Jump to content

Recommended Posts

It's a bit premature yet, but I've really been turning over engine selection options in my mind recently. Jon Matcho posted a link to Kitplanes magazine's 2017 Engine Buyer's Guide which really got me going, and right now I'm seriously considering 3 options for my Cozy IV:


Option 1: Lycoming IO-360

Pros: It's a proven bulletproof design. The default option.

- Better yet, the guy who sold me his project has got one available

- I already have the appropriate engine mount.

- Decades of unchanged design means that parts and support are ubiquitous

Cons: Included in the (not insubstantial) price is the engine. That's it. No starter, alternator, mags, wiring harnesses, oil cooler, baffling, exhaust. Realistic all-in price is north of 25k USD.

- Because of its nature(direct drive, large torque pulses), inexpensive propellers marketed to the homebuilt market are unsuitable (IVO, warp drive, etc.)


Option 2: Jabiru 5100

For those of you who recognize the engine, there's only one guy as far as I can tell who ever flew with it on a Cozy (Larry Hill) and this is his engine.

Pros: Cost. Larry is selling the engine and associated accessories(in his words "starter, generator, mags, carbs, and mufflers") for < 6k USD. The mount would be extra.

- Light. All-in weight < 260 lbs

- Still direct drive, but 8 smaller cylinders makes it "smooth and quiet" relative to the Lycoming. 

- Parts aren't as ubiquitous as the Lycoming, but are available relatively cheaply.


- Cooling. Some of the cylinders are hard to keep cool, and Larry eventually gave up on the design after a 45 minute taxi at Oshkosh caused one of the cylinders to overheat, stuck a piston ring, and blew a bunch of oil out the breather tube. (FWIW it will be a cold day in hell before I go to Oshkosh)

- Despite smaller torque pulses the IVO prop still proved itself to be unsuitable for Larry. I wouldn't take my chances on a warp drive either.

- Rarity. Larry had the only Cozy flying a Jabiru and not many mechanics will be familiar with the design.


Option 3: Automotive Conversion (Mazda 13B-MSP with Powersport PSRU)

According to Kitplanes' guide, Atkins Rotary will still build a complete kit with Renesis engine, Powersport PSRU, ECU, EFI, EI, alternator, and starter for 16k USD. I'm focusing on this design in particular because the available Subaru and Honda conversions are more expensive than Lycomings and use unproven PSRU designs. There are some proven one-offs (Ross Farnham's Subaru RV-6) but I'm not an engineer and I don't have their expertise.

Pros: Cheaper than the Lycoming. Cheaper even than a brand new Jabiru factory-direct, though not as cheap as the one mentioned above.

- Very smooth engine (though not very quiet, really)

- Engine loves a turbo. Even modest boost pressure results in significant HP gains.

- Engine design simplicity and permissive failure mode. Engine can't be seized, loss of apex seals results in reduced power, but not complete failure.

- Price includes modern features other engines lack (EI, EFI, ECU)

- Use of a PSRU puts many more inexpensive propeller options on the table. (IVO, warp, Meglinsky)

Cons:  System complexity. Need for a PSRU creates additional potential for failure.

- Liquid cooling system issues cause problems for auto conversions.

- All-in weight is actually slightly heavier than a comparable Lycoming installation.

- Rarity. Rotary engines aren't even common among Mazdas. Your local Mazda dealer might know a rotary mechanic, let alone actually have one. If they do he probably has a neck beard, a computer that runs on Linux, and a Laserdisc player (because betamax was too mainstream). Even Mazda doesn't make rotary engines anymore. Aviation related rotary enthusiasts with actual experience seem to have all moved on, or are so rare that they're rumoured to exist somewhere, but nobody seems to know any. Even google searches pretty much only lead to defunct websites and my 5 year old post in the Vans forums.


What do you guys think? Am I missing something obvious? What issues did you have with your own engine selection and eventual installation?

Share this post

Link to post
Share on other sites

I partial to the Lycoming.  I don’t want to have any doubt about the reliability of my engine and an airplane engine will usually warn you before it lets you down  

As you say, The history of canards is that rotary installations are often removed for a Lycoming after a while and/or they are more difficult to sell.  

Edited by Kent Ashton

Share this post

Link to post
Share on other sites

This is certainly a topic worthy of plenty of time and research. I have been for years, and I'm still years away from installing an engine. But I have a  fair idea of what I'm going to do.

I might argue with the idea that Lycomings are 'bulletproof'. Yeah, they are generally reliable, but they have their flaws and issues (I've been aboard a twin that suffered an unidentified failure). It is just that they are so old that the flaws and fixes are very well known.

For the Jabiru, clearly, you'd need to design a very different cooling setup to make it work. Possible, perhaps with an effective eductor.

I studied and liked the rotary for a long time. I've read and re-read John Slade's site, and the experiences of others. It can be a good engine... but. It appears to be a 'dead-end' design at this point. You would need to design and integrate a turbo setup, adding to the complexity. You'd need a better cooling design. I'm just not convinced the rotary is worth it at this point.

I do like some auto conversions. Looking beyond the canard world, there are a great number of successful implemetations to study. Keeping it simple (so far as possible) and not being tempted to 'make it better' yourself (ie swapping cams, pistons etc), seem to be prime indicators for success. The Alternative Engines volumes are educational reading on the topic.

One engine that could be a great fit for a Cozy (or even maybe a Long) and one I am watching with interest is the Aeromomentum AM20T. 260hp in a lightweight package built new for aircraft use. As yet unproven, but the company and its other engines appear to have a great reputation and expertise in the field so far. The same cannot be said for some other similar engine conversion companies.

Edited by Voidhawk9

Share this post

Link to post
Share on other sites

I gather Aeromomentum uses Suzuki engines? They look pretty good! That being said their unbelievably cheap gearbox gives me pause. A Powersport PSRU is like $9k, which fits pretty well with what guys like Marcotte and Crook were charging back when they still made theirs. I found a company that is making their own gearbox for aviation (specifically to transmit 250HP for Mazda rotaries) that is charging $5500. The fact that the Aeromomentum gearbox is only $1600 is a serious red flag for me. Plus to get the 260HP out of a 2L engine it looks like they needed a turbo and 10.5:1 cylinders. I wonder if a turbo could be put on the AM15 147HP version to get it to ~180? These guys are definitely worth watching. Hopefully not another Viking.

The Lycoming O-320 and O-360 are bulletproof by just about any definition(minus the infamous O-320-H2AD). Flight schools all over Canada and the US have racked up millions of hours on these things over the years, and it's the odd one that doesn't make it to TBO. I've seen some pretty gnarly failures - a friend of mine had to land on Virginia Beach after part of his O-320 decided to depart the aircraft by way of blasting itself right through the crankcase - but those stories are exceptional in part because they are so rare. It's just a shame that being the big name in the market means they still command such high prices for carbureted, magneto driven, early 20th century technology when others are offering FADEC for much less.

I've kept my ear to the ground on the alternatives, I even really considered Diesel for a while there, but the offerings are still too slim and those that are out there are far too expensive. Deltahawk, if they ever become a thing, is apparently asking $65k. Not 100% sure WAM is still producing? And Continental still doesn't seem that friendly to single purchases, more looking to power a new fleet of certified aircraft. I'd considered a Subaru EE20, but they got infamous for crankshaft failures that Subaru disavowed. The availability and relatively low cost of Jet-A keeps the dream alive though. I'd really love to see someone succeed in this area, I just feel like it's going to have to be someone much richer's passion project.

Share this post

Link to post
Share on other sites

I followed the plans and went with the least expensive option.... a flying mid time Lycoming O-360.  I sold some attached components when I bought it (P-Mags, Carb, small oil cooler, automotive alternator, Skytech starter).  I had to buy a few components while installing (B&C starter & alt, FI servo, Cozy exhaust, LSE Ign, bigger oil cooler).  I'm in about $14k now(engine and accessories), with an estimated 1500 hours before recommended overhaul.  Mid-time lycoming is a bolt on solution, and the plans make is SO EZ... having everything fit (cowls, baffles, components).... all that really is a big deal.

Most Cozy's never get finished (flying), and many that do get finished don't often accumulate many hours.  If I ever get up to 1500 hours, I'll be in a VERY small minority so I truly believe a mid-time 360 is a good choice.  Yeah, I know its boring... but its in a Cozy MKIV (NOT Boring).  (but ya gotta pay attention to cam rust and exhaust valves)

IF I had to have an alternative engine.... I would consider the UL520.  Its a modern airplane engine, and several in our community are flying or installing them.


Share this post

Link to post
Share on other sites

I flew my Velocity for about 15 hours with the Mazda.  It was smooth and fast.  I used the inflight adjustable IVO prop.  I even had cooling licked.  However, I was having to tinker a lot.  The first time I took it out of the pattern to a nearby airport, I lost the engine when about to enter the pattern....came down fast, with the wind, threw down the speed brake and even remembered to use the rudders as "brakes".  No injury and no damage....even started back up and taxied to the tie down.  While that turned out to be a clogged fuel line and not specifically rotary related, it did give me pause.  So, at around that time I had some money fall out of the sky, so before I did something stupid with it like invest or pay off bills, I bought an aircraft engine (that's another story where since I mentioned I had turboed the rotary, the guy convinced me to go with the Continental TSIO-360..... then the cost increased by about $10K...to almost the point of a new Superior .... or flavor of the day....took over a year for delivery and THEN the A&P went to federal prison for selling an unairworthy prop as airworthy......but that's another story)


I still like the rotary, a lot.  However, I put a LOT of time in figuring things out.  With my knowledge today, I think I could get it to work as a good alternative engine.  But, that's after years and years of trial and error.  One of my key factors in finally abandoning the rotary, other than realizing my original goal was to have what I hope to be a safe and reliable airplane and not just prove the rotary as a viable option, was the retirement of Tracy Crook, the maker of the PSRU and electronics.  Tracy was the first to tell you his stuff was not plug and play...and boy, did that turn out to be true.  My ignorance combined with that created a large learning curve.  Dont get me wrong, even with some serious frustration, I really enjoyed the process.  Still do.  I crave going out and working at the hangar. 

It would have been easier, and I would have likely been flying the last several years if I had not convinced myself that spending a bit over a period of time on the rotary made sense.  I should have likely just saved during that same period of time and bought a Lyc instead.  Hopefully soon, I will fire up the Conti for the first time and hopefully, and with solid learning and experience, I will have that fast, cool, safe and reliable Velocity I crave.

All the best,


Chris Barber


Edited by CBarber
  • Thanks 1

Share this post

Link to post
Share on other sites
On 11/10/2018 at 8:30 AM, CBarber said:

So, at around that time I had some money fall out of the sky, so before I did something stupid with it like invest or pay off bills, I bought an aircraft engine...

Ha -- that was good for a morning laugh!  Thanks for sharing Chris!

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now