Scratch - Alabama Skeeter {Scratch} Original Design / Scratch Built

Contributed by Bob Hvarven

Manufacturer: Scratch
Alabama "Skeeter" 
(Contributed - by Bob Hvarven) 

Note: This is a slightly shortened, edited version of Bob's article with fewer pictures.  Visit Bob's site for all the pictures and to write him for the fin template and comments.

[Rocket Pic]The following is the result of a scratch built "Stretched" Mosquito project. The idea came from the Holiday, 1996 Issue of Sport RocketryMagazine. On page 33 there is an article titled "A Big and Bigger Mosquito", showing how to make a 3X and a 4.8X upscale of the old faithful Estes Mosquito. After reading the article, I figured bigger is better and went to work getting the stuff together to make the 4.8X version. During this process I also thought a bigger motor is also better and opted to make it to fly on "G" and above motors. I have seen a smaller Mosquito than this fly on the LDRS videos with an I284 without any problem. So, let's get started and I will explain my changes. (Click on Thumbnail for larger view)

Fins: The first thing I did was take the page out of the magazine and use the fin template to make one out of folder material so it would be stronger for outlining on the plywood. I added 3/4" to the length of the fin since I was not going to be using a surface mount of the fin, and it would take the extra 3/4" to make up for the internal distance to make it a "thru the body tube" mount. From there I made a "tab" extension to allow the fin to be glued to the engine tube, making a really strong fin and motor mount assembly. (1/8 Ply was used for the fin) Photo shows the template and fin after cutting out with modifications mentioned.

Body Tube: The tube is LOC 2.6" material cut to 15" length. The 4.8X Mosquito body tube in the article (Keeping to scale) is only supposed to be 9.6". I wanted some more room for longer motors and still have enough space to keep my parachute stuff from getting fried during ejection. It will also help in the CP/CG category as well. I made a template to mark the three fin slots (120 deg. apart) and cut the slots with a "NEW" sharp Xacto blade. A sharp blade is worth it's weight in AP if you want a trouble-free, smooth cut. The slot is 4 1/4" long; the same as the root length, and is cut out the bottom of the tube. The motor tube, centering rings, and fins will be installed as one complete unit from the bottom.

[Rocket Pic]Fins, Motor Tube, Centering Rings: The Motor Tube and Centering Rings are also LOC parts. (The motor tube is 29mm, 7" long) You can see clearly the "tab" I added to the fin units. These parts will be assembled together to make the fin and motor mount assembly that will be installed complete into the body tube as a unit.

Motor Mount/Rings: I used thin CA to tack the Centering Rings into place. I glued the bottom on first flush with the end of the tube. Then used a fin to determine the position of the top Centering ring, and tacked it into place. After CA was set, I used 30 Min. Epoxy to place a fillet around the top of each ring for added strength.

[Rocket Pic]Fins added to assembly: After marking each ring edge at 120 Deg. increments, I aligned each fin and tacked into place with thin CA. The fin makes contact with the Centering Rings top and bottom, as well as each extended fin tab contacts the Motor Tube for a really strong, secure assembly. Each fin was then filleted with 30 Min. Epoxy for added strength.

Upper Body & Fin Assembly: The fin assembly is now ready for insertion into the body tube. Before assembly, attach the Shock Cord to the upper Centering Ring. It isn't a "good thing" to glue it in and then remember the Shock Cord !! I drilled two 1/4" holes and ran the cord through and tied. Use a piece of dowel or something to place some 30 Min. Epoxy into the body tube about 3 1/2" up on each area between the fin slots and insert the assembly about half way in. Then, place some more 30 Min. Epoxy just in front of the rear ring on the body tube. Slide unit into the tube until it stops. The bottom ring should be flush with the end of the body tube. Place in an upright position and let Epoxy set.

[Rocket Pic]Finish: After fin assembly is set, fillet the fin root edges with epoxy, and add the Launch Lug (1/4") Let this set and its ready to paint. I used Dope Sanding Sealer to seal the fins. (throw-back) to my old model airplane days. I used Krylon White for the whole rocket, trimmed one fin with International Orange, and. a clear coat was then added

Completed: Shown with homemade 24" Parachute, and tubular nylon shock cord. Nose Cone is an Estes PNC-80BB. 

[Rocket Pic]Motor Retention: Since I will be using only "G" and above motors, I usually use a couple of small wood screws in the bottom centering ring and then use Safety Wire to hold the motor casing in place. I have never "Spit" a motor casing using this method. As you can see, the bottom is slightly discolored. I launched the rocket on a G35-7 for it's first flight. Flight was straight and fast !! Estimated altitude was Approx. 1800 Ft. Recovery was beautiful and without injury. I was so busy taking pictures of everyone else's flights, that I forgot to take a picture of mine. I will add a launch photo later. 

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