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JK Aerotech Big T

Due to its "bounceable" and generally forgiving nature, and its capability to be set up with three or four channels, the Big-T would make a fine primary trainer or a fun sport plane. Capable of 15-minute training flights with the proper configuration, it provides more than plenty of stick time for most students. Set up with a more powerful motor, it can also be a thrilling sporty platform.

  • Wingspan: 72 inches (183 cm)
  • Wing Area: ~810 square inches (52.3 sq. dm)
  • Length: 47 1/4 inches (120 cm)
  • Height of prop shaft to ground: 7 3/4 inches (19.7 cm)
  • Weight: 83.6 oz. (2.38 kg) initially, 86.4 ounces (2.45 kg) with aileron wing
  • Wing Loading: 14.9 oz./sq. ft (45 g/sq. dm.)
  • Power Systems Used (brushed):
    • Jamara Venti 600, 3.5:1 Master Airscrew gearbox, MA-E 10X7, 11X7 and 12X8 props
    • Kyosho Magnetic Mayhem, 4.3:1 MEC Superbox, APC 14X10 thin e-prop
    • Kyosho EndoPlasma, 4.6:1 MEC Superbox, APC 12X6 thin e-prop
    • Trinity Maxx Mild, 3.3:1 MEC Superbox, MA-E 13X8 prop (this combination only lasted three runs)
  • ESC:
    • Kontronik Sun 4001 controller (w/brushed motors)
    • MGM ComPro TMM-40e-3ph controller (w/brushless motors)
  • Power Systems Used (brushless): Pelikan/Model Motors AXI 2820/10, APC 12X6 thin-E prop (direct drive)
  • Battery Pack: 10 cell packs of P3000 NiMH cells in MEC Power Tubes
  • Available from: JK Aerotech
Are you someone who wants to learn how to fly R/C with electric power, but isn't excited about the small size, lack of usable landing gear, and calm weather needed for most currently available e-trainers? Maybe you're looking for a knockabout sport/utility plane the size of the usual glow-powered "forty-sized trainer" for shooting touch-and-goes, taking aerial pictures, float flying, etc. Perhaps you read about the durability of "foamie" construction, but were waiting for something bigger than a Speed 400 sized plane to come along. On the other hand, maybe you have a JK Aerotech T-52 and want to move up to a bigger and more capable plane that is just as rugged and just as easy to build.
If any of these thoughts have you nodding "yes", then the JK Aerotech Big T is worth serious consideration. Drawing on their experience in making foam and Coroplast glow-powered combat planes, and both glow and electric experience with the tough little T-52 trainer, Jim and Ken Dickman have put together a 6-foot wingspan cabin-plane that can be all of these things. It is three-channel basic trainer when built completely stock. Set up this way, it can give 10 to 15 minute flights, the ability to take off from a grass runway, and generally be flown like a great big park flyer on a very inexpensive 10-cell power system built around a geared S600-type motor. Put more power into it and add ailerons, and then you have a multi-role sport/utility plane that is incredibly rugged and surprisingly aerobatic. Perish the thought, but it can even be had in a version set up for a .25 or larger glow engine, but we won't admit to that here, will we?)
Big T and T-52
In the world of mostly foam airframes, the Big T lives up to the name. Its wing spans 72 inches (1.8m), has over 800 square inches (51.6 sq. dm) of thick, high-lift wing area, and weighs a little over 5 pounds with a 10-cell power system. It has a substantial aluminum main gear and 2 3/4 inch wheels, making operation off hard-surfaced or grass runways quite feasible. This is not another little S400 foamie by any stretch. Moreover, it's filled with all sorts of clever engineering features that belie Jim and Ken's long practical experience with making rugged airframes out of pink foam (EPS), plastic corrugated signboard material, strapping tape, packing tape, and a few odd bits of wood. One of those clever engineering bits is a way to fold the 6-foot wing in half for storage or to transport!

What you get

The UPS man brought a big white box. The boxed used for the Big T measures one foot square and three feet long (30X 30 X 90 cm). Inside are two, three-foot long pink foam wing panels in their core beds, a pink foam fuselage, four 3/16 inch (5mm) square spruce spars, Coroplast tail surfaces, wing joiners, and fuselage doublers. Also included are a few plywood parts, a preformed aluminum main landing gear, wheels, pushrods, miscellaneous hardware bits, and two rolls of colored packing tape. Additionally, there are 18 pages of building instructions and some diagrams. Jim and Ken bundled it all so that things are secure and wouldn't be damaged during shipping.
The spar slots are precut in the wings, and the fuselage is already cut for a 10 to 14 cell battery pack, as well as the landing gear mounting plate. (The glow version has a precut tank compartment rather than a battery compartment.) The Coroplast tail parts, fuselage doublers, and the upper wing joiner are die-cut. However, they need a bit of trimming to free them from the sheets.
A complete hardware package is included. It contains a package of DuBro Lazer Rods, a pair of 2 3/4 inch foam wheels, a 3/4 inch tail wheel, a substantial aluminum preformed main gear (the same one used on the SIG Four-Star Forty), control horns, wire to make the tail wheel strut, axles, wheel collars, and so forth. The only things you need to supply to complete the airframe are a roll of strapping tape, some spray adhesive such as 3M77, and either epoxy, white glue, or polyurethane glue for some wood-to-foam joints, such as the firewall and wing spar installation. (Check with JK Aerotech about using the new 3M77 formula that contains acetone. They will be using 3M78 insulation adhesive in the future.)

What You Need

You need to add a three or four channel radio system. Full sized servos and receiver will be OK, but as always, lighter is better. I used a Hitec 555 receiver, and servos for rudder and elevator that are comparable to Hitec HS-85s. For the aileron wing, I used two Cirrus CS-25s, one driving each aileron. (I will have much more on that later.)
Of course, a power system is also needed. JK Aerotech sells an inexpensive power system that includes a Jamara Venti 600 motor, a Master Airscrew 3.5:1 gearbox, an Ernst four stroke engine glow mount, a pair of Maxx Products clamshell motor mounts, a Kontronik Sun 3000 or MGM ComPro SMM-35 speed control, a 10-cell Panasonic P-1400 battery pack, and a Master Airscrew 10X7 plastic electric prop. This combination is probably the minimum you'd want to use on the Big T, since it only puts out about 170 Watts and doesn't give much power margin on windy days. I'd suggest either a bit more prop or a couple more cells, since if you put 225 Watts or more into the Big T, its performance will range from relaxing to quite sporty. Later in this article, I will discuss some of my power system experiments and results.
Update: JK Aerotech tells me they will be supplying the MA 11X7 prop in future electric packages. I've flown this combination, and the 11x7 prop provides a noticeable improvement over the 10X7 prop.

Building It

The most current version of the instructions for building the airplane, complete with illustrations that aren't included in the printed copy supplied in the kit, is available on the JK Aerotech web site. From the menu at the top of the page, pick "Instructions and Tech Stuff", and then scroll down to near the bottom of the resulting page to "CONSTRUCTION: The Big T - Building the Big T". (The direct link is http://www.jkaerotech.com/BigTbs.htm.) If you're on a dial-up connection, please be patient, as there are 82 pictures on that page as of this writing), so it can take a while to load.
Since the instructions are so complete, and the pictures on the web site are clear, I will not attempt to restate them here, but rather just refer you to them. Instead, I will concentrate on two things. First, I'll go into a few small things that I ran into while building the airplane that I can clarify or improve upon based on my experience. Second, I'll cover how I converted this three-channel airplane to four channels by adding barn-door type ailerons.

General Wing Notes

On all three wings, I chose to install the spars using Elmer's ProBond Polyurethane glue rather than epoxy, mainly because I was curious about the glue, never having used it before. I see now that JK Aerotech is now recommending this as well. I have been pleased with the results, but using it does present a challenge or two.
Since ProBond foams and expands as it cures, in order for the 3/16 square spruce spars to be flush when the glue has fully cured, the grooves for the spars need to be just a little deeper than the precut depth. A small scrap of spar stock can be dragged through the groove with a bit of pressure to make them just a bit deeper. In addition, pressure has to be kept on the spars while they cure. I used the wing core beds with their projecting bumps that fit into the precut spar notches to do this, along with lots of battery packs that served as weights. A layer of wax paper was placed between the wing surfaces and the core beds to help with the removal process after the glue had cured overnight. Even so, there will be some glue that will have to be removed from the wing surfaces, either with a coarse sanding block or a Stanley Surform pocket plane using a very light touch. It also helps to use less of this glue than you may think. I wound up with the spars standing a tiny bit higher than the surface of the wings on the first set, but this small amount doesn't seem to perturb the flying qualities. By the time you're done building the wing, there are layers of strapping tape and packing tape over the spars anyway, which smoothes out the bumps a bit.
Speaking of strapping tape, I used two layers of tape over the spars rather than the single layer called for in the instructions. I applied one layer of 2-inch wide strapping tape and one layer of 3/4-inch tape. I did this because I knew I was likely to be putting more power into the plane than the Dickmans had used. I also knew that the plane wasn't going to be staying in upright flight the whole time I flew it.
The other detail change I made was that I used the Surform plane to bevel the wing tips, rather than rounding them as suggested in the instructions. I like the look of beveled tips better, and I expected them to be easier to neatly cover with tape. By beveling the wing tips at 45 degrees or so (I just eyeballed it), the planform of the tips ended up with a pleasant rounding with no further work.

Fuselage and Tail Group Notes

When building the fuselage and the tail section, I discovered and did only a few small things differently than indicated in the directions.
First, there is a slot in the fuselage between the battery bay and the notch where the landing gear mount plate goes. That mainly was there to let JKA's CNC-controlled hot wire cutter get into the battery bay. They suggest ignoring it, as it will be trapped between the Coroplast battery bay floor, the plywood landing gear mounting plate, and some strapping tape. I just couldn't leave it open, so I filled it with some appropriately thick balsa that I glued in with ProBond polyurethane glue. I also used ProBond to glue on the firewall, rather than the suggested adhesives.
Speaking of the battery bay, I also discovered after I had hinged the battery door that the opening was just a little bit too small for an MEC Power Tube battery pack. I wound up extending the sides down two more flutes in the Coroplast doublers and cutting a second hinge two flutes below the first. If I were to do it again, I'd just cut one hinge two flutes lower than suggested by the precut door outline. It is also helpful to mask the inside of the battery bay door and the bay when spraying the 3M77 for the installation of the fuselage doublers.
By the way, this battery door doesn't need a latch to keep it closed. Just push it in even with the side of the fuselage. A little pull-open tab made from a bit of tape is handy to have though. If the battery is retained with a couple of patches of Velcro on the Coroplast bay floor, then there is no danger of the battery being tossed out through the door, even with some fairly lively maneuvering.
Many have suggested cutting lightening holes in the Coroplast tail surfaces, but based on my experience with the T-52, the amount of weight saved by doing this is very small. Most if not all of the weight will be gained back by having to cover the tail surfaces with tape. On the Big T, I chose to leave them uncovered. However, I couldn't stand to leave the raw cut edges exposed as JK Aerotech does, so I wrapped white packing tape around the edges of the tail surfaces, as you can see in one picture. You have to get quite close to the plane to see the tape. I suppose if your chosen color scheme doesn't work with a white tail section, then you will have to cover the tail anyway.
I also used two 10-24 nylon bolts tapped into ply mounting plate to attach the main gear, rather than the three smaller steel bolts and blind nuts supplied. Even though this plate is cleverly just taped in place with strapping tape (yes, really!) so that it can pull away on a very heavy landing rather than rip up the fuselage, I'd still rather replace a couple of nylon bolts than have to re-install the plate. So far, I have not had to test this.
I also made another tiny change. Instead of using the supplied tail wheel, I used an 11/2 inch Dave Brown Lite Flite wheel. I knew I was going to be operating the Big T off thick grass, and I thought that the supplied wheel would be a problem. By the way, don't be alarmed that the tail wheel strut, which you just bend up from 1/16 inch music wire, is simply bonded to the rudder. The whole fin/rudder/tail wheel assembly is flexible enough that I have not had any issues with the rudder servo taking the loads from the tail wheel. If I flew the Big T off pavement where the tail wheel could grab more solidly, this might be a concern. Even so, the tail wheel isn't on the ground very long anyway.

Three Channels or Four?

As designed by Jim and Ken, the Big T is intended to be a Rudder/Elevator/Throttle three channel trainer primary. Fairly early in the construction, you have to decide whether you want to build it this way or add ailerons and make it a four-channel plane. Early in the wing construction, you sand the wing roots to set the dihedral angle. At this point, you should decide which way you're going to go.
As it turned out, in the course of working on this review I made three wings for my Big T. Two were for three-channel flying, and one with substantial barn-door ailerons was for four-channel flying. I've flown the plane quite a bit in both three and four channel configurations. As I mentioned in the introduction, with moderate power and on three channels, it flies like a great big park flyer and is slow and very easy to fly. Set up this way, it's good for lazily shooting touch-and-goes. It would make a great basic trainer for someone wanting to learn R/E/T controls. With a little more power, around 250 to 300 Watts, it is capable of just about anything you'd expect to be able to do with three channels including slow rolls, loops, a little inverted flight, and combinations of these maneuvers.
With ailerons come much improved rolling capability, more precision, and the ability to operate much more easily in crosswind conditions. It can do very nice sideslips on landing approach. I enjoy flying it in this configuration much more, even though I've been a longtime three-channel flyer. I also really like the simplicity of not having to worry about rigging ailerons or plugging them in every time I put the plane together. Take the power up to 400 Watts, and the plane is amazingly aerobatic, far more than I'm sure the Dickmans had in mind, and will do just about anything my Kadet LT-25 will do with similar power, except 1/2 outside loops. I'm sure an aileron-equipped Big T will make a good basic full-house trainer on anything from about 225 Watts up as well.

Three Channel Building Notes

In order to review an airplane kit properly, one must not make aerodynamic changes to it, or if you do, you can't make those changes and then complain that the airplane doesn't fly right. That said, I would now explain why I built two three-channel wings.
Even before I started to build it, I was suspicious that the wing didn't have enough dihedral for three-channel flying. I looked at the instructions and calculated the dihedral angle that resulted from setting it as indicated in step seven in the instructions. The dihedral is only a little more than two degrees (per panel), and most of the three channel planes I've had over the years have quite a bit more than that. However, a couple of other planes, such as the Modelair-Tech Dimwatt, don't have much dihedral and handle very well on three channels. Since I'm just a mechanical engineer, not an aerodynamics expert, I figured the thing to do was follow the instructions. Besides, as I said, I firmly believe that any proper review must at least start there.
However, it was apparent on the first flight that my suspicions were correct. While it was quite flyable built as directed and had no nasty traits, turning response was sluggish, and under gusty conditions, this made things challenging. Instead of a nice coordinated turn resulting from rudder plus a little elevator input, it would yaw first, hesitate, then bank and turn. One way to improve turning response is to make the rudder bigger or increase its throw. However, I could see that there was enough rudder, as the plane responded immediately to the rudder with a strong yaw. It was the rest of the bank and turn that took some time to happen. This told me the thing to do was increase the dihedral, not mess with the rudder.
Therefore, shortly after the first couple of flights, I sent a note to JK Aerotech asking for another wing set so I could test my theory. Due to the clever way the dihedral is set, by simply blocking up the inboard end of the wing panel and sanding the root, no kit parts needed to be changed to change the dihedral angle. Therefore, for the second set of three-channel wings, instead of propping the root end of the wing up by setting it in the cradle section on a 2X4, I simply stacked two of them. (A 2X4, for our international readers, is a piece of house construction lumber that is supposedly two inches by four inches in cross section when milled from freshly cut logs. In actuality, they are typically between 1 1/2 and 1 3/4 inches thick when you get them.) Stacking two of them gave about 3 1/2 inches (about 4.5 degrees) of dihedral in each 36-inch wing panel.
I told my wife the morning I test flew the second three channel wing that I'd probably know in the first circuit of the field whether the experiment was a success or not. As it turned out, it didn't even take that long. In the first turn away from the runway after takeoff, I knew the plane's handling was much better. Not only did it now feel like a three channel airplane should (at least to me) but now it would roll. Before I increased the dihedral, I could, with difficulty, get it to begin a roll. HOwever, it would always stop inverted and never finish, even with 400W of power.
If you build the Big T in the three channel configuration, I strongly suggest that you block the wing roots up on two 2X4 boards rather than one when you get to step seven in the instructions. If you do, you will have a stable, yet responsive three-channel plane.
Two views of the Big T with the final three-channel wing

Adding Ailerons

Going to four channels by adding ailerons turns the Big T into a good sport/utility flyer. While I haven't yet fitted it for either float flying or night flying, I am sure it will work well in both roles. At some point, I will find out.
For the aileron wing, I used half of the originally recommended dihedral. To do that, I used a 1X4 rather than a 2X4 to support the root end of each wing panel while sanding in the dihedral angle. This results in a little over one degree of dihedral, which is just enough to keep the wing from looking saggy. For the ailerons, I chose to use the "barn-door" type and drive each aileron with a separate servo. In order to preserve the ability to fold the wing (it folds so that the bottoms of the two panels come together), I installed the servos and the control horns on the top of the wing rather than underneath.
Two views of the Big T with the aileron wing
The ailerons were simply cut from the foam wing, faced at the hinge with strapping tape, and then covered with packing tape just like the rest of the wing. Plywood control horns were epoxied into slots in the ailerons, and the servos buried in the wing near the spar using the same approach as JKA recommends for installing the elevator and rudder servos in the fuselage. I made custom servo extensions from some FMA Direct "Powerline" 22-gauge wire and laid them in grooves that I cut with my Dremel tool parallel to the spar. I routed them through the grooves in the wing root and down through the lower joiner, and then soldered them together with a short length of wire to make a "Y" harness.
To get some aileron differential, the horns on the servos were angled aft about 45 degrees. This gives almost enough differential to avoid adverse yaw. A touch of rudder is still needed to make nice smoothly coordinated turns.
Here are the details. The ailerons are 2 1/2 inches wide. They start 18 inches from the center (halfway out along the wing) and go out to the tip. I simply cut them from the pink foam wing with a sharp knife. Since I planned to top-hinge them with tape, once they were cut free, I used the Surform pocket plane to bevel their leading edges to allow the downward motion of the hinged ailerons. I also ran a second strapping tape "spar" along the wing, centered over the trailing edge of the aileron cutout. This allowed the cutout to be reinforced. I also wrapped the leading edges of the ailerons with strapping tape for reinforcement.
Aileron cutout and servo pocket roughed out Beveled wingtip and underside of aileron showing bevel on the leading edge of the aileron

Second strapping tape "spar" reinforcing aileron cutout Strapping tape on LE of aileron
The aileron servos were located near the wing spar where there was plenty of depth. They were placed in pockets in the same fashion that the elevator and rudder servos were mounted in the fuselage, except that the pockets for the aileron servos were deep enough to sink the servos completely into the wing. Clearance for the servo mounting ears and the control arm was also provided. I then used a ball-nosed cutter on my Dremel Mini-Mite with a light touch to cut a groove for the aileron wiring a short distance behind and parallel to the top spar. This groove was the conduit for the wiring from the servos to the center of the wing. I had to slice the strapping tape that is applied over the wood spars to allow the wiring in to the groove.
Aileron servo in pocket with lead in wiring groove
Once the servos and wiring were in place, I covered the wing and the ailerons with the colored packing tape using the same techniques that are used to cover the three-channel wing. The wings were joined according to the instructions; the only modification was to make a hole in the lower joiner at the hinge point for the wiring from the two aileron servos. As I mentioned above, these were then joined into a short Y-harness.
The ailerons are top-hinged by first laying the aileron top on the wing top with the LE (leading edge) of the aileron and the TE (trailing edge) of the cutout aligned. I then put on a layer of matching colored packing tape that formed the "inside" of the hinge. Once this was in place, the ailerons were flexed to the maximum downward deflection, and a layer of tape was put on the top from the wing to the aileron to form the "outside" of the hinge. The control horns were laser cut 1/16 ply horns I had from a prior project. Once the correct rotation of the aileron servos was determined, the horns were epoxied in slits cut in the ailerons, and aligned with the pushrod paths from the servo arms to the ailerons. The pushrods are made of 1/16-inch music wire with a Z-bend in the aileron end, and a solder-on threaded coupler and a Goldberg mini-snap link at the aileron horn end. I have recently had to reinstall one of the horns due to "hangar rash", so I used the polyurethane glue, which worked well.
Of course, once the wiring was joined with a short lead ending in the receiver plug at the wing center section and the horns and pushrods installed, then the individual ailerons were adjusted using a combination of the splines on the servo arm attachments to the servo output shaft and adjustments of the clevises. Pieces of matching packing tape form "hatches" over the ailerons, with slots left for the pushrods to exit. This completes the installation. All of this sounds more complicated to do than it actually was.
All three wings were dressed up with graphics done by Greg Judy at Vinyl Graphics by Greg. He found some interesting silver vinyl that looks like the sort of metal you see on utility boxes and such. They added a nice finishing touch to the airplane.

Flying It, and Power System Thoughts and Recommendations

I made the first flight of my Big T on the stock JK Aerotech power combination, except that I used one of my 10-cell P3000 NiMH packs instead of the 1400 NiCad batteries. I was pleasantly surprised that the plane took off from the thick damp grass at my club field that blustery January morning, though it did take awhile. I even found it would loop from a shallow dive with a relatively low powered system (only 33 W/lb. or 73W/kg). However, as I said, the recommended power system was pretty marginal in any wind, especially in gusts or while turning away from the wind. I recommend increasing the propeller size on the JKA combo to an 11X7, or even a 12X8 MA-E, a 12X8, or 13X6.5 thin APC e-prop. Even with the 13X6.5 APC e-prop, the motor is well within its amp limits on 10-cells (about 23A). Alternatively, you could run the stock motor/gearbox/prop combination on 12 cells.
Jamara motor on stock mounts

With one of the larger props, the stock power system will provide enough power for short grass-field takeoffs, and easy loops from level flight (especially with the 12X8). Additionally, with the correct dihedral or ailerons, the Big T will perform rolls. Shooting wheel-landing "touch and goes" with the Big T is a pleasure. It takes surprisingly little power to keep it in the air, so you have to be sure and reduce power enough to establish a solid descent. Then, if you want, it will roll along the ground for a long way, tail high. With the slightest touch of backpressure on the elevator, it will lift off and climb away again. Only if you drag out the ground roll on thick grass does any tendency toward ground looping appear.
With more power than the stock system, the airplane's capabilities increase dramatically. With about 400W input, a large number of rolling and inside looping maneuvers are possible, as well as sustained inverted flight. Inverted flight must be entered at good speed, though, and are better if entered from a half roll than a half loop. It then only takes a small amount of forward stick to maintain altitude, and it can even climb inverted. If it gets too slow, it needs full forward stick, and still it will sink.
On 400W, after takeoff runs of three to four airplane lengths (less with any headwind at all), climbs are very fast. Performance with this much power is solidly in the sport plane range, yet with some left thumb discipline, eight to ten minute flights are the norm on 3000mAh NiMH packs.
So far, I have gotten this kind of power with two different approaches. I used a Kyosho EndoPlasma buggy motor, geared 4.6:1 (as used in the E3D), and the new Pelikan/Model Motors AXI 2820/10 brushless "outrunner" from Hobby Lobby on direct drive. As it turns out, I found within each motor's limits, the APC 12X6 e-prop to be about the best match to the airplane. Of the two, I much prefer the AXI motor. With that one, there is no brush dust all over the inside of the nose of the airplane, and there's no gearbox noise. (There was quite a bit of dust after the few EndoPlasma-powered flights.) There is also the cool factor of the rotating can of the motor.
The only downside so far is that mounting the AXI is a bit of a challenge. Since it must be mounted from the front, it can't just be clamped into the Maxx clamshells as all the other motors I tried. After three tries, I wound up putting an "extension" plate of 1/4 inch plywood on top of the Ernst glow-engine mount. On top of that, I mounted an Aeronaut L-shaped mount intended for Speed 600 motors. This combination has proven to be solid and reliable.
However you choose to power it, on 200 to 250W it is a good sedate trainer, and on 400W or more it is lots of fun. Still in the future for mine is the possibility of a 550W 14-cell power system. I'll try to have an update posted if I do that.
I have managed to test the durability of the plane once. The current Boeing Hawks flying site has a row of tall, narrow trees that run parallel to the runway, about 30 feet away. To fly there, you stand between the runway and this row of trees. On days when the wind is out of the south, it tries to blow your airplane toward those trees. On one occasion, I was making a making a sideslipping approach over the runway, and between the wind and getting my left thumb confused, the plane wound up in a tree about 50 or 60 feet up. A wind gust immediately blew it out, and it landed nose down at the base of the tree. After a quick check, and after replacing of a couple of rubber bands, I was able to fly the Big T for the rest of that battery charge!
It is also so nice not to have to worry too much about bumping into a doorframe getting the plane in and out of the house and the car, since the springy Coroplast tail surfaces just flex and bounce back. (Coroplast is extruded from springy polypropylene plastic.)

A Balance Point Revelation

For the first sixty or so flights, I'd been flying the plane with the balance point and control throws as specified by Jim and Ken, and having a good time with the airplane. It is necessary for me to have the battery all the way forward in the battery bay to get the plane to balance at the recommended point. I had even suggested to the Dickmans that they might want to change the fuselage and the side doublers to move the battery bay forward an inch or so to make it easier to get the balance point at the correct location.
Set up this way, it feels very solid in flight, and is almost impossible to provoke into more than a very tiny stall. You can fly along at low power, with the elevator stick fully back, and the nose will just bob up and down with the airplane barely dropping its own length after these tiny stalls, with no tendency to fall off in either direction. This is perfect for a primary trainer, as it is nearly impossible to get too slow and have the plane snap out of a tight turn. However, I found it very difficult to land smoothly, especially in a three-point attitude, without bouncing repeatedly. I couldn't seem to find a combination of power and elevator setting that would result in a smooth, bounce-free touchdown with any consistency.
While at the spring Chilliwack, British Columbia electric fly-in, I asked Ivan Pettigrew if he'd like to fly it, since he (along with many others) had remarked about how well the plane flew. He pronounced it "very safe" as he put it through its paces. He then brought the Big T in for a bouncy landing, just as I had often done. He remarked that he couldn't land it very well (even though he's one of the masters of model flying that I know). After a short discussion, Ivan diagnosed the problem. He said the balance point was too far forward, or there was too little elevator throw, making it impossible to bring the plane all the way into a proper three-point attitude before running out of elevator authority. Therefore, when I went back out with the next charged battery, I put it in about halfway back in the battery bay. This time when the plane flew, it seemed pretty much the same in the air, but landing it was easier, though still bouncy. Finally, I moved it as far back as it would go (about 2.5 inches altogether) and flew it again. The plane was noticeably lighter on the controls, and this time doing a three-point landing was easy! I shot several touch and goes, and it hardly bounced at all. I was grinning from ear to ear.
Ivan then flew it some more, and put it through an balance test that he does based on behavior in a loop. He said that the balance point could even come back a bit more, but that it was fine the way it was. He also took it up and did about a 1 1/2-turn spin with it. When the balance point was forward, it was impossible to get it to spin.
Set up with the balance point 4 1/4 inches from the leading edge of the wing (3/4 of an inch behind the balance point suggested), it is a delightful sport flyer, but even more so that it was before. It now can be provoked to stall and possibly drop into a spin. (Ivan has spun it, but I have not yet.) If you're not going to be using it as a primary trainer, I really recommend moving the balance point aft and increasing the elevator throw slightly. I moved the elevator pushrod down one hole on the control horn from the initial location. Now it is just possible to do a full-stall landing. If you're beyond the primary trainer stage, and you set up your Big T this way, I predict you'll really like the results.


I like the Big T a great deal. It is getting as much airtime as I can work in, and it goes with me almost every time I go to a club field. With 400W of power and ailerons, it is capable of doing most of the inside or rolling maneuvers that I can do. Due to its rugged and flexible construction, I'm not as afraid of trying new things with it as I am with my other 10-cell plane, the LT-25. While the Big T doesn't quite have all the abilities of the LT-25, and is a bit more challenging at low ground speeds because of its shorter tail moment, it also has a certain charm about it that I can't quite explain. It even looks nice, vaguely suggesting a scale Stinson in the air.
I also think that due to its "bounceable" and generally forgiving nature, especially with the balance point at the location suggested by JK Aerotech, with anything over 220W or so of power and an appropriate propeller choice, it would make a fine primary trainer. This would be true whether you prefer to learn using three or four channels. It should be able to do 15-minute training flights on P3000s and the JKA electric power combo (with the prop changes I suggest above). That's plenty of time per flight for most students. A great club training setup would include three P3000 packs, two battery chargers, and a field battery. With a combination like that, you could just fly and fly and fly, stopping only to recharge the transmitter. By the way, this power level can be achieved by putting a 12X8 or 13X6.5 APC e-prop on the inexpensive JKA electric combo power system.
It's also a good value. The kit costs a bit more than some wood trainers of similar size, but the Big T kit includes both the wheels and covering (two rolls of packing tape), which most other kits do not include. I have all sorts of ideas for further experimentation with mine, including getting it on floats, adding even more power, rigging it for night flying and aerial photography, and perhaps reworking the first wing with ailerons and flaps. I'm sure it will be doing speed control test bed duty for a long time to support my Controlling Interest column. As I said at the beginning, if you're looking for a durable sport plane or a bigger-than-S400 trainer, the Big T is worth a serious look.
photo by Ken Mizell

From the left, my Sig Kadet LT-25, T-52, and the Big T with the three-channel wing


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