The HAPI Volkswagen Engine

H.A..P.I.
VOLKSWAGEN
ENGINE
By: R. E. and P. J. Taylor (EAA 87893)
P. O. Box 5951
Calexico, CA 92231
3OUT THREE YEARS ago we started designing an
aeroplane to fill the gap left by the lack of the Cub or
Champ type aircraft. Remember how we used to fly?
Putt-putting around the sky, nowhere in particular to go
but loving every minute we spent in the air? We'd fly
around the local airports, no need for a radio, ILS, VOR,
DME, tower or any of the other so called modern conveniencesf?), we simply flew for the sheer joy of it.
We wanted to design a kit aircraft to again capture
that thrill of flying, without the disastrous effect on the
family budget that even a low cost factory built flivver
can cause now. Our aircraft would be two place, side by
side, strut braced, fixed gear, lots of wing area, stable,
safe and FUN! The wings would fold, you take it home
on it's own trailer and keep it there. Assembly for flight
would take less than five minutes.
It would be built by somewhat unconventional
methods, prefabricated similar to a radio controlled
model kit — we spent years as R.C. kit manufacturers
are astronomical! Continental no longer builds engines
smaller than 230 hp and the smallest new Lycoming
available is 115 hp and about $5000 ready to install.
So, sad to say, we all too often see another ad for an
unfinished project, the engine obstacle having been too
great a hurdle for our would-be builder to surmount. In
the past few years we have seen some tremendous advances in homebuilt technology, with designers such as
Ken Rand throwing away the book of years-old methods
and designing an airplane that really preforms on a 36
hp Volkswagen engine. By using a new unconventional
structure Ken's first KR-1 flew on a 36 hp Volksie that
had little more done to it than installation of a magneto
and a prop hub. Rutan and Friends are obtaining fantastic performance from an 18 hp Onan engine in their
Quickie, another fine example of an aircraft being engineered to an engine. Bert Sisler's Cygnet is a beautiful
modern cross-country machine for two standard adults,
reasonably light baggage, a useful fuel load and he does
this on a Volkswagen engine.
The new Windwagon design has very good performance on only the front half of a Volkswagen engine!
These designs are flying proof that an aircraft can carry
a useful load on minimal horsepower engines or be a
very snappy performer on those same powerplants.
It very soon became obvious that Volkswagen was
about the only logical choice for our aircraft. We started
buying conversion drawings from various sources and
trying to gather as much information regarding converting a Volkswagen to aircraft as possible.
We studied the various ways developed by others to
convert the Volkswagen to aircraft use. While most of
these drawings were very complete in details of fabricating the unique aircraft adaption parts, they said little or
nothing about the Volkswagen engine or how to properly set it up for aircraft, none of the many pitfalls in
building an engine that can cause major problems were
mentioned. Since the basic engine is the heart of reliability we wanted to know how best to set it up for flight.
There are other engines being converted to aircraft
but since VW starts out as a horizontally opposed four
cylinder air cooled engine with many similarities with
the Lye's and Continentals and the fact they have been
exported in plentiful supply everywhere in the world has
made them the most common engine in aircraft conversion.
The Volkswagen engine is a very sturdy unit and is
quite capable of taking fantastic abuse and continuing
to deliver service. They have been hopped up in every
conceivable manner and used in about every kind of racing you can think of. They are capable of being modified
to develop over 250 hp starting with the basic 1600cc
engine. You can spend a fortune on racing goodies such
as roller bearing crankshafts and turbochargers to pull
the power out of these little mills or you can use the
wealth of knowledge gained in racing to build a very
strong lightweight engine that will develop a reasonable
— and would require no welding, fiber glass or epoxy
amount of power over a long period of time with a high
work, fabric work or other methods more exotic than a
model aircraft. The design would be capable of being
built by any average model builder. This project is all
very possible but the first step had to be deciding on the
most suitable, and more importantly perhaps, most
available powerplant.
There are homebuilders in this old world who have
degree of reliability.
Our family has been Volkswagen oriented for fifteen
years and we have built several dune buggies and Baja
Bugs for off road use. We had built high performance
engines for our vehicles and over the years learned what
you can and cannot expect from a Volkswagen engine.
We had decided that since this was to be an aircraft engine and we quite literally bet our lives on such an engine, we would not be satisfied with less than aircraft
standards.
bought themselves some plans or sketched out their own
original design to utilize an engine in the 50 to 10 hp
range. Some have gotten well into their projects before
looking for and pricing engines and found that nowadays you really have to turn over a lot of rocks to even
find an engine. Usually when you find one, it needs rebuilding, parts are hard to get or unavailable and prices
34 FEBRUARY 1979
We knew from racing that you can never just assume
that everything is right. You have to tear it down,
clean, inspect, measure, smooth, file, adjust, balance,
reassemble, torque and reinspect to KNOW what you
Ofr
Development of the H.A.P.I. Volkswagen engine and
tooling up for production have occupied our time for the
last year. Following are some of the procedures we consider essential to Volkswagen engine conversions.
Our aircraft is to have the capability for radio so the
electrical systems demand an alternator. Most airports
don't welcome a hand propped aircraft now and many
pilots have never started an engine without a starter.
On the H.A.P.I. engine conversion the starter is a standard feature. We wanted to provide for a larger powerplant on our kit airplane so motor mounts on the VW
accessory case were made the same as Continental A-65
through 0-200. Standard Continental rubber bushings
are used to isolate vibration. The alternator rotor is
immediately behind the starter ring inside the case. The
magneto coupler is attached to the rear of the rotor in
what we call a "stack" arrangement. The stator ring is
around the rotor inside the bulge that can be seen in the
photos and is bolted to the accessory case casting. Our
alternators are 10 amp motorcycle units but can be rewound to produce 20 amps at slight additional cost.
The magneto is a Slick 4016 with shielded harness
and spark plugs as standard equipment. As soon as
Slick releases its new 6000 series magneto which is field
serviceable, we will use it.
Sheet metal ducting directs outside air over crankcase bottom and through rear mounted oil cooler for efficient heat
dissipation.
have if you are to achieve the reliability it takes to win.
In an aircraft we are so much more dependent on this
reliability than in a racer. We can't simply pull off of
the course if something fails.
So the first step in our aircraft kit is the engine and
we gathered people with the expertise to help us design
a conversion to meet our goals.
We are located in Calexico in southern California,
right smack on the Mexican border where Volkswagen
powered off-road vehicles are probably more numerous
than anywhere on earth. There are many racing enthusiasts here with Volkswagen know how and mechanical services in abundance.
We set about to literally pick these guy's brains and
learn everything possible about these engines. Many of
the tricks, of course, aren't applicable to aircraft, but
many others are suitable and desirable It was obvious at
the outset that to hop up or ask for big horsepower
would be to trade off reliability and service life, and we
have kept everything on the conservative side. We have
achieved what we feel to be the best set of compromises,
choosing from among power, high reliability and
reasonable cost.
We had by now decided that the engine conversions
we have looked over in our studies hadn't gone as far as
we felt was necessary, so we started to design and build
our own engines.
We were fortunate in having Joe Cole near us and in
being able to draw upon his many years of experience in
building engines and setting up cars for the "Baja
1OOO", one of the toughest races in the world. Just to
keep engine and car together to finish is quite an accomplishment Joe has worked with us in our develop-
ment program and now contracts certain unique Volkswagen machine work on our engines that he has developed the hard tooling and methods for accomplishing.
The help and services of Rodger Ring, machinist, tool
and die maker has been invaluable, particularly in the
areas of production tooling and methods. Rodger owned
a fifty man shop until his retirement recently and
supplied precision machine parts to Rohr Aircraft.
Engine has low frontal area. Lower cylinder shrouding on
this engine is basis for pressure cowling. Oil cooler is seen
through duct above carburetor.
We do not offer dual ignition at this time. We will be
doing some testing in the future to find out what happens to cylinder heads when extra plug holes are added
and will possibly offer it at a later date.
There are four other castings used in our conversion,
all of which are cast in magnesium and have large cooling fins for both appearance and cooling.
Two identical castings permit remote oil cooler location and circulate the oil via oil lines. These castings as
well as all of the parts we use in building our engines
are available separately if you are building your own
engine and wish to use some H.A.P.I. parts.
Our engines start with a factory new Volkswagen
1600 crankcase which is now being manufactured at the
SPORT AVIATION 35
Mexican Volkswagen plant. Our location on the International border gives us easy access to new VW parts in
Mexico at reasonable prices and instant availability.)
We then machine the case to accept 92mm cylinders
which increases displacement to 1835cc. At the same
time we also modify the main bearings for suitability to
aircraft demands. We then inspect, smooth corners,
clean and ready the case to receive the crankshaft assembly.
This is made up of the crankshaft which has been
machined to accept our forged steel propeller hub, fitted
with all the parts that rotate with it, such as the starter
ring, alternator rotor and magneto drive plate, timing
gear and the propeller hub. The whole rotating assembly
is electronically balanced and marked to insure correct
reassembly.
The piston, wrist pin, ring assembly have also been
balanced to match their weights perfectly. The connecting rods are balanced end to end to each other before as-
This Model "60" engine when photographed had 68 hours
test stand time at power settings from 8(X; to wide open. It
will be installed on H.A.P.I.'s KR-1 with a tuned exhaust system by Dix Homebuilt Supply.
sembly. Rods used are forged steel units much stronger
than stock rods.
Balancing is a race proven absolute essential in engine build-up. You may think your engine was balanced
at the factory but you have now removed the flywheel,
probably changed rods and pistons, put on a propeller
hub and other things that rotate with the crank, so it is
in no way a balanced assembly now. While you may be
lucky and have all the various out-of-balance parts tend
to cancel each other out, usually they seem to go in the
same direction and the engine will shake like the dickens.
Consider these figures: '/4 oz. extra weight four inches
from the center of a rotating element creates forces of
imbalance equal to 7 Ibs. at 2000 rpm, 15.8 Ibs. at 3000
rpm, 28 Ibs. at 4000 rpm, much like whirling a weight
on the end of a string. The whirling weights can and do
exert side loads on bearings that greatly decrease their
life expectancy and increase chances for a bearing failure.
.
36 FEBRUARY 1979
The crankshaft with rods attached, properly torqued
and safetied is then placed in the case. The other half of
the case is placed over the studs with all bolts being
tightened in proper sequence with a torque wrench. (I
can't overemphasize the importance of proper torque
values in building a VW engine.) We then install the
piston and cylinder assemblies, installing special cylinder air baffles to direct air over the bottom side properly. This is an essential on VW engines. If provided
with plenty of cooling air properly circulated around the
heads and cylinders, plus a plentiful supply of clean cool
oil under adequate pressure, these powerplants are hard
to hurt.
We strongly recommend that a H.A.P.I. engine be
pressure cowled. Positive forced cooling is the best way
to avoid the problems associated with a hot running engine, such as burnt valves, cracked cylinder heads, excessive wear and in extreme cases, possible sudden seizure in flight.
Magnesium accessory case houses starter ring and alternator internally and mounts magneto and starter. Motor mount
is same as Continental A-65 through 0-200. Remote oil cooler
and lines are seen below starter.
Next come the cylinder heads which have had considerable work. We use aluminum bronze valve guides
and stainless steel valves. These guides have been
selected because their expansion rate closely matches
the aluminum heads. They have very good wear characteristics when used with the stainless valves. The valves
are single piece relatively soft valves that can withstand
high exhaust temperatures without burning and have a
history free of the breakage problems associated with
the harder valves. Stem to guide clearance is very important and is set up to allow for the troublesome buildup we get in using the so called 100 octane "Low Lead"
avgas, which contains four times as much lead as 80-87.
The cylinder heads have been precisely measured for
combustion chamber volume and metal removed until
volume in all chambers is equal. This is another step in
"balancing' the engine. Combustion chambers as cast
may vary considerably in volume so that instead of a
consistent ratio of compression on all cylinders there
may be variations that can cause engine roughness even
Amigo is powered with a Lycoming 0-290-D2 rated at
135 hp. (Photo page 30, May '77 SPORT AVIATION).
Amigo was built with front and rear cylinders on each
side feeding a separate exhaust. As soon as the new
crossover system was installed and flown an immediate
increase in performance was obvious.
Rate of climb is noticeably better and with throttle
set at 24" manifold pressure, an increase of 160 rpm
from 2400 to 2560 was obtained. Cruise speed is now 10
mph faster at the same MP settings. Ground observers
say that the aircraft is now quieter. Cylinder head
temperature has decreased slightly at full power climb
settings. This was the only change made at the time so
performance increase is entirely due to better exhaust
tuning.
H.A.P.I. has furnished Dix with a test engine to be
installed on the dynamometer and used to develop an efficient exhaust system for VW conversions. We are sure
that a similar performance gain can be obtained on
H.A.P.I. engines or any VW conversion. Dix should have
his testing finished and exhaust system near production
by the time you read this. Carburetor and exhaust heat
muffs when installed on this system will provide safety
and comfort. Dix says that pipes will be tucked in
snugly around the engine so tight cowls will still be possible.
The engines we build are still "Experimental" engines, of course, and cannot be used on a certified aircraft. The aim of our company is to take as much of the
"experiment" out of "experimental" as possible and deliver to you an engine that can be bolted on your aircraft, filled with oil, fueled and run without your having
to be an expert engine mechanic to keep it airworthy.
At present we build the 1835cc model "60" engine
and 1600cc model "50" engine. We also have available a
complete line of engine gauges and accessories compatible with VW conversions.
Our engines, engine instruments and other products
are now being delivered.
H.A.P.I. will have a book on the market by March 1,
1979 that shows you in step by step detail, complete
with pictures, diagrams, torque charts, bearing sizes,
etc., what to do and what NOT to do to build an aircraft
engine out of a Volkswagen. When you start your conversion, it ceases to be a VW and becomes an aircraft
engine. Anything less than aircraft standards of work-
manship and design can be dangerous. We tell you how
and where to get everything you need.
A list of the stock VW parts numbers that work best
in aircraft conversions is included.
We prefer to use a new crankcase, but a good used
engine can be built up also. A used engine should be one
with a traceable history. NEVER use an engine that has
trashed out bearings or any other part because the oil
gallery system will be contaminated with small metal
particles that are nearly impossible to clean out. These
will get into your oil system after rebuilding. If you buy
a used engine, get a 1600cc engine with the late transporter case. Find one that's running. There should be no
knocks or other indications of internal problems. A
wrecked VW totaled from the front end is a good source.
After you find such an engine, tear it down completely
and clean it up spotlessly, measure every part. Don't assume that its good because it ran well and don't be too
dollar conscious to throw away parts that are not of first
quality.
We will build an engine for you or help you build
your own, but whatever you do, don't just go to the local
junkyard, get an engine and bolt on a prop and mag. It
may get you up into the air, but it's not an aircraft engine!
All of the machining operations mentioned in this
article are available to those building their own engines.
An illustrated brochure on all our products is available for $3.00 refundable with order from H.A.P.I.
(Homebuilt Aircraft Products International), P. 0. Box
5951, Calexico, CA 92231. We are located at Hangar 4,
Calexico International Airport, Calexico, CA. Phone
714357-6342.
Our kit aircraft, the HAPICRAFT, is still a long way
off, but we can provide engines for some of the many excellent lightweight designs available now. Perhaps the
day of low cost flying is not really gone, just taking a
new form. Maybe all you need to get your dream into
the air is a H.A.P.I. ENGINE!
Specifications
MODEL 60 1834cc
Horsepower . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 at 3200 rpm
Bore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92mm
Stroke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69mm
Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 to 1
Fuel . . . . . . . . . . . . . . . . . 100 octane Av-gas or equivalent
O i l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 qts. capacity
Garb. . . . . . . . . . . . . . . . . . . . . . . . . Posa Fuel Injector Carb.
Ignition . . . . . . . . . . . . . . . . . . . . . Slick Magneto - Shielded
Spark Plugs . . . . . . . . . . . . . . . . . . . . . . . Aircraft - Shielded
Starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bosch 12v.
A l t e r n a t o r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 amp.
Prop Hub . . . . . . . . . . . . . . . . . . . . . . . . . C1020 steel forging
Oil Cooler . . . . . . . . . . . . . . . . . . . . . . . Standard Equipment
Engine Mounts . . . . . . . . . . . . . . . . . Rubber Isolation Type
All Castings . . . . . . . . . . . . . . . . . Lightweight Magnesium
Dry W e i g h t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Ibs.
Prop Mounting . . . . . . . . . . 6 holes .375 dia. on 4.00 B.C.
MODEL 50 ENGINE
Same Specifications As Above Except:
50 Horsepower at 3200
Displacement — 1600cc
38 FEBRUARY 1979
Calexico Airport's Robert Garcia refueling a test engine. Engines are set up for and tested on 100 octane because of its
universal availability. Fuel consumption is 3.4 at 3200 recommended cruise rpm.