This is an excerpt from a book I bought in Germany.
Title is "The Wankel Engine Today" 1977 Audi NSU

It illustrates just how difficult it was for Felix Wankel to
devise a practical rotary engine out of the hundreds of possibilities.
It remains an enormous achievement and not easily duplicated.

Paul Lamar

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Background to an invention

Rotors instead of Pistons

A smooth-running engine is something that the passengers in a Ro 80 soon
take for granted. They can just hear the engine humming quietly, more

like

an electric motor than a combustion engine. They are not disturbed by
vibration or noise; they can enjoy listening to the radio and talk

without

raising their voices. At the end of the journey they still feel fresh

and

relaxed. But nobody gives much thought to the long story of development
which led to the existence of the rotary engine in its present form.

The history of the engine really goes back as far as the invention of

the

wheel. There is no way of telling just how long ago man first put the

wheel

to use, but as he watched it going round he was fascinated by the

continuous

motion, and since then he has never stopped devising further methods of
exploiting the rotating wheel for his own purposes.  It was only a short
step to the idea of solving his transport problems by fixing wheels to a
cart which was pulled along by animals.  Another fairly obvious

possibility

was to construct a mill-wheel driven by moving water to do his work for
him. But later on it first appeared impossible to generate power

directly in

the form of harmonious rotating motion.  The question arose when

technology

progressed as far as the reciprocating engine with its bulky,

oscillating

crank mechanism driven at first by steam and then later by burning gas.

Ever since the first mechanical prime movers, successive generations of
inventors have visualized a piston rotating without vibration and

without

reciprocating masses. This appeared basically quite simple and logical.

But

again and again inventors discovered how difficult it was to put

something

so apparently simple into practice. The difficulty was that a rotating
piston had to play a part in forming variable-volume chambers to enable

the

engine to draw in, compress, burn and expel gas with the correct timing,

in

other words to run in a four-stroke cycle.  This ideal solution required

a

complex process of thought to visualize the special problems involved.
Right from the very beginning the almost uncanny fascination of this

task

resulted in a flood of inventions and patents, particularly over the
last 150 years. But very little public attention was given to any of

these

developments for the simple reason that nobody is interested in

failures.

At that time there were two main reasons for the failure to produce a
practicable rotary engine design. The first, ironically enough, was that
there were simply too many possible shapes which could be used for the
rotors and their corresponding housings. The number of reasonable
alternatives ran into the hundreds, whereas there is only a limited

number

of configurations suitable for reciprocating engines.  The scope for

varying

the shapes of the rotors proved to be so wide that the problem of

selecting

the correct system appeared insoluble.  And anyone who successfully

picked

his way through the baffling and deceptive variety of alternatives was

then

faced with a fresh obstacle to progress, namely the sealing problems

arising

from the annular combustion chambers or other volumetric shapes. They
require multi-cornered sealing lines formed by sealing parts joining

from

different directions. This presents far greater difficulties than the
single-plane sealing line for the cylinders of the reciprocating engine.

And so it was not altogether surprising that the number of aspiring
inventors was gradually reduced in the face of such obstacles. One man

who

refused to be discouraged was Felix Wankel, who from an early age had
exercised his ingenuity and craftsmanship on research into technical
problems. During the difficult years after the first world war he had

been

forced to work as an apprentice in the publishing trade, but his

thoughts

were occupied by greater things. He was particularly interested in the
smooth-running properties of electric motors and turbines; the latter

were

then being developed as a new type of combustion power unit by the Brown
Boveri Company in Mannheim, not far away from his home town of

Heidelberg.

In 1926 Wankel - at the age of 24 - started what was to prove an epic

search

lasting for many years and marked by promising discoveries and

disappointing

setbacks.  The very first tentative designs on the drawing board were

soon

followed by practical work in his own experimental workshops which he

had

equipped himself. Although it was not long before his financial
means had increased, the kinetic system which was the object of his

search

still remained stubbornly elusive.

The companies sponsoring his work (BMW from 1932-1936 and the German
aeronautical research institute from 1936-1945) were in fact not

directly

interested in Wankel's own objectives. They needed his experience for
sealing rotary disc valves, i. e. for engines in which the conventional
poppet valves, which are subject to banging and to high thermal loads,

were

to be replaced by rotating discs used to control gas flow. Wankel had

really

only worked in this area because he was interested in the difficulties
involved in devising seals for hot gases under high pressure. The

knowledge

he gained was to prove indispensable when designing rotor seals for his

own

engine.  After several failures Wankel had reached the conclusion that

his

project was only going to be successful if he approached the problem

from

two different directions: firstly he had to ensure adequate sealing and
secondly he had to devise a rotary system which would allow a fourstroke
cycle.

In 1951 the piston ring manufacturer Goetze expressed an interest in his
experience of sealing problems and in the same year NSU approached him

about

his work on rotary disc valves. Appropriate research contracts were
concluded with both companies.  By then Wankel's investigation of the
numerous possible rotor combinations had become more systematic.  He had
completed a comprehensive analysis covering all the designs he had
investigated himself and all the proposals put forward by other

inventors

which he had encountered by that time. This was a laborious process

which,

like his work on gas sealing, no other engineer had until then

attempted.

At the end of 1953 Wankel started to follow a promising line of

research: an

arrangement with a pointed oval rotating inside an almost circular

housing

which itself was allowed to rotate. This system induced NSU's chief

research

engineer Dr.  Walter Froede to recommend an extension of his company's
contract with Wankel. Dr. von Heydekampf, who was then Chairman of the
Board, gave his blessing to the new agreement. But while initial

development

was still under way Wankel, who was persistently continuing his

researches

because he was still not quite satisfied, came up with a new design

which

was obviously even better. He combined a rotating, slightly constricted

oval

chamber with a triangular-shaped rotor which fitted inside the contours

of

the chamber. This was the basis configuration of today's Wankel engine,
discovered in March, 1954.  The way was open for a new line of

development,

but at the same time a new decision had to be taken: should both

components

rotate or should the rotor housing remain stationary? Both alternatives

were

possible, each involving different consequences which will be outlined
later.

It was decided to adopt the "pure" rotary engine proposed by Wankel

which

had rotor and rotor housing capable of turning at high speeds, although

this

"single rotation machine" is now largely forgotten.  After laborious and
detailed development work - in which Wankel's chief designer Ernst

Hoeppner

played a leading part - this novel engine came to life on February 1st,
1957.  It was first started up on a test bed in what was then the NSU
motorcycle factory and ran for a short time under its own power.

In 1958 NSU decided to simplify the engine for use as an automobile

power

unit, an application which had been envisaged right from the start.  The
rotor housing was kept stationary and now became the engine housing. The
triangular rotor turned inside this housing, although it now followed a
planetary orbit in order to form the variable-volume chambers as before.
This orbiting motion, instead of simple rotation, meant that the

attainable

engine speeds were to some extent restricted. This was a limitation

which

was readily accepted due to the simplification involved and because

these

lower engine speeds were more compatible with conventional attachments
(power transmission, gearbox, pumps, alternator etc.). The orbiting

rotor

now had to be balanced by means of additional balance weights, although
perfect balancing could be achieved, unlike the situation with a
reciprocating engine where a certain amount of dynamic imbalance cannot

be

prevented.

The development of rotary combustion engines now continued on a visibly
larger scale. The first engine with a planetary rotor and a chamber

volume

of 125 cc was quickly followed by engines displacing 250 ec and then 400

cc

and 500 cc. Smaller engines with a chamber volume of 60 cc were also

tested

for independent drive applications.

In 1960 an automobile was driven by a rotary combustion engine for the

first

time in the history of automotive technology. The car was an NSU Prinz
driven by a rear-mounted 30 HP rotary engine with a chamber volume of

250cc.

The first rotary powered production car, the NSU Spider, came off the
assembly lines in 1964; the power unit was a 50 HP rotary engine with a
chamber volume of 500 cc.

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-Christopher Barber wrote:

Who says there is nothing interesting to read.  Thanks Paul.

So, if his base design emerged in March of 1954, doesn't that make this
month the 50th birthday of the Rotary. (yeah, I know, it was the first
incarnation, but still....)

All the best,

Chris

Hi all,

Paul, does the book mention, that it actually wasn't Felix Wankel who came
up with the final design?
Actually Felix was pretty angry when he found out!
He said something like: Now you made a workhorse out of my thoroughbred!
The then NSU-boss would counter: "I wish we had at least the workhorse
already!"

Today's design was developed by NSU Dipl.-Ing. H.D. Paschke in absolute
secrecy!
The amazing thing about is the layout - the same as today's Renesis (side
intake and exhaust!)
see: http://www.der-wankelmotor.de/Techniklexikon/techniklexikon.html
...all the way at the bottom

Unfortunately the side exhaust wasn't any good for the "edge sealing plate"
and so the exhaust was changed to peripheral. The edge sealing plate was
also changed for the now common side seals. Unfortunately they never tried
the side exhaust again - until today's Renesis.

You can see Felix's desing here:
http://www.der-wankelmotor.de/Wankelmotor/wankelmotor.html

and here:
http://www.der-wankelmotor.de/Techniklexikon/DKM_vs_KKM/dkm_vs_kkm.html

You can translate most of it with: http://world.altavista.com/?kg=XX&il=en
(AltaVista - Babelfish translater)

Thomas J.

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ACRE NL web site. http://home.earthlink.net/~rotaryeng/            
Copyright 1998-2003 All world wide rights reserved.