Fantastic model of a 9-cylinder radial engine, shown operating.

Part 1: https://www.youtube.com/watch?v=qjnQKXNPsk4

Part 2: https://www.youtube.com/watch?v=R71Xhrkc3EQ

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(='.'=) systemd: the Linux version of Windows 10
(")_(")

On Tue, 15 Nov 2016 10:26:23 +0000
Mike Tomlinson wrote:

Fantastic model of a 9-cylinder radial engine, shown operating.

Part 1: https://www.youtube.com/watch?v=qjnQKXNPsk4

Part 2: https://www.youtube.com/watch?v=R71Xhrkc3EQ


I prefer the Rotary:

https://www.youtube.com/watch?v=0jHRuEkvO8E

--
Davey.

On Tuesday, 15 November 2016 10:45:50 UTC, Davey wrote:
On Tue, 15 Nov 2016 10:26:23 +0000
Mike Tomlinson wrote:

Fantastic model of a 9-cylinder radial engine, shown operating.

Part 1: https://www.youtube.com/watch?v=qjnQKXNPsk4

Part 2: https://www.youtube.com/watch?v=R71Xhrkc3EQ


I prefer the Rotary:

https://www.youtube.com/watch?v=0jHRuEkvO8E

--
Davey.

That's the sort of art that I would like to see.

It really beats the Tracey Emin ****.

"Davey" wrote in message
news
On Tue, 15 Nov 2016 10:26:23 +0000
Mike Tomlinson wrote:

Fantastic model of a 9-cylinder radial engine, shown operating.

Part 1: https://www.youtube.com/watch?v=qjnQKXNPsk4

Part 2: https://www.youtube.com/watch?v=R71Xhrkc3EQ


I prefer the Rotary:

https://www.youtube.com/watch?v=0jHRuEkvO8E

Rotaries have always baffled me: how do you get your supply of fuel to the
cylinders without leakage where the stationary fuel tank feed meets the
rotating cylinder block. It's not like an electric motor where slip rings or
a commutator serve the equivalent purpose with electric current: in the case
of fuel, you need to prevent leakage.

What was the advantage of rotating the cylinder block? Was is mainly that
the movement of the block though the air provides additional air currents
over the fins and allows the cylinders to be air-cooled rather than
water-cooled? Or was there any other advantage?

Presumably rotaries tend to be noisier because each cylinder has its own
separate exhaust pipe - or if there is a common exhaust pipe it cannot have
such elaborate silencer because of the need to balance and minimise the
rotating mass.

Can rotaries be made to made with supercharging (ie a compressor to increase
air intake pressure)? I suppose it's possible if the compressor is made to
spin with the cylinder block. Turbocharging (using exhaust pressure rather
than crankshaft rotation to drive the inlet compressor) could be
"interesting" :-) In either case, you've got the problem of not being able
to have a large (and therefore heavy) air reservoir to store boost pressure
for cases where the throttle is opened on a slow engine and high boost is
needed at a time when the engine can't yet generate it.


Is "rotary" the correct word for this type of engine, given that the word is
also used to describe a Wankel engine which works in a very different way.

I'd have thought it was pretty obvious really.
The oones I never understood properly were the Wankel engines with their
rounded sided triangle in a round hole with a gear on the inside and three
spark plugs.

Brian

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"Mike Tomlinson" wrote in message
...

Fantastic model of a 9-cylinder radial engine, shown operating.

Part 1: https://www.youtube.com/watch?v=qjnQKXNPsk4

Part 2: https://www.youtube.com/watch?v=R71Xhrkc3EQ

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(")_(")

"Brian Gaff" wrote in message
news
I'd have thought it was pretty obvious really.
The oones I never understood properly were the Wankel engines with their
rounded sided triangle in a round hole with a gear on the inside and three
spark plugs.

Yes: how does the increase in pressure in one "cylinder" space translate
into rotational movement of the "piston" around the central shaft which then
rotates? Definitely needs a moving model to explain how it works.

The "round hole" is not actually round but more like two semi-circles that
have been split apart and a straight section inserted, to form a shape
called an epitrochoid.

On Tue, 15 Nov 2016 11:51:42 -0000
"NY" wrote:

"Davey" wrote in message
news

snip

Rotaries have always baffled me: how do you get your supply of fuel
to the cylinders without leakage where the stationary fuel tank feed
meets the rotating cylinder block. It's not like an electric motor
where slip rings or a commutator serve the equivalent purpose with
electric current: in the case of fuel, you need to prevent leakage.

What was the advantage of rotating the cylinder block? Was is mainly
that the movement of the block though the air provides additional air
currents over the fins and allows the cylinders to be air-cooled
rather than water-cooled? Or was there any other advantage?

Presumably rotaries tend to be noisier because each cylinder has its
own separate exhaust pipe - or if there is a common exhaust pipe it
cannot have such elaborate silencer because of the need to balance
and minimise the rotating mass.

Can rotaries be made to made with supercharging (ie a compressor to
increase air intake pressure)? I suppose it's possible if the
compressor is made to spin with the cylinder block. Turbocharging
(using exhaust pressure rather than crankshaft rotation to drive the
inlet compressor) could be "interesting" :-) In either case, you've
got the problem of not being able to have a large (and therefore
heavy) air reservoir to store boost pressure for cases where the
throttle is opened on a slow engine and high boost is needed at a
time when the engine can't yet generate it.


Is "rotary" the correct word for this type of engine, given that the
word is also used to describe a Wankel engine which works in a very
different way.


The aircraft Rotary engine was invented before the Wankel, so to me it
has the prior claim.
As to the questions about supercharging etc, I have no idea. I just
like the contrariness of having a huge mass rotating. I also
appreciated watching Tractor Pulling in the US, where a machine with
three Allison aircraft engines would be hauled to a stop by
nothing more than earth.
Try Youtube for 'Starting Giant Engines'.

--
Davey.

En el artículo , Davey
escribió:

I prefer the Rotary:

https://www.youtube.com/watch?v=0jHRuEkvO8E

Ooh, ta for the link.

--
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(='.'=) systemd: the Linux version of Windows 10
(")_(")

On 15/11/16 11:51, NY wrote:

Rotaries have always baffled me: how do you get your supply of fuel to
the cylinders without leakage where the stationary fuel tank feed meets
the rotating cylinder block. It's not like an electric motor where slip
rings or a commutator serve the equivalent purpose with electric
current: in the case of fuel, you need to prevent leakage.

https://en.wikipedia.org/wiki/Rotary_engine


What was the advantage of rotating the cylinder block? Was is mainly
that the movement of the block though the air provides additional air
currents over the fins and allows the cylinders to be air-cooled rather
than water-cooled? Or was there any other advantage?


No flywheel = lighter.

Presumably rotaries tend to be noisier because each cylinder has its own
separate exhaust pipe - or if there is a common exhaust pipe it cannot
have such elaborate silencer because of the need to balance and minimise
the rotating mass.

No aircraft engine ever used a silencer as far as I know. Some night
fighters used some kind of flame baffles so they didnt show up at night.



Can rotaries be made to made with supercharging (ie a compressor to
increase air intake pressure)? I suppose it's possible if the compressor
is made to spin with the cylinder block. Turbocharging (using exhaust
pressure rather than crankshaft rotation to drive the inlet compressor)
could be "interesting" :-) In either case, you've got the problem of not
being able to have a large (and therefore heavy) air reservoir to store
boost pressure for cases where the throttle is opened on a slow engine
and high boost is needed at a time when the engine can't yet generate it.

I am sure it could be done, but tehre is no onterst in WWI style
rotaryty engines at all, except tp power reproduction planes, and those
are pretty faithful to the original designs


Is "rotary" the correct word for this type of engine, given that the
word is also used to describe a Wankel engine which works in a very
different way.

Rotary is applied to any engine where large parts of it go round.

The Le Rhone and Le Clerget's were there well beforer Wankel.

--
"Socialist governments traditionally do make a financial mess. They
always run out of other people's money. It's quite a characteristic of them"

Margaret Thatcher

NY wrote:
"Davey" wrote in message
news
On Tue, 15 Nov 2016 10:26:23 +0000
Mike Tomlinson wrote:

Fantastic model of a 9-cylinder radial engine, shown operating.

Part 1: https://www.youtube.com/watch?v=qjnQKXNPsk4

Part 2: https://www.youtube.com/watch?v=R71Xhrkc3EQ


I prefer the Rotary:

https://www.youtube.com/watch?v=0jHRuEkvO8E

Rotaries have always baffled me: how do you get your supply of fuel to the
cylinders without leakage where the stationary fuel tank feed meets the
rotating cylinder block. It's not like an electric motor where slip rings or
a commutator serve the equivalent purpose with electric current: in the case
of fuel, you need to prevent leakage.

I could be wrong but I think the carb would be mounted on a stationary part
of the crankcase and then the fuel/air mixture was drawn up individual
induction pipes to each cylinder


What was the advantage of rotating the cylinder block? Was is mainly that
the movement of the block though the air provides additional air currents
over the fins and allows the cylinders to be air-cooled rather than
water-cooled? Or was there any other advantage?

Just cooling IIRC.


Presumably rotaries tend to be noisier because each cylinder has its own
separate exhaust pipe - or if there is a common exhaust pipe it cannot have
such elaborate silencer because of the need to balance and minimise the
rotating mass.


Also had problems with huge torque reaction. It would significantly affect
how quickly a plane could sharply bank to the right or left in a single
engined craft.


Can rotaries be made to made with supercharging (ie a compressor to increase
air intake pressure)? I suppose it's possible if the compressor is made to
spin with the cylinder block. Turbocharging (using exhaust pressure rather
than crankshaft rotation to drive the inlet compressor) could be
"interesting" :-) In either case, you've got the problem of not being able
to have a large (and therefore heavy) air reservoir to store boost pressure
for cases where the throttle is opened on a slow engine and high boost is
needed at a time when the engine can't yet generate it.


As you say, turbocharging almost certainly not possible. No reason
theoretically why they couldn't be supercharged but given that better
engine designs were developed, not much point.


Is "rotary" the correct word for this type of engine, given that the word is
also used to describe a Wankel engine which works in a very different way.

The term was in use *way* before the invention of the Wankel so I don't
think it can be considered "wrong" in any sense.

Tim

--
Please don't feed the trolls

On 15/11/16 15:14, Tim+ wrote:
NY wrote:
"Davey" wrote in message
news
On Tue, 15 Nov 2016 10:26:23 +0000
Mike Tomlinson wrote:

Fantastic model of a 9-cylinder radial engine, shown operating.

Part 1: https://www.youtube.com/watch?v=qjnQKXNPsk4

Part 2: https://www.youtube.com/watch?v=R71Xhrkc3EQ


I prefer the Rotary:

https://www.youtube.com/watch?v=0jHRuEkvO8E

Rotaries have always baffled me: how do you get your supply of fuel to the
cylinders without leakage where the stationary fuel tank feed meets the
rotating cylinder block. It's not like an electric motor where slip rings or
a commutator serve the equivalent purpose with electric current: in the case
of fuel, you need to prevent leakage.

I could be wrong but I think the carb would be mounted on a stationary part
of the crankcase and then the fuel/air mixture was drawn up individual
induction pipes to each cylinder


What was the advantage of rotating the cylinder block? Was is mainly that
the movement of the block though the air provides additional air currents
over the fins and allows the cylinders to be air-cooled rather than
water-cooled? Or was there any other advantage?

Just cooling IIRC.

And weight...


Presumably rotaries tend to be noisier because each cylinder has its own
separate exhaust pipe - or if there is a common exhaust pipe it cannot have
such elaborate silencer because of the need to balance and minimise the
rotating mass.


Also had problems with huge torque reaction. It would significantly affect
how quickly a plane could sharply bank to the right or left in a single
engined craft.

Er No . Not banking. Turning. Or zooming. Any yaw or pitch changes would
case a reaction at right angles, so a rapid climbing or diving turn was
likely to result..

Neutral in pure roll, but that wasn't something many pilots did in WWI.

Mostly controilled turns with the rudder.



Can rotaries be made to made with supercharging (ie a compressor to increase
air intake pressure)? I suppose it's possible if the compressor is made to
spin with the cylinder block. Turbocharging (using exhaust pressure rather
than crankshaft rotation to drive the inlet compressor) could be
"interesting" :-) In either case, you've got the problem of not being able
to have a large (and therefore heavy) air reservoir to store boost pressure
for cases where the throttle is opened on a slow engine and high boost is
needed at a time when the engine can't yet generate it.


As you say, turbocharging almost certainly not possible. No reason
theoretically why they couldn't be supercharged but given that better
engine designs were developed, not much point.


Is "rotary" the correct word for this type of engine, given that the word is
also used to describe a Wankel engine which works in a very different way.

The term was in use *way* before the invention of the Wankel so I don't
think it can be considered "wrong" in any sense.

Tim



--
The theory of Communism may be summed up in one sentence: Abolish all
private property.

Karl Marx

On Tuesday, 15 November 2016 12:48:49 UTC, The Natural Philosopher wrote:
On 15/11/16 11:51, NY wrote:

Rotaries have always baffled me: how do you get your supply of fuel to
the cylinders without leakage where the stationary fuel tank feed meets
the rotating cylinder block. It's not like an electric motor where slip
rings or a commutator serve the equivalent purpose with electric
current: in the case of fuel, you need to prevent leakage.

https://en.wikipedia.org/wiki/Rotary_engine


What was the advantage of rotating the cylinder block? Was is mainly
that the movement of the block though the air provides additional air
currents over the fins and allows the cylinders to be air-cooled rather
than water-cooled? Or was there any other advantage?


No flywheel = lighter.

Presumably rotaries tend to be noisier because each cylinder has its own
separate exhaust pipe - or if there is a common exhaust pipe it cannot
have such elaborate silencer because of the need to balance and minimise
the rotating mass.

No aircraft engine ever used a silencer as far as I know. Some night
fighters used some kind of flame baffles so they didnt show up at night.

Bollix.
"Hush kits" are available for many aircraft.
Usually they consist of a silencer and multi-bladed propeller.


Example
https://groups.google.com/forum/#!to...ng/nUcDEM1z674

On Tuesday, 15 November 2016 12:48:49 UTC, The Natural Philosopher wrote:
On 15/11/16 11:51, NY wrote:

Rotaries have always baffled me: how do you get your supply of fuel to
the cylinders without leakage where the stationary fuel tank feed meets
the rotating cylinder block. It's not like an electric motor where slip
rings or a commutator serve the equivalent purpose with electric
current: in the case of fuel, you need to prevent leakage.

https://en.wikipedia.org/wiki/Rotary_engine


What was the advantage of rotating the cylinder block? Was is mainly
that the movement of the block though the air provides additional air
currents over the fins and allows the cylinders to be air-cooled rather
than water-cooled? Or was there any other advantage?


No flywheel = lighter.

ICE aircraft engines don't need a flywheel,the propeller provides this function.
Some have a lightweight starter ring.

On 15/11/2016 11:51, NY wrote:

I prefer the Rotary:

https://www.youtube.com/watch?v=0jHRuEkvO8E

Rotaries have always baffled me: how do you get your supply of fuel to
the cylinders without leakage where the stationary fuel tank feed meets
the rotating cylinder block. It's not like an electric motor where slip
rings or a commutator serve the equivalent purpose with electric
current: in the case of fuel, you need to prevent leakage.

You don't send fuel to the cylinders unless you have direct injection.
So a rotary diesel isn't going to work, but a carburetted petrol engine
as those old rotaries will be fine. The cylinders pull in fuel/air.
Since it's suck rather than blow for that mix, any leaks will result in
more air coming in rather than fuel leaking out, and that's easy enough
to cope with by making the mix a little richer.

Presumably rotaries tend to be noisier because each cylinder has its own
separate exhaust pipe - or if there is a common exhaust pipe it cannot
have such elaborate silencer because of the need to balance and minimise
the rotating mass.

These would be plane engines, where the concept of silencer doesn't
really happen :-)

Can rotaries be made to made with supercharging (ie a compressor to
increase air intake pressure)? I suppose it's possible if the compressor
is made to spin with the cylinder block.

Yes

Turbocharging (using exhaust
pressure rather than crankshaft rotation to drive the inlet compressor)
could be "interesting" :-)

Not a chance :-)

In either case, you've got the problem of not
being able to have a large (and therefore heavy) air reservoir to store
boost pressure for cases where the throttle is opened on a slow engine
and high boost is needed at a time when the engine can't yet generate it.

Turbos and superchargers have been used for years (pre-ww2), and don't
use air reservoirs in the way you describe. Turbo lag is real, but the
get rounds for that aren't air reservoirs, and the lag isn't terribly
long anyway. Superchargers only need to work at the same speed as the
engine (or rather proportional to) if you think about it :-)

"Clive George" wrote in message
...
On 15/11/2016 11:51, NY wrote:
Rotaries have always baffled me: how do you get your supply of fuel to
the cylinders without leakage where the stationary fuel tank feed meets
the rotating cylinder block. It's not like an electric motor where slip
rings or a commutator serve the equivalent purpose with electric
current: in the case of fuel, you need to prevent leakage.

You don't send fuel to the cylinders unless you have direct injection. So
a rotary diesel isn't going to work, but a carburetted petrol engine as
those old rotaries will be fine. The cylinders pull in fuel/air. Since
it's suck rather than blow for that mix, any leaks will result in more air
coming in rather than fuel leaking out, and that's easy enough to cope
with by making the mix a little richer.

Ah, of course. For some reason I visualising the carb on the rotary part,
but if it's on the static part, then a normally aspirated engine would suck
the mixture and hence any leakage would be inwards, and air-only.

Do supercharged petrol engines compress the mixture, or do they compress the
air and then inject fuel into the stream between compressor and cylinders?
In other words, can you have non-fuel-injected carburettor
super/turbo-charged petrol engines? Presumably for a rotary engine, as long
as the supercharger is on the rotating part, it still sucks in mixture (so
leakage will be inwards) and then compresses it after the leaky joint.

In either case, you've got the problem of not
being able to have a large (and therefore heavy) air reservoir to store
boost pressure for cases where the throttle is opened on a slow engine
and high boost is needed at a time when the engine can't yet generate it.

Turbos and superchargers have been used for years (pre-ww2), and don't use
air reservoirs in the way you describe. Turbo lag is real, but the get
rounds for that aren't air reservoirs, and the lag isn't terribly long
anyway.

I hadn't realised that. I assumed that all charged engines had a reservoir,
and that it was in the exceptional case of very hard acceleration from low
engine speed (and hence low pressure) that the reservoir became exhausted,
and that this was what caused turbo lag.

I've learned something!

On 15/11/2016 17:48, NY wrote:
"Clive George" wrote in message
...
On 15/11/2016 11:51, NY wrote:
Rotaries have always baffled me: how do you get your supply of fuel to
the cylinders without leakage where the stationary fuel tank feed meets
the rotating cylinder block. It's not like an electric motor where slip
rings or a commutator serve the equivalent purpose with electric
current: in the case of fuel, you need to prevent leakage.

You don't send fuel to the cylinders unless you have direct injection.
So a rotary diesel isn't going to work, but a carburetted petrol
engine as those old rotaries will be fine. The cylinders pull in
fuel/air. Since it's suck rather than blow for that mix, any leaks
will result in more air coming in rather than fuel leaking out, and
that's easy enough to cope with by making the mix a little richer.

Ah, of course. For some reason I visualising the carb on the rotary
part, but if it's on the static part, then a normally aspirated engine
would suck the mixture and hence any leakage would be inwards, and
air-only.

Do supercharged petrol engines compress the mixture, or do they compress
the air and then inject fuel into the stream between compressor and
cylinders? In other words, can you have non-fuel-injected carburettor
super/turbo-charged petrol engines? Presumably for a rotary engine, as
long as the supercharger is on the rotating part, it still sucks in
mixture (so leakage will be inwards) and then compresses it after the
leaky joint.

Yes, you can have super chargers and turbos on carburetted engines -
they predate widespread use of fuel injection by quite a long time.

You can have the carburettor on either side of the blower too (with a
super charger, not sure I'd want to try compressing a fuel/air mix with
a hot turbo).

It would be interesting trying to arrange a supercharger on the moving
engine. Probably theoretically possible, but not practical.

In either case, you've got the problem of not
being able to have a large (and therefore heavy) air reservoir to store
boost pressure for cases where the throttle is opened on a slow engine
and high boost is needed at a time when the engine can't yet generate
it.

Turbos and superchargers have been used for years (pre-ww2), and don't
use air reservoirs in the way you describe. Turbo lag is real, but the
get rounds for that aren't air reservoirs, and the lag isn't terribly
long anyway.

I hadn't realised that. I assumed that all charged engines had a
reservoir, and that it was in the exceptional case of very hard
acceleration from low engine speed (and hence low pressure) that the
reservoir became exhausted, and that this was what caused turbo lag.

I've learned something!

:-)

I'll let Peter Hill talk about the ways you reduce turbo lag - mostly
it's about either keeping the turbine spinning or just using a smaller
one which can accelerate faster.

That sounds like a disease of sheep!
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"NY" wrote in message
...
"Brian Gaff" wrote in message
news
I'd have thought it was pretty obvious really.
The oones I never understood properly were the Wankel engines with their
rounded sided triangle in a round hole with a gear on the inside and
three spark plugs.

Yes: how does the increase in pressure in one "cylinder" space translate
into rotational movement of the "piston" around the central shaft which
then rotates? Definitely needs a moving model to explain how it works.

The "round hole" is not actually round but more like two semi-circles that
have been split apart and a straight section inserted, to form a shape
called an epitrochoid.

On 15/11/2016 3:14 PM, Tim+ wrote:
NY wrote:
"Davey" wrote in message
news
On Tue, 15 Nov 2016 10:26:23 +0000
Mike Tomlinson wrote:

Fantastic model of a 9-cylinder radial engine, shown operating.

Part 1: https://www.youtube.com/watch?v=qjnQKXNPsk4

Part 2: https://www.youtube.com/watch?v=R71Xhrkc3EQ


I prefer the Rotary:

https://www.youtube.com/watch?v=0jHRuEkvO8E

Rotaries have always baffled me: how do you get your supply of fuel to the
cylinders without leakage where the stationary fuel tank feed meets the
rotating cylinder block. It's not like an electric motor where slip rings or
a commutator serve the equivalent purpose with electric current: in the case
of fuel, you need to prevent leakage.

I could be wrong but I think the carb would be mounted on a stationary part
of the crankcase and then the fuel/air mixture was drawn up individual
induction pipes to each cylinder


What was the advantage of rotating the cylinder block? Was is mainly that
the movement of the block though the air provides additional air currents
over the fins and allows the cylinders to be air-cooled rather than
water-cooled? Or was there any other advantage?

Just cooling IIRC.


Presumably rotaries tend to be noisier because each cylinder has its own
separate exhaust pipe - or if there is a common exhaust pipe it cannot have
such elaborate silencer because of the need to balance and minimise the
rotating mass.


Also had problems with huge torque reaction. It would significantly affect
how quickly a plane could sharply bank to the right or left in a single
engined craft.

I can fully see that.

I loved seeing that video. Mastery!

It was interesting to note the 2 circles that the piston heads described
as they rotated around. As you watch the heads move as a whole, they
describe an eccentric wheel; a weighting, which, is reduced by the
actual counter weight he has on the shaft. Sadly, both are in the same
rotation plane(Hicc!)and, additive. Good for engine momentum but, as you
say, biased to control.

The 9 head rotary engine has a firing stroke that has a directional
change every 80 deg, albeit, 40 degs per 720 deg of engine rotation.

Does this make for a smoother engine vibration?

I mean; if the engine block is being persuaded to follow a circular
path, does this make for 3 virtual wheels that, between them form
cushioned forces? Do these engines accelerate faster, smoother?

All the rotations of his model looked smooth.


....Ray.




Can rotaries be made to made with supercharging (ie a compressor to increase
air intake pressure)? I suppose it's possible if the compressor is made to
spin with the cylinder block. Turbocharging (using exhaust pressure rather
than crankshaft rotation to drive the inlet compressor) could be
"interesting" :-) In either case, you've got the problem of not being able
to have a large (and therefore heavy) air reservoir to store boost pressure
for cases where the throttle is opened on a slow engine and high boost is
needed at a time when the engine can't yet generate it.


As you say, turbocharging almost certainly not possible. No reason
theoretically why they couldn't be supercharged but given that better
engine designs were developed, not much point.


Is "rotary" the correct word for this type of engine, given that the word is
also used to describe a Wankel engine which works in a very different way.

The term was in use *way* before the invention of the Wankel so I don't
think it can be considered "wrong" in any sense.

Tim

On 22/11/2016 03:41, RayL12 wrote:

The 9 head rotary engine has a firing stroke that has a directional
change every 80 deg, albeit, 40 degs per 720 deg of engine rotation.

Eh?

AIUI the spark hits every other cylinder as they hit TDC. Two turns and
they've all had one. The non-sparking one is a the end of exhaust /
beginning of induction.

Andy