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CD Variations in the real world. 04 Jul 2020 20:46 #1282

Yes! That is the basic concept, although there is now a Legal Eagle XL with a larger wing and reinforcements for a GW of 675 lbs.
I've been watching this space for a long time. The problem was always the engine. I built a RANS S-7 with a Rotax, and hated the high rpm whine.
Aircraft engines are supposed to go pucketa-pucketa-pucketa.......... or in your case, Whoosh.
So if your infused wing is the latest best piece of the mosaic, the Verner three cylinder radial is the second.
Huge slow prop disc, pulls twice as hard as the ubiquitous 1/2 VW and weighs less!
Please see Les Homan Videos of his LE-XL with the Verner 3V.

My favorite video of yours is the infusion of the main Spar with the foam stiffners and Graflite Pultrusions.
I attended one of Marske's workshops and came away with his manual and a hundred feet of material to play with,
but never felt comfortable with a web design until I saw your video using aluminum angles for a caul.
The slight tip in to match the rear of the rib, simple, brilliant.

So, my first of a thousand questions:
You cut the caps and said later that they could have negotiated the curve in the main spar.
My idea for a wing is essentially a double taper from the single strut attach point.
A very small Stinson Reliant.
With a 66 inch chord, 18% rib at the attach point, tapering both back to the cabanes and out to the tip. (American Moth)
Both inboard and outboard spar caps are in compression at the top of the spar above the strut fitting.
It seems to me that it would be inclined to buckle up, right at the point that the caps are bent for the double taper.
Perhaps a local extra rod or two would delay this, but does it then go into the shear web as crippling,
in spite of local reinforcement for load transfer to the lift strut?

I know you modern glider guys never fiddle with lift struts, at least not since the Luton Buzzard,
but I'd love your thoughts.

BTW, my second favorite video is the adult rated second thermal flight in France. (Ribbed indeed!)
Your face is a reflection of the pure joy of flight and should hold you in good stead in the nursing home.
This, of course, assumes you don't forget the Air Brakes in the Alps and never make it to the drooling stage.

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CD Variations in the real world. 07 Jul 2020 17:01 #1283

I am looking to source material in the US.
I see that Easy Composites ships to the states.
I recall your mentioning a carbon twill you felt was the best.
Can you say which that was?

Phil the Larger

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CD Variations in the real world. 08 Jul 2020 09:59 #1284

Hi Phil,

Apologies for the delay replying - busy, busy! I used 195g/sq-m (gsm) carbon twill throughout my build (D-skins, spars, ribs, tail boom, etc) as I was able to get a good deal on a large roll of it at the time. I found the twill cloth easy to work with (it holds its shape when cut, and can be deformed/molded as needed). I did make some comparative test pieces using bi-axial and tri-axial unwoved carbon cloth but found them to be much less stiff and much easier to buckle and deform if unsupported by a foam core.

I used two layers of 195gsm twill in my leading edge D-skins at 45degrees to the long axis with a single layer of 100gsm(?) kevlar at zero degrees, sandwiched between the carbon layers (to protect it from UV), and this was much stiffer than even the equivalent weight of tri-axial carbon.

I later learned that not all carbon cloths are similar - you need to pay attention to the Modulous number of the cloth. High Modulous carbon is stiff, but not as strong as low modulous carbon... which is less stiff but stronger in tension/compression. I got lucky buying my big roll of carbon twill, which turned out to be a medium modulous cloth - a happy medium! I strongly recommend making small test articles with different cloths to see how they perform before committing to buying a large roll!

See this post for an overview of carbon/kevlar/glass properties: carbon-dragon.ihpa.ie/index.php/forum/ca...heir-properties#1252

Hmm... having just re-watched that video, I may have meant to refer to the Tenacity of the cloth rather than the Modulous - don't trust my memory - do your own research!!

You'll almost certainly find a supplier more local to you than Easy Composites, and save a bundle in shipping haz/mat costs in the process. For the resin infusion process, look for a very low viscosity resin system that can be post-cured to a reasonably high temperature (80C+).

Regarding the treatment (bending or cutting+joining) of carbon rods in a double tapered wing - I can't advise you here, as I don't have any experience there! Maybe consult Jim Marske (and post back here with his advice!)

I'm half way through doing the stress analysis on the 15m Windrose wings, which are double taper, but the spars in that wing are straight and do not have any 'kinks' - they're double-tapered in planform, not elevation.


PS - re-watching my 2nd thermal flight video brings back memories of an aching face from all that smiling! Roll on 2021, when I hope to be back in my Alpine playground!! Curse you Covid-19 - you're more dangerous than Snoopie's Red Barron!!

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CD Variations in the real world. 08 Jul 2020 20:18 #1285

Please, no apologies. I'm just thrilled to be having this conversation. Thanks for the materials video. I have been doing my homework. It turns out that the 40 ft of pultrusion I purchased during the Marske workshop, was way back in 2006. Companies have come and gone and the Chinese have entered the market, so there is much to learn.
1.) What size are your rods and how are they stacked?
The ones I purchased from Jim are .092" X .220" These are no longer available in spool lengths from the company that replaced the company that I got them from. Checking Jim's site, I find that he is now selling .060" X .116" rods, @ $1.27 per foot.
I'm assuming it is the total crossectional area that matters and individual rod size isn't crucial. Although smaller will turn dihedral corners better.
2.) Can you talk about component assembly? The videos show leading edges and ribs and trailing edges. How are these assembled? For example are ribs assembled inside the cured LE skin while it is in it's mold? Is the spar set in on top? Or did you assemble ribs on the spar and then add the skin? Did you use epoxy an flox or the construction adhesive shown on the Easy Composites Video? I'm assuming the ribs are capped with 1" carbon. Are these strips scarfed to the LE and TE? Are the Aft ribs aligned with a string or laser. and the TE built on top? Are the LE's less than full span and then joined. Is there a joggle or are they scarfed. Does the seam fall on a rib?
My design has no flaps, so the TE out to the ailerons is very slight. There is no rear spar, just the drag spar and a false spar for the ailerons. This worried me, until I looked at my drawings for the Jodel series. They all have long aft ribs, widely spaced and attaching to a lozenge shaped spruce TE. Surely, capped carbon ribs and TE will be stronger.

BTW, I'm planning on using Oratex to save weight. What are your thoughts on that?

3.) Can you talk about the construction and assembly of the drag spar? Are the ribs that pass through it, pieced or visa versa?

Thank you so much for these conversations. I was gratified to hear that you were building another airplane. It is a joy to have a huge puzzle to solve.
Did you have a chance to see the video of Les Human and his three cylinder radial Legal Eagle? I think thee Verner line of engines is becoming ubiquitous in Europe.
Wear a mask and stay safe. You must stay healthy until I have picked your brain dry.

Warmly, Phil

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CD Variations in the real world. 08 Jul 2020 20:22 #1286

that's Les Homan........damn autocorrect.

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CD Variations in the real world. 11 Jul 2020 11:01 #1287

Hi Phil,

The pultruded carbon rod I purchased from Jim Marske was .092" x .220", and you're correct - it's the overall cross-sectional area of the bundled rods that is important. You should be able to modify my spreadsheet to your own design and the smaller cross-sectional rods Jim is selling now. The spreadsheet is based on the method and formulae given in his Composite Design Manual.

I came across another supplier of continuous pultruded carbon strip (rather than rod) that is being used by AC Light Aircraft in the Netherlands. I haven't got a sample of it yet, but it is another possibility for my next project.

I bundled my rods together using very narrow (2mm) strips of masking tape to hold them together at intervals for easier handling and placement during the wing spar lay-up. You can see how I did this here:

I made a decision early on that I wanted a 3 part wing (which has its pros and cons in daily use... but was definitely more work to fabricate than was worth it!) and so I made two separate leading edge molds for one wing (the inner and outer sections each got a separate mold). For the other wing I decided to just make one long mold and laid up the inner and outer sections of that leading edge in separate operations - this was *a lot* less work... and gave me the option of making a 2-part wing at a later date if I ever feel mad enough to go down that road again!... but that will necessitate either joining my two-part LE molds into one or making an altogether new mold for that LE - naa, I'm not going there!!

I didn't have enough space in my workshop to leave the leading edges in their molds so I could assemble the ribs and spars in one go, so I ended up bonding the forward and aft ribs to the spar followed by the aft spar and finally the leading edge skins. You should be able to follow my process here:

The original plans call for each drag spar to be made in two parts and assembled either side of aft rib #2. I fabricated my drag spars in one piece, and laminated a single .092" x .220" pultruded rod into each of the drag spar caps to help carry the loads. I also molded a recess into the flat edge of the drag spar cap flanges, which I later filled with a twisted 'rope' of carbon and kevlar tows as per the original plans. Again, you should be able to see this in photos 110 - 122.

Throughout the build I used a thixsotropic (stiff / non-runny / will not drip off the mixing spatula) mix of epoxy and cotton flock for bonding ribs to spars and leading edges to ribs, etc. Beware! This is where 90% of unnecessary weight is added to my glider!! Make sure you wipe off as much of the excess squeeze-out cotton flock mix as you can. It is amazing how quickly the weight adds up here! I've lost my original weight measurements for my naked spars, ribs and leading edges, but I do remember that the total weight was significantly more than the combined weight of the individual components! I started out applying the epoxy/flock mix with a spatula but quickly moved over to using a big fat 'horse' syringe, which delivered a more uniform and controlled bead of glue than the spatula method. My pharmacist eventually asked me why I was always buying so many big syringes, and I smiled sheepishly and told him I had a monster drugs habit! :-)

All the rigs were fabricated with a 5-10mm wide flange around their edges. This is fine for bonding to the spar, but I was concerned that it wouldn't be wide enough to bond the wing skin cloth to, so I fabricated a large flat sheet of 2 layers of 195gsm carbon and cut that into 25mm (1") wide strips, which I bonded onto the long curved edges of each rib. The ends of these strips, where they meet the leading edge D-skin and aft spar gap cover are simple butt joints. Any irregularities were sanded out and fared with a skim of car body filler (more weight!) I don't seem to have any photos of the process, but you can see the faring process and end result here:

I covered my wings using products from Stewart Systems Ltd. (Super Flite 103 UL dacron/polyester cloth and their Eco-Poly 2-part paint system), which I am super happy with! I built my glider on a budget (the whole reason for building it was because a mate bought a Swift Light and I wasn't about to let him conquer the skies with that sort of cheque book aviation! The problem was, I couldn't afford to splash that much cash (€30,000+) on a toy, so I built my CD for around just €3 - 4K (including rocket parachute.) My penury also limited my options when it came to covering the wings. I had hoped to use Oratex UL pre-painted cloth, but I just couldn't afford it at the time. I have seen the finish you can get with Oratex on the Archaeopteryx gliders I rub shoulders with in France and it is *excellent* stuff. Oratex also heat-shrinks preferentially along its length rather than across its width, so you will not get (or you'll get less) scolloping between the wing ribs. I really, really wish I could have aforded to use Oratex on my CD, but that's life! As I said, I'm super happy with the system I used, even if it is a bit heavier.

I think that about covers it! I'll investigate the Les Homan video this weekend for my homework!

All the best,


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