Those. To see the opening of the parachute, you have to try very hard. But it's still a beautiful flight.
When the article about the RK-1 project was written, the RK-2 project was only in its infancy. But even then, I expressed the opinion that the rescue system is the most complex in a rocket that does not carry other payloads. Like looking into the water. Most of the time was spent on developing this system. There was, however, a tactical mistake. For such delicate and critical systems, it is, of course, necessary to first conduct a series of ground tests before conducting flights. It was after such a series of bench tests that the successful launch was carried out.
However, water will suffice. I’ll tell you what happened and what I’m sure of. A diagram of the RK-2-1 missile recovery system is shown in Fig. 1. It turned out to be simple and reliable. Let's go in order. The positions of the elements on the diagram will be indicated by numbers in brackets. For example, fuselage (1).
Fastening
Let me remind you that the system is attached to an M5 screw (3) screwed transversely into the fuselage (1). From below, the engine rests against this power screw with its mortar (2). The engine has an original sealing system that prevents the breakthrough of gases from the expulsion charge between the engine body and the rocket fuselage. See article Engine. The thin-walled plastic fuselage must be in mandatory insulated from the inside with two or three layers of office paper glued with silicate glue or epoxy, at least in the area of the mortar and flame arrester.
A flame arrester (4) is attached to the power screw. This simple element is the pride of my scheme. I have not seen anything like this, so I will consider it my development /11/27/2007 kia-soft/. With the advent of the flame arrester, the work of the rescue system immediately went smoothly. Its design is elementary. A piece torn from a steel wool for cleaning frying pans is placed on an axle made of 2 mm steel wire. It is pressed on both sides with washers made from one-kopeck coins. With an internal fuselage diameter of 25 mm, the diameter of the washers is 15 mm. 
The wire is bent on each side in the form of a metal ear. One ear is attached to the power screw, and a flexible cable (5) is attached to the second ear. The length of the working part is 30-40mm. The importance of a flame arrester in a pyrotechnic rescue system cannot be overestimated. As the name suggests, the original plan was to extinguish the expelling charge torch. But the result exceeded all expectations. The element not only extinguished the torch, but also prevented the release of unburned powder to the parachute, and also played the role of a radiator, significantly reducing the thermal load on the remaining elements. Plus, the flame arrester acts as a filter, practically eliminating the formation of a deposit of unburned particles on the internal working surface. After three activations of the system, an audit was carried out: all the fumes settled in the flame arrester, all elements of the system remained clean and undamaged, even the cable at the point of attachment to the flame arrester. Cable
Initially, I had the idea of using a metal cable as a connection between the system and the power screw. However, practice has shown the complete futility of the idea. The only advantage of a metal cable is its heat resistance. Otherwise, it loses to synthetics, both in strength and ductility. The use of a flame arrester made it possible to abandon the metal connecting cable. In the working scheme, I used a braided tape, ~10mm wide, apparently made of thin fiberglass. I say “apparently” because I find it difficult to accurately name the composition from which the tape is made. I found it by accident. I only know that its strength is no less, if not more, than that of nylon, the same flexibility, lightness and fairly high heat resistance. I tried melting it with a lighter, but all I achieved was a slight charring that did not lead to any serious loss of strength. But just in case, I made the cable from double tape. I can only attach a photo, maybe you’ll understand what I’m talking about. If you don’t have such a cable, then I think it’s quite possible to use a regular nylon cable. You may just have to increase the working fluid of the flame arrester. Here you will have to experiment. One end of the cable (5) is connected to the flame arrester (4). The other - with the next element of the system - the piston (6). The length of the cable should be such that the piston extends beyond the fuselage by 10-15 cm.
The piston (6) under the pressure of the gases of the expelling charge comes out of the fuselage and pushes out the parachute. It is carved from a wooden champagne cork. The fit to the fuselage diameter should be fairly accurate. The piston should move freely inside the fuselage, but not have large gaps with the walls. The sealing element is a felt washer 4-5mm thick. By analogy with a flame arrester, a piston with a gasket is placed on an axis made of steel wire with a diameter of 2 mm. The structure is also pressed on both sides with penny washers. The axle is bent onto the mounting lugs on both sides. The piston assembly should move with little friction. As a test, you can insert the piston into the fuselage and blow from the bottom end. In this case, pushing out the piston should not require much effort.
If the rocket is light and does not have a strong axial spin in flight, then the swivel may not be used. It was not used in this system. 
The central line of the parachute is attached to the upper ear of the piston. At a distance of ~15cm from the mounting point we will arrange a shock absorber (7). This distance actually depends on the specific rocket. It is best to choose it in such a way that when the piston is completely recessed, the shock absorber itself is at the upper edge of the fuselage, but is not yet recessed. The shock absorber's job is to soften shock loads when the parachute opens. It is made from any durable rubber ring, for example, cut from a bicycle tube. The elastic band is tied in two places to the sling at a distance of the length of the elastic band in the extended state. It turns out to be a loop that stretches the elastic when tensioned. The fairing (8) can be attached to this loop on the central sling. To do this, I drill a channel with a diameter of 10 mm and a depth of 20-25 mm in the fairing from the bottom side. At a distance of 10mm from the lower edge of the fairing, I screw in an M3 screw, using which I attach the fairing to the system. Parachute PRSK-1
The crown of the rescue system is the parachute (9). Yes, you can make a dome from a garbage bag, as I wrote in one of the earlier editions of the article. But the harsh winter flying conditions put everything in its place. In short, if you want to make a fail-safe rescue system, make a parachute from light synthetic fabric. The best fabric for this is, of course, lightweight nylon from an aircraft drogue parachute. At one time I managed to get a couple of meters. It makes great parachutes. If this is not the case, any lightweight synthetic fabric will do. But even in the case of a fabric parachute, I do not recommend keeping it packaged during storage. The system only needs to be equipped immediately before the flight. Laziness is the engine of progress. Natural laziness and the lack of a good sewing machine forced me to come up with a technology for making a fabric parachute without sewing. Using this technology, a parachute with a diameter of up to 80 cm, i.e. for a small rocket weighing up to 700g, it is even easier to make than from a plastic bag. Knowing the weight of your rocket, you can use my amo-1 program to estimate the size of the parachute required for the desired rate of descent. On the PHOENIX, whose weight did not exceed 200g, a flat hexagonal parachute with a diameter of only 46cm was successfully used. Along the way, I will note that chasing large domes is not only not necessary, but can also backfire. Once I already had to rewind 2 km along the intersection behind a rocket blown away by the wind.
To begin with, we make a hexagonal, and starting from a diameter of 60 cm, an octagonal one is better, a pattern from a newspaper. Using a heated soldering iron, we cut out the dome using the pattern. We make slings from nylon ropes with a thickness of about 1mm. The length of the lines is approximately 2-3 times greater than the diameter of the dome, plus a reserve for organizing the central line, shock absorber, and attachment loop to the piston.
Now we attach the lines to the canopy. This is where the trick is. No sewing. We make a simple knot on the sling and throw it over the folded corner of the dome and tighten it well at a distance of 10 mm from the top of the corner.
Having slightly trimmed the excess end of the knot and corner, we melt them with a lighter until neat round fillets are formed. We melt it so that the fillets fit tightly to the knot. That's it, the sling is attached. We fasten all the slings in the same way. And then, with a little effort, we straighten the canopy at the attachment point of each line. One caveat - the addition of all corners of the dome must be done in one direction (down). Then, after securing the lines, the canopy will not be flat, but will acquire some volume, which increases the effectiveness of the parachute.
If anyone thinks that such a connection between the slings and the canopy is not strong, he is deeply mistaken. I was convinced of this when, on one emergency flight, the parachute opened on takeoff. The speed was very decent, but the rocket quickly slowed down, and for repairs it was enough to fasten one loose line.
Actually, the parachute is ready, all that remains is to connect the lines together, organize the shock absorber, and attach it to the piston.
A lot of time has passed since this article was written. Parachutes made using this proprietary technology were installed on all my rockets, and this, on this moment, about a dozen. They had to work very hard different conditions, including emergency and near-emergency situations under extreme loads. They passed all the tests with honor and if the rescue system was triggered, all the missiles were saved. Many rocket scientists repeated my design and were satisfied with the result. Therefore, I can confidently recommend this easy-to-use, but very reliable parachute for use. I quite deservedly assign it the personal name PRSK-1, or Rocket Rescue Parachute K...-1 (K - from the author).
Assembly
Preparation of the rescue system is almost complete. All that remains is to pack everything into the fuselage. First we recess the cable and piston. Then we fold the parachute. To do this, straighten all the folds of the canopy as on a folding umbrella and place them in one direction in a stack. Next, fold once in the transverse direction and roll into a “sausage” starting from the top. We wrap the “sausage” with a rope of slings. This method of folding a parachute is not entirely “correct,” but it is quite workable. Its advantage is the tight twist of the parachute, which is very useful when the fuselage volume is insufficient. In this way, I was able to easily equip the RK-2-3 "VIKING" rocket with a parachute, the internal diameter of the fuselage of which is only 20 mm. The parachute with a diameter of 46 cm was made of even thicker fabric - calender. 
If the size of the rocket is not limited, you can use the “correct” method. It is based on the standard procedure for collapsing reserve rescue parachutes. We fold the canopy in the same way, like a folding umbrella, straightening the folds. We distribute the folds into two equal stacks (Fig. 2). We place one stack on top of another, folding the structure along the axis of Fig. 3. 
Next there are two options. If the width of the resulting double pack is too large, then fold the upper and lower halves in half again reverse side outward, i.e. top - up, bottom - down, Fig. 4. If it is small, we immediately move on to the next stage - folding Z-shaped small folds in the transverse direction, starting from the top, Fig. 5. It turns out to be a compact stack (see photo at the beginning of the section), which we wrap with slings and pack into the fuselage.
To be on the safe side, you can additionally protect the parachute with a strip of toilet paper. Take a strip of toilet paper twice as long as a parachute “sausage”. We fold the strip in half, press the end of the twist into the fold and crumple the paper around it. You can’t just wind the paper, it will prevent it from opening, and in this form it is instantly torn off by the oncoming flow. Lately I don’t do this, because if you have a good flame arrester, there is no need for it.
Finally, we fill the shock absorber into the fuselage and install the fairing. That's it, the system is ready to work. A well-assembled system works if you simply do not blow very hard from the underside of the fuselage.
As a summary, let me remind you of some nuances. The system was successfully tested on the RK-2-1 "PHOENIX" rocket, weighing ~200g, internal diameter 25mm, ceiling 400m. The working volume of the rescue system chamber is ~145 cc. For such a volume, the required weight of the expelling charge is 0.5 g of “raspberry powder” or “Falcon” hunting powder.
The exact weight for each specific missile must be determined through a series of ground bench tests. Those. take a ready-made rocket, install an engine without fuel, but with an expulsion charge, and initiate the charge. And so on until everything works normally, as in this video of a bench test. After that you can fly.
Do not forget to protect the plastic body of the rocket from the inside by inserting a paper tube, at least in the area of the mortar and flame arrester. This is necessary if the rocket body is made of a thin-walled plastic tube (1mm for PHOENIX). Experiments with a fairly thick-walled polypropylene tube (2.5 mm for VIKING) showed that if there is a flame arrester, such protection is not necessary.
Remember that a seal is required when installing the motor for proper operation.
It is clear that the system can be used for rockets of almost any size, but certain adjustments must be made.
Many rocket scientists use various mechanical parachute release systems. This is mainly done to avoid thermal damage to system elements. Otherwise, mechanical systems, in my opinion, are inferior to pyrotechnic systems. The rocket recovery system I developed was able to radically solve the problem of thermal overloads, and the result was a lightweight and reliable design.
/27.11.2007 kia-soft/
P.S.
The content may be adjusted as experimental data accumulates.
P.P.S.
The last major adjustment was made on February 12, 2008. It’s hard to call it a correction, since almost nothing remains from the old edition. This is due to the fact that the design of the rescue system has been radically redesigned, tested and verified in practice. All fiction thrown out and done detailed description working rescue system for the RK-2-1 "PHOENIX" missile.
At this point, the development of the RK-2 project has been successfully completed. All tasks that were set within the project have been solved. It's time to move on to the new RK-3 project...
***
Before talking about miniature rockets, let's clarify what a model rocket is, and consider the basic requirements for the construction and launch of model rockets.
A flying model of a rocket is propelled by a rocket engine and rises into the air without using the aerodynamic lift of the lifting surfaces (like an airplane), and has a device for safely returning to the ground. The model is made mainly from paper, wood, destructible plastic and other non-metallic materials.
A variety of rocket models are rocket plane models, which ensure the return of their glider part to the ground through stable planning using aerodynamic forces that slow down the fall.
There are 12 categories of rocket models - for altitude and flight duration, copy models, etc. Of these, eight are championship ones (for official competitions). U sports models rockets are limited to the launch mass - it should be no more than 500 g, for a copy - 1000 g, the mass of fuel in the engines - no more than 125 g and the number of stages - no more than three.
The launch mass is the mass of the model with engines, rescue system and payload. The stage of a model rocket is a part of the body containing one or more rocket engines, designed to separate in flight. The part of the model without an engine is not a stage.
The stepped structure is determined at the moment of the first movement from the starting engine. To launch model rockets, model engines (MRE) should be used using solid fuel only from industrial production. The structure must have surfaces or devices that hold the model on a predetermined take-off path.
It is impossible for a model rocket to be freed from the engine if it is not enclosed in a stage. It is allowed to drop the engine housing of model rocket planes, which are lowered by parachute (with a dome with an area of at least 0.04 sq. m) or on a tape measuring at least 25x300 mm.
All stages of the model and separating parts require a device that slows down the descent and ensures landing safety: a parachute, a rotor, a wing, etc. The parachute can be made of any materials, and for ease of observation it can be brightly colored.
The model rocket submitted for competition must have identification marks, consisting of the designer’s initials and two numbers with a height of at least 10 mm. The exception is copy models, the identification marks of which correspond to the marks of the copied prototype.
Any flying model of a rocket (Fig. 1) has the following main parts: body, stabilizers, parachute, guide rings, nose fairing and engine. Let us explain their purpose. The body serves to house the parachute and engine. Stabilizers and guide rings are attached to it.
Stabilizers are needed to stabilize the model in flight, and a parachute or any other rescue system is needed to slow down the free fall. Using guide rings, the model is installed on the bar before the start. To give the model a good aerodynamic shape, the upper part of the body begins with the head fairing (Fig. 2).
The engine is the “heart” of the rocket model; it creates the necessary thrust for flight. For those who want to get involved in rocket modeling, make a working model with your own hands aircraft called rocket, we offer several samples of such products.
It must be said that for this work you will need available material and a minimum of tools. And, of course, this will be the simplest, single-stage model for an engine with an impulse of 2.5 - 5 n.s.
Based on the fact that according to the FAI Sports Code and our “Competition Rules” the minimum case diameter is 40 mm, we select the appropriate mandrel for the case. An ordinary round rod or tube 400 - 450 mm long is suitable for it.
These could be components (tubes) of a hose from a vacuum cleaner or worn-out fluorescent lamps. But in the latter case, special precautions are needed - after all, the lamps are made of thin glass. Let's consider the technology for building the simplest models of rockets.
The main material for making simple models recommended for beginning designers is paper and foam. The bodies and guide rings are glued together from drawing paper, the parachute or brake band is cut out from long-fiber or colored (crepe) paper.
Stabilizers, the head fairing, and the holder for the MRD are made of foam plastic. For gluing, it is advisable to use PVA glue. Making the model should start with the body. For the first models it is better to make it cylindrical.
Let's agree to build a model for the MRD 5-3-3 engine with an outer diameter of 13 mm (Fig. 3). In this case, to mount it in the aft part, you will have to grind out a clip 10 - 20 mm long. Important geometric parameters of the model body are diameter (d) and elongation (X), which is the ratio of the body length (I) to its diameter (d): X = I/d.
The elongation of most models for stable flight with a tail should be about 9 - 10 units. Based on this, we will determine the size of the paper blank for the body. If we take a mandrel with a diameter of 40 mm, then we calculate the width of the workpiece using the formula for the circumference: B - ud. The result obtained must be multiplied by two, because the body is made of two layers of paper, and add 8 - 10 mm to the seam allowance.
The width of the workpiece turned out to be about 260 mm. For those who are not yet familiar with geometry, children in second and third grades, we can recommend another simple method. Take a mandrel, wrap it twice with thread or a strip of paper, add 8 - 10 mm and find out what the width of the workpiece for the body will be. It should be kept in mind that the paper must be positioned with the fibers along the mandrel.
In this case, it curls well, without kinks. Let's calculate the length of the workpiece using the formula: L = Trd or stop at the size of 380 -400 mm. Now about gluing. Having wrapped the blank paper around the mandrel once, coat the remaining part of the paper with glue, let it dry a little and wrap it a second time.
Having smoothed the seam, we place the mandrel with the body near a heat source, for example, a heating radiator, and after drying, we clean the seam with fine sandpaper. We make guide rings in a similar way. We take an ordinary round pencil and wrap a strip of paper 30 - 40 mm wide on it in four layers.
We get a tube, which, after drying, is cut into rings 10 - 12 mm wide. Subsequently we glue them to the body. They are guide rings for starting the model. The shape of stabilizers can be different (Fig. 4). Their main purpose is to ensure the stability of the model in flight.
Preference can be given to one in which part of the area is located behind the cut of the aft (lower) part of the hull. Having chosen the desired shape of stabilizers, we make a template from thick paper. Using the template, we cut out stabilizers from a foam plate 4 - 5 mm thick (ceiling foam can be successfully used). The smallest number of stabilizers is 3.
Having folded them in a stack, on top of each other in a bag, we chop them off with two pins and, holding them with the fingers of one hand, process them along the edges with a file or a block with sandpaper glued on. Then we round or sharpen all sides of the stabilizers (after disassembling the package), except for the one with which they will be attached to the body.
Next, we glue the stabilizers onto PVA in the bottom part of the body and cover the sides with PVA glue - it smoothes out the pores of the foam. We turn the head fairing from foam plastic (preferably PS-4-40 brand) on a lathe. If this is not possible, it can also be cut out of a piece of polystyrene foam and processed with a file or sandpaper.
Similarly, we make a holder for the MRD and glue it into the bottom part of the body. We use a parachute or a brake band as a rescue system for the model, ensuring its safe landing. We cut out the dome from paper or thin silk.
For the first launches, the canopy diameter should be chosen around 350 - 400 mm - this will limit the flight time - after all, you want to keep your first model as a souvenir. After attaching the lines to the canopy, we stow the parachute (Fig. 6). After manufacturing all the parts of the model, we assemble it.
We connect the head fairing with a rubber thread (shock absorber) to the upper part of the rocket model body. We tie the ends of the parachute canopy lines into one bundle and attach it to the middle of the shock absorber. Next, we paint the models in bright contrasting colors. The starting weight of the finished model with the MRD 5-3-3 engine is about 45 - 50 g.
Such models can be used to conduct the first flight duration competitions. If space for launches is limited, we recommend choosing a brake band measuring 100x10 mm as a rescue system. The starts are spectacular and dynamic.
After all, the flight time will be about 30 seconds, and delivery of the models is guaranteed, which is very important for the “rocket scientists” themselves. The rocket model for demonstration flights (Fig. 7) is designed to launch with a more powerful engine with a total impulse of 20 n.s. It can also carry payload on board - leaflets, pennants.
The flight of such a model is spectacular in itself: the launch resembles the launch of a real rocket, and the throwing of leaflets or multi-colored pennants adds to the spectacle. We glue the body from thick drawing paper in two layers on a mandrel with a diameter of 50 -55 mm, its length is 740 mm.
We cut out the stabilizers (there are four of them) from a 6 mm thick foam plate. After rounding three sides (except for the longest - 110 mm), cover their side surfaces with two layers of PVA glue. Then on their long side, which we then attach to the body, we make a groove with a round file - for a tight fit of the stabilizers to the round surface.
We glue the guide tube using the method known to us on a round mandrel (pencil), cut it into rings 8 - 10 mm wide and attach it to the body with PVA. We turn the head fairing on a lathe from foam plastic. We also use it to make a holder for the MRD with a width of 20 mm and glue it into the bottom part of the body.
We coat the outer surface of the head fairing two or three times with PVA glue to remove roughness. We connect it to the upper part of the body with a shock-absorbing elastic band, for which an ordinary underwear elastic with a width of 4 - 6 mm is suitable. We cut out a parachute canopy with a diameter of 600 - 800 mm from thin silk, the number of lines is 12-16.
We connect the free ends of these threads with a knot into one bundle and attach them to the middle of the shock absorber. Inside the body, at a distance of 250 - 300 mm from the bottom cut of the paper, we glue a grid of thick paper or slats, which does not allow the parachute and payload to descend to the bottom of the model at the moment of takeoff, thereby disturbing its alignment. Filling payload depends entirely on the imagination of the model designer. The starting weight of the model is about 250 - 280 g.
MODEL ROCKET LAUNCHER
To safely launch and fly your model, you need reliable launch equipment. It consists of a starting device, a remote control for starting, conductors for power supply and an igniter.
The starting device must ensure that the model moves upward until the speed necessary for safe flight along the intended trajectory is reached. Mechanical devices built into launcher and assisting at launch, their use is prohibited by the Competition Rules for model rockets of the Sports Code.
The simplest starting device is a guide rod (pin) with a diameter of 5 - 7 mm, which is fixed in the starting plate. The angle of inclination of the rod to the horizon should not be less than 60 degrees. The launching device sets the rocket model in a certain flight direction and provides it with sufficient stability at the moment it leaves the guide pin.
It should be taken into account that the greater the length of the model, the greater its length should be. The rules provide for a minimum distance of one meter from the top of the model to the end of the bar. The launch control panel is an ordinary box with dimensions of 80x90x180 mm; you can make it yourself from plywood 2.5 - 3 mm thick.
On the top panel (it is better to make it removable) a signal light, a locking key and a start button are installed. You can mount a voltmeter or ammeter on it. Electrical diagram The launch control panel is shown in Figure 7. Batteries or other batteries are used as a current source in the control panel.
In our circle, for many years, four dry cells of the KBS type with a voltage of 4.5 V have been used for this purpose, connecting them in parallel into two batteries, which, in turn, are connected to each other in series. This is enough power to launch model rockets throughout the entire sports season.
This is about 250 - 300 launches. To supply power from the control panel to the igniter, it is advisable to use stranded copper wires with a diameter of at least 0.5 mm with moisture-resistant insulation. For a reliable and quick connection, plug connectors are installed at the ends of the wires. “Crocodiles” are attached at the igniter connection points.
The length of the current supply wires must be over 5 m. The igniter (electric igniter) of model rocket engines is a spiral of 1 - 2 turns or a piece of wire with a diameter of 0.2 - 0.3 mm and a length of 20 - 25 mm. The material for the igniter is nichrome wire, which has high resistance. The electric igniter is inserted directly into the MRD nozzle.
When current is applied to the coil (electric igniter), it releases a large number of heat needed to ignite engine fuel. Sometimes, to enhance the initial thermal impulse, the spiral is coated with powder pulp, having previously dipped it in nitro varnish.
When launching model rockets, safety precautions must be strictly observed. Here are some of them. The models start only remotely; the launch control panel is located at a distance of at least 5 m from the model.
To prevent inadvertent ignition of the MRR, the control panel locking key must be kept by the person responsible for the start. Only with his permission on the command “Key to start!” A three-second pre-launch countdown is made in reverse order, ending with the command “Start!”
Rice. 1. Rocket model: 1 - head fairing; 2 - shock absorber; 3 - body; 4 - parachute suspension thread; 5 - parachute; 6 - guide rings; 7-stabilizer; 8 - MRD
Rice. 2. Shapes of model rocket bodies
Rice. 3. The simplest model of a rocket: 1 - head fairing; 2 - loop for fastening the rescue system; 3-body; 4-rescue system (brake band); 5 - wad; 6 - MRR; 7-clip; 8 - stabilizer; 9 - guide rings
Rice. 4. Tail options: top view (I) and side view (II)
Rice. 5. Gluing the slings: 1 - dome; 2-slings; 3 - pad (paper or adhesive tape) Dome
Rice. 6. Parachute stowage
Rice. 7. Rocket model for demonstration launches: 1-head fairing; 2 - suspension loop of the rescue system; 3 - parachute; 4 - body; 5-stabilizer; 6-holder for PRD; 7 - guide ring
Rice. 8. Electrical system of the launch control panel
How to ensure reliable and trouble-free landing of model rockets? Many modellers are struggling to solve this technical problem. According to statistics, more than half of the models break down after launch. But time goes by, experience is gained, and methods for rescuing models are becoming more and more diverse.
And although we still hope for a parachute, work continues on the creation of other rescue systems. This is largely dictated by the fact that multi-stage models have appeared, models that are copies of launch vehicles spaceships: modellers spend a lot of time and energy on their production.
One of the mandatory requirements of the “Rules for Model Rocket Competitions” is the descent of stages on a fall-slowing device. Ribbon parachutes and pennants began to be used. There are even international competitions held abroad for the duration of descent of model rockets on a tape measuring 50X500 mm. In model competitions for the duration of parachute descent, Soviet modelers achieved high results - more than 20 minutes.
In the Moscow region they decided to complicate the competition for the duration of the descent - for the first time they began to hold starts in several rounds with a limited number of models. This order made it necessary to “plant” the models through certain time and deliver them to the judges for control.
A way out of this predicament, according to leading modellers, may be the use of a timer. It should be noted that for the first time a primitive timer (smoldering wick) was used by Gomel rocket modelers in 1970 at the All-Union competitions in Zhitomir.
1 - engine compartment, 2 - engine compartment bushing, 3 - nichrome thread, 4 - cover, 5 - imitation frame, 6 - parachute compartment bushing, 7 - parachute compartment, 8 - shock absorber, 9 - parachute.
A crash-free landing is the number one problem for rocket scientists building replica models. They demonstrate flight characteristics very similar to the flight of prototypes: full-scale division of stages, separation of side blocks. And to restart it is necessary to ensure a reliable landing of the model.
Interesting work in this direction is being carried out in the rocket modeling circle of the branch of the Central Scientific and Technical School of the Latvian SSR. The proposed developments, in our opinion, are of interest to readers.
Analysis of the causes of failure of rescue systems prompted us to develop and test several new options. The most interesting one - saving the side blocks of launch vehicles - is shown in Figure 1.
The side block in the area where the frame is placed is cut into two parts: the lower one is the engine compartment, the upper one is the parachute one. They are separated by a cover, which is inserted into the sleeve after the parachute is stowed. The sleeve is glued into the upper part of the side block. The upper and lower parts are joined (connected) by a sleeve glued into the lower part. The junction of the two parts is covered with an imitation frame made in the form of a strip of paper, half of which is glued to the parachute compartment, and the second hangs over the parting line, covering it.
The system works like this: after the engines of the side blocks have finished operating, the latter are separated from the central block of the second stage, and after one second (and this is exactly what the retarder should be) the expelling charge is triggered. The upper part flies out of the sleeve along with the cover, but the ni-chrome threads sharply slow down its movement, tearing out the cover and parachute.
Now let's look at the design of the first stage rescue system using the example of the Cosmos rocket. As can be seen from Figure 2, an oval hole is cut out on the side surface of the cylindrical body into which the container is glued. The outside of the container is closed with a lid, which fits tightly around its perimeter and is thus held in the container. The cover is glued to the body with a thread so that it does not get lost when the parachute is shot. The shooting mechanism itself resembles a slingshot, with the only difference being that it shoots with a parachute.
1 - body, 2 - container, 3 - cover, 4 - parachute, 5 - first stage truss, 6 - second stage, 7 - bead, 8 - spacer tube, 9 - thread, 10 - bracket, 11 - elastic bands of the slingshot.
The design of this mechanism is as follows: two elastic bands are attached diametrically opposite inside the parachute compartment container at a distance of up to 1 mm from the inserted lid. The parachute lines are tied to the place where the elastic bands cross on the outside, and on the inside - a thread (0.5 mm fishing line), which passes through the holes in the bracket attached to the rocket body and is brought out.
The bracket must be installed so that the rubber bands pass to the side of the remote tube. You can tie a bead to the end of the thread so that after docking with the second stage of the rocket, it, together with the thread, seems to be wedged between the body of the second stage and the truss. In this case, the length of the thread should be such that the elastic bands are stretched. Now you need to fold the parachute and place it in the container, close the lid - and the model is ready to launch. After undocking the steps, the thread releases the elastic bands that it held, and the parachute is fired. This rescue option is convenient for copy models in that a well-fitted container lid does not damage general view model and does not affect its copyability. Make sure that the lid does not fit too tightly into the container. The system can be easily checked without running engines.
And another option for saving the first stage of a copy model, where there is no space to install a container, that is, the case when the diameter of the rocket body is only a few millimeters larger than the diameter of the engine compartment. Docking diagram and comparative dimensions of the stage using the example of a missile defense system (Fig. 3).
A - starting position, B - moment of parachute deployment. 1 - body, 2 - engine, 3 - tube, 4 - parachute, 5 - thrust ring, 6-7 - guide bushings, 8 - restrictor ring.
In this case, there is space for installing a parachute only in the annular gap, between the rocket body and the engine bushing.
The design of the rescue system is as follows. The housing contains a motor inserted into a tube, to the ends of which guide bushings are glued. The thrust ring is attached to the inner surface of the housing at the very base. It is best to make the ring from D16T duralumin. It needs to be glued in only after the tube with bushings has been inserted into the body. The parachute is tied to the tube and fits into the annular gap between the body and the tube. A stop ring can serve as a stop to prevent movement of a running engine. To make the bushing move easily in the body, rub it with paraffin. The stage is prepared for launch as follows: you need to pull the tube out as far as it will go, place the parachute around it, then carefully, so as not to tear the parachute, place it in the body, install the engine. After installing other stages, the model can be launched. As soon as the second stage engine starts, a high blood pressure, which will push out the tube with the parachute laid around it. In this case, the bushing will rest against the thrust ring. The parachute, leaving the hull area, will open. At the same time, the stages are uncoupled. The tube moves instantly, and therefore the impact of the sleeve on the ring can cause the parachute compartment to bounce back into the body. Therefore, the mating surfaces of the sleeve and ring are made conical so that, firstly, the parachute does not catch on the edges of the ring, secondly, to reduce the vertical component upon impact, and thirdly, to fix the extreme position of the parachute compartment due to “jamming” of the sleeve in the ring. This system works reliably, but the parachute must be stowed carefully. Do not wrap the engine compartment with slings. Several test runs - and trouble-free operation of the proposed system is guaranteed.
I. ROMANOV, engineer
Surely each of us in childhood at least once made and launched a water rocket. Such homemade products are good because they are quickly assembled and do not require any fuel, such as gunpowder, gas, and so on. The energy used to launch such a rocket is compressed air, which is pumped by an ordinary pump. As a result, water comes out of the bottle under pressure, creating jet thrust.
The rocket discussed below consists of three bottles, each with a volume of 2 liters, that is, it is a fairly large and powerful rocket. In addition, the rocket has simplest system rescue, which allows the rocket to land smoothly and not crash.
Materials and tools for homemade work:
- plastic tube with thread;
- bottles;
- parachute;
- plywood;
- a can of canned food;
- a small motor, gears and other little things (to create a rescue system);
- power source (batteries or mobile battery).
Tools for work: scissors, hacksaw, glue, screws and screwdriver.
Let's start creating a rocket:
Step one. Rocket design
Three two-liter bottles were used to create the rocket. Two bottles in the design are connected neck to neck; a cylinder made from an empty plastic gas cartridge was used as an adapter for the connection. The parts sit on the glue.
As for the second and third bottles, they are attached bottom to bottom. A threaded tube and two nuts are used for connection. The attachment points are well sealed with glue. Also, to make the rocket more streamlined, pieces of a bottle were glued to the joints. The neck is used as a tip plastic bottle. As a result, the entire structure is a single smooth cylinder.
Step two. Rocket stabilizers
In order for the rocket to take off vertically, stabilizers will need to be made for it. The author makes them from plywood.
Step three. Nozzle
The nozzle is made a little smaller than usual when just the neck of a bottle is used as it. To make a nozzle, take a bottle cap and cut a hole in it. As a result, the water does not come out as quickly.
Step four. Launchpad
To make the launch pad you will need a sheet of chipboard, as well as two metal corners. A metal bracket is used to hold the rocket; it holds the rocket by the neck of the bottle. When launching, the bracket is pulled out using a rope, the neck is released, water pressure is generated and the rocket takes off.
Step five. The final stage. Parachute device
The parachute system is very simple, there are no electronics here, everything is done by mechanics based on a primitive timer. In the photo you can see what the parachute looks like when it is folded.
The parachute compartment is made from a tin can. When the parachute needs to open, a special spring forces it through the door in the tin can. This door opens with a special timer. In the photo you can see how a pusher with a spring works.
When the parachute is folded and the rocket has not yet begun to fall, the parachute compartment door is closed. Next, a timer goes off in the air, the door opens, the parachute is forced out and opened by a flow of air.
As for the device of the parachute timer, it is very primitive. The timer is a small gearbox with a shaft, in other words, it is a small winch based on an electric motor. When the rocket takes off, power is immediately supplied to the motor and it begins to rotate, while a thread is wound around the shaft. When the thread is completely wound, it will begin to pull the latch on the door and the parachute compartment will open. The gears in the photo were made by hand using a file. But you can use ready-made ones from toys, watches, and so on.
That's all, the homemade product is ready, in the video you can see how everything works. True, the launch without a parachute is shown here.
According to the author, the homemade product was not particularly productive, that is, the rocket takes off to approximately the same height as an ordinary bottle. But here you can experiment, for example, by increasing the air pressure in the rocket.
Many fundamental concepts in rocket modeling are explained here. If you are just starting to build your first rockets, check out this material.
Any flying model rocket has the following main parts: body, stabilizers, parachute system, guide rings, nose fairing and engine. Let's find out their purpose.
The body serves to house the engine and parachute system. Stabilizers and guide rings are attached to it. To give the model a good aerodynamic shape, the upper part of the body ends in a head fairing. Stabilizers are needed to stabilize the model in flight, and a parachute system is needed to slow down the free fall. Using guide rings, the model is attached to the rod before takeoff. The engine creates the necessary thrust for flight.
Building the model
The main material for flying model rockets is paper. The body and guide rings are glued together from whatman paper. Stabilizers are made from plywood or thin veneer. Paper parts are glued with carpentry or casein glue, and others with nitro glue.
The production of the model begins with the body. In the simplest rocket models it is cylindrical. The mandrel can be any round rod with a diameter of more than 20 mm, since this is the size of the most common engine. To make it insert easily, the diameter of the housing should be slightly larger.
Important geometric parameters of the model body are: diameter d and elongation λ, that is, the ratio of body length 1 to diameter d (λ = 1/d). The elongation of most rocket models is 15-20. Based on this, you can determine the size of the paper blank for the body. The width of the workpiece is calculated using the formula for circumference L = πd. The result obtained is multiplied by two (if the body is made of two layers) and 10-15 mm is added to the seam allowance. If the mandrel is Ø21 mm, then the width of the workpiece will be about 145 mm.
You can do it simpler: wrap a thread or a strip of paper around the mandrel twice, add 10-15 mm, and it will become clear what the width of the workpiece for the body should be. Keep in mind that the paper fibers must be positioned along the mandrel. In this case, the paper curls without kinks.
The length of the workpiece is calculated using the formula 1 = λ. d. Substituting the known values, we get L = 20*21 = 420 mm. Wrap the workpiece around the mandrel once, coat the rest of the paper with glue, let it dry a little and wrap it a second time. You now have a paper tube, which will be the body of the model. After drying, clean the seam and glue residues with fine sandpaper, and cover the body with nitro glue.
Now take an ordinary round pencil, wind it and glue a tube 50-60 mm long on it in three or four layers. After letting it dry, cut it with a knife into rings 10-12 mm wide. They will be guide rings.
The shape of stabilizers can be different. The best are traditionally considered to be those in which about 40% of the area is located behind the cut of the aft (lower) part of the hull. However, other forms of stabilizers also provide a margin of stability, because the elongation of the model is λ = 15-20.
Having chosen the shape of the stabilizers you like, make a template from cardboard or celluloid. Using the template, cut out stabilizers from 1-1.5 mm thick plywood or veneer (the minimum number of stabilizers is three). Stack them (on top of each other), secure them in a vice and file along the edges. Then round or sharpen all sides of the stabilizers except the one where they will be glued. Sand them with fine sandpaper and glue them to the bottom of the body.
It is advisable to turn the head fairing on a lathe. If this is not possible, plan it with a knife from a piece of wood or cut it out of polystyrene foam and process it with a file and sandpaper.
A parachute, rope or other devices are used as a rescue system. It is not difficult to make a ribbon (see the description of the Zenit rocket model). We will explain in more detail how to make a parachute.
The dome must be cut out of light fabric, tissue or mikalent paper or other lightweight material. Glue the slings to it as shown in the picture. The dome diameter for the first models is better to be 400-500 mm. The installation is shown in the figure.
(This method of stowing a parachute is very suitable for fabric canopies or film. In this case, too thin a film may cake and not open in the flow, so carefully check the operation of the parachute if you are not sure of the chosen material. If you use very thin lines, be careful to ensure that they do not get tangled when laying and opening.).
All parts of the model are ready. Now assembly. Connect the head fairing with a rubber thread (shock absorber) to the upper part of the model rocket body.
Attach the free end of the parachute lines to the head fairing.
To make the model easy to see against the sky, paint it a bright color.
Before launching the model, we will analyze its flight and estimate whether our first launch will be successful.
Model stability
One of the difficult tasks of both large and small rocketry is stabilization—ensuring flight stability along a given trajectory. Model stability is the ability to return to an equilibrium position disturbed by any external force, for example, a gust of wind. In engineering terms, the model must be stabilized by the angle of attack. This is the name of the angle that the longitudinal axis of the rocket makes with the direction of flight.
One of the ways to ensure model stability - aerodynamic - is to change the aerodynamic forces acting on it in flight. Aerodynamic stability depends on the location of the center of gravity and the center of pressure. Let us denote them as c. t. and c. d.
With the concept of c. t. are introduced in physics lessons. And it’s not difficult to determine it - by balancing the model on an acute-angled object, for example, on the edge of a thin ruler. The center of pressure is the point of intersection of the resultant of all aerodynamic forces with the longitudinal axis of the rocket.
If c. T. The rocket is located behind the c. etc., then the aerodynamic forces arising as a result of a change in the angle of attack under the influence of disturbing forces (gust of wind) will create a moment that increases this angle. Such a model will be unstable in flight.
If c. t. located in front of c. etc., then when the angle of attack appears, aerodynamic forces will create a moment that will return the rocket to zero angle. This model will be sustainable. And the further c. d. displaced relative to c. i.e., the more stable the rocket is. Ratio of distance from c. d. to c. because the length of the model is called the stability margin. For rockets with stabilizers, the stability margin should be 5 - 15%.
As noted above, c. i.e. the models are not difficult to find. It remains to determine c. d. Since the calculation formulas for finding the center of pressure are very complex, we will use in a simple way his location. From a sheet of homogeneous material (cardboard, plywood), cut out a figure along the contour of the rocket model and find c. t. this flat figure. This point will be c. d. of your model.
There are several ways to ensure rocket stability. One of them is the shift of c. to the tail of the model by increasing the area and location of the stabilizers. However, this cannot be done on a finished model. The second method is to shift the center of gravity forward by making the head fairing heavier.
Having carried out all these simple theoretical calculations, you can be sure of a successful start.
Single-stage rocket model, with parachute
The body is made of two layers of drawing paper, glued with wood glue on a mandrel with a diameter of 22 mm. In its lower part there is a holder for the engine.
The guide rings are made of four layers of drawing paper; the guide for them is a round pencil with a diameter of 7 mm. Three stabilizers made of 1 mm thick plywood are glued end-to-end with nitro glue to the bottom of the body.
The head fairing is turned on a lathe from birch and connected to the body with a rubber thread.
The parachute canopy is round, 500 mm in diameter, made of mica paper. Sixteen lines of No. 10 thread are attached to the head fairing.
After assembly, the entire model is covered with three layers of nitro varnish and painted with nitro paints in stripes of black and yellow color. Model weight without engine is 45 g.
Model of the ZENIT rocket
This model is designed for abseil and altitude competitions.
The body is glued together from paper on a 20.5 mm mandrel. Stabilizers are made of plywood. The head fairing is made of linden.
The tape measures 50X500 mm and is made of mica paper. One of the narrow sides is attached to the body using a shock absorber (rubber thread).
The weight of the model without engine is 20 g.
If you do not have the opportunity to get original rocket engines, then you can experiment with homemade ones (without forgetting about safety, of course). Instead of a homemade engine, you can use fireworks rockets, hunting or rescue signal cartridges.
Source "Modelist-Constructor"
