TOP FLITE GIANT P-51D MUSTANG
PRODUCT TEST REPORT
by Dick Pettit
The North American P-51 Mustang has to be the most often modeled military airplane, and a large number of them are offered in a multitude of sizes. There are sport scale, fun scale, and giant scale, in 1/2A to giant size, slope soarers, and even a kite or two! Attend just about any giant scale fly in and you are sure to see at least one or two Mustangs flying. And they look terrific coming over the field low and fast, followed by a big victory roll as they climb out of sight ... figuratively speaking, of course. And didn't you want to do the same thing with a Mustang of your own? Well, now you have yet another good chance.
Top Flite Models, designers and manufacturers of many fine R/C kits, has recently introduced another Giant Scale Gold Edition kit, this time the famous P-51 Mustang. I've already built the Top Flite Cessna 192 and the Beechcraft Bonanza, both from the Gold Edition line, and the new Giant Mustang seems to be equally as fine a kit as either of the others. Top Flite actually enlarged the .60 sized Gold Edition P-51 to get the 'almost 1/5th' scale Giant Mustang, and the track record of the smaller kit stands on its own merits. The Giant Mustang can actually compete in AMA Fun Scale, Sportsman, and Expert classes of Sport Scale, along with any IMAA event. It is, according to its instructions ... "...intended for scale and general sport flying...loops, rolls, stall turns...". It's not a fun fly plane, though, so the builder is asked to fly the Giant Mustang in the manner for which it was intended.
The large kit weighted more than 20 lbs., and is filled with a small lumber yard of balsa, hardwood, die-cut plywood, and plastic parts. As in the past, Top Flite includes a listing of all the items in the kit, but they put it in the box first, and then add everything else on top of it, forcing you to empty the box to get to the inventory list! And I dare you to even try to get it all back in! After looking at each and every piece in the box, I found that everything was there. What was highly obvious by its absence was any sort of fixed wire landing gear legs. Evidently, Top Flite makes no arrangement for using anything but retracts with this kit, and fabricating a fixed gear would actually take some creative engineering on the builder's part. Prepare yourself for spending at least another several hundred dollars for your retract package. And while you've got your wallet open, plunk down a few more dollars for a 5" spinner, and you'll need 10 servos for the big '51', so you may want to go ahead and consider a second mortgage. But the investment will be well worth it in the end!
I unrolled the plan sheets and found that they need to be cut and then taped together. Here's a $400 kit and you still have to tape the plans together. At least you don't have to turn them over and "oil" them to build the opposite wing panel (remember that?). The plan quality is otherwise top notch, and there are cutaways and details necessary to clarify many of the building steps. The profusely illustrated instruction manual has a listing of all the accessories needed to complete the P-51, and is well written. Next I marked all the die-cut parts and separated them into fuselage, wing, and tail parts; using large freezer bags to keep them separate. The formed plastic parts were put away on a shelf until needed. It was time to start building the Top Flite Gold Edition Giant P-51 Mustang.
Construction will be done using Great Planes' Pro CA adhesives, along with Pro Aliphatic Resin.
Construction begins with the tail surfaces, horizontal stabilizer first. Ribs with standoffs are pinned to the board, and then the leading and trailing edges, followed by the balsa sheeting. I glued up all the sheeting for the complete model first, to make sure there were enough suitable pieces. Once the stab sheeting was in place, the structure seemed to be very light and strong. The vertical fin builds the same way. The elevator halves are ribs and sheeting, with a thick leading edge for hinges. The rudder is built on a center sheet with ribs on both sides, but is not sheeted. Some basic shaping and sanding is necessary to smooth things out, and then the tail parts are just about ready to cover.
Wing construction is done over the plans using basswood spars and a combination of die-cut balsa and laser cut aircraft plywood ribs. I made sure to sand off the darkened edges of the laser cut parts to allow the adhesives to penetrate the wood itself. Several laminated balsa parts are built up and ribs added. Next a shaped leading edge is prepared and added to the front of the rib assembly. Balsa sheeting is then glued up for upper and lower wing skins and aileron sheeting. I made the skins for the entire wing at one time to allow them to dry before sanding. Shear webbing is added to both sides of the main spar and to the trailing edge. Retract rails are added and the retracts are used to ensure correct positioning.
When both wing panels are complete but not sheeted, they are joined using aircraft plywood dihedral braces, with the wing panels set at the correct angle. A plywood wing center section is then built in place, using die-cut ply parts. The wing bolts are in the front of the wing and the dowels are at the back. With the wing structure still on the jig blocks, the bottom sheeting is added. Center section sheeting is added first, followed by overlapping wing sheeting, which is supposed to eliminate the need for any center section reinforcement. (I hope so!) The sheeting is trimmed to size, glued to the leading edge, and pulled back along the ribs that have had medium CA applied. The sheeting adhered pretty well, and a little added CA after the panels were inverted secured the sheeting. The top sheeting is added, making sure the skins adhere to the ribs at all locations. If they don't, you can stick holes in the skin over the rib and use thin CA to stick the sheeting down.
The ailerons are built separately from the wing panels using balsa sheeting and die-cut ribs. A balsa leading edge is added, along with hinge backup blocks, followed by top sheeting. Balsa block wing tips are glued in place and shaped to match the airfoil. The flaps are cut free from the wing and sheeted. They are to be hinged with the point of rotation inside the flap itself to simulate Fowler flaps. Robart large hinge points will be used for the hinges, but they will be added after covering.
The fuselage is constructed from balsa sides with plywood doublers, plywood formers, and several balsa sticks. Holes for control linkages are to be drilled, formers added, and a top crutch then added to align the fuselage to be straight. Right offset is built into the structure. The radiator area is built, sheeted and shaped. The firewall is assembled and epoxied to the front of the fuselage, using a gauge to set the required down thrust. The nose blocks are added and shaped, and then the wing is fitted to the fuselage. The stab and fin are then added to the fuselage, and the required elevator linkages are then installed. Split elevator pushrods are used and a single rudder pushrod is installed. Servo rails are added to suit your particular servo installation. The elevators are built and fitted to the stab and fuselage.
Engine installation is next, using a Great Planes Large Engine Isolation Mount kit. This is a laser cut plywood plate and a set of rubber isolators that mount to the firewall. The engine is mounted to the ply plate, offset to the pilot's left so that the spinner comes out in the center. The fuel system, retract valve, and throttle linkage are added as required.
The top of the fuselage is added using formers, stringers, and sheeting. It takes a little work to get the sheeting and blocks to fit well, but it is well worth the effort. The dorsal fin is built up and added, if desired, since some of the early P-51's didn't have them. I added the dorsal because I think it looks better that way.
The upper balsa cowl is built while the engine and spinner are temporarily in place. Balsa blocks are shaped and formed to size, and the upper cowl is quickly ready for sanding. The lower cowl is made from plastic and is removable to allow engine service. Holes are then cut in the plastic lower cowl for clearance around the cylinder, muffler, and carburetor.
Wing fillets are built onto the fuselage with the wing temporarily installed. This looked a lot harder than it turned out to be, but there is still al lot of filling and sanding to be done. If you use balsa filler, be prepared to sand outside. The die-cut plywood fillet bases make it easy to get the right shape for the fillets, and the careful use of a plastic spoon gives just the right contour. Just be sure to use the right plastic spoon!
While I was waiting for several of the accessories to arrive, I decided to assemble and fit the Top Flite P-51 Interior Kit. The vacuum formed plastic pieces are easily cut out and fitted to the cockpit area. I added a balsa backing to the armor plated seat, and had to cut a few notches in the dash panel to allow it to fit. The only problem is that the dash panel has the rudder pedals molded into the bottom, but they are much to far rearward for a full size pilot to place his feet on. Looking at the photos of the full size P-51, the rudder pedals are well forward of the dash panel, so I cut them off, since they probably couldn't be seen anyway. I plan to paint the inside f the cockpit medium green before I put in the side panels, floor, and seat, because you can still see some of the wooden fuselage sides with the interior kit installed. I'll probably use some of my wife's flat acrylic craft paints to detail both the fuselage and the interior parts. A set of black and white decals are also in the interior kit that simulate electrical panels and gadgets. Some small pins and string are also included for knobs and headphone cords.
Now for the fun part. Covering! I had decided to use Goldberg UltraCote on the Mustang, since their silver is a really good representation of weathered aluminum. I brushed the dust off the wooden structure, followed by a wipe or two with a tack rag. The movable control surfaces were covered first, to get the feel of the covering, and then I started on the wing. The UltraCote applied easily, especially around the wing tips and leading edges, where a little extra heat and some gentle tugging pulled the covering tightly around the curves. Smaller wrinkles come out with a little more heat, and larger ones can be lifted and shrunk without the color staying on the structure. The black and white Invasion Stripes were added with UltraCote Plus.
The fuselage was covered last, and this turned out to be the second hardest procedure to complete. First on the list was fitting and filling the wing fillets, and second was covering them! I covered the fuselage sides, bottom and top, and then the stab and fin, followed by the fillet area. Cutting the covering to an approximate shape, tacking it down, and heating and stretching it around the fillet resulted in a fairly good job. Here is where I remembered the real benefit of UltraCote Silver. Any seam is just about invisible at reasonable distances, and I'm not gonna let anyone get any closer than that! I applied some of the self stick decals supplied in the Top Flite kit and some color details with UltraCote Plus.
Next I fabricated the servo hatches and servo mounts for the ailerons and flaps. Extension wires were added to the servos, threaded down the cardboard tubes I had installed in the wing panels, and connected together at the center. Short, sturdy rods connect the servos to the heavy duty DuBro control horns that were cut down to a shorter length due to the thickness of the flaps and ailerons. I purposely added a slight bend in the 4-40 rod where it connected to the servo arm to allow the clevis to clear the wing surface. The flaps were installed using Robert large hinge points secured with Weldbond adhesive. The ailerons and tail surfaces were attached with trusty Sig Easy hinges and thin CA.
Now for the small details ... you know, the ones that seem to take more time than assembling the whole airplane! I had to cut prop holes in the huge 5" J-Z spinner, using a nibbling tool and sanding drum in my rotary tool. Then on to drilling the holes for the mounting screws, making sure they all lined up. After mounting the US 41 engine on the Mustang for the umpteenth time, I fabricated a throttle linkage using plastic tube pushrod material. Next, fuel tubing was run from the tank to the carburetor via a homemade filler, and the vent line was affixed to the firewall. I made up a kill switch mechanism and drilled the plastic lower cowl for the switch. The only two plastic pieces in the kit are the lower cowl and the air scoop on the bottom of the wing. They were assembled as per the instructions, and fitted to the structure with small screws to allow removal if necessary.
More details include the connection of all the air hoses from the retracts in the wings and tailwheel to the control valve and pressure vessel. The control valve was mounted to a small servo added to provide the desired throw for actuation. The Robert adjustable control valve can be set up for fast or slow retraction motion. I set up mine so that the gear goes up more slowly than it comes back down. I can get up to 10 retraction cycles before the air pressure goes down. I even let the system sit overnight and there was no apparent reduction in the pressure. A little liquid soap on all the joints would show that there was indeed no air leaks. Robert has a neat little in-line pressure gauge that has a small pin that sticks out to indicate air pressure in the system. I didn't want to spoil the clean lines of the P-51 with an air indicator sticking out of the fuselage, so I mounted it behind the pilot on the radio deck. It looks like it belongs there, too!
Back to the details ... The retractable tail wheel has to be steered by a servo connected to the rudder channel. Of course, it needed to be reversed from the rudder servo for correct movement. The actual mechanical steering linkage was made with 2-56 pull-pull hardware from DuBro. I added a rather tight coil spring in each cable so that there was a little "give" in the linkage as the plane tends to drift from side to side during take off. I have heard that most of the full size war birds had tail wheels that locked into the straight ahead position during the first part of the takeoff, and could be unlocked to swivel during ground maneuvering. I still want to have a steerable tail wheel on my Mustang.
And more details ... the canopy, a really nice clear plastic molding, was cut to fit on the scribe lines, masked with electrical tape, and painted to match the fuselage. I had covered the top of the nose on the Mustang with black UltraCote Plus, but it looked a little too shiny for an anti-glare panel. I tried steel wool to rough it up, but that didn't work very well. I finally sprayed it with some matte finish clear acrylic spray and it provided just the right dullness. The self stick decals were added using glass cleaner to float them into place.
The lower cowl and air scoop were sanded smooth, primed, and printed with Perfect paint. The plastic exhaust pipes were cut out, primed and painted, and attached in place with thin CA. Here is the point in the model's construction where it seems appropriate to drizzle a thin line of glue all over a fully covered and detailed wing or fuselage. But this time the glue wicked neatly into the tight joint, and the headers were permanent.
When all the parts dried completely, I assembled all the Mustang parts in my assembly area. I pumped up the retract system, deployed the gear, and set the P-51 on its wheels for the first time. Is this a big plane, or what? Using my trusty baby scale (trusty scale, not trusty baby), I measured 22 lbs. Even, which is a full 3 lbs. more than stated in the instructions and specifications. This was not making me feel any better, but the plane does have a lot of wing area, and functional flaps, so there should be no problems for the test flights. (I tend to rationalize a lot!)
I had been looking for a suitable pilot figure for the Top Flite Mustang, and several were considered for use, but all but one were sent back for one reason or another. I finally decided on Hangar 9's 1/5th scale WWII pilot, which is a latex molded upper body with no legs. It is designed to be filled with cotton or synthetic stuffing, and painted with acrylic craft paints. There are details like a pistol and holster and an oxygen mask molded into the figure, and after painting, he will be installed semi-permanently using hook & loop fasteners in the cockpit.
Well, the day arrived for the test flight session, and it turned out to be a really nice day indeed. The plane was assembled at the field under the watchful eyes of 10 or 15 spectators who "just happened" to be out there. Well, I did mention that I'd be flying a new model for the first time. Anyway, I pumped up the retract system. With the freshly charged 5-cell 2000 mah battery, there were absolutely no jitters or wiggles from the Hitec/RCD receiver and 10 servos. I then took a roll of photos for this review, and proceeded to start up the US 41 cc engine. It roared to life quickly, so I taxied the Mustang to the grass runway for some low and high-speed taxi testing. The plane lifted its tail after a short blast of power, and the big rudder steered it anywhere I wanted it to go.
There was a pretty stiff 15 mph breeze that morning, but it was coming right down the runway, and should not present a major problem. I brought the Mustang back to the pit area, and began looking for anything out of the ordinary. I had heard a jingling sound as the engine ran at idle, and found that two of the eight sheet metal screws holding the J-Z spinner to the backplate had been slung off, and the spinner was rattling a bit. I put in two larger screws with some thread locker, and tightened the other six screws for the first flight.
After topping off the fuel tank and adding a little more air to the retract system, I started the US 41 again and did a full-power radio range check, finding absolutely no radio interference. I taxied the model to the east end of the runway, wiggled all the control surfaces, and said out loud, "God Bless America", like I always do before any test flight. I also remembered something that military test pilots say before they take off, "Lord, don't let me screw up too badly!" Anyway, it was time to fly.
I eased in a little power, the tail rose, the Mustang accelerated briskly as I added even more power, and with a little up elevator, it was climbing at a nice steady rate. I added full power, retracted the gear and turned right for a pass back across the field. The plane seemed to be climbing so I added a little down-trim. No rudder or aileron trim was necessary for hands off flight. After another turn, I came back across the field at about 50' at full speed. The spectators cheered! My heart was going a mile a minute!
As my confidence with the new model grew, I began putting it through its paces. The model will roll and loop very realistically, and tracks as straight as an arrow, even with a brisk wind trying to make it do otherwise. I brought it over the field in a simulated "strafing run" and then pulled up for a victory roll, which seemed to please the spectators. I then did some stall practice with full flaps and low power, which resulted in a near full stop in the air, followed by a drop of the nose, and a quick return to forward flight. I had also set up mixing in my Hitec Prism 7X transmitter that gave me about 20 degrees of flaps and a little down elevator to prevent ballooning. This did slow the plane down, but the brisk head wind would probably have done the same thing.
I just have flown around for at least 15 minutes, which is more than I normally do on a first flight, and then remembered that I should try a couple of approaches to see what would happen with the gear down at low power settings. I set up for a long straight approach, cut the power to high idle, tipped the nose down, and used power to control the rate of descent. I had not gotten the Mustang set up low enough, so I added some more power and went around. No problems here, as it just headed back into the air and turned under complete control. My next approach was just about perfect, using throttle to touch down at the first quarter of the runway. The oleo struts on the Robert retracts absorbed all the roughness from the grass runway, and as power and speed was reduced, the Mustang sat down on its tail wheel and came to a stop. The wind had actually increased during that first flight, which made ground handling a lot harder than before. The Mustang wanted to "weather vane" into the wind, so I killed the engine and walked to the plane to bring it back to the pit area. My mouth was as dry as a bone and my heart was racing again. I turned and asked the spectators if it was alright for me to breathe now!
Back at the pit area, I found that another sheet metal screw had come loose from the spinner, and I had to replace that first. All the control linkages and mounting bolts all over the Mustang were checked for security, and then I took a short but welcome break before continuing.
Subsequent testing only reinforced my original opinion of Top Flite's P-51 Gold Edition Mustang. The flaps really slow the plane down, and are not really necessary unless you want to lose some altitude in a hurry. It performs solidly in the air and, according to several of the spectators, "...it almost looked real...". I can guess a really good plane can make an average pilot look like an Ace.
In summary, the Top Flite Mustang is a really nice kit to build and fly. All the parts and materials included in the kit are top quality, and all can be used to complete the kit. The instructions and plans are well done, if you'll overlook the two-part plans. You'll have to get a set of retracts, but who would ever think of building and flying a giant scale Mustang that always had the wheels down?
I really enjoyed the opportunity to build and fly this particular kit. I feel it would make an excellent model for the first time warbird pilot to break into the scale ranks. It performs rock solid in the air, it looks great on the ground, and it draws cheers and applause from the spectators. It may even win a contest or two, if I ever decide to actually compete in one.
This Mustang lives up to its full size counterpart's reputation. It's a fighter that will shoot down the enemy at the blink of an eye, and return home to tell about it. It sure won me over in a hurry!
Reprinted with permission.
October, 1997 R/C Report
Editor: Gordon Banks