P-51 Mustang PTS
VIDEO FILES
| Mustang PTS – Part One - Windows Media Player – Dial Up / Broadband Mustang PTS – Part Two - Windows Media Player – Dial Up / Broadband |
Learning to fly RC model aircraft is easy or hard, depending on the person or people involved. Everyone is different; therefore every story about learning to fly an RC model is unique. The goal of Model Aviation’s Sport Aviator magazine is to help make each new pilot’s learning experience a success.
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Lucky for us, there are a lot of different trainer aircraft available that suit the needs of the RC student pilot. Up until now, those trainer aircraft resembled the famed full-size basic trainers like those from Cessna and Piper. Ask full-size airplane pilots the question “what’s the best trainer?” and you’ll likely get a lot of different answers, all with good reasons behind them. Typically, the answers are based on their experiences with two very different looking aircraft; the Piper Cherokee 140, and the Cessna 150/152 series.
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Here, I’ve shown you the Top Flite Piper Arrow II (a higher powered version of the Cherokee), which is a kit, and the Hangar 9 Cessna 182 which is an ARF. These models are considered scale; definitely not trainer models. Why? Because of many things, but two main factors stand out. First, to make them scale, they need to have an outline true to the full size aircraft. Modeling the full size aircraft means reducing the size which dramatically changes its ability to fly, and not for the better. Secondly, scale models have a great deal of detail to make them look like the full size aircraft. Such items as rivet detail, cockpit interior, and hatch openings make the model a masterpiece. But they do so at the expense of adding weight. Heavy airplanes take a lot of skill to fly.
In the model aircraft industry, the practice has been to offer trainer aircraft that look as close to the full-size trainers as possible, but to make the necessary changes so that they’re light enough to not only fly well, but are practical to purchase and durable enough to withstand the bumps and bruises that come with the sport.
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The results are closely related to the aircraft in these photos here. On the left is the Hangar 9 Value Series Cherokee 40, and on the right is the Hangar 9 Value Series Cessna 40 (Cessna 152 look alike). Both of these models fly very well and are considered advanced trainers because of their semi-symmetrical airfoils. Judging them from their looks, their flat fuselage sides and rough engine openings separate them from being scale models; they are instead referred to as boxy or blocky.
Sounds like a bad thing doesn’t it? Well let me tell you that models have been built like this for years and have trained a lot of people to fly. The basic trainer concept has been explored enough that not only are there a variety of sizes from which to choose, but you can also fine-tune your trainer selection so that its qualities suit your goals and aptitude as an RC pilot.
It’s important to evaluate a student RC pilot before a recommendation is made to what basic trainer model aircraft is best for them. If a RC student pilot is totally fresh, then they might take longer to teach. In that case I would recommend a model that has great slow-flight handling characteristics.
Every student pilot is different. Their abilities and experiences define their best learning process. For instance, someone with experience flying a full-size aircraft might learn to fly an RC model faster than a person with no piloting experience because they know the limits and language. If another person has video game experience, then their eye-hand coordination skills would give them an edge and therefore they would advance more quickly. Experience flying an RC Simulator gives most student pilots a good head start. In any case, I would recommend a trainer that has more advanced handling characteristics. Such an airplane would teach them to respect the capabilities and limitations of each aircraft, while at the same time offer versatility to teach more than just the basics.
The “Advanced” Basic Trainer
Don’t let the word “advanced” in this context scare you. Its meaning here doesn’t have anything to do with the pilot’s abilities. Advancements in technology from within the sport have brought us better products that are precision manufactured and engineered to a higher standard. The results are airplanes that fly better, engines that are easier to start, and radio equipment that is versatile and reliable.
Horizon Hobby combined all of their knowledge and then did some more homework on how to create a “next level” trainer – an RC basic trainer that satisfies not just the needs of the student pilot, but the needs of intermediate and advanced pilot as well. In other words, you buy one model that can fly like a basic trainer, then easily upgrades to fly at higher performance levels as its pilot’s skill progresses.
Horizon coined the acronym “PTS” for Progressive Trainer System; which simply put means that they’ve developed an RC aircraft package that’s not only an all-in-one; it’s an aircraft that will grow with the pilot as skills progress.
The idea of a progressive trainer isn’t a new one, that’s why Horizon did it one better. Most basic trainers are high wing aircraft with tri-cycle landing gear; meaning that they sit level on the ground and use a nose wheel. They usually look like low-performance, some say “boring,” aircraft meant for doing putt-putt style flying. They are great at making low, slow circles.
Tail-dragger aircraft, those that rest with the tail section on the ground and have a tail wheel, are often overlooked as basic trainers because ground and take-off handling of these aircraft require extra skills to manage. However, high-performance, propeller-driven aircraft rarely have tri-cycle landing gear. So if you were going to design a cool looking trainer aircraft, the last thing you’d want it to look like is a trainer, right?
The design team at Horizon took a long hard look at a lot of tail dragger aircraft. There was a lot to choose from; many of them though had the wing not on the top of the fuselage, but on the bottom. Low wing models are what most student pilots aspire to fly. Therefore a model progressive trainer would likely have to be a low-wing tail dragger aircraft. Therein lay the challenge. Make a low wing tail dragger model that flies like a basic trainer, but later on can be upgraded to a higher performance aircraft.
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The P-51 Mustang PTS from Hangar 9 is the conclusion of all the development study in PTS aircraft by Horizon Hobby. In the above photographs, on the left is the Mustang PTS and on the right is the 1.50 size Hangar 9 P-51 Mustang ARF. As you can see, little in the way of looks was given up to make the PTS model look like a scale version of the same aircraft.
Believe it or not, the Mustang PTS is a basic trainer, and is offered as a ready to fly (RTF) RC aircraft that can be assembled in 30 minutes and flown just as soon as the transmitter and receiver batteries are charged. Yes, it’s a basic trainer… and it looks really cool. Who wouldn’t want the most famous fighter aircraft from WWII as a first RC model airplane?
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Check out the nice little scale details. From the right angle, it really does look like there’s a 12-cylinder engine packed under the cowling. In reality, what does power this authentic looking Warbird is an engine well proven in performance and ease of handling. The Evolution Engines Alpha engine is made with the highest standards and high quality materials.
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Check out some earlier reviews in Sport Aviator on the Hangar 9 line of traditional trainer aircraft (Arrow and Alpha 40 trainers) and you’ll read just how good an engine this is. It’s designed with the novice pilot in mind so that it’s not only easy to start, but safer and easier to operate.
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The needle valves on the engine are preset at the factory, and then limited to a small range of movement so that small changes can be made without fear of harming the engine. The main needle valve is mounted at the back of the engine, away from the spinning propeller (photo 8). Photo 10 shows the idle mixture adjustment. The blue collar prevents excessively rich or lean mixtures insuring a reliable idle. Even the glow plug is canted aft so that hands are kept well clear when removing the igniter.
Building a Mustang and expecting it to fly as a trainer goes against all tradition in RC modeling. For that matter it goes against tradition in full-size pilot training as well. The trick is to design a model that looks like a Heavy Metal Warbird, but doesn’t fly like one. What did Horizon Hobby do to make this concept work?
Let’s start by looking at the landing gear; sort of from a “ground up” review of the airframe. One Achilles heal of the typical high wing trainer is that it has a high lateral center of gravity; meaning its top heavy. Steer them too sharply on the ground and they easily tip over. Low wing aircraft don’t have much of a problem in this regard.
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Tail dragger aircraft are typically a challenge to handle on the ground because they can nose over during taxi, take off and landing. This obviously puts a strain on the airframe, so the pilot carefully manages power and elevator deflection to keep the tail and the nose where they are needed. The Mustang PTS handles this problem in a simple manner by placing heavy-duty wire landing gear as far out on the wing as possible to minimize side-to-side tipping while canting the gear as far forward as possible so that nose-overs are next to impossible. The wheels are large for a model of this size to enhance ground handling.
That pretty much takes care of handling the aircraft on, to, and from the ground. But how can anyone make a P-51 FLY like a basic trainer? Well, the first thing that needs to be done is that it must be built as light as possible. This keeps the wing’s workload down (producing a lower “Wing Loading”) while making the aircraft more responsive and controllable.
Examining the Mustang PTS as closely as possible without tearing away the expertly applied covering was somewhat difficult. Peaking down the fuselage, inside the wing roots, under the servo hatches and feeling under the film covering told a lot about the effort to construct this model as lightly as possible. The balsa wood and plywood parts that make up the airframe structure were cut with a laser. The advantage here is precise fitting of all parts making for a solid assembly that requires less glue to hold it together. Material is removed (we call these lightening holes) wherever it isn’t needed and covered with lightweight heat shrink covering to protect the porous wood parts and streamline the surfaces.
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The fuselage is mostly constructed of 3mm light plywood. The forward portion of the structure is solid to make that area as robust as possible to hold the engine in place. Aft of the first bulkhead there’s lightening holes everywhere, making the space within seem cavernous. The engineering of the parts is smart in that the bulkheads (also known as formers) in the tail section include support openings for the pushrod guides plus holes for the radio antenna tube that runs out to the very end near the tail section.
The top forward and rear sections of the fuselage are sheeted with thin balsa and supported with plywood formers and balsa stringers (sticks that run lengthwise between the formers for support). The clear plastic canopy is painted with a silver paint that matches the covering and is glued in place at the factory.
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The horizontal and vertical stabilizers are built using stick construction as the open framework saves weight. The whole assembly just bolts into place, which I’ll get into later. What’s important about the tail assembly is its size and position. To increase pitch stability, the stabilizer area has been enlarged. The outline and position of the parts have stayed the same to preserve the Mustang “look”.
The thing about fighter aircraft is that they’re designed to fly fast. After all, that’s one of the things that make them so cool. However, a fast-flying trainer can quickly become the last flying trainer that pilot might fly. So the airplane has to have the ability to fly slowly, and in a controllable manner, so that a new pilot isn’t overwhelmed with an airplane that’s flying faster than they can plan ahead.
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The Mustang PTS has some novel features to help reduce flying speed. On the landing gear are speed brakes that add drag. The three-blade propeller also helps to control the airspeed. But something happens when you take a high performance Warbird and start adding things to slow it down. They begin to become harder to control and more critical in how they maneuver. The cruise airspeed starts approaching the stall speed and this is not good.
The wing is the major player in how this Mustang makes a good trainer. Its construction is mostly balsa wood with plywood and hardwood material used at the stress locations. The wing uses limited sheeting to save weight but still maintains an accurate airfoil shape. The airfoil is progressive, the center section is semi-symmetrical, and at the wing tips it is more of a flat-bottom type. This very subtle design feature greatly enhances the wing’s stability without giving up performance.
The wing of a regular Mustang is dependant on higher airspeeds to fly well. The slower it goes, the harder the aircraft becomes to control. So the solution to that problem was to modify the wing for extra lift at slower airspeeds. The flaps on the PTS Mustang have two jobs. One, generate more lift to make the aircraft more stable at slower airspeeds. Two, to add more drag to further slow the airspeed.
Now we have a Mustang that flies very slowly because it has all these devices hanging on it. The flaps add extra lift, but they do not help the aircraft to stay stable while turning. For that job, this Mustang has been equipped with specially designed wing tip droops.
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The purpose of the wing tip droops is to further stabilize the Mustang so that it can’t tip stall, spin or snap roll. These are the three major events that can happen while a high performance aircraft is flying slowly. The clear material the droops are made from is impact resistant and just about invisible while the airplane is flying. They don’t detract from the sleek outline of the Warbird in the air.
Without getting too technical about the aerodynamics, those are the major features that make this P-51 Mustang fly like a trainer. What’s novel about these same features is that any one of them can be removed to change the handling of the airplane. After the student pilot solos, that pilot can progress in their piloting skills while still flying the same airplane.
Mustang Assembly
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This is one RTF model that doesn’t skimp. The P-51 Mustang PTS is a complete Ready-To-Fly RC model package. The airplane is very well packaged within a box that’s compartmentalized and has all its pieces wrapped in protective plastic.
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I really wasn’t worried about damage with everything being packed so well. I liked that foam was held in place with tape over the pushrods on the wing and places where parts might scratch one another. However, there was a course scuffmark in the plastic on the left side of the fuselage. This happened to be where the power switch was for the on-board radio system. When I removed the plastic, I noticed that the switch was in the “ON” position.
This worried me because in the ON position it would drain the 4.8-volt receiver battery down. For the length of time that it could have been left this way, there’s a good chance that the battery was damaged beyond repair. I continued on with the inspection of the box contents.
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With all of the kit contents removed, it is clear that there isn’t much to do in the way of aircraft assembly. The engine is already installed with the muffler attached. All the radio equipment is installed with the pushrods attached. The fin and rudder are temporarily in place for shipping, and the pushrods are, of course, not yet attached to the rudder and elevator.
The wing is basically in two pieces with a light-weight aluminum tube for a wing spar. The landing gear is installed later with screws and nylon straps. The whole wing is attached to the fuselage with nylon bolts through the radiator scoop and hard points in the wing. The radiator scoop is removable, held in place by the wing bolts to ease wing installation and removal.
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The all-wood structure is finished with Hangar 9 Ultracote film covering and a medley of graphics that are made from sign vinyl material, stickers and die cut pieces of Ultracote material. All of these graphic details are pre-applied so there’s no decorating to do.
When I first took all the parts out of the box and plastic bags, the covering was very smooth. Over time however, the Ultracote began to show wrinkles. This is not really the fault of the covering, nor is it because the material wasn’t properly applied. The wood structure expands and contracts with the changes in humidity. The Mustang, like almost every RTF and ARF available today, is manufactured in a climate that typically has a high level of humidity. When manufactured, the wood is close to its most expanded state.
When the parts come out of the bag, they acclimate themselves to the current environment. Often this environment is a lot less humid, so the wood in the airplane shrinks. Over a couple of days, it’s normal to see these wrinkles appear. They won’t really do anything to the way the airplane flies, but they sure don’t look very pretty. I found that, with the modeling covering iron set to 325 degrees F, the wrinkles would disappear without harm to the decals. The red vinyl lettering on the fuselage and tail was more heat sensitive, so don’t leave the iron in place over those pieces for any length of time or they’ll be damaged.
What you don’t want to happen is to have air flowing underneath this covering while the airplane is in flight. Look closely at the front and rear seams of the covering. Examine them for loose edges or portions of the covering that might not be attached. Burnish the seams with the hot covering iron to seal them down.
All the parts were inspected for damage and none was found. The control surfaces are hinged at the factory with flexible plastic hinges. Initially, all the hinged surfaces can be stiff, and need to be flexed back and forth repeatedly.
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The rudder in particular was very stiff. Not really due to the hinging. It seems that the glue used to attach the hinges had seeped into the tail wheel bracket. To relieve the stiffness, a 100 watt soldering iron was used to heat the wire. I removed the tail wheel first to prevent damage (a small 1.5mm Allen wrench comes with the Mustang for maintenance). Heating up the wire allowed the rudder to move more freely. While the wire was hot, the rudder was repeatedly moved back and forth to encourage the tail wheel bracket to expand to the wire diameter. For a second time the wire was heated and a light 3-in-1 oil was added to the tail wheel bracket. Flexing the rudder again back and forth helped the oil to seep into the bracket.
(Ed. Note: I also received a Mustang PTS for a Model Aviation review to be reprinted in Sport Aviator beginning January 20, 2006. The rudder, and all the other control surfaces, moved freely and centered well. Obviously, the stiffness problem Michael encountered was a very isolated case.)
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It was time to inspect the receiver battery; which is easily done. A 3/32-inch Hex head screw holds a hatch cover inside the fuselage. Under the hatch is stored the receiver and the receiver battery, both enclosed in a tri-layer of foam. The receiver battery is mounted forward next to the 11 ounce fuel tank. After lifting the battery out it was noticed that the battery was connected to the switch, and secured with a piece of masking tape.
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I liked the fact that the plug from the battery to the switch was secured with tape. However, since the receiver switch was left on, I thought it would be a good idea to test the batteries. Actually, it is always a good idea to test the batteries before flying a new radio system for the first time. There are many devices on the market that will charge and test both receiver and transmitter batteries for you. If you have one, use it. If not, here is a simple way to insure that your batteries will be there as long as you will need them to be.
Charge both the receiver and transmitter batteries for 24 hours using the charger supplied with the radio set. Assemble the airplane and place it inside on the floor. Find yourself a comfortable chair and put it about 12 feet away from the airplane. Sit down and get comfy. Extend the transmitter antenna fully (very important) to protect its radio signal output system (RF Output circuits) from damage. Turn on the airplane and the transmitter.
Now it is time to do some “hangar flying” so begin simultaneously rotating both transmitter sticks in full circles. Keep this up for 30 minutes. This constant movement simulates about 2 hours flight time. The control surfaces should move at the same speed during the test period. If their movement slows down, becomes erratic or even stops, replace the receiver battery. If everything is still fine after 30 minutes, it is time for the final check.
Take the airplane outside and place it on the ground. Collapse the transmitter antenna and walk 50 steps away from the airplane. Move the control surfaces. If they move on command without “jittering” and remain steady when the sticks are still, recharge and launch. (Ed Note: Recharge, drive to the flying field and then launch. Don’t take off from your backyard.) If the surfaces do not move on command or vibrate quickly, replace the transmitter battery if it was the one turned on, and retest. If neither battery was suspect and the airplane failed this “range check” then have the system inspected before flying.
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Unfortunately, the Mustang’s receiver battery failed this test so Horizon gladly replaced the battery with a brand new 700 milliamp 4.8-volt type. While I waited for that delivery to arrive, I took the time to go over the Mustang with a fine tooth comb. With the hatch and foam padding removed, the fuel tank easily drops out through the radio compartment. This was a relief as normally the fuel tank is buried so deep in the nose it’s a terrible process to remove. I inspected the tank to find that the cap was nice and snug and the clunk on the fuel pickup line was free to move inside the tank as it’s supposed too.
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The servos were well installed with keepers on both ends of the control links. I used the Allen wrench again, this time to ensure that the set-screw on the throttle servo linkage was good and tight. Taking a closer look at the nose, I noted that parts of the engine were touching the aft edges of the cowl openings. I was worried that vibration from the engine would prematurely wear out the cowling. What I realized was that the engine must have shifted backward somehow during shipping. This is an easy adjustment but requires the removal of the muffler and then the cowling.
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Remove the two muffler screws using a 2.5 mm Hex wrench. Next, the needle valve had to be removed. I wanted to know what the factory setting was so that I could return the needle to the original setting, so first I turned the main needle valve all the way in. From the clockwise limit of the stop, the needle could be turned in one-and a half more times. Use a small screwdriver to bend back the needle stop while turning.
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I removed the four Phillips head screws from the cowl and it came off easily. Looking at the engine, I noted that it was positioned up against the rear mounting screws of the clamp bracket, leaving plenty of room to move the engine forward. While inside the compartment I added some extra firewall fuel-proofing over and above the fuel proofing Horizon had added at the factory. Also, there’s always a chance that the screws holding the engine mount to the firewall could come loose. I wanted to make sure they were installed with thread locking compound.
I loosened the clamps holding the engine in place and then removed the screws holding the engine mount to the firewall. I applied a layer of medium viscosity CAA adhesive using my fingers protected with masking tape. An extra amount of glue was used near the edges of the firewall to be certain that the covering along the boarders wouldn’t come loose.
The engine mount was reinstalled, this time with a little thread-locking compound on the ends of the 4.0mm screws. The engine was set into the clamps on the mount so that the rear edge of the mounting lug was about a 1/8th inch forward of the screw. This proved to be a good location for the engine because when the cowling was reinstalled, the openings were well clear of the engine. (Ed Note: This procedure is always a good idea with any RTF aircraft. Remove the engine but rather than remove the mount completely, remove just one bolt at a time, coat it with thread locking compound and reinstall it. This keeps the mount always in the factory installed position. Apply thread locking compound inside the threaded muffler holes and onto the muffler bolts when reinstalling the muffler.)
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The Mustang PTS comes with a 32-page instruction manual that is clearly written and extensively illustrated. The manual is a quick read that follows a logical assembly order. There’s no doubt in my mind that the Mustang PTS could be assembled in 30 minutes or less. However, section one in the manual covers the charging of the batteries. Having to wait on the replacement receiver battery, I took the time to study the radio manual and have some fun on the included flight simulator.
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The transmitter is the highest quality I’ve seen offered in a ready to fly RC aircraft. The JR XF421EX is a five-channel computer radio with memory storage for two models. Its 32-page manual describes all the features and benefits of the radio system. The transmitter comes pre-programmed for the P-51. You’ll note on the LED screen when it’s turned on that the display will read the battery voltage, and the letters P51.
At this stage of the game there’s really no reason to enter the programming mode of the radio although it’s a good idea to get familiar with the commands and menu options. Note on the transmitter that right now all the trim levers should be centered, and both of the top switches should be in the aft position.
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Find the packaging that includes the black cables. One of these cables is for the included Cockpit Master Flight simulator, and the other is the TrainerLink cable, which will be used to connect the 421 transmitter to a “buddy box”.
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The DataLink cable attaches your JR radio to the 9-pin game port on your computer through the “buddy box” connection. The transmitter battery has to be charged for the computer flight simulator to work. JR uses a clever buddy box connection system. The transmitter is automatically turned on when the buddy cord is connected. But the RF output, the transmitting circuit, is not activated. This prevents wear and tear on the transmitter’s most vital circuit while reducing battery draw to a minimum.
The Cockpit Master Computer flight simulator is easy to load on your PC based computer. The program includes four aircraft including the P-51 Mustang. The simulator programming is fairly basic and simple to use. My experience with flying this simulator is that the real-world Mustang PTS is much easier to fly than is the simulated one. Mastering the simulated Mustang will make flying the non-virtual one much easier. Learn from it, have fun with it and take some time to get familiar with the controls. But don’t take the simulated performance as a true guide of how the airplane really flies.
The included DVD is as entertaining as it is useful in getting familiar with the assembly of the Mustang. There’s also some great flight footage with the Mustang in full trainer garb and as it progresses into the sport airplane with all the training devices removed.
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The Hangar 9 TrainerLink is a cable that links your JR transmitter to a buddy box. The buddy box can be another JR transmitter, which I’d recommend, or a Hitec/Futaba transmitter with the round, 6-pin, data plug. Since the Mustang is probably a first RC aircraft, most student pilots will not have another JR transmitter “in stock.” JR sells a complete “buddy transmitter” system for less than $50. I would recommend getting it as its “feel” equals that of the Mustang’s transmitter. But the TrainerLink cord allows the new pilot to use any brand transmitter the instructor might have as well. Horizon actually thought this problem through and came up with a clever solution.
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When my receiver battery arrived it was installed in the model and both the transmitter and receiver pack were put on charge for 24-hours. In the meantime, I assembled the wing. Joining the two wing halves is a piece of cake. The aluminum joiner tube is a snug fit near the end of the fiberglass socket. There were some burrs on the end of the tube so they were polished off with a fine-grit sanding block.
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The two wing halves are held together with a nylon strap and two wood screws. The two aileron extensions that come through the holes in the wing can easily fall back through. Leaving a little wire slack remaining in the wing, tie the two leads together with a nylon zip-tie or rubber band.
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The flap linkage length needs to be adjusted so that each flap is deflected the same amount. Uneven flap deflection would induce a roll toward the higher flap making a lot of aileron trim necessary. Like all nylon clevises, these are somewhat stiff. Great Planes makes a handy 4-in-one tool that makes linkage adjustment easier (Manufacturer Stock# GPMR8035). Square up the flaps by first setting them in the up position (forward hole in photo 51) and adjust the clevises so that both flaps are even with the trailing edge root. Do not adjust the height of the flap torque rods’ control horns unless the right and left flap deflection is uneven.
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When the flaps are even in the “up” position, disconnect the links and move the fixed position point to the rear and reconnect the flap linkage. Sight from the rear and inspect that the flaps deflect the same amount. They travel from the neutral point about 26%, or if you measure from the bottom trailing edge, about 5/8-inch. Remember this measurement for later on when you want to install a servo to control the flaps.
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Flip the wing over and install the landing gear. Three Nylon cable wraps are used to hold the air brakes to the gear legs. They complicate the landing gear installation. To install the nylon landing gear straps over the metal landing gear wire in the wing, gently slide the speed brake toward the axle. Slide the brake upwards until the first cable wrap starts, just starts, to follow the wire axle bend. This movement provides room for your screwdriver to reach the screws holding the gear strap nearest the landing gear wire. Install the landing gear with the provided straps and screws. After installation, slide the brake back down to the wing surface. The speed brake cants slightly to the wingtips using one of the installed strap screw heads for a brace.
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Pop the wheel cover off the inside of the wheel. Use the 1.5mm Hex wrench included with the kit to check the tightness of the wheel collars. There are flat spots factory ground into the axle where the set screw locks into place.
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Now let’s go back to the fuselage and install the tail. Remove the vertical fin from the fuselage by removing the temporary nuts and pulling the vertical fin assembly straight up. Follow the Section-4 instructions in the manual and set the horizontal stabilizer into the bolts, then drop the assembly straight back down through the fuselage.
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Secure the tail to the fuselage with the two Nylock nuts attached to the Addendum sheet. Be sure to use the washers with the nuts, as they will prevent the nuts from tearing into the covering when tightened.
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Since we’re already working on the tail section, let’s turn on the radio system, center all the trim tabs, and attach the linkages to the elevator and rudder. Attach the clevises to the center holes on the control arm as directed in the manual. The rudder and elevator required a few turns of each clevis to bring those control surfaces to the neutral position. Again, the 4-in-1 clevis adjustment tool proved invaluable for this job. Use a set of pliers to hold onto the pushrod while adjusting the linkage to prevent twisting the pushrod out of the servo arm.
Examine each of the control surfaces carefully before moving the clevis keeper to the secure position. The keeper is very hard to move back should further adjustment be made. When the correct neutral point is found, use the transmitter to wiggle the surface back and fourth. Did the control surface return to the same center? If not, wiggle the stick again to confirm that adjustment is needed and adjust the linkage accordingly.
A good practice is to sight down the control surfaces from each end. Examine the hinge line and trailing edge for any warps. Any offset or warps will change the neutral point of the control surface. Sometimes a warp can be corrected by heating the control surface and twisting it straight again. The Mustang PTS has a very solid framework. On my Mustang I didn’t find any occurrence of warping.
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I did however, note that my two elevator halves were not aligned and offset from the center of the hinge line. One elevator half was higher than the other so that one elevator half was positioned slightly up while the other was slightly down. The simple solution is to set the elevator halves equidistant from neutral. The final elevator position would be determined in flight testing. (Ed Note: The elevator halves on my PTS were perfectly aligned and the hinge line centered. I am beginning to think Michael must have sat on his Mustang’s elevator and tail wheel sometime during assembly!)
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Moving up to the nose of the Mustang, it was time to install the simulated exhaust stacks. This was a simple task as the screws to hold them in place were already tapped into the ornamentation. There’s a right and a left exhaust – the shorter one goes on the right side next to the muffler.
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Speaking of the muffler – its exhaust outlet can be rotated to prevent the engine’s smoke and oil from spraying directly onto the side of the fuselage. Loosen the nut on the back of the muffler. Then loosen the through bolt with a flat-head screw driver a turn or two. I recommend aiming the exhaust directly to the outside, not down or up. Some exhaust will still get on the wing and fuselage, but that’s inevitable. Add a touch of thread locking compound (such as the red type included with the Mustang PTS) to ensure that the nut doesn’t loosen.
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Finally, the propeller and spinner can be installed. I like to position the propeller so that one of the blades on the left is at the two o’clock position when the engine begins to get hard to flip over. You’ll note in the photo that I’m tightening the propeller up against the spinner back plate in the wrong position; the propeller blades should be tightened so that they’re up against the other side of the stops. Otherwise the spinner cone won’t line up.
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Now it is time to mount the wing to the fuselage. Section-7 of the manual is very clear about this process and I’d say their advice about leaving the trailing edge high off the wing saddle is very helpful for aligning the screws into the blind nuts. Now the Mustang really takes shape.
Photo 53
W the wing attached, it was time to check the aileron function. Like the rest of the controls on the Mustang PTS, the ailerons were working in the correct direction but the neutral position wasn’t correct. The keeper on the linkage was already in the secure position and I didn’t want to force it at the risk of breaking anything. I noted that the ailerons were off from center the exact same amount, one a little up and the other the same amount down.
Instead of mechanically adjusting each aileron, I took the easy way out and adjusted the aileron neutral position by using the transmitter’s sub-trim programming option. Using the input keys, enter the programming menu and press the scroll button until the “SB-TRIM” function mode appears in the left hand corner of the LCD screen. Now press the channel button until the three characters in the upper right hand corner read “AIL,” for aileron.
What we’re going to do now is change the sub-trim of the ailerons so that the right and left aileron are neutral. On the right hand side of the transmitter, press the +INCR or –DECR button until the ailerons are neutralized. In my case they only needed to be adjusted –13 points, which isn’t really very much. Once the adjustment is complete, exit the program menu or turn off the transmitter. This adjustment wouldn’t have worked if both the ailerons were off from center in the same direction. Had that been the case, I would have had to mechanically adjust the clevis position.
Photo 61
Just a few final checks now and the Mustang will be ready for its first flight. I set the airplane up on a table and sighted down from the horizontal tail and along the wing. What I noted was that the horizontal stabilizer was lower on the left side than on the right. If I leave the model this way, when I use the elevator control, it won’t pull or push the airplane straight.
Photo 62 Photo 63
Using the left over identification card from the TrainerLink packaging, a strip of paper was cut to be used as a shim under the low side of the Horizontal stabilizer. I only had to loosen the nuts holding the tail on just a little bit so that the paper could be slid between the stabilizer and fuselage joint on the left side.
Photo 64
Once the shim was in place, the nuts were re-tightened and then the alignment could be checked again. Just one layer of paper made a lot of difference, but it was still just slightly off. Two layers of paper would be too much so what I did was slide the shim further into the joint. This tiny adjustment brought the stabilizer into perfect alignment and it just took a few minutes.
Photo 69
Because we’re checking everything for this review, the measurement between the corners of the wing to the corners of the horizontal stabilizer were checked and found to be equal on the right and left sides.
The balance point is referenced in the manual as 4½ inches back from the leading edge of the wing at the fuselage joint. My Mustang balanced very nose heavy at this location, and in fact balanced over ½ inch ahead of that point. This didn’t bother me very much as I discovered while weighing the model that it was actually under weight by close to two ounces. I added segmented lead weights to the tail until the Mustang balanced at the exact CG location. I added one-ounce of tail weight as far aft as possible. These stick on model weights can be found in any hobby shop.
Photo 72
At this point its time to confirm the control throws and double check that everything is tight. As I mentioned earlier, the XF421EX transmitter is already programmed so when I went to measure the amount of deflection on all the controls, everything was dead on, even the throttle. The ailerons were set to 75% of full throw at the factory.
Well, its time to recharge the batteries and go flying.
Photo 66 Photo 68
PTS Mustang Takes to the Air
Photo 86
The instruction manual doesn’t give any advice on how to fly the P-51 Mustang PTS. So for the most part, flight-testing was done as if this were a typical basic trainer; as apposed to a low wing sport model. Is there a difference? Sometimes there is, and sometimes there isn’t depending on the potential of the design. A couple of major differences were found in how the Mustang differs in performance from the average trainer. They are not difficult to overcome for the student pilot or the instructor, just different.
The Evolution Alpha engine is a delight to work with both in starting and tuning. Neither the high nor low speed needle valves needed a lot of adjustment, and, with the three-blade propeller, it really seemed to kick up a lot of power. (Ed Note: It should have a lot of power as it is actually a .45 cu. in. engine, not a “forty,” and seems similar in many respects to the very powerful Evolution .46)
Typically, with a tail dragger model, full up elevator is used to control the aircraft on the ground and to keep it from nosing over. Because of the tremendous forward sweep of the landing gear, almost no up elevator was required to hold the tail down while taxiing around the field.
I should note that most of my flight testing was performed from a paved runway. Flying from a paved runway is both a joy and heartache. Steering is very positive which is a benefit; however during take off and landing it’s very easy to over control the model because the steering works so well. The technique just takes some getting used too. The other thing is that pavement isn’t kind to wing tips or tires (and propellers for that matter) as its abrasive properties easily scuff, chip and wear-out whatever touches it.
Grass is the best place to fly a tail dragger as the steering isn’t as critical and the soft surface is gentler.
The small amount of rudder throw didn’t offer a lot of steering authority. It seemed just right on pavement but in the grass the Mustang had to make wide turns.
Photo 77
(Ed Note: Michael did a lot of test flying with this airplane. However, there were some difficulties with the airborne photographs so the flying photos shown here are of a different Mustang PTS.)
At the far side of the runway the Mustang was ready to take to the air. Add throttle control smoothly while at the same time holding full up elevator. The Mustang begins to pick up ground speed and the elevator input becomes more effective. Reduce the amount of input by a little more than half and at that point the Mustang should be at full throttle and ready to leap. Steering with the rudder on the take off roll is a bit of a handful because full right rudder deflection is needed to hold a straight course down the centerline of the runway.
Photo 78
Holding right rudder during take off was a regular occurrence on both the grass and paved runways. It didn’t take long for the Mustang to get airborne, and it could maintain a steady climb angle of about 20 degrees. Once the Mustang is about 10-feet in the air the right rudder can start to be removed, then finally at about 20 feet up, she’s flying straight with no rudder input.
Photo 79
While initiating the first turn it was clearly apparent that this Mustang was flying exactly like a basic trainer. Its airspeed was comparable to most flat bottom high wing trainers of the same size which led me to believe that a student pilot shouldn’t have any trouble keeping up with it. Even downwind, it didn’t go all that fast.
Turns were gentle and didn’t need a lot of up elevator to keep the nose up. Coordinating the turns with rudder wasn’t necessary which meant that an overwhelmed student pilot could just focus flying the Mustang using only the right transmitter stick. Turns to the left seemed to require just a little more up elevator, which is probably an effect of the propeller torque.
Very little transmitter trim adjustment was needed to get the Mustang to fly hands-off. Looking at the transmitter, left aileron was the only input made.
Photo 80
The control throws proved just adequate enough to fly the Mustang around in a very trainer-like fashion. Loops and rolls were possible but I wouldn’t recommend a roll until the student pilot is more proficient because coordinating the rudder and elevator is required. Otherwise a lot of altitude can be lost in the maneuver.
Pulling the Mustang hard, suddenly inputting full up elevator, proved that the mismatched elevators were tuned just about right as there was no course change during the stunt. There was also no tendency to tip stall or fall out of this maneuver. The Mustang handled this abuse exactly as would a basic trainer. Throttle management isn’t really required as about 75% power is used to maintain level flight.
Stall testing was performed first to determine the approach-to-landing characteristics. At an altitude of about 50-feet, the Mustang was guided up the runway, into the wind, and the power was reduced slowly while “up” elevator was added to maintain altitude.
Photo 81
The Mustang quickly slowed down, almost a little too quickly, but nonetheless kept flying straight on as the throttle was moved to idle and the full elevator limit was reached. The Mustang hardly stalled at all but instead just sank slowly though the air with the nose and wings holding level. It took a couple of tries, but on about the third go-around I finally got the Mustang to stall, and it was again almost a non-event. The stall was recognized by just a slight drop of the nose, a slight increase in airspeed, and a small loss of altitude.
It appeared that the landing was going to be a piece of cake. The only issue that made the Mustang different from the typical trainer is the fast rate at which the Mustang looses airspeed and altitude when the power is reduced. So the technique for landing called for the use of some engine power almost to the point of “wheels down”.
Photo 82 Photo 83
Photo 84
Continuing the flight testing with high and low speed stalling; first the Mustang was put into a high speed dive (if you could call it that) and pulled abruptly out of the dive with full up elevator input. Again the Mustang flew straight through the maneuver with the wings level the whole time. Then high speed turns were done where any sign of tip stalling and spin characteristics might form. Nope, the Mustang just kept on flying. In fact, the Mustang was just about impossible to snap and couldn’t be induced into a spin.
During one of the flights the Mustang ran out of fuel (guess I was having too much fun). This is where the high rate of decent and short glide of the Mustang became very apparent. Lucky for us this was a grass field flying day because while trying to stretch out the glide, the Mustang came down hard. Unannounced, this was the durability test and the Mustang again came through with flying colors; didn’t even bend the landing gear.
Photo 85
One of the things that continued to be bothersome was the extreme need for full right rudder on take off. Then one day, while goofing around with the Mustang, I wanted to get into the air in a hurry, so I just punched the throttle to full wide open. On that take off the Mustang needed almost no right rudder what so ever. The effect of quickly blasting a lot of air over the control surfaces seemed to stabilize the forward momentum and help to steer the Mustang straight.
We expect to do a lot more flight-testing with the Mustang. Because this is a progressive training system what will happen is the Mustang will be tested each time one of the training devices is removed.
Photo 32 Photo 75
The thought of flying the Mustang knowing that, if the engine quit at a bad spot, the airplane might not make it back to the field, was a dark spot in my mind. Adding the servo to the flap control would allow me to raise the flaps when needed should the instance ever come up that I would need to stretch the glide.
The modification is very simple to do and is clearly outlined in Section-16 of the instruction manual. Be sure to collect a 9-inch servo extension at the hobby shop the same time you’re picking up that extra servo. Refer to the measurement taken before to know how much flap deflection is needed. When programming the radio, you’ll want to work in the TRV ADJ menu and select the GER channel. Adjust the start and stop flap positions by changing the switch values with the +INCR and –DECR buttons. You’ll need a value difference of 50 to get the correct amount of throw.
Photo 76
The other cumbersome task was checking the batteries while at the field. In the Mustang’s stock form, this meant removing the wing after every flight. Included with the JR transmitter is a direct servo control (DCS) outlet. In this case, it can also be used as an outlet to hold the charge lead coming of the power switch. The easiest place to install the outlet is opposite the power switch in a hole identical to the one used for the switch. Enlarge the square opening about 1/32-inch all around and the outlet will drop right in. The charge plug just snaps into place from the inside of the fuselage.
Well, Is It or Isn’t It?
So, is the Mustang PTS a true basic trainer? Can a brand new pilot actually learn to fly using just this airplane? For 90 percent of the flight envelope, this sleek looking airplane is exactly, without question, a great basic trainer. It is gentle, predictable and will never turn on its pilot. There is no noticeable difference flying the Mustang PTS from flying the typical 40-size basic trainer.
In fact, the Mustang turns better than most basic trainers in that it doesn’t need a lot of “up” elevator to maintain a level turn and it does not gain speed if the nose does drop in the turn. The Mustang does not “pop up” when the wings are returned to level after a descending turn either. The airplane also seems steadier in the air and requires fewer corrections to keep it flying straight.
The other 10% of its flight time is spent taking off and landing. On landing, the PTS requires some throttle, unlike a basic trainer. But you know, so do almost all but the most basic sport airplanes. A new pilot can use the Mustang to learn this skill now. Other than using throttle, the Mustang lands more easily than most basic trainers because it flies a more stable, easier to control, approach path.
The real difference is in takeoff. Employing the standard, slow-throttle addition procedure, the Mustang needs right rudder while most tricycle gear basic trainers do not. But blast the throttle and the Mustang will hold a straight line without rudder. Besides, in these days of composite, difficult to break propellers, most sport airplanes are tail-draggers like the Mustang. The PTS teaches the new pilot how to takeoff those sport airplanes now rather than later when bad habits might have already formed.
So yes, it is a very good basic trainer. But the Mustang PTS goes even further. The airplane will progress as the pilot’s skills improve. Few basic trainers can do that. The next article in this series, which will appear in Sport Aviator around January 20 of 2006, explores the Mustang PTS as changes from basic trainer to an advanced scale fighter.
For more information on this unique trainer, please go to: http://www.horizonhobby.com/Shop/ByCategory/Product/Default.aspx?ProdID=HAN2825
| AIRCRAFT SPECIFICATIONS Manufacturer: Hangar 9 Cost: $399.00 Radio: JR XF421EX 5-channel computer Servos: 5 x JR 537 Engine: Evolution Power System (.45) Length: 50 in. Weight: 6.5 lb. Wing Loading: 24.8 oz./sq. ft. Wingspan: 58.25 in. Wing Area: 627 sq. in.. Airfoil: Semi-Symmetrical with lift devices |
| Special Features Semi-Symmetrical Wing, 3-Bladed Propeller, Quick Assembly, Great Scale Fighter Looks, Advanced Lifting Devices |
| Notable Positives Unique basic trainer styling Extremely fast assembly Very good looks Light flying weight Good basic trainer performance Pre-Run, factory-adjusted engine Notable Negatives Short glide distance with flaps deployed Uses unusual take-off procedure |
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Posted by Michael Ramsey
on Dec 29 2005 Filed under Basic Trainers.
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