SCALE BUILT RC's

30% Scale CX4

A deluxe, professionally engineered all wood scale model kit of a new homebuilt aircraft, the Thatcher CX4. Our CX4 is suited for sport flying, advanced aerobatics, and scale competitions. With a two piece 85" wing, it is easy to transport. Several lower cost 30-40 cc gas engines

can be used.  Only 6 servos are required.

Revision Date:10/06/08

I have decided to produce some deluxe balsa wood kits. The kits will be scale models. Not with exact scale structures like our Great Lakes and Aeronca projects, but scale models that can be competitive in many scale competitions. Our kits will be pretty close to scale, but liberties will be taken in some of the shapes and contours of the structure to allow for an easy to fly scale aircraft and still be somewhat simple to build.

Our kits will be marketed under the name of SCALE BUILT R/C. They will not be inexpensive, but will be of the highest quality possible.

I have chosen for our first kit the CX4. The model will be in 30% scale which will produce a 85" wingspan. Power will be a 30-40 cc gas engine. Many of the larger glow 2-stroke and 4-stroke engines could also be used. Shown below is a great photo of the full-scale CX4.

Our CX4 is engineered with the use of a professional computer assisted drafting (CAD) solid modeling software. This software allows for the creation of unlimited photo quality illustrations in a  three dimension format as well has 3D and 2D full-scale or smaller scale engineering line drawings for the shop or building drawings.

Instruction manuals will be contained in a series of customer supplied 3-ring binders. Step by step, check off, instructions are provided. Customers will receive instruction updates as necessary.  The updates are easily inserted into the 3-ring binders.

Our 3D CAD drawing software allows for an unlimited number of illustrations of any angle or view for any part, subassembly, or completed assembly such as this  3/4 rear side view. Our CX4 is of all balsa construction. 1/16" Balsa wing & tail sheeting. 3/32" Balsa fuselage sides and sheeting. 1/16" Plywood fuselage doublers. 3/8" Birch plywood firewall. 2 piece 85" wing. Scale strip ailerons, scale cockpit detail with room for a full figure 1/4 scale pilot, the canopy will slide rearward, fiberglass cowl. 3 1/2" spinner, 30-40cc gas engines. There is room for a 32 ounce gas tank for the large glow engines. 6 H.D. servos are employed. The 3/16" aluminum landing gear has 3 1/2" wheels. Fuselage width at firewall is 7 inches. Cheek cowl width 9 3/4". Estimated weight 18-20 pounds.

Also in the individual instruction manuals will be a list of materials

that will have to purchased at the hardware store, such as the particle board shelving. The hand tools needed to build the particular assembly will also be listed.

Most likely the person who will be building one of our CX4's will also have a small band saw, a drill press, and a disc or belt sander. These items are not necessary to build our CX4, but they will certainly speed up the building process.

Construction is conventional with mostly balsa, with a few birch plywood and spruce parts such as the firewall, fuselage side doublers, and spars. Cowl & wheel pants are fiberglass. A two piece wing allows for easy transport. Canopy slides aft to get access to wing attachment fittings, servos, and scale cockpit detail.

Our SELECT R/C balsa wood is used in our kits. The various items of balsa wood are selected and identified for their intended application in the aircraft's structure. Soft or light weight balsa is not necessary for many applications. Sure it is light in weight, but also low in strength. There is a compromise in the selection of what density (weight) that is used. I prefer to use thinner heavier weight wood instead of thicker softer wood.

Most of the R/C models I have built have employed the use of building jigs. A little bit of time is required to make the jigs, but the actual time to build the assembly is less and a lot easier. The jigs provide for a very high degree of accuracy. My philosophy on the use of building jigs takes care of a major construction problem during the building of model aircraft. One has to make certain that the left side of the airplane is the same as the right side. If there are differences in the right and left hand components of the aircraft, aerodynamic problems will occur causing difficulty in properly flying the model. Building jigs will make both sides the same.

The building jigs that are employed are made mostly from particle board shelving found at hardware stores. Particle board is inexpensive and free from any warps. Complete drawings and illustrations are provided to build the jigs. The wing and stabilizer assemblies are built on removable aluminum tubing rods that hold the ribs in position. The supports for the rods and the location blocks for the ribs are made with pine molding strips found at hardware stores.

This illustration shows the easy to build building jig for the wing. The base is standard particle board available at hardware stores. The alignment blocks are made from pine molding strips. Not shown is the shop drawing for the wing that is glued to the particle board. The blocks are glued in position as noted in the drawing. Another particle board jig is made for the right hand wing panel.

The wing structure is supported on removable aluminum tubing rods. Two 1/2" dia. rods are used for the constant chord sections of the wing. Two 3/8" dia. rods are used to support the three tip ribs. The wing structure can be easily removed from the jig. Basic wing structure is shown. After the structure is glued together, it is removed from the jig and the leading edge and front bottom sheeting are glued into positron. The structure is then placed back onto the jig. Then the top sheeting is glued into place. With this amount of sheeting the wing is not subject to any twisting. The additional bottom sheeting can be glued into position without the need of the wing jig. Note that the ailerons are built as part of the wing's structure. The ailerons are cut from the assembly and both the ailerons and wing have their final components installed separately.

Several engines can be used. Two engines in particular are recommended, the OS BGX 3500 and Super Tigre 3250. Both of these engines have not been very popular due to their high consumption of glow fuel and the resultant high cost for the fuel. However, both of these engines can easily be converted to spark ignition and gasoline fuel. A Prospark ignition system can be adapted quickly to both engines. Other ignition systems are available too. Gas tank size can be reduced to less than half of what would normally be used for glow fuel. Walbro carburetors can be installed in both engines.

With the spark conversion, both of these the engines provide slightly higher RPM (usually 200-300 RPM more) as compared to using standard glow fuel. With 18 to 20 inch propellers, the RPM increase is quite significant. The idle RPM will also be much lower than when used with standard glow plug operation. The lower idle RPM will allow for easier landings because of the lower thrust being generated by the propeller.

As a side benefit, both engine's mounting hole dimensions in the factory supplied ring type motor mounts are the same making it easy to install either engine in our CX4. Slimline makes Pitts style silencers for these two engines. Both engines are completely enclosed within the cowl without the spark plug or carburetor protruding out of the cowl.

Offered will be complete plans and instructions only, a short kit, a standard kit, and a complete kit.

Complete plans and instructions are available for purchase. There are full size plans of assemblies and parts as needed. Full size patterns are provided that would be used as templates to cut out the parts. The instructions are very detailed and takes the builder step by step through the construction process. Customer supplied 3-Ring binders are used to contain the instructions.

A short kit will have the plans and instructions, laser cut ribs and bulkheads, many plywood parts, canopy, cowl, special metal fittings and parts, and the landing gear. Basically all items that you cannot purchase or would be difficult to make on your own. No wood sheeting, plywood, or strip stock.

The standard kit will have the above items and all the balsa wood and spruce construction materials, but not the hobby shop hardware items such as a gas tank, spinner, paint and covering materials, wheels, control linkage, tail wheel assembly, common fasteners, etc. The standard kit may be cost effective for the customer since he may already have many of the various accessories or would like to select his own items. All the items supplied in the compete kit are available for purchase.

The complete kit will have the above items and all items to finish the model, except some common hardware store items, such as the particle board, sand paper, white glue, etc. All hobby type items are included. Only items to purchase are the engine, prop, and silencer, and the radio equipment. Estimate there will be at least $200 or more of accessory items that one would typically have to purchase to finish the standard kit.

Really, the complete kit includes everything, even the choice of light weight fiberglass cloth or Nelson fabric covering material, Nelson Hobby paint with a choice of colors, aluminum servo trays for JR or Futaba servos, scale instruments for the instrument panel, scale tail wheel assembly, wheels, wheel pants, piano hinges, ball links, clevises, aluminum servo arms and a ball bearing pull-pull aluminum rudder bellcrank, gas tank, aluminum spinner with choice of its adapter nut, T-88 epoxy, and even miniature elastic stop nuts for screws.

Having the complete kit will help those modelers who no longer have a near-by hobby shop to purchase their materials. In today's times there are fewer hobby shops around the country and many of those shops that are still in business have a minimal inventory of necessary items for those of us who still like to build airplanes.  It is possible that purchasing all the components to build the model will be cheaper than buying those items elsewhere.

As previously mentioned, the cockpit can be detailed to a very high degree of scale. Even have the rudder petals if you want. The location of the rudder and elevator servos are behind the scale seat. The servos and their aluminum tray is hidden from view which makes them removable, but with some difficulty. The servos could be located under a removable false floor typical of most aerobatic models as well as many scale models. Instead of a full figure scale pilot, a pilot bust figure could be attached to the the false floor. There is plenty of room for all of the R/C equipment to be located here.  The false floor must be easily removable to allow access to the wing spar attach fittings.

It would also be possible to convert our CX4 to electric power. With the rudder and elevator servos mounted in the original location and a false cockpit floor, there would be ample room for the battery to mounted right on the center of gravity.

I am soliciting preproduction orders for the various versions of the kits that are offered. This will help me judge the interest in the project. With this information it will help the planning of the initial production of the kits. I am not asking for any payment at this time. Payment for orders or deposits for preproduction kits will be requested after the prototype aircraft has been successfully flown and performs properly the expected flight characteristics

A 10% discount will be given for preproduction orders. When the prototype aircraft has successfully flown, then a 25% fully refundable deposit will be requested. When the deposit has been received, the initial selling price offered will be honored. As the kits are ready for delivery, the order of deliveries will be made upon date the deposit was received. Most likely there will be an upward adjustment to the selling price as experience dictates.

Thanks for taking the time to read about my CX4 project. If the reader has additional questions please contact me.

Sincerely,

    Jerry

Jerry Nelson

NELSON Hobby Specialties.

PRICING INFORMATION

Item Number	Description	Price
CX4 Plans	Complete plans, patterns, & instructions. 50% of the purchase price will be credited towards the purchase of any of the kits. Expect to have over 100 pages in the instructions. Probably about 25 full-size drawings and patterns.	A rough estimate will be $100.
CX4 Short Kit	Above items plus cut out ribs, bulkheads, plywood parts, canopy, cowl and wheel pants, special metal fittings, aluminum landing gear. No other wood components are supplied.	n.a.
CX4 Standard Kit	Above items plus everything else except common hobby accessories (wheels, tail wheel assembly, spinner, gas tank, linkage items, common fasteners, covering materials, and necessary hardware store items).	n.a.
CX4 Complete Kit	Above items plus everything else needed to build, cover, paint, install the control systems, servo trays, and the motor mount adapter. Only items to purchase are the engine, silencer, radio equipment, and necessary hardware store items	Would like to have the complete kit sell for around $500 to $600.

Prices and specifications subject to change without notice.

 

This is a view of the rear part of the fuselage without the left and top and bottom sheeting, and other details that allow the viewing of the instrument panel, servo tray, bulkheads and stringers. The instrument panel is a scale size. The red object is the 1/16" plywood seat floor. It is hinged at the rear to provide access to the throttle servo, receiver, and batteries, all of which are hidden from view. The movable floor also allows for the attachment for the four 3/16" dia. aircraft clevis pins that hold the wing panels in place. There is room for a 1/4-scale full-figure pilot. The sides, top, and bottom, sheeting are 3/32" balsa. 1/16" plywood doublers are provided and have lightening holes to save weight. The servo tray has two elevator servos with their push rods going to a slider bar that intern has the elevator push rod attached to it. The rudder servo push rod goes to a pull-pull bellcrank that has the rudder pull-pull cables. The aluminum servo tray is removable for servicing the servos.

Here is the rudder components placed into position onto the rudder jig. Not shown is the rudder jig drawing that is glued to the particle board base. After the components have been glued together, the left side of the sheeting is attached while the components are still in the jig.

The Elevators are built in the same manner as the rudder. The elevator jig drawing is not shown in this illustration. (The drawing software doesn't seem to allow the digitally placing of the jig drawing in position on the jig base.)

 

More illustrations will be added time permitting.