1 : 48 Zubr class hovercraft (проекта 12322 "Зубр")


This RC 1:48 Zubr was designed and built by Mr Benoît Raynal and his friend Didier, an experienced boat models maker. This page contains his explanations.

The following text was translated from French to English, please forgive the imperfect translation. The original French version is available here.

You can enlarge the pictures by right-clicking on them and select "open in a new tab" or "display image".

Zubr class hovercraft - проекта 12322 Зубр
Zubr class hovercraft - проекта 12322 Зубр

(I do not own the two images above, all rights and credit to their owners - original images here and here).

I'll tell you a story of love at first sight. It all started with an ADSL connection : I was finally going to access all these hovercraft pictures, barely glimpsed since they took too long to load. One of my first visits was on the British Hovercraft Museum website. This is where I first saw the Zubr Class hovercraft. Making a model of it was a dream. The image above, on the left, has been my computer wallpaper for a long time !

Making a working machine : not easy but possible. Building the superstructures : I had neither the time nor the skills.

And then Didier came to see me. Before the picture of the Zubr without further explanations, he recognized a soviet / russian machine and gave me its approximate date of construction. He was enthusiastic about making a static model, but making a RC model would be a totally different thing.

Zubr class hovercraft - проекта 12322 Зубр


DESIGN - It’s nice to have a friend who agrees to design a Zubr. Didier will do the superstructures, but before that, you have to make a functional machine. I have pictures of the beast and a blueprint.

From there, you have to think a lot to understand the design of the machine. I pass you the details of research and calculations. The Zubr has 4 different air cushions, each of them is powered by a vertical turbine.

The front ramp and the rear door, when lowered, don't hinder the skirt. The three rear turbines driving the four-bladed propellers are carossed and have a bulb to improve their efficiency. If we want to respect the scale, it will also be necessary to calculate the power of the motors and make a realistic weight estimate.

Two possible options : in a box that looks like the Zubr, I do a classic lift with a motor and a propeller, or else I stick faithfully to the model with four lifting turbines.

I hesitated for a moment between the simplicity of the first option and the technical beauty of the second. The discovery of turbines in the Graupner catalog will make me go with the second option.

(I do not own this image, all rights and credit to its owner - original image here).

From there everything goes on. Given the diameter of a Zubr turbine and that of a Graupner turbine, I calculated the appropriate scale : 1 / 48. From there comes the power : 70,000 CV divided by 48x48x48 = 466 W for a length of 1.30 meter. The motor choices will follow : 4 Graupner Speed 400 ​​7.2V to inflate the skirt and 3 Graupner Speed 480 7.2V for thrust - same voltage everywhere.

The propellers are quadrupal blades of a hydrofoil model, the Fluppy, which will have to be shrinked to the right diameter. Controls : one channel per propulsion motor, one channel for lift, one channel for doors, one channel for management, that makes six.

The plan was redone from photocopier enlargements of the various plans from the Internet. This is how one day my garage was invaded by RC equipment and a big workbench.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр



HULL - After thinking, action.

I preferred not to use resin, but using materials closer to the real machine. The real Zubr is made with aluminum-manganese "plywood". I chose to do the hull with two polypropylene sheets with a long partition in between. A "box construction", with pairs and partitions on a lower hull.

A realization from pairs with polypropylene to get closer to the real thing, which is Aluminum-Manganese sandwich.

All of this was cut with a cutter and sticked with a spray of hot glue.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Hull partitioning. Little weight and a lot of rigidity. We see the recesses in the center for the lift turbines.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Front view : we see the hinge, the ramp and front bulkhead.

The front is more problematic because it is not in the same plane as the rest of the machine and it has to support the hinge. I made a more compact partition to stiffen further, and double partitions to the hinge pin.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

The hinge is sealed by a stretched canvas, real hull in skirt fabric. We see the buoyancy foam that has been added.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Sorry for the poor quality picture - we can see here the detail of the two branches at axis level. This hinge is a single piece flat aluminum. The central part is lower, which is obtained by folding the bar. There is a double thickness under the ramp. The extremities are doubled by reinforcing legs riveted with POP rivets. The axis is piano wire.

Last difficulty for this part : to have a pretty hinge is not everything, it's necessary to make it airproof. On the inside of the hinge bar and on the underside of the hull, I stuck a piece of flexible fabric that I use for the skirts of the smallest models (gray K-Way fabric). I have makes the pattern of the room with paper to have a well developed ... or almost. The fabric of KWay sticks very well to SuperGlue or neoprene glue.

Advantage of the SuperGlue : fewer traces. Advantage of neoprene : sticks on almost all surfaces.

At the end of the day, I have a skeleton that will come the lift turbines, the skirt, propulsion and radio control.


SUSPENSION - I had a nice light and rigid hull. I had to give it life.

The position of the turbines very centered relative to the skirt posed a problem of air guidance. To do a lift, it is necessary that the air arrives in the skirt (part limited by the fabric) and in the cushion (space under the hovercraft which is used, thanks to the pressure therein, to lift the machine). There are about 1/3 towards the skirt for 2/3 towards the cushion. To feed the skirt, I had to offset outwards in being careful not to exceed the future bodywork.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр



Sustent diagram - the motor and the turbine are not drawn.

Wanting to stay as close as possible to Zubr, I was thinking of doing four cushions. Each turbine had to supply a cushion. I have provided 4 identical units obtained by cutting part of the turbine duct and adding a deflector.

Unfortunately, that was without taking into account the fragility of the carbon fiber hulls of the turbines.

You can't cut only part of the circumference without breaking the rest.

Originally, a turbine is 12 cm which suited me perfectly, once broken, it was only 6 cm. I "improvised" distribution boxes under each turbine. These boxes contain the deflector: piece of partition at an angle to separate and guide the air. Anti-reflux valves: pieces of skirt fabric so that the air cannot flow backwards in the event of a turbine failure.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр


Lift turbine with its casing

Even if the finishes are not done, we understand the why of the shape of the air distributors.

Each turbine is glued on a plate which allows the mounting and fine adjustment of positioning and verticality of the turbine. Once the turbine is glued, each well lift will be completed by two lateral reinforcements in canvas to prevent any separation between the two parts and by a canvas on the periphery with the idea of power have a inspection hatch for possible adjustments during the fitting the skirt.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Side view - we see the closing fabrics under tension by the effect of pressure.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

The four lift wells. First test run of the four motors together.

Electric wiring is very simple. These 4 motors are made to work together thoroughly time. I gathered the wires two by two on each side, and put a switch which will be radio controlled. The tests without skirt were satisfactory. An annoying detail: the tightening of the propeller cone has was impossible on one of the 4 motors. The solution was a drop of loctite. This makes disassembly impossible without drilling the screw. After several hours of operation on different models, I have never had to change the turbine. It is therefore not a major drawback.


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THE SKIRT

A specific piece of discipline, the skirt is both very simple and very complicated. Very simple because it’s not as canvas stretched by a flow of air. Very complicated because a small error can make everything miss.

The Zubr's skirt is a soufflé-segmented. Which means that at the top we have a kind of sausage: the blown skirt, in which air flows from the turbines, and below a segmented skirt formed as its name suggests half-glove segments, as the expression goes.

This first difficulty taken into account, it is necessary to pay attention to the profile of front skirt, which is different from the rest of the skirt, as well as the segments of the rear part which should not fill with water when market.

The glove half-fingers are supplied with air from the blown skirt and the cushion.

Last difficulty: there are internal partitions to separate the four cushions. I started by make a cardboard and plastic model the size of the model.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр



First shaping of the skirt

Above the hull, below the first shape of the pattern of the blown skirt

We can see on the shape that if the sides and the back are simple, the front deserves a lot more attention with its variation in diameter. Each couple of the form was calculated from information from plans found on the internet.

I had black skirt fabric in stock for my personal hovercraft. Waterproof and quite flexible, it I seemed to be able to agree. I embarked on the realization of the blown skirt. This fabric cannot that sew, each part has been cut and the shapes put in place on the template, then once adjusted, they were sewn. After, we had to cut the two hundred and twenty segments of the part bottom of the skirt. They were all assembled by sewing.

I re-cut 220 segments that I glued and sewn on an attached strip on the bottom of the skirt blown. That is to say that I glued the upper edge of the middle of the glove half, then using a wire passed in the tapered part on each side, I was hanging each side of the segment on the center of the blown skirt.

When it's done, you still have to make holes in the blown skirt to feed each segment. In taking the value of the surface feeding the blown skirt and dividing by 220, we obtain the surface of the feed hole of a segment. Not wanting to make too big holes, I chose to make three, more small, by half glove.

Using a multi-head cookie cutter, I drilled 660 small holes: three per segment - the most small behind, means on the side and large in front.

I glued the skirt and reworked the air outlets from the turbines to optimize the operation. This skirt being less "tonic" than the previous one, there was too much leakage between the segments. I added a point glue between each segment so that they remain well joined together. Last point of attention: it was necessary that the rear segments do not scoop water during movement.

I didn't want to do specific segments. I stuck a "bib" under the hull which comes to obstruct the half glove fingers under the pressure of the water. Made of skirt fabric, too, it has a shape trapezoidal and sticks to the bottom of the machine.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр



Front skirt at rest - we see the collage on the bar of the door

When I saw the result, I was happy. I didn't have the internal partitions, but the skirt fell like on the big one and the doors could function without worry.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Back of skirt - This is the right rear corner. We sees the blown skirt and the half glove fingers.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Template of a half-glove segment This is the developed form of a half glove. There are 220 under the blown skirt.

During the first tests, nothing worked. I had made holes to refill the cushion from the skirt, but that was not enough. I made some others, which improved the flight without solving the problems. The solution came from a former EDF (french electricity company) worker who knew a lot about fans. Putting four fans to blow in the same enclosure caused interferences. For him, there was a need of balancing between the four lift wells.

I resumed my tests by putting 1, then 2, then 3 motors running. It was good, the non-return valves were working, the machine was lifting. When turning on the fourth motor, the faulty behavior started again. I groped to find the right size of the outputs to the cushion and that of the deflectors.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр


Side view

We can clearly see the half glove fingers when the model is in operation.

Finally it was flying. I caught a few water bottles to load the Zubr. The 4 motors working, the air cushion can lift 8 kg. When I stopped them, the skirt made a black half cylinder all around. It seemed good except that the front door didn't want to lower completely : too much elasticity in the skirt fabric. I left this problem for later and worked on the central partitions instead.

It was a mistake. This forced me to make a lot of changes and cancel them later. In the end, I gave up. In operation we do not see the difference.

When stopped, the appearance of the skirt bothered me. It did not fall naturally on the ground as on the real one. On the other hand, it took too much power on both doors to overcome the elasticity of the skirt. I took the skirt apart and restarted from scratch with the K-way fabric that I used to seal the hinge.

First step : the dye made it pass from gray to brown-black. Second step : as this fabric sticks, I made a new template in pipe insulation tube. The K-way fabric sticks very well to itself with super glue. The skirt has been fitted on the form by collage. I sometimes used small strips to reinforce an angle or a weak point.


PROPULSION AND RADIO CONTROL - I thought I had a quick and simple job ahead of me. The propulsion motors had to be fitted, set up the radio control and connect everything. That is to say: put a speed variator by Speed ​​480, a switch for the lift, the steering control cables and those for the doors.

If the beginning was easy, I encountered difficulties of development.

The three Speed ​​480 motors are each mounted on a fiberglass mast. To stiffen everything, the three masts are connected together and the pushing force is taken up by an oblique leg which is supported on the hull. The four-bladed propellers were originally much too large for the Speed 480 and for the size of the model. Once mounted on a motor, each propeller was reduced to appropriate size : we start the motor, not too fast, and with a sandpaper or an electric file we use the tips of the blades. Going slowly is no problem. To respect the plan and diameters of the turbine casings, the propeller holder is mounted with a series of washers so as to move the propeller shaft as far away from the motor as possible. The motors are temporarily mounted with Serflex. The final supports must take into account the internal supports of the propeller bulbs.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр




View of the 7 motors : three Speed 480 and four speed 400 for a total power of 200 W


Homemade RC hovercraft - Zubr class - проекта 12322 Зубр


Top view with buoyancy foam

Each cell was filled with two-component polyurethane foam with closed cells, for buoyancy and rigidity



At this stage, each cell of the hull will be filled with two-component polyurethane foam to ensure rigidity finality of the assembly and its buoyancy. This foam has the particularity of not taking the water because of his cells closed.

The implantation of the radio control is done on a plate stuck directly on the foam between the four lift turbines, under what will be the island of Zubr, with the intention of trapping this place. In the rear, close enough to the propulsion motors, the three variable speed drives are put vertically to keep ventilation efficient. Just ahead, I put the current distribution. The Zubr is designed to operate with three 7.2-volt batteries: two for propulsion and one for sustenance. I did a parallel installation of the three motors and two batteries. Then I put on one line all switches: one per dimmer, plus that of the power supply radio control that I preferred to keep independent of the batteries. In the foam, the receiver, and in before the three servos. The one on the far left (in the background on the photo), a mechanical control of two lift switches. I did not dare to put four variators in parallel and, with only one variator for all motors, I no longer had the maximum motor speed. In the middle: the servo door control.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр


View of the layout of the servos

On the left the three variable speed drives, in the center the switches and receivers. Right, forward, the door, steering and servo control servos lift motors.

This servo controls a different cam system (two to be precise) to operate both doors. The difficulty came back from the lack of space to set up the mechanism and towards the back before the difference in axis between the door hinge and the skirt hinge.

The last servo controls three cables for the three steering fins. At this point, I have them simply mounted without connecting them. The steering fins being part of the superstructures, their realization will be done later.

The three batteries are provided at the front to balance the weight. Their final fixing will not take place only at the end, when their ideal position has been defined during the last attempts to adjust the attitude of the Zubr. I have provided a support that will allow you to adjust their place without having to make an additional trap.

After many static tests to settle on the one hand the motor thrust centers (easy), and on the other hand door openings (with great difficulty), the big day has finally arrived. Three full batteries, new batteries and...

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

To steer it, you have to play on the three propulsion motors.

On the right stick of the radio, I put the motors right and left. On the left stick, I put the central motor and the steering. Without the fins, the Zubr heads easily thanks to the motors. At full speed, the ailerons will steer it without losing any thrust.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр



Radio control diagram

One beautiful September evening, we found at the water's edge. Some tests static to check the orders and then I deposits the Zubr in the water. Of course, the plate is not not horizontal and after a short turn on the water, I brought it back to the edge to rebalance in moving the batteries. Separate control of the three motors makes the Zubr hypermaniable forward like back. Although not bodied, without its propeller bulbs and its steering fins, we estimated its speed at 25-27 km / h at peak.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Water test - if the steering fins are not mounted, that doesn't stop him from behaving like the real one.


Contract fulfilled for my part ! Now with Didier my teammate, we're going to tackle superstructures. And there it was another funny story...

SUPERSTRUCTURES - From now on I pass the pen to Didier. He did considerable work with thoroughness and patience that I admire. The first fundamental thing is to put yourself in the shoes of a pilot hovercraft. This helps to understand and take into account the important differences between the construction of a boat and that of a hovercraft, in particular in terms of weight. It’s not easy.

According to the information available, photos and plans, it was necessary to review the dimensions, point always delicate because the plans are not necessarily on a constant scale. So I opted for a structure in balsa and firstly for using the 0.75mm thick plastic for the decks.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр



Balsa structure - balsa cleats (10x10) are glued and embedded in neoprene in the expanded foam base from the bottom of hull. We guess a beginning of form.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр




The plastic deck - First try for the deck as well as for motor supports : cerflex type collar.

It was a mistake. The plastic card used without problem for small parts on mockups is not a good solution for a large boat. A thickness of 1mm, even 2mm, but in this case the weight of the whole would have been too important. The decks are finished at 95% plastic card, I went back and the whole main deck was rebuilt. For avoid deformation of the deck, the plastic has been reinforced with a balsa base (light structure).

The structure remains unchanged. It is made of balsa batten (10x10) glued and embedded in neoprene in the expanded foam base from the bottom of the hull. On these "pillars" we have glued the sleepers balsa to make the shapes of the deck.

The upper deck is now made of 0.75mm thick plastic card plate, and, by top, 1mm thick balsa baking sheet.

All sanded, sanded and re sanded to obtain a correct surface. The vertical parts and the deck of on each side of the boat will still be in 0.75mm plastic.

The lifting motors were protected during sanding and painting. The edge of these motors was made of Miliput, sanded and re sanded to obtain a smooth shape and facilitate the flow of air. Now you have to make the protection grids of these motors.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

The final deck - a plastic / balsa sandwich, light and solid. The vertical parts and the sides are in map 0.75 plastic

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Motor support - the first collars were sufficient for tests but did not authorize the assembly of the nozzles. He has it took several versions to have a satisfactory one.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Nozzles - including all tests and broken during production, there are about twenty nozzles that have been started!

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PROPULSION - This is a big dilemma. To have a correct set (boat motors), the motor supports must be reviewed. Always taking into account the weight of these supports. After different tests, I opted for aluminum supports. The motor chairs are under construction.

For the nozzles, the choice was very difficult. Between Balsa, or synthetic foam! For greater flexibility and great lightness, so I chose synthetic foam. A big rough draft then adjustment was carried out to obtain the correct shapes. This very light synthetic foam caused me a lot of problems. The first nozzle, almost finished, broke during sanding.

To avoid this problem again, I therefore covered with syntofer the surface of the nozzles and the sanding this is done in small passes (very long I grant it).


THE COMEBACK - I gave the Zubr to Didier in 2006. The first months went well and the superstructures were started to go up. Also taking care of my larger hovercrafts, I trusted my colleague to continue. Unfortunately the vagaries of life have not allowed him to progress. Sometimes we crossed paths and he reassured me by promising to do it next month.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Motors - 2009

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

The island - 2012

For my part, I made a first 1 seater hovercraft for the "Raid Rhône" and then I made another one with two motors. After that, finding some free time, I got back in touch with Didier who had advanced slowly but the machine was still not finished. As his work didn't let him enough time, I got the Zubr back.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр
Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

If the island and the front attachments are well done, it lacks a lot of details.

  • Railings and grids of the lift motors are missing

  • Propulsion motors are not functional

  • The control surfaces are blocked for reasons of ease of construction.

  • The skirt suffered from not being used: I see loosening between the pieces.

  • The rear door is under construction but not assembled.

When I lift the Zubr, I discover a really heavy weight. If a hovercraft goes on water, its construction is similar to that of an airplane : weight is an enemy. On the balance, it weighs 8 kg, but it should not exceed 6 kg to respect reality. To gain weight, I will remove material. The superstructures cannot be dismantled, so I decided to work from the underside.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр


First step : repair the skirt and check its good functioning.

Second step: open the hull by cutting the bottom.

Fortunately, I kept photos from 2003. I can incise without taking too much risk. I'm going to cut two long strips and take out all the accessible buoyancy foam. I will replace it with bubbles of air used to wedge fragile objects. The hatches on the top do not give access to the entire radio control. I'm going to take advantage of the site to relocate it.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр


Picture : opened hull



Third step: redo the layout of the various servos.

There are the three propulsion controllers, the steering, the two doors, the lift. In 2003 I used 3 NiCd batteries. Today, LiPo is here. I will take advantage of it to lower the weight.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр


DOORS AND STIRING


Once the bottom was opened, I removed everything I could remove. Bulkheads and buoyancy foam which will replaced by packaging bubbles. There is still a lot of void inside, and elements on the right and left like servos, motor drives and radio control.

To begin with, I’m interested in rudders. They are fixed and it is not satisfactory. On the real they are in 3 parts, one fixed and two mobile. After unsuccessful attempts to try to make planes drifts, I do a search on my favorite site and I find the principle of the Becker rudder in the article on rudder control. It remains to adapt this to my personal use.

After several plans and sketches I make a first draft which turns out to meet my needs.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

The study of a two-fold rudder

I’ll take inspiration from Laurent’s article and make them cardboard, with line orders.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

The three steering flaps, made of recycled cardboard

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр




The control wire comes out of the small plastic tube

In this photo the shutters are still fixed but I already have past the ropes. To do this I will use sewing thread which I use to repair the skirts of large hovercraft. he is very solid and goes very well in the small tube plastic. I put one on port and one on starboard and I connects the three components by a common line. The servo will thus always work in traction. I will fix the servo very forward for reasons of weight and add tensioners on my son. They are very simple since a true copy of those used for the tents ropes ...

Then begins a long phase of adjustments. The value of tensions is very important for everything works well, as well as the point of application of these voltages. I had to take it several times the hooks on the outside of the port flap to obtain satisfactory operation.

The back door: as the cardboard collected from the pharmacist gave me satisfaction (one side is I will use it for the back door. I make a sandwich to get the thickness and shape desired. I add a rod control and I fix everything on a hinge made of a piece of skirt fabrics. The result is immediately satisfactory. I’ll just have to adjust the travel when the front door will be made since I want a single order for both doors.

The front door: the construction of the front door is much more difficult. First difficulty: the bar holding the skirt is broken. Second difficulty: the waterproofing fabric between the skirt and the hull has been painted and didn't support it. It will tear during one of my attempts to repair the bar hold before. I live this as a disaster. Without this fabric, the skirt is non-functional and the Zubr becomes a static model!

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр



Then begins a difficult disassembly of all this part skirt but luck is with me. The black skirt goes withstand takeoff without tearing. After a day of work, I finally see the hull and I can repair the bar before and put back a new cloth (luckily, I was staying!)

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр


The hinge: the old control having disappeared with repair, I'm going to have to rethink the whole door hinge. With the superstructures, I have more access to strategic places. This complicates the In several tests, I develop a double hinge with differential control. She is not entirely in accordance with the original but is more beautiful effect. Having a significant documentation on the Zubr, I keep comparing the small and large.

Zubr class hovercraft - проекта 12322 Зубр

I fall for the chains that support the door real Zubr. In reality, the doors are controlled by cylinders, the chains are in rescue. I decide to add them on the models.

On the first try, they get stuck by blocking the doors. The solution: make them functional.

With old cable sheaths and skirt wire, I make chain paths which will end on an extended arm of the servomotor.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр



We see the tensioners identical to those of control surfaces.

A few adjustments later, I’m happy to see everything working.

VEHICLES AND MOTOR HOODS - The ferrules: Didier's ferrules are very beautiful but at the rate of 115g / piece, the Zubr is left with a rear overweight. Unlike boats that need ballast to be balanced, the hovercraft to fly must remain fairly light with well distributed masses. I will try different techniques to make them lighter. After testing with hot-formed polypropylene, I give up.

I can't seem to have the correct adjustments or the rigidity I need. Of course it's light but impossible to reproduce the different parts reliably. The memory of molds made of paper chewed leads me to try a model. He is obviously missed.

Yet I feel the potential. It's light and with two crossed thicknesses, the rigidity is there. I speak about it around me and a friend brings me back some glue that she uses at her school. The paper glued with varnish glue will prove to be the easiest to use. After a few attempts to develop the technique, I arrived at a 36g ferrule including the inner cardboard reinforcement circle.

The icing on the cake, I manage to make three identical with a few details. Adjustment to propellers is not so good. Added to the thickness of the paper. I will resume their diameter later when I paste the interior uprights. Before that I will launch out in the realization of the nacelles of the motors.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр



The motor nacelles

Again, I will pass a lot of time figuring out a way to do them. My enemy is the weight on the back. Paper models glued to varnish require an internal structure which makes them too heavy. The sculpted foam models are prettier but still too heavy.

I'm going to make a polypropylene molding of a bottle. They have almost the desired shape and the plastic shrinks well when hot. I have never drunk as much bubble water as I did at that time!

So I manage to make a dozen models. Unfortunately the bottles are either too small to that I have both the front and back well molded, is too large and does not shrink enough. I go make an assembly between a well molded front and a conforming rear. The technique is simple: I used one of the foam models to put in the bottle.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр



The three front pods

Before joining the two parts, I make the air intakes that I want functional to cool the motors. The closure will be done with paper and glue varnish. For the guardrails, I used the same wire only for the control surfaces.

I glued it with glue varnish. Once stiffened, I got it placed with a drop of resin which polymerizes UV, soliq type.

In view of some achievements on Navimodélisme, I still have a lot to learn: my level of finish is insufficient. At this point, I test the motors and they respond perfectly.

Like on the real one I make ferrule supports in underneath, then I glue the ferrules in their place by wedging the propellers all around to have the correct centering.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр
Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Lower ferrule support

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Last step, the internal stiffeners: They are made thin corrugated cardboard, open in half at both ends to improve support.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

View of the rectifiers

When everything is dry, new conclusive tests. The propellers rotate without touching anything.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Hot molding: random

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Bonded paper ferrule: 36 grams

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Manufacturing of nacelles - foam nacelle form

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Shaped gondola

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Before nacelle and ferrule test

First tests: of course some problems with the radio control which has been stored for too long. I will have to change the battery holder which only holds thanks to the repair tape. Still with duct tape, I close the bottom and make a first test "for real" on my terrace.

The result is mixed: It takes off and advances but the rear is still too heavy. Back to the workshop where after taking off the skirt I will again remove foam on the back. The Zubr thus loses 150 g. Once everything is closed, I weigh it: I reach 6 kg in working order, including battery.

New tests. The balance is better. After adjusting the battery position, because it leans too much to port, it is now going straight and maneuveurs correctly. But the rear remains too heavy. Therefore I have, unfortunately, to add weight at the front. I try with 150 g then 300g. On land, the addition of 300 g at the bow level balances well and makes it handy... if we can say that for tests made in a too small space for such a big model.


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THE ZUBR: BEFORE & AFTER

Rear : on the first photo, I already dug the upper openings and I stuck behind a cover in cardboard, then I glued small bars made of black wire coated with glue. All the details will be in cardboard of different thicknesses glued and coated with this varnish-glue of which I have already spoken. From either side, we see the (closed) exhaust outlets of the lift turbines. In front of each exit a small platform supported by brackets. On the biased edges, we see the rungs made of staples. We drill the holes with a template and glue with Soliq which has the advantage of taking immediately that we put the UV lamp.

The pedestrian door is like all doors : in cardboard highlighted by pressure on a model and I glued hinges and drilled the porthole which will be painted black.

The vehicle carrier is driven by a cable and, as before, receives two channels for decoration. The bottom is closed with cardboard. On the outside, the documentation shows some details that I add, like this circle whose usefulness I do not know well. All around various small “legs”, “hooks” that I can find in the photos, are symbolized by small pieces of cardboard which will take on the color of the superstructure when painting.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр
Homemade RC hovercraft - Zubr class - проекта 12322 Зубр
Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

The front is going to be overhauled. On the documentation, the hinge bar fits into the superstructure. I start by remodeling on both sides of the door the slopes of the bow using compensators and I dress the metal bar by covering the fabric so that I can paint it.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

The door is clad in several thicknesses of cardboard, the last of which is engraved. The top shows the cutouts of the moving parts of the door. On two levels, I will make the series of holes that exist on the door before gluing this part. Finally I will put the two square headlights but without equipping them with light and I'm going to use a photo box cover to make the chain well where I will stick a fake anchor.

Overview : If we compare the side port with starboard, we notice differences. There are two doors further in front of the air intake of the turbine, hatches and plates which don't exist on the other side.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр
Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

I will use the same technique to achieve all the details. There are also two recesses. The first in front is used to put the containers of the emergency boats for the 27 men crew. I will put them in place at the end. The rear overhang which was too deep has been resumed, but since I have no documentation on what it can contain, I will leave it blank.

Little Zubr starts to look like actually to a Zubr, which complicates seriously his travels.

Impossible to carry it easily without damage a piece of railing or a detail. You should be able to wear it while lifting. I remember one of the RC Navimodelism articles. We see a strap system to put on water boats. Unfortunately the width of the Zubr makes this system little convenient. I owe it to the Chinese to find the solution ! On the video they are going to post on the net to welcome the delivery of their first Zubr, we see the hovercraft loading on a freighter. This is exactly what I need. So I'll make the four hooks on the deck functional.

For this, I will pierce the deck and go look for the hull structure to fix steel bars ending in a covered loop on both sides of cardboard cheeks. The most delicate will be to put the Zubr on the back to peel off the bottom strips so to put them in place. During the tests, it’s much more effective.

Zubr class - проекта 12322 Зубр

I do not own this image, all rights and credit to its owner - original here

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр
Homemade RC hovercraft - Zubr class - проекта 12322 Зубр
Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Details : when I got the Zubr back, it's beautiful but lacks details that gives it life. Unfortunately, l have no experience with this. I get started, learning by doing.

Always coming back to my documentation, I notice that there are several Zubr whose details vary. At the sight of the island, it cannot be one of the models sold to China, it is on the other hand compatible with one of the four Greek Zubr. But as it was done in the USSR, I ended up choosing the model : it will be N°782 “MORDOVIA”, built in 1991 by Primorsky Shipyard in Saint-Petersburg, and based in the Baltic. On the front view, we see that the machine guns are out of place, I’ll talk about that later. By scrutinizing all the photos, I will pierce the sides to simulate the portholes which will be underlined with a little protection, then make the doors as in the back with cardboard thicknesses shaped on a mold. The two scales are made of glued staples at the Soliq. We also see double mooring bittes made of criterium body with a pin for make the horizontal bar and fairleads carved from a piece of plastic. Various hatches, and openings are glued or dug. They will be painted later.

I add the stairs on the falling side. I take this opportunity to rearrange the front a little by sticking a partition to improve the congruence between the hull and the skirt. Finally, I drill forty holes to receive the candlesticks on which I will stick stiff wire to the glue to simulate the cables of guardrails. To improve the finish, I will put two details above each door, a circle for simulate what could be a bell and a light (unfortunately not functional) composed of a small white tube stuck on a cardboard square. At the back, there is a fairly generous shape made of a half-round. Like the rest, it's cardboard. This represents the air intake of the turbine. On the Mordovia, it is wide and unique, on other models, there are two smaller.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр
Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

On the top, there is a plethora of details and unfortunately some faults. Yes we play the game of the 7 differences between the two images, we especially notice the rocket launch tubes, the shooting station and the central island.

My friend used the two AK 630 machine guns to hold the front inspection hatch. In reality these two units are on the side hovercraft and smaller. I go so start there. By taking off bases, the cover breaks.

I will do it again in cardboard on stiffeners. I decrease the height of the bases, the height of the supports of the turrets taking over what exists. For turrets and multi-tube guns, I will redo them in hard foam that I will stretch to have a correct finish. Multitub cannons are sheaths of control cables. In the middle, the outdoor shooting station, with its sight, will reuse elements recovered on the basis of AK 630, like the ladder, and to be completed with cardboard elements.

Thanks to a report recently discovered on the net, I obtained more precise documents on these retractable units. They came back in current navigation and to be loaded. They went out time of use. I find that they "Dress" well in front, so I decide to do more than the platforms on deck. First problem, I can't find a good tube plastic diameter. Rocket launch tubes will be made entirely of paper. On a mandrel I rolled each tube and coated it with varnish glue. Once mounted in battery, I did the supports and the cover.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр




Detailed view of the left rocket launcher (not painted yet)

While it dries, I do the details of the deck. The vents are made of pieces of tubing topped with a sculpted foam cover. Fairleads and other mooring bittes are made of plastic. The base of the capstan will use a piece of plug from a tube of glue. The rest will be assembled with different pieces of plastic recovered.

Last modification: by taking profile pictures of my little Zubr and comparing them with the true, I am aware of an anomaly in the position of the island. He is too far back. I will resume all the electronics and make a cardboard base for the island by lengthening the back to hide the openings. This rebalances the silhouette and the weight of the machine. We will have to resume balancing but it will be after the paints.


THE END OF THE STORY - The Zubr is now complete. It received all the necessary equipment, but we can guess the various boxes that I used to make them.

To paint it, I disassembled the propellers and closed the holes in the lift shafts, then I surrounded the whole skirt with paper. I used a car paint that my friend had used before: from MOTIP brand, this paint provides color stability. Just order the same number to be guaranteed to get the same shade.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Before painting - side view

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Painting (skirt is protected)

The front hatch and the island will be painted separately. The cylinders which represent the survival channels will be painted white. I'm also going to need black and of red. For this, I will buy touch-up pens for car paint.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Side view - skirt not inflated

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Detailed view of the island

I'm going to add small details. The lifebuoys are made of coated cardboard. There are four that will be fixed with Soliq. The stars and the Russian Navy flag come from images got on the internet. I printed them on the right scale before gluing them. I painted black all the interior of the portholes, the ladders edges, guns, and hardware details.

We can see that the island is further forward. The silhouette is thus more balanced. The numbers are printed on clear plastic. Only the silhouette is printed in black. White is painted on the back side which is glued.

On this view of the deck we see Didier's work with this superb finish that I do not get again. He used plastic card and balsa. The guardrails are also made of the same material, stuck to the superglue. The scales are mid staples sunk into the balsa. I added the star, the plate with name and buoy.

Finally comes the time for testing : a good weather day without wind, we left for a small pond, with the Mordovia in its box, placed on a support that allows the skirt not to be folded. Above the bow there is a shelf for the radio control and accessories.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

For transport, the model is held in place by large packaging bubbles. I had not thought about transport when making the calculations. The box barely fits into my car !

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

The Zubr on its ramp

After this first test, the battery was pushed backwards to give Mordovia a better balance. The very old radio control was replaced by a new one to avoid disturbances (you can see on the videos the rear door opening/closing by itself and the patchy skirt inflation).

To conclude this 10 years story, I will say that I learned a lot. For the next model, I will try to do what I didn't do on the Zubr : lights or radar animations to make it more realistic.

Homemade RC hovercraft - Zubr class - проекта 12322 Зубр

Model exhibition in France - October 2019

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