Hobby King Dassault Alpha Fighter EDF
Michael Ramsey
A fun-to-fly, semiscale jet with a high-output power system for the adventurous RC pilot
The global market has expanded in all directions in the last decade. Today it’s possible to order anything from halfway around the world and have it arrive in roughly the same time it takes priority mail to travel coast-to-coast.
Mention Hobby King and you’ll likely hear many stories—charred evidence might even be offered. Despite the customer-service learning curve, the China-based hobby retailer (HK) continues to pump out products at an unbelievable rate with too-good-to-be-true prices.
Swashbuckling modelers around the world apparently want to try out HK personally, and here at MA we’re no less immune. For HK to be on our radar, the company had to meet our U.S. distribution-location requirement. As it turns out, HK now has a warehouse in the U.S. from which to order directly and, in at least a few countries, the company is beginning to open dedicated hobby stores. Clearly HK is influencing the way the RC hobby is enjoyed, and it’s growing. Say what you’d like about the company’s development methodology; I like to think it’s maturing and, despite its colorful reputation, is challenging the market to be more innovative and compete for our business.
This is an exclusive review of HK’s Dassault Alpha Jet PNF, sized for a 90mm-class EDF power system. Don’t judge this model solely on the brief comments in the Pluses and Minuses sidebar. There is much to this product story including drama, edification, and, gratefully, a happily-ever-after ending.
What I learned is that when a product is sold cheap, the money saved must be spent on taking the time to thoroughly inspect everything down to the last screw and wire. Take nothing that was factory assembled for granted and avoid guessing at the specifications of the provided electronics. The extra time spent scrutinizing will pay you back with a more trouble-free model that should better fulfill the original intent of the retailer.
My Alpha Jet was released and delivered approximately nine months ago. Although the sample was built quickly, teething problems along the way kept the project from taking flight. Hobby King worked with me as well as it could, considering overnight email communication variance. Because China is literally half a world away, instant help isn't really available unless you're a forum hunter. HK does have some website resources, but the service is still in its infancy.
Instead of becoming aggravated, we optimistic modelers call such product issues a challenge and accept that even an RTF project still requires patience. Instead of jumping to negative conclusions—or worse, dumping our anxiety on Internet forums—today's global modeler should stand tall, scratch one's scalp with a calm agitation, and submit to the question, "What could I have done differently?"
Although my Alpha Jet was shipped with some definite factory defects, at least one of my solutions could have been handled better. HK's customer-service personnel responded to my issues to the best of their ability.
For the major electronics failure encountered on the bench, substitute equipment took more than six weeks to restock and ship. Certainly the ironic frustration of an RTF model waiting on the bench for parts tried my patience. When the model did finally fly, the hard work put into the project paid off with a good-looking model that flies extremely well.
As I write this, I have nearly 30 flights on the Alpha Jet. I'm excited to share it with friends and offer my lessons learned so that they, too, can get a great deal on a cutting-edge model and ride out any hurdles successfully along the way.
Although not famed as a frontline fighter from Lockheed or Mikoyan, a large number of Franco-German Alpha Jet multirole aircraft have been in service since 1973. The aircraft is respected by dozens of countries in need of a high-performance attack jet with handling qualities that allow it to double as a jet trainer. To this day it remains a venerable asset and has even entered the private aircraft sector.
I chose this high-powered, electric-ducted-fan model of the Alpha Jet from HK because it seemed to represent a benchmark sample among the company's higher-end RTF selections. HK calls this one "Plug-n-Fly" because the roughly $250 purchase (+ S&H) does not include the radio or battery. I call it "high end" because it uses an expensive 6S Li-Poly battery.
It also includes operational flaps and retractable tricycle landing gear—complexity points that place it in an upper-crust RC classification.
Packaging and materials A cushy EPO foam container provides a luxurious ride for shipment of the Alpha Jet components. The compartmentalized box prevents the bagged parts and assemblies from chafing against each other.
The foam used to mold the Alpha is expanded polyolefin (EPO), which is the technical name for what many manufacturers call Elapor, Aerocell, or Z-foam. It's more resilient than expanded polystyrene (EPS) foam and, depending on how it's utilized, can produce a smoothly finished model that's resistant to temperature changes, easy to repair, and—best of all—exceptionally lightweight.
The paint used to decorate the Alpha is acrylic and can be removed with household alcohol. Its surface bond can fail if adhesive tape is applied and then peeled off. Oversprayed areas where glue is expected to stick should be cleaned with isopropyl alcohol, then scored with 60-grit sandpaper if you expect a strong bond.
HK's Alpha Jet is available in two color schemes. Shown in this review is a replica of the lead French-built Alpha Jet E flown by the demonstration team Patrouille de France. The other striking scheme offered is a replica of the German-built Alpha Jet A used by the flight display team Asas de Portugal. The paint is generally well applied, as are the crisp, opaque water-slide graphics.
Airframe design and controls As a semiscale model, the shoulder-wing design features inherent stability similar to that of a high-wing trainer. Its anhedral wings and generously sized stabilizers keep the aircraft positively neutral without any fancy mixing or pilot-input magic.
Conventional control surfaces make the model easy to set up using standard linkages and micro electronics that are light and reliable. The design is a little tricky because of the narrow-spaced undercarriage that allows it to tip if turned on the ground too quickly.
A soft outer mat over the building surface is excellent protection against adding unwanted weathering to the airframe. Take the time to closely inspect every part out of its sealed plastic bag. Tug on the installed servos and be sure the molded hinging is free from defects.
Manual and assembly The instructions included with the Alpha are provided in poorly translated English in a small brochure-like booklet with color photos that are a strain to interpret. The CG is spot on and the assembly order is sound, but otherwise the manual provides little support.
Each servo is neatly flush-mounted in formed pockets with rubber cement and clear tape that hold well enough but can be relieved if necessary. The universal servos are custom-wired with the appropriate lead length. The black- and red-case servos weigh 9 grams and offer roughly 12 in·oz of output power at 4.8 volts. Black servos operate with a clockwise rotation and the red rotate counterclockwise. The three retract servos have metal gears and provide approximately 18 in·oz of torque at 4.8 volts.
The labeled servo extensions are easy to organize and reach well into the radio compartment so that connections to the receiver can be neatly bound while connected. To ensure that each servo operates correctly and is centered, test each one before final assembly. New servos are a cinch to replace before the airframe is assembled.
EDF bay and power system inspection The lower body of the fuselage contains the EDF system and landing gear. Inspection of this assembly is crucial; failure of any part could cost the entire airframe at the field. My sample included a number of faults, but none were terminal. Some I caught early; other problems presented themselves during their moments of disintegration.
A wise customer should take apart everything that is screwed into place and tug hard on everything glued to the airframe. I assumed the power-system installation was sound and proceeded to test the EDF in the workshop. Three momentary slow-throttle input cycles drastically overheated the motor. The ESC temperature was cool as was the battery. Vibration from the whirling fan was also outside comfort levels—especially for a power system expected to rotate at roughly 35,000 rpm and draw 70 amps of current. The required inspection of the motor proved to be revealing, but repairable by an experienced modeller.
The fan shroud was only spot-glued into the recesses of the ducts and floated over what should have been hard points not installed by the factory. Thread-locking compound would have been nice to find on the motor screws (which were loose), and the motor leads were dangerously bent around the sharp edges of the composite fan shroud. This fan system was not at all ready to run.
It appeared that the motor lead wires were poorly insulated both inside, next to the motor windings, and outside. The motor test caused the provided heat-shrink tubing to weld together. I poured a small amount of epoxy over the windings and the output leads to prevent internal chafing. A twin layer of heat-shrink properly insulated the leads and an extra helping of solder reinforced the 3.5mm bullet connectors.
The six-blade impeller needed a few strips of correctly located adhesive-backed foil to balance it dynamically. Once everything was reassembled using a thread-lock compound, and plywood plates were glued in for shroud support, the system was tested again—happily with no issues evident. I also made a smooth recess notch in the shroud to comfortably route the motor leads to the ESC nested inside the internal ducting.
Landing gear and canopy None of the shock-absorbing landing-gear mounts were adequately glued in place. Before a rubber adhesive such as Welders or Goop was applied, all of the recoil strut mechanisms were disassembled and rebuilt with thread-lock and the correct amount of torque on the hardware.
Retraction of the gear, although functional, lacks authority because of the marginal power of the provided servos. The gear does lock positively in the down position, but in flight they sag somewhat and the buzz of the servos tells me they're working hard to hold the wheels up.
The oversized canopy hatch is designed to snap into place and is center-secured with magnets; it also has a built-in oversized molded tongue to catch the front end. The catch plate on my hatch was missing and was critical for keeping the hatch in place. Instead of asking HK to replace the part, a spare GWS landing-gear plate was carved to fit and secured with epoxy, as was the spring-loaded fuselage-mounted latch mechanism that loosened after only a few uses.
Cockpit and finish The black-painted interior of the cockpit can be finish-detailed by the user. I kept it clean, but I regret not adding at least paper-profile pilots to the inside. Rubber adhesive is best to secure the poorly trimmed and masked canopy. Cleaning up the outer edges is easy, and the overspray on the clear windows can be made bright again by scrubbing with a soft towel soaked in alcohol.
Battery tray and airframe fit Carefully inspect the plywood battery tray. At the rear there is a minimal amount of support and the front end is attached with a minimal amount of rubber cement. The tray should pull free easily and be much stronger after it's reinstalled with epoxy.
The fit of the major parts into the molded sockets is exceptional. They fit snugly and are polarized so there's no guessing about the location or alignment. Hobby-grade 20-minute epoxy was used to attach the EPO sections.
The multipoint composite spars supporting the wings are permanently attached to the fuselage. This makes the model cumbersome to store and transport; however, I wouldn't trade the integrity of the airframe for anything.
Electronics recommendations The Alpha Jet does not need nose weight, so consider a lightweight, full-range receiver such as the Spektrum AR6255 and a minimal battery such as the Turnigy 3.6 Ah (22.2V) Li-Poly that has a constant-discharge rating of 30C.
Because no documentation is provided concerning the electronics, the safe assumption is that the provided BEC supplies at best 3–5 amps. I strongly suggest adding an extra BEC to the power system. The 11-servo operational load could overstress the system, so a Castle Creations 10A CC-BEC was wired in for peace of mind. Do not set the BEC voltage higher than 5.0 volts.
Even with inspecting and repairing the factory assemblies, the Alpha only took about 10 hours to assemble.
Bench problems and replacements The first flight attempt was interrupted by a failed ground-power test. This time the ESC overheated and ceased to function for reasons I can only suspect. A replacement ESC on hand produced a working motor again; however, its 6.0-volt BEC setting overloaded the servos, which caused all but three of them to terminally fail on the bench. Admittedly, some of the fault was mine for guessing at the electronic specifications that were not provided.
Hobby King stepped in and replaced the ESC with a selection of my choosing, but could only replace the clockwise-direction servos. Through trial and error, I found that Hitec HS-55 and Bluebird BMS-371 micro servos operate in the opposite direction from the HXT900 micro servo sent as substitutes and match the stock specifications.
The substitute Turnigy K-Force 100A ESC is overkill for this model, but it added a level of protection I wanted to ensure many seasons of flying fun. Its switch-mode BEC has an output of 3 amps at 5.0 volts. The additional 10A CC-BEC was set at the same output. Full throttle produces gobs of thrust with only a 63-amp draw, and every servo operates with quick response.
Trim and weight To achieve the recommended CG, 2 ounces of ballast was recessed into the tail cone and concealed with foam and touch-up paint. With the recommended battery installed, the flying weight came in more than 8 ounces underweight. Time to go flying!
Flight setup With no instruction provided regarding control-surface deflection, using my Spektrum DX8 transmitter I set full throws at 100% ATV and cushioned them with 30% exponential on all control surfaces. The low rates were cut by 50% with no exponential. The flaps were set with 11° and 35° deflection for takeoff and landing modes respectively. Roughly 10% mix of down-elevator in the landing mode keeps the nose from ballooning dramatically.
Flight characteristics and performance Other than the loud noise the power system makes, the Alpha Jet flies like a well-mannered sport airplane. Its mix of delicate retracts and foam construction is reason for me to advise against flights from grass fields unless the turf is very well manicured. I recommend smooth pavement departures and arrivals for this EDF.
Even with a small crosswind against the narrow undercarriage, before throttle is at 30% the control surfaces are effective and ground taxiing to a takeoff roll is easy to manage. Full power isn’t even necessary to break ground; instead of "popping" off as many jets do, the Alpha Jet rotates smoothly and climbs out with authority. At full power and takeoff flaps the Alpha can climb out at a 75° angle with no sign of instability.
Accurate molding and correct center positioning of the control surfaces allowed the Alpha to fly neutrally with little trim input. High-rate control response offered authoritative feel without a sense of twitchiness. The harmony of the controls felt scale-like with a touch of reserve surface movement available to safely and abruptly correct a heading if necessary.
I calculated that about 4 minutes of flight time would leave a 20% reserve for go-around and discharge margin. Approximately 50% power is enough to maintain a steady cruise, depending on the headwind. Full power is very impressive and should be applied only for dramatic, low high-speed passes or vertical show-offs and loops.
Battery notes Besides the Turnigy 3.6 Ah (22.2V) Li-Poly sent from Hobby King, I used other 6S packs on hand to rack up flight time with the model. Although the Alpha is overpowered and lightly loaded, the full potential of performance won’t be realized without a fresh, high-quality battery pack. My older battery samples were not up to the output delivered by the Turnigy pack. The Alpha Jet flew with the weaker packs, but flying was far more enjoyable with a healthy battery.
A lighter 3,200 mAh 25C 6S pack will improve climb performance slightly, but the minimal inertia of the foam model doesn’t push the Alpha much faster. I’d guess that the top down-line speed of the Alpha is no more than about 100 mph. Full-house composite aircraft in this power class have been said to fly at 130 mph; however, they probably lack the low-speed predictability of this Alpha Jet.
Handling notes Roll rotation naturally wobbled slightly, but is crisp. Point rolls that hesitate long enough for corrective pitch and yaw input are stunning to witness. Inverted flight takes the typical amount of down-elevator pressure. At full speed, knife-edge flight can be maintained as long as you mix out the aileron/elevator adverse coupling.
High- and low-speed stall testing revealed no bad habits. Positive-spin maneuvers are easy to enter and exit predictably. I have yet to test inverted spins. In the intermediate book of Aresti patterns, the Alpha is quite capable. Stall turns are honestly ugly; however, pull and push recoveries when airspeed is low are within the friendly mannerisms the Alpha Jet can deliver.
When the winds are up, flaps aren’t even necessary. Un-jetlike about the Alpha is its ability to slow on landing to where the rollout hardly exists. Using flaps makes it possible to carry power through the landing approach without much airspeed, which benefits the delicate retracts. The retracts have lasted flawlessly through my testing thanks to diligent landing procedures and the Alpha Jet's easy handling.
Conclusion The availability and price of the Hobby King Alpha is a tempting offer. If I had another sample and applied the inspection lessons learned, I would likely have been able to fly it with the original electronics. If you’re looking for a fun and very jetlike experience, the Alpha Jet could be the answer to your RC adventure.
—Michael Ramsey [email protected]
Supplemental Equipment List:
- Turnigy K-Force brushless ESC
- HXT900 micro servo
- BMS-371 micro servo
- BMS-375MG servo
- Hextronik MG-14 servo
- Turnigy Li-Poly pack
Sources:
- Spektrum RC — www.spektrumrc.com — (800) 338-4639
- Castle Creations — www.castlecreations.com — (913) 390-6939
Transcribed from original scans by AI. Minor OCR errors may remain.
