i would like you to shed light on those materials, and why there are better, since i fully agree that reliabilty is the biggest issue with a factory rotary

 

Well I know tititinum dosent do as well as softer materials like iron when it comes to rapid cooling and heating, that's why it's kept away from those situtations. As far as Inconel I've never heard of that metal.

 

there are so many metal alloys i mean, why isnt there a clear answer, what about chromoly, and kryponite, or some combo of all these metals

 

True but there are certin requriements that the metal alloys need to stand up to and that in it's self eliminates alot of the metals. Price is also a consideration that needs to be kept in mind. The more exotic the more expensive.

Then after all of that R&D needs to be done that that takes more time and money.

 

Well, one of the ones I've been focusing on are Al-SiC metal matrix composites... silicon carbide particles embedded in aluminum. Honestly, some aluminum alloys would probably work, but Al-SiC has some neat properties. For a minimal gain in density compared to plain aluminum, the Al-SiC composites have a lot lower thermal expansion, are stiffer, stronger, more wear resistant and don't conduct heat as well. In fact, at the higher densities, the mechanical properties look a hell of a lot like cast iron, but the density's about 40% that of iron (2.7-2.9 gm/cc vs. a bit over 7gm/cc) Oh, and it's castable. Only downside is because of the SiC particles, tooling for machining the slots has to be diamond coated, but with investment casting, the things can be gotten pretty close to final dimensions.

Going for high RPM usage with no budget limits, I'd go with a billet multi-part e-shaft, adding not only a bearing in the center housing (a journal bearing, not needle) but a double sided stationary gear, and obviously modifying the rotor castings to have a ring gear on each side.

... that just leaves the very interesting question of how to get it to breathe at high enough RPMs to make use of all that.

 

I like your thinking, I'm an aspiring engineer at Cal poly Pomona, are you an engineer or in a related field. It seems like you have "that" engineering mentality. I know what a needle bearing is but remind me what a journal bearing is? You think this should be added to help reduce the flex? If so you dont think a ring gear on each side would be sufficent?

 

Yeah, I'm *cough* almost a mechanical engineer... senior, and looking at gradschool for automotive specific stuff. One of those freaks that studies stuff related to their major instead of having a social life.

Journal bearings are plain, or hydrodynamic bearings... the ones that you pump oil into. Needle bearings have a tendency to start just sliding instead of rolling at high RPM, which is why they're not used in engines much. And yeah, by putting a bearing in the middle, it's just that much more support. The stationary gears don't do anything to locate the shaft on their own, but they do make the rotor move the right way... I figure that at sufficiently high RPM, it wouldn't hurt anything to spread the load. Plus, this means the rotor's loaded evenly at both sides, so that much less tendency to misalign.

Pretty much overkill, since I don't know how you'd make power at a high enough RPM to need all of that ****... but at least you could run it at lower RPMs with confidence that nothing is going to break.

 

yea man mechanical engineering is a good field, I wanted to minor in it but there is no real mechanical minor. I'm an EE with a minor in energy, I'm trying to take as many mechanical based classes in the engery field as possible. I like the EE stuff more and understand it better but I'd like to be able to design or redesign an engine from the ground up. The electronic side is not a big probem it's the mechanical side and that damn thermo.

You probaly have seen my Project Rotary site already the link is below, just click on the picture. Anyway I have a pathetic forum section, not that I dont have anything to talk about, but I want the majority of it to be quality discussion, like the one we just had. If I started a discussion on the topic we just had are you down to add to the discussion?

 

KENKO, I do agree with your thoughts on lite weight material rotors ,I think all of us would benefit in the future of these projects. what im saying is the two main parts of a rotary are rotors and e-shaft, now a real hi-performance engine of any kind wouldnt be using old worn out flexed to death internal parts, so Im saying 1st a much stiffer (he-he) shaft, a proper material forging would absorb flex better than a billet of the same material, but 8620 in billet may be OK. without going so far as a two pc. shaft with a center brg. and double ring gears. I didnt mean that inconel or titanium was answer to it all ethier. and of course the cost of R&D would have to be looked at. I am simply saying 2 components,, e-shaft and lite rotors would sure help in looking at the future of rotarys. thanks RON

 

Interestingly enough, according to the Yamamoto book, the stock e-shafts are forged chromoly... though they don't say what alloy. But look at the things; they're quite blatantly forgings. But... y'know, Ferrari is using (or at least in 2000 when the book was published) billet cranks in their F-1 motors. Don't recall which alloy though, but it was something relatively sane. Point is, on something loaded like an e-shaft, the grain properties you can get by forging doesn't seem worth the trouble.

Anyway, I'm at a loss to how you propose to stiffen the eccentric shaft enough by changing the material properties (at least to anything reasonable) which is why I'm proposing to reduce flex by adding more supports to the thing and balancing out the forces acting on the rotors moreso. means sure, make it out of 4340 as long as you're at it, but I doubt that'll fix it on its own.

 

KENKO you said earlier about the hydrodynamics of lubing the bearings, can you imagine what they go thru when the shaft bends out of shape, hi spots low spots ruin the princple of the hydralic wedge, you could run much tighter clearences, if you can keep the shaft from fexing so much , and keep everything in better alignment, have you givin thought to what the seals,apex and side seals go thru with the rotor thrashing about trying to stay straight, im sure they are not at peak efficency! and do the shafts get softer and more flexable after 10-15 yrs.of use. the factory made them somewhat flexable so as not to crack or break over a long period of time, anyway we could go on forever , like I said just trying to look ahead, also looks like someone some day might make 1000hp on a 13b, has anyone ever run a load of nitromethane thru one yet! YEH it will take a tuff motor for sure your friend RON

 

I think all of this is being blown out of proportion. For one I work for a company that makes titanium components of Pro-Stock drag racing. Every Titanium alloy I have seen is soft and disappates heat extremely fast. I don' t know how well compared to aluminum but compared to iron as mentioned before it is extremely soft, dissapates heat fast, and parts made out of titanium wear out extremely quick unless they are well engineered and coated. Most of your hard titanium substances are not the typical Ti-Al alloys you would make parts out of, Titanium Nitride is a coating that is extremely hard but titanium itself is soft. Almost all of our valve stems are moly coated because of these factors. Mind you I'm not talking about the practicality of using titanium for rotors just the properties. The titanium alloy we use to make our valves and other components is in the range of $22 an inch of 1.5" diameter bar. The cost of one rotor made out of titanium would be astronimical.

Chromoly is extremly strong but it is also extremely brittle. It is going to be much more rigid but also is extremly brittle.

Also consider what other racing series use. NASCAR for one, they mostly use billet cranks with "honda bearings." Not that they are actually honda bearings but they are about that size which is like 2 or 2.1". My mazda pickup has bearings larger then what they are using. These engines are putting out 800+ hp and some of the developers here in town are hitting 10,000+ rpm non have hit the track at that kind of rpm but they are holding a good 9,000. Once you start considering that the crank is pysically longer then an E-shaft, NASCAR says it must be made out of a magnetic material to keep them from spending a fortune on something exotic and it is dealing with thousands of pounds of recipricating force per piston that is comming to a complete stop 2 times per stroke?

I think if an engine was built like what was being discussed in a way to prevent flexing and have tight clearances it would hold just fine. Last week I was up at Rotor Sports Racing and he claimed to have an engine that would do 12k rpm. Of course it was strictly a race engine and it costed like $16000 for the engine alone. He claimed he was running the 2 piece E-shaft with tight tolerances, ceramic seals, and I think he side a huge bridge port although I might be mistaken on the port details. He would not discuss anything else about it. I didn't see a dyno sheet so I think at most it might have been making power up to 9 or 10k an although ran up to 12k I don't think it was making enough power to be worth the extra rpm but thats just what he told me and what I think.

 

E-shaft breakage is a non issue.

No, they actually *are* Honda production bearings. At least, that what the engine builder I was talking to told me. He said that Honda has a proprietary coating on their bearings that is like a microscopic diamond-like (or maybe pyramid-like) shape, that does a wonderful job of keeping the oil on the bearing, which is one of the reasons why Honda production engines can run such extremely tight clearances. Scuff the surface of the bearing while cleaning and you pretty much ruin it and turn it into a standard type bearing...

 

[QUOTE=... that just leaves the very interesting question of how to get it to breathe at high enough RPMs to make use of all that.[/QUOTE]

Trust me that's the easy part!

 

[QUOTE=crispeed]I'll take your word for it, for now. I'm just wondering how high a range you could tune for before you had a powerband that looked like a 1000rpm wide spike... or alternatively, how high a powerband before you run out of material to port out.

 

No, they actually *are* Honda production bearings. At least, that what the engine builder I was talking to told me. He said that Honda has a proprietary coating on their bearings that is like a microscopic diamond-like (or maybe pyramid-like) shape, that does a wonderful job of keeping the oil on the bearing, which is one of the reasons why Honda production engines can run such extremely tight clearances. Scuff the surface of the bearing while cleaning and you pretty much ruin it and turn it into a standard type bearing...[/QUOTE]

The team or engine manufacturer has the choice of using whatever bearing they like. The ones my intructor at school used on bush series engines where Clevitte and had a very similar coating. He said if need be you could lightly burnish the surface with some 1000+ grit sandpaper but really it was unessisary. But enough with piston engines, lol.

I think the 12,000 rotary issue is mainly just money and practicality for what you want to use it for.

 

To get the power band of a motor that is capable of running those rpm's you would have to have a variable length intake system. The runner lengths will make or break a motor that is capable of achieving those rpm's. Also you would want to use an interesting technique that the renisis motor uses; a pressurized airstream that is on the outside 'corners' of the intake runners, thus enabling the air to enter the chambers. (kinda like a bearing for the air).

I also imagine you'd want to incorperate a airflow deflector on the intake runners, much like what the exhaust port has on the N/A motor. Good piston engines utilize a swirl in the combustion chamber to encourage fuel atomization, and I'd imagine that a similar effect would work on the rotary. I believe a double swirl would work best, as theres a port on either side of the rotor. (much like the vortex flow pattern from the Concord's wings.) Should aid in the power production as more fuel n air will be atomized upon entry.

My thoughts of the motor being able to support the rpm's.. well, i've heard that the first thing to break on a rotart is the stationary gear (which may deform?). I'm sure that adding another gear to the equation will help the rotor stay on track, as i'd imagine the rotor would be fighting alot of lateral forces to keep the side that doesnt have a stationary gear. I know the e-shaft would prevent this to some extent, but think about it- there would be an uneven load on the bearings between the rotor and the eshaft.

Anyways, I'm new to the rotary motor, but am trying my best to learn about it, and to incorperate it with some of my other concept motor ideas. Also- I too am an mechanical engineering student in training...

 

Oh ya- while I'm on the topic- What if the rotor's were the same weight, but more of the weight was located towards the center. I'm not sure of all the variables, but shouldnt the rotors only have to hold force from the surface (face between the apex seals) and the bearing? Actually- looking at a cutaway pic of the rotor.. guess not much else can be removed... oh well

Does anyone have any thoughts as the rotor's shape? Perhaps if there was more of a concave feature on the rotor's main faces? It would allow more air to be used, and would alter overall timing. Considering the forces, the rotor would have to be heavily reenforced to hold a concave shape as opposed to a convex sufcace. Wouldnt the shape of the rotor possibly aid in the evacuation of exhaust gases, and induction of fresh air n fuel?

-sorry for hijacking the thread.. seems like its now a engineers playground...

 

grr.. forgot about overall compression... so much for altering the rotor to have a convex surface... guess one thing to update is preventing exhaust to travel into the intake chamber during its transition. I know the Rx8 does this with some rather interesting rotor placement.

 

Wrong Thread , delete please!