2ndgenrx

I was just wondering what are some of the advantages and disadvantages of having a rotary engine, and why they are better than piston engines.

Evil Aviator

Rotary advantage:
Flatter power band
Power to weight ratio
Size to weight ratio
Displacement to weight ratio
Fewer moving parts
More receptive to alternate fuels
Unique

Piston advantage:
More maintenance and performance support
Inexpensive rebuild
Brake specific fuel consumption (gas mileage)
Torque

Ryde _Or_Die

Higher revving engine than most piston engines(and less chance of something breaking when doing it).

milkman2k52

Rotary advantage
no valvetrain = less parasitic loss

disadvantage
higher exhaust gas temps

I know those are pretty weak but its all i could think of that hasnt been said yet.

E6KT2

Well, that is still Advantage:Rotary

You can't gear more power, but you can gear for more torque. Problem solved.

lowpro

A rotory fires twice as much as a 4 stroke
revolves in one direction. piston engines change once per revolution
low vibration
no timing chain
ect...

robbys rex

NO VALVES TO ADJUST

twint78

flattter power band my ***.rotary has the peakiest band ever.a v8 has the flattest ive ever seen

Node

iTrader: (1)

linear power band
I've seen a streetported carbed 13b in a RX-5 pull 150rwhp, 100lb/torque
and you wouldve thought the hp curve was a ******* escalator.
The big ports and 6th ports have the peaky curves

DELTA_Rotary

A rotary is a 4 stroke.

REVHED

Nope, a more accurate way to describe it is that it's a 4-cycle 2-stroke. It has the 4 distinct phases of the Otto cycle but the same number of combustion events per revolution as a 2-stroke.

madaz07

Since they have no valves to open and close the torque curve is flater if that what was ment

DELTA_Rotary

*cough*

and I quote...."Rotary engines use the four-stroke combustion cycle, which is the same cycle that four-stroke piston engines use." And there is 3 combustion strokes per revolution not 2.


http://www.howstuffworks.com/rotary-engine4.htm

REVHED

LOL... 3 combustion strokes? Yes, in one complete revolution of a rotor but in one revolution of the eccentric shaft there are two combustion events. Again, it's a 4 cycle engine that works at the same rate as a 2-stroke. ie, 4-cycle 2-stroke.

Jeff20B

iTrader: (13)

So then it's a 3 stroke! blah blah blah.

I think what he wanted to know was more about performance issues, not all this **** stroke BS. Strokes are for old people and piston engines. Cycles are for people who like two wheels (RE5) and rotary engines.

Evil Aviator

Yes, that does flatten out the curve some, but that's not what was meant. As far as street engines are concerned, the rotary engine generally produces a high percentage of useable power throughout a larger rpm band than a piston engine of the same peak hp rating. The downside is that the piston engine has more torque (ie low-end power) than a rotary of the same peak hp rating. This is why rotary-powered sportscars were more successful than rotary-powered pickup trucks.

No, a 2-rotor engine has 2 combustion strokes per revolution. Don't forget that there is a 1:3 ratio on the eccentric shaft, so 6 rotor faces / 3 = 2.

The rotary is a 4-cycle, 5-event internal combustion engine. IMO there are no "strokes", but this can be debated.

From "Aircraft Powerplants", 6ed, Kroes, Wild, Bent, McKinley (The standard textbook for basic engine theory at the world's leading aviation university):
Stroke - The distance traveled by a piston from the top to the bottom of its stroke.

From "Auto Math Handbook", John Lawlor (A common textbook for high school auto shop courses):
Stroke - the distance the piston travels downward or upward in the cylinder.

Show me the distance traveled by a piston in the rotary engine, and then I will agree that it has a stroke.

DELTA_Rotary

I guess we should just say spins instead

momo11

how many nacho's are in a rotar engine?

Snrub

iTrader: (1)

Uh oh anality time: The rotor bobs up and down in the triochiodal (sp?!?!?!) chamber. Must be a 1 stroke.

Frankly I don't get the constant debates over "what type of engine is it?" It was settled in the 60's by the Ausi equivilent of the SAE.

cmartinp28

if its a 13b then 2 nachos....... if its a 20b then 3 nachos......... r26b then it has 4 nachos

Node

iTrader: (1)

You're making me hungry. Anyone have any cheese dip?

Evil Aviator

How about some hummus and pita? Sorry, I'm all out of tabouli.

Jeff20B

iTrader: (13)

So you're saying a 20B in a pickup truck would have been better than a heavy flywheel on a 13B in the same pickup truck? That's a project on my to-do list.

I've got some Mt Dew, cheese dip and some rotors. Mmm! That would be antifreeze, grease and disk brakes with a few 12A rotors on the side. Anyone want some chocolate syrup and moles'asses?

KevinK2

Well, selected definitions specific to piston engines are not very helpful. The rotary stroke is just not a simple strait line.

The stroke of a piston engine can be described as the motion of the piston face, relative to the chamber in the head, and is alwayes defined as 2 x e. The main use of this 'stroke' variable is in determining the engine displacement, which for ea piston is:

(projected sealed piston area) x 2 x e

A similar 'effective' stroke exists in a wankel, regarding the motion of the rotor face relative to the expanding dynamic housing surface. Just like with pistons, it is this motion that drives the 'crank', and just like with pistons, it produces little/no power at the beginning and end of the stroke, where the eccentric or crank offers no moment arm.

Each rotor face displaced volume is equal to:

5.2 x e x R x width, where R is dist from rotor center to apex seal contact with hsg.

As it turns out, this is also equal to:

1.5 x (face projected area) x 2 x e.

No coinsidence in that the stroke occurs during 3/4 crank/eccentric rev, vs 1/2 rev for piston eng (1.5 x).

The effective wankel stroke is 3 x e, as compared with 2 x e for the piston engine. The rotor face does a great job of chasing the eccentric offset, but it does take 3 crank revs to do it.

Red Rotary Rocket

If you're interested, here is what the power curve for the new Renesis engine is supposed to look like...not very peaky at all...