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It's time to load the servos and other gear into the fuselage that keeps looking smaller and smaller as I put stuff in!
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Top Flite™ Giant P51D Mustang ARF Review – Segment 2

The sleek fuselage gets crowded

Text, photos and video by Tom Hintz

Posted – 11-1-2016

Elevator and Rudder Linkages

I wanted to start getting the radio stuff in the Top Flite™ Giant P51D Mustang ARF so began by installing the wooden aft servo tray. This one tray will hold four servos and the photos in the instruction manual showing how their positions relate to the linkages are important. There are pre-installed tubes that guide the steel push rods between the servos and the tail feathers so we need to place the servos mounted where they do not conflict with each other or induce additional friction between the control rods and these tubes. Those tubes are where I encountered a bit of an issue with the Top Flite™ Giant P51D Mustang ARF.

All three of the pushrods running into the tail had a tight spot that increased the torque needed from the servo as they passed through that part of the throw. In all three cases the trouble spot appeared to be near the rear end of those tubes. I tried just running the pushrods in and out of the tubes by hand dozens of times and that helped a little but I wanted less friction. Then I put the smooth end of a pushrod in my cordless drill so I could insert the rod into the tube from the rear end and use the threads as a type of gentle reamer as I moved the control rod in and out as the drill spun it. That seemed to free the pushrods up some so I continued that for several minutes, adding a bit of dry lube spray into the tubes along the way. In the end I reduced the friction a bunch. I think that the friction that remains in the tail feather pushrods will work itself out as the Top Flite™ Giant P51D Mustang ARF flies, aided by the normal vibrations of a gas-powered model.

The Top Flite™ Giant P51D Mustang ARF uses steel pushrods that need clevises soldered on one end and silver solder is the only safe choice for this.
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Silver Solder

All of the steel pushrods, aileron, elevator, flaps and rudder need to be trimmed to length. Then we have to solder on one of the steel clevis’ included in the Top Flite™ Giant P51D Mustang ARF kit. I am not a big fan of this kind of pushrod but that is simply my opinion. Done correctly there is nothing wrong with steel pushrods and they certainly are tough.

I know there are people out there who will use regular solder, often the electrical-specific version even though the instructions call for silver solder. Silver solder does need a bit more heat to get a solid joint but most modern soldering irons have enough. My soldering outfit falls into the latter and while it takes a little longer to get the parts hot enough, it does work and the bond is very strong. As with any soldering getting a solid joint depends on using the correct flux. Remember that the flux not only conditions the metal at the joint it helps draw the heat and then the solder into the joint. It is that drawing of the solder into the joint that gives it the strength. I have seen silver soldered control rods come out of major crashes all bent, stretched and twisted but the silver solder joint was just fine.

Mount the EME 60

Installing the EME 60 took a little trial and error to get it at the right length to fit the firewall to prop washer dimension that works with the cowl. The cowl on the Top Flite™ Giant P51D Mustang ARF is tapered so it only goes so far back on the fuse before locking out. That meant having to come up with the right standoff length to get the spinner back plate so it is close to but clears the front ring of the cowl. I must stress that the standoff length I used works for this combination but may not be right for your engine.

After a few tries I found that a set of 2-1/2” aluminum standoffs I had from another plane worked great on the Top Flite™ Giant P51D Mustang ARF. They provided the overall length I needed to fit the cowl and plenty of room between the carburetor and firewall to insure good air flow into the carb.

I decided to use a choke servo on the Top Flite™ Giant P51D Mustang ARF because of the close quarters within the narrow cowl and the location of the choke arm on the EME 60. Besides, when installing the pushrod for the throttle I accidentally put it on the wrong side of the fuse. The good news is that mistake lined up well for running choke linkage so I put a second pushrod assembly on the other side for the throttle and my mistake sort of looks like a good idea!

I used a 24 ounce RotoFlow tank (let) with a three line setup. Leaving the lines a little long made fishing them through the fuse (right) a bunch easier.
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RotoFlow Fuel Tank

The Top Flite™ Giant P51D Mustang ARF comes with a quality DuBro 32-ounce tank but I am partial to the RotoFlow tanks and had a 24-ounce version on hand so that goes into the Mustang. As always I use the three-line setup; one to the carb, one for filling and a separate vent line. Top Flite designed a fuel tank “tray” into the Top Flite™ Giant P51D Mustang ARF which makes installing and later servicing the tank much easier than could be. The tray is secured to a pair of hardwood blocks that were factory installed so that it remains stable now but can be removed later to service the tank. The nose area of the Top Flite™ Giant P51D Mustang ARF is confined but there is sufficient access to get all of the lines strung and exiting at the correct points. I added some spiral warp to the carb line to prevent abrasion where it passes through the firewall.

I did have to drill a hole in the firewall to bring the carb line through at a better angle to the fuel fitting on the EME 60. I don’t mind a little extra air flowing through the fuselage anyway. The tank is secured to the light ply tray with double-sided tape giving the strip of ½”-foam that the RotoFlow tanks sits on more than enough grip to keep the tank from moving. A combination of plastic tie wraps and stranded packing tape hold the tank to the tray and secures the vent line without crushing it.

Loading the Servos

As so often happens the cavernous-looking fuselage gets crowded quickly when 10 servos, a receiver and ignition kill circuit and assorted linkages are installed. Top Flite helps this by providing special servo mounting fixtures and specific places to put them. Because of the metal control rods running to the tail there is a certain arrangement of the servos that provide interference-free operation.

I found that a set of 2-1/2" standoffs I had (left) gave me the right firewall to prop washer distance for a good fit with the Dave Brown 5" parabolic spinner (right) I used in place of the spinner Top Flite included.
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I spent a little time working on the spacing of the tail feather servos to get the servo arms aligned with the tubes guiding the pushrods. There is some drag within these tubes and more drag caused by the tubes bending to where they exit the fuselage. I found two hard spots that I worked out by sliding the metal control rods in and out repeatedly and even chucking one up in my cordless drill and using the threaded end to “worry” the hard spot down. The control surfaces all move well and do not act like they are being held back so I am hopeful that with the vibrations of a gas engine this will all work itself in once I start flying the Top Flite™ Giant P51D Mustang ARF.

Y-cords

I know, it’s better to not use Y-cords in a plane and I certainly would like to have a grand total of none in the Top Flite™ Giant P51D Mustang ARF but real-world fiscal life means that I have a 9-channel radio and receiver to work with so there will be Y-cords – three of them to be exact. One for the elevator halves, ailerons and another for the flaps. The need for the Y-cords comes from on-board systems like ignition kill, retracts, flaps, throttle servo and choke servo. I am simply out of channels. To bolster wiring security, I am adding shrink tubing to all possible Y-cord connections to be as sure as I can be that nothing vibrates apart.

This wiring dilemma further justifies my having bought my HiTec HFP-25 Digital Servo Programmer & Tester. This tool has been invaluable to me and when I discovered the elevator halves going in opposite directions I only had to plug one of the servos into the HiTec HFP-25 Digital Servo Programmer & Tester where I could reverse that servos’ rotation. Problem cured. The longer I have the HiTec HFP-25 Digital Servo Programmer & Tester the more I wonder how people live without one.

Mounting and Cutting the Cowl

When the model manufacturers create a plane that retains the look and lines of the original there can be liabilities. The Top Flite™ Giant P51D Mustang ARF used a long narrow Merlin engine that allowed the original designers to narrow the fuselage as well. Staying true to the original means we get a cowl that lacks the width to fully conceal my EME 60 with the Bisson wrap-around Pitts style muffler. There are compact mufflers out there but I have good results with them over the long haul and it is doubtful that one of those would fit within an uncut cow. Besides, I already had the Bisson muffler that has been on the EME 60 from day one.

I decided to start the Top Flite™ Giant P51D Mustang ARF out on the included fixed landing gear (left) as some of you encouraged me to do. I took the time to make sure that the main gear wires are parallel (right) so I don;t have a bunch of toe in acting like a brake and nosing the plane over on an expensive prop!
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It took some trial and error but I got the cowl so that it goes on and fits around everything. There is more muffler hanging out than I like but like most of you my budget does in fact have a bottom and a custom exhaust to fit inside the cowl just is not possible. Even with the money I would be concerned that such a small exhaust would hold the engine back some o some extent which is never a good idea in a thoroughbred aircraft alike the Top Flite™ Giant P51D Mustang ARF.

Trim Pieces

At this writing I am unsure if the “scale exhaust” pieces will be installed on my Top Flite™ Giant P51D Mustang ARF. They do not look right to me in terms of size and they are longer than the cowl so hang off its rear edge. I know the exhaust is part of the P51 aura and I think I will keep looking for aftermarket pieces that look better and might fit better. I am not going to let these prevent me from flying the p51 when it is ready.

I also installed the wing fillets and again made a change to what the plans say. They want the fillets to be CA’ d to the fuse but it is not hard for me to imagine seeing one of these things fall off in flight when the vibrations eventually break down the glue bond. I did use CA to install the fillets but added screws through the inside of the fuse and into the fillets.

The bottom of the wing also gets a cooler scoop at the rear edge that plays a big part in producing the famous P51 profile. A smaller fillet at the front of the wing smooths that transition from fuselage to wing. Both were installed without issue.

I am not into scale very much so installed a basic cockpit and a civilian pilot bust. I figure there are few P51’s being flown by military pilots these days so a scale civilian works for me. Since I am building the Top Flite™ Giant P51D Mustang ARF as a personal tribute to my father who loved the P51’s so much I opted to use a slightly out-of-scale pilot and placement. My father had been chided his whole life about “short legs” and to be sure he was not tall but he took the ribbing good naturedly. I think he would understand my “jab” in the form of a “short” pilot and his “closer-to-the-pedals” placement in my Top Flite™ Giant P51D Mustang ARF cockpit.

Landing Gear

I also used the included fixed tail wheel (left) and found that fabricating the pull-pull cables, especially at the servo (right) was the toughest part of the build for me because of the wing mounting block that limits access to those cables during adjustment. I got it though and all works fine.
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The plan was and remains to install retractable landing gear on at least the mains. Adding a retractable tail wheel is expensive, in the $190.00 range for the tail wheel assembly itself. Email I have received since announcing the Top Flite™ Giant P51D Mustang ARF project shows that there is a significant group of RC’rs out there that are using the included fixed landing gear at least initially. I want to include the widest range of RC’rs in the content we provide so I am installing the fixed gear that Top Flite includes and we will maiden the Top Flite™ Giant P51D Mustang ARF on that gear setup and eventually go to retracts later.

Installing the main fixed gear is fast and easy with the included hardware. The only word of caution I have is to take the time to align the gear with each other to avoid excessive toe in or toe out that can act like brakes and make the Top Flite™ Giant P51D Mustang ARF want to nose over. I installed the screws that secure the main gear to the wing loosely then used a straight edge to make sure that the portion of the wire gear where the wheels mount are aligned with each other. Then the screws can be tightened and the alignment checked once again. This procedure takes a minute or two but can prevent killing a bunch of expensive props, spinners and mufflers.

The fixed tail wheel is not very difficult to install but the cable pull-pull system that turns it is a different story. We make small loops at the tail wheel end that slip over ball studs on the arm that steers the tail wheel. Top Flite installs plastic tubes that guide the cables to the servo where we have to make the final loops that engage brass threaded ends for connecting the cables to the servo arm with the included clevis’s. Making this more difficult is the servos being located under the block to which the wing bolts. The lack of space and working at an angle made finishing the pull-pull cables the hardest single part of the Top Flite™ Giant P51D Mustang ARF build for me. I did get it completed and have plenty of steering range at the tail wheel. It is important to remember that tail wheel steering tends to be sensitive so the amount of steering needed is very small.

The layout in the Top Flite™ Giant P51D Mustang ARF is intended to use a separate servo for tail wheel steering. That allows us to use a simple mix to the rudder so we can adjust the amount of steering without changing anything about the rudder movement. Using the mix usually means we never have to mess with that hard-to-install cable system to make those adjustments.

Video Tour

Nearing the End

There are some final tweaks and small pieces that need to go into the Top Flite™ Giant P51D Mustang ARF but it is very close to being ready for balancing and setting the control throws. I plan to get the EME 60 started at the house and run that some to be sure I have the throttle set up before going to the flying field. So, barring any unforeseen problems the next Top Flite™ Giant P51D Mustang ARF segment should include the maiden flights! Stay tuned!

See the Top Flite™ Giant P51D Mustang ARF Segment 1 – Click Here

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