# STOL Inspired Composite Ultralight

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#### random_people

##### Member
Status Update: Initial OML (Outer Mold Line)

I have spent the last couple of weeks working on my initial loft that relies on only 2D curved surfaces. This is ensures all composite parts are compatible with the "soft tooling" lamination process which will require only the hotwire cutting of foam and then a bit of finish sanding before parts can be splashed off the molds. Design is looking pretty similair to the Merlin Lite when overlaid in CAD. Im holding onto a bit of additional tail volume at the moment, will see how weight and balance works out as I detail some of the bulk bodies out with realistic mass.

To loft the fuselage I have a 95 percentile male figure from GrabCAD as well as a Polini 250 DS that I sketched up based on manufacturer drawings. I have shared the engine CAD on grabcad for any of those also planning to use the Thor in their design.

Gotta take a few glory shots while I'm here

Besides airplanes I am also into surfboard building, so I am keeping an eye on the baggage size to ensure I can take one of my smaller boards with me. Will be challenging to ensure I dont get stabbed in the back by it during a crash, but I think I can get it to fit.

.step CAD file of the STOL UL Initial OML with major components: here
Design Notebook google slides where Ill keep all the images I generate/collect

Next Up: Add some realistic skin thicknesses and densities to the CAD major components to get rough mass and CG info. Will then take that back to aero analysis and start iterating!

#### patrickrio

##### Well-Known Member
I love this direction. Similar to what I am contemplating but I am more interested in high efficiency at the expense of STOL possibly. Essentially I am interested in the limit of low HP engines/motors still keeping a high cruise speed and also keeping sufficient climb rate.

I think that CAD/CAM tech used for D-tube manufacturing with female molds is a place where some decent improvements can be made in part 103 designs.
1. Low cost of carbon fiber fabric and uni-pulltrusions now make the material costs alone for CF construction extremely competitive.
2. BOKU's surface color/finish in mold plus foam noodle form/strengthening tech is pretty time effective.
3. 3D printer tech is now essentially commodity priced, and I think it can be used to make a good D-tube mold CNC inexpensively.

With this tech you can also perfectly create laminar D-tube molds for wings that continually morph from one airfoil to another as both Reynolds number requirements and lift requirements change along the span of the wing. Something that really isn't available on scratch built/home built part 103 ultralights currently.

A huge disadvantage of the current state of tech for wings/airfoils at part 103 Reynolds numbers is that tests are lacking in the relevant Reynolds ranges. There needs to be a way to rapidly prototype and test different airfoils to get better real world data to incorporate into CFD. The above tech might speed and bring such testing into a cost range where it can be done by hobbyists.

#### Lucky Dog

##### Active Member
@Victor Bravo : Agreed, but strong legs are a must for my fantasy contest. Weak landing gear is the nemesis of all ultralights. Perhaps 2G gear would be an improvement. I'd wager that Quicksilver, Rans and Kolb make more money selling axles and four-foot lengths of tapered aluminum or 4130 tubing to their UL customers than they made selling them airplanes. HA!