How many fins ??

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Andy Greene

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So - if you where building a close to min diam 24mm that flew on single use 24mm f motors and reloads -
And performance ( altitude and speed ) was the goal - would you go 3 fins or 4 and why ??
 
I would think the same thing 3 fins vs 4 , But :eyeroll: If Im gonna use smaller fins - as most performance type MD rockets I have seen have - Would 4 make it more stable .
Dont get me wrong, my initial thought was 3 fins for the same reason, then of course- a few good friends with WAY more KNOW than I suggested 4 for my plan. This is the mock up- not actual parts being used - thoughts ?
2hnoqk1.jpg
 
The answer may be you can't have everything. Three will be lower drag and will be best for speed. Four, if they add stability, may result in straighter flights and thus offset a small penalty in drag? I thought I have heard 3 is best, but I forget the source.
 
The answer may be you can't have everything. Three will be lower drag and will be best for speed. Four, if they add stability, may result in straighter flights and thus offset a small penalty in drag? I thought I have heard 3 is best, but I forget the source.

Im not out to try and set records by any means - just a hot rod sport rocket for cheap flights on F reloads and single use with a jlcr -
Thinking about 4 just for durability-consistency - it aint gotta be special.... :wink:
I cut 2 fins- one a little smaller than the one pictured , if I do 4 I will use the smaller fin.
 
Ya mean like this one?

DSCN5354.jpg

3 Tiny carbon fins...carbon tube....7-1 VonKarmon NC

That's a 24mm 6xl motor with turned tailcone. Telemini altimeter/tracker combo...fits in NC apogee only eject with streamer.
 
If you use 4, then figure sq.inch surface area of the 3 fins & divide it by 4. That will determine correct size, then adjust the span so it's a caliper. Bevel from Hell & drag increase is minimal, if any, due to frontal area and size reduction of fins.
Really only necessary on larger rockets 75 and up.

For this.... a waste of time, stick to 3.
 
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You should...he's been so busy with new baby...bet he forgot.
Oh, that’s great news (human baby, I take it?).

What’s that tail cone, by the way? Looks like a sweet research bolt on!
 
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Looks like Andy's is a single use rocket. Seriously, unless it comes down right on top of you, you ain't going to find that thing without some kind of tracking strategy.

"Im not out to try and set records by any means - just a hot rod sport rocket for cheap flights on F reloads and single use with a jlcr"

Be a tight fit with the JLCR though can be done. You really want to risk losing a JLCR? Without a tracking strategy that's what the recipe looks like from my end. If you simulate the heck out of it and it looks like you'll have a visual on it most of the way,
it should be doable with lower loss risk. If it goes to "outta sight" land for any length of time, the upper air winds are going to throw that thing all over the place and you won't know where to look. One half mile away and I don't care what kind of chute or colors
you paint that thing, you "ain't" gonna see it. It's likely not going to be visually tracked easily at a quarter of a mile.

The other stupid mistake is having the JLCR deploy down "really" low. Why? Your best chance at seeing the rocket at a distance is with the chute out with a slowed descent. If you pop it at 300 feet, you ain't gonna have much time to get a visual on it before
it lands. Sure, if you got a visual on descent all the way down fine, but holee molee you lose sight and have to frantically get a visual before it's down might be a better strategy to blow it a little higher. Of course if it's still "outta sight" blowing it higher could
carry even farther away from you but either way you're screwed.

As an example, I've flown a Wildman Jr a dozen times all but one completely out of sight the entire flight. It's fluorescent red with a yellow main chute bay. I've had several recoveries where it was a half mile away with a 36" parachute I have deployed
at 800 feet. I know where to look for it on descent because I live track on a map. A lot of times, I can tell the main is out because the APRS/GPS tracker tells me the descent rate has slowed. I know where to look and call out and nobody sees it either.
I walk up and it's lying there so pretty with the main chute out and not a mark on the paint job.

I've tracked other folk's projects and several instances where everyone is looking the wrong direction (based on surface winds) I've called and pointed out where to look. Sometimes we see it under the main, sometimes we don't because the rocket is too far
to be seen. Blowing the main up high actually gives time to see on the altitude indication on the ground station that the main is fully deployed and nothing to fear. (Descent rate slows) Just walk out and pick it up.

Andy, fly that thing down low many times so you can get a feel for it. Simulations are fine and should be used as a guide. They're not gospel. Walk your motor size up stepwise and you might find yourself getting a bit nervous and
halt at a motor that gives a satisfying flight without as much risk for loss. (Of course that might vary with windspeed) Again, think of your "poor" JLCR! Do you want to make it homeless?:jaw:

It seems I have some old beater cardboard rockets I stuff some big SU motors in 'em cause I don't care if God decides to keep them. Most of the time, I swear some guardian angel grabs the danged things and I get 'em back!!
The pretty ones He usually keeps!!

Kurt
 
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Bevel from Hell & drag increase......... {IS} minimal, if any, due to frontal area and size reduction of fins.
.

Put super, duper bevel [say 7 degrees] on fins. Reduce size of fins by going to 4 [smaller thinner,] instead of 3 [larger thicker] and you have reduced drag to a minimum,[ possibly less or same than the original 3.]

In other words: using 4 fins instead of 3, does not automatically result in a large increase in drag.
 
Man, I need to ping Charlie on mine.

Ummmm, where can I buy this piece of wizardry?

Young grasshopper, you have the answer before the question. :) Also check out the forward anchor.

I found it helpful to soap my tailcone threads and run them into to all of my 24mm cases. Some of them fit easily, others needed practice.

Wear a good glove, I got a pretty nice cut from an excess of brutishness.
 
Looks like Andy's is a single use rocket. Seriously, unless it comes down right on top of you, you ain't going to find that thing without some kind of tracking strategy.

"Im not out to try and set records by any means - just a hot rod sport rocket for cheap flights on F reloads and single use with a jlcr"

Be a tight fit with the JLCR though can be done. You really want to risk losing a JLCR? Without a tracking strategy that's what the recipe looks like from my end. If you simulate the heck out of it and it looks like you'll have a visual on it most of the way,
it should be doable with lower loss risk. If it goes to "outta sight" land for any length of time, the upper air winds are going to throw that thing all over the place and you won't know where to look. One half mile away and I don't care what kind of chute or colors
you paint that thing, you "ain't" gonna see it. It's likely not going to be visually tracked easily at a quarter of a mile.

The other stupid mistake is having the JLCR deploy down "really" low. Why? Your best chance at seeing the rocket at a distance is with the chute out with a slowed descent. If you pop it at 300 feet, you ain't gonna have much time to get a visual on it before
it lands. Sure, if you got a visual on descent all the way down fine, but holee molee you lose sight and have to frantically get a visual before it's down might be a better strategy to blow it a little higher. Of course if it's still "outta sight" blowing it higher could
carry even farther away from you but either way you're screwed.

As an example, I've flown a Wildman Jr a dozen times all but one completely out of sight the entire flight. It's fluorescent red with a yellow main chute bay. I've had several recoveries where it was a half mile away with a 36" parachute I have deployed
at 800 feet. I know where to look for it on descent because I live track on a map. A lot of times, I can tell the main is out because the APRS/GPS tracker tells me the descent rate has slowed. I know where to look and call out and nobody sees it either.
I walk up and it's lying there so pretty with the main chute out and not a mark on the paint job.

I've tracked other folk's projects and several instances where everyone is looking the wrong direction (based on surface winds) I've called and pointed out where to look. Sometimes we see it under the main, sometimes we don't because the rocket is too far
to be seen. Blowing the main up high actually gives time to see on the altitude indication on the ground station that the main is fully deployed and nothing to fear. (Descent rate slows) Just walk out and pick it up.

Andy, fly that thing down low many times so you can get a feel for it. Simulations are fine and should be used as a guide. They're not gospel. Walk your motor size up stepwise and you might find yourself getting a bit nervous and
halt at a motor that gives a satisfying flight without as much risk for loss. (Of course that might vary with windspeed) Again, think of your "poor" JLCR! Do you want to make it homeless?:jaw:

It seems I have some old beater cardboard rockets I stuff some big SU motors in 'em cause I don't care if God decides to keep them. Most of the time, I swear some guardian angel grabs the danged things and I get 'em back!!
The pretty ones He usually keeps!!

Kurt

Sound advice - :wink:
 
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