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Sidewinder 80% scale November 22, 2008

Posted by rluhman in Rocketry.
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Now that I have a blog, I think it is time that I begin to document the steps that I’ve been taking to build my 80% scale AIM-9L Sidewinder.
 
rocksim drawing

Rocksim drawing of AIM-9L rocket.

I started out with just a nose cone.  I had found that Performance Rocketry was selling a Sidewinder nose cone that fit a 4 inch tube.  From there the rest would grow.  I started scaling up the AIM-9 drawings found on Jim Ball’s website.  They were quite good and show enough to detail to build a rocket of this size.

I determined that I was going to need three 34 inch sections of fiberglassed Loc tubing to get the length I needed.  The rocket body needs to separate in at least three places to work properly.  With this in mind I tried to set my separation points at corresponding separation points on the real missile or at least points where the separation joints could be hidden.  I also decided to use a PML CPR2000 type dual deployment system for recovery.  With those specifications I started laying out the parts that I would need.  Then I fired up RockSim to get an idea if I could make it stable.

With stability assured, I began fiberglassing the tubes.  Using some glass from Impulse Aerospace and West Systems epoxy,  the tubes turned out great.  Very smooth and strong.  That was the easy part.

Attaching fins

Using the laser level to square up the fins.

Next I took one of the 34 inch sections and cut it off at the 30 3/4 inch mark for the first separation point.  This will place the joint at a place where there is a reinforcment band on the real missile, thus hiding the joint.  This would become my booster section.  First I had to build the fin can which would hold the motor mount and fins.  The fin were made out of 3/32 inch G10 fiberglass sheets.  After going through two band saw blades, I finally figured out that I needed to be using a metal cutting blade.  This made the job much easier.  I now had four G10 fiberglass fins.  At this scale they are quite large and with the 3/32 inch G10, they are also quite heavy.  If I were to do it again I think I would use a thinner sheet of G10.  I used the fins to help position the forward and aft centering rings on the motor tube.  I put in a third centering ring about half way in between the other two for extra strength.  This required me to put a slot in my fins.  Finally I epoxied the centering rings in place.

 Next I needed to attach the fins.  I really needed the fins to be on straight and as square to the tube as possible.  For this I got a new toy, a Black & Decker laser level.  Using this set to cross-hair mode I was able to get the fins dead on.  After completing the fin attachment, I then glassed all the root joints for extra strength.  I beefed up the joints where the fins met each centering ring and added a wood slat between two of the fins to give a place attach a rail buton later on. 
slotted tube

Body tube slotted so it will slide over the fin can

The next thing to be done was to slit the body tube so that it would slide over the fin can.  I started doing this with my dremel tool with a router bit.  Apparently my dremel skills are not what they need to be as it rapidly became obvious that this was going to be a disaster.  I stopped and got out my trusty razor saw.  It took longer to cut the tube this way, but I was able to get straight lines this way that would never have happened with the dremel.  I then epoxied the tube over the fin can.  The excess slotting between the trailing edge of the fin and the end of the body tube was filled with epoxy.  Hopefully after painting you won’t be able to tell it was ever slotted. 

Fins

Laminating the balsa skin to the G10 fin core.

With the body tube in place I could now start laminating the fins.  The fins have a pronounced 3d appearance.  Sort of wedge shaped.  I decided I would laminate each G10 fin with 1/4 inch balsa.  This would then allow me sand the proper profile into the fins without too much trouble.  It would also let me cut away areas so that I could add some of the detail items such as hinges for the rollerons.

Next I took the part of the tube that I cut off and cut it into four sections lenghtwise.  These four sections were then epoxied inbetween each fin.  This represents the aft tube reinforcement band.  Then I shaped and epoxied into place the balsa filets at the base of each fin.  Then It was time to carve the balsa skin to show the location of the rollerons and remove sections of the skin for the hing details.

Once all the detail items are in place I plan to paint the blasa with a wood hardner and then glass over the balsa with lightweight fiberglass.  Finally, I should be able to attach rail buttons and a U-bolt to the top and the booster section should be finished.

Well, that’s it.  That is the build status as of now.  I really do hope to get some time this off-season to get more progress done.

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