Is this crazy for my first scratch build?

My son and I love the Flutter-By (or is it bye bye?) and we have built several. I have always thought that a BT-80 size version would be cool so I played around with OR and ended up with something that looks like it is within my reach.

I came up with two plans. One is simply an upscale clone of the original design. It seems as though it would be a simple build.

View attachment Flutter-By Up Scale.ork

The other plan uses TTW fins to reinforce a weakness on the original.

View attachment Flutter-By Up Scale.ork

I do have to refine the fin shape some. I have a scan of the kit balsa that I will use to produce upscale drawings. If there is a way to import my drawings to OR, it would be helpful.

I invite you to pick apart my design and I would love a replacement for the BNC-80HAH, I chose it because it was the only long ogive NC I could find.

Please understand, that not everybody uses OR or Rocksim. Just like some of us don't do smart phones. A PDF is worldly recognized.

Gary Byrum said:

Please understand, that not everybody uses OR or Rocksim. Just like some of us don't do smart phones. A PDF is worldly recognized.

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I don't even use Cellphones.

And come to think of it, what's a PDF????

Gary Byrum said:

Please understand, that not everybody uses OR or Rocksim. Just like some of us don't do smart phones. A PDF is worldly recognized.

Click to expand...

Geez this forum can be rough.... and unhelpful...

OpenRocket will help you design a stable rocket, but it won't help you model the unique recovery mode that the Flutter-By uses during descent. I don't have any easy answers for you, but I will enter into the discussion. I wonder if the flight characteristics of the original depend on its low mass. Looking at your OpenRocket file, I wonder if the 1-ounce of nose weight is just going to make that half of the upscale plummet like a rock. The bottom half of your design has a heavy spent E12 casing in it, unless your plan is for motor ejection. I'd try to make the model as light as possible, and I'd go with balsa fins rather than basswood.

Thanks Astron!

I am not sure about the nose weight my self, without it CG and CP are just about the same, so I stuck the weight there to see what happened. As for the fins, I used the basswood for strength but thought it may be over engineered. If I go with balsa, I'll paper it and put the fin rib back in.

I kind of figured OR would not be the best for simulating this. I'm really using it for more of a drawing medium since I am no draftsman. Since it has capability to calculate stability, I am playing around with stability factors.

Here are PDF files of each version. I think that the necessary information is there, let me know if there is a better way to present it.

View attachment Flutter-By_Upscale2.pdf

View attachment Flutter-By_Upscale1.pdf

I'm sorry. I wasn't trying to be mean. Just trying to bring attention to a file viewing matter. If you want opinions or 'points of view' on your posted files, it's best to use something anyone can open. Regarding the nose cones, I'm not sure what the scaled version gives you for a length, but the 80HAH is a 10.5" cone, and the PNC 80K is an 8"cone. I'm sure what ever you decide to use would be adequate. TTW fins might not be necessary if you plan to use BP motors up to E & F.

Thought about it some more, and I think Gary is right about the TTW fins are not necessary. There is/was a recent thread about what mid-power means to people. Mid-power rockets (like your upscale) sit in that area between High Power and Low Power rockets. As a result, people build for mid-power in two ways - they either scale down High Power building techniques, or they scale-up low power building techniques. Maybe there's a third way which is a hybrid of both philosophies. All can be made to work with mid-power motors. I think your proposed design is one that will benefit from low-power-style building rather than introducing high power concepts like TTW fins, which will just add weight. Balsa, Estes tubes, and wood glue are your friends for this project.

My two cents...
-Wolf

astronwolf said:

I think your proposed design is one that will benefit from low-power-style building rather than introducing high power concepts like TTW fins, which will just add weight. Balsa, Estes tubes, and wood glue are your friends for this project.

My two cents...
-Wolf

Click to expand...

I agree. Also, you're not limited to using BP in a LPR build. I recently built an upscale Arapahoe to use 29mm motors, and launched it with an F 26 composite. Absolutely no issues with the surface mounted fins.

I'm not real familiar with the Flutter-By. Is it supposed to separate at the lower joint then the 2 components "flutter" down? Are they connected with a cord?

Keep in mind, as the mass of the rocket goes up, so will the velocity that it comes down with. With that in mind, your fins will hit harder and thus TTW mounting may be advantageous so it is more robust. Surface mount will take the force of MPR motors and of landings under chute (ex. 20-25 FPS), but this may come down faster/harder as it "flutters down".

The real challenge here is trying to upscale a design that depends on a tight balance envelope and some aspect of "featherweight" recovery. Every gram of weight added kinda defeats that idea. My guess (yes, just a guess) is you'll have two pieces of airframe coming down fast and straight. Any way to rig an active recovery device in the extra airframe space ?



CZ - no connection between the two pieces. Estes brought this back a few years ago in their Classics Series.

No offense taken Gary, I like the direct approach 'cause it leaves very little room for misinterpretation. Thanks for the heads up, I'll just post both in the future.

The good news, I seem to have been considering the same issues that y'all have brought up. The bad news, I haven't decided which way to go on any of it.

FINS- I have come across several reports of these losing a fin when it meets the ground. This has not been my experience and I was leaning toward surface mount any way. I think that a good double glue joint with fillets should be strong enough. Thanks for the confirmation here.

NOSE CONE- The stock cone is a long ogive cone and the BNC-80HAH is the closest match for the shape that I could find. I think that it is about a 4:1 profile while the shorter ones are around 3:1. I may end up using a shorter one to save weight but the long NC helps keep the CG in a better place. The search continues and the final word will come when I glue some parts to glue together and swing it.

RECOVERY- I have no experience with active recovery gear so I am hesitant to use it for the first time in a scratch build. OR is showing a high ground hit velocity (131 FPS) so I may add spin tabs to help destabilize the sections as they fall. I have thought about spitting the motor but it would have to have a recovery device and weight is not my friend here. It is possible that the fin ribs on the original contribute to instability during the tumble, I just don't know how to add them in OR. My ultimate goal is an upscale clone of the original but I am open to chute options too. Maybe I can use a loose fit for the booster and NC with the laundry in the middle but this doesn't seem to pass the common sense test.

Hopefully I'll have parts so I can start building around Christmas.

Sorry to be unclear Bill, by active recovery I meant parachute or streamer attached to a shock cord. Weight is most definitely not your friend here. Maybe you could build a fin framework and skin it with thin plywood (1/64 or 1/32) like the Der Mega Red Max.

I have worked a lot with BT-80, and I think you might be able to work out an upscale here. The catalog picture by Samb helps a lot to understand the concept.

My suggestions:
- This plastic nosecone >>> Link
- This inexpensive and light BT80 tubing >>> Link
- TTW Lite Ply fins made from 1/8 lite ply - Bill @ https://www.balsamachining.com/ has the right stuff (very light)
- A 24mm motor mount so you can upscale the power with Aerotech 24/40 E, and F reloads. Best power to weight ratio.

By keeping it light, you might be able to retain the "flutter" recovery. If not, It should not be too much trouble to add a good size streamer to each piece.

- Good Luck!!

I think you should consider a chute. To deal with double the weight, you need a square (4x) more aerodynamic breaking surface. Don't think you'll get that...
a great example is the Applewhite stealths - look at the size difference between 38 and 54 mm versions.

samb Just blame it on different backgrounds. I have been thinking along the lines of your fin idea.

scsager That is the the one that I need! Since it is hollow plastic, it will be easy to adjust weight if needed for CG. The BT looks like a good choice too. Good idea about the 24mm mount. I am not equipped for the higher power of the reloads but why not design it for that option from the start?

cbrarick You make the point that has been the puzzle in this whole concept. I have a spot where I can do a 50ft drop test on to grass to get some idea of how it will behave in free fall, if I have to put add laundry it will complicate the stability problem though.

Hopefully I will have parts in a few weeks and can start working this out. I think that I have balsa around that I can start playing with next weekend, maybe I can get the fins worked out early on anyway.

Thanks for all of the input folks!

"Upscale" and "featherweight" - two words that do not belong together. :lol:

Unless you modify the design to land with a streamer or parachute, preferably two of them if you want it to separate like the original Flutterby, expect fins to be knocked off. If they are surface mounted, they will probably come away cleanly and be easily glued back on. If the fins are mounted TTW, they won't come off as easily but when they do they'll break. You'll either need to clean out the TTW mount before fitting a whole new fin, or glue the fin back on resulting in a messy crack and a joint which is now no better than a surface mount anyway.

adrian said:

"Upscale" and "featherweight" - two words that do not belong together. :lol:

Click to expand...

Let's just say that this build could benefit from some "featherweight" design concepts.

I have decided on surface mount fins and, in light of your comments adrian, won't be taking any measures beyond the basic double glue joint with good fillets. That will provide the most strength/gram and it will be easily repaired.

As long as I can maintain safety, I have no problem re-gluing fins. There are a number of large fields close to the house that will allow a significant safety margin (hopefully I can score the sod farm). If drop tests pan out, I'll start with tumble recovery. I'll have to build it so that I can add recovery gear if it is needed.

Although probably no one would get hurt, the concept of a rocket with recovery that is ANTICIPATED to break off the fins on landing (better termed in this case "impact") seems to be pushing the safety code a bit. That sort of "breakaway" recovery is a bit different than the Odd'l Rockets Break Away ( https://www.jonrocket.com/?main_page=product_info&products_id=322 ) and the Estes Wacky Wiggler ( https://www.amazon.com/dp/B0006N6ZZA/?tag=skimlinks_replacement-20 )

Going up to a BT-80, you should have some room between motor mount and engine to pack two small streamers. if you combine these with an EXTERNAL shock cord attachment to each segment that allows each segment to fall oriented horizontally (with the fins perpendicular to the descent path) you may significantly slow the descent rate AND have the advantage that the segments may hit "body tube" first rather than on a fin edge.

It may come down to a difference between what you CAN do and what you SHOULD do. IMHO, if you are going to pursue an upscale of an existing design, your anticipated outcome should include (as you have acknowledged) definitely a SAFE recovery but also a "damge free" recovery. Just my :2:

Good luck.

Tom

Just put in a shock cord to tie the two halves together--then you've got "breakup" recovery and it should come down safe enough even without a streamer.

BABAR I'll be doing drop tests from 50' before I do a launch. If broken fins are a consistent issue in drop tests, I plan on finding another solution. I will not launch something that does not exhibit a reasonable degree of 'control' during recovery. Reminders like yours are part of why I started this thread though. Keep then coming.

Cookie and BABAR I like your thoughts on recovery. I have an idea or two on saving weight that may provide an ideal space for at least one streamer, maybe two.

You'de really build some Building Skills by just building it and Flying it without Spectators. Wear a Helmet too if it makes you feel better, but a lot of EVERYBODY on here is so "Hanged Up" on Sims and even then they sometimes go "Poorly".
You need to find the Balance in your MIND!!!
Everything can be Stabilized!!!
Take a Chance and Light up the Sky!!!

"If you don't Build it, "They" won't come."

:wink:

TopRamen said:

You'de really build some Building Skills by just building it and Flying it without Spectators. Wear a Helmet too if it makes you feel better, but a lot of EVERYBODY on here is so "Hanged Up" on Sims and even then they sometimes go "Poorly".
You need to find the Balance in your MIND!!!
Everything can be Stabilized!!!
Take a Chance and Light up the Sky!!!

Click to expand...

I'm gathering just info while I gather materials! 21 years in the Army does have Composite Risk Management rattling around in my head, but 18 years as a crewchief tells me that the sims are simply a source of dynamic information. If it passes some common sense trials, it will go up and, hopefully, fly. It would be nice if I get to shoot a second time though.

TopRamen said:

You'de really build some Building Skills by just building it and Flying it without Spectators. Wear a Helmet too if it makes you feel better, but a lot of EVERYBODY on here is so "Hanged Up" on Sims and even then they sometimes go "Poorly".
You need to find the Balance in your MIND!!!
Everything can be Stabilized!!!
Take a Chance and Light up the Sky!!!

Click to expand...

GO YOU!!! Personally I think a lot of building rockets is over teched anymore. Along with the flight simulations. Granted, some people have a sincere respect for the technology, but this old fart learned it by trial and error. There is STILL, is nothing wrong with that method. Opinions are like a*%$#$%s, everybody has one. Take the given info as something to think about, but use your modeling skills to perfect your design/build. nuff said

I am one of those caught in the middle!

Technology has much to offer. It is amazing what is available to me through this silly little box in front of me. I can design a rocket and get an idea of the relationship of characteristics which can have a significant effect on the rocket's performance. I can play around with design parameters and get an idea of how they affect performance. After I am done playing on the box, I can build the rocket according to the design in the box. Now, the moment of truth; it is time to launch and pray, pray that the box was close enough to right.

Now we are in the real world, dealing with real wind and imprecise estimates of actual direction at the pad. This is where we find how close the magic box got us. You can find a number of ways people have to trick the box to get it to play nice with certain design elements, and these tricks often amount to adding something to the simulation that doesn't exist in reality. There is no substitute for live data. You don't have to trick a rocket so that it knows how to behave with ring fins. Even the big boys have to eventually risk some hardware to see if things work right. Besides, that's the real reward in scratch building. The uncertainty of the first launch is where the real fun is.

I figure that OR has done its job at this point. I have a design that shows some promise, now I have to make it work. I'll follow my gut feeling and get started on fins this weekend. I figure on going with sheet on frame construction with spin tabs to help destabilize the components on descent.

Don't get me wrong, I've had to rely on this "little box" as a means to support myself. I never thought this would be my job someday. As far as designing rockets, people often wonder why I use Autocad instead. Why? Because it's what I have. I sampled OR many months ago, only to be discouraged with it. I really could go on a rant, AGAIN, about how OR and Rocksim robs you of the skill of building and designing, but I'd be wasting my breath. To some people, it's all they have. And it's an easy route with around a 50-60% accuracy history. Don't believe that? Just read the threads here. Still, they believe it's the way it's done and refuse to acknowledge the truth, or facts. All of this was created without the use of computers, and gave you a real hobby, rather than a project. I need only a tool to draw what I have in mind, and that used to be a pencil. CAD is the chosen tool, because I don't need software telling me what to expect. Prolly a lot of good ideas and designs gone down the toilet these days because, the software said it was under stable or over. When realistically, they were just fine. This is what I learned by trial and error in my youth.

Not going to drop any names here, but I know people that have no design or tailored building skills, yet, they are building rockets that are terribly unstable. And some of those are HPR rockets that they relied on software to design and simulate. Bill, I employ you to do your drop tests. Make a first flight when no one is around so you can see if what you did was right. You learn better by your mistakes, than you do by marching the beat of someone elses drum.

I envy your drawing skill Gary! I figure that if I am going to use the software to "draw" it, I'll check and see what the sim says. I do subscribe to the axiom that if it looks like it will fly, it has a chance to work though and software is not the end all be all for me. I decided to build this thing a while back and figured that the experience of the forum members would contribute more to its success than any other resource.

Some of the fun in this is trying to prove OR wrong by getting it to tumble enough to safely recover an intact rocket without using any recovery devices and there is no substitute for physical testing. OR also wants a lot of nose weight to maintain stability, well a swing test is will help me see how much I can shave that down. Heck, testing this thing to get it flyable will be half the fun!

The bottom line is this. This is a hobby and we have fun with it. If OR or ARFs get people interested and keep and keep them flying they are a good thing. Once they are hooked, old school builders like your self have the opportunity to help them expand their horizons and build their skills.

Right now, OR is kind of like having training wheels for me. As time goes by, it will become more of a drawing program than anything else. It will probably always be in my tool box but only one tool among many.

Laying out plans for the fin frames right now.

BTW, if we learn better from our mistakes, just call me Wiley Coyote, Super Genius

No need to envy me dood. My drawings all look like 2 finned rockets. But that's enough for me to size up the stability. Pretty much the way I've always done it. The reason I like using CAD is because I already have additional software to work in a color scheme. The CAD file is turned into a PDF, and the PDF is imported into Corel Draw where I can colorize it, put stripes on it, lay out the text in whatever font I want to use. And above all, my CAD drawings look way much better than my hand work, and it's to scale. It basically my drawing tool by default. When I'm doing upscale designs, I usually run into one that there is no known nose cone for, so I just make a turning template from the nose cone drawing. This is way convenient since most of my upscale designs require a special nose cone. Even if I could buy that special nose cone, it's way more cost effective to just turn my own since I usually already have the balsa blocks. It's not likely I'd order just a nose cone unless I can add a lot of other parts and what not to justify the shipping cost. And on that note, I'm usually well stocked on parts. You learn to appreciate having a well stocked shop, so when you get one of those brainstorm design ideas, there's no questioning if you have every thing to build it.

Another option. If you're willing to give up the split flutter of the flutter-by, you could do something like the Semroc Golden Scout. What it does, is glue in the NC and add a hook at the bottom of the rocket 1-2 inches lower than normal, to allow the motor to spit backwards till it hits the hook, which keeps the motor still in the rocket. There are holes in the BT that are uncovered when the motor shifts backwards, releasing the pressure of the ejection charge. When the motor moves backwards, the empty casing's mass shifts the CG back enough to make it unstable, so the entire rocket flutters down. Of course, doing this with the flutter-by means making it with only one piece, not two.

If modeling it in OR, make a mass component the size, shape, weight of an empty case and place it where it would be when the motor is spit backwards. Then override the mass component to zero. With motor installed, the mass component will not have effect on the sims. Then click on "no motor" and turn off the override of the mass component, and this will show you the stability of the rocket when the motor burns out and shift backwards. Don't forget to add the mass of the hook (heavy metal wire or retainer clip mounted 1-2 inches lower). This also means you only have to track one component as it falls, not two.

Sounds like a pretty good system Gary. The ability to scale could be very useful to have. I have tried using SketchUp, but I am finding it to be a cumbersome and confusing right now. I think that it could be used in a similar fashion and I could even turn simple shapes using my drill. As for the parts bin, I think that I will be getting the 34" tubes from BMS for that very purpose, leftovers will be useful in the future.

CZ- I am keeping the option of a motor hook on the table and I have an idea that might allow me to add one after the fact If I determine that there is a need for it. If drop tests in the planned configuration are unsuccessful, your idea would be closer to the concept that I am going for. That will be option 2 before I start adding recovery gear.

Here are the two basic plans for the fin frames. The perimeter frame will be 1/4" wide and the interior braces will be 1/16 square stock. I plan on sheeting the fins with 1/16 balsa. My LHS has had 1/32 balsa and birch sheet in the past but I'm not counting on it. If I feel the need for a bit more stiffness, I'll paper the fins (tissue paper may be the ticket here)

Angles on this one would need to be refined if chosen. The basic idea here is more bracing for a stiffer structure.
View attachment MegaF_U1.pdf

The concept for this one is minimal bracing to reduce weight. There is a place or two where additional bracing could be added but I think that what is here should suffice. I will probably go this route unless someone sees an issue that I missed.
View attachment MegaF_U2.pdf

Once the upper body fins are done, I'll use the same concept for the booster fins.

As always, thank you all for your input. I have learned quite a bit so far and the light at the end of the tunnel looks more like a Volkswagen than a train.