Swashplate: Hirobo SDX 50

Author: WILLIAM RAMSEY

Edition: Model Aviation - 2010/12
Page Numbers: 66,67,68,71,73,75

William Ramsey

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 custom-painted 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 crack-rolling 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 for, though. It’s likely something to do with the head mechanics, which I’ll explain in a bit.

The CYE MP5-50 SB pipe 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 O.S. 55HZ fits perfectly in the two-piece SDX main frames.

The tail blade grips are miniature versions of those on the main shaft, with triple-bearing support. Hirobo’s new stock tail 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. Engines. Hirobo designed the SDX for ease of service. Balance the fan before mounting.

The SDX head mechanics are new, and they are a major factor in why the helicopter excels in 3-D. Massive blade grips house a robust 8mm spindle. Dampening is firm.

Pluses and Minuses

Pluses:
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 120° and 135° CCPM mixing.
All three control bellcranks rotate on a single pivot.
Extremely quiet as built for this review.

Minuses:
Not the lightest machine on the market.
Tons of metal and carbon-fiber upgrades available (which means they don't come standard in the kit).
Frame stiffening options required to survive 3-D crashes.

Specifications

Rotor diameter: 1,348 mm
Weight: 3,400 grams
Length: 1,200 mm
Height: 395 mm
Pitch range: Maximum 30° 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: 600 mm (not included)
Tailboom: Cylindrical aluminum
Canopy: Special-edition factory-painted fiberglass
Landing gear: Single-piece nylon
Fuel tank: Dual-port 480 cc
Requires: Radio, servos, tail servo/gyro, receiver battery, governor (optional)
Price: $449.99

Test-Model Details

Engine: O.S. 55HZ Hyper, CYE MP5-50 SB muffler
Fuel: Rapicon 30% Max Power RC Helicopter
Radio system: Spektrum DX7se transmitter, Spektrum AR7100 receiver
Servos: 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 600 mm 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

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 low-profile 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 worn-out 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 solvent-resistant. 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.

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-ounces of torque command 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 11 ms. 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 600 mm 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 10 mm 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 8 mm 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 head-speed 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 rpm 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°. 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, 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 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 "Steady 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]