Troy,
It is a pressure fed liquid I had opted for skin and stringer air frame
with supports throughout (front and back of each tank, top and bottom and
may put a couple more depending on results from FEA). Attached is a quick
and dirty model for reference. I could pretty easily make the structure of
the rocket the tanks and it is looking better and better the closer I get
to final numbers. I would just need to figure out what to do about the
connections between the tanks if I went that route.
Zachary Martinez
Aerospace & Mechanical Engineering
Missouri S&T
On Tue, Sep 13, 2016 at 10:55 PM, Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx>
wrote:
Depends on more details like… is it an HPR solid rocket or is it a
pressure fed liquid or hybrid? If it’s a pressure fed liquid (which I
assume it is), you could design it as essentially a monocoque structure so
most of the structure will be propellant tankage which will be pressurized
for most of the flight including the moments of max Q. Pressurized tankage
for pressure fed designs are pretty damn tolerant of bending and buckling
moments – like you seriously don’t have to worry about them on that part of
the structure.
Such rockets (high fineness with much of the propellant forward of the
Center of pressure point) generally tend be over stable. This can be
manageable, but could make active dynamic control challenging (if you were
doing that) or the rocket more prone to issues like windcocking.
Troy.
*From:* arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx]
*On Behalf Of *Zachary Martinez
*Sent:* Wednesday, 14 September 2016 1:30 PM
*To:* Arocket List <arocket@xxxxxxxxxxxxx>
*Subject:* [AR] Fineness Ratio
Hello All,
I know that amateur rocketry very often uses high fineness ratios in
comparison to industry and understand some of the reasons why (drag). What
are the technical challenges I should be aware of as you scale up a rocket
with high fineness ratios? PSAS mentioned something about not being able to
model the rocket as a rigid body during flight and I am not sure if this
would affect stability. I am looking at a height of 5.1m and a diameter of
.2m for a fineness ratio of 25.5. Any insight would be valuable as I can't
seem to find many resources. I am assuming this is still "small" so my gut
feeling is that I should be good.
Note: I am considering all types of buckling as failure modes and designed
the air frame accordingly.
Thank you,
Zachary Martinez
Aerospace & Mechanical Engineering
Missouri S&T
Attachment:
Rocket.PNG
Description: PNG image
