STOL Inspired Composite Ultralight

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random_people

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Nov 4, 2013
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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.
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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.
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Gotta take a few glory shots while I'm here
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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.
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.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

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Aug 15, 2020
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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.

I posted earlier about a super low cost CNC D-tube mold cutting rig I am working on that is designed to use off the shelf consumer 3D printer controllers and Cheap mechanicals shooting for parts cost in low $ Hundreds. It is designed for the mechanicals to be easily collapsed and accurately expanded/reassembled so that harder to source mechanicals can be shipped cheaply from user to user. This allows a builder to easily sell on the machine to a new user or let another use the CNC easily without waiting months for parts to arrive from China (Chinese parts really seem to be the only way to build these cheap enough for hobby use, unfortunately.)
 

proppastie

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99.99% likely to be "airplane style" Dacron fabric covered
The Greg Cole Sparrow Hawk weighed in at Part 103 Glider weight....(150 # ?) All CF .....looking at your past work and experience I think you might consider the CF skin......of course his plane used Pre Pregs had fairly massive CF fe-male molds and was cooked in an autoclave... ....probably ways around that though at only a small sacrifice of weight?
 

dave wolfe

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Dec 7, 2019
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Unpowered ultralights dont have the stall speed reqs that powered ULs are supposed to meet. So the sparrowhawk would not have enough wing area for a powered ul.
 

proppastie

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Unpowered ultralights dont have the stall speed reqs that powered ULs are supposed to meet. So the sparrowhawk would not have enough wing area for a powered ul.
but it is 100 lb lighter.....the wings have a very large moment arm, and were fully cantilevered ..... I believe it is technically possible to have a CF skinned UL if you are on your numbers and are very technically proficient.... design wise and fabrication wise ....which perhaps the OP fits that description....
 

proppastie

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"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.
Foam molds?.....not foam filled? OML against the mold?
 

Victor Bravo

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looking at your past work and experience I think you might consider the CF skin
I have to stand by my original post, but I will also repeat that I agree it is absolutely possible to achieve a 103 airplane in molded CF. Marek Ivanov already did most of it in glass, with maybe 1/3 of the wetted area in fabric. Careful use of infused, molded, minimalist CF could probably deliver one of his Viera UL's with no fabric.

My whole point is that it is possible but achieving this type of STOL airplane in CF is going to be more work than it's worth.
 

proppastie

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CF is going to be more work than it's worth.
yes....a UL with a max allowable speed of 65 miles and hour does not need CF skin......however were one to want say a part 103 in electric with a decent range (small output for longer battery life) a very slippery aircraft probably would be better....and fabric would not fill that bill. Or maybe I am wrong.....how good were the fabric covered gliders compared to the plastic ones.
 

Gregory Perkins

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May 25, 2019
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The composite molded wing used by the XTC UL used an airfoil that was supplied or created by NASA and had the name of E749. I seem to remember that it was designed to be hi performace at the low reynolds numbers. I would also recommend investigation into some of the airfoils used by the Human Powered Airplanes. I have always thought the ATOS instructor glider two seater would have to be using one of the most technically evolved composite
wings. I think I have heard of some of those being powered and flown as legal UL's single seat.
 
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