David M Eno's Posts (1)

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Bixler/Sky Surfer EPO foam repair


The most recommended plane for a starting drone researcher is the Bixler or Sky Surfer (depending on what company re-branded the model).  These planes are all made of a foam material called Expanded Polyolefin "EPO".  A topic that most people that use EPO planes encounter is how to go about repairing crash damage.  I present for your consumption the boiling water method, which has been presented a few times before in RC group posts.

First, if we examine Figure 1 below it will be noted that my 2nd bixler has the characteristic front crumple zone damage associated with a nose in landing.

Figure 1

In order to repair this crash damage I prepared the apparatus pictured below in Figure 2.  This consisted of a 4500mL beaker, supports, and a Bunsen burner.  I also used an RTD senor to measure the temperature at specific points during the process  Conceptually, one could easily employ a standard boil kettle, but care should be taken as chemicals may potentially leach out of the foam during boiling, so if possible use a canning pot or other vessel that does not come into contact with foodstuffs.     

Figure 2 


Using this apparatus.  I determined that in order to re-expand EPO foam the required temperature is quite high ~90 Celsius.  I personally used 1 minute as my dip time, as I wanted to minimize the servos exposure to moisture.  Longer dip times might yield similar results at lower temperature, but I did not investigate these.  In order to check the temperature without a thermometer you could either wait for a rolling boil or dip a wing tip in the water for a minute and observe.  If you see the characteristic "pearling" or "lizard skin" pattern where the EPO pellets have expanded out after ~1 minute you are at the right temperature for your dip.  The horizontal stabilizer of my first bixler, which has been partially dipped is pictured below in Figure 3.  


Figure 3 


I dipped my planes nose into ~90C water and held it there for ~1minute until I could visibly see "pearling" thru the glass of the beaker.  I then removed the plane and attempted to foam safe CA glue the now de-stressed rifts back together.  The result is presented below in Figure 4.  

Figure 4


All in all, this method does work to some extent particularly for eliminating bent areas especially on the rudder, wings, and horizontal stabilizer, but it probably will not restore a plane to factory condition.    

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