Removeable fins on BIG rockets

[Voyhager3]

As I begin looking into my next large project, I ran into the problem of, "How fit big thing, in mid size sedan?", lengthwise isn't a problem, just fold down the seats, and I probably could fit it in with the fins, measuring in with I diameter close to 2 feet, but, that's just impractical to drive 1100 miles, each way.... and then all the way down to Argonia, probably, hopefully with a co-driver, hopefully, I hate driving by my self. But then I remembered that I saw a post at some point in time about some removable fins on a l3 or big rocket, so I tried to find it, and I looked, and I looked. Then I found an older thread, but most of the useful links were no longer. Or just not too useful.
So I did some thinking and messed around in CAD, and I came up with this, it's not perfect, maybe a bit hard to follow, but it's not really to a perfect scale or anything.

Some basic assembly views:
iso


Side

Bottom/top

Fins are darker gray, 1/8" ply in yellow, then inner and outer tubes.

Views W/O fins:

iso

Side

Bottom

The ply in yellow would be what is permanently attached to the booster, with ALL of the internal fillets, to inner and outer tubes, and external fillets. And then the fins would just bolt into the fin "holder" thingies. I'm fairly confident in it.

I can try and make a proper drawing if need be, but I too tired, and I should probably be sleeping, and so should you! But let me know if you would like a drawing.

I'd like some input, but mainly, I would love some examples of what you have done!

Thanks

 

[Tim51]

Interesting idea. Never done it myself but if you search Jerry O'Sullivan's superb 'Two Stage Iris sounding rocket LDRS 31' you will see he used a similar removable fin system using aluminium angle. He has posted here and on Youtube as 'vahpr'. Admittedly his seems to be a kind of surface mounting, which may well be less total weight than your through- the-wall version.

 

[Hobie1dog]

Interesting idea. Never done it myself but if you search Jerry O'Sullivan's superb 'Two Stage Iris sounding rocket LDRS 31' you will see he used a similar removable fin system using aluminium angle. He has posted here and on Youtube as 'vahpr'. Admittedly his seems to be a kind of surface mounting, which may well be less total weight than your through- the-wall version.

They've been using aluminum angle instead of the yellow pieces of wood for many years.

 

[teepot]

I was thinking the same thing. Aluminum angles. Or something similar. You would have to be able to bend the angle to match the curve of the BT and motor tube. A thin slotted angle that is used to reinforce the corners of the studs.

 

[cls]

Maybe these are available?

http://binderdesign.com/store/Max-Q-Aerospace.html

 

[Voyhager3]

Maybe these are available?

http://binderdesign.com/store/Max-Q-Aerospace.html

Expensive, yet cool! But it doesn't fit with the fins I may or may not already have.

 

[DeeRoc29]

Removable fins were necessary for transport/storage of a 14" diameter rocket I built a few years ago. The fin tabs plugged into slots in centering rings and were secured at the joints with aluminum angle and a bunch of screws. It worked well.

 

[sr205347d]

I did bolt-on fins with 3D printed brackets. Not BIG rockets though, just big. See this thread:

Thread 'Bolt-On Fins'
https://www.rocketryforum.com/threads/bolt-on-fins.178405/

 

[Hobie1dog]

I did bolt-on fins with 3D printed brackets. Not BIG rockets though, just big. See this thread:

Thread 'Bolt-On Fins'
https://www.rocketryforum.com/threads/bolt-on-fins.178405/

yeah you did an awesome job on that stuff, I remember those

 

[Last Ox]

Big rockets?

The Terrier missile was tight-packed in magazines, and stopped on the way to the launcher to allow 12 sailors to fit 3 sets of 4 fins. Needless to say, this slowed firing rate a bit.

https://www.navalgazing.net/The-3T-Missiles-Launch-Systems#fnr1_2
All Navy air defense missiles went to folding (or no fins) fins long ago, but to this day many air launched missiles are stowed without fins.

The only AAM I've personally handled was the smaller Tarter with folding fins, so I have no insight on how they were attached (but it took much less than a minute to put the on). If this photo caption is to be believed (since the only tool in view is a thumb) the AGM-88 HARM fins must be attached with "thumb screws".

https://www.dvidshub.net/image/2644359/tightening-missile-fin

 

[crossfire]

Rent a van for you transportation.

 

[PSLimo]

I was thinking the same thing. Aluminum angles. Or something similar. You would have to be able to bend the angle to match the curve of the BT and motor tube. A thin slotted angle that is used to reinforce the corners of the studs.

You wouldn't have to bend the angle to conform to the BT if you mount the angle on the inside which was suggested to me trying to address the same problem. Have the fin slide into an aluminum channel on the MMT and bolt the fins to the aluminum angle on outside of the BT. Should be able to get a good bond filling the void of the angle on the inside of the BT.

 

[Voyhager3]

Rent a van for you transportation.

I would, but broke college student, with his money at the wrong priorities.

 

[Voyhager3]

All good advice, and keep it coming! I'm trying to absorb as much as possible.

 

[tfish]

how handy are you?

I made some http://www.arliss.org/ fins and bolted them to glassed on blind nuts in the body tube. I've done it to 2 rockets now..



This is a really old ARLISS rocket.



Tony

 

[Voyhager3]

how handy are you?

I made some http://www.arliss.org/ fins and bolted them to glassed on blind nuts in the body tube. I've done it to 2 rockets now..

View attachment 628612

This is a really old ARLISS rocket.



Tony

Hmmmmmm, I do have quite a few reources at my disposal..., but the big thing, is that you did it with a glassed tube, which is what I plan on, so more info absorbed.
Thanks

 

[Art Upton]

how handy are you?

I made some http://www.arliss.org/ fins and bolted them to glassed on blind nuts in the body tube. I've done it to 2 rockets now..

View attachment 628612

This is a really old ARLISS rocket.



Tony

I had a set of those, really nice fins.

 

[Bob Yanecek]

The fins look upside down to me.
Given through the wall mount, is there a way you can eliminate the external attachment technique and lock them in from 'inside'?

 

[kjhambrick]

Great Flight Tony !

Too bad about that poor NASA sticker though

I noticed you had backup charges for drogue and main ... were there two altimeters onboard ?

I really liked the nice, orderly drogue descent -- thats the way it should work !

So ... did ARLISS invent that fin design and Black Sky borrowed them for the Optimal series or vice-versus ?

Thanks for the Video !

-- kjh

 

[SolarYellow]

Another advantage of removeable fins is that they are easily replaceable. I built a couple "utility rockets" out of Estes Booster-55 and Booster-60 fin cans and realized it's not necessary to glue the fins in because they are held in position by the screw-on motor retainer caps. It's nice to be able to throw them in a mailing tube and then put that in my luggage and know it will get halfway across the country without damage. And when I've had a chute tangle and streamer in on the lake bed, I just replaced the one damaged fin while I was changing the motor for the next flight.

 

[SolarYellow]

IN THIS ISSUE: Model Rocket Replaceable Fin System

https://www.apogeerockets.com/education/downloads/Newsletter555.pdf

 

[NTP2]

IN THIS ISSUE: Model Rocket Replaceable Fin System

https://www.apogeerockets.com/education/downloads/Newsletter555.pdf

Tim must be reading minds…

 

[tfish]

Great Flight Tony !

Too bad about that poor NASA sticker though

I noticed you had backup charges for drogue and main ... were there two altimeters onboard ?

I really liked the nice, orderly drogue descent -- thats the way it should work !

So ... did ARLISS invent that fin design and Black Sky borrowed them for the Optimal series or vice-versus ?

Thanks for the Video !

-- kjh

Konrad..Yes dual systems.
The fin design was before my time. A year or 2 ago..I did see an old 4" "Optimal rocket" that used the same concept. The fin shape was different.
I'm willing to..guess..that it was a joint effort at coming up with the current shape and (maybe) method of attachment.

Tony

 

[Art Upton]

Someone I can't remember who, came up with an Internal Aluminum fin can that slipped into the inside of the 6" ARLISS body tube and then the fins screwed into the holes of that inside fin can. I had one but sold it quite some years ago.

 

[cerving]

The original Vashon Valkyrie cold-fuel rockets had some plastic rails that you epoxied onto the motor tube, the balsa fins slid into the rails. They worked "ok"... they would have been better if they had been deeper (they probably weren't more than 1/8" deep). The Apogee concept is similar, but plastic isn't gonna cut it for a 2' diameter rocket. Giant Leap made some extruded aluminum brackets they call "frackets" that were there supposedly to make putting the fins on easier, not for removability (they definitely did NOT make it easier... just more things to glue and fillet).

I like your idea of sinking the fin brackets into the tube... I may try it. It's probably going to be heavy, though.

 

[Alan Whitmore]

I came up with a removable-fin design that I have used in several rockets since 2018. The fins are built from the 1/4" honeycomb foam with carbon fiber on the sides. The fins are attached to wooden stringers that support the centering rings, and the body tube is not attached (permanently) to the fins in any way. I was concerned that the strength may not be up to an N motor launch, but they have had no problems except for the one time I forgot the quick-link attaching the fin section to the rest of the rocket, and the fins fell from 10,000' without benefit of parachute. Even on that occasion, replacing the broken fin only took a day or two.
The slotted body tube is attached to the centering rings with 16 small screws. Other pictures available on request.

Alan

 

[G_T]

https://www.rocketryforum.com/threads/sprite-6-and-a-baby-o.37382/
Here's another example. A rather detailed rocksim file is present and there are lots of pics. For those with interest, I also covered vacuum bagging the fins pre-painted, chute packing, etc.

Gerald

 

[Handeman]

The first large rocket I saw with removable fins was one @ben had used for his L3 back in the '90s. It was similar to what @Alan Whitmore did, except it wasn't a removable fincan, just removable fins. The removable fins were for ease of transport and storage. He brought the rocket, four fins and a bag of nuts and bolts to the field. The 3/4" ply fins fit in the slots, he reached inside the 98mm motor hole and bolted each one in. After flying it, he unbolted the fins, packed the rocket, fins, and bag of nuts and bolts away and headed home.

 

[bobby_hamill]

I have been toying around with an fin attachment for my 6" Black Brant 2 using all-thread rods
and T-nuts inserted in the fin tabs . To remove the fin you would just screw out the all-thread and
lift the fin out . There would be a bottom centering ring added to hide the all-thread ends

 

[G_T]

When designing a removable fin system, keep in mind the leverage of the fin vs the mounting. If the fins are 14" semi-span, and the mounting is 1" for instance, there are going to be problems.

Gerald