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prkaye

Well Known Member
The Rotax 914 UL DCDI 115HP is an engine that can run on MOGAS. It actually looks to be more expensive than the O-235, although apparently Lycoming's prices go up next month.

A few questions:

1) Would 115hp be enough for an RV-9A? It looks like the smallest Vans recommends is 118hp...

2) I've heard the problem with Rotax engines is they're too light (the 914 is 166.4 lbs installed). Couldn't this be overcome just by adding some dead weights in front of the firewall?

3) Anyone know of an RV-9 or -9A installation that has gone this route? I guess if you want lower Octane, the O-290 would be a better option?
 
Avoid the Rotax 914

prkaye said:
The Rotax 914 UL DCDI 115HP is an engine that can run on MOGAS. It actually looks to be more expensive than the O-235, although apparently Lycoming's prices go up next month.
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I would avoid the 914. It is a turbocharged 912S, and the engine is already high strung without the turbo. On the plus side, if you do decide to go with it, the 914 will provide plenty of power at altitude due to the blower.

I'd suggest Lyc O-235, TCM IO-240B or Lyc / ECI / Superior O-320 as better options. There is a large critical mass of RV-9 O-320 installations. The O-235 and IO-240B are good choices for economy, but will hamper you in the mountains - just not enough power for good climb and altitude performance. IMHO.
 
My hesitation about the models you listed (the standard models listed on Van's forms) is that they all have an octane requirement of 100LL. I would much prefer an engine with a lower octane requirement, since I'm paranoid about rising fuel costs (which has been discussed at length in other threads).

Lycoming does provide a couple of options: there is a 150hp O-320, and the O-290... these have an Octane rating of 80. I'm guessing that if I went with one of these options most of what comes in Vans standard finishing kit would be compatible, and I wouldn't have to do any really serious modification or retro-fitting. If I went with the Rotax engine I probably would have to do some serious custom firewall forward work.

Problem is I don't thank Vans has OEM pricing on these Lycoming models, so I may have to try to hunt one down on the used market.
 
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Go for a clone

No reason to buy a Lycoming (unless you like spending money for no reason that is). Superior, Mattituck and Aerosport sell exactly the same thing for less cost.

All of these motors will run on premium mogas as long as the compression ratio is not hopped up beyond the standard 8.5:1 and you keep away from the dreaded "detonation zone"...This means having a full understanding of how the mixture control works.

It is better to go for a fuel injected motor because this gives you much better mixture control which is even more desirable if you intend to burn mogas...I know I certainly do!

Frank
TMX IO360..Still not sure how to find peak EGT without going thru the "detonation zone"...But not necessary for break in anyway.
 
What do you mean that it is high strung? Have you seen any documentation about unreliability on this engine?

the_other_dougreeves said:
I would avoid the 914. It is a turbocharged 912S, and the engine is already high strung without the turbo. On the plus side, if you do decide to go with it, the 914 will provide plenty of power at altitude due to the blower.

I'd suggest Lyc O-235, TCM IO-240B or Lyc / ECI / Superior O-320 as better options. There is a large critical mass of RV-9 O-320 installations. The O-235 and IO-240B are good choices for economy, but will hamper you in the mountains - just not enough power for good climb and altitude performance. IMHO.
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The rotax 914 is an extremely reliable engine. Yes it operates at a high rpm, but thats what it is designed for. The 912S and 914 engines are as bulletproof as the lycomings. Dont mistake these for the smaller 2 stroke engines that are prone to sudden stopage. The 912S is even a certified engine. I think some versions of the 914 are as well. As to whether it should go in a -9 or not, its up to you and you only.
 
Want a smooth running, extremely reliable engine that costs less than 1/4 the Rotax or Lyc's initial cost, runs on reguar (89) mogas, 200Hp@200 lbs? ;)

answer: Mazda Rotary :D

Just bought new Renesis motor for $2K+ 300 shipping. redrive ~$3K...
 
prkaye said:
3) Anyone know of an RV-9 or -9A installation that has gone this route? I guess if you want lower Octane, the O-290 would be a better option?
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Phil,

There is a guy in this area with a 108 hp O-235 in his -9A and he is VERY happy with it. Flight plans for a 150 mph at almost no fuel burn.

I'm in the process of installing an O-290-D2 (135 hp / 140 hp for takeoff) in my -9 and am currently working with Van's to identify the differences in this engine installation. They might offer a FwF kit in the future. So far, I have run into nothing of significance and the install is looking good. (I'm documenting the install on my web site.)

My only issue with the Rotax engine is the W&B thing. I would extend the engine mount before I added weight, it might look funny but it will give you another option in terms of baggage storage.

Good luck with whatever you do.
 
Mike, do you have a build site? I'm interested in finding out more about this Mazda engine installation... did you have to make your own cowling? What other non-standard things did you have to make yourself?
 
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Prkaye,

Here are a few excellent sites:
http://www.flyrotary.com/
http://www.rotaryaviation.com/
http://www.rotaryeng.net/
http://www3.telus.net/haywire/RV-9/C-FSTB.htm
http://members.aon.at/wrathall/rotary/

One interesting thing about rotary use, is that data is widely available if you know where to look- you can buy most of the needed parts over-the-counter or construct your own from plans and existing project ideas.

You will need to construct/modify a motor mount from several existing designs, build cooling ducting around an automotive radiator, build or modify factory intake and exhaust manifolds (OEM is too bulky and heavy). Excellent aircraft FI/ ignition systems and redrives are available over the counter.

The Wankel is quite small, therefore the Vans cowl works fine with lots of room under the hood, or you can look at several tighter alternatives, like the Sam James cowl which is popular.

I picked the Mazda mostly because I feel it is a superior aircraft motor with a very high level of design reliability and simplicity, and because it is not air cooled. It has high power output and light weight. It is designed for high speed operation w/low internal stresses (similair characteristics to a turbine). You do need to be careful with heat removal and noise reduction. FWIW, The rap about excessive fuel use is grossly overstated by uninformed critics, and you CAN use the cheap/light IVO adjustable prop with a smooth-running Wankel.
 
Thanks for that information Mike! I'm going to do some reading... this option intrigues me. I'll be interesting in hearing how yours works out when you start flight-testing.
Question - can you run 100LL safely in that engine, or does it have to be unleaded car gas?
 
100LL will eventually "lead" up sparkplugs, otherwise it runs fine in a rotary. Most rotary guys carry a can of lead scavanger if they burn 100LL a lot, or at least have a set of replacement plugs handy. FWIW, Ive always understood that any engine runs best on the most volatile (lowest octante grade) fuel it can handle without detonation.

I was an environmental engineer in my former life- my bet is that 100LL will be outlawed within the next few years for the same reason that leaded fuel was outlawed- tetraethyl lead is extremely toxic. The majors will eventually come up with a high octane fuel substitute, but it will be more expensive than the 100LL we have today- probably some exotic aeromatic or alcohol fuel blend.
That approach pretty much ignores problems with lubricating hot exhaust valves, a job that lead does quite well. We will probably need some other additive to handle that task (no exhaust valves in a rotary- and rotaries are very detonation tolerent under normal circumstances).

A combination of high fuel and pollution control economics will force the eventual changeover to more modern design clean-burning engines. I wouldn't be too surprised to see a 5-10 year phase-out of all new high-compression piston GA engines either. Our lawnmowers and motorcycles/ATV's are already on the chopping block.
 
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I am putting the turbo Rotax 914 in My plane. Oh, by the way, I 'm building the Titan T-51 Mustang,and not a Vans. (DUCKING)
 
Rotax, geared, water cooled, turboed

prkaye said:
The Rotax 914 UL DCDI 115HP is an engine that can run on MOGAS. It actually looks to be more expensive than the O-235, although apparently Lycoming's prices go up next month.
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I am not sure what you mean looks more expensive. I think it is more expensive at $24K or $30k (us). The expensive one is constant speed.

High strung?

Well the Rotax is turbo'ed, which is more mechanically.

The Rotax is geared and turns high RPMs to make power. Where the Lyc is a big bore (relatively speaking) direct drive air cooled engine. :) simple.

The Rotax is water cooled. Where are you going to put the radiator? More weight, complexity.

The Rotax is less than 73 cubic inch displacement! :eek: The Lyc is 235 cubic engine. Which one do you think is working harder to make 115 or 118 hp respectfully?

Where do you get a Rotax worked on? Lycoming any where any time, probably locally.

I can see where people would say the Rotax is high strung, they sound that way, like they are screaming. Leave the Rotax for the ultalights and LSA's. The RV-9(A) is a real plane. (I AM KIDDING, JOKE :D ).


However I got to be honest, I am not sure why people resist the obvious choice, the Lyc. At $22.5k BRAND new. It's a bargain in my opinion.

Too bad Van does not have a mount for a TCM IO-240, listed at $19.5k at Mattituck. I like Lyc's better, than Continentals, but the little TCM O-200 was a nice little engine, which the IO-240 is based. I believe aircraft makers like Diamond are going away from Rotax, in favor of the TCM IO-240.

Personally I don't think the Rotax makes the power they say they do, but that could be an ugly rumor. However at less than 73 cu-in, there is not much engine there. What did we say in hot rodding, there ain't no substitute for displacement.


What I would do (and did with my O-360)

There are so many O-235's in Yankees, C152's, Tomahawks, I am sure used cores are not impossible to find. Some elbow grease, a little wrenching, shipping parts to a overhaul/repair station, some new parts, more wrenching and elbow grease, you can come up with an overhauled O-235 cheaper than $22.5k. If you can't find and rebuild a O-235 for less than $15k, you are not trying.
 
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gmcjetpilot said:
Where do you get a Rotax worked on? Lycoming any where any time, probably locally.
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This is an excellent point. Rotax service is few and far between right now. If Cessna produces its LSA with the 912S, that will all change.
gmcjetpilot said:
Too bad Van does not have a mount for a TCM IO-240, listed at $19.5k at Mattituck. I like Lyc's better, than Continentals, but the little TCM O-200 was a nice little engine, which the IO-240 is based. I believe aircraft makers like Diamond are going away from Rotax, in favor of the TCM IO-240.
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I agree - the IO-240B seems to be a great choice for the RV-9. Light, compact, economical, good track record. Too bad it's barely cheaper than a Superior XP-320, which IMHO is another great choice, perhaps the best due to Van's support.

I think the biggest issue with Diamond getting rid of Rotax has to do with perception and not performance. As you said, leave Rotax for the LSAs, etc. The Katana DA-20s that have been upgraded from 80 Hp 912 to the 912S 100 Hp Rotax are supposedly very good performers, given that they have CS props and are lighter than the IO-240 versions.
 
my FBO is at 5400 Alt., and I frequently go over 14,000 mountains, and my Titan T-51 Mustang empty will be under 900 lbs., so the Turbo Rotax will be a great set up with the constant speed prop...
 
prporter said:
my FBO is at 5400 Alt., and I frequently go over 14,000 mountains, and my Titan T-51 Mustang empty will be under 900 lbs., so the Turbo Rotax will be a great set up with the constant speed prop...
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I'd agree that the 914 is a good match for mountain flying due to the turbo. However, be darn sure that you get enough cooling (thin mountain air), use the Evans NPG+ coolant, and if there's any way to back off on the boost, great.

I don't know about how well it works in practice, but I've always liked the idea of a turbonormalized or low-boost engine - you're never straining the engine itself that hard, just the turbo at higher altitudes.
 
prporter said:
I am putting the turbo Rotax 914 in My plane. Oh, by the way, I 'm building the Titan T-51 Mustang,and not a Vans. (DUCKING)
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If you haven't purchased the Rotax yet, you might want to look at the Suzuki V6 option for the Titan. The factory has test flown Dan Hawken's conversion and endorsed it. He has shipped dozens of conversion kits. It sounds like a mini Merlin unlike the Rotax and has way better performance especially with 2 aboard. I can put you in touch with Dan if you are interested.
 
It is a good engine, but at my altitude, it doesn't perform past the Rotax, and at twice the fuel consumption.
 
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