Rotax 914 UL DCDI 115HP

prkaye · #1 08-28-2006, 10:30 AM

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?

the_other_dougreeves · #2 08-28-2006, 10:58 AM

Quote:

Originally Posted by prkaye

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.

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.

prkaye · #3 08-28-2006, 11:58 AM

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.

frankh · #4 08-28-2006, 12:28 PM

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.

prporter · #5 09-12-2006, 06:48 PM

What do you mean that it is high strung? Have you seen any documentation about unreliability on this engine?

Quote:

Originally Posted by the_other_dougreeves

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.

jedimike007 · #6 09-13-2006, 10:47 AM

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.

cobra · #7 09-13-2006, 11:40 AM

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

Just bought new Renesis motor for $2K+ 300 shipping. redrive ~$3K...

N941WR · #8 09-13-2006, 11:44 AM

Quote:

Originally Posted by prkaye

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?

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.

prkaye · #9 09-13-2006, 11:58 AM

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?

cobra · #10 09-13-2006, 01:11 PM

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.