Rudder Control

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In this installment of the blog we work on fabricating and assembling all of the parts required for a working rudder.  We start with machining the rudder pedal bushings and finish with connecting the rudder cable.  See the pictures below for all of the steps in between.

Machining the rudder pedal bushings from 2024 aluminum round stock.
Drilling out the center to a size large enough to accept the cutting tool. Then we begin to enlarge the inner diameter to the correct dimension.
The bushing meets tolerance and is ready to be cutoff.
The 4 required bushings have been completed and are then test fit on the 4130 steel tube.
We created a CAD model of the EMG-6 designed rudder pedal with the bushings to ensure that everything would fit together.
We then 3D printed the rudder pedals and installed them on the fuselage frame to test their function.
Following the functional test of the originally designed rudder pedals we decided to make some modifications and designed a custom E-Hawk pedal that would later be fabricated from aluminum.
Engineering drawing for our custom pedal with bending parameters.
The flat panel of the rudder pedal cut on the waterjet from 1/8" 6061 aluminum. The part then gets annealed and sent to the hydraulic press for bending.
After bending is complete we polish the rudder pedals with fine grit sand paper and install onto aircraft.
Rudder cables are prepared by terminating the end with stainless steel cable thimbles and tin plated sleeves.
Once all the parts are aligned we swage the sleeve onto the cable.
The completed end of the cable is then attached to the forward rudder control horn via a shackle. A second sleeve will be swaged onto the cable for redundancy.
Time to route the cable from the control horn around the lower fuselage frame pulley, up through the tailboom pulley, and then down the length of the boom to the aft rudder control horn.
Rudder control cable routed along the lower pulley.
Rudder cable running along the upper pulley.
Rudder cable exiting the tail boom and making its way to the rudder.
Attaching the rudder control cable to the rudder control horn.
The control cable is temporarily secured to the rudder control horn. We will wait to permanently terminate via a swage.
For now we hold the cable in place using a 3D printed clamp that we can tighten with a wing nut.
Coiling up the excess of cable from the right side. Next we duplicate our efforts on the left.

Flight Controls

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In this installment of the blog we continue to work on the flight controls.  A number of tubes on standoffs are strategically located and fitted with nylon bushings to act as pivot points for the torque tubes.  We also weld up the control stick and add pulleys for the rudder cables to run on.

Fitting the torque tube standoffs into position just prior to welding.
Holding the parts in place for tacking.
Elevator control stick torque tube.
Aft bulkhead control mount standoffs are fitted and clamped into place for tack welding.
Checking the drawings for the control stick.
The wire brush will remove the burr from the control stick tube prior to welding.
Drilling holes in the control stick using a 3D printed drill fixture.
Locating holes to be drilled in control stick.
Aileron torque tube bearing being prepped for welding.
Completed aileron torque tube bearing with nylon bushings inserted.
Enlarging and deburring the holes in the elevator bellcrank.
Elevator control stick torque tube installed with control stick and elevator control horn attached. The 3D printed saddles are temporary until we machine the the real parts from aluminum.
Another view of the control stick mechanism.
We 3D printed a temporary u-joint from red TPU flexible filament to couple the control stick with the aileron torque tube. This way we can test the movement of the system.
The aft torque tube is shown here with elevator bellcrank and aileron bellcrank in place. The pulleys for the rudder cable are also installed. The red parts are temporary 3D printed shaft collars. The real collars will be machined from aluminum.

To The Paint Hangar

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The fuselage frame is at the stage where a coat of primer will help protect it from oxidation.  Although our shop is climate controlled during the day, the high humidity in the Hawaiian air will find a way to infiltrate.  So it’s off to the paint hanger to apply a coat of primer.  We will still have to do some welding (e.g. motor mount) in which case we will simply strip away the paint in the affected area.  

More Fuselage Frame

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In this blog we are able to finish most of the welding associated with the structural part of the fuselage frame.  We also fully attach both the upper and lower keel tube to the frame.  Coming up next will be flight controls.

Deburring some the bolt holes that will attach the nose skid to the fuselage frame.
Nose skid saddle being prepped for welding.
This is the rudder bar that the rudder pedals will pivot on. The lower keel tube is clamped into place so that we can drill through both parts for guaranteed alignment.
Rudder pedal bar is being positioned with respect to the lower keel tube.
The left-side seat to lower keel tube is positioned and tacked into place on the saddle. The right side is next to be installed.
The forward portion of the fuselage frame is mostly complete.
Final drilling to fully attach the keel tube to the fuselage frame.
Here we are taking some measurements for where the control stick will mount. With the basic structure of the fuselage frame mostly complete, it's time to start adding all of the structure for flight control actuation. In our next post we will cover the first part of the flight control system.

Building Egress Test #2

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With both upper and lower keel tubes now part of the fuselage frame the full length of the fuselage is known.  Bolting it to the tail boom and empennage gives the full length of the aircraft which now allows us to determine if the assembly can be removed from the building.  The partially assembled aircraft also allowed for a photo op.

Bolting the fuselage frame to the fuselage boom.
Preparing the assembly for transport.
It's not looking so good as we enter the first turn in the stairwell.

Here we attempt to get the fuselage out of the building.  Although we were unsuccessful here we may still have a shot if we have more people available help with the lifting and negotiating.

Forward Fuselage Frame

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Now that we have bent the lower keel tube and installed it we can proceed with fitting the rest of the forward fuselage tubes.  The keel pockets are located on the keel tube and clamped in place so that we can properly fit the Rudder Bar, Nose Skid Tube, Instrument Panel to Rudder Pedal Down Tube, and the Lower Instrument Panel to Rudder Pedal Down Tube prior to welding.

Completed forward section of the fuselage frame.
Rudder bar is clamped to keel pocket via standoff for welding.
Keel pockets located on lower keel tube.
Nose skid tube tacked into place.
Instrument panel to rudder pedal connection.
Clamping the instrument panel keel pocket to the upper keel tube for drilling.
Appears to be a perfect fit.
Now with the lower keel back in place we drill through the keel pocket into the keel tube for correct alignment.
Drilling the forward keel pocket.

Fabricating Wing Parts

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As we wait for the bulk of the wing parts (mostly aluminum tubing) to arrive, in-house fabrication has begun.  We can easily cut most of the 2.5D parts out of flat stock, be it aluminum or 4130 steel, on the waterjet.  We also produce our own CAD for the parts that are missing drawings within the EMG-6 builders database.

Here is a finished set of 20 Diagonal Attach Plates plus a spare. These will be used to reinforce the attachment of the diagonal struts to the leading and trailing edges of the wing.
Here we are using the provided PDF drawings to recreate the parts in Onshape, our CAD software of choice. From there we can generate the DXF files to be loaded in the OMAX layout program.
Here we have loaded the DXF file into the OMAX program and begin laying out the 20 copies of the part. Tabs are added, the cut quality specified, and the material parameters set prior to generating the machine path.
In this step the machine is homed and the z-height set.
Test firing the machine, first with water only followed by water and abrasive at high pressure.
What's left of the 0.125" 6061 aluminum sheet.
The tab remains and will have to be grinded flush.
The cut parts will be tumbled overnight to smooth out any sharp edges.
The next morning parts are removed from the tumbler and cleaned.
Although Hawaii does not have many fireplaces, this student has managed to find one. Please contact us for our chimney sweeping rates.

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.