DIY Two-Stroke Engine Construction Methods

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

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

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.

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.


As someone whom has done lost wax casting, I wouldn't recommend doing
that for something I was going to bet my life on...not without investing
LARGE amounts of capital in equipment - a centrifugal or pressure
injection foundry...sand casting (which I've also done) is a far better
alternative for casting a raw engine casing. Make a durable wooden
master model, preferably of a hardwood.

In any event, you're still going to have to sleeve the cylinders with
some alloy of machined, durable steel - which will have to be hardened
and polished in some way and interference fit into the block or stud.
And you need to match coefficients of thermal expansion when choosing
your materials in order to keep it all tight - same goes for choosing
and tolerancing your bolts and every other component in direct
contact...which means you also need to do some thermal analysis and
figure out how hot, as well as how, your engine is going to run...

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.

Brock

Again - big investment in big machines to insure uniformity of the
casting...which will kill the project (and the pilot) if you screw it
up. Hot spots, porosity, voids...not that simple. Best way to
spot/find/quality check castings involve die penetrant or x-ray.

Also - don't overlook the fact that you are going to have to heat treat,
case harden, or otherwise machine or post-work any part you produce
depending on choice and application of materials...I don't know what
kind of tools and resources the OP has at hand, but if he's starting
from scratch he better be prepared to spend the amount of money he'd
spend on a mid-size car in tooling just to get started with such a
project...make it a large luxury car, now that I think about it...

The far easier (and safer) alternative is to modify an existing engine -
like a motorcycle engine - strip it down and just build the parts and
accessories required to make it turn a prop. And along the way one can
also machine it's component parts down to lighten it...run it on the
ground, if it breaks, you know you went too far.

--
- Rufus (pilot, engineer, jeweler, model builder...yadda, yadda...)

On Mar 10, 9:02*pm, Rufus 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.

As someone whom has done lost wax casting, I wouldn't recommend doing
that for something I was going to bet my life on...not without investing
LARGE amounts of capital in equipment - a centrifugal or pressure
injection foundry...sand casting (which I've also done) is a far better
alternative for casting a raw engine casing. *Make a durable wooden
master model, preferably of a hardwood.

In any event, you're still going to have to sleeve the cylinders with
some alloy of machined, durable steel - which will have to be hardened
and polished in some way and interference fit into the block or stud.
And you need to match coefficients of thermal expansion when choosing
your materials in order to keep it all tight - same goes for choosing
and tolerancing your bolts and every other component in direct
contact...which means you also need to do some thermal analysis and
figure out how hot, as well as how, your engine is going to run...

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.

Brock

Again - big investment in big machines to insure uniformity of the
casting...which will kill the project (and the pilot) if you screw it
up. *Hot spots, porosity, voids...not that simple. *Best way to
spot/find/quality check castings involve die penetrant or x-ray.

Also - don't overlook the fact that you are going to have to heat treat,
case harden, or otherwise machine or post-work any part you produce
depending on choice and application of materials...I don't know what
kind of tools and resources the OP has at hand, but if he's starting
from scratch he better be prepared to spend the amount of money he'd
spend on a mid-size car in tooling just to get started with such a
project...make it a large luxury car, now that I think about it...

The far easier (and safer) alternative is to modify an existing engine -
like a motorcycle engine - strip it down and just build the parts and
accessories required to make it turn a prop. *And along the way one can
also machine it's component parts down to lighten it...run it on the
ground, if it breaks, you know you went too far.

--
* * * - Rufus (pilot, engineer, jeweler, model builder...yadda, yadda...)

Anything that flies a person has to be certified by the FAA anyway.
Especially homebuilts due to some fatal crashes early on.

frank wrote:

Anything that flies a person has to be certified by the FAA anyway.
Especially homebuilts due to some fatal crashes early on.


When did this start???

cavelamb wrote:
frank wrote:

Anything that flies a person has to be certified by the FAA anyway.
Especially homebuilts due to some fatal crashes early on.


When did this start???

It didn't. Experimental class is still around
and my friend still flies a VW engined plane.

Jim Stewart wrote:
cavelamb wrote:
frank wrote:

Anything that flies a person has to be certified by the FAA anyway.
Especially homebuilts due to some fatal crashes early on.


When did this start???

It didn't. Experimental class is still around
and my friend still flies a VW engined plane.

That's a heavier aircraft than an ultralight...not sure what they do
with ultralights, or light sport...anybody know about certs for those
two Categories/Classes?

--
- Rufus

cavelamb wrote:
frank wrote:

Anything that flies a person has to be certified by the FAA anyway.
Especially homebuilts due to some fatal crashes early on.


When did this start???

Which? Stupidity on the internet or stupidity in our government?

Charles

On Mar 11, 8:17*am, Charles Vincent wrote:

When did this start???

Which? *Stupidity on the internet or stupidity in our government?


Government stupidity came first. Al G. just wanted to bring it to the
general public .................
===============
Leon