GREAT PLANES PERFECT TRAINER 40
PRODUCT TEST REPORT
by Jerry Festa
Great Planes refuses to sit by and watch the competition get the upper hand. They therefore took their very popular PT-40 trainer (yes, the same one which won Model of the Year some years back) and improved it! They borrowed some ideas from the PT-60 (like the interlocking I-Beam Wing construction for the wing) and incorporated them into this new kit.
In discussion with Gordon (and he was carrying the bigger stick), we came to the conclusion this plane should be built for a typical novice (flying skill-wise) and evaluate those "Perfect Trainer" flight performance claims made by the manufacturer. So of the two wing configuration options, A for the beginner, or B (with ailerons and less dihedral) for more aerobatic flight, I went with wing A and the optional ailerons.
The manual strongly suggests this wing be used without ailerons for the first-time pilot, and I agree. They also suggest the ailerons should be attached at this time, but locked in neutral for the first flights. Then, when desired, the additional servo can be added and ailerons activated. Again I agreed. I also opted for the rubber band method of attaching the wing, as opposed to the bolt-on version, as most trainers are sooner or later going to ding a wing tip on landing, and the damage, especially to the fuselage, should be less with the rubber band attachment method. Parts and instructions are included for both methods of securing the wing, however.
Construction: The tail feathers are 1/4" sheet balsa glued together to form the shape indicated on the plans. Next, the fuselage is built, and without ever placing it on the plans, a straight fuselage was constructed! This was mostly due to the number of interlocking parts that assured a straight piece of construction. Almost all fuselage parts were die-cut, and only a light sanding was needed to get all parts to line up and fit exceptionally well. With this and the instant glue working for me, the fuselage was constructed in a single evening. Novice builders may take a bit longer, but the parts count is low, and the fit is good, so there's no need to rush it!
The wing was next and this took the most time, mostly due to the strong, warp free construction that resulted from the above average parts count. Part of the wing is sheeted, and both top and bottom leading edges, and an additional spar on the bottom is used. The I-Bema method of framing up the wing has all the ribs glued to both top and bottom spars along with the leading and trailing edges. One unique feature of building the wing is building in washout. Two plywood jigs are temporarily fixed to the tip rib, and then all the wing sheeting is done, resulting in permanent washout.
It was here that I came across something I considered unusual. The jig's relation to the tip rib is logical, but one can see where a rank beginner might still position it backwards (the round part goes under the leading edge, and the square part under the trailing edge), so if I could be so bold as to make a suggestion to Great Planes, it would be to provide an illustration showing the correct position.
Because of all the built-in washout, no twisting of the wing would be needed while Monokoting. And with this amount of washout, stalls are going to be very gentle, if at all! For those beginners wondering what "washout" is, I'd like to oversimplify the explanation, and just say that this is the raising (or twisting of) the trailing edge of the wing near the tip, in respect to the leading edge. This results in the inner part (root section) of the wing stalling sooner than the tips, which keep flying longer. If there isn't enough airspeed, the nose on any airplane will drop (not a good thing on landings) but without general washout, this is both delayed and softened, because the wing tips keep generating lift even when the root section has stalled (too much angle of attack with too little airspeed). This is especially nice for your first landings (or controlled crashes, as my instructor used to say). If a stall does occur, the airplane will gently drop its nose and quickly recover. So in a trainer, washout is a good thing to have.
Overall, construction of the PT-40 involves nothing weird or difficult. The great instruction manual is loaded with pictures and drawings, and the two sheets of full size plans will result in a well built model. The instructions assume the builder is a first timer, and indicates not only which parts to glue and when, but what kind of glue to use on each. Many helpful hints are included throughout the booklet, too. If one can read and follow directions, no construction problems should occur with the PT-40.
My PT-40 MKII was covered in MonoKote, and all control surfaces were hinged with the supplied CA-type hinges. The SuperTigre 40 was removed from another model (a Great Planes Easy Fly 40), and bolted in place with very little trimming of the fuselage required.
The music wire landing gear legs may cause some concern for beginners. The supplied 3/16" landing gear is needed for those bouncy landings beginners have been known for, but few wheels come with axle holes that size. This requires the builder to drill out the standard 5/32" holes to accept the larger wires. But when it comes to the question of doing a little drilling in order to have more robust landing gear, I vote in favor of the stouter landing gear.
The servo tray slid in right on target, and with the battery tucked under the tank, the plane balanced slightly nose heavy, which is great for the initial test flights. Radio installation was easy, as all the pre-cut pushrod holes were "right on the money". With a wing loading of just over 19 oz.sq.ft., I anticipated some easy flying!
Test Flights: The day of the first flight was a beautiful day. There was a slight breeze, a clear sky, and no one else at the flying site! After my usual range checking procedure and a thorough last minute pre-flight inspection of all the controls and connections, the ST-40 started easily, and I prepared for some taxi testing. Except the airplane wouldn't move. The grass was too tall! So I opted for hand launching vs. going home. It took only about two quick steps while the engine was at full throttle to get the feeling that the PT-40 wanted to fly. So with a gentle toss toward the horizon (never upward!), it was soon climbing like the proverbial homesick angel.
By applying some down elevator trim, the rate of climb was slowed, but the plane was still flying too fast for a trainer. I throttled back to about 1/4 throttle before the model began to descend, and a click or two of up elevator trim cured that. Now the PT-40 was flying like a trainer should—nice and slow!
The biggest surprise to me was the sensitivity of the ailerons and rudder at this speed ... this plane is sensitive! In fact, in making any turn, almost no stick movement was required! Despite having set all control surface throws according to the instructions, I suggest reducing them by 50% as long as you make your hinge joints tight like they're supposed to be. I can imagine that many beginners might leave a large gap, in which case more control surface movement would be required. So if using a radio with dual rates, set the low rate at 50% and the high rate at 100%, of the recommended amounts.
I was disappointed to find that my PT-40 would not recover from the dreaded "death spiral", which many beginners find themselves in all too often. If you happen to find yourself in this predicament, just let go of the sticks and watch what happens. The model should quit spiraling, and that's just what the PT-40 does. But the nose might still be pointed downward, which is also just what my PT-40 does. Some beginners will at this point have enough experience to pull back on the elevator stick and save the airplane. Some planes will actually recover all by themselves once the spiral stops, and if yours doesn't, try making it a bit more nose heavy. This is exactly what I'll have to do to my PT-40 before I use it to teach a beginner.
I feel that the PT-40 is as good or better than most other trainers available today, and will recommend it to any beginner as a first airplane and even as a first kit.
Landings that first day proved to be slow and very stable. Later on, while flying from a paved surface, I noted what I consider to be too much movement of the nosewheel, even though the control is set for minimum travel (innermost hole at the servo arm, and outermost hole on the nose wheel steering arm). In addition to seeing how it responds on the runway, my personal feeling is that if you can see the wheel turn from 10 or 12 feet away, then it's too much!
So is the PT-40 really a "Perfect Trainer"? No, I can't really call it perfect, but I do feel that it's about as close as you are going to get from a kit right now. Is it overpowered with a .40? I feel that it is, but then again, engines have throttles, so it doesn't have to be flown as fast as it will go. Does it stall? Yes, but practically any airplane can be made to stall. And the PT-40 does so only very gently, and with no tendency to snap when it does stall. Will it fly and land slowly and with good stability? Yes, and this is where it shines! Beginners need all the help they can get in those first few hours of flight training, and the PT-40's flight characteristics are exactly that, helpful. Would I recommend the kit to a beginning builder? Without a doubt, Yes. Can this plane do aerobatics? Even with the A-style wing, many maneuvers can be completed, such as rolls, hammerheads, and loops, but inverted flying is quite difficult with a wing having this much dihedral, because it really wants to fly right side up. On the other hand, once you can fly this bird inverted for extended periods, then you know you're ready for a more aerobatic design.
A perfect trainer, no, but a greater trainer, yes. Absolutely.
Reprinted with permission.
April 1997 R/C Report
Editor: Gordon Banks