tinvestor

Really? The amount of rotating mass has nothing to do with torque? then why when you buy a lightened flywheel are you told that it will have an adverse affect on torque?

RXBeetle

Awee crap the old Hp vs. Tq. arguement.
HP can be defined as the ability to move 550 lb. one foot in one second.
Now if i have an engine with a pully on it with a rope and a weight at the end and another identical setup with a HUGE flywheel on the engine the flywheel will cost HP and slow acceleration of the weight.
Now if I put a 10,000lb. 200' flywheel on my torque wrench... and 100ft./lb. is still 100ft./lb. of torque.
A lightened flywheel does not have as much stored inertial energy (hp) as a full weight flywheel. But that is only because you haven't "spent" that hp to spin the heavy flywheel up. Who says you will get less torque from a lightened flywheel?

Valkyrie

Not on torque, on drivability.

The lighter flywheel will lose RPMs much faster, which means you're going to engine brake more (harder to cruise), and it'll be a bit harder to start (more stalls).

And the difference between a 3-pound stock rotor and a 2-pound aluminum one, compared to a stock 30-pound flywheel and a 12-pound aftermarket one is a very small one. The flywheel will have a much, much bigger effect.

Kenku

9.5-11.5lbs per rotor actually, but yeah a flywheel will still do more for rotating inertia. I'm concerned more with making the internals live at higher RPMs more reliably.

drago86

Because you ask on internet forums where (some) people have no concept of what torque is of course. Rotating mass has nothing to do with the torque output of the motor.

drago86

The only real (big) advantage of lighter rotors would be the ability to reach stupid high rpms. 3 pound rotors would increase the redline to something insane due to reduction in crank flex. If you used aluminum rotors and an e-shaft with a center bearing you could probably surpass formula one engine speeds by a considerable amount.

Kenku

Dunno about that... would be interesting to find out for sure though. Might as well go with a central stationary gear too, in order to have the rotors evenly loaded on both sides.

... while I'm dreaming of expensive things, I'd like a 792P too.

peejay

Redline would still be limited by bearings and seal longevity. Even carbon seals will have a limit to how much abuse they can take.

Mainly, though, I severely doubt 3 pound rotors. Note that aluminum racing wheels do not weigh 1/3rd of steel racing wheels, they are only a couple pounds different size for size.

tinvestor

This is a discussion about finding a material that can be substituted for steel not weight for weight but shape for shape. aluminum rims are thicker than steel to give the same strength. So if you could produce an alloy that has a similar strength to steel with half the weight, the rotors could weigh 4 pounds.

The thread title was a ploy to attract interest.

The bearing issue can be overcome using higher oil pressure, synthetic oil, cryo treated and impregnated bearings and side seals, with an addition center housing "guru" style E-shaft

Life? who cares this about sick RPMs high power/performance engine that will last 1000 miles on the optimistic side

Falcoms

The truth is that running a 3 rotor at upwards of 20,000 RPM would be possible if the internals were light enough, but the down side would be that survivability would not exist without running stationary gears on both sides of the rotor to prevent horizontal wobble (I belive that somebody already mentioned this). Running the guru style e-shaft with the center bearing would only last so long becuase it's a caged needle bearing and it would be limited to the heat handling ability of the cage. The next problem that you would have is that to run the engine at these high RPM's, you would have to flow so much air and fuel that you wouldn't have ANY torque below 8 grand becuase the only way that this would work is with a full bridgeport, peripheral port, or a sick combination of the 2, as well as a big *** turbocharger.

The main purpose for turbocharging the application is that it will alow less air flow at lower revs, and therefore more torque to build, but above 9 or 10 grand the turbo would take over and would give you your top end rev's.

Also, as per the apex seal wear abilities, if you run ceramic coated housing and side plates, as well as ceramic apex seals, the coefficient of friction would be nearly zero due to the fact that ceramic on ceramic creates the lowest ammount of measurable friction between 2 surfaces known to man thus far (hence why Porsche's with ceramic disks have warnings EVERYWHERE about not running ceramic disks).

Overall, I belive that the cost would be so damn astronomical to build an engine (probably $150,000 for a 3 rotor because of the high costs of tooling), that nobody, even factory funded pro race teams, would touch it. The only way this would work is if Mazda decided to build it for there production cars, and even then the profit margin for R&D alone would be so low that I don't think that it'd go through.

peejay

Any time someone mentions cryogenics as an answer to a simple yet fundamental problem, my "pie in the sky non-engineer dreamer" meter goes off the scale. How will cryogenics help lubrication and bearing stability?

One quote I have is that on an engine that had an 11k redline, engine life was six *hours* before the carbon seals were shot. (Before you mention ceramic seals and the oh so ******* holy 787B, note that at LeMans they had an 8000rpm redline with 9000rpm permissible "for emergencies", meaning they were KEEPING THE REVS DOWN)

That's "only" 11k. Note that the same seals in a street engine can be expected to last over 100,000 hours.

Clearly, it's a non linear, so how many MINUTES will they last at a 14k shiftpoint?

Kenku

Well, castable aluminum alloys vs. steel is one thing... but cast iron is far from steel. *shrug* LIS, from not-completely-rigorous research, Duralcan-type MMCs have numbers that suggest a 1:1 swap, volume-wise. In theory. Even there though, still 4 pounds per rotor (okay, maybe a little bit less if you plan on investment castings only and use that to optimize the things) In theory.

Seals? Can't fault peejay's skepticism... I'm taking more of a "damned if I know / wouldn't it be fun to find out?" stance. I mean, there's the redlines that people are claiming with the Guru shafts, but that's about it for what I've heard in that range. And... okay, I realize it's the typical thing of people being reluctant to talk in detail about competitive engine/whatever packages, but I've personally never seen proof. I don't live in Austrailia either though, so who knows?

Speaking of them, I still wonder why they decided to use needle bearings instead of another journal bearing in the center. Journal bearings just plain work.

Anyway, I'll be frankly astonished if anyone posting in this thread (not including me, of course, because I are teh geenious. ) goes to the trouble of experimentally finding these things out, so it's kind of a moot point. A fun point to think about, though.

Valkyrie

If you're gonna rev an engine to F1 speeds, you would only expect the engine to last long enough to finish a Gran Prix race anyway (ie, 1-2 hours) :p

Also, consider that F1 engines have very short strokes, and a lot of pistons for their displacement. If you were gonna make a Gran Prix rotary engine, you'd probably have to make a four-rotor with very narrow rotors to prevent shaft flex.

Also, wouldn't having some sort of bushing or bearing in the rotor housings help shaft flex? Yes, I realize it would make the engine MUCH harder to put together...

tinvestor

Valkyrie check this link it is for the "guru" three piece (he calls it two but whatever must not be counting the center housing bearing)

http://www.xtremerotaries.com/main2/guru.htm

Falcoms I always wondered about why he chose needle bearings (less friction?) but I dont think it would be too hard to change that to a journal bearing.

Peejay cryo treating (correct me if I am wrong oh god of engineering) realigns the structure of the given object this helps with both strength and a more even heat distribution. The lightened rotors coupled with a larger bearing surface (guru stle center bearing E-shaft) = much less stress on each bearing than stock at stock RPM. We are talking about higher than stock RPM so obviously the stresses increase in a non linear way however this still leaves plenty of room for higher (above stock) RPM's

People also seem to be forgetting that the concept of reducing rotating mass in the engine has more than 1 effect, allowing for higher RPM operation. The other is that if you use less power to turn the engine there is more available for turning the wheels.

Back in the 40's just before jets became a useable engine for comercial airlines, an engine was developed that very few have ever heard of because it was replaced so quickly by the jet. It was used mostly in the DC-9 on the mercedes 18 cylinder engines. The concept was as follows: A turbine collected the exhaust gases using the heat to turn a compressor wheel (nothing unusual so far) and also was used to turn a gear reduction box at 9:1 which ran through a fluid coupling to the crank shaft where it essentialy turned the engine with the heat of the exhaust thereby making ALL of the power from forces of combustion available for use at the propeller this made much longer flights possible (double) on the same amount of feul.

The point is when you reduce the weight of the rotating mass by half (19 pounds of rotors and 44 pounds of clutch and flywheel, 63 pounds total, down to 24 pounds total plus E-shaft and counter weights, when all is said and done it is about half) you have much more power available for moving the vehicle forward.

Let us not forget that when you are only throwing around 8 pounds of rotors not 19 pounds your counterweights do not need to weigh as much either.

Kenku

Oich, where to start.

Cryotreating... is, if anything, an incremental gain. But looking at it for hydrodynamic bearings, which really shouldn't be in contact and wearing anyway is... missing the point. If the bearings are being loaded such that they're in metal to metal contact, they're already as good as failed and no treatment in the world (save adamantium!) is going to save it.

Next, you're being a bit confused... you're talking about turbocompounding, which Mercedes never did in production form. It was used on Wright R-3350 powering the DC-7 and Constellation... the DC-9 is a jet. BSFC was better, but only by about 30%, not double. And that is at altitude... the amount of power recovery that takes place at sea level is far less because the outside air pressure is much higher. But finally... how is that related to anything in this thread at all? I mean, I could harp on about how the Rolls Royce Crecy would have been the worlds greatest aircraft piston engine if it had gotten into production, but I won't.

And as for weight... as was mentioned, rotational inertia has *NO EFFECT* on power output aside from transient conditions. Even ignoring that, reducing the mass of the rotors has very little effect compared to everything else in the system due to the fact that they're turning 1/3rd output shaft speed, and have a relatively small diameter. The MOI of the flywheel/clutch dominates the system, light rotors or not.

rarson

Right, transient conditions. However, those of us without CVT transmissions see transient engine speeds almost constantly. Seriously, how often do you accelerate without changing engine speeds?

Kenku, I respect your opinions a LOT because you are a smart guy. I'm just pointing out that transient engine speeds are a common occurrence, and that I feel any gain from transient engine speeds is a good thing, is it not? I agree with everything else you've said.

Kenku

Enh, granted but... like flywheel weight, it's more a response issue than a power issue. You're never going to see more horsepower on an engine dyno from a lighter flywheel, which is the only setup that actually isolates the performance of the engine from everything else, y'know? If you look at inertia of the spinny bits, then you have all sorts of strange situations.

Say, with a drag oriented setup, you rev it to the moon and dump the clutch. The inertia from the flywheel adds a lot to the torque going into the driveline, but, for round numbers, would you say the engine's putting out an extra 200ft/lbs of torque? I wouldn't; clearly it's coming out of the flywheel's inertia. Is the power absorbed by the various things when the engine's trying to speed up mean the engine's producing less power? If so... then you get into funny things where your wheel/tire combination is affecting your engine's power output.

Nitpicking? Exaggerated examples? Maybe, but if you want to use the numbers for things, the math only works out consistently right if you isolate the various factors.

BLUE TII

iTrader: (9)

Enh, granted but... like flywheel weight, it's more a response issue than a power issue.

It may not raise power, but it does improve performance in a measureable fashion and not just response.

When you ditch the stock 24# TII wheels for 12# Volks and 27# flywheel for 11# flywheel you have lost 36# (only rear driven wheels count) of weight the engine has to accelerate to move the chassis.

You will easily see the improvement in acceleration with a stopwatch. Acceleration is only a transient phenomenon, but it is the one we care about.

With a reduction of "Wanking" weight the redline could be raised and seal technology would catch up to improve seal life. Renisis side ports would help apex seal life as well.

Carbon aluminum seals are so 60s

Ceramics DO hold promise, especially in an NA sideport motor where you can reduce seal thickness and height to reduce weight.

High RPM seal life just hasn't been an issue YET as anything turning 11,000rpm is a race motor and is overhauled so often seals can just be replaced.

Kenku

Okay, yes... but you've still not gained any horsepower. Ah, forget it, not really an important enough point of semantics to argue over, especially given the QM clutch waiting to go on the race car.

Carbon seals are still workable, especially on something overhauled often. I'm pretty sure they're lighter than ceramics as well... worthwhile for a testbed dyno mule anyway.

BLUE TII

iTrader: (9)

Carbon seals are still workable, especially on something overhauled often. I'm pretty sure they're lighter than ceramics as well... worthwhile for a testbed dyno mule anyway.

Sure, but I was thinking if the motor had very little e-shaft flex and no p-ports the apex seals could start to look more like piston rings in cross sectional size- that is where I think ceramic would work better than carbon.

peejay

Are you suggesting that the front wheels are not accelerated at the same given RPM/second rate as the rear wheels?

The front wheels most certainly *do* count, unless you're dyno racing, in which case you might be better off with a couple of posts sticking out of the frame to insert into prepositioned holes in the dyno.

peejay

[QUOTE=BLUE TIISure, but I was thinking if the motor had very little e-shaft flex and no p-ports [/QUOTE]

No peripheral ports? Then what is the point? If you want to make power, you need the mostest and bestest port area you can fit, which means peripheral ports.

Kenku

And possibly bridgeports in addition. I mean, there's only so much metal you can take out of the rotor housings, and you're going to run out of flow on a peripheral at *some* point.

GtoRx7

iTrader: (5)

Aluminum rotors that are half the weight, (4.5 vs. 9lbs est.) would be a drop in rpm enhancement. With less weigh to spin, a center bearing wouldnt even be needed until about 16,000 rpms, where the centrifugal forces are the same as 8,000 rpms in a standard rotor engine. The bearings would have less load until this rpm as well. The biggest problem I see, as already said, would be ports large enough to support that rpm.

Kyrasis6

Ok, I stopped reading posts around the middle of page 3 I think. I think someone mentioned something about silica having a high rate of expansion? Silica is extremely brittle and has a low rate of expansion, that is why hyperutectic (sp?) pistons are advertised to be able to maintain tight clearances for low piston slap, which is about the only good trait they have.

The silica composite material, sure it looks good on paper but I'm sure it lacks enough grain structure unity to be able to withstand the shockwaves of combustion, I would guess yea they would be lighter, thermal expansion would probably be acceptable but when they let go it would probably be like a shrapnel bomb going off.

I'm sure with the many titanium alloys out there titanium could do the job but the cost for one rotor would be astronomical. For alloys probably capable of doing the job 1.5" diameter grade 5 titanium bar is going for like $35 an Inch and I wouldn't trust grade 5 in a rotary engine. American Aerospace grade I'm sure is going for much more than that, I think the CNC shop I worked at that made strictly NHRA valve parts out of titanium was getting 12 foot 1.5" aerospace grade bars for like $2,000 a bar. Just for the material alone you are probably looking at that much each rotor before labor, forging, machining, heat treat, R&D, etc....

There are steel alloys out there that are stronger and lighter then titanium but I cannot speak about that, lol.