My Head is Spinning! (Long) > Webra 1.60 Mix question.

Sat Jan 10 07:45:44 AKST 2004

Brian - Thanks.

Interesting feature of the 9C.  The older Webra Dynamix carbs actually had a
fuel resevoir of sorts in the main jet that "dumped" a little extra fuel
into the intake when the throttle was advanced.

I've been running an MC in a sport plane and have actually played a bit with
differing servo speeds/response (another way of mimicking the accelerate
feature) to see what works best.  What I've found is the best thus far is
having the throttle servo and fuel mixture servo absolutely matched in
everyway possible.  I also run the mixture towards the rich side pretty much
from idle to full, as this keeps the engine cooler and quieter (and doesn't
seem to hurt power or throttle response at all).  Setting on the rich side
of the curve likely reduces the need for an accelerator pump/feature/curve.

Aside - for all you rules gurus out there - I'm not exactly sure how the 9C
accelerate mixing feature works, but if it uses a timing circuit, how does
this fit with the current FAI rules (I haven't seen an official copy of the
2004-2005 book yet)?

Regards,

Dave Lockhart
DaveL322 at comcast.net

----- Original Message -----
From: "Brian Young" <b4598070 at yahoo.com>
To: <discussion at nsrca.org>
Sent: Friday, January 09, 2004 12:16 PM
Subject: Re: My Head is Spinning! (Long) > Webra 1.60 Mix question.

> Dave or others, Ive setup the Webra MC 1.60 on my 9CAP
> Futaba, 5 point mix curve. A feature of the 9CAP
> throttle mix is an accelerate feature, if you arent
> familiar I liken it to an accelarator pump on a
> carburated automotive engine. When active this feature
> advances the mix servo beyond the mix curve as the
> throttle stick is advanced and then pulls it back to
> the curve setting when the throttle postion is
> established. The manual for the 9C advises it may
> improve throttle response. I am curious if you or
> others are familiar with a similar feature, and have
> used it on the 9C or other radios.
>
>
> Good comments btw.
>
> --- David Lockhart <DaveL322 at comcast.net> wrote:
> > A lot of good points and discussion being made in
> > this thread - and nice to see no "feuding" amongst
> > brands.  It truly is nice that options are out
> > there.
> >
> > A couple more items to consider -
> >
> > Initial price vs. secondary costs -
> > - fuel - the average 2C is running on lower nitro
> > than the average 4C (do the math based on the number
> > of times you fly in a year).
> > - vibration - the average 4C vibrates more than the
> > average 2C (makes your own estimates for airplane
> > longevity, servo gears, servo pots, etc - and don't
> > forget to include your time for completing the
> > maintenance).
> > - maintenance cost of engine - parts  is parts, they
> > all wear, and all cost money to replace/fix.  4Cs
> > have more parts.  Again, based on the number of
> > flights you fly in a year, add up the cost for parts
> > and the time to make the repairs.
> > - Use the number of posts on this list as resource
> > to gauge what engines need more repairs.
> > - when I do the math, the 2C wins.
> >
> > Throttle linearity and consistency -
> > - In my opinion, throttle linearity is far
> > over-rated - everyone has there own idea on what a
> > linear throttle is - is 50% stick = 50% RPM and 90%
> > stick = 90% RPM?  Linear to one person is not linear
> > to another - which is why you see many identical
> > setups using different throttle curves in the hands
> > of different pilots.
> > - Throttle consistency is what we really care about
> > - if the throttle is consistent and predictable, it
> > is easy to fly - and if it doesn't feel linear, the
> > "curve" can be adjusted to make it feel "more
> > linear" - the curve can be adjusted mechanically or
> > with the radio.
> > - The other thing we care about is that the throttle
> > is symmetrical and without hysteresis - meaning
> > throttling up to 50% stick will get you the same RPM
> > as throttling down to 50%.  The biggest instigator
> > of hysteresis is a poorly setup piped 2C (but other
> > things on both 2Cs and 4Cs can and do cause
> > hysteresis).
> > - I've not had a problem getting 2Cs or 4Cs to run
> > consistently, so for me, this is a wash.
> >
> > Influence of exhaust system on engine
> > - We all know the exhaust system is primarily to
> > quiet the engine, and secondarily to not detract
> > from the power the engine makes (or  maybe increase
> > the power the engine makes).
> > - How the exhaust system effects a 2C is very
> > different than a 4C - primarily because a 4C has
> > dedicated intake and exhaust phases, while a 2C
> > shares them (gross simplification).  Keeping things
> > simple, in a 4C, the best the exhaust system can do
> > is scavenge the exhaust gases from the combustion
> > chamber and efficiently exhaust them out the
> > tailpipe, and depending on the design of the exhaust
> > system, the torque curve might be enhanced in some
> > RPM ranges to a small extent.  In a 2C, the exhaust
> > system can have a far greater influence on how the
> > engine runs - it can not only scavenge exhaust
> > gases, but it can increase the volume/density of the
> > intake charge, AND it can affect the pressure (or
> > vacuum) at the carb itself.  And with the 2C, the
> > specific design of the exhaust system can have a
> > huge effect on the torque curve, peak power, and
> > "linearity" of the throttle.
> > - If you understand the above, you will also
> > understand that 2Cs do not suffer from lack of
> > midrange torque and do not suffer from poor throttle
> > response - a poorly setup 2C may lack midrange
> > torque and throttle response, but so will a poorly
> > setup 4C.
> >
> > If you think your engine has a linear throttle AND
> > consistent throttle, and you aren't using a throttle
> > curve, an EFI, or an MC carb (or the OS equivalent
> > carb), then you don't need a throttle curve, an EFI,
> > or an MC carb (or the OS equivalent carb).  If you
> > don't think digital servos work better than analog,
> > you don't need digital servos either.  Point being,
> > people (myself included) often don't realize the
> > flaws in a current system until they try a "better"
> > one - nothing more than adaptive human nature at
> > work.
> >
> > Many of the 2Cs available today and in recent years
> > have been labeled as poorly carbureted - because the
> > carb appeared to have rich/lean spots, flat spots,
> > hesitations, etc.  The majority of the time, it is
> > not the carb that has the problem - it is the fault
> > of a poorly setup or designed exhaust system (or one
> > that is designed for max power, not throttle
> > response).  Because it is possible for the exhaust
> > system to influence the pressure (vacuum) at the
> > carb inlet, it can also affect mixture at the carb.
> > So, if your 2C carb has rich/lean spots, there are 2
> > ways to fix it - re-tune the exhaust system, OR,
> > adjust the carb mixture at that throttle setting.
> > Fixing with the exhaust system is where the whole
> > art of 2C tuning comes into play - Odds are, if you
> > copy the setup (prop, plug, fuel, pipe, tune length,
> > header) recommended by the manufacturer, you won't
> > have any carb issues - the manufacturer has already
> > done the 2C tuning so you don't have too.
> >
> > At this point, I haven't been brand
> > specific.........
> > - The most linear consistent throttling engine I
> > have ever run was a prototype KB150 using a Bolly
> > 590 muffler - 20% nitro and NO PUMP - just muffler
> > pressure (yes, I did have to change the jetting in
> > the carb several times to get it perfect, but the
> > production version wouldn't need that tweaking).  A
> > shame the engine never made production.
> > - I've run and seen countless examples of Bully145s,
> > Webra145s, OS140RXs, OS160FXs, OS140/160 EFIs,
> > Mintor 140/170s, and most of the YS 4Cs that all had
> > very consistent throttle response using a variety of
> > exhaust systems and fuel.
> > - I've also run and seen all of the above engines
> > running poorly with a poorly setup exhaust system.
> >
> > Why use an EFI?  Why use an MC?  Because it allows
> > the carburetion to be matched to a greater variety
> > of exhaust setups - and it does increase the
> > linearity and consistency compared to the majority
> > of setups being used (but you might not believe it
> > until you try it, and maybe the amount of difference
> > won't convince you to change).  The OS EFI system
> > allows the mixture to be set at 3 points - idle,
> > midrange, and high speed - and then it self
> > regulates the mixture (to an extent, only
> > effectively within a limited regime).  The MC (and
> > OS equivalent carb) allows the setup to be adjusted
> > just about anywhere (8 points is easy with a JR 10X,
> > I can't speak for other TXs, but figure they are
> > close to the same).  And as has been pointed out,
> > both systems have some advantages so far as no
> > needle valves.
> >
> > A 140 EFI is $1,000.00 and while the mechanicals are
> > very durable (with the SS rear bearing), the
> > injectors can be a problem.
> >
> > A 160 MC is under $500 and should be very durable
> > (based on the track record of the Webra145s).
> >
> > Regards,
> >
> > Dave Lockhart
> > DaveL322 at comcast.net
>
>
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