Two Stage Thoughts

[Bruiser]

So I have been wanting to build a two-stage rocket for some time now. I have been building mostly 1/10th scale rockets and I did start a Semroc Nike Tomahawk but have run into some technical/design issues of the gap-staged booster so it's hanging out while my brain sifts thru the best way to do it.

In the meanwhile I have been thinking about building a simplier two-stage rocket. My first design is a direct staged designed based on D12 engines. I was a little concerned about the altitude so I was thinking about a chute release so I had a thread about that. Here's a screen snap of the rocket:


I like it but I saw the Estes Red Nova and thought that would be a nice looking upscale (1.64 like the one above) so I drew it up, sans the nose cone. It was also based on the Estes 24mm motors. It has a gap of about three inches between engine, nothing too big or complicated. I did not draw up just the booster to see if it will tumble or not.


Then I started thinking about how I like the looks of the Nike X and how I'd probably build one if it was slightly larger. I decided to draw one up and I remembered about the altitude issue with rocket one so I thought if I build it slightly larger that would help with decreasing the altitude and the larger diameter would also help with a chute release if it turns out I need one, like if I use E engines instead of Ds so I drew it up with a two inch tube. This has a larger gap stage though with about 6 inches between motors. I did draw just the booster and the CP and CG are very close. I think it would tumble based on what I've read but I would like to get the expert's opinions on that. The caliber is good on just the sustainer as well.






I tried googling Nike X two stage and to my surprise, turned up nothing. So I'd like to here any thoughts on this Nike X two stage design if anyone would care to share their thoughts.

Thanks,
-Bob

 

[Wallace]

Personally, I like the 1st one..And gap staging has never been a problem, at least in my experience(s). Just remember to add motors before you believe stability in sims..

 

[Wallace]

Forgot to mention: adding ANY device that is WAY more valuable than the rocket itself seems to increase the stress level...

 

[mbeels]

I prefer gap staging, because it allows for using engine hooks for positive motor retention. Direct staging with the motors taped together requires relying on friction fits.

 

[Bruiser]

So are you comfortable with 3 or 6 inches between motors for gap staging? What about tumble recovery of the booster? DO you find that is true that the booster will tumble if the center of pressure and center of gravity are almost the same?

-Bob

 

[Wallace]

If the booster becomes too long, it will have a tendency to become stable. Sims are your friend in that regard. Otherwise, tumble recovery has worked fine for a long time.

 

[mbeels]

So are you comfortable with 3 or 6 inches between motors for gap staging?

As Wallace said, it may become stable if it is too long. A short gap, like 1", allows for motor retainer springs and much easier and faster prepping and flying. My personal preference.

Another approach folks have done for longer gap staged boosters is to use rear ejection on the booster along with a streamer, but that adds a bit of complication.

 

[BABAR]

gap staging not a problem, as long as vent holes are appropriately positioned.

As other have said, the longer the gap, the more likely the booster will be stable

Second problem is however MASS. Larger longer boosters with bigger motors come down harder even when they DO tumble. Not a big safety issue, but likely to break a fin on impact.

 

[Bruiser]

So I have drawn up the estes BT55 Nike X as a two stage. Was getting plenty of altitude with the 18 mm engine but the rod speed was too slow. I went to 24 mm in the booster and the rod speed was good but it was hard to keep under 1,000 feet.

I decided to do an upscale to BT60 and that seems to work out well with a 18mm sustainer and a 24 mm booster with commonly available engines. I just need to figure out if the booster will tumble...



I already have a Star Orbitor that I bought for parts. It can donate the nose cone, body tube and misc parts. Hobby Lobby stocks the Nike X so I can pick one up when I get home from visiting my in-laws Wednesday. It will be used to verify sizes of parts and it can donate the motor mount tube, engine block, parachute, maybe the launch lugs and other asst parts. I have plenty of balsa and a ST9 tube for the 24mm mount. Seems like all I will really be lacking is centering rings. Oh and I'll get to try my hand at decals. I'll scan the kit decals, enlarge and print out on Testor's paper.

Thanks
-Bob

 

[Wallace]

Bob; You have everything you need to know from what I'm seeing. Run the sims and get your answer. And don't forget to enjoy...

 

[Bruiser]

So I have decided on an overall size and motor mount sizes. I've narrowed it down to two designs. Please find my new thread in scratch built or the staging forums and vote

Bob

 

[jqavins]

A short gap, like 1", allows for motor retainer springs and much easier and faster prepping and flying.

I've been liking a very low profile engine retainer made from piano wire. Among other advantages, it allows for a "gap" of about 1/16", which might as well be direct. Pictures when I get home Thursday.

 

[mbeels]

I've been liking a very low profile engine retainer made from piano wire. Among other advantages, it allows for a "gap" of about 1/16", which might as well be direct. Pictures when I get home Thursday.

Is that based on a square U-shaped piece? I was actually contemplating that for an engine mount I was assembling last night, but wasn't sure how to best attach it.

 

[jqavins]

Yes, that's it. I poke or drill holes in the aft centering ring and push the ends of the wire through, then glue on the top side.

 

[mbeels]

Yes, that's it. I poke or drill holes in the aft centering ring and push the ends of the wire through, then glue on the top side.

How do you glue the music wire? Just rough it up and epoxy?

 

[jqavins]

I've just used globs of wood glue. It doesn't need t be real strong. If I were concerned then I'd bend the ends of the wire over away from the tube, or one away and the other tangent, then apply the globs of glue.

The main advantage of the technique, for me, is that it's nearly invisible and regular engine hooks are unsightly. It should be good for staging, though I haven't used it that way yet. I first enounntered it in a Peak of Flight article on minimum diameter motor retention, where the wires are glued alongside two fin edges then burried in the fillets.