Zachary:
I assume you are planning on a "skin and stringer" airframe with the tanks
set inside and non load bearing. This is both heavy
and--importantly--expensive.
Assuming you use sheet stainless to roll wrap the barrel section and buy
standard semi-elliptical domes, your wall thickness-for a typical 12"
diameter tank--will be way more than strong enough to carry flight loads.
There is no reason to burden yourself with the expense of a built-up
airframe.
Bill
On Friday, September 2, 2016, Zachary Martinez <znm3m8@xxxxxxx> wrote:
Sent from my iPhone
On Sep 2, 2016, at 16:41, George William Herbert <george.herbert@xxxxxxxxx
<javascript:_e(%7B%7D,'cvml','george.herbert@xxxxxxxxx');>> wrote:
Bill is correct, but you get very fragile rockets and minimum gauge
problems this way.
Not impossible, just... Be careful.
I am not going to have tanks be load bearing for obvious reasons, but I
will still have to check to make sure I still have a decent factor of
safety against buckling during expected g loading. Using aluminum rather
than stainless should help as it increases the wall thickness.
Sent from my iPhone
On Sep 2, 2016, at 12:04 PM, William Claybaugh <wclaybaugh2@xxxxxxxxx
<javascript:_e(%7B%7D,'cvml','wclaybaugh2@xxxxxxxxx');>> wrote:
Zachary:
You can do as little as 50 psia against vacuum and 150 psia to sea level
air; look into Bob Truax's Sea Dragon work for reference.
That said, note that he was planning on using Lox / LH2 to recover the
lost Isp. But as a general rule mass fraction improves as the operating
pressure of a pressure fed liquid drops...and mass fraction has an
exponential effect on performance, whilst Isp is merely linear.
Bill
On Friday, September 2, 2016, Zachary Martinez <znm3m8@xxxxxxx
<javascript:_e(%7B%7D,'cvml','znm3m8@xxxxxxx');>> wrote:
Hello all,
Are there any issues operating at a relatively low chamber pressure for
an engine ~180-220psi other than the poor Isp. For a pressure fed rocket
with a relatively high thrust to weight ratio the benefits of using a lower
chamber pressure are really tempting, but I imagine there are some design
challenges that I am unaware of. My main concerns are difficult ignition or
possible flame out but I don't really know.
Thank you,
Zachary Martinez
Aerospace Engineering | Missouri S&T
