Using values to derive the general shape of a rotor

[vex]

Given:

R'=105 mm
e=15mm

Given that information what does the eccentricity dictate? From my experience with eccentricity it should be unit-less, but everything I've seen dictates that it's actually a distance unit for rotors.

How do I use e?

I 'assume' that the R' is the distance from the center of the circle to the edge of the rotor.

Thoughts?

[Mobius]

If someone on this forum actually understands what vex is asking, I will give that person an e-cookie :) Because all i got was:

Given:

R'=105 mm
e=15mm

Given that information what does the _________________? From my experience with __________________________________________________ ______ rotors.

How do I use e? You usually take it as a pill?

I 'assume' __________________________________________________ rotor.

Thoughts?

[josh18_2k]

just measure a rotor and figure it out?

im guessing 105mm is the arc radius of the face, and then the midpoint is offset 15mm (to the inside obviously) to clear the peanut shape. but i dunno, ive never even seen a rotor IRL lol

[vex]

Alright looks like I need to give RCC a refresher course in geometry. More specifically in conic sections.
If someone on this forum actually understands what vex is asking, I will give that person an e-cookie :) Because all i got was:
Eccentricity (e) is the term used to describe a conic section. For instance in the case of a circle e=0. Eccentricity in geometric and orbital understanding is unit-less, thereby the term an eccentricity of 15mm is outside my understanding of the term usage.

Furthermore e is the ratio between c and a, where a is the semi-major axis value or the distance between the center point and the longest edge, and c is a geometric constant which is resulted from the sqrt(a^2-b^2) where b is the semi-minor axis or the distance from the center to the shortest edge.
just measure a rotor and figure it out?
I would, but I don't have one readily available. When I had my engine apart I couldn't take the time to get all the dimensions I need so I am stuck doing things this way.

im guessing 105mm is the arc radius of the face, and then the midpoint is offset 15mm (to the inside obviously) to clear the peanut shape. but i dunno, ive never even seen a rotor IRL lol

That was my thought as well, but using those values produces a rather 'bloated' rotor from what I remember. As this is a link to where I'm pulling the values from:

Rotary History ('http://www.rotaryaviation.com/rotaryhistory.htm#Part 6')

[NoDOHC]

You are confusing yourself by thinking too hard. The eccentricity measurement you seek is actually the distance that the eccentric shaft is offset from center. (15 mm).

The R' is the distance from the center of the eccentric shaft to the intended apex of the rotor. These constants describe the rotor housing by a set of parametric equations.

I have a parametric equation that I developed empirically by carefully measuring a rotor a while back. It should be pretty close (it yielded a net displacement of 653.8 cc per eccentric shaft revolution per rotor).

I can get it to you, but it will require some explanation, as it was developed for a math model of the rotary engine that I was working on at the time. It is a function of R in terms of some theta (which I don't remember what angle theta represents now).

I will PM you once I get to the bottom of this math.

[hades]

what do you plan to do with this data?

[vex]

3d model followed by a cfd analysis of the entire combustion process.

[Rx7Evan]

Vex,

I wanted to do the same thing a while back. I have never been able to find proper equations or numbers to build a good model. I do however have a ROMER CMM with a perceptron laser scanner at my disposal, so i was hoping one day i could get some scans of a housing and some rotors. I build CAD models for RF signatures, CFD, and other analysis for a living. What software will you be using for modeling and analysis?

Evan

[vex]

Vex,

I wanted to do the same thing a while back. I have never been able to find proper equations or numbers to build a good model. I do however have a ROMER CMM with a perceptron laser scanner at my disposal, so i was hoping one day i could get some scans of a housing and some rotors. I build CAD models for RF signatures, CFD, and other analysis for a living. What software will you be using for modeling and analysis?

Evan

Modeling and FEA will be done using Autodesk Inventor, CFD will be done using Autodesk Algor simulation software.

I'm a little busy with school work at the moment so I may have to hold off on this for a little bit, but I'm still planning on doing it.

[NoDOHC]

Vex,

I wanted to do the same thing a while back. I have never been able to find proper equations or numbers to build a good model. I do however have a ROMER CMM with a perceptron laser scanner at my disposal, so i was hoping one day i could get some scans of a housing and some rotors. I build CAD models for RF signatures, CFD, and other analysis for a living. What software will you be using for modeling and analysis?

Evan

Wow! Those could be some very useful skills! I would love to see some simulation guys working on this and some validators building and testing the designs. I have argued for years that if performance parts for rotaries were as readily available as they are for the small-block Chevy and small-block Ford, people would realize how much potential the rotary engine really has.

[Rx7Evan]

Good ole Inventor! Well if you get some good measurements please share! I currently use NX, Pro-e, solid edge, solid works, and inventor... We have a wide customer base, and because they all use different software we pretty much have them all.

[NoDOHC]

Good ole Inventor! Well if you get some good measurements please share! I currently use NX, Pro-e, solid edge, solid works, and inventor... We have a wide customer base, and because they all use different software we pretty much have them all.


If you are really serious, I have a good set of measurements (actually parametric equations, which you can plot and extrude in Solid works or ProE).

I am not good at computer drawing, or I would model them myself.

PM or post here if you want the data.

[Rx7Evan]

Bring it on!

[Rx7Evan]

If you are really serious, I have a good set of measurements (actually parametric equations, which you can plot and extrude in Solid works or ProE).

I am not good at computer drawing, or I would model them myself.

PM or post here if you want the data.

After looking at the data you sent me about four times i finally realized what was going on. So I walked down the hall and got one of the RF analysts to plug the equations into MatLab. The epitrochoid housing curve came out quite nice, but the equation you gave me for the rotor gave some funky results. They could have made a mistake punching it in.

Shouldn't I be able to interpolate the correct shape of the rotor from the housing curve? If one apex is centered at the neck of the epitrochoid curve (narrowest center point), then the opposing apexes will be on the housing and the center of the face between them will be tangent to the opposing "neck". There is only one arc that will solve that. It will be somewhat untrue because the rotor wouldn't actually be modeled with apex seals... Need more data for that.

[vex]

roar, I wish I could be doing that right now... (I'm still swamped with Homework and projects for ship dynamics, boundary layer theory, astro mechanics, and a freakin' lab report!)

[NoDOHC]

You have to let alpha vary from -60 to 60 degrees. R is in inches from the center of the rotor. You have to plot it on polar coordinates.

I should send you an excel file outlining how it must be plotted.

Unfortunately, the shape does not match the curve that would fit the housing. I once thought as you do until I measured.

I will get you an equation for the dish too.

[vex]

So...I've been looking over all the things I never had time to finish when I was in school. Looks like I have a lot to get back to work on. Among which I have a parametric equation I think everyone would be glad to have:

x=e*cos*al+R*cos(al/3)+a*cos(al/3+d)
y=e*cos*al+R*sin(al/3)+a*sin(al/3+d)
R=105 mm
e=15 mm
a=3 mm (I'm not 100% on this one)
d=26.2

Change al = t in inventor and plot from 0-1080 (degrees). That will give you the rotor housing; from which you can develop a rotor.

Now to scour for the internal dimensions of the rotor...