Considering a Rotary conversion, need help

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rv7charlie

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A core 13B weighs around 190 lbs; a Renesis maybe 10 lbs less. I weighed my FWF Renesis, including intake, exhaust (including muffler), psru, rad, oil cooler, motor mount adapters, etc; everything except what was left of the original firewall side motor mount (which would be there anyway). The entire package weighs 310 lbs, dry. I could have saved another 4 or 5 lbs with a more efficient mount adapter design. This is very close to (likely less than) the FWF weight of an O-320 Lyc. But the Renesis is capable of 180 HP when just loafing. They will do north of 220 HP with no internal mods, though most don't push them that hard in a/c. Cost, running on the plane (with careful financial management), is about the same as a mid time Lyc. The 3 rotor versions (20B) are roughly 50% heavier with 50% more HP. There are several 20B's flying now, including one with a fixed pitch wood prop on an RV-8 (weight ~= to an IO360 with c/s prop), and a peripheral ported 20B on a Lancair ES. They are capable of 270-300+ HP. The 20B installations are going to be lighter than angle valve 6 cyl Lycs.

Mazda has a prototype smaller rotary designed to be a range extender for hybrid cars. It appears to be just about the right size for light sport. :)

I've flown a couple of long cross countries in my 160 HP RV-4 with a Renesis powered -4 at the same speeds & flight profile. We both burn mogas, but he burns the lowest octane egas he can find, and I must burn e-free premium, to run mogas safely. I'm not afraid to lean the daylights out of my Lyc, unlike most Lyc drivers. At low cruise power (near the most efficient speed for RV's), he burns about 10% more fuel than my Lyc, but his fuel is about 30% cheaper. Probably half what avgas would cost.

The Wankels Ross referred to were Powersport rotaries. The test protocols required by Van's to do the flyoff had the potential to penalize the rotaries' performance. They still did pretty well. Here's a link to an old ANN article that mentions them; I think there's a detailed writeup in an old RVaitor.
Van's Homecoming 2004 Features Rotary Power | Aero-News Network

Charlie
 

narfi

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Sounds like day to day local flying (within a couple hundred miles and stol) the rotary is better but if looking for pure range it looses out to the more traditional engines?

Do you know what kind of life expectancy he was looking at?
 

Lendo

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Bob Mears, I heard Tracy retired!?
DL Rocket 89, The rotary is a great choice if your prepared to get involved with building one. The PSRU - Tracy's is OK it uses a Planetary from the Ford C6 gearbox, I believe there's a stronger and better one from Ford now available. The issue with the Planetary is has some Lash because it self aligns with 6 Planet gears in the Planet Carrier and also needs a Damper because of this Lash - this is both good and bad. Powersport did a massive amount of development with the PSRU and settled on an Internal Sun Gear in a Ring gear arrangement. The benefits are, very little Lash, no need for a Damper because of the smoothness of the Engine. It has minimal off-set approx. 2" - which is ideal for may installations, lowering the Engine. The beauty of the Internal Sun Gear is that as the PSRU heats-up the Sun gear only expands the same amount of the Ring Gear and there are no unnecessary stresses transferred to the gearing teeth. With an external sun gear there are tolerances for expansion needed much like the Planetary.

Now with Aluminium Side Housings no applied thin hard surface can survive the pressure of the side seals in the side housings - as any surface treatment will fail due to the soft Aluminium Substrate. Only surface to stand up to side seal pressure and wear is Detonation Gun treatment ( can be expensive). Naturally the Rotor housings are extremely good with porous Chrome over Steel.

The best Volumetric Efficiency is found with the Peripheral Ported Housings (about 42mm to 44mm) for our RPM range, will give you the 200hp at modest RPM.

BTW the RX8 isn't the best engine for Aviation.

I know of 2 people developing the Housings and the PSRU for the Rotary, why aren't they available now - it's because their full time Engineers working for a living and low volume production/ sales won't support them or their families. So they will release their development when they can, but I hope that information helps you in your search. There is plenty of information for research on the Internet.
George ( down under)
 

rv6ejguy

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Wankel engines still have torsional vibration like any other IC engine and while the internal pinion gear arrangement is probably the best out there for a PSRU, it does not always remove the need for a damper.

PowerSport went with an ultra stiff arrangement to tune the high amplitude TV above the operating range of the engine. This results in more weight but probably less maintenance. PowerSport did some great work, too bad it withered away with only a few parts produced. Unfortunately there was never enough time put on any one FF package to know its longevity or reliability.
 

rv7charlie

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Bob Mears, I heard Tracy retired!?

BTW the RX8 isn't the best engine for Aviation.
Tracy Crook has retired from production, but still supports existing customers.
Care to explain why the RX8 (Renesis) isn't the best engine for aviation? (I assume that you mean 'the best *rotary* engine'.)

Charlie
 

Lendo

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Rv7Charlie, I believe it's the side ported exhaust which causes a hotter side housing heating the oil, it's not as efficient at expelling the exhaust as the straight out (PP) Rotor housing port either. Also the straight in Peripheral Ported intake is also the better arrangement for 200 hp at a reasonable rpm. If you were to consider PP exhaust for the RX8 rotor housing you will fins the side seals are also short (allowing blow-by) as they expand under the heated side exhaust, and I don't think even the largest of the RX7 side seals would be long enough to fit even if they could, as their a different design. I don't believe there are different sized sixed side seals for the RX8.
If you run the RX8 as it is there are few issues it's when you want the higher power, best VE, best exhaust port, these issues become a problem. It's better to modify the RX7 engine than play with the RX8 - hence my statement.
George (down under)
 

Lendo

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Just going by memory now, Powersport developed a 160 lbs. Twin Rotor, with 42mm inlet PP, producing over 200hp at 6,000 rpm (can't remember PSRU ratio, sorry) no forced induction used- however it was two expensive for public release. The company was sold off when one of the partners died in a Aerobatic accident (not Rotary related). As the Intellectual property was also sold with the business, so to all that development to that date. With current technology this can now be achieved with even better designs - I am advised of this by a very experienced Mechanical Engineer. The testing that Powersport did was invaluable in eliminating all but the best design features. I am yet to find something that can beat that performance for weight. One of the issues of PP is that the Port itself must be done properly as many leak after a period - doesn't do the engine any good. I believe that has been overcome with a new design.
BTW I am restricted on what I can say due to keeping some/ most info confidential, like who, when where how! To divulge any further information would cut-off my direct line of information. I would dearly love to see some release myself for one of my designs.
My calculations suggest the better inlet port size is 44 mm and I believe that will be tested next, to see the improvements if any for our RPM range and power requirements.

There is another development with similar goals, again the information is confidential, but I believe it's targeting Government contracts for UAVs.

I've toyed with the idea of exhaust down installation, inlet up and exhaust down. There are some design issues, but I've managed to design around them. The beauty of exhaust down is that with any flooding it just pull out the plugs or Exhaust and let it drain.
George (down under)
 

rv6ejguy

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There is still plenty of Wankel development going on around the world, in fact the original Wankel design and some tooling was bought by a business associate in Germany and he's slowly working towards production engines for smaller niche markets like sport vehicles, UAVs and aviation. Financing hurdles are slowing development unfortunately.

Plugs up Mazdas have been tried and proven to work years ago despite serious opposing views from PL. No new ground there.
 

rv7charlie

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Rv7Charlie, I believe it's the side ported exhaust which causes a hotter side housing heating the oil, it's not as efficient at expelling the exhaust as the straight out (PP) Rotor housing port either. Also the straight in Peripheral Ported intake is also the better arrangement for 200 hp at a reasonable rpm. If you were to consider PP exhaust for the RX8 rotor housing you will fins the side seals are also short (allowing blow-by) as they expand under the heated side exhaust, and I don't think even the largest of the RX7 side seals would be long enough to fit even if they could, as their a different design. I don't believe there are different sized sixed side seals for the RX8.
If you run the RX8 as it is there are few issues it's when you want the higher power, best VE, best exhaust port, these issues become a problem. It's better to modify the RX7 engine than play with the RX8 - hence my statement.
George (down under)
So, there are no upsides to the side exhaust port? What about downsides to the peripheral exhaust? Agree that it would be a bit silly to cut a peripheral exhaust port in a Renesis.

What's a reasonable rpm?

What's the BSFC of a 13B at 75% power?

What's the BSFC of a Renesis at 75% power?
(Hint: Which gets better gas mileage in the car?)

Has someone down under flown both a 13B & Renesis on the same airframe & compared performance?

What are the issues with the Renesis that have been demonstrated to cause problems in a/c use?

Charlie
 

rv6ejguy

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The Renesis had lots of problems in the cars with compression loss at very low mileage in the first few years at least. Not sure if that was ever fixed to consumers satisfaction.
 

Lendo

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RV6jguy, Compression loss at low mileage (I believe) was a build-up on the Apex Seals to do conservative driving habits. To remedy that the Mechanics used to run it hard on a test run (flog it). From what I hear!
RV7 Charlie, The only down side to RV7 PP is that it slings the unburned fuel (from the squish areas - another story) into the exhaust and why the Rotary has a reputation of being a hot motor - it certainly is hot in the exhaust and is why Mazda went to the RX8 to sweep the unburned fuel into the next combustion event.
I think The BSFC is about .5 to .55 for the Rotary (don't quote me have a look at PL's web site), however it can leaned aggressively - as it has no valves, and may be close to any air cooled Piston engine, that uses fuel for cooling. I will check with my contact with what he things with fuel Injection- - it may be better than that!
No comparison that I'm aware of.
I think (could be wrong) most of the issues are with the PSRU of the past designs. The limit on Tracy's Planetary is again from memory about 160 hp continuous and a littler higher for a short brief of time. Another problem is, if not checked properly is the Apex Seal Gap - if too big through wear, it can spit out the seals, however these can be re-machined to accept the 3mm 12A Seals. Incorrect sized or poorly cooled water and oil coolers, can be an issue, but that's with anything.
Hope that helps
George ( down under)
 

rv6ejguy

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How could most people drive an RX8 without enjoying those smooth revs? Wankels beg you pound on them. You shouldn't release an engine for sale if it goes south in 20,000 miles like many did, no matter what the cause. The warranty claims and your reputation loss will cost you dearly.

We're seeing today that most any piston engine can also be leaned aggressively, in fact that is the new norm for most Lycoming RVs. The EGTs and CHTs are substantially lower than ROP, as are the fuel flows. PL has brainwashed too many followers about the "scary" mechanical shortcomings of piston engines with a bunch of unsubstantiated nonsense on his website. Hundreds of Lycomings reach their 2000 hour TBO and beyond every day, worldwide without throwing rods or breaking cranks. I haven't heard of a single Wankel going to 2000 hours in aircraft use yet without coming out to have parts replaced.

The Wankel has its place but it's hardly the all wonderful engine PL gushes about. All engines have their shortcomings and advantages. Best to leave it at that.

I am surprised at the following PL has, given that he's never flown an airplane with a Wankel engine he built to my knowledge. He was kind enough to send me an email last year after my cooling article in Kitplanes saying that I should embrace the Wedge diffuser concept as should all others in aviation, including unlimited Reno racers. It was far superior in his view. When I asked Paul for his flight test numbers to back up his opinion, naturally he failed to respond.

PL was also the guy who sent me another unsolicited Email about 13 years ago saying that I was crazy to put an auto piston engine in my RV as it would blow up. Here I am 11 years and 400 hours later and no rods through the side... and PL STILL has zero hours on a Wankel. We need more people like Tracy Crook who are doing it and less people like PL who only theorize and have no practical experience, yet love to tell people what experts they are on various subjects.
 
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Lendo

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RV7charlie, I got a response from my contact (BTW not PL) on BSFC of the RX7 and it varies, Powersport experimented with the injection position and with a mechanical injection at the port it was in the High .4 (I said .5), seems close enough. The injection along the runners were BAD. RX 8 - who knows, I don't know of anyone who tested it!

Direct injection into the housing may be even better than we think, but they have no data on that. Their 42mm PP is ready to be tested on the Dyno, so should have some numbers after that.
I wouldn't mind betting a direct injection into the housing and right sized PP for the desired rpm to match the PSRU gearing (everything is relative), we could see an excellent BSFC, through aggressive leaning.
George (down under)
 

rv7charlie

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Ross,

IIRC, the issue with low compression on the early RX8's was due to inadequate oiling of the apex seals in an attempt to keep the engine 'cleaner' for emissions purposes. Pretty sure it got corrected fairly quickly. Obviously wasn't good for PR, but not that uncommon for an auto mfgr to make a mistake. I think you were the one that pointed out the Subaru diesel crankshaft issues on another forum.

Wholeheartedly agree about PL. He's obviously had some brilliant insights in the past, but seems incapable of recognizing anyone else's.

George,

Just about all the stuff you've mentioned is inconsistent with the experiences of friends of mine who are actually flying rotaries. Do you know of planes that are flying down under who have had the issues you describe?

My question was what you knew about the Renesis that made it a poor choice as an a/c engine. P-porting is unrelated to the question. I can only think of one Renesis that flew with P-port induction, and IIRC, it was damaged (unrelated to the engine). I also know of at least two planes currently flying that use Tracy's reduction drive on 3 rotor 20B's, one of which *is* P-ported. He did have issues with the riveted coupler plate (harmonic damper), but has replaced the rivets with bolts which seem to be holding up fine. I'm also aware of at least three Renesis powered a/c with hundreds of hours each (one of which is actually running a supercharger).

I'm kinda running out of energy to cover any more of the points. Where are you getting your info?
 

Lendo

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RV7 Charlie, I said the RX8 wasn't the best choice for Aviation, I supported that with the fact it's difficult to modify especially for PP for best VE. I get my information from the Engineers that are developing and testing the engines, one has Powersport Background - are you not reading my posts - am I not communicating effectively? All my comments are related to NA engines.

BTW I'm a Supercharger advocate for Aviation, there has been many issues with Turbo in the past but I don't know enough about it to recommend what's needed, however I believe most issues have been overcome with the newer design changes.
Personally I want a light weight Rotary with a Powresport style PSRU - it has been redesigned /upgraded and modified. Can't get it soon enough - so the last thing I want to do is put-down the rotary, however it's the weight issue for me, it's got to be lighter.
Det Gun impregnated Al side housings is the optimum at this point in time - but very expensive. Steel wear plate in Billet machined side housing, is still heavy because of the 6mm plate - and also very expensive. Others have tried every conceivable surface treatments and all have fails due the Al soft substrate. Cast Iron is hard to beat, but heavy.

If your unhappy with my comments and you have your own view - I happy with that. I merely put up my view for those contemplating the Rotary and have little to no experience, so their aware of any pitfalls.
George
 

nucleus

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The Renesis had lots of problems in the cars with compression loss at very low mileage in the first few years at least. Not sure if that was ever fixed to consumers satisfaction.
Seal lubrication in rotary street cars is a compromise between emissions and lubrication - the apex seal in particular are dependent on oil injection on the periphery, this was the problem with the RX-8. People weren't driving hard enough to kick on the additional oil for high RPMs.

For aviation/off road purposes many disconnect the oil injectors and just add two stroke oil to the fuel. I did that with my hot-rod RX-7 in Montana as well, make for very good lubrication.
 

Lendo

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Some news to those interested in the Rotary motor, Steve Beckham has put up a video on U-tube for his 1,5" P-port Rotary engine idling nicely at 1,100 rpm. Can't give further details until power is confirmed - but I believe it's very good. Reduction gearbox is 2.322 to:1, with an option of a 24:1.
George (down under)
 

narfi

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475 is a nice idle prop speed from 2.322:1 but what is the 24:1 used for? 6000rpm @ 24:1 gives a prop speed of 250.

Edit:
My bad. I just realized you ment 2.4:1
 
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Lendo

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Narfi, They are restricting the max rate to 6,000rpm and cruise to 5000rpm for longevity. As you might be aware 6000 rpm is the sweet spot or least stress on the engine, it could sit on that all day without an issue. There has been claims that the engine can't idle below 2000 rpm, but the proof is in the Video. I suspect it boils down to tuning the Inlet Tube, the Inlet velocity, and the Volumetric Efficiency(VE). With the bigger ports like 2" the Inlet velocity is lower, so the VE is lower. There is no Torsional damper as the frequencies is out of the rpm range used with a rigid PSRU system which is the internal spur gear internal to the ring gear. This arrangement makes for tight tolerances as the expansion rates of the ring gear and spur gear are almost identical, so no extra slack (lash) is allows for expansion, like other types of arrangements i.e. planetary or external ring gear. I personally would like to see more like 2.5:1 ratio, but the only other ration considered at present is a 2.322:1. It's a matter of swapping out the spur gear, but I'm unaware of the issues of reducing 2 teeth to the spur gear. Modifying the spur gear would be the cheapest and easiest option and is what is intended for the 2.4:1 ratio option.
There are plans for a slightly bigger P-port but that will be down the track after all testing on the 1.5" is concluded.
George (down under)
 
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