Phil Lardner's All-Carbon Dragon
2012 - Started Building...
- Phil Lardner
- Wing Stress Analysis
- Construction Articles
- Construction Videos
- Errors in the Plans
The devilishly handsom dude, above, is me - Phil Lardner. I've been flying flex-wing hang gliders in Ireland and around the world since 2000 and, for my sins, have been the Training and Flight Safety Officer for the Irish Hang Gliding & Paragliding Association for much of that time also. Flying is one of the great passions in my life... and like most of my other passions, I ain't getting enough of it! So to keep my impishly inquisitive hands busy and out of mischief I decided to build myself a Carbon Dragon. My decision to go for a Carbon Dragon was partly dictated by lust and partly by pragmatism - I wanted something with a lot more performance than a hang glider but without the regulation, licencing and price tag of a sailplane!
Enter the Dragon...
The original Carbon Dragon, by Jim Maupin with airfoils by Irv Culver, was designed to be built out of spruce, 1/4" mahogony plywood and 1/32" (0.8mm) plywood, reinforced here and there with the judicious use of carbon fibre rovings bonded to the wood. The prototype CD, now owned and flown by Gary Osoba, was a masterpiece of minimalism - Jim Maupin's philosophy in building the Dragon was "if you want to add to or change the design, first take it outside and toss it up in the air. If it comes down... it's too heavy!"
Spruce and plywood are incredible materials - their strength to weight ratio is very hard to beat. It's easy to make something stronger, but it's very difficult to make it stronger and lighter. Even modern composites struggle to beat natures own wonder materials. Where spruce and thin plywood do fall down is when it comes to humidity. Wood is naturally hygroscopic - that is to say, it absorbs and releases moisture depending on the relative humidity of the atmosphere around it. Over time, the thin (0.8mm thick) plywood leading edges of the flight surfaces begins to deform and go out of shape and, as a result, looses aerodynamic efficiency and strength. Ireland, sadly, is not noted for its dry, desert-like climate, so building such a light, flimsy glider out of wood in this country is probably not the smartest idea!
Various builders have replaced some of the wooden parts with composite materials to a greater or lesser extent. No one, as far as I could make out, had ever built a Carbon Dragon entirely out of carbon fiber, or had done a thorough analysis of the loads and stresses on the wings and airframe. If I was going to build one of these gliders and fly it, then I certainly wasn't going to trust life and limb to a lot of guess work and wishful thinking. I wanted to know exactly how strong each individual part and assembly of the glider needed to be and I was going to verify those numbers through destructive testing first...
Later incarnations of the Carbon Dragon, with Steve Arndt leading the way with his beautiful Magic Dragon, replaced the wooden wing spar caps with much stronger and lighter pultruded carbon rod. However, when I started seriously looking at the Carbon Dragon, there was no information about how much of this new wonder material was to be used, so I decided to analyse the loads and stresses on the wings from scratch. You will find a record of my calculations, along with an interactive spreadsheet into which you can enter your own design criteria, on my Wing Stress Analysis page.
As my study of the design progressed and I learned more about the strengths of carbon fibre cloth, I decided to fabricate the leading edges out of two layers of carbon twill cloth laid up at 45°. The carbon leading edges will likely turn out slightly heavier than the original 1/32" plywood skins, but they will be much stronger and not subject to warping in humid conditions. I hope to save weight else where to compensate. [Note: Rick Mullins talked to Steve Arndt about the construction of his Magic Dragon. Steve says that he built carbon fibre leading edge D-skins for his wings and has successfully towed behind an airplane at speeds in excess of 70mph with no sign of wing flutter.]
The original wing ribs were fabricated out of 5/16" x 1/4" spruce, reinforced at the joints by 1/32" plywood gussets. These looked very fiddly to make up and would require the rib caps to be steamed and formed if they were to assume the desired curves accurately. After some experementation I arrived at a method for fabricating ribs out of 5mm PVC foam, wrapped and fully encapsulated in carbon cloth. These carbon/foam ribs performed extremely well under load testing. A full report on the rib fabrication experements and load tests can be found on the Rib Construction page. My aim is to completely eliminate the use of wood in my glider and (hopefully) to end up with a stronger and lighter aircraft.
The design load-limit for my wing is +8g / -4g at a maximum pay-load weight of 260lbs. The ultimate load limit (catistrophic failure point) is +10.5g / -7.5g. Both sets of figures may seem to be overkill, and indeed it is not anticipated that the glider will ever experience more than +2g or possibly +3g in flight, but account most be taken of the instantaneous shock-loads that the glider may experience during ground handling, launching and especially during a rough landing! You can view the full details of the design weights and loads I used in my wing stress analysis spreadsheet.
Playing with Gerolf Heinrichs' Moyes Malibu at Monte Cucco in Italy during the 2009 Hang Gliding Pre-World Championships
Sensational legs, huh?!
Analysing the Loads and Stresses Along the Wing
My wing calculations are based on the formulae and method described in Jim Marske's Composite Design Manual. If you don't yet have a copy of this manual then I strongly recommend that you buy a copy, even if you don't intend to do the calculations yourself for your own design loads - it contains a large amount of practical knowledge about working with and fabricating composites. The photos, below, are of my initial hand written calculations, refrencing the appropriate pages in Jim Marske's manual, and show the formula and description of the method used to arrive at the numbers in my spreadsheet.
Download my spreadsheet here - it summarises all the calculations below and allows you to enter your own initial design loads to see what effect they have on the various parts of the wing.
I designed my Carbon Dragon to my own specific load criteria. I take absolutely no responsibility or accept any liability whatsoever for any adverse consequences should you build your own Carbon Dragon to the same design configuration as detailed in my calculations or for using my spreadsheet and any design numbers that you may obtain from it by modfying the initial circumstances. You use my calculations and spreadsheet entirely at your own risk.
17 Dec 2015 - Work in progress... I finally sorted out my colossal and ever growing unsorted gallery of photos! Hopefully you'll find finding relevant photos a little easier!!