E-Hawk Team @ Hawaii EAA Fly-In

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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.


Fuselage Frame Progress

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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.

Aft bulkhead tubes have been coped and fitted into the tooling.
The top and bottom tubes of the aft bulkhead are placed in the jig to confirm proper fit yet they will not be welded.
A tight fit will simplify the welding.
The aft bulkhead moved to the welding area.
Completed forward bulkhead.
The main spar tube is for fitment purposes only. The forward bulhead will be welded to the main spar tube that is already part of the wing box.
Landing gear end of forward bulkhead.
Landing gear box assembly placed in tooling fixture.
Landing gear box assembly ready for welding.
Landing gear box assembly with lower aft keel pocket in place. This will not be welded until the keel is ready for installation.
Instrument panel assembly fitted in the tooling.
Close-up of the instrument panel mount tube.
We designed and 3D printed tooling to help get the correct placement and angle of the mount tube holes.
Boring the holes using the mill.
Welded instrument panel and landing gear box assemblies.
Completed sub-assemblies. Next step will be to weld the aft bulkhead, forward bulkhead, and wing box to create the main triangular structure of the fuselage frame.
Here's what we are working toward.

Horizontal Stabilizer Outboard Rib and Aft Elevator Push-Pull Tubes

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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.

Elevator Bellcrank Fabrication

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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 dxf files for the control horns are loaded into the water-jet software where the layout and machine setup take place. The parts on the screen will take 10 minutes to cut and use about 7 pounds of abrasive.
The 4130 alloy 1/8" plate is loaded and clamped to the bed of the machine.

The water-jet in action.

After the completed cut you can see a risidual layer of the abrasive on the plate. The spent abrasive collects at the bottom of the tank. After about a year of use we drain the tank and remove the used abrasive and waste material from the parts.
Close-up of the cut parts. Note that we added tabs so that the relatively small parts don't fall between the slats and sink to the bottom of the 'swamp'.
Note also the precision of the cut. After minimal deburring the parts are ready for assembly.
Here we do a quick tolerance test on the 3/4" holes. The fit is so perfect that the control horns hold their position on the tube.
Next, using the lathe, we machine some aluminum tubing that will be used to firmly hold all the parts together for welding.
The tooling is in place and checked against the drawing for correct alignment. Threaded rod is used to fasten the assembly in place.
After the assembly has been welded, we will remove the fasteners and unfortunately have to destroy the tooling because it cannot be removed without cutting it free.
The center control horn has been tack welded here. Now we do a final fit check of the assembly installed on the tail boom prior to completing all of the welding.
All welding complete.
Completed assembly installed.
Since we do not have all of the linkage hardware at this time we quickly modeled the missing fork bolt and 3D-printed a couple so that we could connect the control horn to the elevator and test the elevator range of motion.
The 3D-printed fork bolts are threaded into the elevator push-pull tube and attached to the corresponding eye bolt for a quick test. The 3D-printed parts have just enough strength to do the test. They will eventually be replaced with flight certified hardware.
A view from the other side.

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.

Elevator and Lift Struts

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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.

Assembled left and right elevators ready to be hinged onto horizontal stabilizer.
The lift strut extrusion is being measured for correct length. The streamlined strut material had a circular pocket that will accept a threaded insert on each side. Fork bolts will screw into the inserts.
Cutting the strut extrusion to length.
Using the calipers to measure and scribe where the holes for the threaded inserts will be drilled.
Drilling holes for the rivets that will fasten the strut to the insert.
Three 1/8" stainless rivets are placed on each side of the strut per insert.
Attaching the bottom end of the horizontal stabilizer lift strut to the bottom of the trailing edge of the vertical stabilizer using a fork bolt to eye bolt connection.
And the same for the right lift strut.
Right elevator being attached to horizontal stabilizer.
Top of the lift struts being attached.
The finished product. The tail section is now complete and the next task will be to cover the surfaces of the tail feathers. We are currently researching Oratex which is a fabric that is easy to apply and requires no paint or other protective coatings.

More Tooling – 3D Printed Bending Die

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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.

CAD model of the tooling die. The screw holes allow for mounting if necessary.
Printing on our Makergear2 with PLA and 70% infill.
Rib clamped to die, ready for bending.
Tooling is removed after this step and flanges bent further to perpendicular.
The finished part installed in the rudder.

“Rudder You Doing Today?”

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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.

Converting the decimal inch dimensions to millimeters to make it easier to transfer the hole locations using tape measure.
Using a C-channel extrusion to mark 4 lines every 90 degrees on the rudder spar.
Marking the rudder spar for drilling. The nylock nut plates have already been drilled and clecoed.
Filing the top end of the rudder spar to eliminate the interference with the top rib.
Removing the protective plastic film and deburring the rudder ribs prior to assembly.
Enlarging the holes in the nut plate.
It's coming together.
More cleco's.
Looking down on the rudder. Shiny goodness.
All that remains is making it permanent with some rivets.
Photo-op presented itself after performing the egress test from the building.
The school's 'Io (hawk) approves of the work we have done so far.

Horizontal Stabilizer Installation

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Friday started out with us discussing the emails which we received from Brian Carpenter addressing the issues concerning part placement and assembly. Once the issues were adequately resolved amongst the team, we proceeded with the assembly of the horizontal stabilizers. We began this process by laying out the parts for the horizontal stab on two separate tables. Once the general shape of the horizontal stab was achieved, we gathered the screws, nuts, and washers that were needed to fasten the parts of the horizontal stabilizer.

When we returned to work on Saturday, January 20th, we discovered that we needed to drill the holes that were required for proper assembly of the horizontal stab, so we spent a solid two to three hours prepping and drilling the leading edge, main spar, and rib tubes. Afterwards, we were able to attach the horizontal stab to the tail boom.

– Dylan F.

Laying out the parts to make sure we have everything to assemble that horizontal stabilizer.
Checking the specifications on the AN bolts.
Grip length and overall length are as expected and within tolerance. Now we know how to decipher the part numbers for the fasteners.
The left and right horizontal stabilizers are starting to take form.
Starting to drill the holes in the inboard and mid rib tubes.
We designed and 3D printed another flanged collar to ensure that we hit top dead center and stay lined up all the way through. The set screws prevent the tube from rotating during the drilling process.
The left side mostly complete except for the sheet metal ribs.
Leading edge of horizontal stabilizer and inboard rib tube interface.
Main spar and inboard rib tube interface.
Both left and right sides installed. Note our reserved N-number (November-One-Eight-Six-Three-X-Ray). The number 1863 represents the year our school was founded. The X is for experimental (E for electric was not available). We have the number for a year and if we don't get certified by then we will have to renew. Maybe that's incentive to pick up the pace.
It's getting dark outside. Time to go home. Ribs and vertical stabilizer next week.

A Riveting Experience

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Before beginning to rivet as we had planned, the boom was checked for the twist that we had corrected the previous day, and no correction was needed.  Once that it was confirmed that the twist had been corrected, riveting began on the top and bottom of the boom, being that any
place that shouldn’t be riveted at this time would be very obvious (not drilled yet or too large a gap for the 4-2 stainless steel rivets).  

For each rivet, the thickness of material being riveted was checked; more than three layers would signify that the part was either incorrectly placed, or would need a rivet with a longer grip range.  Aside from a single rivet, the the process for both top and bottom went smoothly.  The top was riveted first, with two teams on each side of the boom, beginning from the front and moving toward the back at the same speed.  The boom was then flipped, and work on the bottom began in the opposite direction, advancing toward the front.  

At periodic intervals, the twist of the boom was checked, and if noticeable, was corrected with the same 2-1/2 “ PVC pipes.  Before riveting the sides, the locations where a rivet should not be placed were marked, and the riveting began.  Aside from a few rivets which had been discovered to need bolts instead of rivets, the process went smoothly, and those few locations were marked to be removed at a later date.

-Braxton L.