Broken Heart

[jqavins]

A little while ago I bought a pair of plywood hearts from the craft section of Dollar Tree or General or whatever. I cut them down their middles so that each one gave me two fins. I wrote about that in the What Did You Do Today Rocketwise thread.

Here's a quick and dirty, very rough design file.

In order to keep things simple, since the plan is to use this for a cert flight, I plan to use motor ejection plus a JL chute release. I want a tube coupler for length, so I figure to build a baffle into it since it's there. I may attach the coupler/baffle with removable rivets so that I can take it out to clean or replace when it gets a lot of ejection gunk inside.

The fins are thin and not of the best quality plywood, so I will definitely be glassing them, a first for me. I'll probably also glass over the fin-tube joint, in the fillets. But I'm thinking I don't need to do the whole tube if I use LOC heavy wall cardboard. I know plenty of flights have been successful on J or K motors with that stuff unglassed. But maybe I'll bite the bullet, swallow my insecurity, and glass it anyway. Or maybe I'll just by some fiberglass tubes. Or Bluetube. Opinions?

Getting the fin shape into RockSim was an interesting process, so I think I'll write a tutorial and post it to the Techniques subforum. It involved hacking the .rkt file in a plane text editor, so not for the faint of heart.

 

[lakeroadster]

A little while ago I bought a pair of plywood hearts from the craft section of Dollar Tree or General or whatever. I cut them down their middles so that each one gave me two fins. I wrote about that in the What Did You Do Today Rocketwise thread.

Here's a quick and dirty, very rough design file.

In order to keep things simple, since the plan is to use this for a cert flight, I plan to use motor ejection plus a JL chute release. I want a tube coupler for length, so I figure to build a baffle into it since it's there. I may attach the coupler/baffle with removable rivets so that I can take it out to clean or replace when it gets a lot of ejection gunk inside.

The fins are thin and not of the best quality plywood, so I will definitely be glassing them, a first for me. I'll probably also glass over the fin-tube joint, in the fillets. But I'm thinking I don't need to do the whole tube if I use LOC heavy wall cardboard. I know plenty of flights have been successful on J or K motors with that stuff unglassed. But maybe I'll bite the bullet, swallow my insecurity, and glass it anyway. Or maybe I'll just by some fiberglass tubes. Or Bluetube. Opinions?

Getting the fin shape into RockSim was an interesting process, so I think I'll write a tutorial and post it to the Techniques subforum. It involved hacking the .rkt file in a plane text editor, so not for the faint of heart.
View attachment 612417

How thick are the fins?

Seems like making them from plywood, with TTW fin tabs, would make for the same end result... but much more durable.

 

[jqavins]

They're 1/8" thick and, as I said, came from a dollar store craft section; the quality of the plywood is unknown and I just don't trust them. I may well go TTW, but that doesn't keep them from fluttering or cracking.

 

[BABAR]

If you are looking at some high altitude flights, your fin profile is ideal for a streamer recovery. It should land on the motor casing, sparing the fins initial impact.

Just don't name it "Suicide King"
https://www.rocketryforum.com/threads/open-body-missile-build-for-my-level-2.24733/page-2
see posts 57 and 88.

I do kinda like the name Cupid!

 

[NTP2]

I once considered doing this but didn’t, I will be very interested in how it turns out!

 

[jqavins]

The current name is based on the fact that I cut the hearts in half to make the fins. I'm not totally committed to it.

 

[cwbullet]

Nice, pleas post photos of the flight.

 

[jqavins]

Sure, but it won't be until next year, and likely not early next year if I'm true to my normal building pace.

 

[BABAR]

Sure, but it won't be until next year, and likely not early next year if I'm true to my normal building pace.

Takes time to mend a broken heart…..

 

[lakeroadster]

 

[David Schwantz]

Great idea. Most of the time that cheap ply has some cheap really soft wood as the center ply. So paying attention to the direction the ply on the 2 outer layers will help greatly against flutter.

 

[David Schwantz]

l was thinking there should also be an arrow through the hearts

 

[boatgeek]

Looks like fun!

There’s lots of examples of cardboard rockets of this size flying on J and K motors unglassed. I don’t think that you need to glass the tubes unless you want to for learning, fun, or hangar rash prevention. Glassing over the fillets may also be unnecessary, but that’s a slightly harder call from a distance.

 

[Alan15578]

The current name is based on the fact that I cut the hearts in half to make the fins. I'm not totally committed to it.

So it truly is a half hearted attempt to scratch build a rocket.

 

[tsmith1315]

So it truly is a half hearted attempt to scratch build a rocket.

Half hearted would be a great name, too!

 

[jqavins]

Great idea. Most of the time that cheap ply has some cheap really soft wood as the center ply. So paying attention to the direction the ply on the 2 outer layers will help greatly against flutter.

But I don't get a choice about that, since the heart shape is what I bought already made and ready to be cut in half.

l was thinking there should also be an arrow through the hearts

Maybe In the paint scheme. But no shaft, feathers, and arrow head extending beyond the plywood.

 

[BABAR]

OK I will let my ignorance show here. Does fiberglassing fins provide that much more strength over papering fins. Say with Manila? Does it matter if it is going supersonic or not?

If you want to learn or practice fiberglassing skills, that’s a whole ‘nother Matter.

But if you can achieve adequate strength with papering (or “super-plying” with adding 1/32 layer of either balsa or base wood on each side) it saves you time, trouble, and money.

 

[jqavins]

Well, I'll answer ignorance with more ignorance, but this is my understanding. Strength: yes, it's a bunch better. Stiffness: heck yes, it's a whole bunch better. If I'm wrong, I sure wouldn't mind papering with manila folders. But I'm going to have to learn FG sooner or later; I've got a half build rocket with a phenolic tube.