Reducing weathercocking effects

Are there any techniques to reduce the weathercocking tendencies on a given rocket ? I know this is kind of a general question and I'm sure the answers would be different for different models. I'm thinking you have two main areas to look at: modifying fin area or modifying weight distribution within a safe stabililty range. Maybe higher acceleration off the pad also ?

My Big Daddy seems to like to find the wind on D12's. I'm thinking the effect with E9's would be worse because of the lower max accel. IIRC back in the day it seemed like my Big Bertha could fly straight up thru a category 5 !

Thanks

Great question, Sam! The recent NAR safety study at https://www.nar.org/launchingsafely.html talks about this very issue...

Excellent. Thanks for the link, Will.

Does the black dot on the envelope make me a bad person

Originally posted by samb
Does the black dot on the envelope make me a bad person

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It simply indicates you've posted to the thread.


This thread has more info about the forum icons & meanings.

https://www.rocketryforum.com/showthread.php?s=&postid=318883#post318883

Originally posted by brianc
It simply indicates you've posted to the thread.


This thread has more info about the forum icons & meanings.

https://www.rocketryforum.com/showthread.php?s=&postid=318883#post318883

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Thank you much, Brian.

The smaller the fin area or lateral profile of the rocket, the less the tendancy to weathercock. Tube fins which have about 1/3 the profile of a flat fin with an equivalent surface area, have less tendancy to weathercock. Spool rockets with their minimal profile also weathercock less. Reducing the lateral profile means reducing the fin area of a flat fin; but this comes at the price of moving the CP of the rocket forward, and hence may require the additon of nose weight to achieve stable flight. Short wide rockets like the Big Daddy may not require all the fin area they are designed with. I recently published a few articles on base drag stabilization that may help you select a better/smaller fin area for these types of designs visit:

https://www.apogeerockets.com/education/downloads/Newsletter154.pdf

and

https://www.apogeerockets.com/education/downloads/Newsletter158.pdf

Bruce S. Levison, NAR #69055

Originally posted by teflonrocketry1
The smaller the fin area or lateral profile of the rocket, the less the tendancy to weathercock. Tube fins which have about 1/3 the profile of a flat fin with an equivalent surface area, have less tendancy to weathercock. Spool rockets with their minimal profile also weathercock less. Reducing the lateral profile means reducing the fin area of a flat fin; but this comes at the price of moving the CP of the rocket forward, and hence may require the additon of nose weight to achieve stable flight. Short wide rockets like the Big Daddy may not require all the fin area they are designed with. I recently published a few articles on base drag stabilization that may help you select a better/smaller fin area for these types of designs visit:

https://www.apogeerockets.com/education/downloads/Newsletter154.pdf

and

https://www.apogeerockets.com/education/downloads/Newsletter158.pdf

Bruce S. Levison, NAR #69055

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Thank you very much for those links, Bruce. Hmm... mass-less conical transitions. You didn't come up with that in chemistry class did you

Originally posted by samb
Thank you very much for those links, Bruce. Hmm... mass-less conical transitions. You didn't come up with that in chemistry class did you

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The mass-less conical transitions are not really part of my chemistry background, but it sure sounds like it might be.

"Bending" simulation programs like RockSim to handle structures which are beyond the original scope of the program is something that I have routinely done in the various laboratories that I have worked in.

Bruce S. Levison, NAR #69055

Spin the rocket axially.

Doug

Originally posted by dknight
Spin the rocket axially.

Doug

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Hi dknight,

As a matter fact I'm interested in spin stabilization and have starting some web searches to see what info might be out there. The V2 had spin tabs, didn't it? Von Braun probably knew a thing or two or three! Besides the kits like the Texas Twister I would think it would be a good technique for cutting through the wind on alot of different designs. Maybe canting each fin a degree or two and using motors with a high initial thrust. Are there any "thumb rules" that you've used ?

Some kits, such as the Estes (now OOP) Cineroc/Omega, were
designed to be very overstable and therefore weathercocks easily. Always gave the recovery system problems (i.e. shroud
lines ripping off, plastic chute material ripping, etc.). I eventually
designed and built a payload carrier with marginal stablility (smaller fins; three fins instead of four, but also added strapon
booster pods for powerplant flexibility). The scratch built design
worked perfectly, giving excellent, straight up boost and safe
recovery everytime.

Originally posted by dwmzmm
Some kits, such as the Estes (now OOP) Cineroc/Omega, were
designed to be very overstable and therefore weathercocks easily. Always gave the recovery system problems (i.e. shroud
lines ripping off, plastic chute material ripping, etc.). I eventually
designed and built a payload carrier with marginal stablility (smaller fins; three fins instead of four, but also added strapon
booster pods for powerplant flexibility). The scratch built design
worked perfectly, giving excellent, straight up boost and safe
recovery everytime.

Click to expand...

That was my first idea when I posted this thread, reduce the fin area. I saw you space shuttle pic in the "crapload of orange peel" thread. How did you come up with the reduced fin size ?

Originally posted by samb
That was my first idea when I posted this thread, reduce the fin area. I saw you space shuttle pic in the "crapload of orange peel" thread. How did you come up with the reduced fin size ?

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The first time I flew the Estes Space Shuttle (March 2004), I flew it "as is," with the "paddle styled" add on fins. The C6-3 gave it
a pretty good boost, but at about 60 feet altitude it then went
horizontal for the rest of the powered flight; I was terrified that
it would end up impacting the ground before the ejection charge
went off (it didn't, but came very close). Between that flight and
the next one, I thought real hard about reducing the fin size on
those addons, and thought ("experimented") hacking one inches
off of each fin should do the trick. That flight came on January 9,
2005 (the pic you mentioned), and even though we had a pretty
good breeze for the duration of the club launch that day, the Space Shuttle flew virtually straight up perfectly. If you look at many of model rocketry's great achievers, you'll find that there's
quite a few who succeed through the trial and error method...

Originally posted by dwmzmm
The first time I flew the Estes Space Shuttle (March 2004), I flew it "as is," with the "paddle styled" add on fins. The C6-3 gave it
a pretty good boost, but at about 60 feet altitude it then went
horizontal for the rest of the powered flight; I was terrified that
it would end up impacting the ground before the ejection charge
went off (it didn't, but came very close). Between that flight and
the next one, I thought real hard about reducing the fin size on
those addons, and thought ("experimented") hacking one inches
off of each fin should do the trick. That flight came on January 9,
2005 (the pic you mentioned), and even though we had a pretty
good breeze for the duration of the club launch that day, the Space Shuttle flew virtually straight up perfectly. If you look at many of model rocketry's great achievers, you'll find that there's
quite a few who succeed through the trial and error method...

Click to expand...

Ok, thanks Dave.