LENSback, and ours will be no different. Let’s start with the
pointy bit at the front (technically, this is known as a
nose cone).
Click on Nose Cone in Add New Components, and
you’ll see a roughly triangular shape appear in the
side-view panel. You’ll also get a dialog box that lets
you customise this. Enter the following options:
- Nose cone shape: Ellipsoid
- Nose cone length: 8 cm
- Base diameter: 3 cm
- Wall thickness: 0.2 cm
- Material: PVC
We’ll also need to add a shoulder that lets it fit into
the main body tube. Click the Shoulder tab and enter
the following:
- Diameter: 2.6 cm
- Length: 2 cm
Click Close to get back to our design.We’ll now create the main part of our rocket. Click
on Body Tube, and enter the following in the dialog:
- Length: 45 cm
- Outer diameter: 3 cm
- Set material: Cardboard
The inner diameter should automatically set to
2.6 cm, giving a wall thickness of 0.2 cm. Double-
check that this is correct, then click Close to return to
our rocket.
The final part of our rocket outline is the fins at the
back. To add this, click the Trapezoidal icon. You will
need to have the body tube highlighted in the plan
view for the fin set icons to be available to select.
Either click on the body tube itself in the plan view
area, or click its name in the component tree area.In the dialog box, set the following:- Number of fins: 3
- Root chord: 4 cm
- Tip chord: 4 cm
- Height: 2 cm
- Sweep: 1.5 cm
- Sweep angle: 36.9
- Fin cross section: Rounded
- Thickness: 0.3 cm
- Material: Birch
Then click Close.You should see now that the centre of pressure
(CP) symbol (red dot inside red circle) is behind
(toward the fin end) the centre of gravity (CG) symbol
(blue quartered circle). The top right-hand corner of the
plan box contains some text about their positions. The
‘Cal’ number is to do with stability. It is the number of
calibres (diameter of the body tube) behind where the
CG the CP is. We ideally aim for the CP to be between
1 and 2 calibres behind the CG. Over 2 calibres is OK,
but is classed as ‘overstable’ and may turn more into
any prevailing wind, resulting in a ballistic flight. At the
moment, the stability is 2.26 Cal, but this will change
as we continue to alter the design.EXAMPLE
ROCKETS
We’ve built a simple
rocket, but you can
browse the other
example rockets for
some other designs.
Click on File, then
Examples, to see
the list of available
designs. There are
some showing more
advanced capabilities
such as clustered
motors and multiple
stages. You can
tweak these, or build
new rockets based
on them, but make
sure that you match
your designs with
your skill as a rocket
builder – don’t jump
straight to advanced
builds without gaining
the necessary skills
first. Rocketry clubs
are a great place to
get guidance on how
to proceed.Figure 1
The layout of
OpenRocket has all
the key information
split up into
three panes