1/3-Scale Cessna L-19 "Bird Dog" Kit by Peter Goldsmith Designs

[JimD]

About two years ago, Peter asked me what plane I would like to see in kit form. While I think he was asking about what sailplane I would like to see, my mind went straight to what tow plane I would like to see.

In my book, the gold standard for a scale tow plane is the Cessna L-19. Ten years ago, researching the Soaring Society of America website "Where to Fly" interactive map, the top three most common tow planes in use in the U.S.A. were the Piper Pawnee, Cessna L-19, and Piper Super Cub.

What makes the Cessna L-19 stand out (beside the fact that it looks cool) is its built like a model airplane! Simple landing gear, simple struts, simple tail group (unlike the other two).

Peter didn't immediately seize upon this idea, but I guess my persistence finally won out...and look at that smile on his face, he likes it, he really likes it!!!



In the design phase, the first decision was what scale should it be...seems 1/3-scale has become the "standard" for many of the scale sailplanes in common use now, so 1/3-scale was the obvious pick. This scale also suited the very reliable DA-150 engine that our trusty Bidule 170 tug was using.

Once these parameters were decided, Peter was off to the races and produced the prototype pictured above in an amazingly short period of time. Now the pressure is on me...with kit in hand, time to finally build the plane that I have wanted for decades!



The scheme we decided to use is from this full-scale example:

[JimD]

This forum suffered a ransomware attack around September 23 and was down for close to two months. I was finishing up the TG-3 build and starting the L-19 just when this happened. The consequence was that access to the TG-3 thread was lost and the L-19 build thread could not be started.

In the intrim period of time, we attached a forum (that WiX offers) to our WiX based website and started a build thread for the L-19 there. The WiX forum proved to be rather clunky to use and thanks to Dustin's efforts, this forum was restored to operating status. Now the task is to move the build thread we started on the WiX forum to this forum.

[JimD]

The L-19 fuselage is not a simple shape to duplicate. Having built numerous kits that Peter has designed (Schweizer 1-26 and TG-3, Slingsby Swallow and Skylark, Foxbat and Sapphire, and the Cmelak Z-37-2 tow plane, we have come to appreciate not only the quality of his kits, but also the quality of his designs.

This model can be built with a minimum of tools and, of the tools needed, a minimum investment. The one most important thing for success with any of Peter's kits is a good workbench. In my opinion, having a minimum 2' x 8' flat and level surface is essential. Given this, the surface can be made very user friendly by covering it with a piece of Homasote Sound Board (available from most local lumber stores).

Peter has designed the L-19 to be built on a flat surface thus keeping the structure straight and the necessary tools to a minimum.

Many first time builders of giant scale planes fear they may not be able to build a structure that is straight and true causing a major loss in time and money. Peter has greatly reduced that possibility by his innovative design on this model...okay, let's get started!!!

[JimD]

The main adhesive for building this model will be Deluxe Materials Aliphatic Resin. Attachment of the 1/32" plywood sheeting will mostly be done using Deluxe Materials Speed Bond. In a few instances, Zap thin CA glue will be used. In high stress areas, West System epoxy and 404 filler will be used. Hinge Points will be installed with West System Gflex Epoxy.

We have found landscape paver bricks to be great tools to hold things in place on our building board. They are readily available at home hardware stores. Strips of steel and aluminum also make great tools and again are readily available at home hardware stores.

Various sizes of binder clips form your local office supply store are another low cost and extremely handy tool for clamping parts together while glue cures.

As for specialized tools, one of my favorite and most used tools are a collection of Irwin Quick-Grip Bar Clamps in several sizes (the micro size being the most used).

And probably the most important tool for wooden model building is an assortment of good quality sanding bars, plus an X-acto knife (#11 size) and razor saw.

[JimD]

As is often the case, we started with the tail feathers!

Fin/Rudder

First step is to locate all of the wood parts and separate them from their carrier sheets. Peter has cleverly designed a tab and slot format to help the builder align the parts during construction.

Glue the 1/16" balsa fin sheeting together using a glue that can be sanded easily. Our pick for general construction is Deluxe Materials Aliphatic Resin (available from your local hobby shop or Horizon Hobby)

Clamp Fn1 to a flat surface and add Fn2, Fn3, and Fn5b perpendicularly to it.

[JimD]

For now, we will move on to the stab and elevators.

[JimD]

Stab/Elevators

Again, locate all of the parts.








Note that rib S1 is angled to match the taper of the fuselage sides. There is a laser cut plywood angle gauge to help set this angle.


Use scrap balsa to add shear webbing on top and bottom sides of the wing tubes.


Drill a pilot hole through the intersection of the center of the spar and front wing tube. This will help to locate the stab mounting screws.


Speed bond was used to glue the 1/32" skins to the framework. Glue is applied to both sides of joint and allowed to dry to clear. A hot iron is then used to activate the glue and fuse the skins to the framework.


A slot for the elevator servo control arm is precut in the bottom skins. Use this slot to locate the skin when gluing it to the framework.




Thin balsa leading edge is added to the elevators. Draw a line down through the center of the hinge point holes. This thick balsa gets sanded to a "V" to allow left and right movement.


Add scrap balsa to fill in the thickness of the inner balsa blocks. These blocks get sanded to the taper of the adjacent ribs.


Tip plywood parts are test fit to the elevators before balsa blocks are added to check clearance between tips and stabs.

Balsa blocks are added to both sides of the plywood tip plates and then get sanded to match the contour of the tip ribs and stab (after stabs are sheeted).

[JimD]

For now, we will move on to the fuselage construction.

[JimD]

Fuselage

As mentioned at the beginning of this thread, Peter has designed this model so that the structures only require a flat building surface. No complicated jigs or stands or building "in the air" as some aircraft designs require. Peter has designed the fuselage to be built as a top half and bottom half.

Fuselage is built as bottom section first, then the top is added. The bottom section is built upside down on a "crutch" which allows for construction on a flat surface and greatly simplifies the building process. It also makes for a nice straight and true structure.

Establish a centerline reference on your work surface. We used a sheet of Homasote 440 Soundbarrier to cover our workbench. It holds pins nicely and can easily be replaced when the surface becomes worn.

Locate the 1/4" (6mm) plywood "crutch" assembly, bulkhead template, and fuselage formers. Center these parts on the workbench centerline using the formers to set the spacing between the right and left sides.

Locate all of the lower fuselage parts.



Glue parts of crutch together.



Mark centerline on bulkheads.




Without gluing, align the crutch and bulkheads over the centerline drawn on your workbench.

The lower fuselage bulkheads are not perpendicular to the crutch. Peter supplies a plywood template gauge to set the angle of the bulkheads F1, F3, F3a, F6, F7, F8, F9, F10, and F11. We used some of the scrap plywood to make a second template gauge.

The crutch has slots and the bulkheads have tabs to assist in correctly locating them. Because of the angle that they lean, you may need to lightly sand a taper on the tabs so that they fit into the slots at the correct angle.



We started by gluing F6 and F8 in place using the angle template gauges.



A piece of the 1/8"x1/4" basswood was pushed into the slots of the bulkheads as a temporary brace (do not glue). Note the use of the bricks to hold the structure in place.

Once F6 and F8 were securely in place, we proceeded to add formers F7, F9, and F10 plus formers F3 and F3a.

Note that Former F4 does NOT install at the same angle as the others. Use the plan to measure the distance along the bottom stringers between F3a and F4, and between F4 and F6.

Mark the stringers and install F4 to match this spacing. Paving bricks make handy weights to holds things in place during the assembly process.

The three bottom stringers (on top in this configuration) can be glued to the bulkheads from F3 to F10. do not glue the stringers to F11 and F12 yet.

[JimD]

Locate the aft fuselage side pieces F13 and F13b. These get laminated together and the location of F13 together with the slots in F13b and the tabs on F11 and F12 all help to set these parts in place and at the proper angle to the crutch. The middle side stringer terminates in the slot in F13 (see pictures below).





T-nuts for mounting the tail wheel assembly are added to F14 and glued in place.



F13 assembly together with F11, F12, F14, and side stringers can now be glued into place to complete the aft end of the fuselage structure.

[JimD]

Working forward, assemble the tank floor parts.



Add the tank mounts at the proper width to accommodate the size tank you intend to use.



Add the canister muffler supports F2c and F2d to the bottom of the tank floor.



F2 plus the tank floor assembly are added to the crutch.

[JimD]

Locate the engine mount box parts and former parts F1 and F1b.



Peter added F1 to the crutch and finished out the bottom fuselage before adding the engine mounting box.

We opted to assemble the engine box parts and add them to F1/F1b before adding F1 to the fuselage crutch. This requires the fuselage crutch assembly to extend beyond the edge of your workbench because this whole assembly (engine mounting box plus F1/F1b) extends below the workbench surface. Either way works, but Peter's sequence avoids having to move the crutch assembly to accommodate the top parts.

Add the landing gear mounting T-nuts to the landing gear mount plate. Note that the T-nut neck is a little longer than the thickness of the plywood UC mount plate. We cut some scrap plywood to fit on the top side of the UC mount plate between F2 and F2d to add thickness to accommodate the T-nuts.

Add F2c to the bottom of the UC mount plate using F5 as a spacer. Stringers are added between F1 and F3 leaving a space for the Landing gear between F2 and F2d.

Cut silicon tubing into 9/16" lengths and fit these pieces into the slots in F2c and F2d.

[JimD]

Locate the 1/8"x4"x48" balsa sheeting. In a step-by-step fashion, the sheeting is glued to the fuselage framework. Regular Windex can be used to assist with bending and forming the balsa sheeting to the fuselage frame. Start by gluing one edge of a piece of sheeting to the frame starting at F4 and extending back to F12. Wait for the glue to cure and then wet the sheeting with Windex and gently bend it over the frame. Once satisfied, add glue, bend the sheeting over the framework, and use masking tape to hold the sheeting in place until glue cures. Once cured, cut the sheeting along the centerline of center stringer. Repeat this on the other side.













To finish the aft fuselage sheeting, cut another piece of 48" sheeting to fill in the center. Note that this sheet will extend forward to F3.

[JimD]

Next step is to add the liteply fuselage sides. Pay attention to the placement because the edge along the crutch fits at the midline of the crutch. The lower edge of the liteply window frames will cover the other half of the crutch.




Now the balsa sheeting between F3 and F4 can be filled in. We did this in three parts.








Now add the 1/8" balsa sheeting between F1 and F3 leaving space for the landing gear and an opening for canister cooling air exit.



Sand joints to a smooth contour.

[JimD]

Strut mount parts are glued together.



Be sure to make a right and a left side!



Note the notch in the strut mount fits over the stringer inside the fuselage and is glued to the backside of F2d and the liteply fuselage side.



Measure and drill a starter hole through the outside of the fuselage...oops...we were a little off!!! Use a small plunge saw to cut out an opening into the strut mount pocket.