Comments, notes, corrections and questions for the

Carbon Dragon Plans Set

by Steve Adkins


Jim Maupin has produced an outstanding set of plans.  There are 23 drawings 2' by 4'.  Most of the parts are shown full size.  This fact is amazing when you consider that the plans are drawn for a sailplane which has a wing span of 44 feet.  Of course, you don't need a full size drawing of the wing ... and the wing is made out of many small parts.   One drawing that is essential is a full size drawing for each of the 13 nose ribs. Irv Culver individually designed each rib to a unique airfoil so that the wing could be built without any twist or washout.   The curve for each rib is nestled inside the next larger rib ... allowing very compact coverage.  Again, for the mid-ribs, one rib is drawn in full detail, then the outline for each mid-rib is automatically developed using a clever drafting technique..  A 1/4 scale top view of the wing is provided ... but 4 sections from the wing are blown up full size.  All fittings, formers, templates, pod frames and bulkhead templates are shown full size. (One symetrical bulkhead has only one side drawn ... note: the line of vertical symetry is off at a slight angle, see below.)  A few 3-D exploded views are provided where additional understanding needs to be imparted to the builder.  Many people have bought these plans just to study ... the plans are that good and the sailplane is very unique with its use of carbon.  The drawings and handbook coupled with membership in the SHA are sufficient to enable the builder to create a Carbon Dragon.

Below is what I have noticed so far ... mostly nits.  I am in contact with builders and am building ... so more will be known.  Check this site often.   Most of the text below is comments adding clarification and cross-reference to faciliate finding related drawings.  In the few cases where there is a serious problem, I will highlight the text with red and a graphic like this [tbd] .  One final note:  The stuff below is one man's interpretation, subject to error ... if you have a better understanding  ... This email address is being protected from spambots. You need JavaScript enabled to view it. 

Black, minor change, note or comment
Light red, an assumption I have made
Dark red, warning about critical error
Dark yellow, warning about known changes being made by another builders which I deem wrong
Green, a question I have that is unanswered ... or possible design change to be evaluated

Below, I am using a "parts locator" convention to enable the reader to easily find the reference part on the applicable drawing. [Note:  For locating a part the following convention is used, thus a part on Dwg 9B1.

    A    B    C    D    E
1        xxx
2                                    Can be found on Drawing 9 part way across on the top (see xxx)

Various Locations: Width of the fuselage - It is apparent from the plans that the fuselage was originally 16 inches wide and increased to 17.0  inches (the two dimensions are found on different drawings).  Also, this is mentioned in one of the articles on the sailplane.  Due to my size, I further increased the width at Station 24.0 to 18 inches on a mockup after trying 16 inches (due to triangulation of the structure, spring-back has resulted in 17.5 inches).  I have made full size templates of the seating in a K-21 and found the Carbon Dragon to be very comparable but with slightly more elbow room.   Adding width to one former requires little change in other areas.  Note:  the fuselage side must be absolutely straight between stations 24 and 54.  Any bend will result in binding of the aileron torque tube.  I am considering building the side formers slightly large to give more clearance. Other areas to check plans for measurements:
15C5 Half Pod Bulkhead template Sta 54.50:  8.5 x 2 = 17.0 inches.
14C1 Top view, measurement across fuselage between longerons from Sta 24.00 thru 54.50:  16.0 inches
15B5 Pod Bulkhead template Sta 55.50:  16-7/8 inches [this could be the start of tapering the rear pod]
Note: many peope have sat in my mockup and found it comfortable.
Another change being considered is making the seat sling full width and supported totally across the top and bottom like a lawn chair rather than a narrow sling which allows foot launch and requires a pillow and head rest cushion  for comfort.  No pillow nor head rest is required with my design.  My sling canvas  was taken directly from a lawn chair and fits perfectly.  I am looking at the carbon seat pan designed for the Duster sailplane.  This pan looks strong and comfortable ... note: Maupin produced kits for the Duster before designing the Woodstock.

Various Locations: Plywood thickness - Often the plywood thickness is indicated as "  8 mm " when in fact it is " 0.8 mm".  (This is the 1/32 plywood that is ubiquitous to most of the aircraft.)

Dwg 2B4:  Rudder Pin Bearing -  The prototype has a part not shown on the drawings ... a load bearing block placed immediatly under the lowest hinge pin of the rudder.  This part eliminates the vertical force of the rudder weight on the female carbon hinges.

Dwg 15C5:  Pod Frame Template Sta 54.50 - Center line is not drawn correctly.  Since this template is drawn full size showing only ther right half ... when flips the drawing to trace the left half, you obtain an incorrect part.  At the bottom, the distance from inside the frame to CenterLine is 8.5 inches ... at the Sill Line, the distance is 8.4 inches.  Use 8.5 inches.

Dwg 1:  Dihedral - Note the dihedral in the wing on the frontal view, Dwg 1 by laying a clear straight edge on the front view.  Dihedral is moste notable when evaluating Dwg 9D1 thru 5 wherein the lower spar assembly pins are 1/4 inch further from the #1 rib than the upper pins.  You do the math ... 1/4 is to 11-1/16 inches as    is to 264 inches; thus, the center of the wing tip will be 5.96  inches higher than if no dihedral.  Careful measurement on Dwg 1 confirms this calculation.  Don't decide to use a different dihedral ... it can effect the stability and handling of the glider (I know of a builder doing this on a different aircraft). 

Dwg 4C3:  Epoxy bath - You may think the word "flame" should be "flare".  Not so.  The intention is to use flame to achieve a very smooth flare so that the fibers in the carbon tows are not broken when passing through the sqeeze hole.

Dwg 7A1:  Add cross reference for Detail F as follows, "See Dwg 9D1  or 9a4  ?

Dwg 7B1:  Dacron pieces are installed inside or toward the front of the wing ... a point made clear on the drawing, but easily missed by the builder.

Dwg 7B1:  Add cross-reference, "see Dwg 9 for section F"

Dwg 7B1:  See Dwg 9D4.

Dwg 9E5:  Under F2L fitting add, "see Dwg 7E1 or A5 ????

Dwg 11A3:  Add, "Lead weight weighs 0.75 oz, see Handbook pg 17".  Do not leave off counter-weight.  Flutter and destruction of the sailplane may result.

Clearance between Wing Spar and Boom Front:  [Change impacts position of Compression Beam on the Boom, Boom is moved to the rear; thus, boom cutouts in bulkheads should be slightly smaller and length of aileron carbon torque tube]  One thing I learned when building the pod mockup is that there is a critical conflict between several drawings. Dwg 15D2 calls out seven 1/2 by 1 inch spruce blocks between the 54.50 bulkhead and 55.50 bulkheads. Dwg 14C1 thru 14C5 shows a top and side view of the two stations. One-inch blocks means that bulkhead Sta. 55.50 should really be Sta. 55.75 to account for the thickness of the 54.50 bulkhead. If you use 3/4 inch blocks ... you will have interference between the installed wing and the top end of the boom due to the 4 degree incidence of the wing which results in the top of the spar web slanting to the rear. . The top of the boom is 4.15 inches higher than the top of bulkhead 54.5.

Solving for: distance back = height x sin(4 degrees) = 4.15 x 0.07 = 0.29 inches. Constructing a small drawing gives 0.3 inches.

So 0.29 inches + the thickness of the spar web at that point which is 0.9375 = 1.2275

Sta 54.50 + 1.2275 results in Sta 55.7275 as contrasted to 55.75 above.

Therefore, there is 0.0225 clearance between the rear of the spar web (minus the two layers of 8 oz fiberglass (0.008 inches thick times 2 plus epoxy thickness).  Seems small to me. Possibly 1-1/4 inch blocks would be appropriate.

Moving the bulkhead back may impact the length of the aileron torque rod.