Like most fans of aviation, I have a soft spot for the P-51 Mustang. It's pretty much the quintessential WWII fighter plane. For some, it's the only WWII fighter plane. When it comes to RC models, however, I tend to stay away from the Mustang. The problem is that I usually favor rare and unique subjects. With oodles of RC P-51s in the world, they're hardly rare and seldom unique.
Tower Hobbies recently released an updated version of their electric-powered Mustang. I thought that this new model was distinctive enough to warrant further inspection. The most noticeable attribute of this P-51 is that the same basic airframe is available four different ways. You can buy it in the popular P-51D model with a bubble canopy. This variant is offered in military or racing paint schemes. Next up is a version representing the earlier "B" model Mustang with a greenhouse canopy. The final option is the one I chose. "Racer Red" emulates a post-war P-51s that has been modified and streamlined for air racing. Basically, this kit offers all the appeal of a P-51 along with the dash of variety that I crave.
What's in The Kit
Tower's Mustang ($120) is a receiver-ready kit made of molded foam. It includes everything except a transmitter, receiver, and flight battery. With a 40" wingspan, this P-51 can be considered a park-flyer or club field model.
The servos and power system are all factory-installed. Some of the variants also have the decals pre-applied. Racer Red, however, comes with a sheet of self-adhesive decals that you can apply yourself.
I used my Futaba 14SG transmitter with an R617FS receiver. Although the 14SG has tons of different programming options, I didn't need to dig very deep for the Mustang. The basic model is a 4-channel airplane. There are options for utilizing more channels by adding flaps and retractable landing gear. I didn't add flaps, but did take advantage of the available retracts. More on that later.
My kit had a slight bit of shipping damage. The rudder had been torn free from the vertical stabilizer. These things happen. The fix was super easy and quick. It's still holding strong after a lot of flight testing.
The first assembly step is to remove the large hatch that provides access to the battery bay and radio equipment. Different hatches are what give the variants of this model their individual shapes. The hatch is held very securely with magnets at the rear, more magnets in the middle, and a tab in the front.
I was concerned that I would eventually scar the paint when gripping the hatch for removal. So, I added a small grip made from the plunger of an insulin syringe. The flanged end of the plunger is glued to the inside of the hatch. The shaft of the plunger protrudes from the top like an antenna.
The horizontal stabilizer uses a very unique retention method. When the parts are properly positioned, two holes in the stabilizer align with holes in the lower fuselage. Foam dowels are inserted into these holes to key everything together without any glue. I was skeptical at first, but everything fits tightly and securely.
All of the control pushrods use an EZ-connector on one end. The other end is either a z-bend or 90-degree bend with a nylon keeper. EZ-connectors are basically small brass blocks with a setscrew. They allow you to adjust the effective length of the pushrod very easily. They typically work fine and lots of modelers use them. I'm not a fan because I think they introduce a potential failure point (the setscrew) and their mechanical connection to the servo arm tends to get sloppy over time. I decided to omit the EZ-connectors on the Mustang.
Each of the pushrods had sufficient excess length that I was able to use a z-bend on the ends that previously interfaced with the EZ-connectors. After careful measurement, I used my Z-bend pliers to put the bends exactly where I needed them. Now the pushrods have no slop and no likely failure scenarios.
The kit includes mounts for fixed landing gear. You can plug the gear into place for normal takeoff and landings. Or, you can remove the gear for hand-launches and belly landings. A third alternative is to use retractable landing gear. That's what I did. Flyzone's electric retracts ($30) work just like a pair of servos. They bolt directly to the existing mounts in the Mustang's wing. You simply screw them down and attach the wire leads to your receiver. A switch on the transmitter controls whether the gear is extended or retracted.
After several flights on my P-51, I noticed that a few of the tiny machine screws on the retract units had become loose. One screw actually backed out completely and was lost. I added a drop of Loctite to the remaining screws and retightened them.
The kit includes a strip of self-adhesive Velcro for securing the receiver and battery. There is also a 2-sided Velcro strap, but it was not mentioned in the instructions. I decided to utilize the strap as an extra hold-down for the battery. I used an X-Acto knife to cut a small slit on each side of the floor where the battery is positioned. I then routed the strap through the slits so that it runs under the battery floor and wraps around the battery. That battery isn't budging!
It's a good idea to balance the propeller before installing it on the model. Mine required a slight bit of tape on one blade. Plastic spinners like the Mustang's can sometimes be tricky to get running true. But this one has been working well without any massaging necessary.
The flight-ready Mustang weighs 31.3 ounces with an ElectriFly 3S-2200mAh 30C battery. I was able to balance the P-51 at the suggested location without having to add any ballast to the nose or tail. In fact, the model balances just slightly nose-heavy without a battery installed. Since the battery is located over the center of gravity, moving it fore or aft will let you tweak the balance point.
Flying the Mustang
Conditions were not very favorable during my first outing with the Mustang. The weather man said that winds were blowing 10 to 20mph, and I believe him! That's a lot of wind for a lightweight model such as this P-51. I would have waited, but the long-range forecast actually looked worse and I really wanted to fly the Mustang.
The steerable tailwheel allows reasonable control when taxiing…as long as the wind isn't too bad. I've confirmed this on subsequent outings in less wind. I noticed, however that the main wheels are located very close to the center of gravity. This makes the Mustang prone to nosing over excessively easy. It helps to hold full up elevator while taxiing to keep the tail planted on the ground, but it's not a cure. I'm planning to add shims to the rear landing gear mounts, which will tilt the gear forward somewhat. Hopefully that will take care of things.
I've been flying from a paved runway. I don't think the P-51 will work well on most grass runways because of its smallish wheels. As with taxiing, it helps to hold some back pressure on the elevator as you start your takeoff roll. Once the Mustang builds speed, you can ease off of the pressure and let the tail come up. The airplane will be flying soon afterward. I'm probably making it sound more complex and difficult than it really is.
This P-51 really shines in the air. The stock power system provides plenty of power for strong climbs and a decent turn of speed. Of course, any self-respecting model of a fighter has to have aerobatic chops. Loops, rolls, spins, inverted flight. All of the usual moves are on tap here. The Mustang also flies knife-edge quite well, with just a little coupling towards the canopy.
The manual provides suggested control throws for high rates and low rates. I've been flying with nothing but high rates. I find that those settings are good for aerobatics and not too twitchy for smooth cruising.
The stock power setup on the Mustang provides a nice balance between performance and flight times. Flights lasting 10 minutes are possible as long as you're not too heavy on the throttle.
I expected the P-51 to be a real handful in the wind because of its light wing loading. It turns out that I was overly concerned. While it does not ignore the wind, it isn't at its mercy either. Even on that first blustery outing when I was practically landing backwards into the headwind, I never felt like I wasn't in full control.
Like the full-scale Mustang, this model is not intended for beginners. You'll want to build your confidence on a trainer and a sport ship or two before taking on this bird. But for those pilots who are comfortable on the sticks of a 4-channel model, it is a well-rounded performer. It also looks really great during high-speed passes in a steep bank with the landing gear tucked away.
Upgrading the Mustang
The Mustang's 30-35-1000 brushless motor is also used in several other planes by Tower Hobbies and Flyzone. I know from experience with some of those other models that the Mustang's setup does not max out the motor's potential. There is a lot of headroom for a performance boost.
Both the motor and the stock 30-amp ESC are capable of operating with a 4-cell LiPo battery. But you can't just go throwing a 4-cell battery in the Mustang without making other changes. If you want to avoid a meltdown, you have to understand how the motor, ESC, propeller, and battery interact. Changing any of those components will affect how the others work…sometimes in a dramatic way. If you do not yet have the knowledge and tools for this sort of tinkering, you should stick with the stock setup.
With the Mustang, upgrading to a 4-cell battery meant that I would also need to use a smaller propeller to prevent the system from exceeding the ESC's amperage limitation. In my backyard static testing, I found that an 8x8 prop caused the system to pull 30.4 amps…right at the ESC's stated limit. I also tested a 9x6 prop, which resulted in an amp draw of 31.7 amps. While this is slightly above the max amp rating, I was comfortable trying it in flight because the numbers reflect static testing. Dynamic loading in flight should actually fall below the 30-amp level. It's a calculated risk.
Take all of my amperage measurements with a grain of salt. The altitude here in Lubbock is 3200 feet. So my systems will pull less current than an equivalent setup at sea level. Again, don't do this stuff without the tools and knowledge to do so safely.
The 4-cell battery I used is a Flight Power 4-cell 2450mAh 30C LiPo. It is only slightly larger in physical size than the 3S-2200 pack, so it fits in the same location without any trouble. At 9 ounces, it weighs 3 ounces more than the 3-cell unit, which also poses no concerns.
For the sake of comparison, the stock 3-cell setup draws 23.5 amps and produces 261 watts of power. Power was considerably higher with my 4-cell options at 455 watts (8x8) and 476 watts (9x6). To summarize, going to a 4-cell battery resulted in a 75% power boost, but only a 10% weight increase. I think you can guess how this changed the Mustang's performance.
With a 4-cell battery upgrade, the Mustang has a completely different feel, flying like a bigger airplane than it is.
The upgraded Mustang is obviously faster than stock--much faster. I don't have reliable numbers, but my loose calculations suggest that it's hitting more than 80mph in level flight with the 8x8 prop. Not bad for a hunk of foam! Performance with the 9x6 is very similar. The 8x8 has a slight edge in speed while the 9x6 provides better climbs.
The performance differences extend beyond just speed. The airplane has a completely different feel on 4S power, even at speeds that overlap the stock capabilities. Maybe it's the added weight, or possibly the effects of a smaller prop disc, or maybe it's just placebo effect. Whatever the cause (or causes), I think that the 4S-powered Mustang flies like a bigger airplane than it is. I don't even know how to explain it other than to say it feels different on the controls. It still slows down well and is easy to land. I like flying the Mustang on 3S. I love flying it on 4S!
Given the higher amp draw, there is a tradeoff in flight time when using the 4S battery. I typically set a timer for 6 minutes and still have reserve power when I land….not to mention goosebumps.
I've only tested the Racer Red version of the Tower Mustang. My podcasting buddies, Fitz Walker and Lee Ray, got their hands on the "Berlin Express" P-51B, and "Miss America" P-51D models respectively. We recently recorded a conversation about our relative experiences with the different variants of the same kit. I think it is interesting that we each found different things to like and dislike. Check it out if you'd like to hear about this model from more than one angle.
Terry is a freelance writer living in Lubbock, Texas. Visit his website at TerryDunn.org and follow him on Twitter and Facebook. You can also hear Terry talk about RC hobbies as one of the hosts of the RC Roundtable podcast.