Swashplate: Hirobo SDX 50 - 2010/12

66 MODEL AVIATION
Swashplate: Hirobo SDX 50
WILLIAM RAMSEY
A well -defined
3-D helicopter
with bri lliant
heritage
Carbon tail fins shown are from Custom Heli Parts. Trim for upright or inverted flight is
virtually identical. Radix Stick Banger blades offer crisp response and decent autorotation
ability.
The low-profile skid set and sleek canopy are modern and
visually appealing. On top is a robust head mechanical
control system. The best accessories are worth every
penny in performance on the SDX.
THE HIROBO SDX is not a new
machine. It was released roughly two years
ago, but only recently was it offered as a
Special Edition that includes a custompainted
fiberglass canopy (item 1403955
from distributor Model Rectifier
Corporation). This is a beautiful machine
with one-of-a-kind looks and
impressionable handling for those who
range from students to dedicated crackrolling
fliers.
Hirobo seems to be well versed in
staircase design techniques. As lessons are
learned and skills are gained, the company
applies those factors to existing frames and
calls it “Step 3,” or in this case the “SDX.”
I have no idea what those letters stand
12sig3x.QXD_00MSTRPG.QXD 10/21/10 11:25 AM Page 66
December 2010 67
The MP5-50 SB pipe from CYE offers strong, low-exhaust-note
performance. Hirobo frame-stiffening options are well worth adding.
The PushGlo ignition accessory makes engine
starting far less cumbersome. An oversized
carburetor on the 55HZ fits perfectly in the twopiece
SDX main frames.
The tail blade grips are miniature versions of
those on the main shaft, with triple-bearing
support. Hirobo’s new stock tai l blades are
exceptionally stiff.
The SDX can maintain forward speed
very well, which offers the pilot an
FAI-style presentation, and the
forward energy transitions brilliantly
into dramatic 3-D maneuvers.
The 55HZ Hyper is the latest engine class offering
from O.S. En gines. Hiro bo designe d the SDX for
ease of service. Balance the fan before mounting.
The SDX head
mecha n ics ar e
new , and they
are a maj o r
fac t or i n w h y
the he li copt e r
exc e ls in 3 -D .
M a s siv e bl a d e
gr ip s h o use a
r o bu s t 8m m
s p i n d l e .
Damp e n i n g i s
firm.
Photos by Michael Ramsey
12sig3x.QXD_00MSTRPG.QXD 10/21/10 11:34 AM Page 67
68 MODEL AVIATION
Specifications
Pluses and Minuses
+•
Full kit is easy for a beginner to
assemble (good instructions).
• 3-D-ready and more tunable than any
50-class machine.
• Beautiful canopy with a thick
protective clear coat.
• Heavy-duty blade grip with 8mm
spindle and thrust bearings.
• Oversized aluminum center hub over
10mm hardened main shaft.
• Designed for 120º and 135º CCPM
mixing.
• All three control bellcranks rotate on a
single pivot.
• Extremely quiet built as shown in this
review. -•
Not the lightest machine on the
market.
• Tons of metal and CF upgrades
available (which means they don’t
come standard in the kit).
• Frame stiffening options required to
survive 3-D crashes.
Test-Model Details
Engine: O.S. 55HZ Hyper, CYE MP5-
50 SB muffler
Fuel: Rapicon 30% Max Power RC
Helicopter
Radio system: Spectrum DX7se
transmitter, Spektrum AR7100 receiver,
four JR DS8717 servos for cyclic and
throttle, JR DS8900G tail servo
Accessories: CYE Mini-G gyro, CYE
ATG V.3 governor, PushGlo igniter
Main blades: CYE Radix 600mm
carbon-fiber Stick Banger series
Power: Hobbico LiFe 3200 mAh, 6.6-
volt battery (four to five flights
available)
Upgrades: 89T Duracon main gear,
SDX-G fan cover, SDX crossmembers
Ready-to-fly weight: 8.14 pounds
Flight duration: Eight to 12 minutes
Rotor diameter: 1,348mm
Weight: 3,400 grams
Length: 1,200mm
Height: 395mm
Pitch range: Maximum 30º stroke
Gear ratio: 8.7:1 main, 4.7:1 tail
Construction: Fiber-reinforced plastic
and aluminum
Control system: 120°-135° CCPM
Drive system: Mono main gear, belt-drive
tail
Main rotor blades: 600mm (not
included)
Tailboom: Cylindrical aluminum
Canopy: Special-edition factory-painted
fiberglass
Landing gear: Single-piece nylon
Fuel tank: Dual-port 480cc
Requires: Radio, servos, tail servo/gyro,
receiver battery, governor (optional)
Price: $449.99
JR high-speed, high-torque servos effectively deliver the SDX’s
performance potential. Accurate pushrod geometry is essential.
Ball links require minimal sizing. Lighter than the optional header tank, a sintered fuel-filter pickup
from Du-Bro solves tank-foaming issues. A Du-Bro brass barb
soldered in place reliably secures the fuel line.
A CYE Mini-G Gyro and Active-Throttle-Governor (ATG V.3)
combined are infinitely adjustable when used with the G-View
programming module. The head speed and tail control might
spoil you.
Right: The author with a kit helicopter he built in a week of evenings.
Only organizing
the wiring was a
stumper. His
talent increases
with every tank
of fuel burned.
(See the motto
on his T-shirt.)
12sig3x.QXD_00MSTRPG.QXD 10/21/10 11:39 AM Page 68
for, though. It’s likely something to do with
the head mechanics, which I’ll explain in a
bit.
Although the step-design process seems
less than professional (why doesn’t Hirobo
just come out with the best kit possible in
the first place?), being an owner of the
“step-2 airframe” it’s good to know that my
investment isn’t treated like wastepaper. The
previous 50-class leader in the Hirobo line
was the Sceadu Evolution, which I am very
happy to still own.
The SDX main frame and tail section is
from the Sceadu Evolution, but the
accessory tray and mechanics that bolt to it
are new. The model uses sleek new lowprofile
skids as well.
I could convert my Evolution if I wanted
to. Hirobo has a downloadable spreadsheet
that details required exchanges with part
numbers.
The effort wouldn’t need to happen all at
once and would cost close to half the price
of a new SDX. I can do it in steps. The idea
is worth considering, especially on a wornout
machine or something derelict but
deserving of resurrection.
You might have issues with the fact that
Hirobo machines are made with an awful lot
of plastic parts. And I’ll add that their
pricing isn’t all that competitive.
However, a Hirobo helicopter is an
investment. Its parts support is great, and the
company’s models have an outstanding
reputation in FAI aerobatics circles as being
products of precision. Based on my three
years with the “Evo,” I vouch for the
products’ ability to last.
What’s so bad about plastic anyway? It
doesn’t corrode, and it’s totally solventresistant.
If you’re hard on a machine and its
aluminum, you’ve surely noticed that
scratches become obvious at some point—
especially if the parts are anodized. The
color of plastic is through and through.
However, having the right plastic
material makes all the difference, and smart
engineering is everything. Plastic parts are
typically lighter than those made from other
materials.
Concerning hardware, sheet-metal
screws grip nylon-reinforced plastic really
well. There’s no need for thread lock on
those parts, and the meaty threads hold up
well.
Think of the SDX as a helicopter made
from “smart plastic” that is also frugal,
because plastic is usually less expensive to
replace after a crash than the aluminum
counterpart. If you want a Hirobo machine
made from carbon fiber and aluminum,
those options are available but are
expensive.
I liked my first Hirobo helicopter so
much that I decided to get another. And,
yes, the painted canopy sold me, but that
was simply a visual thing. When the SDX
kit arrived and I dove into the parts bags, I
knew I had made another wise investment.
Assembly: Building the SDX required half
the time it took my father and me to
assemble the Evolution. The new model had
close to half the number of pushrods to
thread and size than the old servo linkage
system. Touted as the child of the
Turbulence D3 90-class helicopter, the SDX
shares the superior layout and mechanics of
that larger machine.
“D3” was the designation given to the
Turbulence mechanics. So we have “S” for
Sceadu and “D” for the D3 mechanics in the
SDX name. Let’s find “X.”
Hirobo meticulously followed the rule of
90 on the SDX. The three CCPM (cyclic/
collective pitch mixing) servos are aligned
vertically, side to side, with push-pull
linkages perpendicular to the swashplate and
SWB mixing arms. I don’t know what
“SWB” means either, but that single axle
where all the pushrods down from the
swashplate connect is apparently significant
to the mechanical harmony of the machine.
The builder has the option of either a 120°
or 135° swashplate setup. I went with the
120°, because the programming in my DX7se
is easy to follow. I’m told that the SDX works
even better using the 135° setup, but I’m
incredibly pleased as things stand.
The mechanics follow the Hirobo lineage
of Bell-Hiller mixing systems. It apparently
offers the least amount of control interaction
and requires less movement for aggressive
flying styles, and therefore gives up less
energy and speed to perform.
I followed the included instruction manual
and recommended linkage attachment points
to the letter. Every linkage connection on the
head has at least three selectable points at
which a 5mm precision ball can be secured.
Mechanical programming is all the rage, and
my plastic SDX has it. I think I got my
money’s worth.
Every accessory and bit of equipment I
selected for my SDX is the premium, and it
cost quite a bit. I bound an AR7100 receiver
to my Spektrum radio, because this receiver’s
internal voltage regulator is proven and simple
to use.
The AR7100 is powered by a 3200 mAh,
6.6-volt LiFe battery from Hobbico, of which
the heavy-duty servos take full advantage.
This receiver steps the power down to 5.2
volts to keep the gyro and tail servo healthy.
Almost 600 inch-ounce of torque
commands my SDX swashplate. The benefit
of JR DS8717 servos is also the fact that their
transit speed is almost matched to the transfer
rate of the DX7se radio; it’s 11ms. The way
my SDX flies made me a believer in the
saying “You can never use a servo that’s too
powerful or too fast.”
I also used a JR DS8717 digital servo on
the throttle. It’s overkill, but I see it as a useful
spare in case one of the cyclic servos glitches.
How well the CJ Youngblood Enterprises
(CYE) ATG V.3 governor works is another
testament to servo-overkill reasoning. A fast
throttle servo helps the governor to do its job.
Tail command is provided by the precision
JR DS8900G servo, which is blindingly fast.
To manage that is a Mini-G Gyro from CYE.
CYE products have pleased me for a long
time. Rightfully, my equipment order included
600mm Stick Banger (SB) blades from Radix
and a Muscle Pipe 5-series muffler for the 50-
class engine. CYE sells a standard and SB
version of the 50 pipe, and the SB muffler was
recommended because of my engine choice.
The O.S. 55HZ was my choice, and it is
impressive mostly because its reputation
formerly as a .50 cu. in. displacement engine
is so phenomenal. For ease of running, tuning,
and performance, the older 50HZ is top-notch.
My .55 has a carburetor that is sized more
as if it should be bolted on a .90-size engine;
the venturi opening is massive. If burning
more fuel means more horsepower, the 55HZ
should do the job well. Total fuel metering is
now offered with the addition of a third needle
to better tune in midrange demands.
To make use of the extra power from that
bigger engine, MRC advised me to exchange
the stock 87T black fiber-filled main gear for a
Duracon 89-tooth upgrade. I was also told to
expect a quieter machine, and that was the
result.
In that same conversation I was asked if I
planned to do 3-D and if I might crash more
often. Okay, I don’t expect to crash and heck
yeah I plan to do 3-D! To that end, MRC
recommended fore and aft frame stiffeners.
Those came in the form of an aluminum
plate that mounts in front of the engine, and
separately packaged were two frame braces
that fit above and below the rear end of the
fuel tank. I was told that if an impact occurs,
frame damage would be far less likely.
I liked that thought and bought the parts. I
don’t know if the frame will do a better job of
surviving a crash yet or not, but a stronger
frame is a great thing.
A hardy belt commands the tail-rotor drive
system. The belt is thick with mighty teeth. A
Teflon-like material is bonded to the inside of
the belt. Rubber teeth cause friction on the
gears. Perhaps some efficiency is gained with
the Hirobo type of belt material.
My favorite part of the SDX is the head
mechanics. It’s new in Hirobo’s 50-class
machines and has many smart ideas. The
main mast is a hardened hollow shaft that is
10mm thick. It’s supported by three bearings
in the frame. At the top of the mast is a robust
head block that is clamped and pinned in
place with four screws.
Flybar cage drag has been minimized by
making it the bare minimum size. The flybar
support has a broad face to prevent side play,
and it is supported by oversized pivot
bearings (that fit because of the oversized
head block).
On top of the head block is mounted the
yoke assembly, which houses the enormous
8mm blade-grip spindle. The blade grips are
also new and built hefty to absorb the loads of
3-D flying. That’s eight bolts holding the
head to the main shaft. I don’t think it’s going
anywhere.
Flying: The instruction manual offers
universal details about throttle and pitch
curves, plus recommendations on the headspeed
limitations.
The ATG V.3 has spoiled me. Connected
with the G-View monitor, I can see exactly
what adjustments are made, and made easily.
I have two head speeds programmed: one at
1,500 in the normal mode and the other at
1,800 rpm for Stunt modes 1 and 2. When the
engine is fully run in, I’ll try the 2,000-rpm
speed in the Mode 2 position.
I programmed the pitch range to
maximum, which is 15° positive and
negative. My SB blades have a lot of bite.
Even though they’re the lightest blade going,
autorotations are comfortable. The mechanics
as shown in the manual do not interact in any
way when the sticks are pushed into the
corners; I don’t need an e-ring or preventive
electronic mixing.
Setting up the SDX was a snap. Since the
first hover flight, I knew that I had built
something special. It was a feeling at first, but
the more playing I did, the more I learned to
love this machine.
I’m flying with half the weight available
for the stock paddles and feel sensitivity to be
comfortable, but with the right amount of
authority. The tail crisply obeys my
commands, corrects without bounce, and
holds well during backward high-speed flight.
The Mini-G Gyro has my complete
confidence.
Pitch and roll cyclic have no apparent
interaction; the model loops and rolls straight
as long as I move the transmitter stick that
way. Collective input carries the SDX straight
up and down, as it should.
I’m altogether satisfied that the commands
given are what I see happen. Now I know
what they mean when experts comment that I
have an “honest” helicopter.
Every 3-D flight drains the 3200 mAh
LiFe pack 600-700 mAh. After four flights I
take the 20 minutes to recharge the pack.
Rapicon 30% helicopter fuel seems to
be a healthy mix for the O.S. engine.
Cooler running temperature was the most
obvious benefit when compared with
similar fuels I tested. I feel better about
trying leaner settings, knowing that the
fuel treats my engine so well.
Even with the engine sloppy rich, the O.S.
55HZ drives the SDX without a whimper. At
the low-speed governor setting, forward flight
and 12-minute hovering sessions can be
expected. At the 1,800 rpm setting, I’m given
all the opportunity I could ask for to explore
3-D flight. Eight- to 10-minute flights are
normal when I am flying hard.
Besides the great design and engineering
of the Hirobo SDX, the equipment choices
play a big part in how much I enjoy this
helicopter. If I fly smartly and maintain my
machine, I think my enjoyment will last a
long time.
I’m glad that this project came as a kit. Now
I know the helicopter inside and out. Taking it
apart or experimenting with the settings is not
a scary thing because of that.
I’ve learned a lot attending helicopter
events such as the IRCHA (International Radio
Controlled Helicopter Association) Jamboree
and especially this year’s AMA Nats. And
without my father’s help I probably wouldn’t
understand half of it. He has helped me,
especially with this review, whenever I ask,
and even when I’m afraid to. Thank you, Dad!
In this equation I’ve found “X” to equal
“Excellent,” but I also call the SDX the
“Sceadu Deluxe.” It’s brilliant as was my old
Hirobo machine, but it’s a new breed of 50-
class helicopter. Consider investing in one for
yourself. MA
William Ramsey
[email protected]
Manufacturer/Distributor:
Model Rectifier Corporation
80 Newfield Ave.
Edison NJ 08837
(732) 225-2100
www.modelrec.com
Sources:
Spektrum RC
(800) 338-4639
www.spektrumrc.com
JR
(800) 338-4639
www.jrradios.com
O.S.
(217) 398-8970
www.osengines.com
CJ Youngblood Enterprises
(979) 779-2172
www.curtisyoungblood.com
Hobbico
(217) 398-8970
www.hobbico.com
Rapicon Fuel:
Common Sense RC
(866) 405-8811
www.commonsenserc.com
PushGlo
(818) 709-0268
www.switchglo.com

66 MODEL AVIATION
Swashplate: Hirobo SDX 50
WILLIAM RAMSEY
A well -defined
3-D helicopter
with bri lliant
heritage
Carbon tail fins shown are from Custom Heli Parts. Trim for upright or inverted flight is
virtually identical. Radix Stick Banger blades offer crisp response and decent autorotation
ability.
The low-profile skid set and sleek canopy are modern and
visually appealing. On top is a robust head mechanical
control system. The best accessories are worth every
penny in performance on the SDX.
THE HIROBO SDX is not a new
machine. It was released roughly two years
ago, but only recently was it offered as a
Special Edition that includes a custompainted
fiberglass canopy (item 1403955
from distributor Model Rectifier
Corporation). This is a beautiful machine
with one-of-a-kind looks and
impressionable handling for those who
range from students to dedicated crackrolling
fliers.
Hirobo seems to be well versed in
staircase design techniques. As lessons are
learned and skills are gained, the company
applies those factors to existing frames and
calls it “Step 3,” or in this case the “SDX.”
I have no idea what those letters stand
12sig3x.QXD_00MSTRPG.QXD 10/21/10 11:25 AM Page 66
December 2010 67
The MP5-50 SB pipe from CYE offers strong, low-exhaust-note
performance. Hirobo frame-stiffening options are well worth adding.
The PushGlo ignition accessory makes engine
starting far less cumbersome. An oversized
carburetor on the 55HZ fits perfectly in the twopiece
SDX main frames.
The tail blade grips are miniature versions of
those on the main shaft, with triple-bearing
support. Hirobo’s new stock tai l blades are
exceptionally stiff.
The SDX can maintain forward speed
very well, which offers the pilot an
FAI-style presentation, and the
forward energy transitions brilliantly
into dramatic 3-D maneuvers.
The 55HZ Hyper is the latest engine class offering
from O.S. En gines. Hiro bo designe d the SDX for
ease of service. Balance the fan before mounting.
The SDX head
mecha n ics ar e
new , and they
are a maj o r
fac t or i n w h y
the he li copt e r
exc e ls in 3 -D .
M a s siv e bl a d e
gr ip s h o use a
r o bu s t 8m m
s p i n d l e .
Damp e n i n g i s
firm.
Photos by Michael Ramsey
12sig3x.QXD_00MSTRPG.QXD 10/21/10 11:34 AM Page 67
68 MODEL AVIATION
Specifications
Pluses and Minuses
+•
Full kit is easy for a beginner to
assemble (good instructions).
• 3-D-ready and more tunable than any
50-class machine.
• Beautiful canopy with a thick
protective clear coat.
• Heavy-duty blade grip with 8mm
spindle and thrust bearings.
• Oversized aluminum center hub over
10mm hardened main shaft.
• Designed for 120º and 135º CCPM
mixing.
• All three control bellcranks rotate on a
single pivot.
• Extremely quiet built as shown in this
review. -•
Not the lightest machine on the
market.
• Tons of metal and CF upgrades
available (which means they don’t
come standard in the kit).
• Frame stiffening options required to
survive 3-D crashes.
Test-Model Details
Engine: O.S. 55HZ Hyper, CYE MP5-
50 SB muffler
Fuel: Rapicon 30% Max Power RC
Helicopter
Radio system: Spectrum DX7se
transmitter, Spektrum AR7100 receiver,
four JR DS8717 servos for cyclic and
throttle, JR DS8900G tail servo
Accessories: CYE Mini-G gyro, CYE
ATG V.3 governor, PushGlo igniter
Main blades: CYE Radix 600mm
carbon-fiber Stick Banger series
Power: Hobbico LiFe 3200 mAh, 6.6-
volt battery (four to five flights
available)
Upgrades: 89T Duracon main gear,
SDX-G fan cover, SDX crossmembers
Ready-to-fly weight: 8.14 pounds
Flight duration: Eight to 12 minutes
Rotor diameter: 1,348mm
Weight: 3,400 grams
Length: 1,200mm
Height: 395mm
Pitch range: Maximum 30º stroke
Gear ratio: 8.7:1 main, 4.7:1 tail
Construction: Fiber-reinforced plastic
and aluminum
Control system: 120°-135° CCPM
Drive system: Mono main gear, belt-drive
tail
Main rotor blades: 600mm (not
included)
Tailboom: Cylindrical aluminum
Canopy: Special-edition factory-painted
fiberglass
Landing gear: Single-piece nylon
Fuel tank: Dual-port 480cc
Requires: Radio, servos, tail servo/gyro,
receiver battery, governor (optional)
Price: $449.99
JR high-speed, high-torque servos effectively deliver the SDX’s
performance potential. Accurate pushrod geometry is essential.
Ball links require minimal sizing. Lighter than the optional header tank, a sintered fuel-filter pickup
from Du-Bro solves tank-foaming issues. A Du-Bro brass barb
soldered in place reliably secures the fuel line.
A CYE Mini-G Gyro and Active-Throttle-Governor (ATG V.3)
combined are infinitely adjustable when used with the G-View
programming module. The head speed and tail control might
spoil you.
Right: The author with a kit helicopter he built in a week of evenings.
Only organizing
the wiring was a
stumper. His
talent increases
with every tank
of fuel burned.
(See the motto
on his T-shirt.)
12sig3x.QXD_00MSTRPG.QXD 10/21/10 11:39 AM Page 68
for, though. It’s likely something to do with
the head mechanics, which I’ll explain in a
bit.
Although the step-design process seems
less than professional (why doesn’t Hirobo
just come out with the best kit possible in
the first place?), being an owner of the
“step-2 airframe” it’s good to know that my
investment isn’t treated like wastepaper. The
previous 50-class leader in the Hirobo line
was the Sceadu Evolution, which I am very
happy to still own.
The SDX main frame and tail section is
from the Sceadu Evolution, but the
accessory tray and mechanics that bolt to it
are new. The model uses sleek new lowprofile
skids as well.
I could convert my Evolution if I wanted
to. Hirobo has a downloadable spreadsheet
that details required exchanges with part
numbers.
The effort wouldn’t need to happen all at
once and would cost close to half the price
of a new SDX. I can do it in steps. The idea
is worth considering, especially on a wornout
machine or something derelict but
deserving of resurrection.
You might have issues with the fact that
Hirobo machines are made with an awful lot
of plastic parts. And I’ll add that their
pricing isn’t all that competitive.
However, a Hirobo helicopter is an
investment. Its parts support is great, and the
company’s models have an outstanding
reputation in FAI aerobatics circles as being
products of precision. Based on my three
years with the “Evo,” I vouch for the
products’ ability to last.
What’s so bad about plastic anyway? It
doesn’t corrode, and it’s totally solventresistant.
If you’re hard on a machine and its
aluminum, you’ve surely noticed that
scratches become obvious at some point—
especially if the parts are anodized. The
color of plastic is through and through.
However, having the right plastic
material makes all the difference, and smart
engineering is everything. Plastic parts are
typically lighter than those made from other
materials.
Concerning hardware, sheet-metal
screws grip nylon-reinforced plastic really
well. There’s no need for thread lock on
those parts, and the meaty threads hold up
well.
Think of the SDX as a helicopter made
from “smart plastic” that is also frugal,
because plastic is usually less expensive to
replace after a crash than the aluminum
counterpart. If you want a Hirobo machine
made from carbon fiber and aluminum,
those options are available but are
expensive.
I liked my first Hirobo helicopter so
much that I decided to get another. And,
yes, the painted canopy sold me, but that
was simply a visual thing. When the SDX
kit arrived and I dove into the parts bags, I
knew I had made another wise investment.
Assembly: Building the SDX required half
the time it took my father and me to
assemble the Evolution. The new model had
close to half the number of pushrods to
thread and size than the old servo linkage
system. Touted as the child of the
Turbulence D3 90-class helicopter, the SDX
shares the superior layout and mechanics of
that larger machine.
“D3” was the designation given to the
Turbulence mechanics. So we have “S” for
Sceadu and “D” for the D3 mechanics in the
SDX name. Let’s find “X.”
Hirobo meticulously followed the rule of
90 on the SDX. The three CCPM (cyclic/
collective pitch mixing) servos are aligned
vertically, side to side, with push-pull
linkages perpendicular to the swashplate and
SWB mixing arms. I don’t know what
“SWB” means either, but that single axle
where all the pushrods down from the
swashplate connect is apparently significant
to the mechanical harmony of the machine.
The builder has the option of either a 120°
or 135° swashplate setup. I went with the
120°, because the programming in my DX7se
is easy to follow. I’m told that the SDX works
even better using the 135° setup, but I’m
incredibly pleased as things stand.
The mechanics follow the Hirobo lineage
of Bell-Hiller mixing systems. It apparently
offers the least amount of control interaction
and requires less movement for aggressive
flying styles, and therefore gives up less
energy and speed to perform.
I followed the included instruction manual
and recommended linkage attachment points
to the letter. Every linkage connection on the
head has at least three selectable points at
which a 5mm precision ball can be secured.
Mechanical programming is all the rage, and
my plastic SDX has it. I think I got my
money’s worth.
Every accessory and bit of equipment I
selected for my SDX is the premium, and it
cost quite a bit. I bound an AR7100 receiver
to my Spektrum radio, because this receiver’s
internal voltage regulator is proven and simple
to use.
The AR7100 is powered by a 3200 mAh,
6.6-volt LiFe battery from Hobbico, of which
the heavy-duty servos take full advantage.
This receiver steps the power down to 5.2
volts to keep the gyro and tail servo healthy.
Almost 600 inch-ounce of torque
commands my SDX swashplate. The benefit
of JR DS8717 servos is also the fact that their
transit speed is almost matched to the transfer
rate of the DX7se radio; it’s 11ms. The way
my SDX flies made me a believer in the
saying “You can never use a servo that’s too
powerful or too fast.”
I also used a JR DS8717 digital servo on
the throttle. It’s overkill, but I see it as a useful
spare in case one of the cyclic servos glitches.
How well the CJ Youngblood Enterprises
(CYE) ATG V.3 governor works is another
testament to servo-overkill reasoning. A fast
throttle servo helps the governor to do its job.
Tail command is provided by the precision
JR DS8900G servo, which is blindingly fast.
To manage that is a Mini-G Gyro from CYE.
CYE products have pleased me for a long
time. Rightfully, my equipment order included
600mm Stick Banger (SB) blades from Radix
and a Muscle Pipe 5-series muffler for the 50-
class engine. CYE sells a standard and SB
version of the 50 pipe, and the SB muffler was
recommended because of my engine choice.
The O.S. 55HZ was my choice, and it is
impressive mostly because its reputation
formerly as a .50 cu. in. displacement engine
is so phenomenal. For ease of running, tuning,
and performance, the older 50HZ is top-notch.
My .55 has a carburetor that is sized more
as if it should be bolted on a .90-size engine;
the venturi opening is massive. If burning
more fuel means more horsepower, the 55HZ
should do the job well. Total fuel metering is
now offered with the addition of a third needle
to better tune in midrange demands.
To make use of the extra power from that
bigger engine, MRC advised me to exchange
the stock 87T black fiber-filled main gear for a
Duracon 89-tooth upgrade. I was also told to
expect a quieter machine, and that was the
result.
In that same conversation I was asked if I
planned to do 3-D and if I might crash more
often. Okay, I don’t expect to crash and heck
yeah I plan to do 3-D! To that end, MRC
recommended fore and aft frame stiffeners.
Those came in the form of an aluminum
plate that mounts in front of the engine, and
separately packaged were two frame braces
that fit above and below the rear end of the
fuel tank. I was told that if an impact occurs,
frame damage would be far less likely.
I liked that thought and bought the parts. I
don’t know if the frame will do a better job of
surviving a crash yet or not, but a stronger
frame is a great thing.
A hardy belt commands the tail-rotor drive
system. The belt is thick with mighty teeth. A
Teflon-like material is bonded to the inside of
the belt. Rubber teeth cause friction on the
gears. Perhaps some efficiency is gained with
the Hirobo type of belt material.
My favorite part of the SDX is the head
mechanics. It’s new in Hirobo’s 50-class
machines and has many smart ideas. The
main mast is a hardened hollow shaft that is
10mm thick. It’s supported by three bearings
in the frame. At the top of the mast is a robust
head block that is clamped and pinned in
place with four screws.
Flybar cage drag has been minimized by
making it the bare minimum size. The flybar
support has a broad face to prevent side play,
and it is supported by oversized pivot
bearings (that fit because of the oversized
head block).
On top of the head block is mounted the
yoke assembly, which houses the enormous
8mm blade-grip spindle. The blade grips are
also new and built hefty to absorb the loads of
3-D flying. That’s eight bolts holding the
head to the main shaft. I don’t think it’s going
anywhere.
Flying: The instruction manual offers
universal details about throttle and pitch
curves, plus recommendations on the headspeed
limitations.
The ATG V.3 has spoiled me. Connected
with the G-View monitor, I can see exactly
what adjustments are made, and made easily.
I have two head speeds programmed: one at
1,500 in the normal mode and the other at
1,800 rpm for Stunt modes 1 and 2. When the
engine is fully run in, I’ll try the 2,000-rpm
speed in the Mode 2 position.
I programmed the pitch range to
maximum, which is 15° positive and
negative. My SB blades have a lot of bite.
Even though they’re the lightest blade going,
autorotations are comfortable. The mechanics
as shown in the manual do not interact in any
way when the sticks are pushed into the
corners; I don’t need an e-ring or preventive
electronic mixing.
Setting up the SDX was a snap. Since the
first hover flight, I knew that I had built
something special. It was a feeling at first, but
the more playing I did, the more I learned to
love this machine.
I’m flying with half the weight available
for the stock paddles and feel sensitivity to be
comfortable, but with the right amount of
authority. The tail crisply obeys my
commands, corrects without bounce, and
holds well during backward high-speed flight.
The Mini-G Gyro has my complete
confidence.
Pitch and roll cyclic have no apparent
interaction; the model loops and rolls straight
as long as I move the transmitter stick that
way. Collective input carries the SDX straight
up and down, as it should.
I’m altogether satisfied that the commands
given are what I see happen. Now I know
what they mean when experts comment that I
have an “honest” helicopter.
Every 3-D flight drains the 3200 mAh
LiFe pack 600-700 mAh. After four flights I
take the 20 minutes to recharge the pack.
Rapicon 30% helicopter fuel seems to
be a healthy mix for the O.S. engine.
Cooler running temperature was the most
obvious benefit when compared with
similar fuels I tested. I feel better about
trying leaner settings, knowing that the
fuel treats my engine so well.
Even with the engine sloppy rich, the O.S.
55HZ drives the SDX without a whimper. At
the low-speed governor setting, forward flight
and 12-minute hovering sessions can be
expected. At the 1,800 rpm setting, I’m given
all the opportunity I could ask for to explore
3-D flight. Eight- to 10-minute flights are
normal when I am flying hard.
Besides the great design and engineering
of the Hirobo SDX, the equipment choices
play a big part in how much I enjoy this
helicopter. If I fly smartly and maintain my
machine, I think my enjoyment will last a
long time.
I’m glad that this project came as a kit. Now
I know the helicopter inside and out. Taking it
apart or experimenting with the settings is not
a scary thing because of that.
I’ve learned a lot attending helicopter
events such as the IRCHA (International Radio
Controlled Helicopter Association) Jamboree
and especially this year’s AMA Nats. And
without my father’s help I probably wouldn’t
understand half of it. He has helped me,
especially with this review, whenever I ask,
and even when I’m afraid to. Thank you, Dad!
In this equation I’ve found “X” to equal
“Excellent,” but I also call the SDX the
“Sceadu Deluxe.” It’s brilliant as was my old
Hirobo machine, but it’s a new breed of 50-
class helicopter. Consider investing in one for
yourself. MA
William Ramsey
[email protected]
Manufacturer/Distributor:
Model Rectifier Corporation
80 Newfield Ave.
Edison NJ 08837
(732) 225-2100
www.modelrec.com
Sources:
Spektrum RC
(800) 338-4639
www.spektrumrc.com
JR
(800) 338-4639
www.jrradios.com
O.S.
(217) 398-8970
www.osengines.com
CJ Youngblood Enterprises
(979) 779-2172
www.curtisyoungblood.com
Hobbico
(217) 398-8970
www.hobbico.com
Rapicon Fuel:
Common Sense RC
(866) 405-8811
www.commonsenserc.com
PushGlo
(818) 709-0268
www.switchglo.com