Engine Desing

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

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 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.

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

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

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

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