Greg Covey

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 overwater 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-desination 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 [link=http://www.boeing.com/history/bna/p82.htm]North American History[/link] section of Boeing's on-line library.

Greg Covey

The World Models Manufacturing Company has re-created a scale version of the [link=http://www.theworldmodels.com/para/products/airplanedetails.php?airplaneid=34#]P-82 Twin Mustang[/link] meant for two .40-size glow engines.

The quick build ARF has the following features:
[ul][*] 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
[/ul]

Specifications:
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

Greg Covey

My conversion project will use two [link=http://www.hobby-lobby.com/brushless-axi4120.htm]AXI 4120/14[/link] outrunner motors with the radial mount set.

Note that the less expensive [link=http://www.hobby-lobby.com/brushless-axi2826.htm]AXI 2826/10[/link] or /12 motor would also work well in converting this classic warbird to clean and quiet electric power.

Greg Covey

Here are some images of the fuselages. 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.

Greg Covey

The wing comes in three sections that are ready to be attached together with only a few screws. 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. I will be using the [link=http://www.hobby-lobby.com/servos.htm]Servo Delay Module[/link] from Hobby Lobby with a standard high-torque 120oz/in servo to obtain a realistic retract speed for a great scale look!

Greg Covey

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

Greg Covey

I'm using [link=http://www.hobby-lobby.com/servos.htm]Hitec HS-422 Pro servos[/link] 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!

Darrell B.

Greg,

WOW!!
Another great conversion from the master of conversions! This looks like an awesome project. I love the way you keep cranking these out. With two 4120s in the noses of those slim fuselages this think will really haul. I look forward to your results.
Good Luck,
Darrell B.

Greg Covey

Thanks, Darrell. I've been wanting to convert a twin-engine plane for a while now since I had several 4120 motors sitting around after upgrades to 4130s.

Everyone I talk to says that the P-82 flies great! The real challange here is in a proper split of the brushless power system functions but using Opto-isolated ESCs makes it easy. I have also been looking for a more scale travel speed for mechanical retracts on my Hangar 9 Corsair so this delay module from Hobby Lobby will be a good test on the P-82 conversion.

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.

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.

Darrell B.

Greg,
Were you able to get those blind nuts at Lowe's? That looks like one of their packages. I'm sure that they were less than a $1.
What size of cap is that for the stand off?
Darrell

Greg Covey

Darrell,

Yes, this is all 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.

Greg Covey

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.

Last year, 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.

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.

In the third image below, note that I mixed up the left and right aileron labels. The wing is being viewed from the front top side.

Greg Covey

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.

Greg Covey

The Simprop [link=http://www.hobby-lobby.com/servos.htm]SI0809[/link] Servo Delay Module works great with my Blue Bird BMS620MG servo. The delay is adjusted with a small screwdriver to provide a realistic scale speed for the retracts on my P-82.

The Blue Bird [link=http://www.balsapr.com/catalog/Servos/bluebirdStandardServosView.asp?ProductId=U093661]BMS-620MG[/link] servo has metal gears and a torque of 126oz/in on 4.8v or 144oz/in on 6.0v. A great value at $20!

Gordon W

Hi Greg

To help we limeys discover a similar item, what does PCV mean, and what would the coupler be used for in real life?

Thanks

Gordon

Darrell B.

Gordon,

PVC stands for PolyVinylChloride, and it is a plastic used to make drain pipe for household plumbing.
The piece Greg is using is used for caping off a pipe.

Darrell B.

Gordon W

Thanks Darrell

It hadn't occurred to me that Greg might have spelt PVC wrongly

Gordon

Greg Covey

Sorry Gordon, sometimes my fingers go faster than my brain when I type.

Below is my new 4-cell Kokam 3.2AH (20C) pack that 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.

I'll be using one of these Kokam packs in each fuselage of my P-82 Twin Mustang to power the 4120 motor.

pmmartin

Greg,

A little off the topic of this thread however you are talking about packs so--. What would you suggest as a Lipo replacement for a 20 cell 3300 Nimh pack?

Greg Covey

Hi Paul,

Long time no see (or post).

I hope that you're not really still in Buffalo but rather down in Florida staying dry and warm.

A 20-cell NiCd/NiMH pack can be replaced with a 6s Lithium pack. A 10-cell NiCd/NiMH pack with a 3s Lithium pack and so on.

Regards.

pmmartin

Greg,

Just got home for Christmas. I joined the Airmasters R/C Club in Sebastian Florida. I took half my fleet and have been flying at their great field.

This fall I finished a Somthin' Extra and am just now finishing up a Bruce Tharpe Venture 60 E which is a great kit. I am waiting for my new MaxCim setup for it. These will have to wait for spring to fly as I have no way to get them there now. I did take 7 planes with me when I went in October. We left shortly after we were supposed to go to NEAT. On a hunch I decided not to go the last minute. Was it a good choice?

I am getting ready to go Lipo but I think the spring may now be the right time. To convert my whole fleet I could probably buy a new truck and be money ahead?

You certainly have continued to be one busy flyer. I am glad you learned what I had been telling you - "big planes are better!".

I like this present project that you are working on.

Paul

Greg Covey

Paul,

I wish I could go down to Florida after the holidays are over!

You can read my take on the 2004 NEAT Fair [link=http://www.rcuniverse.com/magazine/article_display.cfm?article_id=439]here[/link].

I learned plenty from you over the years...hence my extensive use of PVC for motor mounts.

bigbobed

Greg, are you running counter rotating motors?

Greg Covey

No, at least not initially.

I can change the brushless motor direction easily enough by swapping any two wires to the ESC but I'm not sure if APC makes a reverse direction 14x7 e-prop.

Greg Covey

I've discussed the counter rotation issue with several pilots and the consensus is that it is not needed because the amount of torque can be easily offset with the ailerons.

I was about to test my servo delay module with the Blue Bird 620MG servo and discovered that only a low-profile servo will fit in the retract bay. Since I already had a Hitec HS-75BB retract servo, I decided to use it on my P-82 and save the delay module for another project.