Re: Maybe tracing is easier but ...

David J. Gall


Page 8-2 shows the 2.9" dimension on the firewall. Page 8-4 repeats the image with the "Shell Split Line" explicitly labeled. The firewall template on Appendix Sheet 3 shows WL 12.1 explicitly as the line splitting between the fuselage upper and lower shells. WL 12.1 is 2.9" below WL 15....

David J. Gall

-----Original Message-----
From: <> On Behalf Of Johannes Weissmann
Sent: Thursday, October 6, 2022 10:19 AM
Subject: Re: [Q-List] Maybe tracing is easier but ...

Thanks Jay,

I have used these drawings as the reference. What is lacking, or maybe I am not seeing it, is how to properly constraint WL15. In particular, I never found a way to properly define the vertical position of WL15 on the bulkheads or the firewall.

The way I set up the constraints is that I took the fuselage end, at which the 1" vertical distance from WL15 is given as a dimension. I then rotated the sketch such that the firewall is vertical. This is how WL15 is approximated in my model.

I don't have any reference to the position of the fuselage split line at the firewall, so the 2.9" dimension at the firewall doesn't help.

Once that was fixed, I adjusted the fuselage skid "by hand" to match the fuselage profile to get the WL of the table surface.

Side note: the drawings seem to be distorted. I traced and scaled these drawing as well as the three view, compared and measured them. I believe the three-view profiles are properly scaled while the drawings on page
17-20 are not.

// Johannes

On 06/10/2022 15.23, Jay Scheevel wrote:
Johannes. For WL reference sketches please see pages 17-20 of the
following linked document

On Oct 6, 2022, at 6:43 AM, Johannes Weissmann <jo@...> wrote:

´╗┐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:
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: <> On Behalf Of
Johannes Weissmann
Sent: Thursday, October 6, 2022 3:41 AM
Subject: Re: [Q-List] Maybe tracing is easier but ...
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

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

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

Johannes Weissmann

Johannes Weissmann


Johannes Weissmann

Join to automatically receive all group messages.