Tube fin calculator

I've been thinking of building a tube fin rocket. The obvious solution is six of something around itself.

Why be obvious? I was wondering if there were any combinations of the tubes out there that would line up perfectly with four, five, seven, etc tube fins. There seems to be no spreadsheet for this, so I made one with common tube sizes from 13mm to 5.5".

Left side is center tube, top is fin tube. Cells are highlighted if the number of tubes is within 0.05 of 4, 5, 7, 8, 9, 10. More than 10 and you barely have any fins. 6 is not highlighted for obvious reasons.

Screenshots of the interesting stuff

Hope someone finds it useful

Have you read the Apogee article or the Larry Brand articles it references? This is great stuff btw.

Here's my crappy uncleaned up version that I never got around to making fit for consumption.
https://docs.google.com/spreadsheets/d/1I_YrucR3LuIMg1G0HSneY3eo-dgtewzbp3i8V1fZb2g

I'm particularly proud of the 7x BMS t908 around Apogee Aspire parts, that's the fastest tubefin you can do on no-haz no-cert AFAICT.

The other very interesting series is Blue Tube with a 38mm core.

EDIT: Apogee Rockets, Newsletter335,
Explorations in Modular Tube Fin Rocket Design
https://apogeerockets.com/education/downloads/Newsletter335.pdf

dhbarr said:

Have you read the Apogee article or the Larry Brand articles it references? This is great stuff btw.

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Thanks: that plus Bluefin Tuba is what was making me think of this. Didn’t want to do six around one, so I went looking for sevens.

I'm particularly proud of the 7x BMS t908 around Apogee Aspire parts, that's the fastest tubefin you can do on no-haz no-cert AFAICT.

Click to expand...

I believe you are right. I was thinking of 29mm blue tube core and BT50 fins. No-haz/no-cert on G77 LMS, and probably strong enough to take the biggest 29mm motors.

On the smaller side, BT50/7xBT20 will go plenty fast on a big CTI 24mm. Too small to fit a tracker, so it’s effectively single use.

The other very interesting series is Blue Tube with a 38mm core.

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That’s actually what I am filling shopping carts for right now: 38mm blue and 7xLOC 29 MMT.

7 fin tubes cut back like a Kraken. To honor the Seven, I plan to name it The High Sparrow.

Should go fast on non-haz Loki reloads. I’m also interested in seeing if the big Loki 38mm reloads can push a tube fin past the number. After all, aerodynamically it’s just a small grid fin with a motor in the middle.

IIRC i405 gets you there but I haven't simmed it in a while.

Avoid the kraken cuts IMO as they have stress areas at the sharp points.

My best idea so far was flat front, half-dia tip, ~22.5 deg aft for some added strength.

Now the problem is launch lugs. 38mm fins is the minimum to go over 8020 rails. That means a 29mm/24mm fin is limited to launch rods, which puts a maximum on weight

1010 is not the only rail in the world; also you can use the triangle between two tubefins as an aft guide with a single lug at CG.

I had an unexpectedly good flight with the t908/aspire combo. Even with only a 6in chute and a 20% spill hole it floated about a thousand miles away.

Have you seen this? https://www.rocketreviews.com/by-airframe-diameter.html

Maxter said:

Have you seen this? https://www.rocketreviews.com/by-airframe-diameter.html

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I had not, thanks for the reference. It occurs to me that programmatically iterating across all permutations of tubes in the OR DB would be the ultimate form of this work. Very handy.

You guys seem to be assuming that rods/rails have to go throught the gaps between tubes. To use a tube fin rocket on a standard launch rail, you can align the buttons with the center of a tube fin as well. Just use a piece of scrap tubing (the same thickness as the tube fin) as a spacer under the rail buttons. The scrap tubing is curved and will conform to the body tube.