1/3rd Scale Mita Type 3 Production Notes
The tenth part of a twelve part series.
You may want to read the ninth part of this series before proceeding to this article. Also if you prefer, you can read this article in its original Japanese.
Fabrication Part 45: Canopy Frame
Canopy Frame of Mita Type 3 Revision 1
Drawing 55 showed the canopy of this plane. The frame of the forward canopy is made up of two circular frames, one touching the nose cowling and the other touching the rear canopy, connected at the bottom by two longitudinal timbers running back and forth. The front frame is perpendicular to the bottom, while the rear one is slightly inclined to the rear. The bottom side bars are not straight, but kinked about 2/3 of the way from the front.
The bottom side bars are 15 mm high at the front and about 30 mm at the rear. The cross-sectional shape of the canopy is semicircular at the front, but the lower part at the rear is flat. The position of this change is shown in drawing 58.
The rear canopy frame also has the shape of two frames connected by two longitudinal rails, but the big feature is that the longitudinal rails hold the main wing (See drawing 55). As a result, it has an extremely complicated shape. In particular, the longitudinal material in contact with the upper surface of the main wing has a complicated shape, with a wing shape when viewed from the side and a tapered shape that narrows at the rear when viewed from above, and a cross section that matches the semicircle shape of the canopy.
Fabrication of the Frames
The first step was to make the frames. Since they are thin, I was concerned that they might break. I prepared two pieces of 4 mm thick plywood, pasted them together with the grain orthogonal to each other, and cut it out with the actual size by pasting the drawing on it.
The parts running horizontally at the bottom of the frames are temporally left to prevent the frames from being broken by unintentional force during the fabrication process. They are cut out after the transparent part is attached. I learned this tip in the process of making 1/5 models.
The center two pieces are the front and rear frames, and have nearly the same shape. I put them together so that the contact parts are flush with each other and prepared the outline.
Since the cross-sectional shape changes slightly due to the thickness of the circular frames, I pasted actual size drawings at three locations: front, center, and rear, and shaped them.
Assembly of the Front Frame
The front frame bases are made of laminated paulownia wood, which is easy to work and has adequate rigidity. Two pieces of wood on each side were combined because of the kink in the middle. In order to assemble the frame, an assembly jig is necessary to attach the vertical frames at an accurate angle to the non-parallel base. I made the jig shown in the Photo 224 and assembled the front frame.
Rear Canopy Frame Assembly
As the longitudinal members of the rear frame located under the main wing is a flat shape, I cut it out from two pieces of 4mm thick plywood and attached it.
The problem is the longitudinal members located on the upper surface of the main wing. It was difficult to find the exact shape. First, I drew the intersection line with the main wing.
I cut out the approximate shape from 12mm thick laminated paulownia wood, make a cut to match the contour of the upper surface of the main wing, place it on the main wing, and shape it along the intersection line as shown above. This will determine the shape of the lower outer part of the longitudinal members. After making two of these, I attached the frames to the front and rear.
Next, a jig with the outer contour of the longitudinal members is made and placed on the assembled frame to shape the contour of the members.
Now the contour of the longitudinal members are set. The rest of the work was done by cutting and shaping along the contour, leaving the height and thickness of the members.
Completed Canopy Frame
Photo 226 is the completed canopy frame. It is quite large.
I put it on the fuselage.
The rear canopy is positioned in front of the center wing fairing with two pins. There are two holes visible in the center of the front fittings of the center wing fairing (Photo 228).
Problems Encountered
I managed to build the canopy frame with a lot of effort, but I encountered
some defects along the way, and it took me a while to fix them.
Defect #1: Gap between Forward Frame and the Nose Cowling
There was about a 2 mm gap between the nose cowling and the top of the canopy frame. The frame of the forward canopy frame was precisely aligned with the design angle using the assembly jig, but the nose cowling was installed without a jig. I think the cowling was installed with the nose slightly lowered because of this.
I put a piece of wood between the gap and attached it to the wooden frame of the cowling.
Defect #2: Gap between the Bases of the Front Frame and Fuselage Structure
When the front frame was placed on the fuselage, a gap of about 1.5 mm was found between the rear of the longitudinal bases of the frame and the fuselage structure. The frame was assembled on the assembly jig in such a way that the bottom surface is exactly flat. However, for the corresponding part of the fuselage, it was necessary to assemble two carbon pipes bent in a shallow “V” shape, about 200mm apart, in a flat manner, but I could not find an appropriate way to ensure the flatness, so I assembled the frame in a rather rough manner.
I put a piece of wood on the bottom of the longitudinal bases of the frame to fill the gap.
Defect #3: Gap between the Rear Frame and the Center Wing Fairing
A slight gap was found between the rear frame and the right front side of the center wing fairing. It turned out that the center wing fairing was attached with a slight deflection to the right. On its own, the fairing deflection is unnoticeable. This was due to the fact that the aluminum channel supporting the rear of the fairing was not exactly perpendicular to the aircraft axis because the fuselage structure of the truss assembly has no discernible centerline, making it very difficult to install at a right angle.
I removed and reattached the channel.
Defect #4: Gap between the Rear Canopy and the Center Wing
The front part of the center wing that covers the fuselage is cut to form a cabin. On the other hand, the rear of the canopy is tapered and is narrower than the front. Because of this, the cutted width of the center wing is wider than the width of the rear part of the canopy frame, and there is a little gap when viewed from above (See Drawing 59). I designed the cutting width of the center wing by looking at the fuselage structure, but I didn’t realize that the canopy width was narrower than that. When I looked at the drawing of the actual aircraft again, I found that the cutting of the center wing was not parallel as in my drawing but tapered to fit the canopy.
I will cover this part later by pasting the filler wood on the center wing side.
Most of the problems were caused by working without jigs. I should have used more jigs.
Hinges and locking mechanisms still need to be fabricated before the frame is completed.
Production Part 46: Painting of Fuselage Truss Structure
Paint Color of the Structure of the Mita Type 3
The steel pipe truss structure of the actual aircraft is painted with zinc chloride to prevent corrosion, which is the original color. However, the JA2103 on display at the Shizuoka Aviation Museum is white. This is because Mr. Kimura, the original owner, painted it white while it was in his storage.
Since the 1/3 model that I am making is based on this JA2103, the seat pillars and other parts that have already been made are painted white. So I decided to paint the carbon pipe fuselage truss structure in matte white.
Painted Fuselage Structure
Photo 229 shows the fuselage structure after painting. Three spray cans were needed.
The white color makes the fuselage look smaller than the black color of carbon.
The weight of the fuselage was measured to be 1,542g. All legs and servos are removed.
Mr. Takamura Provided Me Metal Cutting Parts
I asked a fellow club member, Mr. Takamura, who is good at metal processing, cut some metal parts for me. He has a mini lathe, so I often ask him to cut some parts that I can not make without the lathe.
1) Motor Shaft Collar
The FUTABA FMA-5065 motor is designed to drive an airplane propeller, and the included propeller adapter has a Φ8 shaft on a Φ29 base. The propeller is pressed against the base and tightened with a Φ8 nut.
If I was to install the folded propeller using this adapter as is, the base of the Φ29 propeller adapter would have to pop out of the nose cowling. This would be too awkward, and the short distance between the motor and the base would cause the motor to hit the tapered cowling. So, I decided to put a collar of appropriate thickness in front of the base and make that part stick out from the cowling to attach the propeller. This is the drawing.
For this reason, a propeller shaft collar was needed, and it was machined from aluminum. Photo 230 is a magnified view of the collar installed on the motor. This will allow me to install the folded propeller neatly.
2) Instrument Case
All instruments of the Mita Type 3 are round. The size of the instruments on the actual machine are two types, Φ72 and Φ53. In order to make instruments that mimic these, round cases are needed, so I had them machined out of aluminum. There are four large ones and two small ones for the front seat, and two large ones for the rear seat.
The ones for the front seat are made very thin to save weight, since the back of the instrument panel will not be visible, but the ones for the rear seat are mounted naked near the center of the cockpit, so the entire instrument can be seen. For this reason, I had it cut down to a suitable length. Each case is made of two parts, the main body and the top cover, and they are fitted together. When opened, it looks like Photo 231.
The left sides are the main bodies and the right sides are the top lids. The top lids have a flange on the top. The body is lightly machined and the printed scale will be attached there. There is a small gap between the flange of the top lid and the body. I plan to put a transparent plate between them for the appearance of a glass. Once finished, they will be painted in matte black and attached to the instrument panel with fine screws of 1.4mm diameter.
3) Turnbuckle
The turnbuckle that I asked him to make this time is the one that is placed between the tow rope release mechanism and the servo that operates it. The turnbuckle is made from a thin brass rod with a diameter of 3mm. The turnbuckle is small, but when disassembled, it consists of three parts as shown here.
One side is threaded right-hand and the other side is threaded left-hand, and turning the middle part will extend and retract the left and right rods.
The turnbuckles made from a larger brass rod with a diameter of 5 mm have already been installed in the rudder and elevator control system. Now I have all the metal parts I was worried about.
Fabrication Part 47: Canopy Accessories
Canopy Accessories
The canopy has the following four accessories:
- Hinge: This is the fulcrum for opening and closing the canopy. It is located on the right side of the canopy frame.
- Locking Mechanism: A locking mechanism to prevent the canopy from being opened accidentally. It is located on the left side of the frame.
- Canopy Opening Holding Mechanism: This mechanism holds the canopy from falling too far to the opposite side when it is opened.
- Rear Canopy Fixing Mechanism: This is a mechanism to fix the fixed rear canopy.
These parts were made and attached to the canopy frame and fuselage structure.
Installation View of the Accessories
This is a picture showing the overall installation of the completed canopy accessories.
1) Hinges
Hinges are mounted in two locations on the right side of the frame, front and rear.
The hinges are a brass stay attached to the fuselage frame, with a 2 mm diameter piano wire soldered to it. On the other hand, the canopy side has an L-shaped brass stay attached to the outer side of the frame, and a 2mm inner diameter brass pipe at the end of the stay. Attach the canopy from the rear by inserting the piano wire through the brass pipe.
2) Lock Mechanism
Photo 235 shows the locking mechanism. It is attached to the inside of the left frame and slides back and forth.
When the spheres attached to both ends of the mechanism are pushed forward with the front or rear seats, the mechanism slides and locks into place. To unlock, pull the spheres backward. The center of the sliding mechanism is as shown in photo 236.
The tip of the piano wire goes in and out between the conduit attached to the fuselage side. The photo shows a locked state, and the white part is the conduit. The fuselage side conduit is attached to the left side longitudinal material as shown in photo 237.
Up to this point, the mechanism is the same as that of the actual aircraft, but this lever, which is not found in the actual aircraft, is installed.
This is a thin plate lever connected to the sliding mechanism, and it appears on the left-outside of the fuselage. This is for operating the mechanism from outside the aircraft. In the real aircraft, the sliding mechanism is operated by opening a small window of the canopy and inserting your hand into the cabin. This mechanism was installed because the model does not allow access to the sliding mechanism through the small window.
3) Holding Mechanism When the Canopy Is Open
When the canopy is opened, the weight of the canopy causes it to open too far and collide with the side of the aircraft. This is why there is a retaining mechanism to prevent this from happening. The retaining mechanism is a simple wire connection between the three parts of the canopy and the fuselage. This is the situation when the canopy is opened and held.
The pipe structure is not only for attaching the wire, but it is presumably also for opening and closing the canopy. In this photo, you can also see the lever to operate the lock from outside the aircraft.
4) Rear Canopy Attachment Mechanism
The rear canopy, which does not open or close, has its trailing edge inserted into the hole in the center wing fairing with a pin, while the forward part is screwed to the fuselage structure with hardware attached to the bottom of the frame. Currently, there is a dummy bar running across the bottom of the frame, so the fittings will be installed only after the canopy is completed. However, I have prepared the fuselage side to receive the fittings by attaching 3mm nut receivers.
Now all the canopy accessories are ready.
Tail Fairing Made by the Vacuum Process
I had been wondering what to do about the tail wing fairing since I failed to make its plaster mold. But when I consulted with Mr. Toyama, who is a master of the vacuum manufacturing method and is now making the canopy transparent for me, he agreed to try the vacuum manufacturing method if I send him the wood mold.
Tail Wing Fairing Made by Vacuum Process
The wooden mold I made was for plaster mold making and was made of balsa. Therefore, I was worried about whether it would be able to withstand the vacuum process, which applies quite a lot of pressure, but Mr. Toyama reinforced it. This is the tail wing fairing made by the vacuum process using the wooden mold.
The 0.5 mm thick PVC I had assumed was not rigid enough, so he also made 0.7 mm and 1 mm thick ones. The part extending to the lower part at the rear seemed to have a hard time to extend properly, so he took a measure to increase the slope of the boundary between the vertical and horizontal tail wings. This seems to be the know-how of many years of experience in vacuum manufacturing.
Fit Check
The fairing will cover this part of the vertical/horizontal tailplane intersection (Photo 242). It should fit on both tail fins.
I immediately cut out the required shape and did a fit check. First is the horizontal tail fin.
It fits perfectly. Next is the vertical tail fin.
There is a gap on the right side due to the spring back. However, this is not a problem because it can be fixed by the way the fairing is installed.
Installation
In the end, I found that 1mm thickness was good enough to ensure sufficient rigidity. I painted it and installed it immediately. The paint is matte white, the same as the fuselage.
Now the tail wing fairing, which I was wondering what to do after the plaster mold was broken, is completed.
Model Checking of the Small Canopy Windows
Small Canopy Windows of the Mita
There are two small windows on the canopy of the Mita Type 3 glider for ventilation. The drawing looks like this.
The small windows are sliding type and are installed on the left side of the front seat and the right side of the rear seat. The front seat’s small window slides backward, and the one for the rear seat slides forward to open.
In my 1/5 scale model, I put printed stickers on the canopy, but in this 1/3 scale model, I wanted to reproduce this part. However, the small windows must slide inside the canopy when it is opened, and its outer surface must match the outer surface of the canopy when it is closed. I was not sure if it was possible to make such a mechanism with a 1/3 scale model, so I made a model to check.
Confirmation Model
Here is the drawing of the confirmation model.
This is a model made based on this drawing.
In the 1/3 model, the size of the hole for the small window is 41.6 mm (length) x 60.0 mm (width), so I cut out a 1 mm PVC board as if it were a canopy, and cut it to the size of the small window. Originally, I wanted to make a curved surface like the canopy, but I made it flat this time for ease.
Around the cut window, I attached a window frame made of the same 1 mm thick PVC board. The window frame is 2.1mm larger than the window itself, and this part serves as a sliding part as well as a support to keep the window from coming off when it is closed. Two knobs made of round bars are attached to the window. Originally, the knobs were made of transparent acrylic round bars, but since I didn’t have any suitable ones at hand, I used wooden ones instead.
The rails are made of 3mm x 3mm acrylic square bar and 1mm thick PVC board cut out to 7.2mm width and pasted on. I made two of these and attached them to the top and bottom of the window holes on the board that look like a canopy. Originally, I should have used a special adhesive to attach them neatly, but I used CA adhesive to attach them for the purpose of checking the function, and the adhesive flowed out and made a mess.
Function Check
Slide the small window inward to open the window, and then slide it to the other side to see if the small window pops out and is flush when it matches the window hole in the canopy. This is the point to check. The rail width is 3 mm, the small window is 2 mm thick together with the window frame, and the window frame is 1 mm thick, so it can be opened smoothly if nothing is done, but of course the window will not pop out when it is closed.
So first, I put a sponge gap seal on the outside of the window frame where it meets the rail. The thickness of the seal is about 5mm. After fitting the window into the rail while crushing the sponge, opening and closing the window is a little tight, but somehow possible. Furthermore, when the window is aligned with the window hole, the sponge is released and the window pops out nicely. Thus, I was able to confirm that this method also works. The problem is that the sponge is not beautiful.
Next, I replaced the sponge with a thin sheet of aluminum, curved and attached. Photo 247 shows the condition.
I was worried that the thin aluminum sheet would have too little spring effect to work, but the window popped out when the window closed. It looks like I can get away with this method.
Conclusion
There are many possible ways to make the window pop out, but it seems to be possible. However, it seems to be quite difficult to attach the rails to the canopy with the correct rail width. There are many examples of screwed rails. That seems to be a more reliable and neat way to attach the rails.
Fabrication Part 48: Electrical Wiring and Weight and Balance Check
After installing the receiver, servos, motor, amplifier, power supply for the receiver, etc. and wiring the electrical components, attaching the seats and cowling, I checked the weight and the center of gravity.
Electrical Wiring
After installing the motor, I mounted the amplifier and the receiver power supply on the top panel inside the nose cowling as shown in the drawing, but it turned out that the wiring for the 100A amplifier was too thick and the wiring between the motor and the amplifier was unexpectedly long, so there was no space for it. Therefore, I decided to mount the amplifier on the back side of the top panel. Photo 248 shows the mounting situation.
The long wires between the amplifier and the motor were adjusted by running them over the top panel. The receiver was initially intended to be installed under the front seat, and I had completed its wiring. However, after installing the front seats, I found that the receiver and the seat board were touching. So I changed it to under the rear seat floorboard. The receiver is a FUTABA R3008SB (Photo 249).
The power supply S/W for the receiver and its charging port were unexpectedly troublesome, as the cord attached to the S/W was too long. Initially, the S/W was mounted on the instrument panel same as in the 1/5 model, but the cord extending from the S/W did not fit neatly. So, by mounting the S/W and charging port on the floorboard of the front seat, I was able to fit it neatly (Photo 250).
The thick cord and connector beside it is the wiring for the power supply. There is no way to hide this. It may look ugly, but considering the ease of handling, this is how it is done.
Photo 251 is the state where the wiring is finished, and the seats, cowling, etc. are installed.
I was able to install the wirings to the servos, etc. were almost hidden.
Since the receiver FUTABA R3008SB has 8 channels, I was planning to allocate 2 channels to the left and right ailerons, 2 channels to the elevator and rudder, 2 channels to the left and right spoilers, 1 channel to the motor, and 1 channel to the tow rope release, for a total of 8 channels. However, when I read the instruction manual carefully, I found that I could only use up to 7 channels with ordinary servos that were not S-BUS-specified. So I decided to use only one channel to move the spoiler left and right. For this purpose, I put a reverser in one of the servos.
The Eighth Examination of Weight and the Center of Gravity
It’s been a while since I’ve examined the weight and balance. The reason for this is that I have been having problems with where to put the LiPo. Initially, I was planning to put the LiPo near the front seat, but after installing the seat, there is no space to put it. The only place where I could place it is between the front and rear seats, which is about 150mm behind the position I had initially assumed. I’m not sure if the center of gravity will match. However, the weight of the motor and amplifier has increased significantly due to the change from the 1200W class motor to the 2000W class. Also, the weight of the LiPo has increased from 5 cells to 8 cells, which is also a big increase. In addition, I have installed tow rope release mechanisms, which were not originally planned, so in a word, the weight and balance has to be re-examined.
So, I mounted all the so far completed items such as the nose cowling, center wing fairing, seats, and tail wing fairing on the fuselage and measured the weight and center of gravity. The result was a weight of 3,580g and a center of gravity of STA660.
The fuselage is expected to have 550g canopy, 60g front instrument panel, 75g rear instrument panel, 75g for covering and 70g for painting. Therefore, the total weight of the fuselage is expected to be 4,410g and the center of gravity is STA663.
The LiPo for power is expected to weigh 1,050g, and its mounting position is only around STA530mm. The eighth calculation of the center of gravity is shown in the table below, adding the weight of the main and tail wings, which is already half completed.
From this table, the total weight is 9,955g and the center of gravity is STA839, which is slightly ahead of the target position even if no weight is added. The target center of gravity is set at the same position as the 1/5 model.
Actually the center of gravity is not a single point, but has a range. After that, I was able to obtain information on the allowable center of gravity range of the actual model. According to this information, the allowable range is 30% MAC to 40% MAC. This is 104mm-139mm from the leading edge of the main wing, and STA825–860 when measured from the nose. Therefore, it seems that the center of gravity can be accommodated without weights.
©2021 Norimichi Kawakami
This is the ninth part in this series. Read the next article in this issue, return to the previous article in this issue or go to the table of contents. A PDF version of this article, or the entire issue, is available upon request.
