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Written by Richard Landis and Barry Yarkon
Digital Exclusive
Follow along as a real-life beginner modifies the Thunder Power OBL Trainer to Electric Power under the tutelage of an experienced electric power instructor.


This review is the deliberate collaboration of a very skilled RC flyer and modeler, Richard Landis and Barry Yarkon, a “beginning RC Pilot”. In addition to his long RC piloting experience, Richard also has a great deal of experience with electric power systems.

Barry’s introduction to R/C flying, as an adult beginner, contains several lessons for anyone of any age who is attracted to this sport and who wants to start off on the right foot. It didn’t always happen that way for Barry.

Lesson One:

Barry tried to fly a radio-controlled P-47D foamy with electric power before he had access to an AMA club and field. He quickly learned that flying a tail-dragger Warbird in too small a space was simply a recipe for disappointment. After one too many unplanned collisions with the surrounding trees and two bottles of foam-safe CAA used up, what remained of the Thunderbolt was retired to the Red Cross hangar.

Lesson Two:

Barry recovered the electronic components (receiver, micro servos and Lithium Polymer battery packs) from the P-47. Still not a member of a flying club, he chose a second airplane in which those same parts were useful. This was an intermediate, aerobatics-capable sport biplane, the Reactor Bipe EP.

The Reactor Bipe had small main wheels, complete with wheel pants that caught in the field’s grass. Again, the Reactor was also a tail-dragger. At this point Barry became a member of the Rockland County Radio Control Club (RCRC), an AMA chartered club in the lower Hudson Valley area of New York State. Barry found that, even after intensive practice on an excellent computer RC flight simulator using that same model biplane, that the biplane was too fast and too frisky for him to make much progress learning how to fly RC. He did notice it was a lot of fun for many of the other club members who volunteered to “check it out” at the field.

Lesson Three:

The common sense advice from experienced club members was for Barry to take a step back and learn to fly with a traditional trainer aircraft, one with a high-wing, flat-bottomed airfoil and tricycle landing gear. The Thunder Tiger Trainer OBL 40 ARF is a perfect match for their descriptions.

OUR PLAN

The underlying motive for this review is to see how successfully a beginner like Barry can assemble the Thunder Tiger Trainer OBL 40, install an electric power system, and then learn to fly RC. Could Barry make up for the lost time and earlier discouraging results by re-learning how to fly with a proper trainer?

Richard will be available during Barry’s assembly to answer his questions and afterwards, Richard will check out the build, its CG balance and then will test fly the Trainer. Richard will act as his flight instructor until Barry can solo with the Trainer.

That said, this review contains suggestions that may be helpful for builders of all skill levels. Read on to see how we made out....

Twelve years ago, Thunder Tiger of Taiwan purchased the former ACE R/C of Higginsville, MO. and incorporated into what is known today as ACE Sport Distributors, Inc. (www.ace sport.com). Ace provides retailers in the U.S. with airplanes, helicopters, cars, boats, engines and various other sport products down to the nuts-and-bolts aspect of the sport (which is where ACE R/C started 53 years ago).

Because Barry is relatively new to the sport, the Thunder Tiger brand was unfamiliar to him. He discovered that Thunder Tiger’s aircraft line is quite extensive. It includes Trainers, Gliders, Scale, Sport airplanes, Helicopters and Jets. Their smaller Park Flyer and Aerobatic aircraft have become famous. Ace even has a Tournament of Champions aircraft series that John Glezellis recently used to place 4th at the XFC 2009. John was flying a Thunder Tiger TOC Extra 260 at this event.

It was comforting to find four Rockland, NY retailers listed on Ace’s website. After some minor confusion and a little trial-and-error, the box’s contents morphed into a great looking airplane. Fortunately, Barry did not need assistance beyond Richard’s expertise and the well-illustrated 28-page assembly manual, http://www.tiger.com.tw/product/4579-K10.html.

If you are a beginner considering buying a trainer aircraft, or if you are about to build the Thunder Tiger Trainer OBL 40, we suggest you download the manual and carefully cross-reference this review. Also, be sure to read the Sport Aviator articles, Building an ARF Trainer Parts 1, II and III.

The Airplane

Photo Courtesy of Thunder Power Taiwan

Designed for both glow and electric power, this is the newest addition to the family of eight Thunder Tiger Trainer models. It is a prefabricated ARF (Almost Ready-to-Fly) meant for beginning model pilots like Barry. “OBL” is short for Outrunner BrushLess motor. [For beginners: “40” indicates the approximate size of a model aircraft based upon the size of the appropriate 2-stroke glow engine. The GP-42 engine has a displacement of 0.396 cu. in. and is recommended for “.40-size aircraft,” hence the “40” in this trainer’s name.

The Tiger Trainer is available in two structurally identical models, the 4579-K10 for glow engine power systems and the 4579-K11 for electric motor power systems. The glow-powered version is also reviewed in Sport Aviator’s On The Flight Line Section as the Thunder Power Easy Trainer Plus.

The K10 airplane (TTR4579-K11) is meant for glow engine power and it contains extra parts to facilitate the use of either of two suggested glow engines: the Thunder Tiger GP-42 or the F54S 4-stroke. These parts include: 300cc. fuel tank and full accessories; and an adjustable engine mount with hardware.

For electric power, the K11 (Prod. No. TTR4579-K11) airplane comes instead with Thunder Tiger’s Ripper OBL36/11-40A brushless outrunner motor (No. 2368), an ACE BCL-40A Electronic Speed Control (ESC) (No. 8027), and an OBL motor mount (No. AS6458).

So, if you prefer to set up your Thunder Tiger Trainer with a glow power system, then specify the 4579-K10 and add the appropriate engine. If you prefer to set up your Trainer for electric flight, purchase the 4579-K11 model. Your retail dealer can advise you.

Authors Note : The K10 (glow) model was provided for this review. We preferred to electrify it by setting aside the glow power parts and installing an ElectriFly RimFire 35-36-1200 brushless outrunner motor and an ElectriFly Silver Series 35A SS-35 brushless ESC from Barry’s other airplane. The motor mount is a Great Planes GPMG1255 Medium Motor mount. We were not able to test the Ripper OBL36/11-40A brushless outrunner motor (No. 2368) and ACE BCL-40A electronic speed control combination but their specifications are similar.

 

Photo 2

 

Photo 3

The Thunder Tiger Trainer OBL 40 came packed in an attractive, sturdy box with all of the parts thoughtfully bagged and packed. See Photos 2 through 5. Photo 6 shows an exploded view of the kit’s parts (courtesy Thunder Tiger Taiwan).

 

Photo 4

 

Photo 5

Even the little super magnet that will hold down the access hatch was sealed into its own corner of one parts bag. There was no “hangar rash” and no shipping damage. We did discover that the nose gear mount was missing. Richard fabricated a nose gear mount for the steerable nose wheel.

(Ed. Note: This was supposed to have been the K-11 version but the K-10 was sent instead as the K-11 was not yet in stock. The K-10 nose gear mount is part of the engine mount and therefore was absent once that mount was eliminated. If you are converting a K-10 to electric power use Du-Bro bearing blocks number 156 and steering arm number 155.)

Photo 6

Photo Courtesy of Thunder Power Taiwan

We were also pleased with the handsome, streamlined design of the Tiger Trainer OBL 40 – white with a screened four-color scheme and matching side-stripes. Quality of construction was obvious from its drum-tight film covering (not a wrinkle or a bubble) to the extensive use of sheeting in both the fuselage and the wing halves. The entire top section of the fuselage is a white plastic molding that was permanently bonded to the balsa and plywood sides and bulkheads at the factory.

We learned from the manufacturer that the covering material used is "OPP" a form of Biaxially-Oriented Polypropylene (BOPP) film. Thunder Tiger was not able to specify a retail brand of covering, so if you need to do repairs or construction on your Tiger Trainer OBL 40, try speaking with the dealer you purchased it from or any one of Ace’s listed dealers. One such brand, Solarfilm, is available in the USA and is compatible with BOPP films according to the manufacturer, Solarfilm Ltd., UK.

Barry would like to share this anecdote with you. While he was doing some of this research via the internet, he was pleasantly surprised to have an email sent to Thunder Tiger Support at 10:30pm on a Monday evening from New York, answered within a few minutes! Turns out that Thunder Tiger Taiwan is almost exactly 12 hours ahead of New York time, for them it was 10:30am the next morning (Tuesday).

Photo 7

Photo Courtesy of Thunder Power Taiwan

Back to the Tiger Trainer. Construction was laser square and Thunder Tiger’s concern for quality showed in the extensive use of model grade plywood bulkheads and hardened points. There is also an attractive red spinner and backplate. According to Ace’s website, the MSRP for the K10 Trainer is US$150. and the K-11 is $199. Considering the K-11 arrives with an outrunner motor and ESC, the $49 extra is a great deal.

Photo 8

The broad wing seems to have a modified flat-bottomed airfoil of about 13-14% with a constant chord of 11 inches. Photo 8 shows the Tiger Trainer airfoil.

Photo 9

Each of the wing halves has 8 ribs and is generously sheeted top and bottom for 7” out from the root edge and for 5” in from the neatly beveled wingtips. The full-length ailerons are beveled where they hinge into the trailing edge of the wing and each aileron has 18 circular lightening holes (¾” diameter, see Photo 9). There is even a clear plastic wing protector that slips over the center trailing edge and an included strip of white covering tape to hide the wing join seam, no heat gun necessary.

Pre-Assembly Thoughts

 

Photo 9A

 

Photo 9B

Photos courtesy of Futaba

Richard and Barry chose the 6-channel Futaba 6EX 2.4 GHz transmitter and matching R606FS receiver. This Futaba system is reasonably priced ($220) for a beginner and avoids interference problems and their potential shoot-downs. A new RC pilot already has enough challenges to contend with and really doesn’t need the extra one of frequency interference.

The ESC used has a battery elimination circuit (BEC) built in. The receiver and servos will get their power directly from the motor battery without the need for a separate receiver battery pack. The motor battery is composed of two 3S 1P 2100mAh 20C Lithium Polymer battery packs in series for a 3S 2P power system (2 3-cell battery packs wired in parallel).with Deans connectors for on-board power that were used with my biplane. Barry already has a PolyCharge4 field charger and two Equinox LiPo balancers for these batteries.

Photo 10

Photo courtesy of MPI Maxx

Safety arming switch: Just recently, Barry had a safety incident at the field when he retrieved an electric-powered model that had landed on the runway and someone else inadvertently jiggled the transmitter throttle stick starting the electric motor [that would not happen with a glow engine]. This type of accident-waiting-to-happen can be avoided by installing an arming switch between the flight battery and the ESC. He chose to use an MPI Maxx Products International #6970 High Current Arming Switch with Dean’s connectors, pictured in Photo 10. It will mount into the fuselage side and cut-off power to the entire system when the red/black arming plug is pulled out. In Photo 10, the left-hand image is disarmed and the right-hand image is armed.

Servos: Using an electric power system eliminates the need for a throttle servo because the “throttle” function is handled by the ESC. Three Futaba 3010 servos were used to power the aileron, rudder, and elevator surfaces. A single aileron servo activates both the right and left ailerons simultaneously and it is hidden from view within the fuselage when the wing is attached. Also, a 6” (or 9”) servo extension cable will connect the aileron servo to the receiver to allow enough slack for easy wing removal and attachment when traveling.

Questions often come up on the forums, when a builder’s radio system has more channels than necessary for the four basic controls, about adding flaps to a model and about separating the two ailerons onto two different channels to allow for differential mixing.

Thunder Tiger rightly warns: “Please assemble your model exactly according to these instructions. Do not attempt to modify or change the Tiger Trainer OBL in any way as doing so may adversely change its flying characteristics.” We decided to build according to plan for this review knowing that once Barry masters the Tiger Trainer OBL 40 as is, we can revisit these questions and consider adding either or both of these more advanced capabilities in the future.

(Ed. Note: As regular readers of Sport Aviator know, I strongly favor using flaperons when the airplane uses twin aileron servos. I even installed flaperons in a HobbiStar 60 MK III in an article in the Pri-Fly Section. But the Thunder Tiger Trainer really doesn’t need flaperons although installing them, which is a lot of work on this airplane, would allow adjusting the ailerons to compensate for adverse yaw. Mechanical adjustments are possible as noted in the Midwest Aero-Star Review. )

BARRY’S ASSEMBLY NOTES

Here are my notes roughly in the order of the manual’s assembly steps. Again, you may want to download a copy of the assembly manual and follow along. http://www.tiger.com.tw/product/4579-K10.html).

The Assembly

The printed Assembly manual is heavily illustrated with as many as six black-an-white photographs on a page, but for those that lack contrast Barry refers to the PDF version of the manual and enlarges any critical photos.

As a shortcut we will refer to Thunder Tiger’s steps and photos by Page and Step, for example Page 6, Step 3 will be referenced to as 6/3.

Thunder Tiger’s suggested order of assembly is: Wing Assembly, Fuselage Assembly, Tail Feather Assembly, Landing Gear Installation, Electric motor or Glow engine Installation (including cowl), Radio Installation, Control Throws, Balancing, and Pre-Flight instructions.

Parts

First I needed to check the included parts. I pencil-checked the parts drawings on pages 4 & 5 as each part was located. The parts drawings are not to scale. Use a metric ruler for the millimeter sizes. This step took about 30 minutes because the parts are in many sealed plastic bags, (photo 11).

Photo 11

A set of eight rubber bands was also found in the box. You will want to use at least eight rubber bands to hold the wing in place each time you assemble the Tiger Trainer at the flying field. Since rubber bands tend to break, we recommend that you secure an ample supply from a local retail stationery store. We bought a ¼ lb. bag of #64 (3-1/2” x ¼”) rubber bands at Staples® that will probably last a year.

I put aside the glow engine related parts: 10oz. Fuel Tank and accessories, engine mount kit and OBL motor mount. All of the needed parts were found except the two mentioned earlier, the nylon torque rod horns and the nose gear mount.

Wing Assembly .

 

Photo 12

 

Photo 13

We began the assembly of the wing by gluing the three plywood wing joiners together using 5-minute epoxy and clamps, 6/1 (remember, page 6, step 1).

 

Photo 14

 

Photo 15

Allow the spar assembly to set and dry overnight (photo 12). Meanwhile proceed to 6/4 and 6/5. The aileron servo tray process was not easy to visualize from the manual’s photo, so I viewed the PDF. Test fitting one of the three Futaba S3010 standard servos before marking and cutting into the wing halves is a good idea. Leave the wing halves in their plastic sheaths while you handle them to better protect the covering.

Further work on the wing halves will wait for the wing joiner to cure.

Fuselage Assembly

I admit that I had trouble understanding how to best perform these steps. I wished Thunder Tiger had included better instructions or additional photographs here. It was nerve-wracking to cut into the plastic fuselage and the molded plastic parts without the confidence of fully understanding how these parts worked together. So, follow along in the manual but study my photos, too!

Photo 16

Cutting into the plastic of the fuselage, step 9/1, is meant to remove the material that will later be covered by the removable access hatch. I found the caption misleading. To better see the cut, run a thin black marker in the mold line groove first (photo 16).

Photo 17

Photo 17 shows the material removed revealing the battery compartment (electric) or fuel tank (glow). This material will be discarded. The edges of the cut in the fuselage will be covered over by the Kwik-Access Cover but do use a fine file or sandpaper to smooth the edges.

Photo 18

Cutting the shiny black windshield was more difficult because of the curves. There is a warning in the caption (9/2) that the remaining black plastic of the molded part will be saved for later use. I never did use the excess black plastic. I found it difficult to actually see the windshield mold lines in this shiny material as I cut. There also seemed to be a lot of plastic for the relatively small windshield component, 9/3. In Photo 18, the part released is at the bottom and the pieces that remained are shown toward the top of the photo.

It took a number of trial fittings and trimming to get the black windshield to fit well on the fuselage. Be patient and be conservative in removing material. You can’t easily undo a mistake or a slip of the knife (watch your fingers!). Make sure to use a new, very sharp hobby razor knife and change blades frequently as needed.

Photo 19

I chose to skip the decal application for the moment and jumped to step 10/8 to trim the white plastic Kwik-Access Cover. By now I was feeling more comfortable with this procedure. The Cover was released and the edges sanded smooth rather easily (Photo 19).

Be very careful not to accidentally trim away the front tab of the Cover since that is what aligns the Cover to the fuselage. The Cover is secured on the rear edge by the metal washer and super magnet.

Photo 20

First test fit the black windshield and white Cover, trim and sand until they fit snugly. As you can see in Photo 20, even a beginner can make a nice looking fit. If you have access to a rotary cutter (such as Dremel) you can more easily finish the plastic edges – be careful not to over do the touch up.

Returning to the skipped steps, I glued the super-magnet into the hollow plastic nipple from the inside of the fuselage (9/4) – by turning the fuselage upside down, applying thick CAA around the edges of the super-magnet and then placing the 4mm metal washer on the dry side of the nipple to hold the magnet firmly until dry. Meanwhile cut out the front and rear windshield decals (9/5) but do not cut out or separate the side window decals yet.

I found the decal material extremely sticky and difficult to place without bubbles. You can make a small cut into the larger “blisters” and firmly squeeze the trapped air out. Do the rear windshield decal first for the practice.

(Ed. Note: As a true-life beginner assembling his very first ARF airplane, Barry did not yet know about the water and dishwashing liquid method of applying large decals. Learn how to apply large decals easily in the Liberty Review article, page 3.)

Before you do the front windshield and Kwik-Access Cover, use medium CAA to glue the 4mm washer to the underside of the top of the Kwik-Access Cover where it will align over the nipple with the super-magnet in it (10/10). When dry, place the Cover onto the fuselage and apply the front windshield decal (10/11-12). I found this tough going. The decal actually covers the upper two-thirds of the Kwik-Access Cover AND the black plastic windshield appliqué. After smoothing on the decal, run your hobby razor knife around the outline of the Cover to release the Cover from the fuselage.

Now, do the side window decals (10/6). Before you cut, understand that you will make two horizontal strips, each with two windows showing. Do not cut the decal into 4 pieces. Align each two-window section with the slopes of the front and rear decals taking care to use the correct pair on the right and left sides of the fuselage. Smooth and release any blisters.

(Ed Note: Again, use the water/dishwashing liquid method as outlined in the Liberty article. Click on this link and then go to page 3.)

This section of the assembly was probably the most difficult. I spent about 2 hours trying to get this done as well as possible. How does it look? Not bad! Remember, when the wing is attached most of the imperfections will be hidden.

The fuselage holes for the wing mounting dowels that hold the rubber bands in place must be drilled into the fuselage. Use an awl to puncture each of the four dimples and then a tapered reamer can be used to carefully enlarge each opening until the wing dowels slide through for a snug fit. Use thin CAA to glue the dowels in place. Use a thick black permanent marker to blacken the protruding ends of the dowels.

Wing Assembly and Dihedral

By now the wing joiner has thoroughly set (6/1) and we can resume the Wing Assembly, 6/2. Before test fitting the wing joiner, we need to talk about the shape of the joiner.

Photo 21

Look carefully at the joiner. Notice it is not a rectangle. It is a shallow ‘V’ in shape. The reason for this is that the wing halves are joined at a slight angle to each other. The wing halves are meant to be angled upwards a slight amount to form a dihedral angle. This is a feature of trainer aircraft design that adds to their aerodynamic stability and self-righting tendency – all good things for a beginner learning to fly.

The manual does not explain that there is a right way and a wrong way to insert the wing joiner. Here’s what you ought to do to ensure proper wing set up. First, mark the exact center of the wing joiner with a vertical line on both sides of the middle – this will be about 4-3/8” in from either end. Next, use a fine line marker to write an ‘L’ on either end and then an ‘R’ on the other end of the joiner, (photo 21).

Now, look at the wing halves and determine which one is the left half and which is the right half. Remember that on the assembled airplane the all-white flat side of the wing faces downward and the curved and colorfully printed side of the wing faces upward. The photo (6/3) in the manual shows the Left or ‘Port side’ wing half from the pilot’s perspective (it’s the half that has “Tiger” printed on it). The Right or “Starboard side’ has the word ‘Trainer’ printed on it.

Do test fit the wing joiner, but always slide the correct side of the joiner into the corresponding wing and always have the bottom of the ‘V’ pointing downward. On the review model the ‘L’ side of the wing joiner needed more filing and sanding to fit snugly into the slot on the left or ‘Port side’ wing half. Tests fit both halves onto the joiner and verify that the top, printed surfaces of the wing halves form the raised arms of the ‘V’.

Photo 22

Looking at the angle that the joiner creates, it is about 3/8” from the middle of the joiner to each end of the joiner. Measured with a protractor this angle is about 2 degrees of dihedral angle, as shown in Photo 22.

We suggest using 30- or even 60-minute epoxy to glue the wing joiner into the wing halves and butt glue the two wing halves at their roots, as instructed in 7/6 and 7/8. This will give you sufficient time to make the assembly and double-check that the wing halves have the proper angle – yes, it’s that important. [If you detect that the angle is wrong, quickly pull the wing halves apart, remove the wing joiner and flip it 180 degrees before you apply more epoxy and slide the halves back together.]

Photo 23

When the wing is fully set, we left it overnight, complete the aileron servo tray assembly as instructed (7/9, 7/10, and 8/11), using Gap Filling CA. There is enough white tape to cover the wing join seam, 8/12, and still have enough to slit in half lengthwise and cover the top of the plywood servo tray if you’d like (Photo 23).

Photo 24

You will need to remove the two foam blocks that encase each of the two torque rod ends, which kept them from accidentally piercing the covering material during packing ad shipping. You can replace them or skip to step 8/16 and force thread a nylon torque rod horn onto each exposed threaded torque rod. Be sure the two horns are at equal height above the wing surface, (photo 24).

Photo 25

I sanded the plastic wing protector and glued it to the middle of the top of the wing, flush with the trailing edge using Gap Filling CAA and two clamps (see Photo 25). (Ed. Note: Scoring the underside with a sharp hobby razor knife a few times, do not cut through but only score the plastic, allows the plastic to conform to the wing more easily.)

I followed the manual using Thin CAA sparingly to mount the two ailerons to the wing (8/14, 8/15). Study the Sport Aviator article, “Installing Mylar Hinges” in the Flight-Tech Section for complete details on this installation method. Then I threaded each of the 12” threaded pushrods into a clevis and attached them to the torque rod horns, 9/17. Cut small sections of the supplied silicon tubing to slip over the clevis to keep it from opening (photo 26).

 Photo 26

The beveled edge of the ailerons do make a close fit to the wing but take care not to make them too close or to use too much CAA so that the ailerons will move up and down easily. Photo 26 shows the aileron torque rod and servo installation.

Installing the Tail Feathers

“Tail Feathers” are, of course, the horizontal stabilizer, left and right elevators, and the vertical stabilizer with its rudder. I followed the manual’s steps on pages 11 and 12 with success. We suggest that when you cut to remove the covering for the areas to be glued on the horizontal stab, rather than 1/16”, cut away the covering 1/8” inside of the lines to avoid seeing any raw balsa when the fairing is pinched and glued later. I needed to use Gap Filling CAA and a “hit” of CAA Accelerant to get the plastic fairing to hold in place. It makes a nice-looking streamlined tail.

The process of assembling the elevators to the horizontal stabilizer and the rudder to the vertical stab is similar to what is done for the wing ailerons. I used Thick CAA to glue the linkage wire into each elevator half. (Ed. Note: This task is best completed using 30-minute epoxy as that reinforces the balsa wood more deeply than will thick CAA.)

Note: if the photo in your manual for 12/9 shows the horizontal stabilizer and elevators flat on a work surface, know that you have already assembled the horizontal and vertical stabilizers to the fuselage in 12/8 – not to worry as the control surfaces can be installed at any time.

Photo 27

I found the two white plastic outer tubes that support the pushrods through the fuselage and on to the tail surfaces inside the fuselage taped together (they are not shown on the parts drawings). I found the tape to be very sticky and it took a cloth with alcohol to remove the residue. When you locate and cut the pushrod exit slits (13/11), use a flashlight to shine through each side of the fuselage – the cutouts will be easy to see. I used a curved probe or a needle-nosed plier to fish the end of each tube out then pull the tube through (see Photo 27).

Keep in mind what each outer tube is for. The Starboard side tube (pilot’s Right) is for the Elevator control and the Port side tube is for the Rudder. Use Thin CAA sparingly along the outside of the tube at each end to secure them.

I attached the control horns to the starboard elevator and to the rudder as shown in 13/13 – 13/16. Take your time and use care to align the holes for both sides of the elevator and rudder as accurately as possible. There will be extra thread showing above the bolt retention plate when you are done. You may want to use a T-pin forced through the balsa to mark the placement of the exit holes, then remove the T-pin and drill the 5/64” holes.

Landing Gear Installation

Photo 28

Next I assembled the landing gear to the fuselage (14/1 – 14/5). I had to do some searching before understanding the instruction in 14/1 “... into the holes in the fuselage.” On the bottom of the fuselage, about 11” back from the firewall there is a gap in the sheeting but it is under the covering material and is not obvious. Look inside the fuselage just forward of the servo mounting plate and you will see the two reinforced hard points that each gear wire slips into (see arrows in Photo 28).

 

Photo 29

 

Photo 29A

Push a probe or small screwdriver into each of these holes to puncture the covering on the bottom of the fuselage – these are the insertion points (photo 29).

Photo 30

Cut along the slot’s center of the covering. Then use a covering trim iron to adhere the covering into the slot. Test fit the short vertical ends of each wire all the way into its hole until the wire is almost flush with the bottom sheeting.

Note in photo 29A that a recess is cut into the bottom just inside the gear hole. This recess allows the landing gear cross leg to sit completely flush into the fuselage slot. Check fit each gear leg into the hole and that it fits completely inside the cross slot. If you are using a glow engine, apply thin CAA to the exposed wood inside the slot to protect it from exhaust residue.

Do not glue the legs into position. They must remain removable in case one is damaged during landing practice. If that happens, you can remove the gear leg by simply removing the nylon cross straps and using a vise to straighten the gear leg back to factory specs. Photo 30 shows the gear wires inserted. Use the supplied nylon straps to retain the gear legs.

Slide each wheel onto its wire (14/3). Use blue Locktite on the threads of the 3x5mm screws that secure the wheel collar to the landing gear wire. Be sure to face the screws aft to minimize snagging in the grass if your field, like ours, is not paved.

Nose gear assembly

The nose gear mount was missing from our parts bag. (Ed. Note: The nose gear bearing is part of the engine mount. Since this was a glow to electric conversion, no extra nose gear bearing was included. The K-11 electric version does include a nylon nose gear bearing. If your Thunder Trainer is also a K-10 conversion, use a Du-Bro nylon nose gear bearing available at any hobby shop.)

Photo 31

Richard fabricated a nose gear bearing for me from discarded black plastic motor mount material. He found that we needed to add a ¼” block of scrap wood between the firewall and the mount to give enough clearance for the steering arm (see Photo 31). Otherwise the mounting was done as described in 14/3 – 14/5. We used a dab of blue Locktite on the set screws to keep them from loosening.

Power Unit Installation

Photo 32

I chose to re-purpose a Great Planes RimFire 35-36-1200 Outrunner Brushless motor to power the Tiger Trainer. Because of this we could not use the included black OBL Motor Mount. I needed to custom-fit a Great Planes GPMG1255 Medium Motor Mount to the firewall by removing and re-drilling three of the blind nuts to the dimensions of our motor mount as shown in Photo 32. We kept the blind nut in the upper left and re-drilled the others to keep the alignment similar.

If you are using the Thunder Tiger OBL motor and electronic speed controller (ESC) that come with the 4579-K11 version, follow the instructions for a straightforward installation (the second 14/1 – 15/3).

Photo 33

I improvised installing our medium motor mount and RimFire motor, which proved to be a very close fit to the dimensions of Thunder Tiger’s parts. We placed the ESC on the starboard side of the motor mount close to the air opening in the cowl for good cooling, Photo 33.

Note: If you choose to use an electric motor power system, as we did, disregard the steps for installing a Glow Power Unit on pages 16, 17 and 18/11-18/13.

Photo 34

I installed our battery choice, a 3S, 1P 11.1V 2100mAh 20C Lithium Polymer battery pack in place of the recommended 9-cell 10.8V 3600mAh nickel metal hydride battery, 15/4. Again, this was because we already had several Li-Polys and the appropriate charging equipment. Also, Lithium Polymer batteries weigh less. The removable nylon tie strap is handy, see Photo 34.

Cowl

 

Photo 35

 

Photo 36

I followed the instructions to release the cowl from the molded form, test fitted and mounted it. By this time I felt confident cutting away the waste using various Dremel cutting bits to open up the central circle and the air vents.

 

Photo 37

 

Photo 38

Then test fit the cowl and spinner and add the decorative stripe extension decals on each side and secure the cowl with the four 2x8mm wood screws as described in 15/5 – 16/9, (photos 35 - 38).

Radio Installation

I chose to use my existing Futaba 6EX 2.4GHz FASST transmitter and matching 6-channel receiver. I did purchase three Futaba S3010 HT servos and use four channels to control Ailerons, Elevator, Rudder, and Throttle. I added a 6” servo extension to the Aileron servo, which controls both left and right Ailerons.

Photo 39

Rather than the light duty switch shown in 18/1, I mounted the MPI Maxx High Current Arming Switch discussed in Pre-assembly Thoughts. Richard then soldered longer leads to the assembly for easier access in the battery compartment. The safety “switch” was mounted into the starboard side of the fuselage as shown in Photo 39.

Photo 40

I recommend that you mark the plywood servo tray for Elevator and Rudder. Our electric motor assembly uses only two servos in the tray; the space for the Throttle servo is empty. If you are installing a Glow power system, follow the set-up in the manual, 18/3. Photo 40 shows the completed servo installation, note position of pushrod ends on arms.

Note: Be certain that the swivel EZ Connector that holds the nose wheel pushrod is free to turn, or else the pushrod will bind. We clipped off excess steering pushrod material.

Photo 41

When mounting your servos, the correct way to install the metal grommets into the rubber shock mounts is from beneath, with the metal lip on the bottom as in Photo 41. Rather than the circular disc servo output arms, I chose to use the 4-armed horns and clipped off unused arms.

The photo also shows the Z-bend ends of the Rudder and Elevator pushrods that Richard taught me. I had never seen this approach to making up flexible (yellow) plastic push rod bodies by force-threading a Z-bend end and a double threaded end onto each one. Use the longer yellow tube for the Rudder, the shorter for the Elevator as shown in 20/11 – 21/17. These tubes are not shown in the parts drawings.

Make sure the control surfaces are taped in neutral position and that each servo is centered before you install and adjust the pushrod assemblies. Be sure to center the trim levers on your transmitter as well. It is better to adjust and check multiple times until you have a reasonable geometry than to use the trim settings in your transmitter once airborne.

Note: Particularly for electrical power systems, never test and adjust the control surface servos, linkages or Throttle with the propeller mounted on the motor. Always treat the motor as if it did have a propeller on it and could start to spin at any moment without warning because, it can do that at any time. You do not want to see how easily an unexpectedly spinning prop can absolutely ruin your day.

Photo 42

We used a Futaba 2.4Ghz FASST R606FS receiver. This type does not recommend wrapping in foam rubber.  We mounted the receiver on the floor sheeting forward of the servo tray with matching pieces of sticky back hook and loop tape, Photo 42. The antenna on this type of receiver is a short pair of insulated antenna leads. There is no need to run the antenna wire outside of the fuselage, just tape the insulated antenna legs at right angles to each other for best reception. If you are using FM or other technology, run your antenna as suggested in 19/5 and 19/6.

We completed the Aileron Servo mounting, 21/8 – 22/21, using two solder-on metal clevises rather than making Z-bends in the aileron pushrod. This was pictured in Photo 26. (Ed. Note: I am sure that Richard suggested this since he well knows that the longer, unsupported length of the aileron control arms will cause the “Z” bends to rotate inside the servo output arm as they move. This quickly enlarges the output arm’s holes causing loose aileron control and eventual flutter after a hundred or so flights.)

Assembly Completed

Photo 43

Our Thunder Tiger Trainer OBL 40 is now fully assembled. Notice how closely the completed Tiger Trainer resembles the illustration on the box, Photo 43. It is a very nice looking aircraft – definitively sculpted and streamlined, with a high-value finished appearance. The Thunder Tiger Trainer is anything but a “boxy” airplane.

But before you run out to the field to fly, take this time to carefully go over all instructions, every fit and every screw. Then you should carefully adjust the Control Throws and Balance (CG) point before you go.

Control Throws (Page 23)

The manual’s illustrations and description explain how much each control surface should move in response to the control sticks on your transmitter in Low Rate and High Rate switch positions. We recommend that you start with the manufacturer’s recommendations for the first (maiden) flight. That said, Richard suggests that beginners like Barry be urged to have an experienced flyer review these settings before the Tiger Trainer is flown. It could mean the difference between a successful maiden experience and a disastrous one.

Note: Be sure to “lock” each clevis to its control horn by slipping a piece of clear tubing over the prongs of the clevis.

Balancing Your Airplane (Page 23)

If you have ever been a passenger in a small full-size aircraft, or in a kayak for that matter, you can appreciate the importance of proper balance and weight distribution. For a model aircraft balance is critical.

The Thunder Tiger Trainer OBL 40 is an ARF aircraft that allows substitution of some of the components, such as the motor or engine, the ESC, the Receiver and the Battery. Because of this flexibility there is a good chance that your assembled Tiger Trainer will not balance at the manufacturer’s recommended Center of Gravity – 3-1/4” aft of the wing’s leading edge (23/1). Be certain that you have the wing mounted and rubber-banded before you lift the airplane. Check that the electronics are properly seated and won’t move. Install the spinner and propeller before checking the CG.

In a Glow powered system, the fuel tank should be empty and your receiver battery held in place using a hook and loop fastener. In an electric powered system, such as ours, install the flight battery but do not connect it to the ESC (disarm with your cut-off switch to be doubly safe).

In our configuration, the Tiger Trainer was tail heavy even though we mounted the flight battery and the ESC as far forward as possible. We added self-adhesive ¼ oz. lead weights to the firewall and even on the motor mount until the Trainer balanced at the recommended CG. In our case we had to add 3-1/2 oz. of weight from a package that held 6 oz.

READY TO TEST FLY

Photo 44

RC pilots call the first test flight the “Maiden Flight”. A beginner should never attempt to first flight a new airplane. Leave this to the best pilot you can find who is willing to help you. Most clubs have several people who regularly do this for others.

Photo 45

Our Thunder Tiger Trainer OBL 40 first flight was on a Sunday afternoon in September 2009 at RCRCC’s (Rockland County Radio Control Club - http://www.rcrcc.com) Clarkstown Model Aerodrome. Clarkstown is a neatly manicured grass flying field (Photo 44). Our original plan was for Richard, shown in Photo 45, to do the test flight but he handed our Tiger Trainer to his son, Daniel Landis, who is a highly ranked national R/C Pattern (Precision Aerobatic) Pilot who also flies reconnaissance UAV’s.

 

Photo 46

 

Photo 47

Despite a gusty wind that blew the wind sock horizontally, Dan quickly had the Tiger Trainer in the air, surfaces trimmed and capable of hands-off level flight. Dan’s adjustments were saved in the model memory of Barry’s transmitter.

 

Photo 48

 

Photo 49

After a few minutes Dan had the Tiger Trainer doing Rolling Circles (don’t try that at home, folks). The 2100mAh LiPo battery pack gave a 6-minute flight envelope. See Photos 46 – 49.

Photo 50

On the ground, using an 11x7E APC propeller, there was only a small amount of clearance in the grass. We made a note to consider exchanging the 2-1/2” wheels for 3 or even 3-1/2” wheels. If we do that, we might have to re-balance the aircraft. But, since we would be using very light foam wheels, there will most likely be no change to the CG at all. In either case, always remember to re-check your CG whenever there are any aircraft alterations.

Photo 51

Another change was suggest, is to replace the 2100mAh battery with a 3600mAh pack. Again, if we do that we will have to re-balance the aircraft, hopefully by removing some of the added lead nose weights.

Photo 52

Richard and Barry enjoyed watching Dan put the Tiger Trainer through the pattern and he did a graceful approach and landing. Barry began to feel the awe that comes with seeing an airplane you’ve assembled from a boxful of miscellaneous pieces transformed into a graceful flying machine silhouetted against the clouds. See Photos 50 – 52.

 

Photo 53

 

Photo 54

With a new flight battery in the battery bay of the Tiger Trainer, Dan took it up and then handed the transmitter to Barry (wearing the blue shirt). Barry’s first flights were far more sedate than Dan’s but that is what a good trainer like the Thunder Trainer OBL is for; teaching new pilots. While a little “Hot dogging” is possible with this airplane, its primary mission is to teach Barry how to become another Hot RC pilot in his own right.

 

Photo 55

 

Photo 56

The wind seemed calmer at 200 ft and the Tiger Trainer was easy to control and easy to see. Barry found that normally problematic right-hand turns were comfortable and only a small elevator input was needed to complete the turns. The Tiger Trainer maintained altitude through the turns well.

 

Photo 57

 

Photo 58

Compared with the two airplanes Barry had tried to train with, the Tiger Trainer was responsive but docile and forgiving.

Photo 59

To end the maiden day on a positive note, Barry asked Dan to do the landing. The airplane flies at about the same speeds as do most trainers. The landing approach might be just a bit faster than usual, maybe 3-5 mph faster. But the airplane is forgiving at all times; even when flying trough deep stalls (full “up” elevator is held continuously through a series of oscillations). The ailerons lost some effectiveness at these very slow airspeeds but continued to work as needed. Rudder response in the deep stalls was always immediate and very effective.

Photo 60

The airplane was always very honest and never exhibited any snapping tendencies even when full “up” elevator at high banked slow airspeed situations. Snap rolls were slow and very large. They resembled more a barrel roll than a snap roll. Takeoffs were excellent but the nose-high attitude required to provide propeller clearance for the larger electric propeller reduced ground steering control as the airplane began to reach lift off speeds. Fortunately the rudder was by then fully effective so keeping the Thunder OBL Trainer going in a straight line posed no problems.

The landing flare needed to be exaggerated a little, again for ground clearance. But again this proved a non-problem. With its very light wing loading of just over 13 ounces per square foot, the Thunder Tiger OBL is easy to manage on approach and touchdown so this was easy task, even for a beginner.

SUMMARY

 

Photo 61

 

Photo 62

We found the Thunder Tiger Trainer OBL 40 to be well conceived and of high quality construction. Without counting time spent with the additional challenges of fitting a custom electrical power system and taking notes and photographs for this review, Barry estimates he would have been able to complete the assembly of this ARF in about 8 -10 hours.

Because the objective of this review was to gauge the assembly and performance of the Tiger Trainer from the vantage point of a beginner, we decided not to clutter up this review with technical speed and performance and flight data statistics that most beginners are not equipped to measure or to act upon.

Barry had expressed a concern that the Tiger Trainer lacked the “training wheels” seen on certain other basic trainer models, such as air speed brakes, airfoil extensions or pilot-assist devices. Once he felt the Tiger Trainer in the air, that concern was put to rest. Barry is now looking forward with confidence to getting more “stick time” with this new trainer. His goal is to practice the requirements of the Solo Checklist.

We can heartily recommend the Thunder Tiger Trainer OBL 40 as a “first airplane” choice for aspiring flyers of all ages. For more information on this versatile and superb basic trainer, go to: http://www.acehobby.com/ace/TTR4579.htm

 

 



Additional Aircraft Specifications

Manufacturer: Hangar 9                     Length:           51 in.              

Cost: $350.00                                     Wingspan:       69.5 in.

Radio: Futaba 6EX FASST                  Wing Area:     902 sq. in.

Servos: 3 x FUT S3010                       Wing Loading: 13.5 oz./sq. ft.

Motor: RimFire 15 35-36-1200kV      Weight:           5.3 lb.

Outrunner                                            Propeller: APC 11 x 7 Thin Elec.

Airfoil: Flat Bottom                             ESC: Great Planes Silver Series 35A

Battery: ElectriFly BP2100 – 2100 mAh Li-Poly

Special Airframe Features: Flat Bottom Wing, Attractive airframe, Definitely not the average box-like trainer



Notable Positives

Aerobatics good for a Basic Trainer

Excellent Basic Trainer performance

Very good looks

Light flying weight

Versatile glow or electric power.

Notable Negatives

Some manual steps could be explained better

Needs a larger 3,600 mAh battery for longer flights.


Authors: Richard Landis and Barry Yarkon

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