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Hammer Down Catapult Glider

 

by Bill Kuhl   http://www.scienceguy.org

 

 
          

 

                                                   

 

                          
Building a model plane from materials other than balsa has been a challenge I have experimented with for some time. I built a couple of radio control planes that use foam board for part of the construction including one plane with a 9’ wingspan powered by a chainsaw engine. Another radio control plane I designed used mainly cardboard in the fuselage. More recently I built a foam catapult free flight glider I named “Foam Jet II” because it had jet-like style.   After some revisions, Foam Jet II flew rather well but I thought it was really more work building than most people would want in a foam glider. To build the wing you had to splice several sections of foam plates together and then reinforce with clear tape.

 

 

 

Download plan in PDF formatPage # 1     & Page # 2 

 

                  
Back a few years with plane I designed with foam board used in fuselage over a pine structure.
       

 

             
Hammer Down catapult glider was based on my discovery that you could build a foam wing from a meat tray with a crude airfoil shape by pounding part of the wing with a hammer. A further discovery was that it was possible to bend the dihedral in the wing just by pressing hard through the center of the wing. For a wing span of only 9” the wing was stiff enough to withstand a moderate speed catapult launch with no reinforcing. Like Foam Jet II, no balsa is needed in this plane at all. The cost to build is almost nothing and the materials are easily obtained from recyclable materials.

 

 
                                                        

Two of the prototype gliders, the first glider in the foreground did not have the bamboo skewer boom.

 

 
                                                                

This the first glider I built entirely from foam. When the cardboard doublers were added to strengthen the nose area, the foam would break behind where the cardboard left off.

 

 

                                                       

The basic materials needed to build Hammer Down foam catapult glider.

         
These are how the skewers I used for the tailboom were packaged, the smaller ones to the right in package were used. Should be able to find these in most grocery stores.

 

 

   
    
 
I would suggest using a slightly smaller foam tray for creating the foam pods so that all available larger trays can be used to make wings.
  Low temp hot glue gun can be used for the entire construction.
 
 

 

 
   
 
The wing of the foam glider is made a foam meat tray that measures approximately 10 3/4” By 5 3/4”. Wash the tray thoroughly and remove any stickers.
 

One tray will make two glider wings. Use a sharp blade to cut wings instead of a dull one like I used for these wings resulting in a jagged edge.

 

 

 
 

Mark half way across the back of foam tray. The foam tray will be split in half lengthwise.

                                            

It might be easier to cut foam sides after cutting the foam tray in half, I have tried cutting foam sides first also.

 

 
 

The sides of the foam tray are cut so there is a flat surface all the way across, turning the tray over there will be a nice curve for the leading edge . Use a very sharp blade and be careful not to cut yourself.

                                          
If the first cut did not get the side trimmed down flush, carefully trim until it is flush. 

 

 

 
 
Hammer down, that is how the airfoil is formed. Starting in the middle of the chord hammer the length of the wing, harder towards the trailing edge. This compresses the foam and the shape seems to hold.
                                     

Creating the dihedral, the V-shape that helps with stability is created by pushing in the center of the wing with your thumbs.

 

                                                
 
Looking at the back of the wing it is easy to see the dihedral bend. This wing should hold up to catapult launches with 1/8” rubber, do not try ¼” rubber, it will break.
   
The foam for the nose can be cut with a sharp knife although it no doubt will take more than one pass through the foam which is around ¼” thick.

 

 

                                                          
 

I have been experimenting with using a hot wire foam cutter which is sold where model railroad supplies are sold.

     

Hot wire cutter worked well if you can keep template from moving around while cutting.

 

                                                     
 

The sharp end of a bamboo skewer is poked straight into the rear of the foam nose. Be really careful that it goes in straight as possible.

   

Put hot glue in the hole in the foam created by pushing in bamboo skewer.

 

 

                                                                
 

Again check the alignment of the bamboo skewer before hot glue is hard.

   

Check alignment from the top, if it is not straight it will cause the glider to turn one direction. Aslo,  check from the side the alignment of the bamboo skewer, if it is not straight it can cause the glider to dive or stall.

 

 

                                                      
If you trace the cardboard doublers in this manner, the shiny side will appear on both side of the glider    

The cardboard should cut easily with a scissors.

 

 

                                                 
 

Work fast spreading the hot glue out evenly on the foam nose pod.

                                                

Doublers are glued on both side of foam nose pod, this must be done quickly as hot glue sets up quickly.

 

 
 

Squeeze hot glue in gap between cardboard doublers underneath foam nose pod.

                                                    

Pinch the doubler halves together quickly, this forms the catapult hook.

 

 
 

The stabilizer and vertical fin are cut from foam plate material. Cardboard used for template for tracing.

                                                   

The thin foam of the plate can be easily cut with a scissor.

 

 

                                                                      
 

Bamboo skewer is cut off 3 ¾” from the rear of foam nose pod.

   

Stabilizer glued to rear of bamboo skewer.

 

                                                          
 

Make sure the stabilizer is not high on one side as would appear to be the case in this photo.

   

The vertical fin is glued to the top of the stabilizer.

 

 

                                                    
Check the alignment again of the tail surfaces.    

Hot glue small sub-fin that is used to pull the plane back for catapult launch.

 

                                             
 

Measure from the rear of the foam nose pod ¾” for the location of the trailing edge of the wing.

                                

The bottom of the wing is glued to the top foam nose pod. Make sure to locate the center of the wing so one half is not longer than the other.

 

                          
 

No doubt additional nose weight will needed to be added to arrive at the proper center of gravity location.

   Completed glider, ready for trim adjustments.

 

Notes on Trimming

 

Small adjustment that are made to your glider will make the difference between a glider that goes a few feet and one that
will fly well. 
 

 

 

 

 


Trim adjustments have to be very small on a glider that goes so fast right after launch. You can put small bends into the trailing
edge of the wing or the rear of the stab. My glider has been trimmed to turn slightly to the left, I bank it to the right on launch.
The glider turns gradually to the right on the way up and then turns to the left gradually on the way down, just before the glider
was ready to stall. Launch at no more than 45 degree angle, otherwise it will either loop or come straight down after it reaches
the top of the launch
.

 

 

 

     
      Making up parts for upcoming workshops.    

 

 

 

 

This is a short video of the prototype Hammer Down Catapult glider flying: http://youtu.be/YL7bV0d8QK8

 

 Simple Gliders in the Science and Mathematics Curriculm by Gary Hinze
    
Gary had written this detailed lesson plan using a simple glider.

 

Glider Event for Distance and Accuracy by Paul LaChance - Good activity for kids and gliders.

 

Watch my video Fun With Foam Gliders

 

 

 
                                                                      Looking for even simplier Foam Plate &  Plastic Straw Gliders