-blade airmaster is 26.6 lbs, while a fixed pitch Catto prop is only about half of that.

I would therefore think that the 915 would indeed have to be installed further forward than an O-235 or O-320 but probably not by a crazy amount.
Click to expand...
When you use the real numbers, it sure seems like this is solvable and viable configuration!
 
German guy said:
Supposedly, the RV9 was designed around the O-235, which I understand is around 245 lbs dry. The 915 is about 60 lbs less. However, the 915 requires a (heavy) constant speed prop. The 3-blade airmaster is 26.6 lbs, while a fixed pitch Catto prop is only about half of that.

I would therefore think that the 915 would indeed have to be installed further forward than an O-235 or O-320 but probably not by a crazy amount.
Click to expand...
From what I have read you can put a fixed pitch prop on 915 just fine...
https://www.rotax-owner.com/en/915i.../7372-rotax-915-fixed-pitch-propeller-variant
 
The Rotax is better in nearly every parameter over an O-320. Designed from scratch to burn auto gas, rather than just compatible with unleaded gas. Water cooled cylinders, 5000 RPM cruise with prop driven off cam (which turns half speed) instead of the crank. If memory serves the prop is clutch based alleviating prop strike inspections.

Also has a FEDEC and lower fuel burn. It would make the RV-9A an amazing plane, assuming CG issue is workable.
 
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German guy said:
Now, while there is probably truth to this, I would still take it with a grain of salt: Van's is (very) fat and happy and they haven't launched anything new in years. I would therefore be very surprised if they would pursue the integration of a new engine type, for an airframe that isn't their hottest seller anyway, if any amount of development is needed to make it work.
Click to expand...

You're way off base.

Vans' just worked with Lycoming to develop/integrate a new version of the IO-390 engine into the RV-14. Better all around than the original -390 and they redesigned the induction system, cowl, and exhaust for the installation, plus incorporated a fuel injection system normally used on the IO-540. In addition, they rolled out the RV-12A in the last year or so, with numerous significant upgrades to the aircraft.
 
kyleb said:
You're way off base.

Vans' just worked with Lycoming to develop/integrate a new version of the IO-390 engine into the RV-14. Better all around than the original -390 and they redesigned the induction system, cowl, and exhaust for the installation, plus incorporated a fuel injection system normally used on the IO-540. In addition, they rolled out the RV-12A in the last year or so, with numerous significant upgrades to the aircraft.
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I would consider this mere product improvements. I certainly applaud them for their thorough approach to engineering, but they show little motivation to expand their customer base.

I'm still puzzled that a relatively new company like Sling can launch a well engineered, pulled rivet, relatively fast, 915 powered, 4-seat high wing aircraft, only a bit over two years after they launched their low wing Sling TSI in 2018.
I also predict that the Sling High Wing will sell like hot cakes, as it checks pretty much the same boxes as the most popular aircraft of all times, a Cessna 172, but is faster, consumes less gas and can be build in somebody’s garage.

The last truly new aircraft from Van’s, on the other hand, was the RV14, which has been introduced in 2012!

I certainly don’t want to bash them and actually like their planes, but think that it is quite obvious that they have lost the hunger for growth and just want to stay fat and happily where they are right now.
 
German guy said:
I would consider this mere product improvements
Click to expand...

You're bitching about Van's not offering new engines and I just showed you one. But you won't count that one.

OK.

As far as hunger for growth goes, they are backlogged to hell and back. They need to focus on getting out their current kits and support their current customers before they add to the product line. They are offering 6 prepunched kits these days and two non-prepunched. 8 kits. And they continue to support the RV-6, the most popular kit built airplane ever.

That's a lot of inventory to manage with all of the different parts...
 
kyleb said:
You're bitching about Van's not offering new engines and I just showed you one.
Click to expand...

I wasn't bitching about anything.
I simply stated that I see little motivation at Van's to introduce an entirely new engine for an airframe that already has several engine options that are working perfectly fine. I also stated that most RV9 buyers would probably go with the less expensive O-320 over the 915 anyways.

And no, I am not considering the introduction of the 912iS as an alternative to the 912ULS for the RV12 or the support of an updated IO-390 as even remotely comparable to the introduction of an entirely new engine, like the 915, for the RV9.

kyleb said:
[..]. As far as hunger for growth goes, they are backlogged to hell and back. They need to focus on getting out their current kits and support their current customers before they add to the product line. [...]
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Exactly. Glad to that we can at least agree that they are (very) fat and happy.
 
German guy said:
Exactly. Glad to that we can at least agree that they are (very) fat and happy.
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From their communications with the builder community, they are working their assets off to catch-up on their backlog and are rolling out a new web store to replace the rather mediocre one that has served them well for a decade or more. Seems to me they are anything but fat and happy.

And I think both the RV-12A update, which includes an entirely new fuselage, and the FWF updates to the RV-14 were pretty big development efforts.
 
kyleb said:
From their communications with the builder community, they are working their assets off to catch-up on their backlog and are rolling out a new web store to replace the rather mediocre one that has served them well for a decade or more. Seems to me they are anything but fat and happy.

And I think both the RV-12A update, which includes an entirely new fuselage, and the FWF updates to the RV-14 were pretty big development efforts.
Click to expand...

Did I say anything contrary to that? Not sure why you are reacting so triggered.


German guy said:
[...] Now, while there is probably truth to this, I would still take it with a grain of salt: Van's is (very) fat and happy and they haven't launched anything new in years. I would therefore be very surprised if they would pursue the integration of a new engine type, for an airframe that isn't their hottest seller anyway, if any amount of development is needed to make it work. [...]
Click to expand...

Unless someone is a die-hard Van's fanboy, I don't see why anybody could feel offended by this statement. You actually seem to agree that they can't / don't want to pursue anything fundamentally new at this time.

This discussion is about whether the 915 would be a good fit for the RV9, not whether your beloved Van's is providing good kits, customer service or if they are long-term on the right track with their product strategy.

I was making the point that even though Van's abandoned this project, this doesn't necessarily mean that it would not have been feasible.
Actually, that they even tried is IMHO proof that the 915 could be an excellent choice for the RV9. If anybody knows what the installation of a 915 on the RV9 would mean in terms of performance and w&b, before actually installing it on the airframe, it would be Van's.
So, why would they even have built a prototype in the first place if they wouldn't have figured that this makes sense?
 
German guy said:
Did I say anything contrary to that? Not sure why you are reacting so triggered.

Unless someone is a die-hard Van's fanboy...
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Responding to facts with petty responses makes it clear that you are more interested in being a jackass than actually having an adult conversation on the subject. AMF.
 
German guy said:
I certainly don’t want to bash them and actually like their planes, but think that it is quite obvious that they have lost the hunger for growth and just want to stay fat and happily where they are right now.
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Hard for Van's Aircraft to lose something they never had. Van does what he's into, and if you like it that's great. One of the things they have always wanted is to be lean.
 
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Can't quite imagine what new thing they'd do. They made a tandem and side by side airplanes, then remade them. Then they made a tame side by side, this a four place. Then turned the four place into a really big two place. Then made an LSA. I suppose they could still make an ultralight, or maybe a glider or something.
 
We regularly travel in our -9A and usually stay between 9-12k. LOP we are around 62-64% at 6.7 gph, 147 kts TAS. The 915 would be a tempting replacement to my IO-320 given where we fly but I'm no engineer, someone waaaaay smarter than I would have to do the "cipherin'".
 
They have announced the RV15. It will be a high wing, back country aircraft.
 
Rotax for the win. A modern contemporary single lever fadec engine. No ridiculous mixture finagling and Rube Goldberg 1940s tinkering

I doubt anyone's legacy engine actually gives the advertised 100% power during typical takeoffs after all the considerations for temperature density altitude and a who's who grab bag of mixture settings, mag timing, and leaning techniques
 
Yea I really like what Rotax has been doing. You can run ethanol car gas, newer model ones have proven stellar reliability, super light weight and compact. I would skip the carbureted models as they are finiky but the iS and newer are real gems. I especially like the new 915 turbo. Maybe they will up the displacement or boost to get that magic 150hp number at sea level that I suspect is hurting the sales even though in real life it's likely producing more power on a summer day than an O-320.
 
Grum.Man said:
Yea I really like what Rotax has been doing. You can run ethanol car gas, newer model ones have proven stellar reliability, super light weight and compact. I would skip the carbureted models as they are finiky but the iS and newer are real gems. I especially like the new 915 turbo. Maybe they will up the displacement or boost to get that magic 150hp number at sea level that I suspect is hurting the sales even though in real life it's likely producing more power on a summer day than an O-320.
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Agree! Look at the performance of the Sling TSI. It does better on 140HP than any airframe with 1000lb useful has a right to.
 
..and you can run it at 95% all day long. That's much better than the 55% or whatever most people are getting..
 
NordicDave said:
The Rotax is better in nearly every parameter over an O-320. Designed from scratch to burn Av gas, rather then just compatible with avgas. Water cooled cylinders, 5000 RPM cruise with prop driven off cam (which turns half speed) instead of the crank. If memory serves the prop is clutch based alleviating prop strike inspections.
Click to expand...

I had no idea the rotax motor ran the prop off of the cam. That's... pretty darn clever. So is the cam beefy with large bearings on a rotax?
 
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