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The ProMuffler is something of a work in
progress. We've never made a secret of how much
harder it's been to deliver a high quality, quiet
and powerful, tuned-muffler, which has an easy to adjust,
i.e. non-critical/un-finicky needle valve. It's been far
more difficult than we ever dreamed it would be and frankly, it's
been something of a thorn in the side of the crew at
ProModeler to achieve the goal.
Fortunately, we're a bunch of persistent hardheads and thus,
have stuck with the project despite all the work and
frustration. In fact, to this day, whenever we get a
chance, we're still fiddling with the design, which results in
occasional changes in the production runs as we learn somehting
worth incorporating into the product. Speaking of which, the
present production version is the PDR0053-2, which
is pictured below.
- As supplied, PDR0053-2,
complete with long silicone exhaust-extension (PDR0062)
for cleaner models upon landing.
Did we mention how getting to this stage has been time
consuming beyond belief? In partly due to how computer
programs predict one thing with respect to flow and timing of the
pressure wave returning to the exhaust port as it's uncovered by
the piston, and the real world delivers a different lesson!
Why? Simple; it's because the real world has such a
complex interaction of variables like temperature, atmospheric
moisture, variables like which fuel a customer is using (0% to 50%
nitro) as to defy accurate computer modeling of the process.
Quite frankly, it's proved impossible for anyone without the budget
of NASA, plus a time slot on a supercomputer to nail it down
with simulation! Consequently, the results owe as much,
or more, to art as to science. Ultimately, we attribute
our success to perserverance and good luck. More of the
former due to lots of trial and error, and fortunately, a little
bit of the latter, which we gladly welcomed!
In fact, to get to the ProMuffler v2, we've made more
than a dozen distinct iterations. I.e. before pulling the
trigger on a production run of what you can buy. For
example, after the first one, we kept making it a little
fatter and longer, increasing the internal volume and seeing
improvements in responsiveness. We also varied exhaust
stinger ID (inner diameter), which affects the backpressure and
idle. We also varied the size and placement of intermediate
chambers, and even the diameter of the interconnecting ports, as we
worked to create the best tuned muffler we could. In fact, to
our amazement, seemingly small changes often led to making
more horsepower . . . until we went too far on any given
step. Afterward, it was a matter of figuring out
exactly where "too far" was! I.e. regardless of whether we
were configuring the volume of the chambers, or the exhaust stinger
ID, or even how much primary volume to allocate. Anyway, when
we tested the first ProMuffler sample, our hopes were
modest. We we intent on making a nice, quiet,
variation of the many mufflers offered by our competition because
the helicopter engine world had changed with the introdution by OS
Max of their powerful 50SX-H to replace the OS 46FX-H.
Simply put, when we began development, existing mufflers were
simply too small to allow the engine to breath properly and
thus, reduced specific output. In short, we saw a market
opportunity and moved in to capitalize on it.
In fact, our benchmark was the popular Thunder Tiger
50-class muffler, which frankly, is a perfectly serviceable unit
for modest power applications like beginners learning to
hover. Compare the original ProMuffler
prototype versus the Thunder Tiger muffler (top). Amazingly,
mostly through blind luck, right from the get go we had to
open the needle 3-clicks (richer) and increase main rotor
pitch 1°, which meant we were making more power. Hmmm,
curious about the why, i.e. about comparative relationship between
volume vs. length, we CCed both units and discovered that
though ours was shorter, because it was fatter too, it had
slightly more volume. Naturally, we couldnt leave well enough
alone and promptly hacked theirs apart to learn what we could
learn. Who could have predicted where it would
ultimately lead?
- PDR0053 ProMuffler
prototype (bottom) versus the Thunder Tiger
muffler.
Interestingly enough, because we'd had to open the needle valve
a few clicks, i.e. making the engine's mixture just a tad richer,
we theorized it was because the engine was making a tad more power
(more fuel=more horsepower every time), which was confirmed
emperically by the need to increase pitch. That's because we used
an optical tachometer to actually "see" more power happening (via
an increase in main rotor blade RPM), which meant we had to
increase max pitch to keep rotor RPM constant. Verifying more power
was a repeatable process since switching the mufflers back reversed
the optimal setting by the same 3-clicks. Think about it, a
helicopter unlike an airplane, can almost infinitely vary the load
on the engine by the simple expedient of increasing the pitch of
the main rotor blades and thus, a helicopter can essentially be
thought of as a flying dynomometer, which is handy for
development!
By the way, as mentioned earlier, we started down this road when
the OS Max 50SX-H was the top dog amongst 50-class
engine. Since then, OS released the Hyper, so we changed with
them because OS Max set the standards for engines in the 50-class
helicopter amrket. Sure, there are 50-class helicopter
engines from Evolution, Webra, Thunder Tiger, Align, and YS
but the OS product pretty much owns the market and thus, sets
the pace for the others to play catch up Anyway, that
first muffler became our internal benchmark and we called it the MM
for Muffler Mule. We kept it for back-to-back
testing. similarly, we kept the same set of main
rotor blades (V-Blades), and always used the same fuel
(Wildcat 30% standard heli), plus we corrected for temperature and
humidity. But the key was having the same set of blades and the
orginal prototy to test back-to-back. Anyway, learning
the volume was greater for our prototype than for the Thunder Tiger
muffler, and figuring if some is good, more is better, we
immediately made a bigger prototype (i2) . . . and promptly
lost power! Thus, back to the drawing board we went to try
and "sneak" up on the "right" muffler. We made many
successive units, some a little bigger (until we went too far
again, that is), and long story shortened, more volume generally
leads to more power, but then we began to play around with chamber
volume.
- We crash too, and consistent
with making lemonade from lemons, testing revealed
dents decrease performance!
By the time i9 (iteration number 9) rolled around (the one
that's not polished in the picture below), we were using the OS Max
50SX-H Hyper. Before someone asks, yes, changing engines
seemingly buggered all our previous test result, but by
repeating the test runs we were able to extablish the
previous results were, fortunately, duplicated right down
the line!
- Variations on a theme, as we
worked to discover the volume, length, and chamber configuration,
which works best.
With i10 we are pretty close to what would ultimately be the one
final product - or so we thought! As it turns out, where the
chambers are positioned, and how big the perforations betwen them
are can make a significant difference in power as well as something
not so easily described, which we call "user friendliness".
- By the time we got to i10, its slimmed
back down and a tad longer as compared to i9 . . . we're on
the right track!
Folks, in case you haven't figured it out, all along we were in
pretty much unproven territory. You see, the computer flow
simulation program had already said the mufflers were big enough as
of i1, but because we're just a bunch of Southern boys who
trust empirical evidence more than a computer, we
kept making succeeding iterations, each perhaps a little
bigger, or different chamber volume, configuration of ports, etc.
What's empirical evidence? That simply means that we tested it to
see if the results matched what the computer said, and when it
didn't we were on our own! By then we were developing a feel
for what was going on, i.e. intuition and while the
theoretical computer results were that it had enough volume,
empirically (i.e. by bolting it on and testing it) we kept having
to richen the mixture with different versions and whenever that
happened, we watched the main rotor RPM increase and
thus, knew when we were on the right track - or not!
For what it's worth, 12 iterations doesn't mean there were only
12 protoypes made. Au contraire, there were actually
several variations of each iteration. For example, between i9 and
i10 - the lost one called i9B existed (as well as i9C, i9D, and
i9E) during which we learned you can have too much of a good thing!
Anyway, all in the i9-series got sliced and diced (yeah, cut
open as if with a sharp knife) as we tried to figure out where we'd
gone wrong.
- Here's a comparison of i10 in my
hand vs. i12, which is the first one we first pulled the trigger on
for a production run.
By the way, i11 was an abject failure as again we went too
far. As with most in each series, those too were lost as we sliced
and diced them apart. For example, there was only a 7cc variation
between v12 and v11.
- Production PDR0053v2 (actually v12B1),
which consistently exhibits the best combination of quiet, user
friendly, power.
Take a gander at this little sweetheart! There's a lot of
intricate aluminum welding going on here folks! What's more, in an
attempt to maximize the market, we machined a mount for the
pressure tap which can be bolted in to either side, i.e. starboard,
or right-hand-side exhaust helicopters as well as port-side
mouting.
- Note the smooth welds in the
aluminum sections, which are subsequently polished to fine level of
detail.
Here's a close up of the aft part of the unit. Looks
pretty sweet, eh? by the way, the eight ridges are just for
looks. However, the placement of the internal chambers is
easy to discern due to changes in OD of the body.
- Aft end of the ProMuffler in
close up detail - the eight grooves are just for show.
So where are we now? Why did we change the
PDR0053 to create the PDR0053v2? Well, as
usual, we gain experience with our product through our customers
and thus, we learned a thing or two over time. For example,
the mounting flange of the V2 is more hefty. Wanna harzard a
guess why? Yup, experience taught us a valuable lesson
regarding our initial assumption about how smoothly customer's
helicopters are - or more accurately - aren't. Added to it,
when we have absolutely nothing better to do, we continue to fiddle
with the design and whip up new prototypes.
Naturally, in addition to putting into place what we've
learned with respect to basic strength in the area of the flange,
we've been playing with differences in port diameters vs. volume
(said results we'll keep to ourselves). However, the
most obvious, i.e. very visible, difference is the mounting flange,
which is considerably more meaty in the PDR0053v2 pictured
on the right.
- Where's the meat? Experience is a
harsh teacher because she gives the test before the
lesson! V2 flange on the right.
So there you have it, the development story of the
PDR0053-series of 50-class helicopter mufflers from
ProModeler. Our product is
more quiet, lighter, and far more user friendly than similar
competing products - some offered at nearly twice our price.
However, while you can measure some things, i.e. weigh them, or use
your ears to determine, which is more quiet, there's something
far more difficult to measure. It's termed "user
friendly", and it's a subjective, which means it's
between hard-and-impossible to get a handle on. In
our view, user friendly is the important combination of several
factors like a broad power band, plus an easy to adjust needle
valve, i.e not finicky about its setting, Doing it better
than Hatori, Muscle Pipe, Century, Thunder Tiger, or Align
muffler isn't easy.
In our view, the single most important factor you should
consider is a broad adjustment range for the engine's needle-valve
because a helicopter pilot absolutely depends on smooth transitions
through the power band. Basically, the constantly
changing collective pitch while flying results in near
constant excursions through the engine's operating range to
maintain constant main rotor disk RPM, which means the engine's
throttle is always moving. Moreover, the engine must 'never'
hang at idle as more 'tuned-type' mufflers are prone to
behaving, which affects autorotations. Nor should it
ever hesitate through mid-range. Simply put, it 'must' ensire
a smooth power delivery. These are the two most
important factors to consider. Sure there's weight, and how
loud it is, but performance dominates the discussion.
Meanwhile, each manufacturer leans more, or less, toward
tuning to make power. More tuning is shorthand for more
fiddling with the needle valve as it becomes finicky, i.e.
more affected by changes in the weather like temperature
and humidity. More emphasis on tuning also delivers more
power, which is the flip side to finicky.
Striking a balance between tuning for a bit more power vs. an
easy and consistent needle valve setting is never easy.
If you insist on the greatest consistent power, you will get
it with our product because there's far less frequent need to make
needle valve adjustments. Basically, like the Hatori line of
products, our design lean less on tuinng for power than the Muscle
Pipe line. We depend more on chemical
supercharging, i.e. the nitro methane in fuel which is there
precisely for making more horsepower because nitromethane binds
with oxygen molecules and thereby permits more fuel in the mix
resulting in more horspower - chemical supercharging!
Conversely, tuned designs are relying on the strength of the
pressure wave at the exhaust port, which is more dependent on
teperature and humidity leading them to be more finicky. As
in all things, you pays your money and makes your choice!
In short, our design relies on fine tuning the chamber
volume and interconnecting port diameters, along with broad
measures of length and diameter to create a great muffler.
Added to it, the ProMuffler has a deep, sexy
almost, throaty rasp, which portends the power of the
engine. Here's what an experienced 3D-type,
i.e. aggressive flying customer recently had to say;
"Had a chance to play with an MP-5
back in the fall. Hung it on a Pantera and it weighs almost 2oz
more than the ProMuffler, cost about $50 more than the ProMuffler,
and makes the same power (no noticeable increase or
decrease)."
- Gus Petraits,
Martinsville, IN
In summary, we offer an outstanding muffler,
which is perfect for folks running 15-30% nitro. It's
easier to tune and live with than the somewhat finicky, more-highly
tuned-type products, while ensuring great power and a great exhaust
tone (though it's pretty darn quiet), and we do it for a reasonable
price. What's not to like?
Thank you for considering our product.
John Beech - General Manager (and janitor)
Audacity Models, Sanford, FL