# A home built single rotor wankel engine with aluminum housings

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#### KeithO

##### Well-Known Member
I just found this by accident when googling single rotor wankels. http://www.fairpoint.net/~res12/html/one_rotor_wankel.html

Along with these unique parts

[FONT=Arial,Helvetica,Geneva,Sans-serif,sans-serif]
Configuration Overview.[/FONT]

[FONT=Arial,Helvetica,Geneva,Sans-serif,sans-serif]Engine size 1/2 MAXDA 12A[/FONT]
[FONT=Arial,Helvetica,Geneva,Sans-serif,sans-serif]Excenter shaft Modified 12A with case hardened bearings and 10:1 taper output.[/FONT]

[FONT=Arial,Helvetica,Geneva,Sans-serif,sans-serif]Flywheel Custom design with integrated balance weight.[/FONT]

[FONT=Arial,Helvetica,Geneva,Sans-serif,sans-serif]Oil pump MAZDA 12A[/FONT]

[FONT=Arial,Helvetica,Geneva,Sans-serif,sans-serif]Water pump Subaru[/FONT]

[FONT=Arial,Helvetica,Geneva,Sans-serif,sans-serif]Alternator 30A PM.[/FONT]

[FONT=Arial,Helvetica,Geneva,Sans-serif,sans-serif]Ignition Streetfire CDI , dual coil[/FONT]

[FONT=Arial,Helvetica,Geneva,Sans-serif,sans-serif]Carburetion AeroV Injector.[/FONT]

Anyway, the gentleman involved seems to be doing a heck of a job on this, doing it all himself. No buying parts from Atkins for him... The website has not been updated in about a year, so I don't know the current status.

Looking at the Atkins website, they are now offering many of the unique parts for a single rotor 13B engine from stock.
Atkins Rotary - Rx7 | Rx8 | Mazda | Rotary | Engine | Parts

Their single rotor engine turnkey package is $8500, of course without a reduction drive. Weight is 220lb even with all of the cast iron parts and it makes about 96hp. It would seem that with more aluminum and lighter weight direct drive alternator it could be made lighter still. #### Vigilant1 ##### Well-Known Member Lifetime Supporter Yes, Richard Sohn (the guy you are talking about) has been at this for many years, attacking each problem as it arises. I think the most recent improvement he's contemplating is the use of lightened stock iron rotors. They are machined down to reduce their weight quite a bit, which has a big payoff in a single rotor engine because the counterbalance weight can also be reduced by a lot. Overall, the biggest advantage of lightened rotors is higher operating RPMs = more power. I like the idea of lightened iron rotors rather than aluminum ones because of the thermal expansion relationship between the two metals. Aluminum expands about 2.5 times as much as iron with increasing temperatures, which is why Wankel engines (with iron rotors and aluminum housings) usually don't seize up when overheated. They may lose compression and power, but they tend to keep going for a considerable amount of time. That's a very handy safety feature in a liquid-cooled airplane engine. I don't know if an engine with an aluminum rotor would be as "forgiving." Mark #### KeithO ##### Well-Known Member Weird that there was no contact info on the site except for the email address and I have not got any response from that yet. Does anyone know why he started with a 12A ? I would think parts are very hard to find for those old motors. Mark, thanks for the extra info. If he had started with a 13B then I believe he could have used the Renesis rotor which is lighter than the 13B. The super "lightened" rotor set (sold by one of the tining houses) saves 0.2lb for$2500 + whatever it takes to pull your engine apart and install... I don't see that as being cost effective.

I have noticed that one can get RX-8 motors for about $1700 on ebay now and the Honda Fit motors for about$850. I "really" would like to do a single rotor 13B or Renesis, but the weight has just been such a challenge. After reading about his work, it would be interesting to know if any durability tests were done and how that panned out. Making parts that can be assembled is one thing, but getting it to last is quite a different matter.

#### Vigilant1

##### Well-Known Member
Lifetime Supporter
As it happens, Richard Sohn's plane briefly took off for the first time today under the power of his single rotor engine. It was running rough, so he didn't continue the flight, but he beleives he knows the cause of the trouble.

Keith, Richard frequents Paul Lamar's online Aircraft Rotary Engine Newsletter email list, you could sign up there (here's how). After that you coud ask any questions you like. A note: That list belongs to Paul Lamar and he's got definite opinions of what will work and what won't. Not everyone agrees with him, and he is clear in saying that he's not running a debating society (my paraphrase). I've learned a lot from the list (including Richard Sohn's posts), but the "feel" is a lot different from here at HBA. So keep coming here, too!

Richard also frequents the "Fly Rotary" list, along with many other luminaries of the Rotary Aviation world (Tracy Crook, Ed Anderson, etc). The feel is a bit more "open" over there. They are at: http://www.flyrotary.com . You can go there now, go to the message archives, and see Richard's first flight report.

While Richard's web site is a bit out of date, he's been doing a lot of work on this project for many years. I think the 12A is a test mule and that he'll be scaling things up to the 13B or Renesis once he's got the bugs worked out (especially proving his "hybrid" Aluminum endplate with steel insert).

Comment: A single rotor engine based on the 13B may turn out to be a fine airplane powerplant, and might reliably put out better power-per-pound than any 4-stroke recip. I think (with P-Ports), it can reliably produce 110 HP and with AL endplates it might come in at about 200-215 lbs or so (with PSRU, cooling system, starter, alternator, etc). But if weight isn't quite so critical a twin-rotor 13B has a lot going for it: twice as many power pulses per e-shaft revolution (the same # as a 4-cyl 4-cycle engine) reduces the torque pulse headaches, no need for a custom-made () e-shaft, the engine has lower counterweight mass (because the rotors largely balance each other out) and you get twice as much displacement for the additional weight of just one more (center) plate, rotor, and a bit more e-shaft, (in other words, you need both end plates whether you have a single rotor or a twin). So, HP/lb goes up quite a bit with a twin compared to a single rotor. IOW, compared to a single-rotor with aluminum side plates, a twin rotor with stock (cheap, proven) iron end plates would weigh about 100 lbs more, cost less to build, and have double the HP. But, all of that means nothing if your airplane needs a 215 lb engine.

Mark

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#### Allan McDowall

##### Member
I had a 1986 Mazda RX7 sports car, beautiful. I put 85,000 miles on it at between 19 - 22 mpg ( imperial gallons ) = 16 - 18 mpg ( US gallons. ) It ran like silk, almost silent. I obeyed the makers instructions ( " When all else fails, read the instructions " ) Because they run so hot - it is a 6 cylinder 2 stroke in the volume of a plastic washing up bowl, after all, the inlet air has to be heated by the exhaust, to avoid thermal shock to the ceramic vane seals. The engine takes its 2 stroke oil from the sump, so one cannot use synthetic or detergent oils - only mineral oils. But not motorcycle 2 stroke oil. ( Again, makers' instructions. ) The heat exchangers have to be high pressure - if I recall correctly, 1.55 atm, 22 lbs/in^2. There was no problem with unleaded fuel, because there were no valve seats. ( Unleasded fuel needs hard valve seats, so the timing needs to be adjusted a bit to avoid hard impact of the valves. ) The engine itself is lighter than a piston engine, but the inlet, exhaust, water cooler and oil cooler have to be up mto the task, and maybe a very small refrigeration to help with the cooling might be worthwhile. Provided nthe cooling is adequate for the engine, extra heat does not matter - The engine bay needs to be metal - stainless sheet, exhaust run outside, but can be faired - it does not have to be like a bit of sewage pipe. having a lighter engine means that the whole airframe can be lighter, so the frontal area can be reduced - and, horror - the U/C stowable. With a howler device to sound if the altitude gets under 100 feet, for forgetful people. Flatty landing, Altzheimers, bullet age. Allan McDowall

#### Vigilant1

##### Well-Known Member
Lifetime Supporter
Allan,
Yes, the RX7s engines are very smooth--some people liken them to electric motors in this regard. Not to nitpick, but the engine is not a two-stroke, it is definitely a four stroke (with separate intake, compression, ignition, and exhaust phases), the phases are just accomplished in a single revolution of the rotor. Also, the majority of the folks using them in airplanes have eliminated the use of the oil metering pump that is used in cars. This pump takes a small amount of oil from the sump and injects it into the chamber for lubrication. In airplane use, folks generally just add oil directly to the fuel (approx 50:1, some argue for less). This has the advantage of being more reliable (no metering pump to fail), and the most important advantage is that it allows two-stroke nondetergent "clean burning" oil to be mixed into the fuel while synthetic or detergent oils are used in the sump to lubricate everything else.

Regarding the preheat of air for the ceramic vane seals--were you running a turbo?

For builders going the normally aspirated route--many are modifying the engines for peripheral porting instead of the Mazda-standard side ports. The downside is somewhat rough idling (which is why this isn't standard procedure in cars) but the advantage is considerably better "breathing" and higher power at the RPMs we typically use in airplanes, plus a simpler/lighter induction system.

To the project in the original post: Richard Sohn's one-rotor engine development continues. He was struggling a bit with getting a ROTEC carb set up right and a few other small bits, but he'll get there. In the HP/weight area, the single rotor won't match the outstanding numbers of the twin rotor (for a couple of reasons)m, but it should still be very competitive with conventional piston engines, but with just two moving parts (and no valves to fail, timing chains, and other fiddly bits).