From: ivan@erich.triumf.ca (Ivan D. Reid)
Subject: Re: Honda 500 GP 'Droner' motor question
News-Software: VAX/VMS VNEWS 1.41    
Organization: TRIUMF: Tri-University Meson Facility
Date: Mon, 5 Oct 1992 06:13:00 GMT

In article <marcl.718057659@os-d> marcl@os-d.isc-br.com (H. Marc Lewis) writes:
>
>I'm tired of waiting for Kevin Cameron (noted American moto-journalist) to
>write an article explaining how the Honda 500cc 'Droner' motor works (or
>Yamaha's or Suzuki's copies of the Honda 'droner').  Anyone here know the
>exact details, and feel like sharing them?  

	As promised, here's Peter Clifford's article from REVS:
===============================================================

        The Big Bang Theory.  Original article by Peter Clifford.
        Reproduced without permission, but with attribution. From
        REVS Motorcycle News, August 19-September 1, 1992.  Within
        quotation marks all errors of grammar and punctuation are, as
        far as my typing permits, to be attributed to the original
        article.

[Peter Clifford is an English motorcyclist and apparently a fairly
competent racer.  He used to come to Australia as a guest commentator on
ABC Television during the end-of-year Swann Series races.  He regularly
produces off-season articles about test rides on some of the previous
season's GP bikes.  I don't know if his articles appear in the US.]

Here are excerpts and summaries from the article:
        "There is no mistaking the close firing order engines, no hiding the
fact that they are different; the low exhaust note is a dead giveaway.
Honda shook the racing world when the new NSR made its debut at the
Japanese Grand Prix and ran away with that and the next three races."

        Suzuki, Cagiva, and Yamaha finally produced their own versions.
There are problems with comparisons due to all the mid-season crashes, etc.

        "It does appear that the others have got close to the Honda's
performance, at least the riders have been thrilled to get the new power
plants.  While no one knows what secrets lie within Honda's 1992 NSR there
is very little that is secret about the Suzuki, Yamaha and Cagiva engines.
All three factories simply revised their crankshafts and ignition systems
to produce a different firing interval.  The current four-cylinder engines
have their pistons paired so that prior to Honda's revolutionary move two
would fire together and then the other two fired 180 degrees later according
to crankshaft rotation."

        "The close firing interval engines still have paired firing but the
gap between is much smaller.  The exact figures are secret but it is said
that Cagiva has an 80 degrees firing interval, the Yamaha is 90 degrees
and that the Honda and Suzuki [are] very close to the same figures."

        "These engines are not mock singles, then, but that is the direct-
ion in which they are heading.  Accepting the fact that more secrets may
yet lie hidden within the Honda but that no other changes have been made
to the other three engines, why should a change in the firing interval
produce such an improvement in overall performance?"

        Total power, or torque at any revs is unaffected by firing interval.

        "The advantage of the close firing interval engine is not to be 
found inside the engine at all and it will not be found on the dyno.  It 
will only be found on the track and is all to do with rubber, that tiny 
patch of rubber that is the tyre contact patch."

         "Tyres are responsible for so much of the mystique and magic of
racing and once more they are the big 'x' factor in this equation.  It is
the relationship between rubber and firing interval that is crucial and to
understand why these engines are so superior we have to consider the
mechanics of rubber gripping road."

        "Warren Willing, the Sydney race engineer employed by the Roberts
team and seconded to Randy Mamola's Budweiser squad for this season, gets
to the nub of the matter."

[Warren Willing was once, in the '70s, one of Australia's top road-racers,
continually battling for first place with Gregg Hansford, amongst others.
He had some successful ventures overseas; I think he did well at Daytona
at least once.  However, he was involved in a fatal accident at the North
West 200 (I think) in Ireland, and received very bad injuries, especially
to his legs.  He was forced to quit racing.  A younger brother, Len, was
for several years one of the top Production racers in the country, and
another brother, Glen, was also briefly in the top ranks of 250 Production,
racing a Honda 3-cylinder.]

        "'The important effect in the tyre is at the contact patch.  The        
malleability and hysteresis within the rubber allows it to mould around
the road particles,' says Willing."

        "Willing points out that you must forget the simple notion of the
coefficient of friction, $\mu$, as it is taught in high school physics.
Racing tyres are more complex."

        "'In theory $\mu$ cannot exceed one.  [Huh?  That's news to me!]
That would limit the angle of lean to 45 degrees but that is obviously
being exceeded and we get an effective coefficient of friction of about
1.4,' Willing points out.  This is achieved by the action of the rubber
moulding around the particles of tarmac."

        "'The important thing is to prevent the tyre from spinning,'
explains Willing. 'As soon as it goes from static to kinetic traction that
generates heat in the contact patch.  When that happens things start to get
hot very quickly, to the point where you can even see smoke coming off the
tyres.  The rubber is being overworked and grip is lost.'"

        "'If you allow the rubber to mould around the particles and then
impart a short sharp push then it will push the wheel forward,' continues
Willing. 'At the same time the rubber starts to deform and come out from
around the particles of the road.  If you give it another push too soon
then it will spin.  If you allow time for the rubber to reform round the
particles it will push forward again at the next power impulse without
spinning.'"

        "'That is why it only really makes a difference on the slower corn-
ers where the revs are lower and the rubber is having a chance to mould
round the particles.  After that the pulses come too quickly.  If you
consider that the tyre contact patch is about 120 mm long it is quite simple
to work out that at low rpm you have two firing impulses per contact patch
with the even firing interval engine and just over one with the new
engines,' he added."

        OK, so why hasn't it been done before.  Marlboro Yamaha [hang on,
later he appears to be working for Honda] engineer, New Zealander Mike
Sinclair [a long-time GP regular] takes up the story.

        "'Suzuki tried it in 1979 [when Sinclair was in the Suzuki team]
but they only tried it on a steady state dyno, and it broke gears and
primary drives.'"

        Breaking parts is still a problem.  While Honda started from scratch
and was able to design for the higher loads, the others retrofitted their
engines mid-season and had parts not designed for the higher torque peaks.
The triumvirate, at least, is solving the problem by throwing parts at the
engine, replacing them earlier than normal.  Rumour also suggests Honda is
doing the same.

        "The problem of the peak torque loadings is obviously very sign-
ificant.  If it is necessary to increase the dimensions of crankshafts, 
crankcases, gears, clutches, sprockets, chains and cush drives to cope with 
the increased loads then this must be considered to detract from the
advantages offered by the revised engine.  This is one of the reasons why
the engines are not actually pseudo singles, why there is still a firing
interval.  There is a compromise between spreading the loads on the engine
as much as possible while allowing as much time as possible for the tyre
rubber to recover.  There is also the ignition system to be considered and
the hurried mid-season redesigns that went on meant that existing ignition
systems were asked to generate more power in less time."

        Simply recording the Honda's exhaust note and replaying it into
an oscilloscope would have shown the other manufactures the secrets of the
new firing interval.

        "It would be a mistake though to assume that the firing interval
is the only special thing about the 1992 NSR.  Honda certainly changed more 
than anyone else and while some of the changes were forced on it by its
single-crank layout there may be more secrets hidden within.  The change
that Honda had to make was to move the primary drive take-off to the centre
of the crank."

        "This reduced the torque on the crank.  Otherwise the far cylinder
was twisting across three cylinders to get to the primary gears.  Earlier,
even-firing interval Honda engines could cope with this and the other
manufacturers have two cranks anyway."

        "Splitting the engine in half thus and firing the cylinders close
together opened another possibility for Honda, namely common crankcase
volumes.  Honda could rid itself of the seal between pairs of cylinders and
thus reduce internal friction and shorten the crank.  Whether or not Honda
has done this or not remains a closely guarded secret but as Willing pointed
out, 'Why wouldn't they do it, there is no disadvantage to it.'"

        Generally the riders weren't impressed with the new engines and
initially they didn't improve lap times but eventually Eddie Lawson said,
"You have to forget the way it feels and just look at the stop watch other-
wise you would never use it."

        The new engine offered more consistency; Sinclair recalls that in
Spain, Mick Doohan did 13 laps faster than anyone else, on several differ-
ent tyres.  More tyres worked well with the new engine. "'The improvements
must be coming from the engine because the frame and suspension are the
same as last year.  We knew last year that there was nothing much wrong
there.'"

        So, for once it appears that the engine designers have come up
with an advance that helps, rather than hinders, the tyre engineers.

        "With this in mind will the next step be a true 'quangle', with
all four cylinders firing together?  It might be possible if internal
stresses can be accommodated without making components too massive."

        An accompanying side-bar explores the causes and consequences of
high-sides;  the suspension apparently plays a role here but the new
engines may also be a factor in avoiding these particularly nasty crashes.
[Personally, I've never high-sided.  I prefer the late Ron Toombs' advice
to keep the throttle open once you start sliding.  But you'd better have
things back under control before you run out of revs...]



========================================================================
Ivan Reid, Paul Scherrer Institute, CH.     			ivan@cvax.psi.ch
GSX600F, RG250WD.	SI=2.66     "You Porsche. Me pass!"	DoD #484