RCU Review: World Models P-82 Twin Mustang E-Conversion


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    Contributed by: Greg Covey | Published: July 2005 | Views: 43610 | email icon Email this Article | PDFpdf icon

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    Manufacturer Info



    World Models
    AirBorne Models
    2403 Research Drive
    Livermore CA 94550
    Phone : 925 371 0922
    Fax: 925 371 0923
    www.airborne-models.com



    Hits
    • Highly pre-assembled
    • Excellent quality construction
    • Unique scale design
    • Great flying characteristics


    Misses
    • Manual sometimes unclear
    • Foam wheels are too soft



    Introduction
    History:

    The P-82 Twin Mustang was essentially two P-51 Mustangs joined together to provide longer range as well as versatility as a fighter, escort, reconnaissance, attack bomber, or interceptor. The purpose of having two pilots was as a relief against fatigue on the long over water missions. The co-pilot could also act as a radar operator since the P-82G version carried a giant centerline pod radar system for night fighting. Although the first P-82 flight was in 1945, they were ordered too late to see much action in WWII.

    The P-82 was the first US aircraft to operate over Korea and destroy an enemy plane. Speeds of up to 460mph could be obtained at 21,000'. The plane had a ceiling of 38,900' and a range of 2240 miles. Armaments included six wing-mounted machine guns and either up to four 1,000lb bombs or up to four auxiliary fuel tanks.

    In June of 1948, the P-designation was changed to F, and the Twin Mustang became an F-82. They spent a brief life flying alongside B-29s and were replaced by jets in 1950. The last Twin Mustang was retired from service in mid-1953.

    For more information on the P-82 Twin Mustang, visit the North American History section of Boeing's on-line library.



    Specifications


    Kit Name: P-82 Twin Mustang
    Manufacturer:
    The World Models

    Wing Span:
    70.5 in / 1790 mm
    Wing Area:
    736 sq in / 47.5 sq dm
    Flying Weight:
    9.5 lbs / 4300 g
    Fuselage Length:
    49.0 in / 1240 mm
    Engine Required:
    2x2C 0.32-0.40 cu in
    Radio Required:
    6 channels, 9 servos

    Features:

    • Step-by-step manual
    • Custom Decals
    • Interlocking Joints
    • All laser-cut AAA premium balsa
    • Sealed Seam Oracover
    • Molded Plastics, custom gear mains
    • Duralumin linkage horns

    Assembly

    The World Models Manufacturing Company has re-created a scale version of the P-82 Twin Mustang meant for two .40-size glow engines.

    The quick build ARF has the following features:

    • Premium hand iron-on covering film
    • Fuel proof decals and factory painted pilot figures
    • Functional split flap and pre-installed retracts
    • Comes with all hardware and accessories

    My conversion project will use two AXI 4120/14 outrunner motors with the radial mount set. Note that the less expensive AXI 2826/10 or /12 motor would also work well in converting this classic warbird to clean and quiet electric power. In either case, I choose the Jeti JESAP40P Advance PLUS 40 Amp Opto Brushless Controller.

    ARF Contents:

    Many of the sections and parts are exact duplicates to provide the needed "twin" items. The model is highly pre-fabricated and the construction quality is excellent. The glow engine mounting holes and tee-nuts were pre-installed. The low-temperature Ultracote (Oracover) needed some touch-ups with the heat gun but the overall covering job was well done.


    The wing comes in three sections that are ready to be attached together with only a few screws. There is no need to epoxy the wing sections together as the manual suggests.

    The locking bars and tee-nuts are pre-installed. Athough the manual has instructions for mounting the ailerons and retracts, everything is already pre-installed. The retracts use a single 90-100oz/in. retract servo.

    The canopy, cowl, rudder, pilot, and spinner are all duplicated and pre-finished!

    Assembly:

    I'm using Hitec HS-422 Pro servos for all the control surfaces. The HS-422 is one of the most durable and reliable servos Hitec has ever offered. With its dual iron-oilite bushings, high impact resin gear train and high performance circuitry, the HS-422 features excellent centering and resolution. They are a great value!

    Mounting the motor, which is often my favorite task, proved to be very simple and inexpensive. I needed a 1.5" motor offset to make a 4" total length between my firewall and the spinner backplate.

    A trip to my local home improvement store (Home Depot) revealed that a common PVC part is a (NIBCO C437-168) 1-1/4" x 1" coupler that has an octagonal end on one side and round on the other. The $0.79 cent part can be used unmodified. I simply sanded the ends on a flat surface to remove the slippery wax-based finish.

    Note: PVC stands for PolyVinylChloride, and it is a plastic used to make drain pipe for household plumbing.

    I then used #8-32 x 2" round head machine screws and #8-32 x 1/4" tee-nuts to mount the 4120 motor with the radial mount set that includes the prop adapter.

    One of the four mounting holes uses an existing hole and the other three were marked with a felt tip pen by holding the motor up to the firewall.

    I drilled a large hole for the three motor wires to pass back into the fuselage and extra airholes for cooling the ESC and battery.

    All the standard American hardware available at Lowe's, Home Depot, or any local hardware store. Of course, metric equivalents will work here just as well. The supplied stock tee-nuts are M4 so you just need 2" (50mm) long M4 machine screws to mount the motor. The mounted motor looked great and followed the right thrust offset built into the firewall.

    The cowl, prop, and spinner mounted nicely. I needed to trim the bottom corners of the fuselage for a snug cowl fit and slightly deepen the slots in the spinner cone for my APC 14x7 e-prop.

    The motor was mounted a bit low but it followed the thrust angle of the firewall. Ideally, it needs to be about 1/4" higher but I'll just follow the same scheme on the other side to match this one since it doesn't look too bad.

    My P-82 wing was built in three sections. The center section had clear fishing line running from each of the outer holes to the flap bay for pulling servo leads. A third line was run from the retract servo bay to the flap bay. After some decision making, I decided to follow the manual servo setup and replace only the throttle servos with ESC control line extensions. Most of the servo leads needed 24" extensions.

    The P-82 has no center pod like a P-38 so the receiver must reside in one side. The manual uses the right pod to house the receiver and Rx. battery and so did I. I will replace the Rx. battery with a UBEC that feeds both Opto-isolated ESCs via the control line. Each pod will have its own motor battery.

    Although I mixed up the left and right aileron labels, the wire layout can be seen on the wing above as it is being viewed from the front top side.

    The HS-75BB retract servo worked nicely with the stock wheel. I used an Astro Flight servo tester and a heavy-duty receiver battery to test the up and down swing. The right photo above shows gear down position of the servo wheel. The rods stop just short of touching and do not cause to servo "hum" or draw current in either position stop.

    The retracts are shown in both up and down locked positions. It is important to test that the retracts lock in both directions and that there is no stress (or force) on the servo at either end point. Always favor the locked down position when setting the linkage. The retract servo bay is covered with a painted plastic piece that I used my own black screws to secure. I added one of the kit's decals over the cover plate but it is not likely a "true to scale" place for the oxygen tanks.

    I finished routing my last two cables from the left side to the right for rudder and speed control.

    After my retracts were finished, I installed the flap linkage. I needed to open the bay slot a bit to allow room for the snap keeper and control rod bend. A longer servo arm here would help. All the hardware shown is included in the kit. I programmed my Futaba Super-8 transmitter for a 15 degree and 30 degree flap offset on a 3-position switch. I prefer this fixed offset instead of using a knob since it eliminates any guesswork during a flight and I can do it with just a glance at the switch.

    My aileron linkage was identical to my flap linkage. Again, the servo arm was a bit short which required me to cut away a portion of the bay hatch. The aileron servos are mounted in a reverse position so I only needed to connect them together with a "Y" adapter and then to a single channel. The wing is now complete with working ailerons, flap, and retracts. I'll finish up my second motor mount and start the final assembly.

    The rudder comes pre-hinged on the vertical stabilizer so it was an easy task to glue it in place. The custom fit provided perfect alignment. I used thick white glue to attach the vertical stabilizer. The custom tailwheel assembly also installed easily. You need to drill a hole in the rudder bottom first so that the swivel is aligned with the hinge area to prevent binding. I glued the metal bar into the rudder with epoxy and also secured the two screws in place with epoxy.

    The rudder linkage is duplicated on both fuselage sections. The manual position for the rudder servo is incorrect so you need to reverse the positions shown since the tubing crosses sides inside the fuselage. The metal rods installed easily since the tubing is pre-mounted. My technique was to push the threaded end of the rod through the tubing and poke it out through the covering. I used the supplied control horns and quick links.

    The elevator linkage only connects on the right fuselage. My third control horn was broken so I used a large white plastic horn that screws to a plate on the other side of the elevator. I expect little movement is needed from either the elevator or the dual rudders so I used low throw setting on both sides of the linkage.

    Battery Mounting:

    The 4-cell Kokam 3.2AH (20C) pack above weighs 12.8oz. It is shown with a 3.0AH NiMH pack for size comparison. Note that the new cell width is the same as a sub-C cell length. The 4-cell Lithium pack has a voltage equal to about 14 cells NiMH which weighs about 26oz or twice the weight of the Kokam pack. This is a pre-production test pack without the taps to monitor each cell. The production version from FMA Direct will be called Skyvolts. I'll be using one of these Kokam packs in each fuselage of my P-82 Twin Mustang to power the 4120 motor.

    To mount my 4-cell Kokam 3.2AH packs, I used the stock glow fuel tanks. After drilling holes in one end and cutting off the other end, I surrounded the Lithium packs with shock absorbing IMPAD foam pads from FMA Direct. This held the pack perfectly inside the plastic fuel tank and will help protect them in a crash.

    I doubt that much air will flow through but I don't expect the packs to get hot in this application due to the excessive power level and type of scale warbird flying. The fuel tanks slide into pre-mounted stock plywood formers. In the photo shown, the pack position resulted in the CG being 1" forward from the recommended spot so I had to slide them back about 1".

    Final Assembly:

    The final assembly went very well although, at the last minute, I realize that I had forgotten to mount an On/Off switch to arm the motors. Fortunately, I keep a spare Tower Hobbies System 3000 On/Off switch assembly on hand.

    I laid the two fuselages on top of the wing to start. The left fuselage needed the rudder servo and ESC connections made to the wing that route over to the right fuselage. Note that my Hitec Electron 6 receiver is mounted in between the unused servo bays with servo tape and a tywrap. The antenna wire is routed under the fuselage belly and will later be partially covered by the final mock air duct.

    The right fuselage has many connections to the receiver. The ailerons, retract servo, flap servo, rudders, ESCs, and elevator. I used a "Y" adapter in channel six to connect both the flap servo and the UBEC output that runs through my On/Off switch. The rudder servos were connected to channel 4 with a "Y" adapter cable. The ESCs and aileron servos were also connected to the reciever with a "Y" adapter cable.

    The horizontal stabilizer is mounting using the supplied screws and washers through the vertical fin into pre-installed hidden nuts.

    The wing can then be screwed in place using the supplied screws and washers into pre-installed T-nuts. The front of the wing is held by dual wooden dowels on each fuselage.

    Once the wing is secure, the mock air scoops easily mount using a single screw into a pre-installed nut. Again, the front of the scoop is held by dual wooden dowel rods. Other than applying the decals, my assembly was compete.

    I checked the balance of my P-82 using the Great Planes CG Machine and discovered that I was about 1" forward of my 3.5" target. I moved both the packs back about 1" and the CG was now just right.



    Flight Time

    Even without the final decals, my twin mustang looked uniquely impressive! I tested all the control surfaces and fired up the dual motors. I was very happy when everything seemed to work just fine. Since my UBEC and switch are on the the right fuselage, I connect the right side battery first and then the left side battery. Once the switch is turned to ON, you can hear both ESCs beep their readiness to the motor. I set the triple position switch on my Futaba Super 8 to offset the channel 6 flap 0-15-30 degrees.

    My P-82 was RTF at 174oz (10.9lbs) which is about 0.4lb heavier than the stock 10.5lb glow version with fuel.

    • P-82 w/o batteries = 150oz
    • Left side 4-cell Kokam 3.2AH pack = 12oz
    • Right side 4-cell Kokam 3.2AH pack = 12oz

    The pilot, Lynn Bowerman, inspects the control surface alignment before flight.

    The pre-flight testing looked good although I did need to re-adjust the retract linkage a bit to insure proper locking in the down position. Note the P-82 "Undertaker" is dressed with decals now.

    The P-82 took off with plenty of authority and it was immediately apparent that it flew with great stability. We trimmed it out and then tried some basic aerobatics like a loop and roll. The video of the P-82 also shows just how well it flies inverted. On the first landing, we did not use flaps and the Twin Mustang came in rather hot but manageable in a 600' runway. During the second flight, we played with the flaps and found no ill effects even with the 30 degree offset. The second landing was noticeably shorter!

    Flying photos by "Papa" Jeff Ring.



    After the test flights were done, the only thing that we didn't like about the P-82 was the small and soft ultralight foam wheels. These are sometimes called "No Bounce" wheels and they were just too soft for a plane of this weight. I will replace them with some rubber wheels that will not deform under the weight. Using larger wheels will not fit in the retract wells. I choose Du-Bro (225TL) 2-1/4" (57mm) Treaded Lightweight wheels.


    Watch the video of the P-82 Twin

    Windows media


    Summary


    One of the biggest advantages of electric powered flight is in the unparalleled reliability gained from using brushless motors. Although this added reliability can be seen in single motor applications, it becomes even more visible in multi-engine conversions like my P-82.

    A few years ago, in the USSMA Scale Masters competition which is dominated by glow and gas-powered entries, an electric-powered scratch-build Chinese Tu-4 Turboprop AEW plane won the Team Scale Championships in Dayton, Ohio. The plane was skillfully built by George Maiorana and masterfully flown by Dave Pinegar. The plane used four MaxCim 13Y brushless electric motors. It was clear that the benefits of electric flight helped increase the reliability of multi-engine models.

    You can use the 2826 motor in place of the 4120 motor. In some cases, especially with glow-to-electric conversions, you may need the extra weight up front. On my World Models P-82 conversion, the AXI 4120 motors provided a good balance point with the 4-cell Kokam 3.2AH packs. Although I started with APC 14" props, I later reduced the prop size to 13" since I had more power than I needed and the smaller props provided a more usable range of power on my throttle stick.

    The World Models P-82 project is best left to intermediate or advanced modelers and flyers. Although the plane was highly pre-assembled, the complexity of routing the wires and dealing with retracts, two rudders, and a flap should be done with some thought. Scale modelers with some experience will likely have a blast assembling the P-82 and it is easily flown by any pilot having P-51 experience or some flap landing experience. The plane itself is unique and was a great deal of fun to fly with clean, quiet, and reliable electric power!


    For more discussions on this plane and electric powered flight visit both the RC Universe discussion forums and the new Wattflyer.com electric only forums




    Manufacturer Information


    World Models
    AirBorne Models
    2403 Research Drive
    Livermore CA 94550
    Phone : 925 371 0922
    Fax: 925 371 0923
    www.airborne-models.com


    Hobby-Lobby
    6535 Premier Drive
    Brentwood, TN 37027
    615-373-1444
    sales@hobby-lobby.com
    www.hobby-lobby.com

    FMA Direct
    5716A Industry Lane
    Frederick, MD 21704
    Ph: (800) 343-2934
    Tech/Service: (301) 668-4280
    www.fmadirect.com


    Tower Hobbies

    PO Box 9078
    Champaign, IL, 61826
    800-637-4989
    217-398-3636
    orders@towerhobbies.com

    Comments on RCU Review: World Models P-82 Twin Mustang E-Conversion

    Posted by: aevazy on 08/24/2014
    Do you Know C.G?
    Page: 1
    The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in products like the one featured in the review.

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