The ProMuffler hasn't been an easy product to develop. In
fact, it's not really a muffler but more properly, a suppressor.
Regardless, muffler is what everyone refers to them as, so we'll play ball, but
we mention this so you know that we know there's a difference! Anyway, this
is our v2 version, which has been optimized with slightly greater
volume for the slightly larger displacement 55-class engines (while still
working about as nicely as the original on the 50-class engines).
What makes it really great for you is installing it doesn't make your
engine finicky to adjust. Nascially, setting the needle valve is
completely uncritical; what we call set-in-and-forget-it easy. Of course this is
a slight exageration but nevertheless you're looking at maybe adjusting a couple
of clicks of the high speed needle between spring and summer, and once again
when winter sets in. Howeevr, it leaves your engine deads nuts simple to
tune - especially compared to those tinny-sounding tuned mufflers claiming
to make extra power (you know the ones), which often has owners fiddling
with the needle setting nearly every day. And all for power differences
even experts couldn't discern . . . unless they're, a) paid company-shills,
or b) 2-gallon experts yapping on the Internet.
- As supplied, PDR0053-2, complete with long
silicone exhaust-extension (PDR0062) for cleaner models upon
How does it work? Through the use of champbers. Partly it's the result
of computer gas-flow software, whihc is useful with respect to flow and
timing of the pressure wave returning to the exhaust port as it's uncovered by
the piston - this is a tuned-muffler, so this is important. However, partly it's
the result of real world experimentation. This is because the real
world has such a complex interaction of variables like temperature,
atmospheric moisture, engine RPM, fuel composition, glow plug heat, compression
ration, e.g. so many variables as to defy accurate computer modeling.
Thus, and quite frankly, absent a NASA budget, plus a time slot on
a supercomputer to nail it down with simulation, this means our
results owe as much, or more, to art than to science! But it's really,
really good art/
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
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
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 between them are can make a significant difference
in power as well as something not so easily described, which we call "user
- 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
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
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
- Note the smooth welds in the aluminum
sections, which are subsequently polished to fine level of
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
- 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
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 summary, we offer an outstanding suppressor, 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. In short, it's got practical power and sounds
great. What's not to like?
Thank you for considering our product.
John Beech - General Manager (and janitor)
Audacity Models, Sanford, FL