[roc-chat] Re: Stability: Time to Use the Mojo
- From: Richard Dierking <redierking@xxxxxxxxxxx>
- To: <roc-chat@xxxxxxxxxxxxx>
- Date: Thu, 11 Aug 2011 15:51:12 +0000
Good point Allen, and this would be approximately 1.25" from the root.
However, there might still be some correcting force from the some-what
triangular area between the strap-on and the fin. There is no doubt that
there's going to be a lot of turbulence created by this configuration. There's
a transition on the top that goes from 4" to 5" dia with a blunt nose too! I
know you can appreciate complicated projects and how much fun they can be to
build (and fly?). On this one, I didn't realize how much was involved until I
got building. Just to give an idea; so far, I've cut over 60 bulkheads and
centering rings. I appreciate all the suggestions.Richard > Subject: [roc-chat]
Re: Stability: Time to Use the Mojo
> From: allen.farrington@xxxxxx
> Date: Wed, 10 Aug 2011 21:02:31 -0700
> To: roc-chat@xxxxxxxxxxxxx
>
> The area of the fin "shadowed" by the strap-ons should not count in your area
> calculation until the pods are shed.
>
> Allen
>
> Sent from my iPad
>
> On Aug 10, 2011, at 8:46 PM, Richard Dierking <redierking@xxxxxxxxxxx> wrote:
>
> > Thank you! After reading the first couple of replies I was beating my head
> > against my desk and saying "why did I make the fins pink and blue!" and
> > "why did I ask those guys!" I did appreciate the humor.
> >
> > If I showed the rocket core without the strap-ons (I'll use different
> > colored paper next time), you might say the blue fins are large enough.
> > But, the strap-ons hide the size. For one side, the pink fin is 120 cm^2
> > and the blue fin is 90 cm^2. So, the pink fin has about 25% more surface
> > area but only sticks-out 3/4" more. 4" Goblin fins have about 85 cm^2 per
> > side There are 4 fins on a Goblin and I usually build with 4 fins. I
> > can't do that with a 9 strap-on configuration.
> >
> > As usual, as the mass of the solid engines is consumed, the CG will move
> > forward. But, the strap-ons will shed during the flight and change the CP
> > and keep in mind that each of the core fins are between strap-ons that will
> > be released during powered flight. This really complicates things.
> >
> > I thought about adding fins to the strap-ons but this creates some
> > additional problems like re-contact after deployment and the possible roll
> > force on the attachment points.
> >
> > (one hour later...)
> >
> > I'm going to use the pink-sized fins.
> >
> > Thank you, and I'm going to blame all of you if the rocket's overstable or
> > I become unstable. :)
> >
> > Richard
> > > Subject: [roc-chat] Re: Stability: Time to Use the Mojo
> > > From: allen.farrington@xxxxxx
> > > Date: Wed, 10 Aug 2011 13:49:29 -0700
> > > To: roc-chat@xxxxxxxxxxxxx
> > >
> > > Pink, definitely. You know, how big should they be if the pods had no CP
> > > effect, but still have the mass? I think that they look small.
> > >
> > > Allen
> > > --------------------------------------------------------------------
> > > Allen H. Farrington
> > > 818-653-2284
> > > web: http://www.allenfarrington.org
> > >
> > > On Aug 10, 2011, at 12:58 PM, Richard Dierking wrote:
> > >
> > > > When you're working on something like this Delta II you start to
> > > > develop mind roll. I realized that I need to make a decision on the
> > > > fins before I become a really old man.
> > > >
> > > > So, please look at the two photos showing a blue and pink fin. There
> > > > will be 3 fins and they will be transparent and the rocket's about 6'
> > > > tall. As Barney would say, "time to use our imagination..." Please
> > > > provide your vote.
> > > >
> > > > Thank you. I'm going off to do something simple like work.
> > > >
> > > > Richard
> > > > <bluefin.jpg><pinkfin.jpg>
> > >
> > >
> > > --
> > > ROC-Chat mailing list
> > > roc-chat@xxxxxxxxxxxxx
> > > //www.freelists.org/list/roc-chat
> > >
>
> --
> ROC-Chat mailing list
> roc-chat@xxxxxxxxxxxxx
> //www.freelists.org/list/roc-chat
>
Other related posts:
