P14231: UAV Aerial Imaging
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Aircraft Design

Table of Contents

The purpose of this build log is to document all techniques, materials and processes that were used in assembling and adapting the aircraft to our needs.

Solidworks 2012 models of components designed and fabricated by the team are found here..

Unboxing the Penguin

The Finwing Hobby Universeye Penguin aircraft, as we received it.
The Box

The Box

Penguin in Box

Penguin in Box

What Comes in the Box

What Comes in the Box

Power System Components

Power System Components

Bag of Hardware Components & Servos

Bag of Hardware Components & Servos

Forward Hatch

Forward Hatch

The Horizontal Stabilizer

The Horizontal Stabilizer

The Vertical Stabilizer

The Vertical Stabilizer

The Wings & Wing Spar Attachment Tube

The Wings & Wing Spar Attachment Tube

We did an initial dry fit of most of the components to ensure that there were no issues with the aircraft upon arrival. We did not dry fit the horizontal stabilizer, because this requires removing some of the temporary structural supports molded on the fuselage and could have led to inadvertent damage prior to construction.

Dry Fit of the Penguin

Dry Fit of the Penguin

The Motor Mount

The Motor Mount

Vertical Tail - note the temporary structural support

Vertical Tail - note the temporary structural support

Penguin Interior

Penguin Interior

The majority of the parts of the Penguin seemed well moulded and fit together reasonably. Some notes regarding the quirks of our particular Penguin:

Overall the aircraft appears to be well constructed and well packed, showing no signs of damage during shipping.

However, it was immediately noted that the suggested method of mounting the battery in the fuselage - simply applying velcro to both - would be inadequate and would not hold the battery in place should the aircraft experience inverted flight. A common and more robust method of holding a battery in an RC aircraft was found - velcro straps.

Replacement Mounting Board & GPS Chip Mount

As noted in the Unboxing section, it was found that the supplied mounting board presented a risk of allowing the battery to shift in flight, and that using velcro straps in place of the supplied sticky-backed velcro was preferred. However, the supplied board fits flush inside the aircraft - there is no space beneath it to run straps. It was decided that a completely new board could be easily fabricated using CAD and the laser cutter available to us through the Aero Design Team.

Design Philosophy

Since the much of the geometric design done on the mounting board could be easily classified as "reverse engineering," the following design philosophy was followed:

Design Concept:

Solidworks was used to create the model for the replacement mounting board and GPS chip mount.

The GPS Chip Mount was designed to be removable, so that a future GPS chip could be attached to the aircraft using an entirely different mounting method (eg. Velcro), and still attached at the same location. The mount consists of a captive section with two 4-40 blind nuts glued to the aircraft tail boom.

Making the Canopy Replacement Mold

The decision to invest time on a replacement canopy was based on the following three criteria:

It quickly became clear that due to the complex curvature of the Penguin's forward hatch, creating the mold for the new canopy would be easier to accomplish while the aircraft's fuselage was still in two pieces. This extended the build time of the aircraft. The mold for the new canopy would be made from blue core foam, since it was available through the Aero Design Team. Several different methods were attempted to create the outline of the canopy base on the mold, including:

All of these methods failed. The only method that proved successful was to simply create a large block of foam, and then use a piece of wire to trace the outline of the penguin, creating a series of holes that were then connected with a pen. The downside of this method is that it requires significant skill to carve the mold and ensure that it remains symmetrical. See the steps below for the process of creating and shaping the canopy mold.

Step 1: Create the Mold Block

Fairly self-explanatory: cutting foam pieces to create a big block that can be carved to shape in the following steps.

In this step we use the following tools:

The 2

The 2" thick foam sheet used to create the mold block

The 2

The 2" thick by 6" wide blocks used to create the mold block

The cut foam sheets were glued together with foam safe Loctite Spray Adhesive

The cut foam sheets were glued together with foam safe Loctite Spray Adhesive

The mold block, ready for outline tracing

The mold block, ready for outline tracing

Step 2: Trace the Bottom of the Canopy Outline onto the Mold Block

In this step, we trace the bottom (the part of the canopy that will interface with the fuselage) onto the mold block. We also do a bit of initial shaping of the mold.

In this step we use the following tools:

The bottom outline of the canopy mold, traced on with a piece of wire

The bottom outline of the canopy mold, traced on with a piece of wire

The outline of the bottom of the canopy, and initial rough shaping of the bottom of the mold block

The outline of the bottom of the canopy, and initial rough shaping of the bottom of the mold block

Step 3: Shape the Bottom of the Canopy Mold

In this step, we shape the bottom of the mold so it fits to the fuselage. Getting the mold block/fuselage interface as close to flush as possible is critical - it will ultimately determine how well our replacement canopy fits to the aircraft. This step includes a lot of "guess and check" - checking the fit of the mold block on the fuselage, making changes, re-checking, etc., until the mold fit is satisfactory.

In this step we use the following tools:

The bottom of the mold, showing the cutout for the screw land

The bottom of the mold, showing the cutout for the screw land

The bottom of the mold block

The bottom of the mold block

The bottom of the mold block

The bottom of the mold block

A test fit of the mold block

A test fit of the mold block

A test fit of the mold block

A test fit of the mold block

A test fit of the mold block

A test fit of the mold block

A test fit of the mold block, showing the gaps that will be filled with Bondo later

A test fit of the mold block, showing the gaps that will be filled with Bondo later

Step 4: Shape "Top View" of the Canopy Mold

The next step in the mold creation process is to shape the foam so that it conforms to the top-down projected shape of the canopy area (i.e. - the sides of the fuselage). This was completed by taping the mold in place on the aircraft with very low-tack (non-sticky) tape to avoid damage to the foam, and then tracing the rough outline onto the foam using a pencil. The foam was then shaped in the same manner as in Step 3.

Note: It is important to remember at this stage that the mold being created is what is referred to as a "male" mold - the part will be created on the outside of it. This means that it should be slightly undersized to accommodate for the thickness of the part. Also remember that we plan to coat the entire foam mold in Bondo for smoothness and hardness, and that the Bondo layer will take up additional space.

In this step we use the following tools:

The mold block, taped to the aircraft

The mold block, taped to the aircraft

The mold block, taped to the aircraft

The mold block, taped to the aircraft

A centerline mark on the mold for alignment

A centerline mark on the mold for alignment

Outline traced on the mold block in pencil

Outline traced on the mold block in pencil

Shaping the mold block

Shaping the mold block

Shaping the mold block

Shaping the mold block

Shaping the mold block

Shaping the mold block

Test fit of the mold block

Test fit of the mold block

Test fit of the mold block

Test fit of the mold block

Test fit of the mold block

Test fit of the mold block

Step 5: Shape the Side Profile of the Canopy Mold

In this step we finally shape how the canopy will look from the side, and how it will define the new profile of the aircraft. The final profile for the canopy was not based on any numerical analysis or CFD, as an accurate CAD model of the Penguin's geometry would have taken far too much time to create and would probably have not been accurate enough to simulate real conditions anyway. This being the case, the profile was based on the following qualitative criteria:

The intended benefit of the replacement canopy is to improve the aerodynamics and handling of the aircraft. A side benefit is that there will be more interior space available for components.

Profile options sketched on with a pencil

Profile options sketched on with a pencil

A centerline on the mold helps keep the two halves symmetrical during shaping

A centerline on the mold helps keep the two halves symmetrical during shaping

Half the mold was shaped to check if the sketches were possible.

Half the mold was shaped to check if the sketches were possible.

Half the mold was shaped to check if the sketches were possible.

Half the mold was shaped to check if the sketches were possible.

As may be apparent from these pictures, the sketches on the foam were simply to get an idea of the desired shape and were quickly abandoned once actual material removal began. After half the mold was shaped to roughly the desired shape, the other half was shaped to match. Cracks developed along the way between the layers of foam, and these were filled in with Bondo to prevent the mold falling apart and give a continuous surface.

Shaping the profile

Shaping the profile

Shaping the profile

Shaping the profile

Filling cracks with Bondo

Filling cracks with Bondo

Filling cracks with Bondo

Filling cracks with Bondo

Testing the fit

Testing the fit

Testing the fit - shows overhang near the nose that will be corrected.

Testing the fit - shows overhang near the nose that will be corrected.

Testing the fit

Testing the fit

Final shaping of the foam before applying the Bondo coat. Notice that several other cracks have developed between the foam sheets, and have been filled with Bondo. Unfortunately, this has the side effect of making it difficult to sand the surface uniformly, as the Bondo is harder to sand than foam. It is recommended therefore that as little Bondo as possible be applied and that it be applied in such a way as to minimize the impact on the profile of the mold.

These pictures were taken after the bottom of the mold had been coated with Bondo and pressed onto the aircraft to make a better fit. This process is described in the next step.

Testing the fit of the final foam shaping

Testing the fit of the final foam shaping

Testing the fit of the final foam shaping

Testing the fit of the final foam shaping

Step 6: Hardening & Smoothing the Canopy Mold

Since this mold is intended to create complex geometry, use of a vacuum bag system will be required. A vacuum bag system of the type we are planning to use essentially utilizes slightly higher than ambient air pressure (due to suction from the system and tension in the bag) to mold complex shapes effectively. This means that the mold must meet the following criteria:

Bondo car body filler was selected because it was readily avaiable and has been used by the Aero Design team before to create molds and parts for aircraft, and is known to be foam safe - solvents in other types of fillers may dissolve foam. The Bondo layers were applied first to the bottom of the mold, and the mold was pressed onto the Penguin canopy area with a layer of painter's plastic in between to prevent the Bondo from sticking to the plane. This allowed the Bondo to form to the exact shape of the canopy/fuselage interface. Several coats may be needed to fill all gaps effectively.

Next, a thin (~1/16") coating of Bondo was applied over the entire "top" of the canopy mold. This allows for any final shaping to be done and hardens the mold. It took two coats to get a good surface, and then flat areas and voids were filled in later.

Bondo should always be sanded and cleaned (we cleaned with compressed air) between coats. At this stage, multiple coats of Bondo were applied and sanded until the mold was entirely covered (no foam showing) and was considered robust enough to vacuum bag.

Constant checking against the fuselage was done to ensure a good fit. The mold was undersized by about 1/32 inch to leave space for the finished part to fit flush with the edges of the fuselage.

Step 7: Final Mold Prep

The final stage of mold prep before creating the composite parts was to paint the mold with a high-build primer. This kind of primer forms thick layers, allowing the final cracks and crevices to be quickly filled in. Any high-build primer paint can be used.

After painting, the mold was wet-sanded with 400 and then 600 grit sandpaper to a smooth finish. Sanding ensures that the mold will have good release characteristics - i.e., the part will not be stuck to tiny imperfections in the mold surface.

Molding the Replacement Canopy

When working with composite materials, appropriate safety equipment should always be worn. To avoid skin contact with the epoxy, powderless laytex gloves were worn, and particulate masks helped ensure no glass or carbon particulates were inhaled by our team members. Eyeglasses should be worn at all times to protect against airborne epoxy drips, especially during application of resin.

Tools & Materials used in molding:

For a series of videos on how to vacuum bag composite parts, general information and product-specific info check here.

The vacuum bagging process used to create the canopy is essentially the same as any wet layup process, with the actual vacuum bagging process as the last step. The process used to create the canopy replacement is as follows:

  1. Mold prep:
    • The mold was coated in a layer of mold release, and was polished off after a few minutes.
    • A spray was used to apply a release film to the mold. This was allowed to dry.
  2. Bag prep:
    • A section of bag larger than the part (large enough to fold over one edge and save tape) was cut.
    • Bag tape was applied to all sides, leaving the paper backing on. All corners were sealed.
    • A small cross was cut in the top of the bag in an area off the part and was ringed with bag tape. The vacuum fitting was inserted and sealed to the bag with the tape. The vacuum fitting top was screwed down and the vacuum tube was secured to the fitting.
  3. The entire vacuum line was prepared and checked for leaks.
  4. The desired number and orientation of composite plys was pre-cut to rough size.
  5. The bleeder material, release film and peel ply were all cut to size.
  6. A bleeder leader, from the vacuum fitting to the part, was made out of folded bleeder felt, at least 4 layers thick. This keept air flowing out of the bag.
  7. The epoxy resin and hardener were mixed.
  8. A light coat of epoxy was applied to the mold.
  9. The first ply of material was laid down and wetted completely with epoxy using foam rollers(repeated as necessary until all plys were applied). Use of epoxy was liberal, since the vacuum bag would remove most of the excess. Between 20 and 30 grams of resin was used for each layup.
  10. The peel ply was applied and smoothed over the composite.
  11. The release film was applied.
  12. The breather cloth was laid over and smoothed down.
  13. The entire bundle was transferred to the bag and the bleeder leader was positioned.
  14. The paper backing was removed from the bag tape one side at a time and the bag was carefully sealed
  15. The bag was checked for leaks.
  16. The pump was started.
  17. As the pump drew out air, the bag and bleeder material were smoothed over the part to avoid wrinkles. These can leave unsightly imperfections in the part, or can be indications of folds in the composite material.
  18. Waited cure time of 24 hours. Because of the quality of our bag/pump, continuous operation of the pump was necessary.
  19. After 24 hours, the layup was removed from the bag, and the peel ply was removed.
  20. After inspection, the part was trimmed to size on the mold.
  21. The part was removed from the mold with compressed air and a flexible plastic propeller (a plastic putty knife could also be used).
  22. Holes for screws were located and drilled using a 1/16 drill bit, then drilled to size.
  23. The molds were wet-sanded with 600 grit sandpaper and water. Do not dry-sand composites without respiratory protection.

Motor Assembly

All the components of the motor assembly

All the components of the motor assembly

The package that we purchased online included an M2815 electric brushless motor and mounting accessories compatible with the aircraft. A list of all the parts and their associated fasteners is below, a picture is at right.

Component Photos

M2815 brushless electric motor

M2815 brushless electric motor

Aluminum motor mount

Aluminum motor mount

Captive wood motor mount

Captive wood motor mount

Threaded prop shaft adapter

Threaded prop shaft adapter

Prop washers - note teeth

Prop washers - note teeth

Lock nut

Lock nut

Below are a series of photos outlining the steps for assembly of the motor.

Notes:

The stationary end of the motor. The four holes pictured are used to attached the aluminum motor mount.

The stationary end of the motor. The four holes pictured are used to attached the aluminum motor mount.

Using a Phillips screwdriver, install the motor mount using the small black screws.

Using a Phillips screwdriver, install the motor mount using the small black screws.

The rotating end of the motor. The four holes pictured are used to attach the threaded prop shaft adapter.

The rotating end of the motor. The four holes pictured are used to attach the threaded prop shaft adapter.

Use a 3/64 Alan key to install the threaded prop shaft adapter onto the rotating side of the motor, then slide on the two prop washers, with their teeth facing one another. Follow with the lock nut.

Use a 3/64 Alan key to install the threaded prop shaft adapter onto the rotating side of the motor, then slide on the two prop washers, with their teeth facing one another. Follow with the lock nut.

Motor assembly completed

Motor assembly completed

Aircraft Assembly

The aircraft was assembled once the replacement mounting tray was completed. The manual was essentially useless in construction, so much of the construction relied upon team member experience. The only portions of the aircraft that required structural construction were the horizontal tail and fuselage. The vertical tail received some reinforcement glue around it's mounting points, but this was not immediately necessary.

A hole was cut in one half of the fuselage where recommended to allow future access to the elevator servo, should it need to be replaced (see picture below).

The fuselage was constructed from two halves. The component mounting plate in the main fuselage was inserted into its slots in the foam. Flexible glue was applied to all faces in contract with the foam, taking care not to get glue in the blind nut threads. Flexible glue was placed on the contacting surfaces of the two fuselage halves, and with all the components above installed, the two halves were pushed together. Rubber bands were used to ensure contact during a 24 hour cure cycle, and foam-safe CA glue was used to fix trouble spots.

Aircraft parts installed in fuselage prior to gluing together halves:

Tools & Materials Used:

The fuselage halves, held together by rubber bands during glue curing

The fuselage halves, held together by rubber bands during glue curing

The horizontal tail with reinforcement rod and glue

The horizontal tail with reinforcement rod and glue

The elevator servo hatch

The elevator servo hatch

Finished wooden motor mount with 3mm spacers to provide downthrust

Finished wooden motor mount with 3mm spacers to provide downthrust

Servo Preparation & Installation

The servo horns provided are two-sided, and the aircraft's configuration requires single-sided servo horns. Therefore, the servo horns must be trimmed. Photos below show the process.

Tools & Materials Used:

The elevator servo was screwed into its mounting point in the tail boom reinforcement plate.

The wing and tail servos were placed in their respective mounting locations and secured with packing tape. Although not as robust as gluing the servos onto the aircraft, if the servos need to be replaced, the tape can be removed with minimal surface damage.

Included servo parts

Included servo parts

Two servo horns, with one half cut off.

Two servo horns, with one half cut off.

Servo horns, finished

Servo horns, finished

Completed Servo Assembly

Completed Servo Assembly

Elevator servo, installed

Elevator servo, installed

Wing servo, ready to be installed

Wing servo, ready to be installed

Rudder servo installed in final tail

Rudder servo installed in final tail

Wing servo leads were hot glued to their extension cables to prevent in-wing separation of the two wires.

Wing servo leads were hot glued to their extension cables to prevent in-wing separation of the two wires.

Control Surface Rework & Control Horn Installation

The ailerons and elevator all had leftover flashing from the injection molding process. This flashing restricted the movement of the control surfaces and was removed with a knife. Control horn mounting holes were cleaned out with a drill bit.
Flash to be cleaned

Flash to be cleaned

A cleaned control surface edge

A cleaned control surface edge

Control horn mounting holes.

Control horn mounting holes.

Light Installation

The lights on the aircraft serve as emergency locators in the case of a crash in low light conditions. First, the LEDs were located on the aircraft with their lenses. The lens mounting hole locations were marked on the aircraft and a small hole was drilled in the foam with a drill bit by hand. A 2-56 blind (Tee) nut was installed with foam safe CA glue in each hole. The lights were soldered to servo extension leads. After the wires had been routed through holes in the aircraft, the lights were screwed down and the wires were taped down with packing tape.
Light controller board

Light controller board

LED light and lens, attached to aircraft

LED light and lens, attached to aircraft

Lights, plugged into the radio receiver in AUX port

Lights, plugged into the radio receiver in AUX port

GPS Mount Installation

GPS Mount

GPS Mount

4-40 blind nuts were installed in the captive piece of wood before gluing it to the aircraft. Two 1/16" plywood spacers and one 1/8" basswood spacer were used to raise the GPS chip above the base plate so that it did not interfere with the 4-40 screws. Wood was used for these spacers because it is non-conductive. It is important to note that one of the washers used to secure the GPS chip was coated with glue-backed neoprene sheet to prevent contact with elements on the GPS chip PCB.

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