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AIM-9 Stability

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CORZERO

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Great flight here:

[video=youtube;Lj3NynZGaDY]https://www.youtube.com/watch?v=Lj3NynZGaDY[/video]

Any ideas how I can reach a decent stability margin?

AIM9.png

View attachment AIM9.rkt
 

markkoelsch

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I would start by adding some mass to the nosecone, and seeing if you can make the rear of the rocket lighter.
 

dr wogz

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If I recall, the old Estes kit of this had larger rear fins (not really "to scale") and that they were slightly canted to induce spin on ascent..

Remember, these things were design to not be stable.. to allow it to manoeuver .. wildly!
 

Nytrunner

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I'm looking into the design of an IRIS-T, and noseweight will likely be the only way to get it of the ground safely also.

By the way, If you turn on Youtube's auto close captioning on the video above, its hilarious!
 

Igotnothing

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As a guy who wears hearing aides - that is what you soft-voiced guys and gals always sound like to me. I hear things, they just make no sense. When I put the aides in, it just confirms that YOU make no sense.

Couldn't be me.

Nah.
 

Igotnothing

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Move the fwd fins aft a bit. Add a super-cooled heat seeker to the front.
 

MikeyDSlagle

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Use a heavier material for the forward fins. Lighter material for the aft fins.
Maybe airfoil the forward fins to reduce their drag a but?
 
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SDramstad

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Reduce the size of the canards. The canards in the video looks smaller then in your open rocket file.
 

Nytrunner

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Reduce the size of the canards. The canards in the video looks smaller then in your open rocket file.
And airfoiling the forward fins will (very) slightly reduce their affect on the CP (Not enough to preclude noseweight though)
 

AeroAggie

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Make the front find free to pivot
+1

New guy here and new to rockets but no stranger to flying things - by allowing the canards to spin on a bearing (ahead of their local Cp), you can minimize the destabilizing effect of fixed canards. I haven't explored Open Rocket enough to know if it can handle something like that or not (I doubt it), nor have I ever attempted to build such a thing on a rocket. In theory, it works. YMMV :D

I see the bumps on your aft fins where the rollerons would go; do you intend to make those functional, or just have a fixed bump out? They're a nifty passive roll damper but I suspect the additional drag could help pull the Cp back a little as well, and again, I don't think Open Rocket can predict that either.

I fly a bit of r/c aerobatics and one thing that's popular among some of the competitors is to add a small trailing edge wedge on both sides of the rudder which pulls the Cp back a bit and damps the yaw oscillations after certain maneuvers like hammer head stalls. You could do that to the aft fins and still maintain a scale profile with a marginal increase in drag. This mod is somewhat predictable in low speed 2D aero codes such as XFoil, but you'll have to do some math to predict the effect on the rocket.
 

CORZERO

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Great tips. Thanks to all who chimed in! Has anyone actually played with the .ork?
 

burkefj

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For modeling pivoting fins, you can model only the area forward of your pivot point as the fin and remove the part behind the pivot. The estes kit also had some spin stabilization from the rear fins as well. As others have said, reduce the rear weight, move the separation point as far forward as possible to move your recovery mass forward, add nose weight.
 
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