"Fritz X" Guided Bomb

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BigMacDaddy

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What do you guys think -- can this be made stable with those massive canard fins?

I saw this in the Air and Space Museum in VA - very cool looking flying bomb... Someone mentioned this in FB so the reminder got me to do this one next.

I sized for a BT60 tube (in bottom portion) but much of this is 3D printed. About 12" long and 2.6" wide at fattest point and planning for D-size engine. Engine retainer cap is a bit off design but it was convenient since I had designed that for past rockets. Could change in future. I could have added all those massive rivets, maybe in Version 2.0.

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p.s., Don't worry still finishing up the Wespe...
 

boomtube-mk2

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All it will take is 27lbs of lead in the nosecone and you're good to go.
Or, you make it hollow and center the motor at the top of the nosecone.;)
 

BigMacDaddy

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All it will take is 27lbs of lead in the nosecone and you're good to go.
Or, you make it hollow and center the motor at the top of the nosecone.;)
Yep, something like that - I need to find my postal scale so I can see the max weight I can put in here w/ D engine and figure out where that will put CG (if I can get it partway up front fins I will be hopeful) - that is about as far as I will push this one. If it winds up being a static model so be it...

I am curious about other innovative approaches to make unreasonable rockets stable -- for example, a telescoping tail that slides back from model on launch ;)
 

teepot

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I've used streamers attached to the bottom of a rocket to make it stable.
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Daddyisabar

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Yep, something like that - I need to find my postal scale so I can see the max weight I can put in here w/ D engine and figure out where that will put CG (if I can get it partway up front fins I will be hopeful) - that is about as far as I will push this one. If it winds up being a static model so be it...

I am curious about other innovative approaches to make unreasonable rockets stable -- for example, a telescoping tail that slides back from model on launch ;)
Canted tractor motors midway up or at the top. Motor mounts placed so far up the tube you invite Mr. Krushnick to the launch. Power, nose weight, base drag, telescoping off the pad. silly kite tales or streamers. Pivoting canard fins, Gas Dynamic Stabilization and gimbaled mounts.
 

BigMacDaddy

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Cool rocket, uhm, err, bomb. ;)

Perhaps allowing the front fins to pivot would make it more stable? Or just make them removable for flight?

I'm betting @Dotini will like that rear ring fin design
Making those front fins removable is probably a good option -- still would be great to get it to fly closer to prototype...
 

Joshua Smith

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Obviously you could also deviate from scale a bit and downsize the canards a little and upsize the ring tail a bit. Basically, as much as you are willing to tolerate, and then augment with nose weight and other techniques
 

BigMacDaddy

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Ok so played around with this and w/ 3oz in nose I can just get the CG 1/2" forward of the middle of rocket (still about 1" behind the rear of front fins). Not looking like this rocket will be stable but hard to say how much that ring tail does vs. the front canards. Maybe I will try a swing test...
 

jqavins

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How about a removable clear plastic fin set? Start with a "ring" that goes onto the one that's there as a sleeve, and has regular flat fins swept out and back from there.

Also, with a 24 mm mount for a D motor, you might have too much nose weight to reach safe road exit speed,; there are 24 mm composites that might help there. The D22 looks like a nice choice for quick but not too high. And the E30 will jump it off the pad nice and fast.
 

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BABAR

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Something along these lines worked well on @hermanjc ‘s Mandalorian rocket


my version


allows you to make just about anything stable, and doubles as a rocket stand when the creation is shelved.

also, the basal ring doesn’t have to be round, you can make it square or presumably just about any geometric shape


the Mandalorian integrated the ring with a nice “Label”,

it also allows you to make the body of the rocket a bit longer, as the motor casing is included in the basal ring length, which gives you a bit more latitude for parachute compartment (although the ring adds potentially substantially more weight, so it may be a wash.)

if you go geometric, you can make the ring pretty light with balsa With three or more flats pieces. If you go cardboard oatmeal container or plastic 3D printed, it’s likely to weigh a bit more. @Rktman and @neil_w may be able to provide some advice if you want to go with a balsa ring, curving balsa is an art I haven’t mastered.
 

KenECoyote

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Perhaps allowing the front fins to pivot would make it more stable?
This combined with nose weight should do it. I've been developing and testing my own stabilization system for large forward finned prototypes and I'll be testing more of that this fall/winter. I'll add the Fritz to the mix if I can.

Some of my posts to the Estes FB group earlier this year. The Tomahawk flew beautifully the last time I launched it and I'll be doing upscales this winter (my long term plan and one of the drivers in my developing this).

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Some of the short videos:
 

Pem Tech

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What do you guys think -- can this be made stable with those massive canard fins?

I saw this in the Air and Space Museum in VA - very cool looking flying bomb... Someone mentioned this in FB so the reminder got me to do this one next.

I sized for a BT60 tube (in bottom portion) but much of this is 3D printed. About 12" long and 2.6" wide at fattest point and planning for D-size engine. Engine retainer cap is a bit off design but it was convenient since I had designed that for past rockets. Could change in future. I could have added all those massive rivets, maybe in Version 2.0.

View attachment 484057 View attachment 484058 View attachment 484060

View attachment 484064

p.s., Don't worry still finishing up the Wespe...
Do it, do it, do it, do it....
 

BigMacDaddy

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I messed around with this and it was not clear that this could be made stable without elongating it, reducing canard fin size, lightening my ring tail significantly, etc... Seemed like too much work for not enough satisfaction...
 

Joshua Smith

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You could make the ringtail out of balsa and maybe reduce the number of fins inside the ringtail. Make the canards really heavy lol. Making them heavy would affect their moment of inertia so that would have to be done smartly, but just get @KenECoyote to do some testing ;) All kidding aside, I never thought to make canards "heavy" before. Or really anything except the nose or a transition right before the nose. Obviously it's likely more work than it's worth unless the fins were already going to be a ply/laminate and if u weren't going to allow them to pivot you'd probably want to concentrate extra weight near the fin root.
 

jqavins

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How about making the ring and pylons out of very thin, lightweight fiberglass, or something lighter still? There is an article or two in Peak of Flight issues on Tim's quest for ultralight body tubes wherein he ends up doing a composite layup with tissue paper. Just be sure to have a large enough parachute to ensure a soft landing, but hey, that's more weight in the front.
 

KenECoyote

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You could make the ringtail out of balsa and maybe reduce the number of fins inside the ringtail. Make the canards really heavy lol. Making them heavy would affect their moment of inertia so that would have to be done smartly, but just get @KenECoyote to do some testing ;) All kidding aside, I never thought to make canards "heavy" before. Or really anything except the nose or a transition right before the nose. Obviously it's likely more work than it's worth unless the fins were already going to be a ply/laminate and if u weren't going to allow them to pivot you'd probably want to concentrate extra weight near the fin root.
One of my designs (the Lacrosse) had lead weights incorporated into the forward fins (inserted into the balsa stock and then papered over). It served two purposes...it brought weight forward, but also was meant to serve as a weighted pendulum. Results were marginal and maybe the same weight may have the same result up forward...not sure. I wish there were two of me to do all the testing I'm planning LOL
 

Joshua Smith

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One of my designs (the Lacrosse) had lead weights incorporated into the forward fins (inserted into the balsa stock and then papered over). It served two purposes...it brought weight forward, but also was meant to serve as a weighted pendulum. Results were marginal and maybe the same weight may have the same result up forward...not sure. I wish there were two of me to do all the testing I'm planning LOL
Very cool. I guess another option is to just use denser wood or fiberglass since you'd also gain the strength increase as well as the weight, at expense of cost and availability. I guess basswood if you just need marginal additional weight
 

caveduck

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That ring assembly will have a ton of drag, especially at the Reynolds number of a model rocket. I bet it's stable or close to stable as-is. Change my mind :)

Swing test recommended however...
 

Joshua Smith

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That ring assembly will have a ton of drag, especially at the Reynolds number of a model rocket. I bet it's stable or close to stable as-is. Change my mind :)

Swing test recommended however...
Good point, tho it'll be hard to get a swing test up to the velocities that will result in those Reynolds numbers. There will also be higher drag likely somewhere past the max diameter of the forward section due to flow separation which is highly dependent on Reynolds number too. I think.

Disclaimer: TBH, all my fluids classes were approx 25 years ago so most everything thing I write is informed from equally old info + 25 years of not using it and I have terrible memory ;)
 
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rharshberger

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Disclaimer: TBB, all my fluids classes were approx 25 years ago so most everything thing I write is informed from equally old info + 25 years of not using it and I have terrible memory ;)
My fluids classes were also +25 years ago and came in glasses....the product tended to erase my memories and induce instability....:eggnog:
 

OverTheTop

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You could really increase the base drag by filling in some if the gaps between the rear fins with clear polycarbonate or similar material. The extra drag should more than make up for the canards. Would make for low and slow flights.
 

BigMacDaddy

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Ok - you guys kept me motivated and I made a leaner version of the ring tail. Dropped all the fins down to 2 layers instead of 3 and thinned out the solid elements as much as I could while maintaining the look of the Fritz-X. I had previously modified the shape of the front bomb portion and the engine retainer clip to match the original better. I will swing test this once it is all done with 4-5oz of weight in nose -- fishing weights are becoming the most expensive part of my rockets ;)

EDIT: So leaner ring tail wound up being 10 grams lighter 34 vs. 24 grams (substantially more fragile so... tradeoffs).

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Funkworks

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Dropped all the fins down to 2 layers instead of 3 ... fishing weights are becoming the most expensive part of my rockets
I'm not sure if they're a good choice here but segmented model aircraft weights are also an option:
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And for forward fins, cutting out the middle and keeping only a contour might also be an option sometimes. Lego Technic fans don't seem to mind this and I suspect it would also look good for forward fins while being functionnal to move CP backward.

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BigMacDaddy

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I'm not sure if they're a good choice here but segmented model aircraft weights are also an option:
View attachment 485985
And for forward fins, cutting out the middle and keeping only a contour might also be an option sometimes. Lego Technic fans don't seem to mind this and I suspect it would also look good for forward fins while being functionnal to move CP backward.

View attachment 485981View attachment 485982View attachment 485983
I have a bunch of car tire balancing weights somewhere -- may need to find those (have foam double sided sticky tape already which is convenient. I really need to make a nose cone locking compartment or something so that I can put weight in and take it out without leaving it in permanently.

I like the idea of the fin outlines - I will try with slightly smaller fins first but may go this this option.
 

Joshua Smith

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I'm not sure if they're a good choice here but segmented model aircraft weights are also an option:
View attachment 485985
And for forward fins, cutting out the middle and keeping only a contour might also be an option sometimes. Lego Technic fans don't seem to mind this and I suspect it would also look good for forward fins while being functionnal to move CP backward.

View attachment 485981View attachment 485982View attachment 485983
That's a really interesting idea to reduce the lifting force and move the Cp backward
 

Joshua Smith

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I have a bunch of car tire balancing weights somewhere -- may need to find those (have foam double sided sticky tape already which is convenient. I really need to make a nose cone locking compartment or something so that I can put weight in and take it out without leaving it in permanently.

I like the idea of the fin outlines - I will try with slightly smaller fins first but may go this this option.
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
 
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