After a long summer break, the E-Hawk Team is back at it again. Today we manufactured the lower keel tube from a length of 6061 T6 aluminum tubing (1.0″ OD x .058″ WT). This part requires two bends with a 9″ radius. We do have a hydraulic pipe bender however we don’t have a die that will make the 9″ radius bend. Instead we decided to design specific tooling that would allow us to make the correct radius bends. For that we used Onshape to create a bending die comprised of two halves of 3/4″ plywood cut on the CNC router (Shopbot). The two halves were then glued and screwed together and mounted to a larger piece of plywood. The assembled jig was then clamped to a sturdy table. The straight length of tube was measured and marked with the bending parameters and then filled with sand (actually waterjet abrasive) to prevent it from collapsing during the bending process. It was then placed in the jig and clamped down on one end of the fixture with an aluminum strap. The team then proceeded to manually bend the tube around the die up to the correct angle. Following the first successful bend the tube was readjusted within the fixture and the process repeated for the second bend.
As the E-Hawk team prepares for exams during the final week of school leading up to the summer break we have quite a bit of progress to share. Our last fuselage frame update included the fabrication of the forward and aft bulkhead sub-assemblies, the landing gear box sub-assembly, the instrument panel sub-assembly, and the pilot seat sub-assembly. Since then we have welded together roughly 70% of the fuselage frame. We have also fabricated more of the flight control linkage hardware including control arms and bellcranks.
We recently made some progress in parts production. Our machine shop includes a Tormach CNC Milling Machine that allows us to easily and precisely fabricate parts for our aircraft. In this post we are drilling and milling seat tabs and water-jet cutting control arms and bell cranks.
During last Saturday’s Hawai`i Fly-In at Kalaeloa Airport, the `Iolani E-Hawk team was able to showcase its progress on the creation of an EMG-6 at a public event, for the first time. Students presented and gave passers-by information about the project, such as its current state and future plans for the aircraft. The E-Hawk booth also featured a six-rotor drone, fabricated by a student in the robotics 3 class at `Iolani, and an altimeter, assembled using Arduino components. In addition to explaining more about the E-Hawk project, students were able to visit decommissioned, as well as active, planes, ranging from the Lockheed C-130 Hercules to the P-3C Orion. Enjoy these photos from the event.
Significant progress has been made on the fuselage frame since our last frame update. In addition to completing all of the welding on the wing box we started on the forward and aft bulkheads. These three sub-assemblies will be welded together to form a very strong triangular structure.
We decided to install the aluminum elevator outboard ribs in place of the foam option. After deburring the CNC cut parts we aligned the ribs, drilled holes in the leading and trailing edges of the horizontal stabilizer, and finished the process by installing the rivets. We also assembled the elevator push-pull tubes using 0.625″ aluminum tube and machined threaded inserts. The inserts were located in the tube and then drilled and fitted with 4 stainless rivets per end. You can see the push-pull tubes in action in a previous blog.
The rear elevator bellcrank assembly is comprised of control horns cut from 1/8″ 4130 alloy steel welded to 3/4″ tube. The process starts with the cutting of the steel plate using our water-jet. Using some custom-machined tooling we temporarily fasten the control horns onto the tube. A quick fit check on the aircraft is followed by welding all of the parts together. Eye bolts are installed both on the control horn and the elevator and then linked with a push-pull tube for actuation.
The water-jet in action.
Checking the throw on the elevator bellcrank linkages. The bright green 3D-printed fork bolts are for testing only and will be replaced prior to flight.
Following installation of the horizontal stabilizer it was time to fabricate and install the elevators. The fabrication technique was similar to that of the rudder. The leading edge and trailing edge were cut to length, all holes were located and drilled, the spars were fitted, and finally the parts were all riveted together. We also assembled and installed the elevator lift struts.
Taking a page from Brian Carpenter’s article and video on using 3D printed parts as bending dies, we created a simple tool that would allow us to bend the flanges on rudder rib #7. We started by importing the DXF file into Onshape, our CAD software of choice and then projecting the bend lines to our sketch. A simple extrusion and fillet to match the bend radius gave us our die. After printing we aligned and clamped the rib to the die. Because the rib is relatively thin aluminum we simply bent the flanges around the die by hand.
We started the day at 1:00 pm and began to take the plastic off of all of the parts we needed. After the plastic was off we de-burred the metal and started assembling the rudder. Before we could do anything else we had to mark and drill holes into the spar that was used to attach the ribs to. The problem that we faced was making sure that the ribs would be aligned and straight. When drilling the holes we had people spot to make sure that they weren’t at an angle. Once the holes were drilled we clecoed the ribs to the spar. Then we attached the assembled rudder to the tail of the frame via the hinge (eye-bolt to fork-bolt). The next obstacle was finding out if we could still get the plane out of the building by carrying it down the stairs. We folded up the horizontal stabilizers and used surgical tubing to hold them in place. Luckily we were able to carry it down and back up but had to turn it at different areas of the stairwell because the clearance was tight.
– Greta J.