DIY Two-Stroke Engine Construction Methods

Jim Logajan wrote:
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

From your link...

"Turns increase sink rate which in turn increase broken bone rate."

Ouch.

On Mar 10, 5:50*pm, Jim Logajan wrote:
Tim Wescott wrote:
Jim Stewart wrote:
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]

Engine failure at takeoff has claimed a lot of aces and test pilots:
http://en.wikipedia.org/wiki/Richard_Bong
http://en.wikipedia.org/wiki/James_McCudden

jsw

Jim Stewart wrote:
Tim Wescott wrote:

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.

Not really.
Low and slow U.S. aircraft of this kind usually have larger tail surfaces
and excellent control authority (at least in pitch) well below stall speed.

It's not like you stall and fall.
Most of them won't really stall at all.

But you can pick up a rather impressive sink rate!







--

Richard Lamb
http://www.home.earthlink.net/~cavelamb/

On Wed, 10 Mar 2010 07:24:54 -0600, "basilisk"
wrote:


"durabol" wrote in message
...
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.

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.

basilisk

Or do like every 2 stroke multi-cyl engine in the past, and devide the
crankcase - basicaly X number of single cyl engines in a row.

On Mar 10, 12:37*pm, Tim Wescott wrote:
...
Trash a cylinder on a monoblock engine and you have to do a complete
rebuild. *Trash one cylinder on an assembled engine and you just have to
replace one part.....
Tim Wescott

Like this:
http://picasaweb.google.com/KB1DAL/T...74948163130882
That's the right inboard engine of the B-17 "909", at an airshow in
Nashua NH. The cylinder cracked and they had to fix it to get home.

I happened to be standing under the wing when they set up the ladder
and made myself useful by taking the cowling pieces as they handed
them down, so by the time security roped off the area I looked like I
belonged there. Eventually the rest of the crew wandered off, leaving
just me assisting the crew chief to disassemble the head and fasten it
onto the good cylinder, then turn the prop while he set the valves. My
hands were too dirty to hold the camera most of the time.

Some day I'm going to make a model radial engine. First I might do a
pocket-sized one with valves timed to compress or run on air.

jsw

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...)

basilisk wrote:
"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
"basilisk" fired this volley in news:J4Nln.198564
:

you will have to provide a slave cylinder or roots type blower
to move the air.


Some variants use a cylinder skirt with reed valving.

LLoyd

You're right, I didn't really consider that before posting.

I supposed it could be worked out but that looks hard to
do in a completely bottom assembled engine, just my 2 cents worth,
I'm not an engine specialist.

basilisk



Try modifying an existing engine...and don't go hard over on it being a
2-stroke. I've often thought of trying to construct a full 9 or 7
cylinder aircraft radial using Harley engine parts - hell, those engines
have more in common with an air cooled radial than about anything I can
think of other than a Pratt & Whitney.

For your ultralight purpose, a basic V-twin would probably do, and I'd
suggest the fuel injected HD 88B counterbalanced one...just to keep
things smoother. The straight Dyna or touring Twin Cam 88 is lighter,
but I'm not sure how much vibration it would produce if hard mounted.

Something else you could do is use Harley studs and design your own
crank and case to make a flat twin, if you just want to build an engine
yourself - that would be a neat project, too.

If you need to use a reducer, you can machine your own pulley plate and
use a wide primary belt. Given that you'll be mounting the engine
behind a prop, you may also ba able to get away with shaving the fins to
lighten it a bit.

I'd also suggest you hot-rod the motor to a high compression setup -
that and the fuel injection will solve some horsepower vs altitude curve
problems for you - or at least help minimize them.

--
- Rufus

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.