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
