Midwest Products Co. Aero-Star .40 ARF

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Since the servo mount is relatively soft lite-ply, and the servos will be retained by wood screws, I prefer to add some exIntro

 

 

The Midwest Aero-Star .40 has in the past established itself as one of the most popular kit-built trainers, due to its very forgiving flight characteristics and slow landing speed, as well as its pleasing lines.

The news that this aircraft is now available from the Falcon Trading co. as an ARF (Almost Ready to Fly) model will come as great news to many – including those instructors who have favored this trainer in the past, but who may have been slightly wary of recommending a kit-build to some beginners whose building prowess they are unaware of.

The high degree of pre-assembly of this model (including pre-hinging of control surfaces, pushrods that require no assembly prior to installation, etc.) means that this model really does require a minimum of time and technical ability to assemble.

All of the structure of the model comes pre-built and covered in Ultracote (a top-quality heat-shrink covering material). It comes in a very eye-catching color scheme consisting of a white base with burgundy, orange and yellow trim, along with graphics for all of the windows.

Let’s have a look at what you get with this ARF, and how it goes together. After that, we’ll head off to the field and pass the transmitter around to get some feedback on the Aero-Star .40 from instructors, student pilots still under training, as well as some recently soloed pilots…

Specifications:

 

 

Hits

 

  • Excellent flight characteristics.
  • Forgiving, as an initial trainer.
  • Fairly aerobatic, as an advanced trainer.
  • Superb construction quality.
  • High degree of prefabrication.
  • Fast, easy assembly.
  • Excellent instruction manual with
    • Lots of detail
    • Plenty of high quality photos
    • Description of parts and tools required at every step.
  • Strong hardwood pushrods, pre-built.
  • Attractive trim scheme & color.

 

Misses

 

  • Packaging
    • Not protective enough.
    • Illogical grouping of small parts.
  • Steering arm misfit (see text).
  • Part of elevator glued to stab.
  • Minor instruction issues: (see text)
    • Suggested hole size for engine mount.
    • How much prop clearance is needed.

 

 

Kit Features Required items
Required Tools.
  • Detailed instruction manual.
  • Fully covered wing, fuselage, tail
  • Fuel tank, tubing, clunk
  • Motor mount & bolts
  • Pushrods
  • Decals
  • Landing gear.
  • Rubber bands (for wing).
  • Control horns, pushrod connectors, clevises.
  • Other assorted hardware
  • Radio: Minimum 4 channel, with 4 servos
  • Engine: 2-stroke .40-.46 cu in
  • Spinner
  • Propeller
  • 1/2″ Foam rubber (Du-Bro #514)
  • Medium CA glue
  • 5 and 30 minute epoxy
  • Thread-lock compound (e.g. Loctite (TM))
  • Rubbing Alcohol
  • Masking tape.
  • Waxed paper.
  • Paper towels.
  • Hobby knife and #11 blades
  • Heat gun
  • Covering iron
  • Drill and drill bits.
  • Diagonal cutting pliers.
  • #1 and #2 Phillips screwdrivers.
  • 3/32″ and 7/64″ Allen Wrenches.
  • 12″ Rule for aligning assemblies.
  • Pencil, fine-point marker.

 

 


Assembly of the Falcon Trading Aero-Star .40 ARF

 

The first step is to unpack everything carefully and inspect it – both to ensure that there is no damage, and to help familiarize yourself with what the different parts look like – this will help to ensure that you know where to find each part when the manual tells you to use it.

In the above image to the right you can see all the parts that come with the ARF. The fuselage, wing, tail feathers & control surfaces are all pre-built, pre-covered, and pre-hinged.

Construction Quality

The quality of construction of the major components is quite simply superb. While some other ARFs use lots of glue to make up for having a poor parts fit, one look inside the fuselage will show you that that’s not the case with the Aero-Star – its parts fit extremely well (I could not see a gap anywhere). The snug parts fit also means that excess glue, and hence excess unwanted weight, is kept to an absolute minimum.

 

The Aero-Star’s wing features a conventional wood construction. It arrives in two pre-covered halves which are joined by adding a hardwood dihedral brace and epoxying the halves together. In addition to using masking tape during the gluing process (per the manual), you may find it helpful to use a small clip (as shown on the right) to keep the trailing edges of the wing halves perfectly aligned with each other during the gluing process.

This is a pretty standard procedure for joining ARF wing halves, but what makes the Aero-Star stand out from some of the other ARF’s that I have assembled is the attention to detail – such as providing a strip of covering material to hide the join, as can be seen in the photo on the left.

The mounting of the aileron servo, addition of the pushrods etc. will be covered later once we have completed the fuselage.

 

 

FUSELAGE ASSEMBLY

As was mentioned in the “Misses” section previously, there was a problem with the packaging of this ARF. The cardboard dividers inside the box failed to keep the various parts properly separated, and during shipping some parts moved sufficiently to break the fin on the review model.

Falcon Trading has been advised of the above, and is taking steps to ensure that future production versions of this model will feature improved packaging. For the review model, we opted to continue with the damaged fin rather than get a new fuselage from Falcon (as regular customers should do). Beginners frequently bump the fin during transport, or turn the model upside down the first time they taxi in a strong cross-wind, etc., and need to make this kind of repair – so we may as well take advantage of the opportunity to show you how easy this kind of damage is to fix.

First, simply realign the fin, making sure that it is both straight and vertical, then use thin CA to glue it back in place. Next, we take a piece of 3/8″ ‘triangular stock’ balsa, and cut a piece of the appropriate length. Sand its ends for an aethetically pleasing shape, then cover it with a section of the excess iron-on trim strip that Falcon Trading provided for the wing center section. (They conveniently provide quite a bit more than you need for just the wing!). Strip a small section of the covering away on the fuselage and fin as shown below (right), so that we will have some exposed wood to glue to.

 

 

Finish by using some 5 minute epoxy to glue the tri-strip to the fuselage as shown in the photos above. Note that the tri-strip on one side must be shorter in order to clear the pushrod.

 

 

Stabilizer

The stabilizer is held onto the fuselage with both bolts and epoxy. The bolts ensure correct alignment, while the epoxy ensures that the assembly is completely secure. The stab is first temporarily bolted on without any glue, so that we can mark the stab to show where it meets the fuselage.

Next, a section of covering film is removed from the marked area, and then we put the assembly back together again, this time adding the epoxy. (Stripping the film is necessary because the epoxy would not penetrate the plastic film covering, and needs instead to be able to bond the two wood components together directly.)

THE ENGINE & GEAR MOUNT

The engine mount used in the Aero-Star .40 ARF is a novel two-piece assembly that includes an integral nose-gear mount. Doing the mount in halves which separate horizontally allows the same mount to be used for a variety of different engines, simply by sliding the halves closer or further apart to allow for differing engine widths.

The engine bay has been treated with a nice solid coating of white paint in order to ensure that any fuel that gets onto this area will not soak into the airframe and weaken the structure. I did find that the paint had also gotten very slightly into the threads of the blind nuts (for the engine mount) as well as the pushrod tubes (for the throttle and nose-gear steering rods). As shown below, a hobby knife makes short work of clearing any such excess paint out.

 

The main landing gear is next. It has some very sturdy torsion blocks inside the fuselage that the main gear legs fit into, so that the aircraft can absorb typically heavy student-pilot landings with ease.

A minor addition that I would suggest at this point, is to take some pre-emptive action to prevent the wheels from being able to accidentally come loose from the axles. There is a surprising amount of vibration in our models, and over time this can lead to nuts, bolts etc., coming loose. You should constantly monitor your aircraft for signs of parts loosening, but you can also help reduce the problem by using a combination of flat spots and thread-lock compound in areas such as the wheel collets that hold the wheels on. Grind or file a flat spot on the axle as shown, at the point where the collet will be placed, then when you put the collet on, add some thread-lock compound.

 

The nose gear fits into the engine mount, and is retained there by a part which is a combination of a steering arm and a built-in collet (to stop the steering arm from being able to rotate on the nose gear leg).

Trial fit the nose gear into the engine mount, without the steering arm on it, and check for freedom of movement. The nose-gear should be able to rotate freely. If it does not, add a touch of light machine oil.

 

 

Now repeat the above process, but this time put the steering arm on the nose gear. I found that the steering arm was too tall to fit in the mount without causing some binding. This was remedied by a combination of using a small file to open the gap in the mount, and sanding the steering arm down until the fit was correct. There should be no slop vertically, but the horizontal rotational movement should be free.

 

 

STICKERS

The Aero-Star .40 ARF comes with two large sheets of nicely printed self-adhesive decals. A few of these go on the wing, but most go on the fuselage, and serve to give the model a more “scale” type of look by adding windows, door outlines, etc.

 

When it comes to determining the location for each sticker, remember that in addition to the pictures in the manual, there are also much larger, clearer and colored pictures on the box-top!

The manual shows you holding the stickers with your fingertips while applying them. Just in case you have oily hands like I do, I would suggest that you should instead use the edge of your hobby-knife blade to hold the edge of the sticker.

Another tip that you might find useful, is to spray a very light coat of Windex (or similar product) onto the surface that the sticker will be applied to – this allows the sticker to be moved / removed and repositioned as necessary without damage to the surface underneath. Once you are happy with the location of the sticker, you can then use a squeegee (or even a credit / business card) to press the sticker firmly onto the surface – this will expel the Windex.

 

 

ADDING THE ENGINE

The next step is to install the engine onto the engine mount.

For the power plant in your trainer, I believe that you should have an engine that combines sufficient power (to get you out of sticky situations easily), with reliability and great user-friendliness (since beginners are generally not engine gurus). For these reasons, I chose the ever-popular O.S. MAX-46 FX for use in the Aero-Star.

First adjust the width of the engine mount to suit the width of the chosen engine – slide the mount halves closer together or further apart as necessary).

Next put the engine on the mount and adjust its position to suit. The manual tells you to check the prop clearance before proceeding, but doesn’t tell you how much clearance you need – that’s because it is not critical. I used 1/2″ of clearance, but as little as 1/8″ is also practical.

Mark through the flange on the engine case and drill the holes for the screws that secure the engine to the mount. This procedure is clearly explained in the manual, though I did find that I needed to use a larger drill for the screws to self-tap into. The manufacturer now states that a 5/64″ drill should be used.

 

 

O.S. MAX-46 FX Closer Look

 

 

The O.S. MAX-46 FX two stroke motor is a non-ringed (ABN) piston motor which puts out 1.62 bhp while weighing in at only 16.5 oz with muffler.

Full specifications:

  • 1-piece crankcase.
  • Twin ball bearing-supported crankshaft
  • Schnuerle ported
  • Aluminum piston
  • Nickel plated brass cylinder
  • Side exhaust
  • Muffler included
  • Rear mounted needle-valve
    (keeps fingers away from spinning propellers)
  • Bore: 22.0 mm (0.866″)
  • Stroke: 19.6mm (0.772″)
  • Displacement: 7.45 (0.455 cu.in.)
  • Power Output: 1.62 bhp at 16,000 rpm
  • Practical RPM Range: 2,500 – 17,000 rpm
  • Crankshaft Thread Size: 1/4-28
  • Weight: without muffler- 13.2 oz (375g);
    with muffler- 16.45 oz (466g)
  • Recommended glo-pug: O.S. #8

The manufacturer recommends this motor be run on fuel containing 5% to 20% nitromethane and oil content at a minimum of 18%.

I chose to use Byron “Premium Sport Traditional” Fuel with 10% nitro and 20% oil (a synthetic / castor blend). It is a truly multi-purpose fuel that I feel comfortable using in everything from a trainer to a ducted fan or helicopter motor.

Props recommended by the mfg. for the O.S. MAX-46 FX include:

  • Tuned Pipe use: 12×7 -> 12×9 ; 11×8 -> 11×10
  • Sport: 10.5×6 -> 11×7 ; 12×6 -> 12×7
  • Break-in: 11×6
  • Fun-fly: 12×3.5 ; 12 x 4

I chose to use an APC 12×7 propeller.

One of the main reasons why I consistently recommend O.S. engines to beginners, is that they have proven time and time again to be extremely user friendly.

Some of the other brands of engines that I own are quite powerful and reliable once you get them sorted out, but frequently need extensive “tweaking” and experience to get to that stage – experience that beginners do not have.

The O.S. engines have a great reputation for running perfectly straight out of the box, and this one was no exception – it started on the second “flick” of the spinner (no electric starter even needed).

Download the manual in PDF format – Click here

Wing Dowels

The wing dowels are inserted through the fuselage, and glued in place. A nice touch that you might care to add, is to seal the exposed parts of the dowel with a thin coat of CA to prevent them from getting dirty and oil-soaked over time. Note that this is purely an aesthetic touch, and there is absolutely nothing wrong with leaving the dowels unsealed.

Sealing can easily be done by adding just a drop of CA to the dowels, then using a piece of wax paper to spread the CA around the dowel. Make sure that you do not get any CA on the covering, as it will “fog”.

 

Servos

Specifications for the JR 537 servo:

  • Torque: 43 oz/in @ 4.8V
  • Speed: .25 sec / 60 degrees
  • Weight: 1.58 oz
  • Dimensions: 0.73″ x 1.52″ x 1.32″
  • Bearing: Single
  • Motor: 3-Pole Ferrite

 

 

The JR 537 Standard servo is ideal for use in small sport planes and trainers. It has a ball bearing on the final output shaft so that even after prolonged use, it will retain its precision (less potential for slop to develop) just a little more than the entry level JR 527 bushed servo will. Note that either of these servos are ideal for the Falcon Trading Aero-Star.

 

Transmitter and Receiver

As mentioned earlier, the transmitter and receiver in use here is considerably higher specification than is strictly necessary for a trainer, and you may find a system such as the XF631 more suitable for your budget and taste.

My reasons for choosing to use the higher-end system includes:

  • My radio equipment lasts me a long, long time, so I prefer a system that caters to growing requirements, rather than using a more entry level system and then looking to upgrade it periodically.
  • For safety reasons, I personally prefer to use a PCM system, with a properly set failsafe (choosing engine kill); some of the more entry level systems use PPM only, not PCM. Note that this is a purely personal preference – many pilots use PPM and are perfectly happy with it.

Transmitter specifications include:

  • Assignable buddy-box capability to allow training to be done easily and safely. (The student and instructor each use separate transmitters linked by a cable; the instructor can then easily take control away from the student to prevent a crash whenever the student makes a mistake.) The instructor may also limit which channels he passes control of to the student.
  • 8 channels, to allow for future growth.
  • 10 model memory. (Allows you to easily use the same TX for multiple aircraft without having to reconfigure anything)
  • Adjustable trim steps – you can determine how sensitive or coarse you want trim changes to be.
  • Dual rates and exponential. I find this very valuable for trainees, because most of them initially over-control their trainer. A typical response to this is to tone down the overall response of the aircraft to the radio, but that means that the instructor also now has to deal with a less responsive aircraft when getting you out of trouble… Having dual rates and expo lets you ‘tone down’ the responsiveness of the aircraft only to the student’s input while allowing the instructor full unrestricted control on the master transmitter. Truly the best of both worlds.
  • Extremely well laid out system – all controls are easy to reach, and the feel and balance of the TX is very comfortable.
  • Ability to transfer model data from one TX to another.
  • JR Datasafe capability.
  • PPM or PCM selectable.
  • JR’s unique trim system – analog for throttle; digital for primary controls.
  • Easy to read LCD screen with well presented information.
  • Very easy to program.
  • More mixing and programming capabilities than I can list here. See the 8103 web page for full details.

 

Battery and charge-switch

 

I elected to use a larger capacity battery pack than comes as standard with some systems – note that JR’s handy “FlexEquip” program lets you pick an overall radio system that you like, and make some changes to it – such as swapping the battery out for a larger capacity one (more flights between recharges), or swapping the regular switch out for one of the very useful charge-switches (more on that later).

 

CONTROL & PUSHROD SETUP

Okay – now that we’ve decided what radio equipment to use, lets install it and the pushrods, control horns etc. that convert the servo’s movements into movement of the appropriate control surface.

Short pushrods, such as those used for the ailerons, need no support – they are not long enough that they can flex. However, the longer pushrods used for throttle, nose-gear steering, elevator and rudder on any trainer could flex and effectively cause unwanted control input if they are not adequately supported. Consequently, manufacturers come up with various ways of trying to ensure that such flexing can not happen, and the degree to which they succeed varies.

I am happy to be able to report that the pushrods provided with the Falcon Trading Aero-Star .40 ARF are the best that I have seen to date in any ARF. The throttle and nose-gear steering pushrods are simple metal rods which run through a plastic pipe that guides and constrains the pushrod – nothing unusual there, except that in this case Falcon Trading has taken the extra step of pre-installing the pushrod guides and ensuring that they are suitably anchored (a nice touch that shows attention to detail). The real difference in the Aero-Star’s pushrods though, is in the rods used for elevator and rudder control…

 

These parts come as pre-assembled units in which a square hardwood strip acts as a stiffener to a full-length metal pushrod.

This is significantly better than the common approach of having a short metal pushrod connected to either end of a relatively soft balsa rod. The improved rigidity of the Aero-Star’s pushrods may not sound like a big deal until you consider that unwanted flexing of pushrods could cost you your model. Falcon Trading has done a great job in preventing such flex.

Servo Tray

Three of the servos will be mounted in the fuselage, and they are all mounted to a single lite-ply servo tray. The tray is not pre-installed, as this allows you to do the work of mounting the servos (drilling holes etc) while the tray is more easily accessible than it will be once it is glued inside the fuselage.

 

Since the servo mount is relatively soft lite-ply, and the servos will be retained by wood screws, I prefer to add some ex.

 

 

 

 

 

 

 

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