[roc-chat] Re: Stability: Time to Use the Mojo
- From: Jeff Gortatowsky <indanapt@xxxxxxxxx>
- To: "roc-chat@xxxxxxxxxxxxx" <roc-chat@xxxxxxxxxxxxx>
- Date: Fri, 12 Aug 2011 11:25:12 -0700 (PDT)
If you'd like I can punch the numbers into ROCKSIM with and without shadowing.
I just need the basic dimensions to get you a CP (not CG but CP).
Just ask.
---------------------------------------
Jeff Gortatowsky, Redondo Beach, CA | Twitter: JeffGortatowsky | Yahoo:
indanapt
"(Scientific) Skepticism is not a set of beliefs, it is a set of methods for
asking questions about reality." -- Doctor Steven Novella
________________________________
From: Richard Dierking <redierking@xxxxxxxxxxx>
To: roc-chat@xxxxxxxxxxxxx
Sent: Thursday, August 11, 2011 8:36 AM
Subject: [roc-chat] Re: Stability: Time to Use the Mojo
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
Silly question... Why not six?
On Wed, Aug 10, 2011 at 20:46, 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>
>>
>>
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>>
>
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