DuraPlane DuraStik 40
Product Review

by Ed Hopkins

Name DURASTIK 40
Aircraft Type Sport ARC
Mfg. By Duraplane
Dist. By Great Planes Model Dist., P.O. Box 9021, Champaign, IL 61826-9021

Mfg. Sug. Retail Price $109.99
Available From Retail Outlets
Wingspan 56 Inches
Wing Chord 11 Inches
Total Wing Area 610 Sq. In.
Fuselage Length 48 Inches
Stabilizer Span 19 Inches
Total Stab Area 115 Sq. In.
Mfg. Rec. Engine Range .40 to .46 2-Stroke; .48 to .52 4-Stroke
Rec. Fuel Tank Size 8 Oz.
Rec. No. of Channels 4
Rec. Control Functions Rud., Elev., Throt., Ail.

Basic Materials Used In Construction
Fuselage PVC Pipe, Alum. Extruded Channel Stock
Wing Foam & Ply
Tail Surfaces Balsa

Building Instructions on Plan Sheets No Plans
Instruction Manual Yes (20 pages)
Construction Photos Yes

RCM PROTOTYPE
Radio Used Airtronics Infinity 600A, 4 Std. Servos
Engine Make & Disp. K & B Sportster 45, 10 x 6 APC Prop
Tank Size Used 8 Oz.
Weight, Ready to Fly 95 Oz. (5 Lbs. 15 Oz.)
Wing Loading 22.4 Oz./Sq. Ft.

SUMMARY
WE LIKED THE: Excellent instruction manual; ease of assembly; smooth flight characteristics.
WE DIDN'T LIKE THE: Aileron material "too light"; plastic wing cover did not fit wing shape well; lack of aft fuselage cover.

The DuraStik 40 is not an ARF, nor is it a built-up kit. Strictly speaking, I suppose the DuraStik 40 is really an Almost-Ready-to-Cover sport aircraft, and through an unusual combination of materials and construction techniques, it has an assembly time rivaling some Almost-Ready-to-Fly aircraft. While I had seen advertisements for the Duraplane line of aircraft in the past, I had never actually either built or flown one. Like (I suspect) many people, my initial impression was that the aircraft kits that Duraplane made were all for novices; basically constructed of material from a building supply store. In actual fact, the manufacturer does not recommend the DuraStik 40 for a novice's first model. After building the DuraStik 40, my impressions have undergone a change, and I have much more respect for the amount of thought behind the choice of materials and building techniques. The easy construction process and the resulting flight characteristics of this aircraft reflect a lot of effort on the part of the designer.

Construction:

For those of you with shipping size restrictions or conditions, the DuraStik 40 kit is packaged inside a 4" x 15" x 44-1/2" cardboard box, decorated with an advertisement and picture of the finished aircraft. The contents were mostly separated from contacting each other, with the exception of the plastic bag containing the metal screws, which had come loose inside the box, and had very slightly dented one of the wing panels. The manufacturer also encloses a parts list with the kit that you can use to order replacement parts or sub-assemblies, should they be needed at a later date.

The aircraft kit is shipped with a really excellent 20-page assembly instruction guide, that details suggested tools, accessories, construction tips, and dozens of photographs and line drawings. Each step in construction has a "check-off" box, allowing you to know exactly where you are in the assembly process, should you be interrupted. No plans are included, nor are they needed. The hardware supplied with the kit is fairly complete; however, you will have to purchase a fuel tank, fuel line, wheels, spinner, and the usual covering, engine, and propeller.

The first steps in construction are the assembly of the tail pieces; the vertical and horizontal tail components are made up of pieces of sheet balsa that have been cut to outline, but not glued together, rounded, or tapered. After slotting the components and trial-fitting the (included) hinges, the vertical fin and horizontal stabilizer are fitted to the extruded aluminum channel that functions as a tail boom. The boom is pre-drilled at one end for the machine screws that secure the tail components to the boom, and at the other end for attachment of the tail boom to the square stock PVC pipe that makes up the main fuselage. Like the tail boom, the PVC fuselage is pre-drilled, with the exception of the firewall and pushrod housing retainer screw holes, and some of the landing gear holes.

Internal reinforcement of the fuselage with plywood doublers is made at the main landing gear mounting areas. The aluminum main landing gear bracket is very strong and is attached both to the aluminum tail boom and to the PVC fuselage. A firewall is assembled from several pieces of plywood that are epoxied together, and attached to the fuselage with eight screws.

The wing uses a semi-symmetrical Selig S8036 airfoil, and is made up of two pre-shaped foam wing sections, with central, doubled, plywood joiners, and is pre-routed (top and bottom) for 3/16" x 1/2" basswood spars. Plywood wingtips and wingtip ribs are glued to the outer ends of the wing assembly, and balsa trailing edges are added along the rear edge of the wing. Following the recommendations of the manufacturer, the joiners, spars, trailing edge, and ribs were all glued to the foam wing with woodworkers' glue; while epoxy could also be used, the aliphatic glue is much easier to sand, and minimized the possibility of damage to the finished wing surface during sanding. Since the wing has no dihedral, it can be assembled on any convenient flat surface. A recessed hole for aileron servo mounting is molded into the foam wing pieces, requiring only plywood servo mount brackets to be glued into place.

The assembly guide suggested tapering the control surfaces to add a "more finished appearance," and I chose to do so. However, once the aileron stock was tapered, the finished ailerons were very flimsy, and were unsuitable for use. I replaced the kit pieces with heavier and more rigid balsa stock. A plastic wing "shield" (which protects the foam wing from the pressure of the eight to ten #64 wing hold-down rubber bands) was epoxied to the wing (after wing covering). I had a small problem here, as the shape of the shield, as it is molded, did not correctly match the contour of the top of the foam wing. Nevertheless, I sanded the wing where I could, and ended up with only a small area of contact between the foam wing leading edge and the rubber bands. A slightly longer plastic shield (front to rear) would have been easier to work with. I would also recommend cutting out the aileron servo access hole in this piece after servo installation, as the "cut-out" lines molded into the shield did not quite match my aileron servo location.

A pre-cut foam wing seat, epoxied to the bottom of the wing, establishes the wing angle of attack. The seat fits the contour of the lower surface of the wing, and sits on top of the fuselage.

A plastic fairing fits over the top of the fuselage from the firewall to the wing. After painting it to match the fuselage, I attached the fairing to the fuselage with silicone adhesive. This fairing makes a huge difference in the appearance of the aircraft, and is well worth the effort to trim, shape, and fit it to the fuselage and wing.

The rear of the PVC fuselage is left completely open, with the two tail control surface pushrods (included) and the receiver antenna exiting the fuselage through the opening. (Just for fun, I later made a fuselage cover for this area.)

The nose wheel steering control is also a little different, in that a pushrod is run from the rudder control horn all the way forward along the bottom of the fuselage to the nose gear control arm.

Covering:

Without a fuselage to cover, even this part of construction goes faster. I used yellow Top Flite EconoKote for the covering, and low-heat shrink covering worked very well, even where stretched over the more complex leading edge-to-wingtip and vertical fin curves. The covering also was a very good match for the Top Flite yellow epoxy spray paint [LustreKote] that I used on the firewall, fuselage fairing, and landing gear. I briefly considered different covering patterns or insignia types, but inevitably went back to "tradition" and used the WWI German insignia available from Major Decals.

Engine:

The manufacturers of the DuraStik 40 recommend that a .40 to .46 2-stroke, or a .48 to .52 4-stroke engine be used. The economical K&B Sportster .45 that I used fit the Great Planes adjustable engine mount (included) well, and I chose to side-mount the engine. I also had the opportunity to use the Great Planes Dead Center Hole Locator, which made the engine mounting process a very quick one, by accurately locating and marking the actual center of the engine mounting holes on the engine mount beams. This sideways engine orientation allowed the muffler exhaust to be aimed away from the aircraft without the use of an exhaust diverter, and has a little "sportier" appearance.

The DuraStik 40 assembly guide did not list any required right-or down-thrust setting, therefore the engine was centered. The K&B Sportster .45 provides good power (with the 10 x 6 APC propeller), with very acceptable noise emissions. It also incorporates a remote fuel metering needle unit (not attached to the crankcase), which allowed me to place it in a convenient position well away from the propeller arc. The first few flights were made without muffler pressurization of the fuel tank, as recommended by K&B, but I later added a small Du-Bro pressure tap to the muffler to counter a surging problem noticed during aerobatics, probably due to relative carburetor and fuel tank height. As recommended by the assembly guide, I used a Great Planes 8 oz. rectangular fuel tank, cushioned with foam rubber.

Radio:

For control, I used an Airtronics Infinity 600A transmitter and receiver system with four standard Airtronics servos, and a Cermark 4.8v, 1100mA flat receiver battery. Servo mounting in a Duraplane is unique, as the throttle, rudder, and elevator servos fit tightly in single file into the extruded aluminum tail boom (inside the fuselage), and then are secured by filament shipping tape wrapped around the servo and tail boom. No servo mounts or screws are needed for the servos mounted inside the fuselage, and there is no chance of the servos loosening or moving around. A single standard servo was mounted in the wing for aileron control. The Airtronics receiver was mounted on a small wood platform to the rear of the row of servos, and is similarly taped in place. The switch was located in the left side of the fuselage, to the rear of the wing mounting.

Every time that I have to set up the flight controls on an aircraft using a computer radio, I can hardly believe how easy and accurate the process is. Endpoints, travel adjustment, centering ... if you haven't used one yet, try one; you won't regret it. As recommended by the DuraStik 40 assembly guide, the high rate control surface travel in each direction was set to 3/8" on the elevator, 1" for the rudder, and 5/16" for the ailerons.

Flying:

The assembly guide called for a balance point of 3-3/8" to the rear of the leading edge of the wing. I used (for the first time) the Great Planes C.G. Machine Aircraft Balancer to check the balance of the aircraft. This tool is very easy to use, can handle planes up to 40 lbs., and is a lot more precise than using your (or my) fingertips. The balance of the DuraStik 40 was close, and I used less than 1/2 oz. of additional weight behind the fuel tank to achieve correct balance. Now I was glad I had spent the time to taper-sand the tail control surfaces.

The first flights of the DuraStik 40 confirmed the manufacturer's statements in the assembly guide, in that the DuraStik 40 was a smooth flying aircraft. During ground taxiing, the tail assembly seemed to be subject to a little excessive movement as the aluminum channel tail boom twisted and flexed slightly, but in flight, absolutely no effect was noticed. The aircraft tracked very smoothly during take-off, with a slight tendency to turn into a crosswind from the left, probably normal for an aircraft with tricycle gear and very little fuselage between the tail and the wing. Climb-out and turns in both directions were smooth and predictable, and the aircraft had no tendency to pitch, roll, or yaw in level flight.

A number of stalls were made at high altitude, and it was noticed that while the left wing dropped first, control of the aircraft was never in question. Loops were easily made, and rolls were smooth and near axial, probably due in a large part to the lack of wing dihedral. Inverted flight was uneventful and easy to control with only a slight amount of "down" elevator needed to maintain level flight. Landings can be made at moderate speeds. During the first flights, flaring the aircraft for landing usually required full "up" elevator, so I added a bit more "up" travel to the elevator control surface.

Conclusion:

While a novice could easily build the DuraStik 40, the flying characteristics are a little too advanced for a beginner. With no wing dihedral or any of the "self-righting" features found in trainer aircraft, it is better suited to be used as a rugged sport aircraft for the intermediate flier.

The DuraStik 40 performs well, and lives up to its promise of quick construction and rugged durability.

Photos by Ed Hopkins. Reprinted with permission.
April, 2001 R/C Modeler Magazine
Editor: Dick Kidd