Re: Maybe tracing is easier but ...


David J. Gall
 

Johannes,

Try to stick to degree-two curves (conic sections) as much as possible, and fit them piecewise with tangent continuity at the joins. Use the control point "weight" on the middle control point to adjust the amount of curve for each degree-two conic curve. This is how the P-51 was designed and (except for the possible occasional use of a French Curve) is likely how the Q2 molded fuselage was formed. (Also much TLAR freehand drawing....)


David J. Gall

-----Original Message-----
From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Johannes Weissmann
Sent: Thursday, October 6, 2022 8:43 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Maybe tracing is easier but ...

At the current stage I simply tried to reconstruct the existing shape based on the available plans and templates.

Basically, I used the fuselage jig and bulkhead templates as reference and in addition traced the fuselage profiles from the three-view of the plans. The templates are to scale, the three-view needed some scaling.

Based on that, I tried to make the templates and bulkheads match with as little error as possible. The main difficulty is to exactly locate WL0 and WL15 as I could not find any references.

Currently, there is no limit on the degree I used to generate the curves. Some curvatures from the templates just can't be fitted with three-degree splines.


Here is what I am not sure of:

What I would *like to do* now, is to construct a design that matches as close as possible with simple mathematical forms.

What I don't know because I am not an aeronautical engineer (I am a
physicist) is how much I am getting into the realm of aircraft design or if the deviations from the original are small enough to not affect the resulting aircraft performance and specs.


// Johannes


On 06/10/2022 14.28, David J. Gall wrote:
Robert,

If your intent is to duplicate the existing QAC shape I would caution you that, although "CAD is fun" it can also lead you astray. The state-of-the-art in the early 1980s was compass and protractor and a wooden batten as a spline; the CAD equivalents are *not* degree-three curvature-continuous NURBS curves and surfaces. Stick to degree-two conics or arcs of circles joined tangent-continuous for cross sections and nothing more than degree-three single-span curves in the longitudinal direction. If more than one degree-three span is needed longitudinally, join degree-three splines at their ends using nothing more than tangent-continuous joins.

If, on the other hand, your intent is to make it "better," first, define "better," then go for it! Coolio!

(If you're surface modeling in SolidWorks, well, there's no hope for
the world.... ;P)


David J. Gall

-----Original Message-----
From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of
Johannes Weissmann
Sent: Thursday, October 6, 2022 3:41 AM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Maybe tracing is easier but ...

Great!

CAD is indeed a lot of fun. I finished the first surface model of the Q2 fuselage yesterday. Not perfect yet, but at least it is spanning the whole fuselage now.

On 06/10/2022 06.27, Robert Schmid wrote:
... this CAD stuff is fun too. First version of panel test cut is
done,

CAD still needs some fine tuning but not bad for a start.
--
Robert "TheFrisco" Schmid
(408) 805-5450

www.facebook.com/TheFlyingFriscos (
https://www.facebook.com/TheFlyingFriscos ) www.theflyingfriscos.com
( http://www.theflyingfriscos.com )

Love building planes almost as much as flying. Latest completed build is "Loki", a Chinook Plus 2 bush plane.





--
Johannes Weissmann










--

Johannes Weissmann

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