Classic Stinson SR-10 Reliant You can Build

Feb 07, 2014 4 Comments by

Construction Article by Pat Tritle

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The Stinson Reliant, a 3-place (Plus Pilot) high wing monoplane with conventional landing gear was built in several variants from 1933 – 1941. The last commercial model built was the SR-10, introduced in 1938. A militarized version was first flown in 1942 and remained in production until late 1943, undergoing several modifications throughout its production history. In all, 1,327 Reliants were built during its 8 year production run.

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 The Reliants were built in two distinct types; the “straight wing”, Model SR-1 – SR-6 and the “Gull Wing”, Model SR-7 through SR-10, and to include all of the military variants. Though both were in the Reliant family, there was little in common between the two types. The early Reliants had wings with constant chord and thickness, and supported by two lift struts with additional jury struts. The taper wing stepped up in chord and thickness out to the wide spot in the chord, and then tapered again out to the tip giving the wing a distinct gull appearance when viewed from the front.  All of the Gull Wings versions were supported with a single lift strut.

 The Reliant saw a good bit of service in WW-II as well, designated as UC-81 Light Cargo and communication duties, and as a Trainer, designated the AT-19. Then after the war, those airplanes were sold into the civilian market under the designation Stinson (Vultee) V-77, a Spartan version powered by a Lycoming R680-E3B, 300 horse radial engine. On those models, the original “bumped” cowl had been replaced with a simpler smooth cowl, had only one door, located on the left side, and the internal structure was beefed up significantly over the commercial models. The V-77’s also included a distinctive triangle shaped counterbalance on the rudder.

 The SR-10 has a wing span of 41 ft. 7 inches and was27 ft. 11 inches long. Empty weight was 3,045 lb. with a gross weight of 4,605 lb. SR-10 variants ranged from the SR-10B to the K model and were powered with engines ranging from the Lycoming R680-D5, D6, or E3, the Wright R-760-E1, E2, or E3, and the Pratt & Whitney R-985 Wasp Junior SB. Cruise speed was 154 knots with a top speed of 177 knots with a range of 739 nmi, a climb rate of 1,330 ft/ minute, and a service ceiling of 21,000 feet.

The Model

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The Stinson Reliant is designed at 1:9 scale with a wing span of 55.8” and a flying weight of just 27.8 ounces. And though rather large for a Park Flyer, due to the effectiveness of the scale flaps can be easily flown in some relatively small venues.

The model is primarily of Balsa and Lite Ply construction, with a vac-formed plastic cowl with the dummy radial engine and wheel pants. Control is 5 channel R/C for the throttle, ailerons, rudder, elevator, and flaps. The flaps and ailerons use a single servo on each control surface. And since the model is quite large, to keep things simple for take-down and assembly at the field, the wings plug into the fuselage on brass tubes with the struts retained with wire pins in aluminum receiver tubes. The wings are held in place with rare earth magnets. The battery is accessed through a plastic hatch on the bottom of the fuselage making battery replacement quick and easy, and as with the wings, no tools are required. If you want laser cut parts, check out my website at: http://patscustom-models.com/

By nature, the Reliant Gull Wing is a very complex model, featuring scale flap hinging as well as a number of scale fairings, so will require a bit of modeling skill to build. However, in spite of its complexity, the design has been simplified in every way possible without loosing its distinct scale outline.

Construction of the fuselage and airfoiled tail planes is of the conventional stick frame type. The wings are done in an egg-crate style with pre-shaped spars to simplify construction so that the distinctive gull shape of the wing would not have to give way to out-of-scale simplicity. The flaps also incorporate double taper, so pre-shaped spars and jig blocks simplify construction there as well. In all, the model is a challenge to build, but the result is a great flying model of one of the classiest airplanes ever to grace the skies.

 Building the Stinson

Stinson Reliant online

To order your own set of construction planes for Pat Tritle’s Stinson SR-10 Reliant, (X0415A) go to: http://www.airagestore.com/stinson-reliant-sr-10.html

Before you begin construction, study the plans thoroughly before building actually begins to become familiar with how the structure is laid out. Cut the parts out next, or if you would prefer to build the model using laser cut parts, a wood and plastic package is available from the author.

Construction begins with the bowed outlines for the wing and tail planes. If you’re new to this technique, there’s a full description of the process at http://patscustom-models.com/bowedoutlinres.html. By getting the bows built up first they’ll be handy when you need them making the building process much smoother along the way.

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The flap leading edge sheeting is pinned to the plan with its outboard end supported with a jig to properly set up the angle.

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The Flap ribs are assembled to the main spar, then the sub-assembly is glued in place on the leading edge sheet.

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A steel wire hinge axle is passed through the ribs to insure proper alignment. The wire must pass through all of the ribs freely to insure smooth operation of the flaps once the hinges are installed.

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The leading edge is sheeted with 1/32 balsa. Wetting the sheeting on the outside will aid in rolling the balsa around the rather tight radius at the outer ends.

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The slot for the pushrod is cut into the leading edge sheeting. The slots for the hinges will be cut in later when the flaps are fitted on the Wing and the hinges set up.

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The wing ribs and main spars are laid out over the plans in preparation for the wing assembly process.

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The Wing panels are built in two segments, the inner and the outer. The spars and ribs are dry fitted together, the pinned over the plan and glued together as two separate sub-assemblies.

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The inner and outer Wing sections are joined flat on the building board and glued together along with the internal joiner bracing. Note the flap assembly in position to check for proper alignment.

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Once the inner and outer panels have been joined the leading edge and tip bow are aligned and glued in place.

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The trailing edge is glued in place and the aileron parts laid out in preparation for assembly.

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The Flap trailing edge is glued in place using the Flap assembly as a guide to insure proper alignment.

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The Aileron is built directly into the Wing. Before assembly begins, a bevel will need to be sanded into the bottom of the hinge spar so it will lay flush on the table.

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If the laser cut parts are used, the leading edge sections will need to be laminated together, then glued in place on the Wing.

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The top and bottom trailing edges are glued in place in the Flap bay, then using the flap to align the hinges they’re glued in place and the Flap removed.

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With everything sanded into contour the flap is installed on the wing using a temporary hinge axle. With the hinges properly aligned the flap should move freely through its full range of deflection.

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With everything sanded into contour the flap is installed on the wing using a temporary hinge axle. With the hinges properly aligned the flap should move freely through its full range of deflection.

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With all of the building sanding and shaping finished, the Flaps and Ailerons are dry fitted into the completed Wing assemblies. At this point the only thing left is to install the servos.

Tail Feathers

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The Horizontal Stabilizer is built directly over the plans. Shims are used to center the leading and trailing edges and tip bows on the ribs and spars.

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While still secured to the building board the airfoil is block sanded into the Stabilizer. With one side done, the assembly is removed from the board and the opposite side sanded to shape.

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The Vertical Stabilizer is built directly over the plans. Shims are used to center the leading and trailing edges on the ribs and spars during assembly.

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Once assembly is completed, the Rudder is removed from the board and sanded to shape. The hinges are cut in and dry fitted, but not glued in until after the frames are covered.

Fuselage

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The Fuselage side frames are built directly over the plans. Both sides are identical except for the elevator pushrod guide on the right hand side frame.

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Landing Gear supports are glued in place on the inside of both side frames. The support can be glued to the right hand frame during assembly on the plans. The left hand side will be glued in place after the frame has been removed from the board.

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The Fuselage side frames are joined beginning with the landing gear beams and upper cabin formers. Machinist’s squares or drafting triangles can be used to insure the sides are vertical during assembly.

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Machinist’s squares are used to keep the Fuselage frame nice and straight as the firewall is glued in place.

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The tail section is pulled together and glued, then the top and bottom formers are aligned and glued in place.

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The top, bottom, and side stringers are fitted and glued in place to complete the basic fuselage assembly.

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The cabin out fill is fitted and glued in place then sanded to contour at each of the cabin window frames.

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The tail section is dry fitted into the fuselage and the rudder cables run in and the dimensions recorded on the fuselage drawings for reference to the exit points making them much easier to locate after the cover goes on.

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Before covering begins there’s that one last dry run to insure that everything lines up and works properly while the internal components are still accessible.

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The Motor Mount box is assembled and glued in place and the motor mounted. The mount is set up for the Super Tigre .10 Outrunner Motor.

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The rudder and Elevator Servos are mounted on hard balsa beams in the Fuselage and are accessed through a hatch on the bottom.

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The Flap Servo is glued to the mount plate with Silicone caulk. The linkage is set up with an EZ-Connector to fine tune the system when the flaps are permanently attached.

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The Flap pushrods are bent from .032 steel wire with a Z-Bend on the aft end. The pushrod is shaped as necessary to align with the servo arm.

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The Lift Strut attachments are made up from 1/2A nylon pin hinges with aluminum guide tubes to make access under the fairings much easier. Pins made from steel wire are used to connect the struts to the wings.

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The lower strut fittings are retained with steel pins. An Aluminum Guide Tube makes getting access to the hinge attach point under the fairing much easier.

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The Lift Struts are test fit one last time before the cover goes on. Any adjustments that are needed should be done now while there’s still easy access to the internal components.

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The Landing Gear Fairings are made from Manila File Folder and glued in place on the landing gear struts. Tongue Depressors and Stationary Clamps are used to insure a nice straight trailing edge.

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Covering begins with the wings and tail surfaces. The flaps are covered first, then the entire wing except for the top inboard section. Once the flaps are permanently hinged and properly adjusted, the remainder of the cover can go on.

 

The top of the Fuselage is covered in halves and includes the side of the vertical fin to form the very distinctive fin fillet.

 

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After the first side is completed the other side is covered in the same fashion. Making the fillet can be a bit tricky, but the Microlite cover is very forgiving making the fillet a bit easier to form then with some of the other materials available.

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The remainder of the fuselage is covered in the standard fashion. The bottom was covered in one piece, which is a real testament to how forgiving Microlite actually is.

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The green trim was sprayed on using latex house paint. The gold stripe was made using automotive pin stripe tape with numbers from Callie Graphics.

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The tail graphics were applied using graphics from Callie Graphics. The gold trim on the wheel pants were hand cut from stock Vinyl sheet.

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All of the fairings were made from balsa wood sub-structure and paper skins. For the full story on how the fairings are done including step-by-step photos and detailed captions go to: http://patscustom-models.com/paperfairing.html

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The Stinson is finished and ready to fly. Note the two hatches on the bottom of the Fuselage; the front hatch is for battery access, the rear gives easy access to the servos and Rx.

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UNEDITED CONSTRUCTION TEXT

Rudder and Elevator

Start with the tail planes since those are easy. Beginning with the rudder, pin down the hinge spars D4 and D5 over the plan. Next, place the 1/16 scrap balsa shims around the leading and trailing edges at the locations shown. Now you can pin the leading and trailing edges, D1, D2, D3, D6, & D7 in place followed by the 1/16 X 1/4 balsa ribs. And lastly, fit and glue the 3/32 sq. balsa diagonal bracing in place on center. When dry, remove the assembly from the board and sand to shape using the provided cross sections for reference. Cut in and dry fit the hinges at the location shown.

 The Horizontal Stabilizer goes together essentially the same way. Begin by cutting the hinge spars from 1/8 X 1/4 balsa and pinning them in place over the plan. Place the shims in the locations shown followed by the leading and trailing edges and tip bows. Add all of the 1/16 X 1/4 and 1/8 X 1/4 balsa ribs and glue in place followed by the 1/16 X 1/8 balsa diagonal bracing glued in on center. When dry, remove the assembly from the board and sand to shape. Cut in and dry fit the hinges to complete the basic assembly.

The Wings

The wing assembly begins with the flaps since you’ll need those to complete the wing assembly. Build both flaps over their individual assembly drawings beginning by scoring and bending FLE at the location shown. Place the jig block FTB at the outboard end, and then pin FLE in place over the plan. Glue the 1/8 Sq. balsa leading edge and the Flap Spar FS in place followed by each of the ribs and the 1/8 X 1/4 balsa trailing edge. FR7 goes in last, and to insure everything is aligned properly, slip a 1/16 wire pin through the flap to insure all the holes are lined up. Proper alignment is absolutely essential if the flaps are to deploy smoothly.

 Once all the ribs are in, add the 1/32 balsa top sheeting. Remove the flap from the board and sand to shape. Cut in the pushrod slots in the location shown to complete the assembly. Build the other flap in the same fashion being sure to build a left and a right hand flap.

The wing panels are built in two sections each. The inboard section is built first by pinning the front and rear spar assemblies over the plan with the inboard end against the plan. Slip the ribs in place and glue. The outboard end of the wing panel is built flat on the board in the same fashion. Once both sections are glued together, the inner and outer sections are joined by first aligning and gluing A1J and A2J in place in the inboard wing section. Then slip the outer section in place, align and glue.

With the inner and outer panel sections joined, pin the wing back over the plans with the outboard section flat on the table. Add the leading edge, trailing edge, tip bows, and the 1/16 X 1/4 balsa top and 1/8 Sq. balsa bottom flap bay caps at the trailing edge. Assemble the ailerons directly on the wing, followed by the aluminum receiver tubes, aileron and flap servo tray assemblies, and the lift strut mount plates. Don’t glue the flap hinges in place yet, we’ll get to those in a minute. Then once the glue has dried, remove the wing panel from the board and sand to shape. Remove the aileron and sand to final shape. Cut in and dry fit the hinges to complete the basic assembly. Build the second wing in the same fashion.

Setting up the Flap Hinges

The plywood flap hinges are aligned into the wing in the locations shown and clamped in place with small spring clamps or clothespins. Find the location and cut the hinge slots into the flaps. Then align the flap onto the hinges and carefully slip a 1/16 steel wire hinge axle through the flap until it engages both hinges. It’s easier if you file the end of the axle to a dull point. Then with the axle in place, align the flap so that the bottom of the flap is flush with the bottom of the wing and the gap is consistent end to end. Carefully roll the flap through its deflection range to insure there is no binding, and when satisfied that all is well, glue the hinges in place. The flap hinge pin and flap can now be removed to set up the servo linkage.

The servos are set up with the arms in neutral position and a micro EZ-Connector at the outer-most hole in the arm, and then glued in place on their respective trays with silicone caulk. Let the silicone dry completely before proceeding. You can also set up the flap pushrod as shown on the plans. If you go that rout, the servo won’t be glue in place until final assembly. Either way works fine. The aileron servos are glued in place, and when dry, the wiring is run out through the root rib. A final detail sanding is done to complete the wings. And now that the hard part is finished, we can move onto easier things.

The Fuselage

The fuselage side frames are built over the plans using the wood sizes and part numbers shown. Both frames are the same except for PRG which is glued flush with the outside edge of the RH frame. With both frames completed, the B2 landing gear mounts are glued to the inside of each frame.

 Make up the landing gear mount beams from 3/16 X 1/4 hard balsa. A notch is gouged into the beams as shown on the plans. To joint the side frames, begin by pinning the LG mount beams over the plan and then glue the frames in place. Add cabin formers 3, 4, and 5 being careful to maintain vertical alignment on both sides. To joint the tail post, first crack B1 at former 5 and angle the top longeron straight back to the tail. The bottom longeron forms a natural curve, so won’t be broken. Align and glue the tail post together, then add the remaining top formers aft of the cabin.

 Remove the assembly from the board and add all of the bottom formers from 5A aft. Bend the landing gear struts using the patterns provided. Fit the struts into the mount beams, align and solder together at the bottom, then wrap the joints with fine copper wire and re-solder. Lash the struts in place with thread and secure with a drop of thin Cya. Now add formers 2A and 4A. Next, crack the upper and lower longerons at the locations shown and join the nose with 1/8 Sq. balsa, then add the remaining formers.

 With all the formers and landing gear in place, fit and glue all of the 1/16 X 1/8 balsa top and bottom stringers and the top CS cabin stringers. Now the 1/16 X 3/16 balsa side stringers and cabin out-fill can be added using the cross sectional views provided as reference.

 The servo rails are added followed by the rudder and elevator servos and elevator pushrod tube. Secure the tube at both ends and at a couple of points in between using the PRG support braces. Tape the rudder in place and run in the Pull/Pull cables. Mark the exact location on the plans where the cables exit the fuselage to reference for locating the exit points after the fuselage is covered. Mount the motor and ESC and check the systems for proper operation. Run the motor with the prop removed to insure the motor is running in the right direction also.

 Build the lift struts per the plans. The top and bottom of the struts will be faired directly on the model after it’s covered, so all you need to do now is get the attach points set up. Then once you’ve done a last detail sanding and a final dry run to insure everything fits and functions properly it’s time to cover the Stinson.

Cover and Trim

There are several options available to cover the Stinson ranging from Tissue or Silkspan and Dope to one of many iron-on films. If you prefer an iron-on Mylar, there are several light weight materials available. However, avoid using materials like Monocoat or Ultracoat as they’re just too heavy, plus the shrinkage is sufficient to do some serious airframe damage when the heat is applied.

Now, because of the internal flap linkage, the top inboard section of the wing will not be covered until the flaps have been installed and the servo set up and adjusted. So, after the wing and flaps have been covered, install the flaps and secure the hinge axle at the root end with a drop of canopy glue. Set up the flap pushrod and adjust the travel using either your Tx or a servo cycling tool. Once it’s all in and working, cover the remaining portion of the wing.

 I covered the prototype with Cream Microlite and painted the trim using latex house paint from Lowe’s HomeCenter. The graphics were custom made by Callie Graphics and applied after the trim had been applied.

Final Assembly

Once all the cover and trim is on its time to button this whole thing up. Start with gluing the tail section in place using the wing for alignment reference. Connect and set up all of the hinges and control systems. Fit and glue all of the windows in place. Mount the cowl, wheels and wheel pants, and do any necessary touch up. Now, it’s time to dig into all those landing gear and lift strut fairings. Patterns are provided on the plans to make up the File Folder paper fairings. If you’re new to this type of thing, there’s a full tutorial on the process complete with photos and captions to walk you through it at http://patscustom-models.com/paperfairing.html.

Once all the fairings are on and the last of the detail painting is done you’ll need to balance the model. Use the battery to your best advantage to locate the CG as shown on the plans. Make a tray from either 1/8 hard balsa or light ply and mount it as needed, then make up the hatch from .010 Styrene plastic sheet and 1/8 X 3/16 balsa.

Flying the Stinson

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 The Stinson is a solid and stable flyer, and with the flaps deployed slows down nicely to land. Take off is best with half flaps, but does well with full flaps as well. One thing about it though, the Stinson is the most neutral flap equipped model I’ve ever flown. Once the elevator trim is set up properly, there is absolutely no pitch change when the flaps are deployed. The only difference is in the reduced landing speed. However, due to the relatively light wing loading, the model can be flown without any flap at all, so for those unfamiliar with flap equipped models, getting used to flying the model first, then experimenting with the flaps is no problem at all.

 Using the Super Tigre .10 motor with an APC 11-5.5E propeller on 2 Lipo cells the model is not “over-powered”, but does have adequate power with a good bit of reserve should it be needed. However, the Reliant is a classy cross country airplane, not an all out aerobat, so keep the nose down and fly it “on the wing” and I’ll bet that you’ll be impressed with how stable and easy to fly the Stinson is. Then for a little added fun, try shooting a few touch and goes. Fly the approach with full flaps, then as soon as the mains touch down, pull the flaps up to take-off position, add a little power and lift off for a smooth steady climb-out.

Specifications:

Scale: 1:9

Wing Span: 55.8-inches

Length: 36.5-inches

Flying Wt.: 27.8 ounces

Wing Area: 464 Sq. In.

Wing loading: 8.6 oz./ Sq. Ft.

Control: 5 ch. R/C (Throt, Ail, Elev, Rud, Flap)

Power & Guidance Components

Motor: Super Tigre .10 Outrunner Motor

ESC: 30A w/ 3A BEC

Propeller: APC 11-5.5E

Battery Connector: Deans 4 Pin

Battery: 2500 mah 2S Lipoly

Servos: 2- 9 Gram Sub-micro Servos (Rudder, Elevator)

             4- 6 Gram Sub-micro Servos (Ailerons, Flaps)

2- 9” Servo Extension

2- 11” Servo Y-Lead

Rx: Spektrum AR-6000

Tx: Spektrum DX-7

Materials List

Wood

Laser Cut Parts Pack (includes vac-formed plastic cowl and wheel pants)

15- 1/16 X 1/8 X 36 Balsa

7- 1/16 X 3/16 X 36 Balsa

4- 1/16 X 1/4 X 36 Balsa

8- 1/8 Sq. X 36 Balsa

2- 1/8 X 3/16 X 36 Balsa

4- 1/8 X 1/4 X 36 Balsa

1- 1/32 X 3 X 12 Sheet Balsa

4- 1/16 X 4 X 36 Sheet Balsa (if laser cut parts are not used)

4- 1/8 X 4 X 36 Sheet Balsa (if laser cut parts are not used)

1- 1/32 X 1 X 1 1/2 Ply

1- 1/16 X 3 X 3 Ply

1- 1/8 X 2 X 2 Lite Pl

Metal

1- .025 X 36 Steel Wire

1- .032 X 36 Steel Wire

1- .041 X 36 Steel Wire

2- .062 X 36 Steel Wire

1- .093 X 36 Steel Wire

1- 1/16 O. D. X 12 Aluminum Tube

2- 5/32 O. D. X 12 Brass Tube

1- 3/16 O. D. X 36 Aluminum Tube

Miscellaneous

1 Pr.- 2 3/4″ Main Wheels

1- 1” Tail Wheel

2 Rolls- Coverite Microlite

4- 3/32 Wheel Collars

4- 3/16 Dia. Rare Earth Magnets

1- .008 X 9 X 12 Clear Acetate

1- .010 X 6 X 12 Sheet Styrene

18”- Sullivan #507 Pushrod Tune

4 Ft.- Nylon Carpet Thread

4- 1/2A Nylon Pin Hinges

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4 Responses to “Classic Stinson SR-10 Reliant You can Build”

  1. Gabor Botka says:

    Absolutely fantastic! I have a PZ Stinson that i love flying, and have been dreaming of building a balsa one. The build log is a great welcome. Perfect timing!

  2. chardesa says:

    Very nice indeed. Good pictures except for the end. Next to the Cessna 195 that was a favorite plane.

  3. Kim Jeppesen says:

    Very nice bird and great work.
    Thanks for sharing!

  4. Pat says:

    What a wonderful job of pics and text. Very alluring. This won’t be my first scratch-built, though as I have no experience in other than foamies. I’m anxious to build a kit first, so I can learn how things should go together. Thanks for the info on the electricals as that’s some I know nothing of. Pat

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