How much canted fin is too much?

I have a proto body tube (aka a poster tube from Staples) that has very prominent spirals. It's just crying out for canted fins to make it spin. Unfortunately, the spirals are at about a 30-degree angle from the length of the tube, and that seems like an awful lot for canted fins. Is there a practical maximum cant angle? Does OpenRocket deal with canted fins well? I'm obviously not going for maximum altitude, just for safe prediction of stability and a reasonable estimate for a delay. Oh, and if I can make the nose cone with a matching spiral, I'm totally doing it.

Thanks in advance!

Yes, 30deg is way too much for canted fins ; without some sort of buttress they'll rip right off if you much more than sneeze at them.

Spirals contribute a certain amount of spin for which ( to my mind ) no sim accounts. Ignore the spiral spin, add fins canted to your heart's desire.

I wouldnt go over 3-5 degrees and that is alot. Go for 1-2 degrees it should still spin like crazy

OR will do canted fins. 30 degrees is a helicopter btw

SpaceManMat said:

30 degrees is a helicopter btw

Click to expand...

Eeeeh, not so much really. It would be a fast spinning draggy rocket, but a very poor copter.

I think that canted fins glued on to match the spiral of a body tube would make for an interesting rocket, very draggy, but should hold up as long as the fins are glued on well, and not weak fin stock to begin with. And use a chute or streamer for recovery as the spin while draggy would not be THAT draggy for a very safe recovery.

Now here's the ultimate extreme. The Tasmanian Devil. The "fins" are actually stubby rotor blades at 2 to 3 degrees angle of attack to horizontal, or 87 to 88 degrees angle of attack to the direction of flight / body tube. The triangular balsa pieces parallel to the body are not intended as fins, but as reinforcing struts.

https://georgesrockets.com/grp/Plans/Sport/Taz.html

Fins will be TTW plywood, so I don't really see them breaking off. Building rockets like tanks is what I do best. The tube is ~2", and the MMT will be 29mm, so it should be fun. Maybe I'll try a launch on the local field before I go to the club launch.

The rocket is built, flown, and given away (as planned). I ended up going with 10 degrees of cant and laid the fins out in Rhino to make sure they would fit right around the motor mount. It turned out that laying out the fins was the hardest part. After a short trip to my buddy's for a lathe and laser cutting session, I had a custom bird's eye maple nose cone and some perfect fins.

The rocket flew really well with lots of spin but straight smoke. I'm pretty sure OR doesn't really calculate the extra drag from canted fins; apogee only dropped ~50 feet (of ~800) from zero cant to 10 degrees. Moral: take the delay down a little from the OR ideal. We did that and had several great flights.

Just found this thread, so sorry for being late to the conversing!

I don't believe there is "too much" cant for a fin. You can go all the way to 90 degrees at which point it becomes like a saucer or annular fin (I think Estes made a rocket with 4 flat "fins" almost like a satellite a long time back and I recently saw a model rocket with flat grid fins); however performance usually suffers due to all the drag and as George and others noted, you have to make it stronger as it cants over more. Spinning action does help to reduce drag over time though and is helpful in stabilizing the rocket, so that is a common method with "flattish" fins.

Here's one of my favorite Oddrocs...the Rocketarium Vortico series:


Good to hear your rocket performed really well!