Bending the Lower Keel Tube

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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.

Lower Keel test fit.
Bend specification drawing.
CAD of the bending die to be routed from two layers of 3/4" plywood.
Cutting the tube bending die halves on the CNC router.
Assembled tooling fastened to a work table.
Closeup of the die wall showing the radius to match the 1" OD tubing.
The bend in progress.
Verifying the angle of the bend.
Emptying the sand after a successful bend.
Triming the end of the lower keel.
Installing the keel by clamping in place prior to drilling.
Pilot fit check.

Progress Up To Summer Break

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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.

This is the first time that the 3 main sub-assemblies (wing box and forward and aft bulkheads) are test fitted together. The initial fit was good and only minimal tube grinding modifications were required prior to weld-up.
Once the tubes were properly fitted it was time to hold the sub-assemblies together using clamps and bungee cords.
The triangular main structure moved into the welding station for tack-up.
Our volunteer expert welder Terry helps the process along.
The main structure of the fuselage frame is fully welded here so an obligatory fit check with the tail boom was performed.
The wing box mounting holes align perfectly with the tail boom and 1/4" fasteners are temporarily inserted to hold the two parts together.
It's looking more and more like an airplane. Once we get the keel on the fuselage frame we will be dealing with the full length of the aircraft. At that point we will make another attempt to move the structure out of the building. If it fits down the stairwell we won't have to find a new location for final assembly.
A view from the other side.
The left and right passenger seat tubes are tacked in place and the aft bulkhead to forward bulkhead diagonal is held in position with tape just prior to tack-up.
The pilot seat sub-assembly is held in place with the plywood tooling fixture. The jig locates the pilot seat precisely and holds it in place during welding.
Clamps are used to secure all of the components.
The fuselage frame moved to the welding station where the pilot seat will be tack welded into place.
The Passenger Seat Transition Tube is shown here connecting the forward bulkhead to the aft end of the pilot seat.
Note the seat tabs are already welded to the pilot seat sub-assembly.
The pilot seat is now welded to the fuselage frame.
The next sub-assembly to be added is the landing gear box. More plywood tooling jigs are used for positioning.
Another view of landing gear box sub-assembly in position.
In addition to the welding fixtures, we measure distances left and right to make sure that everything is centered with respect to the fuselage frame.
Seat braces are added here.
Closeup of the gear box tube partially welded in place.
Here you can see that the Forward Seat to Gear Box tube has been welded in place. The two new parts are the Left and Right Forward Pilot Seat to Gear Box and the Left and Right Brake Mount tube which again are held in place using the tooling fixtures, clamps, and some tape.
Closeup of tube fitment prior to welding.
The Landing Gear Box and Pilot Seat are now permanently installed. The fame now stands on its own.
Next up is the Instrument Panel sub-assembly. More tooling helps to locate the placement of the instrument panel with respect to the rest of the frame.
The 1" tube acts as a temporary keel that is placed into the keel saddle which will be welded to the top of the instrument panel.
The bottom end of the instrument panel is clamped to the front end of the pilot seat. The plywood jig is inserted to ensure proper spacing between the legs of the instrument panel. We then measure left and right to ensure that the instrument panel is centered on the frame.
Instrument panel welded to the pilot seat.
Next up is the Forward Spar Keel Pocket. The 1" aluminum top keel is used to align the pocket prior to welding.
Top keel has been fitted to the keel pocket. It will be trimmed to length such that it reaches about mid-span of the keel pocket. Later the lower keel will be connected using a splice tube.
The keel socket with the top keel fitted and drilled.
Here's what the fuselage frame looks like to date. The top keel will most likely have to be replaced as the bend radius on the existing part is not quite right. We are currently working on creating tooling that will allow us to bend the upper and lower keel accurately per the drawings.
This is the Aileron Aft Bellcrank prior to welding. It consists of the bellcrank cut from 4130 plate which gets welded to a small length of tube. The interface angle is 15 degrees from perpendicular so we designed and printed a sacrificial jig to accurately hold the two parts in place during tacking. The spot welds had to be fast as the heat would quickly propagate to the PLA plastic.
The 3D-printed tooling lasted just long enough to get the tacks into place.
Here's an assortment of some of the fabricated flight control parts.

Machining Seat Tabs and Control Arms

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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.

Using our CNC Mill in manual mode to drill the 1/8" holes into the 30+ seat tabs.
The holes have been precisely located along one edge and centered on the other using the edge finder.
After drilling we use a 3/4" 4-flute center cutting end mill to cut the radius on the end of the seat tab. This cut will conform perfectly to the 3/4" tube that the tabs will be welded to.
Preparing to execute the manual plunge into the part using the jog wheel.
Seat tabs are complete and a quick fit check is performed. Next step is to weld them onto the pilot seat sub-assembly.
Layout of the control parts in the OMAX Make software. These parts are cut from 0.125" 4130 steel and the estimated cut time is 27 minutes.
Another batch of parts cut from 0.090" 4130 steel. Tabs are added to prevent the parts from falling into the water tank. Some light cleaning on the wire brush wheel and the parts will be ready for welding.
The Control Stick U-Joint Mount is comprised of a short section of tube and an arm that needs to be welding together. The tube must be centered about the lower hole on the arm and to accomplish that we once again rely upon 3D-printed tooling to hold the metal parts in place for a tack weld.
Tube centered and ready to weld. The tack welds are quick enough that they don't overheat and melt the plastic tooling. It does not take much heat to melt PLA plastic.
The Control Stick Mount is welded and fit checked with the other half of the assembly.
Elevator control stick torque tube arm.
Control Arm Robot.

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.