DIY Two-Stroke Engine Construction Methods

Jim Stewart wrote:
durabol wrote:
The two main methods for homebuilt construction would be casting vs.
machining or some combination of both (probably the best option).
Forging probably isn't appropriate for home construction (either the
piston or connecting rod).

One method I have thought of is to produce a wax model of the engine
with molds (to a fairly high tolerance to minimize machining) which is
then cast using lost wax casting techniques. I planned to have an
integral cylinder head/cylinder/half the crank case (this is for an
opposed style engine). The only bolts would be to bolt the two halves
together.

A completely machined engine would need a large block of aluminium to
start with which I'm not sure how practical that would be. Perhaps
lost foam casting could be used as a general model of the engine was
made in foam and then cast and the resulting casting could be
machined.

I went back and read your first post to try to
get the big picture here. So what I think you
are saying is that you want to build an engine
that will be roughly equivalent to a Rotax 2-stroke
ultralight engine. I think the best advise I
could give you is don't. Despite the fact that
the Rotax engines are meticulously designed and
built, they still fail and have a 300 hour rebuild
interval. They have exotic coatings and metallurgy
to get the reliability that they have. There's no
way you'll even come close to their performance and
reliability in you garage.

But he wants the performance and reliability in the air, not his garage!!!

(sorry, couldn't resist).

Now if you want to build an engine, that's fine. If
you want to talk about building an engine, that's
fine too. I just have to say that you're taking
on a project with very, very small prospects of working
and a real steep downside if it fails in the air.

You could probably make some weight/reliability trades, though -- for
one example, use iron cylinder liners and conventional steel rings
instead of sooper-dooper nitrited aluminum fancy-pants coatings.

And always fly within an easy glide of a landing strip...

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

Tim Wescott wrote:
Jim Stewart wrote:
durabol wrote:
The two main methods for homebuilt construction would be casting vs.
machining or some combination of both (probably the best option).
Forging probably isn't appropriate for home construction (either the
piston or connecting rod).

One method I have thought of is to produce a wax model of the engine
with molds (to a fairly high tolerance to minimize machining) which is
then cast using lost wax casting techniques. I planned to have an
integral cylinder head/cylinder/half the crank case (this is for an
opposed style engine). The only bolts would be to bolt the two halves
together.

A completely machined engine would need a large block of aluminium to
start with which I'm not sure how practical that would be. Perhaps
lost foam casting could be used as a general model of the engine was
made in foam and then cast and the resulting casting could be
machined.

I went back and read your first post to try to
get the big picture here. So what I think you
are saying is that you want to build an engine
that will be roughly equivalent to a Rotax 2-stroke
ultralight engine. I think the best advise I
could give you is don't. Despite the fact that
the Rotax engines are meticulously designed and
built, they still fail and have a 300 hour rebuild
interval. They have exotic coatings and metallurgy
to get the reliability that they have. There's no
way you'll even come close to their performance and
reliability in you garage.

But he wants the performance and reliability in the air, not his garage!!!

(sorry, couldn't resist).

Good point nonetheless...

Now if you want to build an engine, that's fine. If
you want to talk about building an engine, that's
fine too. I just have to say that you're taking
on a project with very, very small prospects of working
and a real steep downside if it fails in the air.

You could probably make some weight/reliability trades, though -- for
one example, use iron cylinder liners and conventional steel rings
instead of sooper-dooper nitrited aluminum fancy-pants coatings.

And always fly within an easy glide of a landing strip...

That's a given. The problem is an engine out on takeoff
climb. With an ultralight, it's very difficult to
impossible to get the nose down and airspeed up fast enough
to avoid a stall. Of course, you can (and should) carry a
rocket-deployed chute on your ultralight, but it's bad
form to have to depend on one.

Jim Stewart wrote:
Tim Wescott wrote:
Jim Stewart wrote:
durabol wrote:
The two main methods for homebuilt construction would be casting vs.
machining or some combination of both (probably the best option).
Forging probably isn't appropriate for home construction (either the
piston or connecting rod).

One method I have thought of is to produce a wax model of the engine
with molds (to a fairly high tolerance to minimize machining) which is
then cast using lost wax casting techniques. I planned to have an
integral cylinder head/cylinder/half the crank case (this is for an
opposed style engine). The only bolts would be to bolt the two halves
together.

A completely machined engine would need a large block of aluminium to
start with which I'm not sure how practical that would be. Perhaps
lost foam casting could be used as a general model of the engine was
made in foam and then cast and the resulting casting could be
machined.

I went back and read your first post to try to
get the big picture here. So what I think you
are saying is that you want to build an engine
that will be roughly equivalent to a Rotax 2-stroke
ultralight engine. I think the best advise I
could give you is don't. Despite the fact that
the Rotax engines are meticulously designed and
built, they still fail and have a 300 hour rebuild
interval. They have exotic coatings and metallurgy
to get the reliability that they have. There's no
way you'll even come close to their performance and
reliability in you garage.

But he wants the performance and reliability in the air, not his
garage!!!

(sorry, couldn't resist).

Good point nonetheless...

Now if you want to build an engine, that's fine. If
you want to talk about building an engine, that's
fine too. I just have to say that you're taking
on a project with very, very small prospects of working
and a real steep downside if it fails in the air.

You could probably make some weight/reliability trades, though -- for
one example, use iron cylinder liners and conventional steel rings
instead of sooper-dooper nitrited aluminum fancy-pants coatings.

And always fly within an easy glide of a landing strip...

That's a given. The problem is an engine out on takeoff
climb. With an ultralight, it's very difficult to
impossible to get the nose down and airspeed up fast enough
to avoid a stall.

I did not know this -- I fly models, not ultralights. It's scary to
contemplate, though. I would consider a model that can't recover from a
sudden engine-out event to be more than a bit of a turd; I wouldn't want
to get _close_ to a full scale aircraft with that 'feature'.

Surely there are ultralights that don't exhibit this problem!

Is it a consequence of the draggy airframe on the usual ultralight? Or
are you thinking of the flavor of ultralights where you steer by
shifting weight, rather than with a movable elevator? Is there anything
you can do to mitigate the risk during takeoff, i.e. can you trade
climbing performance for safety by keeping the nose down and flying a
bit hotter?

Of course, you can (and should) carry a
rocket-deployed chute on your ultralight, but it's bad
form to have to depend on one.

Or an ejection seat...

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

Jim Stewart wrote:
durabol wrote:
The two main methods for homebuilt construction would be casting vs.
machining or some combination of both (probably the best option).
Forging probably isn't appropriate for home construction (either the
piston or connecting rod).

One method I have thought of is to produce a wax model of the engine
with molds (to a fairly high tolerance to minimize machining) which is
then cast using lost wax casting techniques. I planned to have an
integral cylinder head/cylinder/half the crank case (this is for an
opposed style engine). The only bolts would be to bolt the two halves
together.

A completely machined engine would need a large block of aluminium to
start with which I'm not sure how practical that would be. Perhaps
lost foam casting could be used as a general model of the engine was
made in foam and then cast and the resulting casting could be
machined.

I went back and read your first post to try to
get the big picture here. So what I think you
are saying is that you want to build an engine
that will be roughly equivalent to a Rotax 2-stroke
ultralight engine. I think the best advise I
could give you is don't. Despite the fact that
the Rotax engines are meticulously designed and
built, they still fail and have a 300 hour rebuild
interval. They have exotic coatings and metallurgy
to get the reliability that they have. There's no
way you'll even come close to their performance and
reliability in you garage.

Now if you want to build an engine, that's fine. If
you want to talk about building an engine, that's
fine too. I just have to say that you're taking
on a project with very, very small prospects of working
and a real steep downside if it fails in the air.

If you're interested in the design of the Rotax
engines, you can download the manuals he

http://www.rotax-owner.com/index.php...08&I temid=25


The line drawings of the engine, piston and cylinder
might be of interest.

I should mention at this juncture, that any time you say "never do that,
it's too hard for an individual" you're citing a rule that -- if applied
recursively -- is telling your audience "never do anything".

Raking over all possible difficulties so that someone can take them into
account, however, is more than a little bit helpful.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

On 3/10/2010 7:46 AM, in wrote:

it's not so hard, it just costs a bit more. but it adds a lot of grunt.
the 750 i have puts out almost 90hp. dragster h2's running exotic fuels have
been dynoed at over 400hp!. they need to be rebuilt often, but what drag motor
doesn't.
the quest for hp is expensive but doable. honda built a tt racer that got 18hp
out of 50cc! the 8 speed gearbox got it up to 100mph.
read about the mv augusta racers, you wouldn't believe me.

Suzuki built but never raced a 3 cylinder 50cc engine that was rated at
the highest output per liter on record for use with pump gas. However
to get to one liter it would have 60 cylinders...

Tony

In article , TonyW wrote:
On 3/10/2010 7:46 AM, in wrote:

it's not so hard, it just costs a bit more. but it adds a lot of grunt.
the 750 i have puts out almost 90hp. dragster h2's running exotic fuels have
been dynoed at over 400hp!. they need to be rebuilt often, but what drag
motor
doesn't.
the quest for hp is expensive but doable. honda built a tt racer that got
18hp
out of 50cc! the 8 speed gearbox got it up to 100mph.
read about the mv augusta racers, you wouldn't believe me.

Suzuki built but never raced a 3 cylinder 50cc engine that was rated at
the highest output per liter on record for use with pump gas. However
to get to one liter it would have 60 cylinders...

Tony

yeah, with enough money and resources, pigs will fly.

Tim Wescott wrote:
Jim Stewart wrote:
durabol wrote:
The two main methods for homebuilt construction would be casting vs.
machining or some combination of both (probably the best option).
Forging probably isn't appropriate for home construction (either the
piston or connecting rod).

One method I have thought of is to produce a wax model of the engine
with molds (to a fairly high tolerance to minimize machining) which is
then cast using lost wax casting techniques. I planned to have an
integral cylinder head/cylinder/half the crank case (this is for an
opposed style engine). The only bolts would be to bolt the two halves
together.

A completely machined engine would need a large block of aluminium to
start with which I'm not sure how practical that would be. Perhaps
lost foam casting could be used as a general model of the engine was
made in foam and then cast and the resulting casting could be
machined.

I went back and read your first post to try to
get the big picture here. So what I think you
are saying is that you want to build an engine
that will be roughly equivalent to a Rotax 2-stroke
ultralight engine. I think the best advise I
could give you is don't. Despite the fact that
the Rotax engines are meticulously designed and
built, they still fail and have a 300 hour rebuild
interval. They have exotic coatings and metallurgy
to get the reliability that they have. There's no
way you'll even come close to their performance and
reliability in you garage.

Now if you want to build an engine, that's fine. If
you want to talk about building an engine, that's
fine too. I just have to say that you're taking
on a project with very, very small prospects of working
and a real steep downside if it fails in the air.

If you're interested in the design of the Rotax
engines, you can download the manuals he

http://www.rotax-owner.com/index.php...08&I temid=25


The line drawings of the engine, piston and cylinder
might be of interest.

I should mention at this juncture, that any time you say "never do that,
it's too hard for an individual" you're citing a rule that -- if applied
recursively -- is telling your audience "never do anything".

Agreed. Just the same, there are little steps and
big stumbles. I would offer much encouragement if
the goal was to build and fly a small 2-stroke on
a control-line model. Not much at stake and a good
prospect for succeeding. The last issue of Model
Engine Builder had plans..

http://www.modelenginebuilder.com/elmwood.htm

OTOH, I just finished reading the ATSM consensus
standards for light sport aircraft engine design.
Not gonna happen in a garage.

Raking over all possible difficulties so that someone can take them into
account, however, is more than a little bit helpful.

Tim Wescott wrote:

And always fly within an easy glide of a landing strip...

That's a given. The problem is an engine out on takeoff
climb. With an ultralight, it's very difficult to
impossible to get the nose down and airspeed up fast enough
to avoid a stall.

I did not know this -- I fly models, not ultralights. It's scary to
contemplate, though. I would consider a model that can't recover from a
sudden engine-out event to be more than a bit of a turd; I wouldn't want
to get _close_ to a full scale aircraft with that 'feature'.

I think all engine-driven aircraft have a window
of vulnerability on takeoff. Most general aviation
planes can't return to the runway straight ahead
and successfully land if they are higher than 200'
and can't turn around to return to the field unless
they are higher than 500'. Consider that the headwind
that you took off into is now a tailwind and you
can see how badly your day gets.

That's why takeoffs are *always* full throttle and
best rate of climb. You spend the least amount
of time getting through that zone.

Surely there are ultralights that don't exhibit this problem!

Don't know. I was told that by someone whose knowledge
and experience were much greater than mine.

Is it a consequence of the draggy airframe on the usual ultralight? Or
are you thinking of the flavor of ultralights where you steer by
shifting weight, rather than with a movable elevator? Is there anything
you can do to mitigate the risk during takeoff, i.e. can you trade
climbing performance for safety by keeping the nose down and flying a
bit hotter?

Don't know for sure. I think the combination of
light weight and high drag bleeds off the airspeed
so quickly that you loose elevator authority
before you can put it to use.

Of course, you can (and should) carry a
rocket-deployed chute on your ultralight, but it's bad
form to have to depend on one.

Or an ejection seat...

"basilisk" wrote

Most two strokes are single cylinder that rely on crankcase pumping
action to move the fuel/air mixture, if you go to a multiple opposed
cylinders, you will have to provide a slave cylinder or roots type blower
to move the air.

Or you have each pair of cylinders and pistons moving outward and firing at
the same time, and have each opposing pair separated from the other opposing
pairs. It would still pump like regular single lung 2 strokes, then.

A 6 cylinder opposing pair would be an interesting 2 stroke engine. 3 power
pulses per revolution, and two pistons firing on each pulse. This concept
could mean that each pair could be designed basically identical, and bolted
together. You could add as many pairs as you wanted, to get the power
output you want. 6, or 8 or 10 cylinders! Cool! A 10 cylinder engine
should be as smooth as a turbine engine, but probably with the fuel flow to
match! ;-)

You could keep the cylinder sizes very small, and the engine very narrow but
long. This might be a concept to explore, I think.

If you wanted, you could have each pair rotated a little, somewhat like a
multi layer radial engine, for cooling mainly. It would probably make it
more complex than the benefits would justify.
--
Jim in NC

Tim Wescott wrote:
Jim Stewart wrote:
Tim Wescott wrote:
And always fly within an easy glide of a landing strip...

That's a given. The problem is an engine out on takeoff
climb. With an ultralight, it's very difficult to
impossible to get the nose down and airspeed up fast enough
to avoid a stall.

....
Surely there are ultralights that don't exhibit this problem!

There a Powered parachutes.[1]

Almost certainly other types of ultralights don't exhibit that issue
either, too. (Discounting even ultralight airships.) I suspect Jim
Stewart's source was generalizing a wee bit too much.

[1] http://www.quakerstatepoweredparachu...ne_failure.htm