It’s Mosquito Season!
By Steve Belknap
Recently I finally put together my JR Models Mosquito kit. I bought this kit, and one other, from former club member Fred Harris maybe 15 to 20 years ago at one of our club swap meets. It had spent enough time on the shelf. Time to build.
The kit was made in the Czech Republic 25-30 years ago. The craftsmanship is excellent but the instructions (below) are a bit primitive. The fuselage, inner wings, & nacelles are all one piece of molded fiberglass. The outer wings are built-up balsa and the tail is balsa sheet. All very lightly built.
Here are the original specs:
Span: 49 in.
Weight: 45 oz.
Motors: 2 x Speed 400
Battery: 7 cell Sub-C Ni-MH or NiCd
I looked through the kit and planned my modifications, of which there would be plenty.
First was the obsolete power system. A Speed 400 brushed motor gives an actual output of about 50 Watts due to its 50% efficiency giving a total of 100 Watts of power out for two motors. The plane is supposed to weigh nearly 3 pounds. This would have given just over 30 Watts per pound. I was looking for something more like 125 to 150 Watts per pound. So I went to the Ecalc calculator and found a Cobra C-2814/12 motor that would give me just that. I decided on a 4S-3000 mAh Li-Po and APC 7×5 counter-rotating props. I also bought 7×6 props when I want to go faster.
The Ecalc calculator told me I would get 300 Watts per motor out. A total of 600 Watts. I also checked the performance chart on the Cobra motor page and saw that the actual tested output would be closer to 350 Watts per motor after calculating an efficiency of 80%. This would be a total of 700 Watts and would give me about 175 Watts per pound. (My total weight turned out to be 4lb., not 3lb. as suggested on the box.) On the 4S pack the current would only be 30A per motor, or 60A total. I used Castle Talon 35 Amp ESCs. This turned out to be a very good power system.
The Cobra motors did not fit the aluminum motor mounts supplied so I made new ones from .040″ carbon sheet.
The correct size spinner was hard to find but I finally got them from Ebay. Turns out Ebay has a huge selection of RC parts. Much better than Amazon.
Next is the landing gear. This was intended to be a hand launcher and a belly flopper. The first thing that would have touched upon landing would have been the very thin fiberglass engine nacelles. Those would not last more than a couple landings at our field. I knew I needed gear, both main and tail. I opened up the bottoms of the nacelles to give enough room for installing the gear. First I strengthened the sides of the nacelles with a couple layers of 2oz. fiberglass and epoxy. Then a 1/4″ thick plywood retract mount was fashioned and installed. The retracts did not come with wire struts so I had to make those myself. I found 3mm music wire from Hobby King and created the struts with a my homemade wire bender. The retracts can be found on Ebay as well.
The part of the nacelle I cut out originally was reinforced with glass and epoxy. It was then re-installed with tape after cutting away just enough for the gear to pass through. This was simpler than trying to make functioning gear doors.
To make a functioning tail wheel I also need to make a functioning rudder. It came with a solid tail. I cut out a scale looking rudder. The tail wheel gear was made from music wire.
The wings were meant to be glued on. The kit supplied a short piece of brass tube to act as a wing joiner. I wanted removable wings for easier transporting and storage. To do that I needed a longer wing joiner. It would need to be a carbon tube with an 8.9mm OD. No such thing. So I used an 8mm OD C-tube and used wraps of tape to build up the OD to what I needed. For some odd reason, the kit makers did not build the outer balsa wings with a spar, just ribs and balsa sheeting. The original brass wing joiner only went into the wing about 1 1/2 inch. I wanted to put the C-tube as far into the wing as I could for better support. One end of a C-tube was used as a drill to open up several ribs. Teeth were cut into the end and it worked as a hole saw to cut the holes in the ribs.
Here is the inside. I had to make the servo and battery trays.
The canopy that came with the kit had yellowed due to age so I poured a Hydrocal mold into it and vac-u-formed a new one. Looks much better. The lines on the canopy are made from grey vinyl used for vinyl cutting. Several thin strips were made on my wife’s Cricket. Those were then used those to make the canopy lines. Turns out it makes great striping tape. Use the ‘cast’ type not the ‘calendared’ type. Super flexible for compound curves.
The black invasion stripes on the wings were simple and straight forward. The ones on the fuselage not so much. To cut out the proper shape I used the formulas in the articles I wrote for creating jet exhaust cones. Use: Method 1 or method 2. They fit perfectly.
Originally it was white fiberglass and Monocote (see below). The grey paint is Model Master Gunship grey. The light green on the bottom is half-and-half zinc chromate and white. The military graphics are from Callie Graphics. Some of the others are from Alice’s Cricket.
The paint scheme was an attempt to look like Rod Lewis’ Mosquito.
The initial flight was done before I painted it. I tried to fly a white plane on an overcast day. Man, was that hard to see! I had a mid-air on that first flight with a foam Mustang. My prop sliced through his wing tip. The Mossie was undamaged and landed OK.
Subsequent flight were made with the Mossie fully dressed. It flies and handles very well. Goes quite spritely at full tilt. See video here.