[roc-chat] Re: Stability: Time to Use the Mojo
- From: <kramer@xxxxxxxxxxxx>
- To: roc-chat@xxxxxxxxxxxxx
- Date: Thu, 11 Aug 2011 10:23:59 -0700
Why not have the fins on the strap on boosters?
Solves many problems that way....
Mike
> -------- Original Message --------
> Subject: [roc-chat] Re: Stability: Time to Use the Mojo
> From: Richard Dierking <redierking@xxxxxxxxxxx>
> Date: Thu, August 11, 2011 8:36 am
> To: <roc-chat@xxxxxxxxxxxxx>
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> Not at all; very good question. I considered this. I wanted to keep the fin
> number down to a minimum because the strap-ons are ejected (with pyro bolts)
> and I don't want them hitting the fins. The first six strap-ons that are
> ejected are on opposite sides of each fin. This will leave the last three
> airstarted strap-ons centered between the three fins and should help to
> provide fin area for the correcting force during the last part of powered
> flight.
>
> Richard
> Date: Wed, 10 Aug 2011 21:01:58 -0700
> Subject: [roc-chat] Re: Stability: Time to Use the Mojo
> From: rubr.duky@xxxxxxxxx
> To: roc-chat@xxxxxxxxxxxxx
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> Silly question... Why not six?
>
> On Wed, Aug 10, 2011 at 20:46, Richard Dierking <redierking@xxxxxxxxxxx>
> wrote:
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> 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...)
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> I'm going to use the pink-sized fins.
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> 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
> >
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> > 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
> > >
> >
> >
> > --
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