----- Original Message -----
From: paul lamar <rotaryeng@earthlink.net>
To: A10-Me-Earthlink <rotaryeng@earthlink.net>
Sent: Sunday, January 17, 2016 11:22 AM
Subject: calculating rotary engine CFM



Does anyone have the formula or method to calculate the total CFM air
flow for rotary engines?I need to figure it out to make the
appropriate selection for a blower. I plan on cnc my own roots
blower, seems to fit my needs for the rotary.

david jr.



The tuning has a large effect and the type of intake ports. Tuned
p-ports can give you 120% VE.

Paul Lamar


That is going to be a unique roots blower. It will have to produce enough
air at low speeds and not rip itself apart at high speeds due to
centrifugal force. The roots blowers on Detroit Diesels and drag cars are
2/3 the size of the rotary. A 6-71 turning 2400 uses about 600 CFM which is
what the line on the attached chart goes to for the rotary at 8500. You
could maybe shrink it down and turn it faster but that is a lot of mass to
be slinging around that fast. Lots of inertia.

Do you have any size parameters in mind so far?

Kevin Alderman

Roots blowers are a big hit on the BSFC. Turbo's use otherwise waste
energy in
the exhaust.

Here are a couple of super charged rotaries. The Bobby Hughes version
is being changed to a turbo. Sorry I don't have better pictures.


Paul Lamar


Yes, I did a lot of research and roots type blowers have been used on
several rotary car engines and a couple of airplanes. Standard roots
type blowers, not specialized at all. You control the rpm thru different
size drive pulleys. I will not be using a

diesil engine blower, or a oversized gas engine blower. I will machine
out my own with the appropriate size rotors and that will put out the
right cfm needed.


That is why in the previous post I asked about the formula to calculate
the cfm in a rotary, to match the right size blower design.

I managed to get the sim software to estimate roots and screw type rotor
performance based on rotor size and rpm. I will use that to make the
right size blower for the small two stroke rotary.

David Jr.

Two stroke rotary?


Paul Lamar

not really 2 stroke, just no oiling system for the bearings, all lubricating
oil is mixed with the fuel hence 2 stroke term.

David Jr.

That is called charge cooling David. It is inadequate for continuous high power.
Here is a Wankel GmBH tech paper on the subject.

You can download the complete pdf here:

http://www.rotaryeng.net/Wankel-CC-paper.pdf

Paul Lamar

The Rotary Engine News Letter. Powered by Linux. If you want off the
list PLEASE let me know and I will remove  you.  ACRE NL web site.
http://www.rotaryeng.net You Tube http://tinyurl.com/beqqxas
Copyright 1998-2016 All world wide rights reserved.