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Lab 04 - Ground Test Believer

Overview

In this lab, teams will perform ground testing of their Believer aircraft to complete final setup prior to flight operations. At this stage of the project, the aircraft is assumed to be structurally complete and transitioning from build to operation.

The purpose of this lab is to verify that all control systems and propulsion components are configured correctly and behave predictably before any attempt at flight.

Objectives

By the end of this lab, teams will be able to:

Confirm correct servo centering and control surface neutral positions

Verify correct control direction at both the servo and control-surface level

Calibrate ESCs and verify propulsion system operation

Identify and correct discrepancies using the Ground Control Station (GCS)

Document aircraft readiness

Warnings!

Propellers must not be installed at any time during this lab.

DATX Power On:

Safe State must always be followed for now on. There is a great risk of unintentional connection to another aircraft. This is an enforced rule

DATX Refresh

When powering on your Transmitter it must be in safe state. Please use this PDF as a refresher on the configuration of your switches. Do not bypass the warning screen that appears when you power on. The warnings will go away automatically if the switches are in the correct configuration.

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Servos

When installing servos on the aircraft, they must be mechanically centered in order to operate correctly. Proper servo setup requires both physical alignment and software alignment/verification. These steps must be followed carefully and in order.

Part A – Servo Mechanical Installation and Centering

Before beginning this section, ensure that:

The servo is not installed in the aircraft and servo horn is disconnected

This prevents unintended movement of the control surface during centering.

Important:

If the servo gear is manually moved at any point after this process, the centering procedure must be repeated from the beginning.

The DATX must not have any flap input during this step. Make sure your flap is set to 0%.

Servo Centering Procedure

Obtain a GCS laptop

Power on the Cube

Ensure proper telemetry connection

Set the aircraft status to Manual mode

Plug in the servo

Allow the servo to self-center

Unplug the servo

Servo Horn Installation

Before fully securing the servo in its mounting location:

Install the servo horn so that it is as close as possible to perpendicular relative to the wing and control surface

Minor deviations are acceptable, but gross misalignment is not

Push-rod Adjustment

Adjust the push-rod length to make the associated control surface appear as level as possible when the servo is centered.

Do not connect the push-rod to the servo at this time

The goal is visual neutral, not final trim

Change the push-rod length to try to make control surface as level as possible. But do not install the rod to your servo

After completing these steps, the servo is mechanically centered.

Part B – GCS Trim and Control Adjustment

In previous labs, teams uploaded parameter sets based on a standard Believer configuration. While many parameters are universal, aircraft trim is unique and must be adjusted on a per-aircraft basis.

Teams must identify which control surfaces require trim and determine which direction the servo must move to achieve neutral control surfaces.

GCS Mechanical Trim Verification

Power on GCS Laptop, DATX and aircraft

Set the aircraft status to Manual mode

Observe the distance between the push rod and servo horn connection spot

If the distance is minimal

Power down aircraft and connect your push rods to the servo horn

You may continue to GCS Trim

If the distance is large and major control surface deflection is necessary to connect the push rod to servo

Repeat Part A and alert instructor

GCS Trim

Connect your GCS Laptop, DATX, and aircraft

Move all control surfaces and observe:

Which values change

How the servo responds to each input

Identify the parameter associated with the control surface requiring trim

Modify the parameter value based on observed servo movement to achieve a neutral control surface and fill out the table below

Ensure all control surface params are in the table even if no values are modified

Obtain instructor sign-off of trimmed aircraft: AAT

Trim Parameters

Trim Parameters

Param Name

Corresponding Control Surface

Original Value

Modified Value

SERVO2_Trim

Left Flaperon

1450

1,475

SERVO1_Trim

Right Flaperon

1550

1,600

SERVO5_Trim

Left V Tail

1500

1,510

SERVO6_Trim

Right V Tail

1500

1,500

There are no rows in this table

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ESC/Motor

Esc Calibration

Power on your GCS laptop, DATX and Aircraft. Ensure that the aircraft is not armed. Following the instructions from

Lab 11 - Motors and Controls · AT 209⁠

calibrate both ESCs.

What was your method for calibrating the ESCs?

Throttle to full with slight pressure

Connect ESCs to power simultaneously

Listen for initial double beep then throttle to zero

Wait for finalization of beeping, then check for motor sync.

Instructor sign-off: AAT

Motor Direction

Observe the direction of your motor rotation under power. Take note of the initial direction.

Which direction should the motor be spinning?

Change the relevant parameter to make the motor spin in the correct direction.

Motor

Initial Direction

Correct Direction

Port

Starboard

There are no rows in this table

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Weight and Balance

Each group assembled their Believer independently. Variations in wiring, battery placement, adhesive use, reinforcement, and hardware placement can shift the aircraft’s center of gravity (CG). Before flight, CG must be calculated and verified.

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CG Guiding Questions

What is a datum? Where is it?

The datum is the arbitrarily selected point of reference on an aircraft in order to measure distances of components on an aircraft.

If I state that a sensor is installed at -3 in and an additional battery is installed at +20 in, where are those components located relative to the datum?

The sensor is 3 inches forward of the datum and the battery is 20 inches aft.

What two configuration conditions must the aircraft be in during CG calculation?

The aircraft should be flight ready as it would be for actual operation. The aircraft should also be completely level.

What are some ways to verify that the aircraft is in both of those configuration conditions?

To determine that the aircraft is level, you can either use a level, or plug the Believer into the computer and bring up Ground Control. The onboard IMUs will be able to determine whether the aircraft is level.

What is Tare? How is it depicted in a CG Table?

Tare weight is the actual weight of the aircraft and not the weight included in tools used to perform weight calculations, such as items to stabilize the aircraft (wheel blocks for instance).

What is a plumb bob? How is it used?

Piece of string along the center of gravity with a weight attached in order to establish a vertical reference line.

Verify answers with instructor

Calculating CG

Make sure that this portion is done on one singular table that is not finished to be able to draw on the table.

Discuss within your group and have consensus on your methodology of calculating the CG

Determine where the datum is located

Obtain CG jacks and scales

Weigh each jack individually and record the weight (grams) in the table below under Tare.

Decide where to place the two forward jacks on the aircraft and determine their distance from the datum.

Note: The forward jacks must be placed at the same longitudinal station on both sides of the aircraft.

Determine where to place the rear jack in order to satisfy the required configuration conditions.

Place each jack on a scale and carefully rest the aircraft on the three jacks.

Verify that the rear jack is in the correct location and adjust as needed

Record the weight depicted on each scale in the table below

Using a plumb bob, mark the exact longitudinal location of each jack stand on the physical table and the datum on your CG Table

Ensure that the measuring method used for each jack is consistent.

Determine the centerline between the two forward jacks.

Determine the centerline of the rear jack.

Determine the centerline of the datum.

Measure the horizontal distance from each jack location to the datum and record the value in inches.

CG Table

CG Table

Item

Location from datum(in)

Weight (grams)

Moment

Port Jack Tare

-2.56

-55

140.94

Star Jack Tare

-2.56

-53

135.81

Rear Jack Tare

28.81

-64

-1,844

Port Jack with aircraft

-2.56

2,068

-5,299.25

Star Jack with aircraft

-2.56

2,145

-5,496.56

Rear Jack with aircraft

28.81

380

10,948.75

There are no rows in this table

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Total Weight

4,421

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Total Moment

-1,414.31

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-0.32

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Evaluation of CG

What does

-0.32

⁠

in mean?

It means the aircraft is slightly nose heavy. The center of gravity is 0.32 inches forward of the datum.

Do you think that this number is acceptable? How would you fix this if not?

Well, I thought so, but only due to the fact that I didn’t have a reference for acceptable tolerance. The goal would ideally be inside a 0.1 inch radius from the datum. Given ours is 3x that amount, this is abysmal...on paper. Anestis is confident that our center of gravity is fine. However, our measurements for calculating are erroneous. Essentially, everything is fine, but user error has prevented us from getting an acceptable answer on paper. We will simply adjust the orientation of the battery to be more aft if necessary.

Based on your CG Location, what flight characteristics would you expect during flight?

If the calculations were to be completely accurate, -0.32 in from datum would mean that we would have difficulty taking off and our elevator effectiveness will be stunted.

Discuss your results with your instructor. You may need to fix your CG.

Deliverables

Fully completed document exported as a PDF to Brightspace

.json of exported parameters file name “MMDDYYYYGroup#Param” imported into this document

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02132026Group1Param.json

39.8 KB

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