"Fritz X" Guided Bomb

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BigMacDaddy

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I've been working on a system for this inspired by LOC Precision's RNWS. I've been working with some parts I already have so I don't have any drawings yet, but if you're interested, let me know and I will put some time aside to draw it out
Assuming this is about removable weights? I'd be curious how they do it and how you are thinking of doing it. Thanks...
 

jqavins

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[F]ishing weights are becoming the most expensive part of my rockets ;)I assume that was tongue in cheek, but if not, there are surely cheaper ways to acquire lead.
I have a bunch of car tire balancing weights somewhere...
Where did you get those, for example? What to tire shops do with the used ones they take off of wheels? I wonder if they will give them to you for the asking.

If not, lead ingots really don't cost much. Less than two or three bucks a pound.
 

BigMacDaddy

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Where did you get those, for example? What to tire shops do with the used ones they take off of wheels? I wonder if they will give them to you for the asking.

If not, lead ingots really don't cost much. Less than two or three bucks a pound.
I cannot recall if I bought the wheel weights at Walmart, Advanced Auto Parts, or something... I have not found a source for used weights...

I do have a huge lump of lead that came out of my old stairway (melted and poured into holes in stone / brick structure to hold railing).
 

Joshua Smith

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I cannot recall if I bought the wheel weights at Walmart, Advanced Auto Parts, or something... I have not found a source for used weights...

I do have a huge lump of lead that came out of my old stairway (melted and poured into holes in stone / brick structure to hold railing).
Jeez, let's hope u don't need that much nose weight LOL
 

Joshua Smith

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Assuming this is about removable weights? I'd be curious how they do it and how you are thinking of doing it. Thanks...
Yeah, sorry, it was regarding removable weight. Let me figure out the best way to convey this info. I have at least one photo that's useful, so I may just augment that
 

jqavins

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LOC has one picture of the parts and one of the assembled item in their web site. They leave a good deal to be inferred.
 

BigMacDaddy

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Yeah, sorry, it was regarding removable weight. Let me figure out the best way to convey this info. I have at least one photo that's useful, so I may just augment that
LOC has one picture of the parts and one of the assembled item in their web site. They leave a good deal to be inferred.
Thanks folks --

I just had an idea for how I can create an adjustable depth plate that could be ratcheted into place (using stepped teeth inside of nose cone to lock and could be twisted out (teeth would only be in 50% of nose cone). Could hold various depths of weights (maybe could use paper towel or some other padding to keep weights from shifting inside resulting compartment).
 

jqavins

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If the adjustment range is not large, one can just put a T-nut into a bulkhead then thread in a bolt with enough washers to make the weight needed. It can even be the eye bolt, if you're willing to take that out and put it back with a fresh lock washer and Lock-Tite each time.
 

BigMacDaddy

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If the adjustment range is not large, one can just put a T-nut into a bulkhead then thread in a bolt with enough washers to make the weight needed. It can even be the eye bolt, if you're willing to take that out and put it back with a fresh lock washer and Lock-Tite each time.
hmm... that is interesting as well... washers and nuts are probably cheaper than finishing weights...
 

Joshua Smith

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LOC has one picture of the parts and one of the assembled item in their web site. They leave a good deal to be inferred.
Indeed, and what I inferred is not how it works. It was close enough, but made me think my presumption might be a little simpler and possibly more robust. It kinda depends on the tear out force for T-nuts vs the axial crush force of the coupler tubes used inside the main tube. Also, the LOC solution is very much removable, but not adjustable. It's designed to be weight in, or weight out, not a variable amount of weight in.

For smaller birds, epoxy a bulkhead into the nose that has 4 T-nuts epoxied into it's perimeter with a central eyebolt or similar. Then, thread bolts into the 4 T-nuts as needed and add additional nuts/washers as needed. Probably good to include some locking washers/clips to help with vibration.

For larger projects, you can epoxy a tube behind the bulkhead and instead of a central eyebolt, you remove the middle part of the bulkhead so it leads into the tube behind (so basically a centering ring at this point). Put your weight in that tube, making sure it can't move around and also making sure you have a way to pull that weight back out when you're done. When satisfied with the weight, cover the hole in the primary bulkhead with another (slightly smaller) bulkhead that attaches to the 4 T-nuts in the primary bulkhead. Your eyebolt or other preferred nose attachment mechanism is attached to the center of this second bulkhead (which is attached to the primary using the T-nuts).

I hope that made sense w/o a drawing.
 

jqavins

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Good point. On a small scale I haven't worried about it, but would definitely consider the proper safety steps for large quantities. For example, the time I held a 2 oz. fishing weight over a glass of water by a wire, then melted it slowly from the bottom up so it would drip into the water and make small bits; I did that outside and I wasn't concerned. But melting a pound in a crucible to pour into a mold would be a different story.
 

Funkworks

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What do you guys think -- can this be made stable with those massive canard fins?
Have you thought of making those fins free-pivoting? The idea came while reading jqavins' thread:

Sounds like uncharted territories. No garantees.
 
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BigMacDaddy

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If anyone is considering melting and casting Lead, know that there are health and safety risks to be addressed.

Dave F.
Thanks, yes definitely know this is toxic - that is why the lump of lead is just sitting in the basement... In the past when I needed to reshape lead I just beat it with a hammer ;)
 

BigMacDaddy

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For smaller birds, epoxy a bulkhead into the nose that has 4 T-nuts epoxied into it's perimeter with a central eyebolt or similar. Then, thread bolts into the 4 T-nuts as needed and add additional nuts/washers as needed. Probably good to include some locking washers/clips to help with vibration.
I have been pretty successful at 3D printing a frame for nuts or bolts to slip inside of. I might do this and shape the 3D printed part to fit snuggly in the tip of the nose cone. After printing, slip bolt in place, CA glue the plastic bolt holder into the nose cone, put washers on bolt, finish things off w/ a nut. Alternatively I could print my nose cones with a nut or bolt hole already inside the tip w/ a snap in cover to hide the bolt or maybe a screw-on nose to cover the bolt.
 

Joshua Smith

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I have been pretty successful at 3D printing a frame for nuts or bolts to slip inside of. I might do this and shape the 3D printed part to fit snuggly in the tip of the nose cone. After printing, slip bolt in place, CA glue the plastic bolt holder into the nose cone, put washers on bolt, finish things off w/ a nut. Alternatively I could print my nose cones with a nut or bolt hole already inside the tip w/ a snap in cover to hide the bolt or maybe a screw-on nose to cover the bolt.
Do something to make sure that part won't vibrate out of the tip. Epoxy might be better (tho I claim no knowledge of how best to glue a 3d printed part to the plastic of the nose cone). I know people will often run a piece of brass or two (or in my case, paper clips) through the nose and through the epoxy holding whatever it is up in the tip (like weights). Then clip off the excess and cover with some CA or epoxy or Bondo etc to hide the wire/pin/brass hole
 

BigMacDaddy

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Ok, I made Version 2 of my Fritz-X -- lighter weight ring tail, moving canards fins, and slight redesign of the main sections. I really do not quite understand the CP implications of the moving canard fins. I kinda get it since the canards would move instead of resisting air pressure. However, I assume these still contribute something to CP, how much?

1636943386445.jpeg
1636943398520.jpeg
1636943408966.jpeg

1636943418364.jpeg
 

Joshua Smith

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Yeah, that looks fantastic.

My $0.02: I imagine the effect on Cp is negligible as long as the pivot is low friction under dynamic flight loading. I should say, I'm basing this on recall of decades old fluids classes, not on any canard analysis on rockets etc...

Provided the following: "Low" speeds such that the loads don't make the canards lock in place. No matter the angle of attack, the canards will produce force perpendicular to the canard surface. The force can be summarized as a point force at the canard's Cp. As long as that point doesn't correlate exactly with the canard's attachment point it should always produce a moment that will pivot the canard and it won't flip around because the canard Cp is clearly aft of your canard pivot point.


Of course the canards may flutter like mad :)
 

Joshua Smith

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Worst case, you affix the canards at a slight angle and go for spin stabilization ;)
 

BigMacDaddy

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Thanks everyone... I am getting more confident that this little rocket might actually launch... I was very skeptical after my 1st build...

Someone in an Open Rocket group suggested that I could basically drop the moving elements of the fins from my calculations of CP. So as an experiment I left 1cm portions of fins and dropped the rest. This seems to suggest I can try to fly with either a 1-1.5oz weight in nose and a C5-3 or with 2-2.5oz in nose and a D12-3. What do you guys think is more likely to be stable? Need to check my actual CG and weight of the main body once glued together regardless.

1636987392404.png
 

neil_w

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I like the D12 better, it should get things moving more quickly which will help if stability is marginal.
 

Joshua Smith

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Yeah, that looks fantastic.

My $0.02: I imagine the effect on Cp is negligible as long as the pivot is low friction under dynamic flight loading. I should say, I'm basing this on recall of decades old fluids classes, not on any canard analysis on rockets etc...

Provided the following: "Low" speeds such that the loads don't make the canards lock in place. No matter the angle of attack, the canards will produce force perpendicular to the canard surface. The force can be summarized as a point force at the canard's Cp. As long as that point doesn't correlate exactly with the canard's attachment point it should always produce a moment that will pivot the canard and it won't flip around because the canard Cp is clearly aft of your canard pivot point.


Of course the canards may flutter like mad :)
Actually, now that I think about it more, the drag component probably will have a small effect on Cp, esp since the diameter is so much larger at the canard attachment location, which gives the drag a larger moment effect on the vehicle. I have to imagine the canard flutter would add to that effect. Dampening that with more friction on the pivot point would help. The exact opposite of what I said before. Yeah, experimentation is probably in order
 

Joshua Smith

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Thanks everyone... I am getting more confident that this little rocket might actually launch... I was very skeptical after my 1st build...

Someone in an Open Rocket group suggested that I could basically drop the moving elements of the fins from my calculations of CP. So as an experiment I left 1cm portions of fins and dropped the rest. This seems to suggest I can try to fly with either a 1-1.5oz weight in nose and a C5-3 or with 2-2.5oz in nose and a D12-3. What do you guys think is more likely to be stable? Need to check my actual CG and weight of the main body once glued together regardless.

View attachment 490198
I think ur gonna be a "heads up" flight no matter what. I will say, I bet the canards give you a narrower operating envelope than a typical rocket. Once you exceed a certain angle of attack, you'll most likely diverge rapidly and flip. Not that all rockets don't have that issue, I just think with canards your envelope will be smaller that average. On the upside, esp since the canards can pivot, you may also end up with stable flight while flying backwards ;) (assuming the motor is spent). I recommend a disposable parachute, or a very tough one, for your first couple flights lol.
 

jqavins

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This seems to suggest I can try to fly with either a 1-1.5oz weight in nose and a C5-3 or with 2-2.5oz in nose and a D12-3. What do you guys think is more likely to be stable? Need to check my actual CG and weight of the main body once glued together regardless.

View attachment 490198
It doesn't seem worth speculating until you get the final CG and weight in. But that's never stopped me before. ;)

I'm with Neil, greater speed will be your friend. And keep the nose weight on the low side of that 2 to 2.5 oz range. For the same reason. Maybe even see what it does with a Q-Jet D16 or D20. Less weight than a D12, which means you don't need as much nose weight, and you get higher initial thrust in the bargain.
 
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BigMacDaddy

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Someone also pointed me to this past discussion here:
 

BigMacDaddy

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By the way -- pretty pleased with the way I designed this fin rotating setup... I basically 3D print two brackets that can slip from inside through a 6mm hole in the body of the rocket. These have one long bracket portion that will be glued to either side of the fin as well as a circular block that is too large to fit through that hole. Fins are cut with 6mm tabs that stick through the hole from the outside and will be sandwiched between the two 3D printed parts. Hopefully I can put a bit of thin CA glue along the 3D part / fin which will wick into seam and hold this all together (without this part getting permanently affixed to body tube).

1637013121269.jpeg
 
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