1/3rd Scale Mita Type 3 Production Notes
The eleventh part of a twelve part series.
You may want to read the previous parts of this series before proceeding to this article. Also if you prefer, you can read this article in its original Japanese.
Fabrication Part 49: Completion of the Instruments Panel
The instruments panel is ready to be completed by attaching the scale drawings to the cases of the instruments already made
Making the Instrument Scale Drawings
The instruments of JA2103, the original plane of this 1/3 model, seems to have changed over the years. I wanted to have a clear picture of the instruments, so I asked the Shizuoka Aviation Museum to take a picture of them for me.
However, the instruments on the current aircraft at the museum seem to be different from the ones when the plane was in service, and they were installed when the aircraft was donated to the museum. Furthermore, there is a rear seat instrument panel, but no instruments are installed.
For these reasons, I drew a scale drawing of the instruments based on the instruments in the museum, with some modifications. This is the CAD drawing.
I printed this drawing on a photo paper and pasted it inside the instrument cases. For the front seat, there are four large and two small instruments. The upper large instruments are a speedometer (left) and an altimeter (right), and the lower ones are both altimeters. The left side is in ft/min and the right side is in m/sec. The small instruments are the attitude indicator on the top and the heading indicator on the middle. For the back seat, there are two large instruments, a speedometer on the left and an altimeter on the right.
The two-dimensional CAD system I use only allows circles and rectangles to be filled in, so I can’t draw needles with sharp points. So I had to cut and paste the needles separately. The altimeter does not have a pressure compensation knob, which is strange, but I made it the same shape as the actual one in the museum.
Finished Front Seat Instruments Panel
Photo 252 is the finished front seat instruments panel. It is painted in matte black. I think it looks almost real. Initially, I thought of using a pin to hold the needle above the scale, and I had drilled a hole for it in the case, but it was not easy to insert a pin into the needle, which is less than 1mm wide, so I gave up. The needles are attached to the case.
Mounting the Instrument Panel on the Fuselage
The instrument panel is now installed on the fuselage.
This is the rear seat instruments panel.
Photo 255 shows the panoramic view of the instrument panels. Once the instruments are installed, it looks much more like the real thing.
But why is the red line on the speedometer drawn at 190 km/h?
This speedometer scale diagram was made to match that of the actual aircraft on display at the Shizuoka Aviation Museum, but I later found that the speed limit of the actual aircraft is 180 km/h. This means that the speedometer of the exhibited aircraft is wrong.
As one of the pillars of the famous Nikko Toshogu’s Yomei gate was intentionally built upside down, this case can be accepted as it is.
Fabrication Part 50: Completion of the Horizontal Tail
The horizontal tail, which was already planked, was covered with Oracover and painted.
Finished Horizontal Tail
The structure of the horizontal tail was finished a year ago, but I had run out of Oracover (Oratex) for the covering, so it was left unfinished. Now I procured Oratex and completed it. Soon after the completion, I attached it to the fuselage together with the vertical tail and tail fin fairing that were already completed.
The paint is matte white. The dummy trim tab is located on the trailing edge of the right elevator. In the real aircraft, the angle of the tabs is adjusted by moving the lever on the right side of the front seat up and down to match the subtle changes in the center of gravity position with each flight, so that the steering force becomes zero during steady flight. This is not necessary for this RC plane because it is a FBW (fly-by-wire) machine. However, since it exists in the actual aircraft, it is installed as a dummy.
This is a photo taken from the other side.
It looks pretty good. Next, I connected the elevator to the control system and checked its operation range.
The rear seat control stick was found to hit the rear seat, so it was adjusted. After adjustment, I confirmed that it did not hit anywhere. However, I didn’t notice it at the time of adjustment, but looking at this picture, the downward elevator angle is a little too large compared to the upward one. This is because there is a difference between the plane of the fuselage substructure where the elevator servo is attached and the tilt of the elevator control rod that the servo moves.
This is because the servo horn was mounted at right angle to the rod so that there is no difference in the sensitivity of the elevator angle. This has been corrected later.
Next, I checked that there was no contact with the elevator with the rudder swung to the maximum left and right.
In these conditions, I moved the elevator up and down and confirmed that it did not hit the rudder. The horizontal tail plane is now complete.
It weighs 346g including the three M3 mounting bolts, which is 54g lighter than the target.
Installation of Elevator Mass Balance
Since the elevator was relatively large, its weight caused a large elevator down moment around the hinge, which put a strain on the servo. A jittering sound was always generated, which was unpleasant to my ears.
At the tip of the elevator horn, there is a mass balance attachment space just as in the actual machine to prevent elevator fluttering. But at first I did not plan to attach any weights to reduce the tail weight and I was sure that there would be little concern about flutter. But later, when I measured the center of gravity, I found that it was a little too far forward, so I decided to install a mass balance to prevent jittering noise as well.
This is the elevator horn with the mass balance installed.
I added 38g of lead to the tip of the horn. This amount of lead is not enough to balance the elevator perfectly, but I gave up because I could not mount more than this due to space limitations. Even with this, the load on the servo has been greatly reduced and the jitter sound has disappeared. In addition, the mass balance moved the center of gravity back a little less than 2% MAC to 34% MAC. I think this is just the right center of gravity position.
Fabrication Part 51: Main Wing Is Completed
After covering the main wing, I finished painting it.
Outer Wings
Oratex was applied to the main bodies and ailerons, then painted matte white. After that, I attached the already completed counterweights and wing tips to complete the outer wings.
The counterweights are visible on the underside. It took some time to adjust the aileron differential travel.
Center Wing
Covering and painting was done the same as for the outer wing. Spoiler adjustment took some time.
I lined up the center wing and outer wings on the top and bottom. These are the components of the main wing.
The total weight is 3,925g: 1,002g for the right outer wing, 988g for the left outer wing, 866g for the right center wing, 850g for the left center wing, 55g for both center wing fittings, and 163g for the wing connecting pipes. The right wing weighed 1,977g and the left wing 1,947g, making the right wing 30g heavier. It looks like I need to load the left wing with weights to balance it out.
Wing-Body Connection
I mounted the wing on the fuselage (Photo 264). It looks very nice. I need to paste the JA number on the center wing but it will be done later because of lack of material.
At first, I tried to assemble the main wing and then attach it to the fuselage, but it was too big and too heavy to attach well. So I disassembled the main wing and attached the center wing to the fuselage first, and then attached the outer wings. It seems that the installation procedure is very important.
I would like to cover the fuselage next, but it will be difficult to access various parts of the fuselage when the fuselage is covered, so I will wait until there is no remaining work. One thing that is bothering me at the moment is how to install the 1kg LiPo for power. I need to fix it firmly, and I’m wondering how to fix it to the truss structure without losing the sense of scale.
The Ninth Check of the Weight and Balance
Now that the horizontal tail and main wing are completed, let’s examine the 9th weight and balance.
There is no significant difference from the results of the 8th examination. The completion ratio is 91.16%, so it seems that there will be no significant change in the future.
Fabrication Part 52: Tray for LiPo
I made a tray to put LiPo power supply on the fuselage.
Drawing
The power supply is an 8-cell LiPo. It consists of 5,100mmAh 5 cells and 3 cells in series. The total weight of the power supply is exactly 1 kg, so the center of gravity will be shifted if it is moved by the acceleration of the aircraft motion. Therefore, it is necessary to fix it firmly. After examining the center of gravity, I decided to place it around STA530. I was very worried about how to fix it without destroying the sense of scale.
If the two LiPo batteries are distributed between the front and rear seats, the center of gravity of the batteries will be near STA530. However, I couldn’t find a good way to secure the batteries and had to give up it. In the end, I decided to use the tray method, which is expected to secure the batteries.
Drawing 65 shows the tray. The red line is the tray, which will be hung from a triangular piece of wood with an M3 claw nut embedded at the intersection of the diagonal members of the fuselage side truss structure near STA530. The two LiPo’s are placed on the tray and fixed with Velcro.
The Tray I Made
This is the LiPo tray that I fabricated based on the drawing (Photo 265).
Made of 5.5 mm paulownia wood, 1.6 mm plywood and 2 mm acrylic board. A 20mm thick urethane sponge is attached to the bottom. The urethane sponge shrinks when it contacts the floorboard of the rear seat, distributing a percentage of the weight to the substructure, and the frictional force keeps the tray from swinging back and forth.
Installation
I installed it on the aircraft.
It is attached with M3 bolts with white knobs on both ends, shown in the image from above. I don’t have a lot of Velcro on hand, so only one is applied, but this should be at least two. The cord that connects to the ESC runs along the side of the front seat and is an eyesore, so I plan to modify it to run under the floor at a later date.
It came together quite well. It did not interfere with the rear seat controls. However, considering its shape and mounting method, it might be more appropriate to call it a ‘palanquin’ rather than a ‘tray’. This tray (palanquin) is usually left off and installed just before flight to keep the sense of scale.
Fabrication Part 53: Covering the Body
Covering Film Used
Picture 267 shows the covering film and glue used in this project. The film is SIG’s KOVERALL. This is a large, thin polyester cloth measuring 1520mm x 4500mm, which shrinks when heated. Since the cloth is not coated with adhesive, apply COVER GRIP to the required area on the fuselage side. This is an adhesive that sticks when heated.
In the past, I have always used Oratex, a silk-grained Oracover, whenever needed to apply silk-grained film. This is a very easy to use film that has adhesive applied to the entire backing.
In this project I used KOVERALL instead of Oratex for the following three reasons.
- The body is a truss structure, so only a small part of the film needs to be glued. Oratex, which is coated with adhesive on the entire surface, is useless.
- The length of the body is over 2m, so the Oratex sold in 2m length is not enough. It must be specially ordered.
- It is very light (42g/m2; Oratex is 110g/m2) and cheap.
For these reasons, I used KOVERALL for the first time, but the result was not so satisfactory, as described below.
Applying KOVERALL
This time, I applied KOVERALL to the top and bottom of the fuselage first, and then to both sides. The first step is to apply COVER GRIP to the fuselage structure with a brush and wait for it to dry. COVER GRIP dries quickly, so when I was painting the end of the fuselage, the first part began almost dry. Cut the KOVERALL into pieces slightly larger than the area to be covered. However, I already felt it was difficult to handle here. I usually cut Oratex with a cutter, so when I used the same technique to cut the KOVERALL, it frayed and the cut edges became very dirty. So I switched to a pair of scissors, but the cut edges still frayed a bit because there was no adhesive on the back. With the Oratex, I could cut it to the correct size with a cutter after applying it to the body, but I found that this was not possible with the KOVERALL.
The shrinkage of KOVERALL itself is not that different from Oratex. I was able to eliminate the wrinkles after applying it with an iron in the same way, but the COVER GRIP’s adhesiveness was a little weaker than that of Oratex, and when I shrunk the KOVERALL, some parts peeled off, which was difficult to deal with. After the top and bottom sides were attached, another problem occurred when attaching the two sides. In the area where the film covers the top and bottom surfaces, COVER GRIP is applied on the KOVERALL already attached. I had to apply COVER GRIP a little wider than the width to be attached. This means that the adhesive will stick out, and the laminated surface will not be beautiful. With Oratex, the adhesive is applied to the film, so there is no overflow. I thought about wiping off the overflowing adhesive with a petroleum-based solvent, but it would have rubbed the edges of the KOVERALL, causing the fibers to fray and making it look even dirtier. In the end, I had to put up with the glue sticking out.
After finishing the entire surface, the next step was to cut off the excess on both sides. I decided to use a good razor blade for this. But this was also a failure. I couldn’t cut straight. Also, parts of the fabric would come undone. Basically, it seems that the fibers of KOVERALL should not be pulled . Photo 268 shows the edge of the film cut with a razor blade.
The cut edges are not straight and are partially frayed. For comparison, Photo 269 shows the film edge of the 1/5 Mita that was applied with Oratex.
It has a much sharp edge. Because of this, I once gave up covering with KOVERALL and left it for a while. However, the large size Oratex has to be ordered from Germany. I have to be prepared for quite a few days. So I changed my mind and decided to reattach both sides with KOVERALL. This time I decided to cut the protruding parts with a rotary cutter, which improved things a bit.
Painting
The paint is matte white. Acrylic spray cans are used. But here’s another problem: the KOVERALL is a very thin cloth with no adhesive backing, so it has a fine grain that allows the paint to escape. The instructions suggest that you need to apply two coats of dope to seal the eyes before painting. Dope is hard to come by, so I brushed on a dark clear lacquer and then sprayed on a white acrylic lacquer. With Oratex, a light spray or two is all that’s needed, but KOVERALL is so thin that I had to apply three or four coats to get an even finish. In the end, this probably reduced the light features of the film.
Finished Fuselage
I managed to finish the covering and painting of the fuselage after such hard work. Photo 270 shows the completed fuselage.
Photo 271 shows the edges of the two sides cut by the rotary cutter.
The grade is much lower than if I had used Oratex, but I’ll put up with it this time. I’d like to fly it first to make sure there are no problems. In the future, if I have a chance, I would like to replace the covering film with Oratex.
Fabrication Part 54: Completion of the Canopy
Transparent Part of the Canopy
The transparent part of the canopy was made by Mr. Tohyama (handle name: tkinnsann) in Nagano, who has a lot of experience in vacuum manufacturing. It was completed and sent to me in early August 2019. This is the transparent part.
This is a 1mm thick PVC that was made to fit a wooden mold using the vacuum process. The wooden mold was also made by Mr. Tohyama, and it must have been very difficult to make because it was the largest one in his experience. I am very grateful to him for his hard work. Thanks to Mr. Tohyama, I was able to get the transparent parts much earlier than expected.
He sent me four transparent parts. One of them trimmed off the unnecessary parts and was attached on the canopy frame that I had sent for reference.
Making the Canopy Assembly
I was ready to paint the canopy sent back from Mr. Tohyama and I tried to put it on the fuselage, but I found the wooden frame was slightly twisted with the transparent part attached. I also found the rear canopy that holds the main wing was deformed and there was a gap. This is probably because the wooden frame is not rigid enough for its size. It seems that it is necessary to attach the transparent parts with the wooden frames on the fuselage.
Mr. Tohyama had kindly assembled the canopy for me, but I removed the transparent parts from the wooden frame and reattached them. The gap between the transparent part of the rear canopy was too big, so I cut it out from the spare transparent part that was sent to me and reattached them.
Before gluing the transparent parts, I sanded the wooden frame and painted the inside gray. After that, I glued the transparent parts with Cemedine SuperX and cut off the unnecessary parts at the bottom of the frame. I then painted the outside of the frame matte white, and after it dried, I attached the canopy accessories. This time I also made glare shields for the front seats and attached them to the wooden frame.
The Completed Canopy
This is the completed canopy.
Small sliding windows are also provided right and left. When you turn it over and look at the inside, it looks like this.
The lower parts of the frame shown in Photo 233, which prevented the frame from breaking during production, have been cut away. You can also see the glare shield for the front seats.
The finished weight of the front canopy is 250g and the rear canopy is 117g, for a total of 367g. The planned weight was 550g, so the total weight is reduced by 183g. The reason for this is that the thickness of the transparent part was calculated to be 1 mm on the whole surface, but the actual product is stretched to be 0.4 mm thick in a large area.
Mounting on the Fuselage
I immediately mounted it on the aircraft.
The rear canopy is attached to the side of the fuselage with 3mm screws as in the actual model.
It looks more like a real aircraft. The volume is also quite huge. The canopy is now complete.
Finished!
At the end of August 2019, everything was assembled and checked for operation to make sure there were no problems. The weight and center of gravity was also measured and was OK. Now it is complete.
Final Assembly
I took a break from the autumn rain and assembled everything into its completed form.
It’s big. It fills the yard of my work shed. Let’s take a look from behind. It looks good.
I operated all controls in this condition and confirmed that there were no problems. This is the spoiler test.
As I mentioned earlier, I did not realize that the amount of spoiler protrusion was too small at this point. I was satisfied that the function was OK. This was discovered after the first flight. I also confirmed that the motor turns without any problem. This is the cockpit area.
I was able to reproduce the appearance of the Mita Type 3. Since it is a good opportunity, I took one more picture with the canopy open.
The sense of existence is enough.
Weight and Balance
I measured the final weight and center of gravity with the completed model. As this is such a large model, it was difficult to measure the weight and balance of a whole machine. So I measured its components and made a calculation. Here are the results.
The total weight including the LiPo for power was 9,841g, and the center of gravity was 32% MAC from the leading edge of the main wing. Thermal Studio’s 1/5 Mita model flies at 36% MAC without any problem, so it may be better to set the center of gravity a little aft.
(Note) As described in the section “Completion of the horizontal tail”, I added 38g weight as elevator mass balance, so the total weight is 9,879g and the center of gravity is 34% MAC.
The initial target weight of this project was 7,600 g, so I exceeded the target weight by 2,241 g (29.4%). This is an extremely shameful result. The reason for this was, as I mentioned earlier, the difficulty in determining the target weight. It was a problem before weight management. Fortunately, I have confirmed through strength and performance calculations that there will be no major inconvenience to the strength or flight performance of the aircraft, but I must have avoided such a situation. This is the reason I developed the statistical weight estimation formula which I presented at the first part of this story.
Next Work
I would like to start flight testing immediately, but it can’t be. In order to disassemble this large aircraft and transport it to the airfield, I need jigs to set it up in my car. Also, since it weighs almost 10 kg, it is impossible to launch it by hand. A dolly for takeoff is needed. So there remains further work for these equipment before the first flight.
©2022 Norimichi Kawakami
This is the tenth 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.
