Mistral proceeds toward certification

[rv6ejguy]

Does anyone know why Mazda has not embraced LOP operation at part throttle on the Renesis using wideband O2 sensor feedback? The other OEMs have been doing this for years now, some running 17-20 to 1 AFRs in cruise.

The Renesis has a deserved and real reputation for poor fuel economy. I'm thinking Mazda has very smart people working on this. Is this an emissions issue?

[airguy]

Originally Posted by SvingenB

Comparing the CO2 emmisions (EU standard for cars) of the Mazda RX8 with the state of the art Wankel, the RENESIS engine, to the similarly powered BMW 325 (stright 6), they are 267 and 225 g/km respectively. This means that the RENESIS uses approximately 15% more fuel on average. For the sake of completeness, the much stronger BMW 3.0L diesel with 500Nm of torque only has 174 g/km of CO2 (35% less fuel compared with the RENESIS).

Incorrect.

You cannot compare the CO2 output of the engines when they are running different fuel (Mogas versus diesel) as the Carbon/Hydrogen ratio for the two fuels is different. It's close, but it's not the same. To make an accurate cross-fuel comparison, you would have to look at oxygen content before and after combustion, since the oxygen is used to combust both the hydrogen and the carbon of both fuels. Even then, different blends from different areas of the country will contain varying percentages of compounds with single versus double bonds within the carbon chain, which changes the chemistry further - not to mention oxygenate additives. It's not apples to apples.

[SvingenB]

It's not apples to apples, but close enough "for government work", literaly The point I was trying to make was that a modern Wankel only use 15% more fuel than a modern otto engine for similar cars with similar hp (Mazda rx8 vs BMW 325). This is much less than the fuel consumption of old Wankels and nowhere near the 40% difference reported on RVs.

The CO2 emmisionn is a standardized procedure, and a better measuree than factory reports on fuel consumption, which is more affected on driving habit thaan most otther things (CO2 is of course also a result of driving habit, but the procedure of measuring it is not.

[SHIPCHIEF]

I'm admittedly not an impartial observer.
I'm building an RV-8 with a turbo 13b. I'm using Tracy's engine controller and reduction gear. Hopefully the first engine start will be in a few weeks.
Tracy's engine controller allows manual leaning up to 15% of the standard value you set. You observe the O2 sensor while performing baseline tuning, and 'drivability issues'.
Based on Tracy's comments, the naturally aspirated 13b and Renesis engines can be run quite a bit lean of peak, with fuel consumption 'approaching' that of a lycoming equipped RV-4. I understand that this is a bit vauge and still higher consuming.
My goal is to get 200 Hp, so I know a turbo is required. I want a high sustained climb rate and to reach high alititudes. The Cascade Mountains are nearby and drive this desision.
Likewise, a fast dive for home once I get west of the mountains favors the rotary which should have no shock cooling issues.
The possibility of using auto gas would hopefully make the higher fuel burn a financial wash.
I enjoy the work. It has added years to the building process, and I don't reccomend it. You have to want to do it. But that's just me...and many of us.
Here's a link to the EAA326 site, and my most recent pic. http://gallery.eaa326.org/members/se...F0985.JPG.html you can kludge around from there and see the others, plus EAA326 members projects as well. A neat bunch of guys, and very active RV builders and fliers.

[Rotary10-RV]

Originally Posted by rv6ejguy

Does anyone know why Mazda has not embraced LOP operation at part throttle on the Renesis using wideband O2 sensor feedback? The other OEMs have been doing this for years now, some running 17-20 to 1 AFRs in cruise.

The Renesis has a deserved and real reputation for poor fuel economy. I'm thinking Mazda has very smart people working on this. Is this an emissions issue?

There have often been Oxides of nitrogen emissions trouble when running LOP. The newest rotary is finally exploring direct injection which should allow LOP and stratified charge operation, both of which will work well with the rotary.
Moose did us the favor of posting the pictures of the Mistral power and fuel consumption numbers. Despite George's adversion to wankel combustion chamber shapes those numbers look very good. I hadn't been able to do it (post the charts) from work. I hope that Mistral will do side by side flights so everyone will be able to see how well they have the engine working. In an aircraft they don't have emission troubles so they are able to get much better LOP numbers. Tracy Crook has been telling everyone that the rotary works great there and Mistral seems to be verifying what Tracy has been saying. The higher the needed output the better the rotary works. If that wasn't true Mazda would never have won LeMans outright in 1992 durring a total fuel available limited year. That engine was NOT turbocharged.
Bill Jepson

[RV6_flyer]

An RV 111.1 NM Race took place 5 April 2008. Lycoming parallel and angle valve 360s with Constant Speed props and one MAZDA Rotary RV-6 with Fixed Pitch. I witnessed the fueling BEFORE and AFTER the race. I did the timing. The Mazda rotary was right in the middle of the pack with the 200 HP and 180 HP RVs and had a similar fuel burn. Fuel burn on the Rotary was a LOT LESS than what I tought it would be.

See RESULTS:
http://www.rvproject.com/race.html

Results are near the bottom of the page. Photos of the racers should be up on the site tomorrow.

I am the one that collected and processed all the RAW DATA. I created the master spreadsheet that calculated the results.

[SHIPCHIEF]

That race was very interesting. I'd sure love to participate in something like that.
It looks like a well run, safe and inexpensive event that the 'average rv builder' would enjoy.
The data is encouraging for a rotary builder like myself. There used to be so much negative feedback coming from the conventional engine group. Now I notice a bit of a change. Our group is also getting larger and doing some flying. (that's right, in the not to distant past very few actually flew)
I'm alittle averse to the prepackaged alternate engine (sorry Jan) because I am of the opinion that the builder should have an intimate relationship with his expirimental power plant, and think out, then build it. Of course there are levels of commitment. I don't mean cast your own pistons and build your own connecting rods and cylinders ala Burt Munro.
I fall pretty much in line with the Rotary Engine builders I've come in contact with, buying the few parts available, and fabricating the rest, mostly everything that hangs from the engine or the engine hangs from. So maybe it's just a matter of degrees of ability and commitment, as well as resources.
Anyway, I'm always interested in advancing the art.

[rtry9a]

The question I have about the runoff:

2 lycs were specifically ran for fuel economy, 2 for top speed- George claims that both extremes were representative of the entire group as a comparison to the single rotary. I[m not so sure that approach is valid given other differences.

Since the rotary fell into the middle, and it was the only fixed pitch prop in the bunch, it is probably a bit premature to make an across-the-board assumption other than it performed as well as the others in economy and power, just as we've been saying for the last two years, and a little cheaper to operate. I dare say any fixed prop 180hp Lyc would have also fallen into the middle performance-wise, given that buch of planes...

[SvingenB]

A dane is building this one

Hmm, RV-4 with 190 HP Mistral....

[Rotary10-RV]

Originally Posted by rtry9a

The question I have about the runoff:

2 lycs were specifically ran for fuel economy, 2 for top speed- George claims that both extremes were representative of the entire group as a comparison to the single rotary. I[m not so sure that approach is valid given other differences.

Since the rotary fell into the middle, and it was the only fixed pitch prop in the bunch, it is probably a bit premature to make an across-the-board assumption other than it performed as well as the others in economy and power, just as we've been saying for the last two years, and a little cheaper to operate. I dare say any fixed prop 180hp Lyc would have also fallen into the middle performance-wise, given that buch of planes...

I find it interesting that whenever someone points out that a rotary does well on fuel burn everyone says, "can't be or say isn't so." I am familar with David Leonard's RV-6 configuration and he admits himself it is no where near a "cleaned up" configuration aerodynamically. The engine is turbo-normallized with the Turbo modified to prevent too much boost. The point here is that Dave showed well and got BETTER MPG than some of the Lycs. They were flying fast. David said in another forum that they were averaging 190 knots or 218 mph over the course. It has proven to be true that the higher the needed output the better the rotary does in terms of both P/W and BSFC. It has been shown that in the "tuned" output areas at high RPM the rotary does well on fuel and power. Interestingly everyone mentions the cars, and this is understandable, but as so many people mention the duty cycle, and power requirements in an aircraft are always higher than a car. I have long believed that the rotary was BETTER SUITED TO AIRCRAFT THAN TO CARS.

Now I need to mention that this has as usual started to veer far afield from what I started the thread about. Mistral Engines is certifing the rotary is both 2 and 3 rotor configurations. They have posted excellent power and efficiency numbers. These numbers will need to be proven out in an non-factory unbiased environment to be accepted by the conventional engine contingent. I would love to see a side by side comparison with another Piper Arrow for instance. Mistral has done the grunt work to truly bring the rotary up to a competitive engine on both power to weight, where it has always looked good, and on a fuel efficiency basis as well if their numbers prove out. They are a truly professional and top drawer group from everything we have seen so far so I expect they will do well in independent tests. We simply have another manufacturer of engines that will help to provide us with a really nice way to fill our engine needs if you might like something different.
Bill Jepson