The Acromaster was introduced in 2006 and is the only model in the 40 inch+ freestyle aerobatic class that isn’t conventionally built. Designed by well known aerobatic pilot Martin Muller and manufactured from Elapor foam it’s an all-out freestyle and 3D machine with an element of built-in crash resistance. Moreover, it’s easy to transport thanks to its moderate span and detachable two-piece wing.
At first glance the design bears a passing resemblance to large 2m freestyle machines like the Majestic and Adrenaline. With sizeable double-bevelled control surfaces and lots of fuselage side area it certainly looks like a performer and, dirty though it may be, it’s been my job to find out and report back. So, what did I discover?
The quality that Multiplex is renowned for is apparent from the moment you open the box. Here the first thing you’re confronted with is the huge sheet of stickers that provide the superb colour scheme. The sheet is rolled around the various parts and after carefully removing it from the box I noticed that one end was creased, which I suspected (correctly, as it turned out) might cause a problem or two during application.
Once I’d removed all the parts and laid them out it became quickly apparent that the quality of this all-moulded model was superb. Alas, however, the trailing edge of the right wing root section was slightly crushed where it plugs into the fuselage. Fortunately this turned out to be nothing more than a cosmetic issue and can only be seen on very close inspection.
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Apart from the main airframe parts you’ll also find a carefully bagged accessory pack that’s bulging with all sorts of high quality screws, links, servo heads and motor mount parts. Particularly eye-catching are the wheels, spats and spinner. Moulded entirely from Elapor I don’t mind telling you I had serious concerns about their durability.
In the interests of compatibility I used the suggested Multiplex powertrain, this consisting of a Himax HC 3516-1130 outrunner, Phoenix 45 amp speed controller, and an APC 11 x 51/2“ E prop. Supplied as a complete package that included the prop adapter, I particularly like the fact that the gold-plated bullet connectors for the motor and ESC are also included.
As soon as you have all the parts laid out you instantly want to start piecing the Acromaster together like some kind of oversize Airfix kit! It’s essential, however, that you consult the instruction manual as there are a few key things you have to do before you can start joining any of the bits together. The manual is 40 pages thick, six of which are very clear step-by-step English instructions accompanied by eight pages of exploded pictorial diagrams; these compliment the writing perfectly.
The construction itself is pretty straightforward so there’s no need to get too in-depth about it, however there are a few key points to consider. For starters, the wing panels and fuselage come in two separate pieces which need to be very carefully glued together.
A reinforced plastic joiner (with built-in elevator horn) is used to mate the two elevators and I’m pleased to report that it’s very stiff and does not allow for any flex between the two surfaces, unlike some other methods I’ve come across! Another particularly nice feature is the moulded control run slots for the elevator and rudder snakes. In use the system provides very smooth and precise control for the huge tail feathers, which is clearly a fundamental requirement of a good 3D design.
One thing that does stand out is the hardened plastic motor mount that allows one to easily tweak the thrust angle of the motor by adjusting the four bolts found in each corner. In this respect, then, the instructions clearly define the standard position and explain how to adjust it to fine-tune the flying characteristics of the model – very useful for keeping those up-lines dead straight, although I’ve not seen the need to deviate from the standard position while test flying.
Before you stock up on foam friendly cyano’ remember that normal cyano’ works best with Elapor. The first time I read this in the manual I had my doubts and decided to test it, but sure enough, normal cyano’ works perfectly; better still with activator.
A few cosmetic tasks remain after construction. These include painting the Elapor canopy black and applying the beautifully printed stickers. Now then, as I’ve already mentioned, the sticker sheet was creased when it came out of the box and I could see this would cause a few problems. To try and rectify matters, I heated the creased area very, very gently with a hot-air gun and that seemed to soften the material enough for me to roll out the crease with relative ease.
Although the colour scheme on the Acromaster is very pleasing to the eye, the all-white airframe lends itself brilliantly to any scheme you may prefer. In fact, even Martin Muller has been seen flying a beautifully airbrushed version of the model. It really is a blank canvas in this respect.
Construction was finished without a hitch and took little more than eight hours, including application of the stickers and installing the radio. In this latter respect I used a Futaba 146iP PCM Rx, Hitec HS55 servos on the ailerons end elevator, and an HS85MG (metal gear) on the rudder.
After waiting for what seemed a lifetime, a perfectly calm evening presented itself and after a quick call to master cameraman Ben Dean I loaded the Acromaster into the car and headed for the flying field. Ben soon had the obligatory static and detail shots done, after which it was time to go through the usual pre-flight checks. Once the range check was complete and I’d confirmed the direction and movement of the control surfaces, a fresh battery pack was fitted and the Acromaster lined up on the runway.
In the event she took just six feet to get airborne and one circuit to trim, whereupon two clicks of down elevator and another two of right aileron were all that was required. With this I took her up to check the stall and found it to be non-existent. Instead the model just mushed into an elevator (an almost vertical descent with a nose high attitude) and displayed no sign of tip-stalling. I could already see that this was going to be a capable 3D performer.
Next on the agenda was some smooth aerobatics using low rates, which it performed extremely well. Knife-edge was easy, without any pitch or roll coupling, and one-roll rolling-circuits were very axial and smooth. In truth she performed all manoeuvres in the book with ease.
Flicking the rate switch for large control movements, I set about testing the 3D envelope. First I tried a blender but noticed that the spin would not flatten out correctly during the manoeuvre. This gave me some concern about the C of G I’d set, positioned, as it was, at the furthest forward point of 110mm from the leading edge. A rolling harrier confirmed that the balance point was indeed too far forward, clearly displayed by the model attempting to flick out of the manoeuvre. At this point I chose to land and adjust the C of G rearwards (to 115mm) by moving the battery further aft. Airborne once again the result appeared to be a dramatic transformation that didn’t hinder the smooth flying characteristics I’d enjoyed earlier.
After this, all 3D manoeuvres were flown unremittingly, the Acromaster being particularly adept at the inverted harrier, which is absolutely steady with no wing rock. In fact, I’d go as far as to say it feels decidedly locked in. The model will happily sit in a prop-hang, during which a slight touch of left aileron will induce a torque roll, and the pull out is outstanding. Clearly, there’s little doubt about the suitability of the Multiplex power set-up. And as if that’s not enough, the knife-edge spin, a manoeuvre that lots of aerobatic aircraft can’t do properly, is bread and butter to this little foamie; very impressive indeed.
After a few more passes for Ben and his camera I decided to bring her in for landing as the battery pack was showing signs of power loss; around eight minutes of freestyle aerobatics had passed. The pack I used for the first flight was a Thunder Power 3s 2100mAh job and it performed really well. That said, the pack that I feel is ideally suited to this aircraft is the FlightPower Evo 2170 3s, which has given me more sustained power and longer flights of around 12 minutes. Oh, and while I’m on the subject of hardware, it’s worth noting that the servos I’ve used are more than capable of dealing with any stressful 3D manoeuvres.
Overall, my impression of the Acromaster is that it feels like a much bigger model and will flatter the flying abilities of any pilot. The whole airframe has proven to be decidedly durable and the foam spinner, spats and wheels that I had concerns about haven’t been a problem at all. My dear old Acromaster has even been dragged into some corn crop during one of my knife-edge passes, yet it emerged with no sign of damage. Heck, there wasn’t even a scratch! At the end of the day I guess it’s sufficient to say that this model now comes out with me pretty much every time I go flying. Can there be a better recommendation?
Model type: 3D aerobat
Manufactured by: Multiplex
UK distributor: J.Perkins Distribution – www.jperkinsdistribution.co.uk
Wingspan: 1095mm (42")
Fuselage length: 1150mm (45")
All-up weight: 910g (2 lbs)
Rec’d motor: Himax HC 3516-1130 outrunner
Rec’d ESC: 45 amp
Battery required: 3s 2100mAh Li-Po
Control functions: Rudder, elevator, throttle, aileron
Servos used: Hitec 55s (aileron and elevator); Hitec 85MG (rudder)
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