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Rocket Fins mounted to the motors. Why .?

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Lunarxray1968

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Rocket Fins mounted to the motors. Why .? Is there a reason for this type of mount? Why attach it to the motor mount if your going to reload with another motor?
 
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dhbarr

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I'm not sure I understand the question?

Sometimes the fins go through an outer skin w/out proceeding to the motor mount tube.

Sometimes they go through the outer skin and -do- contact the motor mount tube.

Sometimes the body tube and motor mount tube are one and the same.

Finally, on rare occasions someone will choose to affix the fins directly to the motor casing.

Each of these have different use cases; were you asking what the use case is for one of these you hadn't seen before?
 

Lunarxray1968

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I guess I'm confused why I would choose to cut the fins into the main tube to the motor tube. I have always hot glued the fins to the outer body tube without any problems with fins coming loose.
 

JJSR

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it has to do with the higher forces big motors put on the rocket/fins.
also less breakage on hard landings.
Through the wall fins or TTW as its commonly called, gives you more to glue. two filets on the motor tube, two on the inside of the body tube, two on the outside of the body tube. in turn you end up with a more robust aft section able to with stand greater forces
 
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dhbarr

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I guess I'm confused why I would choose to cut the fins into the main tube to the motor tube. I have always hot glued the fins to the outer body tube without any problems with fins coming loose.
Ah. Because at some point ( d21 minimum diameter comes to mind ) you will find "The Speed of Balsa" or "The Speed of Hot Glue"; possibly both, likely on a warm day.

It would go something like: your weakest joint softens in the sun, comes off under boost. The remaining fins slam into the air sideways, snapping one or two. You have either one or zero fins left attached, so your rocket scribbles all over the sky & slams into the ground. Due to the smashed nose, the ejection charge emits a sad puff of smoke & melts the chute

Stronger fin material, stronger adhesives, through-the-wall mounting, 'papered' joints, tip-to-tip carbon fiber or kevlar or fiberglass....

There's many ways to attempt to keep from tearing the wings off; through-the-wall is one of them. Many people overbuild most of their fleet.
 

watermelonman

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I guess I'm confused why I would choose to cut the fins into the main tube to the motor tube. I have always hot glued the fins to the outer body tube without any problems with fins coming loose.
It is a technique used for additional strength on high power rockets. Glue can be applied to both the motor tube joint and the main tube slot. You can have up to six locations for glue fillets instead of the two you get with surface mount fins, and now the internal portion of the fin is helping with structure as well.

Low power, no need, though some like to apply high power techniques for fun, practice, or strength against bad landings.
 

Ravenex

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I should note the op seemed a bit confuse about reusability. The fins are not glued to the motor, the are glued to a smaller tube that holds the motor. If your rocket is 54mm in diameter and you want to fly 38mm motors the fins go through the 54mm tube to the outside of a 38mm tube. The motor goes in the 38mm tube. Besides more glue area this also creates a level around the outer tube so instead of just breaking the glue you would likely need to snap the fin to break it.
 

Bat-mite

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You should go a high power launch and watch and talk to people. Lots to see and learn.
 

TopRamen

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Is anyone from NJ ? Or know where they have launches?

Sadly, I was born there, but thankfully, we moved while I was still young.

Rocketry and even thinking about rocketry is probably illegal there, so I suggest moving to a different state.

Luckily, NJ is very tiny, so you can likely find some launches in some of the neighboring free states.
 

K'Tesh

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Sadly, I was born there, but thankfully, we moved while I was still young.

Rocketry and even thinking about rocketry is probably illegal there, so I suggest moving to a different state.

Luckily, NJ is very tiny, so you can likely find some launches in some of the neighboring free states.
Could be worse... You could be in St. Louis :wink:
 

TopRamen

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Could be worse... You could be in St. Louis :wink:
I went back there once when I was 15, to try to visit some of my Fathers side of the family, but the ones that had not left were dying, and the smell was repulsive enough to make me vow to never re-visit New Jersey.
The Air quality there is measured in "Sub-Units", meaning you only gauge it in "Beyond Poor" and lower.
Respirators only last for so long, so New Jersey is off limits to me now, even after the collapse of civilization.
 
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JJSR

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Yeah,, you can't go anywhere in the world with out finding someone from Jersey.
I bet even K'Tesh could find someone within 5 miles over there in China from Jersey :wink:
 

Ravenex

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I went to a different part of New Jersey state for a business trip. It was beautiful and clean, and no one had accents, so I asked them about the stereotypes. They said some of it was true closer to New York, but they liked everyone thinking it was the whole state because it kept people away.
 

Micromeister

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Have many friends "From New Jersey"
Most of them tell me "It's a great place to be FROM...the armpit of the nations." Can't say for sure as I've only driven through it a couple time but..Man that seemed harsh LOL!

OBTW: Most of your average, everyday Hot Glues have a melting point just below the allowed temperature of our expended motor casings. HOT GLUE should NEVER be used in model rockets. Elemer's white glue is Cheap, readily available and when used with the double glue joint method dries stronger then the Paper/wood joint materials it is holding.

Fins should NEVER be attached directly to a model rocket motor. It violates both the NAR Model rocket safety code and the manufacturer's purpose. DO NOT DO IT!
 
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rstaff3

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Fins should NEVER be attached directly to a model rocket motor. It violates both the NAR Model rocket safety code and the manufacturer's purpose. DO NOT DO IT!
There are exceptions to every rule :)

G125_1.jpgG125_2.jpg
 

Initiator001

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The FSI RX-1 Thruster System booster for the Dart Mach-1 model had the fins glued directly to the F100 booster motor per the instructions.

I built one of these models for the velocity trials held out at El Dorado dry lake outside of Las Vegas over 25 years ago.

According to the flight data after it was reduced the F100 booster reached 460 MPH.
Good ol' wood glue held the fins on just fine.
 
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