Playing with a sports scale Nike Apache two stage...

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snrkl

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BT60 to BT20, designing for a B6-0 to A8-3 with gap staging...

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I am trying to figure out is booster recovery.. With GAP staging there is no place for a streamer of any kind that I can think of..

From memory, if the Booster CG is behind the CP, this will make it tumble, so I am thinking about adding a tail weight to the back to make the booster unstable after separation... You can see the tail weight object in the schematic... I am not super keen on tumble recovery, so I am mulling over what could be done to get a streamer in there somewhere...

I am also thinking about fin profiling methods.. I have hand sanded enough double diamonds to hate the idea of doing it by hand, but the fins are so small and the bevel so shallow, using the belt sander like I have for my mach1 aspire seems like it would be knuckle grazing territory... I am wondering if I make the fin from 3mm balsa with the fin tabs, then build shaped second layers to carry the bevel, but then that means bevelling even smaller wedges...

I also have no idea where to get a nosecone from... looks like I would have to custom turn from a balsa dowel maybe...

So, here i sit, pondering...

View attachment LPR Nike Apache.ork
 
Adjusted the design to look at a rear eject for the booster, but with a shorter rear eject section than the one @TVM used in his:

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View attachment LPR Nike Apache_RE.ork

Unless people can see reasons why this design sucks, I might move forward like this and continue thinking down the fin profiling and nose cone construction challenges...
 
Construction has begun and progresses well, despite my tired eyes last night not paying attention to the location I was glueing the rear eject pod CRs.

Managed to get them off before the glue hardened. A little messy but nothing that will be seen that can’t be sanded and painted.

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The pic shows an exploded view of the booster internal layout.

Printing/cutting/assembling transitions has to happen next to check the fit and do final alignment.


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Sustainer build update is uneventful - the rear eject pod and MMT/Stuffer tube are assembled.. Not much to look at from the outside, so I won't bother with pics of that part..

More interesting is the fin design and shaping.. These fins are a P.I.T.A, due to the double bevel on the LE and TE, as well as the fin to tip bevel..

I am NOT sanding four of these by hand, so I had to think about how the hell to do this on the belt sander.. Also, the LE/TE the way it is means that the back corner of the fins will be very weak if I put the balsa grain from a single piece aligned with the LE..

So after rummaging through my parts stash, I found two sheets of 1mm balsa from a couple of Estes Designer Special kits, that I was wondering what the hell I was ever going to use for...

This got me thinking: "What if I made my own Balsa Ply", so I started thinking about it and doing some drawings. After drawing up the "Mostly Scale" fins, I realised the beveled edges on the LE/TE are not consistent, which will make sanding these on the belt sander horrible..

A little bit of creating adjustment to make the bevel a consistent angle from root to tip, this is what I am now working towards:
View attachment FinProfile.pdf
FinProfile.jpg



I spent some time thinking about options for how to layout the fin template on the ply. I figure keeping the ply core running root to tip, and the veneer layers running parallel to the airframe will likely give me the best strength (so the top one in the diagram).

Interested in people's thoughts...

View attachment FinLayout.pdf
FinLayout.jpg

Balsa ply was cut and glued up last night and is currently drying with about 4kg of books (and a giant water jug) on it... I expect this will be very hard to cut, especially as the 3.5mm core was some of the HARDEST balsa I have ever seen.. just cutting the 3.5mm piece WITH the grain took 5-6 passes on a new #11 blade..
 
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I use basswood or ply as cores for built up fins and balsa for the outer layers, the balsa is easily sanded, but the harder core keeps you from sanding too deep without noticing.

iirc you can see the build up process in my Nike Hercules, Nike Cajun, and T300 Nike Smoke thread and one of them has a how to for wood laminated fins.
 
I thought about something similar, but given these fins are only 69mm on the root edge, I figured it was a little too fiddly... for me at least.
 
Cut the first fin out tonight.

Holy hell - took 35mins to do one fin with a new #11...

That balsa in the core is hard - almost as hard as cutting through the glue layer that’s had a good 24hrs if of drying time.

I also noticed the sandwich is 1.5mm thinner (7.5mm to 6mm) than the unglued / uncompressed layers were when air stacked, which I figure has got to add to the density.
 
Cut the first fin out tonight.

Holy hell - took 35mins to do one fin with a new #11...

That balsa in the core is hard - almost as hard as cutting through the glue layer that’s had a good 24hrs if of drying time.

I also noticed the sandwich is 1.5mm thinner (7.5mm to 6mm) than the unglued / uncompressed layers were when air stacked, which I figure has got to add to the density.
That and the glue penetrated the balsa probably almost all the way through.
 
4x thirty minute cutting sessions and 3x #11 blades later...

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Tomorrow night I plan to mark out the lines for the root to tip shaping and think about how the hell to build a whole fin sanding jig...
 
Fins striped to make sanding easier.
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Then root to tip profile was sanded
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Then LE and TE shaping
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Then the sustainer fins

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Fins are all now drying after papering.
 
Sustainer fins glued and filleted.

Also got the booster fins on and the first pair of fillets down.

None of the recent steps are particularly interesting.

Once I finish the booster filets, I’ll post pics.

After that, only engine blocks (three of them: sustainer and fwd/aft on the booster) and launch lugs left to do.
 
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Ready for priming and painting.
 
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I'm am thinking of a design similar to this and I have been wondering about something. I see you have the vents in the stuffer tube and the centering rings of your booster. You are also putting your chute or streamer in the space between the stuffer tube and body tube. Well, my question is about the gases that are venting thru the booster. Won't they damage the chute or streamer?

-Bob
 
In short, no it doesn't: The vent holes are designed to let the ambient air that is in the tube already, in front of the hot air coming from the ejection charge, to escape, ensuring that the rocket doesn't separate before lighting the upper stage. If the holes were MUCH bigger, this might be a problem, but some clever people have worked out that two regular hole punch size holes is about right for an LPG gap stage upper holes, and four in the CRs. I walk the path of discovery that many smarter than me forged.

If you walk out the events, you can "thought experiment" your way through it.

Motor one ignition: Zoom!
Motor one delay = 0, so BP charge goes immediately
- Ejection charge rises up the stuffer tube, pushing the ambient air up, and out the vents
- Ejection charge air arrives at the top of the stuffer tube, igniting the second stage - Sustainer: Zoom!
- Ejection charge turns the corner into the vents, cooling down (it's like a baffle - air turning lots of corners slows down and cools down)
- The pressure built up in the lower stage pops the rear eject pod out, pushing the streamer into the air stream
- Sustainer delay = X, recovery completes like any other LPR
 
Well it's very interesting. I've read the Apogee newsletter and seen the video. It's interesting that you have modified that design by only ejecting the rear half of the booster stuffer tube. I am looking forward to seeing your build progress.

-Bob
 
Oh! It’s built, flown and been retired. I never got around to more than a white coat of paint.

I’ve been distracted by HPR rockets, and I lost interest in this one a little - when I did the rear eject setup, I needed to put some CA on the inside of the booster and sand smooth, to aid ejection slipperiness and accidentally got thin CA wicked into the Kevlar shock cord. This made it stiff and EXTREMELY difficult to sing for loading the booster, so after it flew successfully & proved that it was a workable design, I kinda lost interest.

When I run out of HPR things to build, I’ll likely rebuild it and paint it properly. I’ll recycle the fins though.
 
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