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CD Variations in the real world. 13 Sep 2020 22:01 #1295

Well, someone has to be the builder! So, I'm not sure what you are heading for with respect to what you are trying to build. It sounds like you are describing nearly perfectly the Legal Eagle XL to a T! The chrome-molly fuselage you describing already exists, the 3-cylinder radial has been done on it, and the payload is right there, and it doesn't fly very fast. What are you trying to do exactly - make the LE even slower? increase the lift for some reason? Edison said invention was 1% inspiration and 99% perspiration. Tesla said of Edison - if he spent 10% of his time thinking he could save himself 90% of his work! Maybe there is a combination of thinking, and then verifying by build, and iterating as needed, without so much trial and error? In any case I'd be willing to give you a little advice based on what I know, if it would help!
Cheers

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CD Variations in the real world. 08 Nov 2020 02:17 #1296

Kenny Andersen wrote:
I never did hear a final weight of Phil L's or Steve Arndt's Dragons, which would be helpful to know. I would also note that the more carbon parts you have the longer it will take...


I have to wounder if perhaps "some" Dragons are over the 155 lb limit and that is why we do not see weights for them. ...My Aluminum Dragon is way over....hopping to be under 230#

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Active builds 12 Nov 2020 04:21 #1301

Hey Phil L.
What news of the windrogse?
Started my wing. I also follow Rol Klingberg in the Klingberg Wing MKII He developed a neat non-female mold method of constructing leading edge D-tube. He uses 3/32 PVC foam in a sandwich. 3oz FG on the outside, Some carbon UNI on the nose and 5.5oz carbon on the inside. I think they may be both lighter and stiffer than carbon.kevlar,carbon. Do you know his work?
Do you have an opinion?
Phil D.

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Male mold D-Tube Method. 12 Nov 2020 22:14 #1302

Phil L, Here is the link to Rol"s description of his leading edge Method:

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Active builds 15 Nov 2020 11:50 #1303

Hi Phil D,

Apologies for not responding to your earlier posts - things got busy for me and I'm afraid I put you on the long finger!

A foam core, of almost any thickness, will definitely be stiffer than my three-laminate D-tube leading edges, as thicker generally equals stiffer. I wish I had seen Rol Klinberg's videos before I started my CD build, as I think he has developed a really good system for his build. My D-tube skins are very tough, but they do tend to 'oil-can' buckle under stress whenever I fly into a big thermal, resulting in a lot of 'bonking' and 'popping' noises! It's not dangerous, but it is disconcerting for the first couple of flights each year, as I get used to it again! I also omitted to install the non-structural foam 'false' ribs between the main structural D-ribs in my leading edges (to safe a little weight), but this has lead to the oil-canning in turbulence.

If I were to build another CD I'd be tempted to at least fabricate a test section of D-tube using Rol's method to check its weight and strength before committing to a full size part.

The Windrose wings are designed to be fabricated with solid foam cores skinned with S-glass (S=Structural - E=Electrical - see Wikipedia en.wikipedia.org/wiki/Glass_fiber), but I am considering hot-wiring out the cores of the wings so that the foam thickness is reduced to around 1/4" or so, and skinned inside and out with S-glass. The idea being to lighten the wings (especially outboard, so as to increase roll rate) and provide space inside the wings for water ballast towards the root section. I want to be able to experiment with both very light and nominal wing loadings to see if the Windrose can also be made to operate in the micro-lift region... and keep the empty weight under 120kg for regulatory purposes :-)

I've almost finished building my 3-axis 4'x4' CNC mill for cutting out parts (link here) and will shortly start work on a 4-axis CNC hot-wire foam cutter (link here) for cutting out the wing cores.

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CD Variations in the real world. 15 Nov 2020 13:20 #1304

yeah, 155 is pretty light. It was originally made for 150 lb pilot, so...

The original design also uses plywood, which for this application is probably about as light as it can get. However, your local climate, as in Phil's case, may make using certain materials less than prudent.

I'm a structural engineer, so am used to aerospace materials, but have mostly been involved in fighter aircraft and wide-body commercial applications with some rotor-craft/tilt rotor thrown in for good measure. The carbon dragon is a whole other beast entirely, with most of the materials I would usually be accustom to using too heavy, or too strong. Too strong you ask? Steel is stronger than aluminum, right? But we don't use much steel in aircraft, why? Because at the thicknesses required for strength, the steel would be unstable. IMO using carbon for the wing skins is similar. The plywood is thick for it's weight, and I notice that Jim used 45 degree plywood as well to keep the weight down while maximizing the web stability -- that goes for the spar, but it's similar for the D-Tube skins as well. when you merely substitute carbon (or something else) you might be adding strength but reducing stability -- it's a balancing act. You also might allow shear buckling if the load adjacent to the buckled area can be redistributed elsewhere (flanges, stiffeners etc).

Substituting aluminum is similar to that. It's stronger than it needs to be for it's function which will net either added weight, or decreased stability for the same weight. It's very likely in the gauges that you are using you have similar stability, but are surely adding weight. Now, that's not a big deal, but it will result in a aircraft that will be heavier. If you aren't worried about whether you at at or below the 155 lb ultralight requirement then no big deal.

In my case, because I weigh more, and am trying to keep the wing loading low, I'm shooting for increasing the wing area to around 172 sf (+19%) or 177 sf (+22%). Doing so is going to make hitting that 155 lb target pretty much impossible, BUT, if I add a chute I'm hoping to make up the difference. Also, a self launch electric motor like the Archaeopteryx, would allow the gross weight to hit 254 lb and still meet the ultralight weight limit, plus self launch would be extra cool, so that's something I'm looking at during the design process. Hopefully, one could hit both the 155 lb + the excess chute weight with unpowered, and hit the 254 lb + excess chute with the self launch.

Currently I'm thinking that fiberglass is probably better for the skins than carbon because it can be had in lighter weights and would be strong enough. A sandwich is certainly something to think about, though it might be a bit tricky making dead sure the skins stay bonded onto the core. The inner skin could be 1.8 oz and the outer, probably for handling considerations might need to be 3 oz. Considering strength only the outer skin could probably be 1.8 oz as well. You simply cant find carbon in that light of a weave (that I've been able to find).

Most will be heavier than the 155 lb. In Europe I don't thing that's a big deal and in the US I guess you would just need to license it as an experimental glider. One of these days I'll write more about what I'm thinking and show the numbers I've been running.
The following user(s) said Thank You: Don B

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Last edit: by Kenny Andersen.