"kite tail" draggy stabilization for Hindenberg

For the 2006 EMRR challenge, I'm considering converting this plastic model of the Hindenberg:
https://modelingmadness.com/scotts/civil/lz129.htm

This is only about twice as long as the 1/4A engine I would fly it with. On a micro scale, this is really a short & stubby rocket with insufficient fins. My question relates to ideas to make this fly stably.

I've seen pictures of oddrocs with stiff narrow rods (e.g. 4 of them) stretching out from the rear of the airframe at 45-degree sweep angle, like Sputnik. These replaced fins. My idea is somewhat similar.

Suppose that I attach some kevlar thread "restraint lines" to the blimp at its rear edge. Then to the end of these lines, I attach some little draggy or heavy Nazi men. When the rocket launches, these men would be dragged up behind the Hindenberg to their certain doom. I would have the motor eject and use featherweight tumble recovery.

Could this work to stabilize flight? Is it more important that the Nazis are heavy or draggy? (My intuition says drag is more important)? Any ideas how the length of the restraint lines affects things? How will the kevlar fare during thrust?

Thanks!

Geof

If your little ballast people are just dangling from Kevlar thread, they do not add to stability at all, because they are not part of a "rigid body". In fact, they will add chaos to the stability of the rocket, which is what is technically known as a "bad thing".

You might get away with it if you use dowels instead of threads, thus making the whole rocket a rigid body again. But putting weights at the bottom and expecting them to keep the rocket upright is an example of the Pendulum Rocket Fallacy. You'd be moving the CG backwards, which is NOT the direction you want it to move. Rockets with dowels, such as the Sputnik Too, are "drag-stabilized", moving the CP back more than they move the CG; it's aerodynamics, not balance.

In the case of your Hindenberg, the dowels would make it look silly, in my opinion, but that's up to you. The weighted strings, however, will cause nothing but trouble.

Yep, that makes sense. Thanks for helping me see it.

PS. My Nazis weren't ballast they were drag, but the rigid body argument seems good to me.

G

Later Edit: Still thinking about this, and not so sure now. Review
https://exploration.grc.nasa.gov/education/rocket/rktstab.html.
Why wouldn't my draggy Nazis constitute a restoring force acting
through the CP?

This thread brings up an idea I had a while back regarding moving the CP back artificially using a streamer.

Basically, if a rocket had a single eye-screw in the dead center of the bottom (middle of a triple-cluster, for example) with a 5-foot kevlar string attached, and a 30-inch streamer on the end of that. The streamer would in essence, function as a drogue chute and hold the center of the bottom of the rocket back.

Or would the non-rigidity of the kevlar line be a problem?

This differs from geof's original plan in that the aerodynamics of the streamer provide the effect, as opposed to the weight suspended and swinging.

WW

Originally posted by wwattles
This thread brings up an idea I had a while back regarding moving the CP back artificially using a streamer.

Basically, if a rocket had a single eye-screw in the dead center of the bottom (middle of a triple-cluster, for example) with a 5-foot kevlar string attached, and a 30-inch streamer on the end of that. The streamer would in essence, function as a drogue chute and hold the center of the bottom of the rocket back.

Or would the non-rigidity of the kevlar line be a problem?

This differs from geof's original plan in that the aerodynamics of the streamer provide the effect, as opposed to the weight suspended and swinging.

WW

Click to expand...

Interesting question. You'd be generating drag, that's for sure, but my instincts tell me that if the rocket towing the streamer veered off course, the streamer would tend to follow the rocket rather than apply much in the way of a corrective force.

Now if you were towing something flat and rigid (a heavily starched streamer?), that would behave differently from the free streamer, because it would be acting like a strange sort of fin; it would actually have to rotate in the airstream if the rocket towing it changed direction. Would probably still not be very effective. A variation of that would be to have a rocket towing an unpowered smaller rocket behind it, like putting a screw eye into the top of the nose of a Mosquito. Or maybe the towed body would need to be longer and have fins running most of its length to increase its resistance to a change in direction. The towed body would still have to be stable on its own, otherwise it'd be like trying to pull a shopping cart backwards in a grocery store: it's going to fight you and try to turn around.

I suppose if tow aircraft can successfully tow sailplanes to altitude without screwing up their own stability, then a rocket could tow another one behind it. And banner planes can tow banners without trouble. I just believe the tow plane has to maintain its own stability, because the thing being towed isn't going to add to the tow plane's stability.

Hmmmm... a rocket towing one of those little styrofoam gliders behind it on a length of Kevlar thread, with the other end tucked in between the nose cone's shoulder and the body tube... interesting idea. Except that styrofoam BURNS, even if Kevlar doesn't. Forget I even mentioned it.

Looks like Nasa beat you to it again....

Originally posted by andyc
Looks like Nasa beat you to it again....
{img snipped for brevity}

Click to expand...

eek!

Cool ! I want one of those !