Engine Desing

[Chris W]

As most of you probably know the opposing cylinders on most engines are
slightly offset to allow for the piston connecting rods to attach to the
crank at different spots. I know of a few model airplane engines, where
instead of having the cylinders offset and having the connecting rods on
different sections of the crank, the connecting rods interlock and are
on the same section of the crank. I have been told that the engines
that are built like this run very smooth with almost no vibration.
Obviously they have an odd firing pattern, but I guess having the 2
cylinders perfect in line makes it so well balanced. These are all 2
cylinder engines, on a 4 cylinder engine with a spark every 180 degrees,
it seems like it would be even smoother. My question is why don't they
make any engines for real airplanes like that? The 180 - 540 degree
firing sequence probably isn't as big a deal for the high rpm of model
airplanes as it would be for the low rpm of typical GA planes, so it
would probably only be suitable for engines with a multiple of 4
cylinders. It seems like it would be easier to make too, simpler crank
shaft, perfectly symmetrical crank case. The only more complicated part
would be the connecting rods. Just curious.

--
Chris W

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
http://thewishzone.com

[[email protected]]

Chris W wrote:
> As most of you probably know the opposing cylinders on most engines
are
> slightly offset to allow for the piston connecting rods to attach to
the
> crank at different spots. I know of a few model airplane engines,
where
> instead of having the cylinders offset and having the connecting rods
on
> different sections of the crank, the connecting rods interlock and
are
> on the same section of the crank. I have been told that the engines
> that are built like this run very smooth with almost no vibration.
> Obviously they have an odd firing pattern, but I guess having the 2
> ... My question is why don't they
> make any engines for real airplanes like that?

Radial engines are made that way.

http://travel.howstuffworks.com/radial-engine.htm

One or more of the newer paramotoring engines uses opposed
cylinders joined with what is called a 'Scottish Yoke'. If you
imagine the pistons as being horizontally opposed the yoke is
a plate with a vertical slot in it. The crankshaft passes
though a bearing that rides up and down in that slot. This
allows the pistons to be rigidly attached to the yoke, and
therefor to each other--the rods joining the pistons to the
yoke does not swivel or pivot as in the more common engine
designs. This reduces the number of moving parts in the
engine and the associated wear and energy losses.

Whereas in the radial engine many pistons are attached to a
central bearing on the crankshaft, only two can be attached to
the Scottish Yoke and they have to be opposed.

Also the motion of the yoke about the crankshaft is different
than an engine with a pitman. One consequence of that is the
piston moves slower at TDC and BDC. This means more complete
combustion and in a two-stroke, better evacuation of the
exhaust gasses. Combining the scottish yoke crankcase with
fuel injection would seem to be the way to go to maximise
the fuel economy for a two-stroke engine.

There is an engine called a Bourke engine, I _think_ the essential
feature of Bourkes is that they scottish yokes.

I do not know what the downside is of using a Scottish yoke,
perhaps the sliding motion in the yoke causes excessive wear
or maybe there is a timing problem for _exactly_ opposed
cylinders. Or maybe the only real problem is inertia in
management of engine manufacturers.

--

FF

[[email protected]]

I think the Rolls-Royce Merlin was built like that. It was a
V-12 and had forked rods as you describe. There are very few ideas that
would be new in the way of reciprocating engines.
Lycoming and Continental could do this too, but their engines
are already way too expensive. Don't give them ideas.

Dan

[Chris W]

I forgot to include a diagram in case it's not clear what I meant from
the text. Take a look at the piston connecting rods in the drawing.

http://www.thewishzone.com/cdw/index.php?image=Saito182.gif


--
Chris W

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
http://thewishzone.com

[Anthony W]

Richard Riley wrote:
> On 9 May 2005 06:54:35 -0700, wrote:
> :
> :One or more of the newer paramotoring engines uses opposed
> :cylinders joined with what is called a 'Scottish Yoke'.
>
> 'Tis a SCOTCH yoke ya wee buggerin' nit!
>
> http://www.brockeng.com/mechanism/ScotchYoke.htm

Also every prototype scotch yoke engine has battered itself apart in
short order. It seems Otto got it right the first time.

Tony

[[email protected]]

Chris W wrote:
> I forgot to include a diagram in case it's not clear what I meant
from
> the text. Take a look at the piston connecting rods in the drawing.
>
> http://www.thewishzone.com/cdw/index.php?image=Saito182.gif
>

That's two cylinder radial engine. I understand that Harley Davidson
makes one.

--

FF

[[email protected]]

wrote:
> Chris W wrote:
> > I forgot to include a diagram in case it's not clear what I meant
> from
> > the text. Take a look at the piston connecting rods in the
drawing.
> >
> > http://www.thewishzone.com/cdw/index.php?image=Saito182.gif
> >
>
> That's two cylinder radial engine. I understand that Harley Davidson
> makes one.
>

However the Harley Davidson is a Vee, not opposed like the example
above.

--

FF

[Sport Pilot]

The Harley is not made to be smooth. Both pistons connect to the same
crankpin and fire right after each other. This is part of the famous
Harley lope as the engine goes bang bang flup flup.

[Cy Galley]

I don't believe so. Since it is a FOUR cycle engine, Each cylinder only
fires every other revolution. It is timed so that one cylinder fires each
revolution. They alternate but since they are staggered, so is the timing.


"Sport Pilot" > wrote in message
oups.com...
> The Harley is not made to be smooth. Both pistons connect to the same
> crankpin and fire right after each other. This is part of the famous
> Harley lope as the engine goes bang bang flup flup.
>

[Corky Scott]

On Wed, 11 May 2005 23:19:25 GMT, "Cy Galley" >
wrote:

>I don't believe so. Since it is a FOUR cycle engine, Each cylinder only
>fires every other revolution. It is timed so that one cylinder fires each
>revolution. They alternate but since they are staggered, so is the timing.

Cy, I think they really do go bang bang, flup flup because of the
angle of the V. They cannot be timed so that they can fire as equally
opposite as a horizonatally opposed twin.

Harley actually attempted to patten the sound against Japanese copies.
They called it: potato potato potato potato and said it was theirs and
theirs only. Think they lost that fight.

Corky Scott

[Sport Pilot]

Both pistions are on the same crankpin at a 45 degree angle, they share
the same camshaft and lobes. One one revelution both cylinders fire
and on the next revolution they are on the exhaust and intake stroke.
Bang Bang ...... Flup Flup. Listen to the engine next time you are
sitting next to a Harley at a stop light. It is very obvious.

[Sport Pilot]

>Harley actually attempted to patten the sound against Japanese copies.

>They called it: potato potato potato potato and said it was theirs and

>theirs only. Think they lost that fight.

HuH? Harleys were built that way in the 19 naughts! This was done to
save weight. Unlike you the engineers back then knew that you could
provide two crankpins and have one cylinder fire every 360 degrees at
what ever angle they chose. The 45 degree angle is simply to get the
engine into a small space as possible in the frame.

It was the Japanese who copied Harley. Maybe Harley tried to sue them,
but most Japenese v twins use ofset crank pins for a smoother run.
Also the cylinders are more ofset to improve cooling.

[Corky Scott]

On 12 May 2005 10:52:25 -0700, "Sport Pilot" >
wrote:

>HuH? Harleys were built that way in the 19 naughts! This was done to
>save weight. Unlike you the engineers back then knew that you could
>provide two crankpins and have one cylinder fire every 360 degrees at
>what ever angle they chose. The 45 degree angle is simply to get the
>engine into a small space as possible in the frame.

I should have known that, after all I just got finished putting
together my Ford V-6 which is a 90 degree bank angle V-6. It has
displaced crankpins to allow for even firing.

Corky Scott

[[email protected]]

Corky Scott wrote:
> On Wed, 11 May 2005 23:19:25 GMT, "Cy Galley" >
> wrote:
>
> >I don't believe so. Since it is a FOUR cycle engine, Each cylinder
only
> >fires every other revolution. It is timed so that one cylinder
fires each
> >revolution. They alternate but since they are staggered, so is the
timing.
>
> Cy, I think they really do go bang bang, flup flup because of the
> angle of the V. They cannot be timed so that they can fire as
equally
> opposite as a horizonatally opposed twin.
>
> Harley actually attempted to patten the sound against Japanese
copies.
> They called it: potato potato potato potato and said it was theirs
and
> theirs only. Think they lost that fight.
>

IIRC they claimed trademark protection, not patent.

And they won.

My girlfriend says Harley's sound sexy. Now you know why.

--

FF

[Bob Kuykendall]

Earlier, wrote:

> IIRC they claimed trademark protection, not patent.
>
> And they won.

Trademark instad of patent, yes. But as for winning, Unka Cecil tells
it different:

http://www.straightdope.com/columns/000915.html

> ...The Japanese put it more diplomatically when
> fighting Harley's trademark request, arguing
> that all big motorcycles sound pretty much the
> same. After six years of legal proceedings and
> no resolution in sight, Harley caved, claiming
> it had won in the court of public opinion,
> etc...

This SF Chronicle article says that they dropped the trademark attempt
in 2000:

http://www.sfgate.com/cgi-bin/article.cgi?f=/news/archive/2003/08/25/financial1618EDT0176.DTL

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com

[Stealth Pilot]

On Mon, 09 May 2005 01:54:33 -0500, Chris W > wrote:

>As most of you probably know the opposing cylinders on most engines are
>slightly offset to allow for the piston connecting rods to attach to the
>crank at different spots. I know of a few model airplane engines, where
>instead of having the cylinders offset and having the connecting rods on
>different sections of the crank, the connecting rods interlock and are
>on the same section of the crank. I have been told that the engines
>that are built like this run very smooth with almost no vibration.
>Obviously they have an odd firing pattern, but I guess having the 2
>cylinders perfect in line makes it so well balanced. These are all 2
>cylinder engines, on a 4 cylinder engine with a spark every 180 degrees,
>it seems like it would be even smoother. My question is why don't they
>make any engines for real airplanes like that? The 180 - 540 degree
>firing sequence probably isn't as big a deal for the high rpm of model
>airplanes as it would be for the low rpm of typical GA planes, so it
>would probably only be suitable for engines with a multiple of 4
>cylinders. It seems like it would be easier to make too, simpler crank
>shaft, perfectly symmetrical crank case. The only more complicated part
>would be the connecting rods. Just curious.

what you are trying to describe is called DESAXING after a french guy
with the surname desaxe.
the change in alignment is really not that much.
it does work.

I have heard of magic hot rod engine tuneups that just involved a
quiet shimming and refacing of the cylinder base to achieve a freer
and faster running engine by desaxing it.
Stealth Pilot

[Bertie the Bunyip]

Stealth Pilot >
:

> On Mon, 09 May 2005 01:54:33 -0500, Chris W > wrote:
>
>>As most of you probably know the opposing cylinders on most engines are
>>slightly offset to allow for the piston connecting rods to attach to the
>>crank at different spots. I know of a few model airplane engines, where
>>instead of having the cylinders offset and having the connecting rods on
>>different sections of the crank, the connecting rods interlock and are
>>on the same section of the crank. I have been told that the engines
>>that are built like this run very smooth with almost no vibration.
>>Obviously they have an odd firing pattern, but I guess having the 2
>>cylinders perfect in line makes it so well balanced. These are all 2
>>cylinder engines, on a 4 cylinder engine with a spark every 180 degrees,
>>it seems like it would be even smoother. My question is why don't they
>>make any engines for real airplanes like that? The 180 - 540 degree
>>firing sequence probably isn't as big a deal for the high rpm of model
>>airplanes as it would be for the low rpm of typical GA planes, so it
>>would probably only be suitable for engines with a multiple of 4
>>cylinders. It seems like it would be easier to make too, simpler crank
>>shaft, perfectly symmetrical crank case. The only more complicated part
>>would be the connecting rods. Just curious.
>
> what you are trying to describe is called DESAXING after a french guy
> with the surname desaxe.
> the change in alignment is really not that much.
> it does work.

Umm, don't thnk that's what he's talking about. A few early radials used
desaxe cyliners, but that's a cylinder that's been offset form the
centerline of the crank to take advantage of a straighter conrod during the
power stroke. prolly worked OK, bu ti think they only use it in two strokes
nowadays if at all.
What th ewirter seems to be describing is an arrangement where two opposing
pistons share a crankpin. I've seen twins like this and they vibrate like
hell. A boxer (whihc most all flat opposed engines are) is a much smoother
arrangement.


Bertie

[Stealth Pilot]

On 16 May 2005 00:28:47 GMT, Bertie the Bunyip
> wrote:

>Stealth Pilot >
:
>
>> On Mon, 09 May 2005 01:54:33 -0500, Chris W > wrote:
>>
>>>As most of you probably know the opposing cylinders on most engines are
>>>slightly offset to allow for the piston connecting rods to attach to the
>>>crank at different spots. I know of a few model airplane engines, where
>>>instead of having the cylinders offset and having the connecting rods on
>>>different sections of the crank, the connecting rods interlock and are
>>>on the same section of the crank. I have been told that the engines
>>>that are built like this run very smooth with almost no vibration.
>>>Obviously they have an odd firing pattern, but I guess having the 2
>>>cylinders perfect in line makes it so well balanced. These are all 2
>>>cylinder engines, on a 4 cylinder engine with a spark every 180 degrees,
>>>it seems like it would be even smoother. My question is why don't they
>>>make any engines for real airplanes like that? The 180 - 540 degree
>>>firing sequence probably isn't as big a deal for the high rpm of model
>>>airplanes as it would be for the low rpm of typical GA planes, so it
>>>would probably only be suitable for engines with a multiple of 4
>>>cylinders. It seems like it would be easier to make too, simpler crank
>>>shaft, perfectly symmetrical crank case. The only more complicated part
>>>would be the connecting rods. Just curious.
>>
>> what you are trying to describe is called DESAXING after a french guy
>> with the surname desaxe.
>> the change in alignment is really not that much.
>> it does work.
>
>Umm, don't thnk that's what he's talking about. A few early radials used
>desaxe cyliners, but that's a cylinder that's been offset form the
>centerline of the crank to take advantage of a straighter conrod during the
>power stroke. prolly worked OK, bu ti think they only use it in two strokes
>nowadays if at all.
>What th ewirter seems to be describing is an arrangement where two opposing
>pistons share a crankpin. I've seen twins like this and they vibrate like
>hell. A boxer (whihc most all flat opposed engines are) is a much smoother
>arrangement.
>
>
>Bertie

you know I think you are right bertie.
I misread the post. I agree totally with your analysis as well.

shapers use a scotch link as well. they can get quite a vibration up
even at low rpm.
Stealth Pilot

[Bertie the Bunyip]

Stealth Pilot >
:

> On 16 May 2005 00:28:47 GMT, Bertie the Bunyip
> > wrote:
>
>>Stealth Pilot >
:
>>
>>> On Mon, 09 May 2005 01:54:33 -0500, Chris W > wrote:
>>>
>>>>As most of you probably know the opposing cylinders on most engines
>>>>are slightly offset to allow for the piston connecting rods to
>>>>attach to the crank at different spots. I know of a few model
>>>>airplane engines, where instead of having the cylinders offset and
>>>>having the connecting rods on different sections of the crank, the
>>>>connecting rods interlock and are on the same section of the crank.
>>>>I have been told that the engines that are built like this run very
>>>>smooth with almost no vibration. Obviously they have an odd firing
>>>>pattern, but I guess having the 2 cylinders perfect in line makes it
>>>>so well balanced. These are all 2 cylinder engines, on a 4 cylinder
>>>>engine with a spark every 180 degrees, it seems like it would be
>>>>even smoother. My question is why don't they make any engines for
>>>>real airplanes like that? The 180 - 540 degree firing sequence
>>>>probably isn't as big a deal for the high rpm of model airplanes as
>>>>it would be for the low rpm of typical GA planes, so it would
>>>>probably only be suitable for engines with a multiple of 4
>>>>cylinders. It seems like it would be easier to make too, simpler
>>>>crank shaft, perfectly symmetrical crank case. The only more
>>>>complicated part would be the connecting rods. Just curious.
>>>
>>> what you are trying to describe is called DESAXING after a french
>>> guy with the surname desaxe.
>>> the change in alignment is really not that much.
>>> it does work.
>>
>>Umm, don't thnk that's what he's talking about. A few early radials
>>used desaxe cyliners, but that's a cylinder that's been offset form
>>the centerline of the crank to take advantage of a straighter conrod
>>during the power stroke. prolly worked OK, bu ti think they only use
>>it in two strokes nowadays if at all.
>>What th ewirter seems to be describing is an arrangement where two
>>opposing pistons share a crankpin. I've seen twins like this and they
>>vibrate like hell. A boxer (whihc most all flat opposed engines are)
>>is a much smoother arrangement.
>>
>>
>>Bertie
>
> you know I think you are right bertie.
> I misread the post. I agree totally with your analysis as well.
>
> shapers use a scotch link as well. they can get quite a vibration up
> even at low rpm.
> Stealth Pilot

Scotch link? Is that where one big end is forked to go round the other rod?
On that subject, I seem to remember one of the Flying and Glider manuals
from the thirites has insturctions on how to turn one of those diabolical
contraptions into a boxer engine. It meant a new crank and bending the con
rods!
And I thought Moslers were crap...


Bertie

[[email protected]]

Bertie the Bunyip wrote:
> ...
> What th ewirter seems to be describing is an arrangement where two
opposing
> pistons share a crankpin. I've seen twins like this and they vibrate
like
> hell. A boxer (whihc most all flat opposed engines are) is a much
smoother
> arrangement.
>

What is the distinguishing characteristic of a boxer, that opposing
cylinders fire simultaneously?

--

FF

[Matt Whiting]

wrote:
> Bertie the Bunyip wrote:
>
>>...
>>What th ewirter seems to be describing is an arrangement where two
>
> opposing
>
>>pistons share a crankpin. I've seen twins like this and they vibrate
>
> like
>
>>hell. A boxer (whihc most all flat opposed engines are) is a much
>
> smoother
>
>>arrangement.
>>
>
>
> What is the distinguishing characteristic of a boxer, that opposing
> cylinders fire simultaneously?
>

I think the main feature is that the cylinders go in and out in
opposition thus giving very good primary balance. You always have the
torsional vibration from firing and there is also secondary imbalance.

Matt

[Bertie the Bunyip]

Matt Whiting >
:

> wrote:
>> Bertie the Bunyip wrote:
>>
>>>...
>>>What th ewirter seems to be describing is an arrangement where two
>>
>> opposing
>>
>>>pistons share a crankpin. I've seen twins like this and they vibrate
>>
>> like
>>
>>>hell. A boxer (whihc most all flat opposed engines are) is a much
>>
>> smoother
>>
>>>arrangement.
>>>
>>
>>
>> What is the distinguishing characteristic of a boxer, that opposing
>> cylinders fire simultaneously?
>>
>
> I think the main feature is that the cylinders go in and out in
> opposition thus giving very good primary balance. You always have the
> torsional vibration from firing and there is also secondary imbalance.

that's right. I have a BMW bike that's a twin boxer. there's two throws on
the crank and the pistons go in and out in oppostion to each other. AFAIK
all flat four airplane engines are the same, (though I'm sure there's some
ddball one out there somewhere) The ignition is alternating, though..
There have been some twins that have a single throw crank. It's as if
someone said "hey, that old single cylinder engine vibrates like hell, but
you know what'd make it vibrate even more? If we added another cylinder on
the other side!" These engines, while lighter than a boxer, have the added
disadvantage of supplying their power strokes at uneven points in the
rotation cycle. So you get two quick thumps and then a space in between..


Bertie

[Sport Pilot]

Most flat fours are not a boxer, and many twins are not. A boxer
engine will weigh and cost more. It's not really needed on a flat four
anyway, as on a non boxer the pistons on the front and rear pair will
be going opposite directions

[Matt Whiting]

Sport Pilot wrote:
> Most flat fours are not a boxer, and many twins are not. A boxer
> engine will weigh and cost more. It's not really needed on a flat four
> anyway, as on a non boxer the pistons on the front and rear pair will
> be going opposite directions
>

True, but this doesn introduce a "rocking couple" vibration mode.
There's no free lunch WRT to engine design. :-)

Although some configurations come close (I-6, V-8, etc.)


Matt

[Bertie the Bunyip]

"Sport Pilot" >
groups.com:

> Most flat fours are not a boxer, and many twins are not. A boxer
> engine will weigh and cost more. It's not really needed on a flat four
> anyway, as on a non boxer the pistons on the front and rear pair will
> be going opposite directions
>

Well, i can't thnk of an aviation flat four that isn't, and even the humble
VW is a boxer. So are all Subarus. In fact, I'm hard pressed to think of a
flat four that isn't. maybe the Mucculogh...
As for twins, there were a lot of non boxer opposed twins in the early
days, and they were diabolically vibratory. Much worse even than the
paralell twins that came in the thirties. ( I have a an old Triumph and
will knock your teeth out on a long trip, and it was meticulously balanced
when I rebuilt it)
what you say isn't entirely untrue, but the torsional loads on an engine
with pistons paired on crankpins front and aft would be very high and need
to be stiffened to the point it would be just as heavy if not heavier than
it's boxer counterpart.


Bertie

[Rob Turk]

"Matt Whiting" > wrote in message
...
> Sport Pilot wrote:
>> Most flat fours are not a boxer, and many twins are not. A boxer
>> engine will weigh and cost more. It's not really needed on a flat four
>> anyway, as on a non boxer the pistons on the front and rear pair will
>> be going opposite directions
>>
>
> True, but this doesn introduce a "rocking couple" vibration mode. There's
> no free lunch WRT to engine design. :-)
>
> Although some configurations come close (I-6, V-8, etc.)
>
>
> Matt

A very interesting design is the Diesel Air engine (www.dair.co.uk). They
have two pistons per cylinder, moving in opposite directions. The ignition
happens in the center of the cylinder, which is also the center of the
engine. All forces that can cause vibration are supposed to cancel eachother
out, so there's a minimum of vibration. The engine has two cranks which are
mechanically coupled on the outside to bundle the power to the prop.
Pictures are on their site.

Rob

[Bertie the Bunyip]

"Rob Turk" >
sednews:xmXie.4098$184.3491@amstwist00:

> "Matt Whiting" > wrote in message
> ...
>> Sport Pilot wrote:
>>> Most flat fours are not a boxer, and many twins are not. A boxer
>>> engine will weigh and cost more. It's not really needed on a flat
>>> four anyway, as on a non boxer the pistons on the front and rear
>>> pair will be going opposite directions
>>>
>>
>> True, but this doesn introduce a "rocking couple" vibration mode.
>> There's no free lunch WRT to engine design. :-)
>>
>> Although some configurations come close (I-6, V-8, etc.)
>>
>>
>> Matt
>
> A very interesting design is the Diesel Air engine (www.dair.co.uk).
> They have two pistons per cylinder, moving in opposite directions. The
> ignition happens in the center of the cylinder, which is also the
> center of the engine. All forces that can cause vibration are supposed
> to cancel eachother out, so there's a minimum of vibration. The engine
> has two cranks which are mechanically coupled on the outside to bundle
> the power to the prop. Pictures are on their site.
>
A fairly old idea, but it was quite successful for the Germans in WW2, the
engine giving a good SFC and allowing long range maritime patrols.
I've seen a sectioned example of this engine up close and it's fairly
complicated, not to mention absolutely huge!
http://www.billzilla.org/ideas4.htm
But it goes back even further than that, at least to 1898 when the Arrol
Johnston company made that same design into this contraption.
http://www.britishmm.co.uk/history.asp?id=65

[Bob Kuykendall]

Earlier, Sport Pilot wrote:

> Most flat fours are not a boxer, and
> many twins are not...

> ...on a non boxer
> the pistons on the front and rear pair
> will be going opposite directions

First, let me define the terms as I understand them:

The way I understand it, boxer motors are flat opposed engines in which
the connecting rods of opposing cylinder pairs do not share share a rod
journal on the crankshaft. Instead, they connect to the crankshaft at
journals that are spaced 180 degrees from each other. So arranged, each
opposing pair of pistons are both either on the down (power or intake)
stroke or on the up (exhaust or compression) stroke.

Conversely, flat opposed engines in which the connecting rods of
opposing cylinder pairs _do_ share share a rod journal on the
crankshaft are _not_ boxers. And again, that's just the way I
understand it, but a Dogpile or Google search pulls up lots of Web
pages that bear out that understanding.

And by that measure, most flat four motors _are_ boxers. VWs are that
way, and so are Soobs and Lycomings and Continentals. And certainly,
the Ferarri flat 12s are that way, or else the factory probably
wouldn't be calling them "Boxers."

As far as the relative motions of the various pairs of opposing
cylinders goes, I have never heard of that entering into the definition
of "Boxer." I won't say that it doesn't, but I will say that I won't
believe it until I see a credible cite to that effect.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com

[Bill Daniels]

"Bertie the Bunyip" > wrote in message
...
> "Rob Turk" >
> sednews:xmXie.4098$184.3491@amstwist00:
>
> > "Matt Whiting" > wrote in message
> > ...
> >> Sport Pilot wrote:
> >>> Most flat fours are not a boxer, and many twins are not. A boxer
> >>> engine will weigh and cost more. It's not really needed on a flat
> >>> four anyway, as on a non boxer the pistons on the front and rear
> >>> pair will be going opposite directions
> >>>
> >>
> >> True, but this doesn introduce a "rocking couple" vibration mode.
> >> There's no free lunch WRT to engine design. :-)
> >>
> >> Although some configurations come close (I-6, V-8, etc.)
> >>
> >>
> >> Matt
> >
> > A very interesting design is the Diesel Air engine (www.dair.co.uk).
> > They have two pistons per cylinder, moving in opposite directions. The
> > ignition happens in the center of the cylinder, which is also the
> > center of the engine. All forces that can cause vibration are supposed
> > to cancel eachother out, so there's a minimum of vibration. The engine
> > has two cranks which are mechanically coupled on the outside to bundle
> > the power to the prop. Pictures are on their site.
> >
> A fairly old idea, but it was quite successful for the Germans in WW2, the
> engine giving a good SFC and allowing long range maritime patrols.
> I've seen a sectioned example of this engine up close and it's fairly
> complicated, not to mention absolutely huge!
> http://www.billzilla.org/ideas4.htm
> But it goes back even further than that, at least to 1898 when the Arrol
> Johnston company made that same design into this contraption.
> http://www.britishmm.co.uk/history.asp?id=65

Opposed piston (not opposed cylinder) engines of the diesel persuasion are
very close to an ideal concept. Junkers engine division JUMO used the
concept in their pre WWII 200 series. Fairbanks Morse in the US used the
concept for diesel submarines and later diesel locomotives. The Russians
used them in their tanks and the British developed the incredible three
crankshaft, 18 cylinder, 36 piston Deltec. Diesel Air Ltd. has updated the
concept in their very cool light aircraft engine.

These are all two-stroke direct injection diesels with intake and exhaust
ports at the ends of the pistons stroke. One piston uncovers the intake
ports and the opposing piston uncovers the exhaust ports so there is a
'uni-flow' scavenging effect. The cranks for the opposing pistons are out
of phase by about 20 degrees so the exhaust port opens first but closes
before the intake port does. This allows true supercharging of the
cylinder. There are neither cylinder heads nor valves to leak or cool. The
whole cylinder is bathed in coolant.

I wish all the diesel aircraft engine developers the best of luck. Their
day has come.

Bill Daniels

[[email protected]]

The Harley Davidson engine is a copy of the 1898 or so De Dion-Bouton.
HD didn't originate it, and there is no way in hell they can keep
anyone else from building a v-twin engine. They lost their essential
point.

Offsetting the cylinders gives you a "rocking couple". But since the
Japanese imitation Harleys are for people who want approximate Harley
appearance and are mechanical idiots....

[[email protected]]

Experimental builders have no reason to complain about Lycoming
prices, because no law makes them use them.

[[email protected]]

wrote:
> The Harley Davidson engine is a copy of the 1898 or so De
Dion-Bouton.
> HD didn't originate it, and there is no way in hell they can keep
> anyone else from building a v-twin engine. They lost their essential
> point.

As I recall, the Japanese were not imitating the engine, only the
sound. The plan was to mimic the sound electronically.

--

FF

[Sport Pilot]

Rob Turk wrote:
> "Matt Whiting" > wrote in message
> ...
> > Sport Pilot wrote:
> >> Most flat fours are not a boxer, and many twins are not. A boxer
> >> engine will weigh and cost more. It's not really needed on a flat four
> >> anyway, as on a non boxer the pistons on the front and rear pair will
> >> be going opposite directions
> >>
> >
> > True, but this doesn introduce a "rocking couple" vibration mode. There's
> > no free lunch WRT to engine design. :-)
> >
> > Although some configurations come close (I-6, V-8, etc.)
> >
> >
> > Matt
>
> A very interesting design is the Diesel Air engine (www.dair.co.uk). They
> have two pistons per cylinder, moving in opposite directions. The ignition
> happens in the center of the cylinder, which is also the center of the
> engine. All forces that can cause vibration are supposed to cancel eachother
> out, so there's a minimum of vibration. The engine has two cranks which are
> mechanically coupled on the outside to bundle the power to the prop.
> Pictures are on their site.
>
> Rob

Two pistons per cylinder, one piston and two cylinders, etc. It has
been done before.

[Sport Pilot]

Bob, Last time I took apart a VW, and Corvair, they shared the same con
rod. Not sure about aircraft engines, but pretty sure the one in the C
150 and the C 172's are not boxers. So I think you have the definition
right, just misinformed about the commanality of boxer engines. They
are uncommon enough that the manufacture makes a deal about the engine
if it is a boxer, such as Ferarri, and BMW(?).

[Sport Pilot]

Sport Pilot wrote:
> Bob, Last time I took apart a VW, and Corvair, they shared the same con
> rod. Not sure about aircraft engines, but pretty sure the one in the C
> 150 and the C 172's are not boxers. So I think you have the definition
> right, just misinformed about the commanality of boxer engines. They
> are uncommon enough that the manufacture makes a deal about the engine
> if it is a boxer, such as Ferarri, and BMW(?).

My bad, the VW is a boxer, not sure about the Corvair.

[Corky Scott]

On 27 May 2005 08:47:23 -0700, "Sport Pilot" >
wrote:

>Bob, Last time I took apart a VW, and Corvair, they shared the same con
>rod. Not sure about aircraft engines, but pretty sure the one in the C
>150 and the C 172's are not boxers. So I think you have the definition
>right, just misinformed about the commanality of boxer engines. They
>are uncommon enough that the manufacture makes a deal about the engine
>if it is a boxer, such as Ferarri, and BMW(?).

I've never given this much thought before. Which design is called a
boxer engine? Let's keep it simple and talk about a twin cylinder
engine. Is the design in which the connecting rods share the same
journal the boxer, or is it the design in which the two connecting
rods have their own throw and own journals. This second type seems
like it would require greater cylinder offset in order to accomodate
the crankshaft throws, and would probably vibrate more.

So which is considered the boxer design? Is the other design simply
called "horizontally opposed"?

Thanks, Corky Scott

[Matt Whiting]

Sport Pilot wrote:
> Bob, Last time I took apart a VW, and Corvair, they shared the same con
> rod. Not sure about aircraft engines, but pretty sure the one in the C
> 150 and the C 172's are not boxers. So I think you have the definition
> right, just misinformed about the commanality of boxer engines. They
> are uncommon enough that the manufacture makes a deal about the engine
> if it is a boxer, such as Ferarri, and BMW(?).
>

Sharing the same con rod is quite a feat of design. How did they do
that and still get the crank to spin. Oh, you meant shared the same
crank journal... :-)


Matt

[Matt Whiting]

Corky Scott wrote:

> On 27 May 2005 08:47:23 -0700, "Sport Pilot" >
> wrote:
>
>
>>Bob, Last time I took apart a VW, and Corvair, they shared the same con
>>rod. Not sure about aircraft engines, but pretty sure the one in the C
>>150 and the C 172's are not boxers. So I think you have the definition
>>right, just misinformed about the commanality of boxer engines. They
>>are uncommon enough that the manufacture makes a deal about the engine
>>if it is a boxer, such as Ferarri, and BMW(?).
>
>
> I've never given this much thought before. Which design is called a
> boxer engine? Let's keep it simple and talk about a twin cylinder
> engine. Is the design in which the connecting rods share the same
> journal the boxer, or is it the design in which the two connecting
> rods have their own throw and own journals. This second type seems
> like it would require greater cylinder offset in order to accomodate
> the crankshaft throws, and would probably vibrate more.
>
> So which is considered the boxer design? Is the other design simply
> called "horizontally opposed"?

Horizontally opposed is the configuration of the cylinders. Boxer means
that the pistons go towards the crank and away from the crank in unison.


Matt

[Bob Kuykendall]

Earlier, Sport Pilot wrote:

> My bad, the VW is a boxer, not sure about the Corvair.

Here's a picture of the Corvair crankshaft from William Wynne's Fly
Corvair site:

http://www.flycorvair.com/crank.jpg

I count ten journals on that crank (not counting the stuff forward of
the cam drive gear or aft of the distrubutor drive gear). Since it's a
six cylinder car, I have to assume that four of those (the first,
fourth, seventh, and tenth) are mains that ride in bearing shells in
the crankshaft. That leaves six journals for the connecting rods; to my
way of thinking that means that the con rods are not sharing journals.

As to whether it's a true "boxer," it looks to me like it is. I think
that the photo shows that the rod journals in each opposing cylinder
pair are separated by 180 degrees. That shows most clearly in the rod
journal pair near the bottom of the photo. Since its a 6-cylinder
engine the different pairs are separated from each other by 120
degrees, so the other pairs are at odd angles to the photo perspective.

As for the Lycoming, this drawing from the Sacramento Sky Ranch
(thanks, Mr. Schwaner!) shows seven journals, of which three (including
the long one behind the prop flange) are mains and four are rod
journals:

http://www.sacskyranch.com/lyc_crank_gear.jpg

And again, the rod journals of each opposing cylinder pair are
separated by 180 degrees.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24