Steve Adkins

Plans
Manual

Plans
Manual

Manual

Comments, notes, corrections and questions for the

Carbon Dragon Builders Manual

by Steve Adkins

Davis, Brian <This email address is being protected from spambots. You need JavaScript enabled to view it.> has created a Microsoft Word Document or an "electronic manual" which is an exact copy of the manual that is delivered with your plans.

The electronic manual is very easy to read in both electronic and printed version ... but, it allows for electronic searches for a specific item! Each page is full size 8.5 by 11 inches rather than a reduce size with 4 pages on one page as provided Maupin, ltd.

Many of the comments below have been factored into the electronic version.

Jim Maupin is able to describe a fairly complex procedure very succinctly. When I attempt to write a process, the text becomes overwhelmed by minutia. To be honest, I was dissappointed by the builders manual and extremely pleased by the drawings. On the other hand, much of the instructions are contained directly on the drawings. EAA, Chapter 25 holds a plans night about once a year and Maupin's plans (drawings) are much better than most plans sets (which are in a few cases ... one large sheet!). The drawings and handbook coupled with membership in the SHA are sufficient to enable one to create a Carbon Dragon.

The builder's manual appears to have been a preliminary rough draft; perhaps, with parts dictated to a tape recorder and transcribed by a typist ... or typed from handwritting ... thus, many errors are in the transcription process, not made by the designer. Organization leaves much to be desired ... at least one section is repeated with slightly different instructions; perhaps an updated version was slotted in without removing the first version. In any case, these errors are fairly easy to reason out and should not lead to building errors. The purpose of this section is to get new builders a fast start and to provide an exchange of information regarding corrections and comments.

Below is what I have noticed so far ... mostly nits. Much of the "changes" are adding merely clarification and headers to faciliate finding sections. In the few cases where there is a serious problem, I will highlight the text with red and a graphic like this [tbd] ... being, I'm glad we found it! One final note: The stuff below is one man's interpretation, subject to error ... if you have a better interpretation ... This email address is being protected from spambots. You need JavaScript enabled to view it.

Light red, an assumption I have made ... 3 instance
Dark red, warning about critical error ... 0 (first 16 pages)
Dark yellow, warning about known changes being made by another builder which I deem wrong ... 1 instance
Green, a question I have that is unanswered ... 2
... seem to be rather low numbers.

Page 3, 5th line:
Replace "wear tight" with "near right" of "near one" ... to read, "Staple ... near one edge".

Page 4, 1st line:
What part of the stabilizer is place flat on the table?

Page 4, mid page just below first drawing
Place a dividing line with the heading "Elevator" just below the line.

Page 5, mid page:
Replace "8 to 18" with "8 to 8"

Just below the "6 to 16", etc. ... I made a drawing of the tow "layers" to clarify the text description

36"                               24"                               16"                                  8"                                 C/L
                                                                                                                  _______________________
                                                                                                                  _______________________
                                                                            ______________________________________________
                                                                            ______________________________________________
                                      _____________________________________________________________________
                                      _____________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
|               2 tows            |                4 tows            |                6 tows             |               8 tows          |

With each line representing 2 pulls of 12k carbon fiber tows (or yarn). This drawing represents the tow pattern for the center table of values. As you can see, from the root section or CenterLine to the 8" point, the tows are 8 deep.

Page 6, second illustration:
After counting the layer ... I decided there is a total of 7 pieces of cloth required.

Page 6, 7th line:
I might replace "Squeeze off" with "Squeege off". A nit.

Page 6, last line:
A hole for only one retention cotter pin ... I guess that is comparable to other sailplanes. Which bolt?
How do you put the cotter pin in place? ... those bolts are deep in a nicely rounded nose D-section.

Page 7, Above the title "Female Hinges", I drew a dividing line. No big deal.

Page 7, under 4th paragraph (ending with the word, " ... place"):
Draw a dividing line and add the title below the line, "Elevator Horn".

Page 10, the rudder horn
This item has puzzled many people. Jonathon Pitts wrote a dynamite article with photos and detailed decription on how to perform this construction. See Sailplane builder, September 1995, page 6. Back issues are available from SHA.

Page 11, drawings of "plug" 2/3rds down the page with labels "top view" and "side view"
After I puzzled out what these parts are ... I have had arguments with other plans holders who disagree.
The first reaction, is that these are two views of the spruce "box" (see first line of text). But, they are really the drawing of the "plug" that goes inside the box. I assume the plug is made from balsa wood. Also, be sure to note that the plug has rounded edges (see last line in first paragraph). The intent is to have a portion of the carbon spar cap to be a hollow carbon square tube. Structural engineers will attest to the stiffness of a hollow square tube ... much better than a round tube (and more resistant to denting (as when steel square tubes are used in fuselages in place of round tubes).

One builder is leaving out the plug.[tbd] I totally disagree with this change unless some other compensating change is made coupled with design analysis. A flat ribbon in this area may not be stiff enough to resist buckling under high G forces.

Also, note the upper-right most figure shows a vertical line in the spruce box cross-section. This line represent the tip of the balsa plug.

Page 12, first row of fractions:
Replace "3/5" with "3/8" ... yes, I know this is obvious!

Page 12, second row of numbers:
There should be a drawing of square under 5/16 x 5/16 similar to the two drawing to the right.

Page 12, second paragraph:
Change "larger piece" to read, "larger plug piece". ... well that's my guess ... what's yours?
Do the same in the spruce box sides?

Page 12, 3rd paragraph, 5th line:
Change "nails are" to read "nails in the plug are".

.... Time to take a break ... having fun yet? If not, wait for the carbon "pulls" for the spar cap! ....

Page 13, mid-way down the page on the right
I would replace the word "Ribs" with "Rib Numbers"

Page 13, bottom row of numbers:
Replace "14" with "15" ... also, between "23" and "19", you might want to place the total, "21"

Note: The bottom row is the total number of tows at the corresponding position in the spruce box (don't add the Rib Number into the total!).

Page 13, second figure from the bottom:
I drew a side view of the carbon material which is a long wedge shape of carbon.

Page 14, immediately under the second paragraphs ending with the word, "...curves".
Draw a dividing line. Below the line, write the heading, "Wing Ribs".

Page 14, to the left of the third paragraph:
Write "Nose" for nose ribs.

Page 14, to the left of the fourth paragraph and illustration:
Write "Center Ribs".

Page 14, draw a dividing line under the figure followed by the heading "Wing Main Spar Shear Web"

Phil Lardner

Description
Analysis

Description

Designing a Three Part Wing

The original Carbon Dragon, as designed by Jim Maupin, had a two-part wing joined at their root, at the centre-line of the glider. With a full wingspan of 44 feet, this means that any trailer built to haul the glider around would have to accommodate two 22 foot long wings - not only unwieldy for a single person to handle and assemble (especially in a breeze) but also likely to incur extra charges every time the glider is taken by ferry to the continent from Ireland. Splitting the wing into three sections would reduce the longest component to around 15 feet.

A number of issues arise when considering a three-part wing:

Where to split the wing:

If we split the wingspan roughly in three, each section will be 14.66 feet (or 176 inches) long. It makes sense to split the wing just outboard of the nearest rib. So if our centre section of wing is approximately 176 inches long, dividing this dimension by 2 (half, either side of the centre line of the glider) we get 88 inches. Looking at the drawings, Rib #5 is closest to 88 inches outboard of the root, 94 inches out from the centre-line. The total length of the centre section of wing is therefore 94 x 2 = 188 inches or 15.67 feet long. The length of the two outer sections of wing then become 44 feet less 15.67 feet = 28.33 feet divided by 2 = 14.165 feet or 169.98 inches long.

Dihedral:

Dihedral must be built into the centre section of the wing if we are to maintain the inherent stability of the design. We can work out the amount of dihedral by carefully examining and measuring the drawings.

On Drawing #1 we see that the wingspan of the glider is 44 feet, so one wing length, root to tip is 22 feet or 264 inches.

Drawing a line perpendicular to the vertical centre-line of the glider, from the vertical midpoint of the spar-web at the root out to the vertical midpoint of the spar-web at the wing tip, we can measure how much higher (dihedral) the centre-line of the wing tip is above the centre-line of the wing root. I measure this as 12/64ths (or possibly 13/64ths) of an inch... approximately!

wing dihedral

Ignoring the scale given on the drawing (because the printout of the drawing from the PDF file cannot be trusted) we can derive the true scale by dividing the wingspan dimension indicated on the drawing (44 feet or 528 inches) by the physical measurment of the drawing of the same dimension (16.75 inches). Thus the true scale of the printed out PDF drawing is 528 / 16.75 = 31.522x.

Multiplying our 12/64ths of an inch by the correct scale, 31.522, gives us the slightly odd dimension of 5.9 inches. Given the thickness of the lines on the drawings, it is difficult to get an exactly accurate measurement, and we could easily be out by more than 1/64 of an inch, and indeed Steve Adkins reckoned it to be 6 inches exactly, which seems not unreasonable.

Steve Adkins notes: "As to the dihedral: dihedral is provided by building the lower spar cap 0.25 inches longer than the top spar cap. The assembly pins are 11 and 5/64th inches apart at the bolt centers. From this, you can calculate how much a wing tip would be raised. I am thinking the center line of the wing tip would be raised nearly 6 inches above the wing root center. One builder mentioned to me he was going to build a flat wing which I discouraged (I wouldn't second guess Irv Culver)."

With this new dimension quantifying the dihedral built into the wing (how much higher the centre of the wing tip is to the centre of the wing root) we can, by simple trigonometry, work out the angle at which the wings tilt up from the vertical centre-line of the glider. This angle is 1.3°. It is critical to know this angle when it comes to laying out and fabricating the centre section of a three part wing.

Spar Cap Root Junctions:

Attention need to be paid to how we treat the stresses on the upper and lower spar caps where they come together at the root. The pultruded carbon rods used in the spar caps will not bend at the root / centre line to accommodate the 2.6° (2 x 1.3°) of dihedral built into the centre section of the wing. [NB: actually the rods *will* bend to accommodate the built-in dihedral, as I later discovered, but an unbroken bundle of rods does make the lay-up and bagging process a bit trickier] The bundles of rods must therefore terminate at the centreline and a load transfer bar must be designed and incorporated.

In designing the load transfer bars which transfer the spar cap loads from the carbon rods to the wing root metal fittings for a two-part wing we calculated that the bar must have a minimum thickness of 0.184". The 284 Twill Carbon Fibre cloth I am using has a thickness of 0.011" per laminate, so therefore we need a minimum of 0.184 / 0.011 = 17 layers of cloth in our load transfer bars (for both upper and lower spar caps) spanning the space between the two root ribs.

It would do no harm (and add little weight) to beef up the centre section of the spar web, between the two root ribs, to make the whole assembly a little more robust. One way to do this is to sandwich a plate of 5mm thick PVC foam board between the root ribs and the upper and lower spar cap load transfer bars. As luck would have it, 0.184" = 4.67mm thick, so by adding just one more laminate of carbon cloth to our load transfer bars (making them 18 laminates thick) will allow us to create a perfectly flush surface between the root ribs and the spar caps of the centre section!

Note: When the centre section of the three-part wing is not connected to the rest of the glider (i.e. during rigging / de-rigging and transport) the root section of the spar will be liable to experience large bending forces if it is not properly braced and supported at the drag spar connection points, and there is a very real possibility of damaging the spar. Inserting a short beam of plywood between the drag spar connection fittings will prevent the spar from bending in the wrong direction.

Wing connections:

Splitting the wing at a rib position allows us to close off the ends of the centre section of the wing by incorporating a blanking plate into the rib to prevent dirt and insects from getting in. By replicating this rib (Rib #5) we can also close off the outer sections of wing also and provide a solid mating surface to the two parts of the wing. As we will see below, the wing connection fittings and load transfer bars will need to protrude through all of these wing section end ribs.

While we can safely use the 17 layer (minimum) load transfer bar to transfer the loads from the spar caps across the root section of the wing, the loads on the wing spar caps and shear web are considerably less when we move outboard along the wing. At Rib #5, where we plan to split the wing, the loads are considerably reduced (less than half) from those experienced at the root. It is sensible, therefore, to recalculate and redesign the load transfer bars and the metal wing connection fittings so that weight can be saved where possible.

Redesign the connection fittings and method...

(to be continued...)

Flaperons:

Joining the sections of flaperon - maintaining stiffness!

(coming soon...!)

Analysis

Click here to download an archive of Phil Lardner's 3-Part Wing Analysis

View the embedded image gallery online at:
https://ihpa.ie/carbon-dragon/index.php/component/content/article/24-plans/65-notes-modifications#sigProIddef598be29

Air Brakes

THIS ARTICLE IS INCOMPLETE - check back later... possibly much later!

I am investigating the possibility of replacing the single delta shaped spoiler, behind the pilot's head, with proper Schempp-Hirth air brakes inside the wings, just inboard of Rib #5, and just outboard of the H-Stab to elimenate any interference (by turbulated air) with the rudder and elevator. I have a basic design concept on paper but it has yet to be prototyped and load tested up to and beyond Vne by attaching it to the roof rack of my car and driving it up and down the motorway! I will need to construct a small section of wing (leading edge, wing spar and trailing edge...) between Ribs #4 and #5, where the air braek will be fitted, so that both the air braek and the wing section (against which the braek forces will react) can be tested to see how they perform.

http://en.wikipedia.org/wiki/Air_brake_%28aircraft%29

Although this type of air brake will probably add a little weight to the glider overall, I want my Carbon Dragon to have a cockpit layout that will be familliar to any sailplane pilot. I also believe that the new Schempp-Hirth brakes will be easier to use with greater finess. Some pilots report the original delta shaped spoiler is difficult to open fully at higher airspeeds. Maintaining a constant glide slope requires accurate and fine adjustment of the air brakes - something not possible with the original delta spoiler.

(Details coming soon...!)

Tail Boom

I am making the tail boom removable from the pilot pod - this requires a new attachment method using high shear strength pip pins.

I am making the tail/rudder removable from the tail boom for more compact transport - this requires a new attachment method using high shear strength pip pins.

Both of these changes will also require modification of the control wire system for the rudder and elevator.

Details coming soon...

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