Beautiful modern rotary at a non-so-amazing price! 3

[RodRico]

I ran across this beauty when searching for "modern rotary engine." It's specs are pretty darned close to the very popular Rotax 912/914 series engines used in light civil aviation applications: 2.8L, 110 HP @ 2450 RPM (implied 236 lb-ft torque), 220 LB dry weight, 31" diameter (

https://www.rotecaerosport.com/r2800).

The $2,250 price is amazing and must be close to the cost of manufacture.

EDIT: As VE1BLL notes, $2250 is the down payment on the $22,500 total price. Duh.

A motorcycle using one of these engines would be a fun project! If nothing else, it would sound awesome (hear it at

https://www.youtube.com/watch?v=pm3WpZ7DF78)!

EDIT: It's been done, and makes it clear why Harley Davidson elected to use only two cylinders.

In case anyone is wondering, my own engine (a form of rotating cylinder radial) would have roughly the same specifications, but would have a diameter about 33% smaller, have lower emissions, and use a lot less fuel. Mine, however would not be nearly so beautiful to the eyes and ears. It's hard to beat the traditional rotary for looks and sound!

 

[VEBill]

Re: "The $2,250 price is amazing and must be close to the cost of manufacture."

The 10% Deposit is $2,250.

"FULL PRICE - $22,500"

 

[RodRico]

VE1BLL,

LOL! That price makes a lot more sense; it's close to the price of the Rotax.

I can't believe I missed that!

Rod

 

[PJGD]

If you hankered after a radial with a touch more power, you could always consider:

http://www.clearenergysystems.com/arc_technology.html

PJGD

 

[berkshire]

Pjgd,
The Achilles heel of most radial engines when mounted with the crank shaft horizontal, has been oil collecting in the bottom cylinders. How does this design address this problem ?
B.E.

You are judged not by what you know, but by what you can do.

 

[enginesrus]

So where is the picture of the rotary?

 

[GregLocock]

Depends on your frame of reference. He meant radial.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[RodRico]

enginesrus,

Sorry, I searched for "modern rotary engine" and found the Rotec picture in the results, but it's not a rotary, it's a radial as Greg notes. To be called a rotary, the cylinders must rotate around a stationary central shaft like the old WWI era rotary shown below from Wikipedia's article for "rotary engine" (see

https://en.wikipedia.org/wiki/Rotary_engine

and

https://www.britannica.com/technology/rotary-engine

agrees).

Rod

 

[dgallup]

Yes and a rotary engine makes a really bad motorcycle. I think the Megola was the only one ever produced. Can you imagine the unsprung weight and amount of gyroscopic precession?

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[RodRico]

dgallup,

Indeed. I worried about precession in regards my own engine design (a rotating-cylinder radial rotary) until I compared the mass of my rotor to the combined weight of crankshaft balancers and flywheels in a "normal" engine. I do worry a bit about precession in large versions of my engine, but my target is aviation (where large rotary radials have been successfully employed in the past), and I'm open to using pairs of counter-rotating rotors in those engines if need be. Note, by the way, that my estimated power to weight ratio is between that of a Wankel and a traditional four-stroke (I won't make any solid claims as to actual power-to-weight ratio (or efficiency) until I complete prototype test and a few rounds of optimization).

Rod

 

[VEBill]

compared the mass

Presumably you also included the geometry as well, since rotational inertia (and such) includes consideration of the radius value.

A rotary engine of the spinning heads variety kinda maximizes the mass distribution radius.

 

[dgallup]

If the Megola had the engine mounted to the frame I don't think the precession would matter that much since it's probably pretty low revving but in the front wheel that thing must have been pretty near impossible to turn at speed. Probably it didn't go all that fast. The complete lack of a clutch might have been a much bigger problem.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[RodRico]

VE1BLL,

Yes. It's the radius of the larger engines that causes me concern with precession. My engine doesn't have heads as it's an opposed piston two-stroke with a scavenge piston, and the weight is distributed more toward the center than the outside radius. The engine is quite compact; a 250cc version would have a total diameter of 9.088" with thickness of 4.800" containing a rotor of 8.682" diameter and thickness of 3.686." These dimensions include everything (air filter, fuel and oil pump, radiator fan, radiator, fuel injectors) except a starter/generator, control computer, and fuel/oil tanks.

Rod

 

[enginesrus]

In the old days the radial rotary was designed mainly for cooling I think. They didn't think of or understand shrouding or ducting in those days I guess. I can not see any logic in designing any engine that would mimic that design in any form or fashion. With all the various systems, lubrication the main one, and then of course the fuel management system, and connection of various transducers / sensors, why would you want to deal with high centrifugal forces on something that is so totally unnecessary? Also on a said rotary mounting a propeller and mounting the engine, or mounting shafting to the rotating engine, just all seems so back wards. If your design is like the old aircraft rotary I'd drop that idea quick. It will be a hard sell, maybe its a nice little demonstration item that is to look at and not be used . No one will want a spinning engine in a drone. If it is set back into the fuselage then it will need a heavy shaft to drive a prop, and what ever mounting hardware is used, as well as the mount to the stationary portion. If it runs like you think I'd just make it like any other normal engine, with a power output shaft. If I was the person you where trying to sell the spinning engine too, I'd just laugh and show you the door. When you originally won or showed your design did everyone know it was to be a spinning engine? When I saw rotary in the beginning I just thought it was how you described the internal workings. And I bet so did everyone else.

 

[RodRico]

enginesrus,

I assure you there's good reason to pursue my approach, and my experienced engine design consultant agrees.

I only yesterday switched from a 50cc prototype design to a 122cc prototype design for a variety of reasons (all engine sizes are dimensioned using my Excel model and the designs are parameterized in Solidworks, so it's not a large disruption at this point in the process). Analysis indicates the 122cc prototype will have 8.85" diameter with 3.5" thickness. It has a 26.6:1 compression ratio at sea level (higher at altitude, but intake mass is conserved via manifold pressure regulation) and should have 66% theoretical thermal efficiency (brake efficiency will be much lower). This performance is attained with lean combustion temperatures below 2150K which means it does not produce soot or NOx emissions.

Lubrication and cooling are not issues. I run oil into the rotor near the center, route it around the cylinder walls, tap some off of specific surfaces, then pass it to radiators in the rotor periphery before passing it out of the rotor (note the oil pump is centrifugal, and that eliminates a key accessory). Air passing over the radiator in the periphery of the rotor is from a centrifugal fan incorporated into the rotor, and I use variable inlet control to maintain oil temperature.

The prototype will produce theoretical power of 6.7 HP and 13.4 lb-ft torque at 2,626 RPM in a 126 cubic inch volume. The Honda GXR120 engine (

http://engines.honda.com/models/model-detail/gxr120)

produces 3.6 HP at 3,600 RPM and 4.2 lb-ft torque at 2,500 RPM in 334 cubic inches (roughly adjusted to remove fuel tank, air filter, starter, etc.). Thus, my theoretical performance relative to the Honda engine is 1.9x better in HP and 3.2x better in torque as well as a 2.6x advantage in volume. The HP and torque figures give me a lot of room to accommodate heat loss, friction, etc. and even if I only *meet* Honda's performance, I still have a 2.6x advantage in volume and associated weight.

If you don't think this design is worth pursuing to prototype test, you either think you know engines and markets better than Honda or you're just trolling me. I may yet fail for a variety of reasons, but it's worth pursuing.

Rod

P.S. I'm not selling my engine design to your or anyone else until I complete prototype testing and have test rigs available for use of 3rd party reviewers. This is required because I'm breaking many "rules of thumb" such as those that seem to guide your thinking. The only way to overcome the skepticism of reviewers and potential investors is to prove it works before pitching it, so that's what I'm planning.

 

[enginesrus]

Yes lets all wait till its running agreed. Its just funny how the term trolling has to come up when someone is trying to get some point across that some just don't like to hear, I guess its an internet thing. So I'll stop here, but I do want to see and hear how it goes when you have a running example. And believe it or not I'm supportive on what you are trying to accomplish, I just see it simpler to do it in the normal fashion rather than go back in time.

 

[RodRico]

enginesrus,

Forgive me if I have mislabeled your comment as "trolling." I use the word to describe non-constructive negativism in social media responses. Our social media society seems to have forgotten the difference between constructive criticism and plain old criticism as well as the once valued behavior of keeping the later to ourselves. I suppose I'm more sensitive to criticism than I should be.

In any case, I hope I have provided the logic you were looking for when you said "I can not see any logic in designing any engine that would mimic that design in any form or fashion." It may not be logic you agree with, but it's logic nonetheless.

Rod

 

[enginesrus]

I just hope you keep us all posted on the progress and how things are working out as you move on with your project.

 

[itsmoked]

Fascinating Rod, I wish you success.

Do you have to machine everything or are you able to use OTS pistons, or cylinders, etc.?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[RodRico]

enginesrus,

I will keep you posted as to progress and results whether positive or negative.

itsmoked,

Thanks. I will be making nearly everything other than bearings, seals, and misc hardware myself at first, both for the fun and the savings. If I fail in my fabrication efforts, I will send it out. I may also have to send some work such as the cam grinding just because it's so hard to do. Note, by the way, that I'm working to reduce the amount of machining required and am focused on centrifugal investment casting instead. I'm going to 3D print the parts, clean the models up on a desktop mill (DSLS 3000), then cast the parts and do only minor cleanup of the metal component after it's cast.

Rod