MS Composit Pitts S2 Bulldog Review

Specifications

The MS Composit Pitts S2 Bulldog is a park flier-sized foam biplane with a true airfoil. The majority of the plane is made of heavy-duty EPP foam, with the exception of the tail group (stabilizers, elevator, and rudder), which is Depron. The kit comes prepainted with a yellow and black scheme and the basic hardware needed, and comes in a simple bag.

The entire kit comes in a bag.

All of the kit parts before starting construction.

Right away, you'll notice that this model has a lot of potential, and also a number of shortcomings. I'll skip to the end of the review a bit by saying that if you make a number of replacements and modifications, this can be a great flying plane. However, the kit as sold off the shelf is only mediocre.

The upgraded wheels on the left, the stock plastic ones on the right.

Let's get a few negative things out of the way up front. The manual is quite poor compared to other manufacturers. This eight page leaflet is vague and meant for experienced builders, and will leave beginners used to a step-by-step manual out of luck. Fortunately, there's not as much work to do as with a balsa ARF.

The included wheels are just lightweight plastic discs, and are fragile to boot. Plan on replacing them with some real rubber wheels, or moving the aileron servo(s) to the top of the bottom wing, and flying without gear. If you do attach the landing gear, you'll want to bend it forward, as the stock position will cause the plane to nose over on almost every landing.

Building

I began building with the wings. The bottom wing comes as one piece, while the top comes in two halves which need to be glued. Although the manual suggests CA with kicker, I used UHU for all similar steps with great results.

Cutting the ailerons out of the wing cores.

Hinging the ailerons with Transpore tape.

Transpore and Blenderm tapes compared.

The Bulldog has four working ailerons, which makes it great for rolls. MS Composit cuts their wings such that the ailerons are built it - the foam itself is the hinge. I didn't care for this arrangement, as it makes the surfaces stiffer than necessary, and more likely to warp when moved. I decided to cut the ailerons free like most other foamies. I applied a small amount of UHU to the foam before using Transpore tape for the hinge. If you have Blenderm on hand, it will work at least as well if not better.

EPP wings have a natural tendency to flex, and like many foamies, these need to be stiffened. MS Composit has a very clever and inexpensive way of doing this. First you cut a slot 2-3 mm deep from wingtip to wingtip. Then you insert a length of string (included in the kit) into the slot, and soak it in thin CA. The string gets hard almost instantly and is quite effective in preventing flex. Many people choose to substitute carbon fiber instead, but it's not necessary.

Using string and CA to stiffen the wings.

The string is used on top and bottom, then trimmed.

The Depron tail is somewhat disappointing, being more fragile than the rest of the plane. I would have preferred EPP, or EPP covered with a plastic film, the way the ElectriFly Yak 55 does. As it is, the rudder and elevator both need to be cut out from their stabilizers and bevelled at 45 degrees before being hinged. I found the best way to do this was to make a 90 degree cut to separate the pieces, then hold the piece on an angle and sand it down to create the bevel.

The beveled edges on the rudder and vertical stabilizer.

I would not have cut the elevator backwards if the graphics had been face up.

Plenty of throw on the rudder.

At this point I have to confess to a building mistake which is entirely my fault. I happened to cut the elevator out with the graphics facing down. By not paying attention, I cut it the wrong way. That is, I made the stabilizer oversized and the control surface undersized. While it functions fine, a serious 3D pilot would no doubt find this setup lacking. The lesson is, pay attention: the edge with the notch is part of the elevator, and faces the rear of the plane.

The elevator slides into a slot in the fuselage and secures easily. However the vertical stab and rudder attach poorly. The stabilizer simply abuts the top of the fuselage and is glued there, which has no strength. A better design would have been one or two tabs on the stabilizer which would lock into holes in the top of the fuse. The rudder has a single hinge into the fuselage which is fine.

I used this stronger hinge to connect the rudder.

The assembled tail with the too-small elevator.

Things are starting to shape up.

Installing the servos takes some improvisation. If you're used to scratch building foamies, this will be second nature, but for everyone else it might be disconcerting. To start with, the manual uses one aileron servo for all four surfaces. I don't like the geometry of these setups, and wanted more torque, so I decided to use two Futaba S3110s for the ailerons with a Y cable.

This step is easier to do before attaching the bottom wing to the fuselage. The holes for the servos need to be cut out, with special care not to cut too deeply. You could also mount the servos on their sides if desired. I spaced them out as much as possible without adding extensions so that the force of the linkage would be closer to the center of the control surface. If you place the servos (and hence the control horn) too far inboard, the ailerons will bend excessively. Even with my setup I found the ailerons warp rather than staying flat while deflected. One solution is to add carbon fiber strips to the trailing edges.

I anchored the bottom wing with two carbon rods.

The Y cable to the aileron servos, with nice straight linkages.

The placement of the elevator and rudder servos is also up to you. I used the approximate locations suggested by the manual, choosing the height of each to get a straight shot to the control horn. One thing I didn't care for is the way the pushrods and their plastic tubes are supposed to be sunk into the fuselage. This bends them a fair amount and adds some friction. In the end I went with it, but standoffs would have worked better. On the upside, the pushrods come with z-bends already made, and adjustable pushrod keepers which make setting the linkages easy. I glued all four servos in place with a hot glue gun to make them easy to remove if needed.

Cutting a hole for one of the tail servos.

The servo lead from the other tail servo needs to come through the fuselage to reach the receiver.

The pushrods can be cut down once installed.

The tail control surfaces hook up in the standard way.

Attaching the wings is not hard but it is important to pay attention to the alignment. Again I used UHU plus a lot of weight to keep everything flat. The struts between the wings interfered a bit with the top ailerons but were easy to trim back. The linkages between the top and bottom ailerons are thin metal and tend to bend a bit. You may want to replace them with carbon rod.

Using lots of weight to glue the wings.

The stock connector between the top and bottom ailerons.

Installing the power system.

Close up of the power system.

All the electronics mounted on one side.

Just one servo and the battery on the other.

For power I used the BP Hobbies 2217-9 brushless motor and the ElectriFly SS-25 ESC, which I happened to have on hand. The plastic motor mount does not secure well to the foam - you may need to experiment to make sure it is retained well. This motor is a bit on the heavy side at 2.6 ounces. I put the ESC and receiver on the opposite side to offset the battery, although lateral CG still proved to be a problem. Use the flattest three cell LiPo you can to prevent unwanted roll towards the battery, and attach it with a velcro strip so you can adjust the longitudinal CG (front to back).

Flying

Since I fly off grass, I always hand launch the Bulldog. There's room to grab the fuselage in front of the top wing, but be careful of the prop. I use an APC 10x4.7 SF with good results. The BP motor has plenty of power to climb out with a gentle toss.

For the maiden I used a 3S 1500 mAh pack, which worked but felt heavy in the air. A 1250 mAh LiPo felt better, and convinced me to order some 1000 mAh packs, which help offset the weight of the motor. With these smallest packs I set my timer at 8.5 minutes and never use more than 80% of the capacity. With very aggressive flying 7.5 minutes is still doable.

The Bulldog ready to hand launch.

Doing a harrier around the field.

Looks pretty...

... and flies great.

Flying the Bulldog makes the lousy hardware, upgrades, and modifications worthwhile. It's stable and floats very well at slow speeds. The roll rate is great as you would expect from four ailerons, and there's plenty of rudder available. Although my setup will hover and perform outside loops, it doesn't punch out strongly the way a 3D plane should. I'd suggest a lighter motor and leaving off the landing gear if you want that kind of performance.

Landings are pretty easy. I tend to keep a little power on, but you could glide in deadstick too. As I mentioned earlier, the stock landing gear is positioned too far back, and will cause the plane to nose over. You may be able to prevent this with full up elevator, but I just bent the gear forwards.

Long Term Report

I've been flying the Bulldog for four months now, long enough to get a good feeling for its durability. Overall it's pretty tough. Those nose over landings never did any harm, and the wings can handle an impact well. I don't hesitate to fly it on windy days, unlike my wood planes. The Depron tail surfaces can break though, especially the thinnest part of the rudder, next to the control horn.

Look how the motor's torque twisted the wires!

Another shot of the broken nose.

Notice the scotch tape on the Depron rudder.

Both chopsticks were inserted this far.

The one notable exception to this toughness is the nose. When built stock, it is almost guaranteed to snap in a crash. The simplest solution is to use some wood chopsticks or BBQ skewers and run them through the motor mount, down through the nose. Try to get it past the plastic landing gear mount to make the entire nose rigid. A side benefit of using chopsticks is that the motor mount will glue onto them in addition to the foam, for a stronger bond.

Conclusion

The Pitts S2 Bulldog is a lot of fun and a good flier. It's a bit expensive for what you get, and some of the hardware is junk, but it can be turned into a great plane with a little time and effort.

Be sure to check out this excellent build thread on RCGroups for additional upgrades and changes you can make, like building EPP tail surfaces.