flyrotary@lancaironline.net Mailing List Archive

I am about theorized out for evening, but it has been an enlightening and simulating discussion. Certainly, it appears that the rotary appears as many different things depending on the viewpoint and analytical approach. I -for one think- that the rotary doesn't care about an individuals chosen perspective but will keep on being our favorite engine regardless of arguments over the angels on the head of the pin.

However, I also believe to develop any new insights, you need to try a different perspective and I know Monty has a project that he will unveil at Shady Bend for the first time. His project undoubtedly is based on Monty's perspective of a certain aspect of the rotary. So the results will be his first evidence of success (or not) to him as to the rest of us. Looking forward to it. Now if my gear leg would just get here.

'Nite All

----- Original Message -----

From: Monty Roberts

To: Rotary motors in aircraft

Sent: Monday, October 17, 2005 11:27 PM

Subject: [FlyRotary] flyrotary Displacement

Okay this one is for David, Ed, Bob and Ken because they are actually having an adult discussion with me on this. Unlike the Pope. For everybody else, If this hurts your head (it is beginning to hurt mine) just skip down to the last few paragraphs.

I am looking at this from a thermo standpoint as a mechanical engineer. If I were going to analyze this and make the numbers work theoretically. You have to break this down to it's smallest component.

To do this you follow one INDIVIDUAL induction, compression, expansion cycle from beginning to end. It does not matter what kind of hardware we are looking at.

When I look at a single cylinder 4 cycle engine. It takes two complete crank revolutions to complete this cycle on some displacement of air.

I draw a PV diagram for this and get the work required to induct, compress, expand and exhaust. Some of these terms are negative, some are positive. The balance is the work output for this ONE cycle and individual cylinder.

For a multi cylinder engine, these work outputs are all just added together at different phase angles based on the crank throws.

Now for the wankel:

It takes one complete revolution of the ROTOR to complete a cycle for a single rotor face (same charge) and perform the previous analysis. The eshaft will rotate 3 times for each rotor rev..

The additional rotor faces are just like additional cylinders added on to a single cylinder engine. The mechanism for extracting power is a bit more arcane but it is the same thing. Stick on another rotor 180 degrees out of phase and it is the same thing. 3 more cylinders.

So you are correct the 3.9L 6 cyl equivalent engine will rotate at 2/3 the wankel speed not 1/3 as I misstated. And that matches with practice, a well tuned 240 cubic inch 4 cycle multi cylinder engine spinning at 6000 rpm (8500*2/3) is capable of making around 240 hp. Likewise the Wankel makes the same kind of power at 8500 shaft rpm. with the same number of cycles performed on the same amount of air charges as a 6 cyl engine for a given amount of time.

Likewise, keeping the rpm the same: a 2.6 liter 4 cylinder at 8500 rpm can make 240 hp. Or how about a two cylinder 1.3 liter 2 cycle, or a .65 one cycle.

Your argument of one packet in one packet out only works from a black box standpoint, you cannot analyze what happens in the black box using this approach. You could pick any combination of rpm, cylinders, and cylinder volume that gives the same number of events per unit time on the same mass flow and say it was an equivalent engine. So you are also correct that you could have any number of rotor faces and get the same result (there actually are such engines in theory using the same math as the wankel with different ratios of gearing and rotor faces)

The statement about not understanding pretend RPM is correct. It is not revolutions per unit time that matter, or mass flow per unit time, but volumetric and pressure changes on each packet per unit time.

To have thermodynamic equivalence, the engine must be doing the same thing to the working fluid per packet per time. If you do this you can actually integrate the rate of change of volume per unit time and see how the Otto process is performed in the rotary vs the crank and piston engine. Varying rates of compression/expansion at different times lead to different efficiencies and cylinder/chamber pressures-ie stroke to rod ratio.

I have changed my mind- it is now a .325L half cycle engine.

I'm all spent on this subject. Call it whatever you want as long as it gets the desired result.

What is really important to all of us is to figure out what the heck to do with the damnable packets after they are (vigorously!!!) expelled using your equivalent cycle of choice. OR-how to make the stupid thing sound more like a Merlin and less like the model airplane from hell with something less than a 30 lb boat anchor or the size of a 30 gal drum.

That is what I am working on now. I have little hope for the outcome. I will however bare all at Tracy's in full view of the public, you can witness my triumph, failure, or puzzled looks.

Monty