Now that the SGS 1-26E is complete and ready for cutting in quarter scale, I've put the 1938 Lawrence Tech IV, Yankee Doodle Sailplane NX18459 back on my desktop for final development at third and quarter scale.
Beginning with the larger of the two at 186" (15 1/2 ft. or 4.7 meters) span it will be drafted in exact scale (as much as possible) using scaled same wing, empenage and fuselage structural member spacing. Airfoil will be the scaled full size NACA 4418 transitioning to NACA 4416 at mid-section and to NACA 4409 at the tip with 4 degrees of washout. This should provide great slow speed turning to center in smaller thermals while still providing the ability to range well between thermals at this large scale. I will draft it with the earlier four-light flat-wrapped glazing on the canopy and will likely offer a vacuum formed part to replace this at some time in the future.
This is another fine example of the short-span theory of design of that era which resulted also in the 1937 Harland Ross - Harvey Stephens RS-1 later known as Zanonia which used the similar NACA 24 series airfoils and went on to set and hold more records than any other sailplane of its time. I've decided to complete plans and kit of the Laister first over the Ross-Stephens due to the relative lower complexity of designing and building a fuselage that is stringer on frame with fabric covering vs. the plywood-on-bulkhead monocoque construction of the latter. We will however release similar scale RS-1s in the very near future.
Here are the full size aircraft specifications for the LT IV as we will be designating it for those of you who love to do area vs. cubic vs. span loading calculations:
Structure Weight: 124.7 kg
Flying Weight: 214.3 kg
Wing Span: 14.173 m
Wing Area: 12.5 sq m
Wing Loading: 17.14 kg/sq m
Root Chord: 137.2 cm
Tip Chord: 50.8 cm
Aspect Ratio: 15
Fuselage Length: 5.867 m
Stabilizer Span: 269.2 cm
All for now.
CONSIDERATIONS FOR KITTING THE LAWRENCE TECH YANKEE DOODLE
I've done quite a bit of research into possible solutions to the method I would like to employ in the design of the Lawrence Tech IV sailplane kit. Some of the considerations are a given based upon the methods of construction I've used in the past for previous kits such as bulkhead and stringer fuselage. Others needed considerable more thought and analysis of the advantages and disadvantages from both a design and buildability standpoint while still offering the most scale interpretation of the original design.
Those areas of wing construction assessed include a faithful reproduction of the arc of the wing at mid-span, a viable and simple method of wing joint to the fuselage, ease of building the faired wing root area, and a simple and effective way to build washout into the outer panels. The methods chosen for these are to build the spars as complete double-tapered (both in frontal and plan view) assemblies first which allows the wing to be built without jigs or fixtures as single-piece left and right panels. By extending the spar into the fuselage by protrusion from the root rib, wing joining can be accomplished without the use of separate joiner rods, plates, or coupling devises.
By using slots fore and aft of the boxed wing spar assemblies, fore and aft rib sections are easily cemented to the faces of the spar by simply clamping each to the workbench while this operation proceeds, using only a square and the notched leading edge to fix the ribs square and parallel.
Many designs simply join to flat panels to make the gull-wing anhedral bend of the wing at mid-span but I didn't find that to be a satisfactory trade-off to scale realism and quality, so a different approach was needed without adding complexity to the parts or build.
Similarly, washout can be easily achieved in this method by simply varying the half-rib shapes and therefore their angle relative where each tabs into the face of the spars. As stated above too, a spar constructed in this fashion lends itself to being tapered in plan view, reducing mass at the wing tips and in a much simpler method than would be needed using the method employed using cap-and-web constructed spar systems. In addition, this method vastly reduces parts count and construction time by eliminating multiple shear webs being placed between each rib pair in tedious progression or the need to custom cut or fit each of these as the wing build progresses. The shear load bearing is accomplished instead by the completely boxed spar assemblies with the added benefit of highly accurate anhedral and wing mounting angles more easily accomplished than using other methods.
For movable surfaces, the use of enclosed hinge lines with gap seals for all such joints was studied and simple methods of building these features into the sheeting and hinge spars was chosen for these.
Finally, fuselage construction is designed to proceed likewise without the aid or need of any jigging fixtures or special tooling. By building the square and parallel wing root area flat on the work table first and using a removable center spline to align and cement in the forward and aft formers this may easily be accomplished. Lower formers in the forward fuselage along with the attendant formers for the lower stringers will be added after the majority of the fuselage construction is complete.
As has been the case with previous designs, features will be designed in to allow removal and replacement of major assemblies such as hinged surfaces and empenage for servicing and transport and instrument panels and decal kits will be standard equipment as planned with all of our "Giant Scale" kits and provision for pilot seat and fully hinged canopy is also being considered.
Fuselage Length: 92.4" (235 cm)
Overall Height: 25.2" (63.8 cm)
Rudder Span: 18" (45.7 cm)
Stabilizer Span: 35.3" (84.7 cm)
Wing Span: 186" (4.7 m)
Airfoil: NACA 4418-4416-4409
Wing Area: 2312.5 in.2
All up Weight: 24 lbs. (11 kg) (estimated)
Wing Loading: 24 oz./ft.2