Tube Fins--what are optimal and maximum acceptable length/diameter ratios?

[BABAR]

Recent post which i now cannot find mentioned boundary layer problems with too long tubes. I am not sure how much impact velocity has (i suspect a lot) but in my case i would be dealing with LPR rockets and specifically gliders so definitely not mach levels.

Again,
what is optimal?
What is max acceptable?

[o1d_dude]

I've never built a tube fin glider so this is just speculation.

Typically most high performance tube fin ROCKETS have the tube fin length approximately equal to or slightly less than the tube diameter. Ignore the Estes Super Neons and the Custom Razors. They work but that's all I can say about them.

My recommendation is to visit My.RocketReviews.com and do a search on "Larry Brand". He has done a lot of experimental research on tube fin rockets. I've had great success with cloning/copying his designs and did my Level 1 cert on his Sardo XXL design.

Tube fin ROCKETS have a very high coefficient of drag that is inversely speed dependent. The faster they go, the lower the drag. "Normal" rockets mostly have much lower Cd and no speed dependencies.

[boomtube]

I have a question about designing tube-fin rockets.

As we all know six tubes will fit perfectly around the circumference of the same size tube. Example: six BT-60s around another BT-60.

Is there any simple way, some math formula for example, to determine other “Perfect combinations”? Such as 5 BT-55s around a BT-50 or some such.

As for the aerodynamic effects what if anything does cutting the leading and or trailing edge do for performance?

How would that affect the desired length to diameter ratio on high power rockets?

And who invented liquid soap and why?*



*Extra points awarded for knowing where that came from.

[Scotty Dog]

And who invented liquid soap and why?*



*Extra points awarded for knowing where that came from.

William Shepphard 4 washing dishes

[Rocketbuilder]

To determine "perfect combinations," I have two suggestions: experimentation, and using circles of the appropriate diameters in Microsoft Word.

Thanks for starting this thread, BTW. I now have at least some rudimentary knowledge of tube fins.

[o1d_dude]

Actually, I have a printout that I refer to in cases when I'm considering different tube fins build. I'd like to credit the person who developed it but I don't remember from what site I downloaded it.

Anyway, it's attached to this post....er, scratch that. I found the link.

Mycroft's Tube Fin Rocket Resources

[UncleVanya]

My understanding is that tubes that are 3x long their diameter work OK but longer than that and you start to collapse the flow. I have generally stuck to my favorite dimension which is a "square" tube - 1:1 - length = width.

I also second Larry Brand as a good source for info and designs of these rockets.