Rocket Design

[Sparky2Participant]

I know this question has probably been discussed over a MHM or Octoberfest campfire but I’ll ask anyway. Why don’t most heavy lift launch vehicles, Delta 4, Atlas 5, Ariane 5 etc have fins? I understand CP and CG but what is it about the big birds that they don’t need fins? Just curious.

[Anonymous]

John, the fins would only work if there was sufficient air in which to steer. As the rocket climbs, the amount of air gets thinner and this means less efficiency of the fins.

Large rocket motors are on gimbels (spelling?) which are hooked to gyroscopes and the nozzles are slightly redirected to hopefully keep the pointy edge up.

In other words, it is serious rocket science. Truly.

This may be worthwhile http://yarchive.net/space/rocket/rocket_steering.html

[Sparky2Participant]

Thanks John, I didn’t even think about the steerable motor. That has got to take some serious computer and motor mount engineering. That type of steerability is not legal in HPR right?

[Anonymous]

That has got to take some serious computer and motor mount engineering. That type of steerability is not legal in HPR right?

It is my understanding that we are NOT allowed to have steerable rockets. Not a big deal to me, because I’m not smart enough to pull that off if I wanted to…

[new2hprParticipant]

Actually, it’s been done in mid-powered (F motors), and is totally acceptable to mess around with.
http://www.ukrocketman.com/rocketry/gimbal.shtml#gimbal13

I don’t think there are any safety codes that prohibit guidance or active stability controls. I know our own Doug Gerrard has played around with active spin control to try and stabilize his movies.

Ken

[new2hprParticipant]

I believe that team started with D motors and progressed through G so far. Here’s a video of that creation…
http://www.ukrocketry.com/index.php?option=com_weblinks&task=view&catid=15&id=21

Pretty cool how it drifts downwind, but stays vertical the whole time. And no fins!

Ken

[Sparky2Participant]

Very interesting website! There you go John, no fins- less drag= more altitude! Thanks for the info Ken. It amazes me how high tech and multi-facetted you can get with this hobby.

[new2hprParticipant]

Only “=more altitude” if weight of sensors and gimbaled motor mount =0.

Still cool. I think that system is begging to be stuffed into an upscaled Mars Lander with NO recovery system. Just a nice long-burn up and down.

Ken

[Warren B. MusselmanModerator]

All commercial and government liquid fueled rockets use active guidance systems, usually using gimbaled exhaust nozzles and in some case entire combustion chambers. Gyros were used as the reference for birds like the Atlas, Saturn and other large boosters. There are some interesting quotes from Apollo astronauts about how “nervous” they got while the big F1 motors gimbaled beneath them trying to keep the Saturn stack in balance until they passed the tower.

There have been experiments done with hobby rocket motors, but given the short burn times, it’s difficult unless you have a very high speed data acquisition system and cameras to fine tune the stabilization algorithms.

By the way, active guidance systems aside from sun seekers and seeking true vertical trajectories, are seriously frowned upon. Public experimentation with such is likely to draw the attention of men in suits with mirrored shades and funny earplugs with coiled wires dissapearing under their suits.

Warren

[Dreasher]

Warren,

“men in suits with mirrored shades and funny earplugs with coiled wires dissapearing under their suits.” they mutter alot into their sleeves too. 😉 The suits were always fun to talk to when I would do photography for politicians.

Ron

[Author]

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