@@bainc ⚠️ God has said in the Quran: 🔵 { O mankind, worship your Lord, who created you and those before you, that you may become righteous - ( 2:21 ) 🔴 [He] who made for you the earth a bed [spread out] and the sky a ceiling and sent down from the sky, rain and brought forth thereby fruits as provision for you. So do not attribute to Allah equals while you know [that there is nothing similar to Him]. ( 2:22 ) 🔵 And if you are in doubt about what We have sent down upon Our Servant [Muhammad], then produce a surah the like thereof and call upon your witnesses other than Allah, if you should be truthful. ( 2:23 ) 🔴 But if you do not - and you will never be able to - then fear the Fire, whose fuel is men and stones, prepared for the disbelievers.( 2:24 ) 🔵 And give good tidings to those who believe and do righteous deeds that they will have gardens [in Paradise] beneath which rivers flow. Whenever they are provided with a provision of fruit therefrom, they will say, "This is what we were provided with before." And it is given to them in likeness. And they will have therein purified spouses, and they will abide therein eternally. ( 2:25 ) ⚠️ Quran
Not just the aspect ratio, but the lack of taper and the fact that they're made of a material which is pretty floppy for its weight. Both the chord and thickness of the fins should be considerably larger near the root. A stiffer, lighter material would be appropriate. Balsa fins would probably be far more flutter resistant, though perhaps some very light glass and epoxy, with the weave on the bias, would help. It also seems possible that the paper towel roll was a bit too flexible and contributed to the flutter. Maybe it needs glass. If it was me, I might make a balsa tube.
Yep you'd be right. I rebuilt and launched about 2 months ago with a much better design: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-bv-awFMz66g.html
Try laminating/filleting the fins to the body with something like fiberglass or even paper if you're going for a minimum diameter rocket. I would also try to increase the length of your root cord for more surface area to adhere to. Nice work with all the hypothesizeing and data analysis, keep it up.
I knew when I saw you actually used that thin cardboard tube it would do this, the tube compressed and the fins were glued on. Use pvc pipe and bolt on fins and you might make it work but then, that's why ghey have rules and Regulations about Super Sonic Flight. Because,when it goes that fast it's not a toy any more. Models are toys, supersonic flight is Ballistics
3D printed body tubes are no good. At least not with your typical domestic 3D printer. It will buckle under stress because of how the layers are made. And if you manage to design it structurally strong enough, it will end up too heavy. However, you can almost certainly print the fin “can” as you described.
If you're going to show a rocket launch that indicates or includes a 'supersonic' flight; regardless of whether it makes it or not, at least show the 'normal' launch first; at least here, we get to see it all as it is happening. Then, if necessary, show the slow-motion version to illustrate the point you would like to make. This, in my opinion, makes for a better 'viewer' experience.
The fins exending below the body into the engine wash might be the issue. Every high speed rocket/missile design I've seen has fins no lower than the end of the body and often high a second set of fins high up on the body.
Sweet rocket! I think you should rebuild this exact rocket but use through-the-wall fins and fillet the fins, attaching them with something even as easy as 5 minute epoxy (to make it super strong you can mix 50% chopped fibreglass tow and 50% epoxy). I think the fins came off because of a lack of surface area in contact with the tube, which would explain why only one of them shattered, and the rest were still intact. Try a different fin design that has a longer root chord and a shorter tip chord. Good stuff.
Thanks! I just launched the new design a few days ago. No trough the wall because it's minimum diameter but I used fin fillets and papered the fins. Video coming soon!
I think the main reason the fins broke off was due to you using what looked like wood glue on plastic fins. A better idea would probably be to use some sort of epoxy or plastic cement. Also, it could have been the structure of the body tube itself. Because you used an aluminum foil roll, it's likely that it could have ripped since it was not designed for rocketry like the ones you can buy online. Other than that, it looked like a great design and build. Good luck with your next launch! (It seems I'm a bit late so you may have already flown your new design)
Was the leading edge of the fins squared off? Or sanded down in the shape of a sharp airfoil? There's a pressure wave ahead of the leading edge of the fin, just like there's one ahead of the nose cone. Its drag effect is negligible at the subsonic speeds of low-power model rockets. As you reach the transonic range, though, the drag of the pressure waves rises sharply, putting stress on the rocket structure. Pointed nose cones and sharp leading edges are less affected by this external pressure - intuitively, they "pierce / slice through" the dense air of the pressure wave. I second the commenter who suggested fin flutter as a possible cause. Supersonic fins need to be stiffer than those on low speed rockets. Most plastics are not very stiff. Plywood made from balsa or basswood is often used on mid-power rockets like yours. If you can't find any, you can easily make it from thin sheets of balsa and Gorilla Glue. As far as fin attachment goes, I'm not surprised wood glue didn't do the job. The way wood glue works, it has to soak into both surfaces to be most effective; it can't soak into plastic. I second the commenter who recommended epoxy. Fin joints are stronger if they're glued not only on the edge, but also with fillets where the fin meets the tube (popsicle sticks are great for making clean fillets). Since you have access to a 3D printer, have you considered printing the whole rocket, with fins, as one unit? (I do understand, though, if you have sentimental attachment to the aluminum foil tube 😉)
Yep I didn't make great design choices for the first design but I was trying to be as cheap as possible. The next design will be much stronger, using airfoiled and papered fins using balsa and attached with epoxy fin fillets. And no I have no sentimental attachment with the aluminum foil tube🤣 (new tubes will be used). I like that 3d printing idea though but I'd be worried about melting. Might do it with a different rocket in the future.
This is all great and well done etc., but model rockets have been breaking the sound barrier since the '70's. The Crown F67 was, I think, the first proven to do so in a photo study.
That’s all great and well, but that’s not the point. The point is to work a project that teaches him something about design and trial and error. Otherwise by your logic, there is really no point on building model rockets today, since it’s all been done before.
Hi Max. Thanks for your question. We used wood glue on only 2 millimeters of attachment for each fin. Wood glue doesn't work that well on PLA plastic which has to be part of the reason why they disconnected. New video coming soon of me analyzing the simulation data and figuring out what we can do to improve attachment.
I'm planning to launch a rocket similar to this but I have some questions. How were you able to connect the motor to the rocket body and how far away was it recovered? I'm launching in a field about 800 feet across surrounded by water, so I'd hope that it doesn't stray too far away. :)
The launch was a fail so it didn't go super far. The way we connected the motor though was just with a friction press fit in the body tube. The rocket is minimum diameter meaning there's no room from the edge of the motor to the inside of the body tube. Just wrap tape around the outside of the motor to slightly increase its diameter and it should be tight enough to stay in. These types of rockets go super high, but they're relatively light so just use a streamer for recovery. My new design for this rocket should be launching very soon!
Also depending on where you live, you might be able to find a better launch site. Go to the NAR website and look for club launches then find their schedule.
Cool! I launched a rocket that went mach .3 but I want to go faster, so I'm trying to break the light barrier! I won't tell you my secret to going the speed of light but my rocket is almost done
@@motechspace you will know when I'm sending people like you in my rockets to mars I will give you a hint: You will step on the mars surface and safely make it back earth and step on the earth surface, and it will take 3 minutes 10 seconds at least, but you won't live through even the launch. Bet you can't guess how it works and why I make fins that work 😏(I'm not a jerk I was just joking (the fins on my rocket actually store mass (bet you can't guess why), and are not used for stabilization anyways)) 😏so yeah, I guess you could say NASA Shmasa
The fins tore off because the contact surface is too small. On most mid power rocket kits that can support the thrust of a G80, the fins are slotted through the rocket's body. If you use a 29mm tube that both acts as an engine mount and rocket's fuselage then the fins must be more swept back and they need to be bolted to the rocket's body or perhaps glued to a much larger surface. I would use Lepage's 2 hour curing marine epoxy which is insanely tough and white in color.
@@motechspace Then please tell me how many newtons of force does the air resistance exert on a single one of your fins when your rocket reaches its highest speed ? The motor pushes at up to 108.5N or about 24.5lbf. At first, when the rocket takes off, most of that is used to accelerate the rocket where F=m*a. Once the rocket has reached "terminal" velocity, all the thrust is opposed by air resistance and gravity. There is also vibration aka air flutter shaking your fins. Before flight, I would suggest attaching a 5lb diving weight at the tip of each fins and lift the rocket by grabbing the tube. If the fins tear off then you know they won't survive the flight.
@@motechspace Your sim (drag + acceleration forces) says 44.3 N or about 11.07N per fin that's 2.5lbf but you want the fin to take double that for safety margin and I suggested a weight of 5lb for testing. I think my suggestion makes perfect sense.
@@motechspace The weights you have used were attached at the root of the fins and therefore do not account for the moment of rotation of the fins imparted by the air resistance which is applied evenly over the fins (from root to tip). Your test weight is no good. You should have attached them to the tip of the fins to replicate a worst case scenario.
IMHO : The 7 second delay is too short. The G80 is available with 13 seconds delay. The small rocket can go fast but this means it will go high and will decelerate for quite some time.
@@motechspace Having launched Aerotech rockets/motors since 1993 I can tell you 7 seconds would have been appropriate for a rocket like the Initiator which is more than 400 grams and 2.6" diameter. Your rocket had a smaller diameter than a Mustang and the weight was about half so clearly you didn't enter something correctly in your simulator. Note a Muitang is usually flown with a G80-10T -> 10 seconds delay! Your rocket obviously would require more.
@@francoisleveille409 The supersonic speeds cause the deceleration rate to be a lot quicker. Also keep in mind that those large fins create a lot more drag. I made sure every single value in the sim was perfect and I'll do it again for the next iteration which will have smaller fins. We'll see how that affects the optimal delay time.
@@motechspace Your rocket - according to your sim - only reaches Mach 1.18. So the question is, what portion of the acceleration phase is supersonic ? What portion of the deceleration phase is supersonic? If you simulate that you'll realize your rocket exceeds the speed of sound only for a fraction of a second. Your "large fins" are pretty much the same in terms of air resistive surface as those on Aerotech kit Tomahawk. But the rocket weight is much lower and so is the diameter. The Tomahawk uses 1.9" tube (48mm). Also, the air pressure and resistance decreases with higher altitude. The breaking of your fins caused a brutal deceleration but if it had not occurred then your rocket would have gone to about 5000 feet.
You shear strength is not good enough. I would 3D print the entire fin can and probably still do epoxy/fiberglass from tip to tip of each fin set. Videos out there on how to do this on Rocket Vlogs and John Coker's channel. Anything over mach 1 should have this.
I just learned something interesting here. Could be useful for your project. As I suspected an ogive shaped cone is not adequate for supersonic speeds. Low altitude supersonic projectiles usually have cone shaped front ends. The Igla and Igla-S supersonic portable surface to air missiles have a spike at their front tip to create a small supersonic shockwave which reduces air resistance. See: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-t_5cwfvKW70.html So perhaps installing a piece of wood at the tip of your cone - the kind you can buy at the dollar store and normally used for chicken kebab - and re-enforced with marine epoxy could play the same role on your rocket.
That's really interesting. Thanks for the suggestion. Yeah I've read that ogives are really bad for the low supersonic region but the new design will use a Von Karman shape which is supposed to be really good. I'll see what the spike does in the sim (hopefully the sim will know how to deal with the different aerodynamics)
Your fin design is inconsistent with high speed or rapid acceleration. Tip chord must remain over root chord. Root chord must be longer and span must be reduced. They are wayyyyyyyyyy too flexible. You could taper them from root to tip. You'll need to fillet them onto the paper tube unless you thicken the root.... a lot. Bottom line... put some Mach+ fins on that bird.
Yep I made some pretty bad design choices. I'm currently building the new design with using papered and filleted fins and the tip chord is fully over the root chord.
