Parpar RC model

BACKGROUND

The Parpar (Butterfly) RC model is a small (95x85cm) Bi-Plane model. It was designed and published by the Israeli Tisan-Heifa shop. It was designed for gas engines - size of 0.15 to 0.26 Cu-In

CONVERT WING RUBBER-BAND MOUNT TO SOLID CONNECTION

Two strips of Fiber-Balsa-Fiber will be used instead of the rubber bands.

The nylon sheet will prevent the Epoxy glue from connecting to the top of the wing.

After the Epoxy has solidified, the structure will be flexible and will keep the original curve of the wing.

Placing a nylon sheet on top of the Fiber-layer will cause the external epoxy layer to be very clear and smooth.

BLDC ENGINE INSTALLATION

For the bellow sections I had to make a CAD model of 80% of the RC-Model ( Just for the 10% modifications)

I use a Trunigy C3530-1100 engine with a 9x6 prop, which I expect will deliver 15KN (~1.5Kg) propulsion force in static air.

ADDING AN AIR-COOLED BLDC-ESC AND LIPO MOUNTING

Internal arrangment of all the components

The Blue parts are the ones I am going to 3D-print

The ESC locking mechanism

The spring mechanism ensures that the ESC will always have the correct amount of pressure.

An opening should be made in the Gas-Tank floor for the heatsink fins

WELL-VENTILATED BATTERY COVER

I didn't like the idea of directly connecting the battery pack to the ESC without a quick power-off option in case of an emergency.

I designed a simple DC solid-state relay with a Voltage/Current monitor and assembled it into the gas tank cover.

WELL-VENTILATED BATTERY COVER

From previous flight experiences with 3S 2600mAh LiPo, I noticed that the LiPo was overheating due to two main reasons:

Lake of proper compartment ventilation

The LiPo mounting was made with pieces of sponge, which acted as a thermal isolator (Very bad).

I redesigned the gas tank cover to include a ventilation inlet and outlet.

I also added my commercial version of the SSR-60A

Thermal-Test Results

The test was done in static air, with an ambient temperature of 28C° and a relative humidity of 50%.

As can be seen, at full power (300watt), the engine's temperature increases rapidly and will probably stabiles on ~95C°

Running the motor at idle RPM can significantly improve the cool-down of the engine.

The LiPo-Battery's temperature increases to ~40C°

EMI / RFI Test Results

I wanted to determine whether the non-FCC ESC and the entire power electronics circuitry could potentially cause any RFI. To do this, I used a portable Spectrum Analyzer from TTi PSA2701T.

Please note that the measurements are not absolute since I am not using a calibrated antenna. However, I believe they are sufficient for identifying any noticeable issues.

My conclusion was that the power electronics associated with the ESC, including the BLDC motor and wiring, do not generate any significant RFI in the 72 MHz region.

The EM-spectrum of the transmitter (Peak-Hold for 60sec)

The EM-spectrum of the environment when everything is turned off (Peak-Hold for 60sec)

The EM-spectrum when the motor is running in various RPM and the transmitter is turned OFF (Peak-Hold for 60sec)

RADIO SYSTEM

I was worried about a worst-case scenario that if one of the following components failed during the flight I would lose any control over the RC-Model:

The main-LiPo.
The internal BEC circuit of the ESC.
My SSR-60A.
Any one of the high-power wires from the LiPo -> SSR-60A -> ESC.

There are too many single fail points that will cause a total-lost crash. To solve this problem, I added a backup power source for the radio system (RC receiver + servos). It will automatically be engaged if the main 5v coming from the ESC drops below 5v.

I measured that the maximum current consumption of the radio system with 3x 9g Micro-servos is 1[A].

For this fact, it was a relatively straightforward design.

The backup power source is based on a simple 7805 (TO-220 case) voltage regulator and two 1N400x diodes.

To keep the backup circuit as reliable as possible, I didn't do the following:

Did not add under-voltage protection for LiPo cells
Used simple linear voltage regulator instead of a DC/DC converter

Here is the schematic:

I also noticed that my old transmitter's battery capacity was down to 100mAh (instead of 600mAh).

I designed and 3D-printed a mechanical container for the new 3S AA-Litium battery pack.

I didn't add any protection circuitry for the same reasons I mentioned in the backup battery section.

The new pack weight 2.5 times less then the original NiCd pack.

UNDERCARRIAGE COVER

I am currently utilizing DU-BRO 2.00T wheels for my project. To determine the cover shape, I selected airfoil NACA0021 as a reference due to its relatively thick profile and low drag coefficient of approximately Cd=0.1. I modified its aspect ratio (Z, X) to accommodate the wheel's dimensions, and I'm hopeful that these changes haven't significantly compromised its aerodynamic qualities.

Test Flight!!!

ADDING PILOT-TUBE AND 10DOF UNIT

First, I will use my SmartLogger_10DoF with my miniature Pitot-Tube.

The Smart-Logger has a built-in Blue-Tooth MODEM with an effective distance of 25m. It is way too short for real-time telemetry. So, I will use its data-logging feature and post-process the data later in offline mode.

Weight:

Pitot-Tube + Mount = 20 + 7g
SmartLogger = 22g

The current Pitot-Tube mounting is too big and too heavy. But has the following advantages:

Highly modular.
Simple to assemble/disassemble and change between different models. In fact, on several occasions, I disassembled the entire setup and assembled it on other models on the field in a matter of minutes.
Located in a good location.

It can be improved with the following changes:

Keep the pitot-tube electronics and pressure sensor inside the airplane body.
Measure the static pressure inside the airplane body.
Locate the total pressure with a single pipe ahead of the wing's leading age and aside from the propeller air-stream.
Direct the total pressure into the pressure sensor with a fine silicon tube.

Adding a DVR (Proved to be the wrong way)

The low-cost DVR is oriented 5deg below the horizon

DVR is 14 grams and mounting is 10 grams

The DVR mounting with easy access to USB and micro SD

Currently, I am using the 808#3 camera, which offers the lowest video quality at 740x480 resolution. I'm considering an upgrade in the future to either the 808#24 or the 808#16, which can achieve 1080p and 720p resolutions, respectively.

Currently, the DVR mounting I'm using is heavy and bulky. Additionally, it keeps the propeller within the field of view, which significantly impacts video quality. However, there are some notable advantages to this setup:

Highly modular and versatile.
Easy to assemble and disassemble from the model.
Simple to mount on different models.
Utilizes a commercial off-the-shelf (COTS) DVR solution, which is fairly inexpensive (around $10).

To enhance the setup, the following improvements could be made:

Remove the DVR from its enclosure and use just the electronics (optionally including its battery).
Position the DVR inside the main wing, which would minimize drag and help keep the propeller out of the field of view.
Incorporate a fine USB extension cable for easier access between the DVR and a more accessible location on the model.
Consider changing the optics to a higher-quality lens for a more ambitious upgrade.

Overall, the current camera placement has proven to be suboptimal for a couple of reasons: