Maiden and Test flight program

This is an article written from my 20 year experience in flight testing airliners and industrial/ military UAV.

This article in now way is trying to explain how to flight test the above vehicles, but rather is an adaptation of the core philosophy to the hobby/ UAV world.

This is a rather slow and resource intensive method but it is quite essential to the designer who puts a new airframe in the air. The procedure below will also be useful to the professional modeler who wants to flight test a very complex scale model.

The flight phase must be started after the pre-flight tests have been completed. All the snags discovered during the previous phase must be cleared before the flight test phase.

The core philosophy of a flight test program is to progressively open up the flight envelope.

It starts from low speed, flaps extended, gear extended to progressively retracting the drag elements and increase the speed. The test program is completed when top speed has been validated as well as all the high G maneuvers intended for the plane. CG position in all configuration must also be validated. For this purpose, a digital balancing equipment is a vital tool.

For all of this, 2 spotters are recommended. One program spotter who will announce the next program maneuvers announce the stall speeds, max speed, configuration changes, compute 1.3 Vs etc , one flight spotter who will check the airspace and possible conflicts and give feedback on the airplane behavior ( nose attitude, CG behavior etc ).

An additional camera operator is also recommended to capture every flight.

A full telemetry system with ground return is recommended to get a feedback of the flight speeds as well as model parameters like remote link quality, battery voltages...

 The typical flight test program is described below:

 

Taxi tests:

Configuration: fixed, gear down takeoff flaps.

Program: 

Low speed taxi, validate the steering effectiveness.

High speed taxi, validate the steering effectiveness

Rejected takeoff medium speed: validate the brakes effectiveness

Rejected takeoff high speed: validate elevator effectiveness by pulling near Vr. The nose should start to lift.

Post flight verifications: Steering servo, brakes wear, tire wear, gear components, turbine parameters, battery consumption, fuel consumption, air trap air quantity ( should be full ).

 

Flight 1, configuration stalls and approach speed validation: 

Configuration: semi fixed, gear down takeoff flaps then landing flaps.

Program: 

Takeoff,

One to two patterns for trimming with takeoff flaps. Check CG behavior in turns ( how much up elevator ? ). Check the controls throw and adjust if required ( via dual rate ).

Extend landing flaps.

One to two patterns  for trimming with landing flaps. Check CG behavior in turns  how much up elevator ? ). Check the controls throw and adjust if required ( via dual rate ).

Climb and stall at comfortable altitude. Record stall speed, implement 1.3 vs that is the approach speed ( spotter's job ).

Come back for landing. Approach at 1.3 Vs.

Landing and full stop.

This flight takes typically 4 to 5 minutes.

Post flight verifications: Steering servo, brakes wear, tire wear, gear components, turbine parameters, battery consumption, fuel consumption, air trap air quantity ( should be full ) internal components fastening, servos fastening, servo arm, pushrod, control horn, fuel system, flight controls slop, gear slop, bearing and gear pin slop.

Make a snag list and clear it at the workshop. Wait one week before flight 2 and review all the flight parameters and data. Briefing with the spotters. Modify the dual rate/ control throws if required. Modify the CG if required.

 

Flight 2, CG validation/ fine tuning: 

Make this flight when the previous snag list is clear.

Configuration: semi fixed, gear down takeoff flaps then landing flaps.

Program: 

Takeoff,

One pattern to confirm trimming with takeoff flaps.

One pattern to confirm the new CG behavior further ( if changed ).

Extend landing flaps.

One pattern to confirm trimming with takeoff flaps.

One pattern to confirm the new CG behavior further ( if changed ).

Climb and stall at comfortable altitude. Record stall speed, implement 1.3 vs that is the approach speed ( spotter's job ) with the new CG position.

Come back for landing.

Landing and full stop.

This flight takes typically 4 to 5 minutes.

Post flight verifications: Steering servo, brakes wear, tire wear, gear components, turbine parameters, battery consumption, fuel consumption, air trap air quantity ( should be full ) internal components fastening, servos fastening, servo arm, pushrod, control horn, fuel system, flight controls slop, gear slop, bearing and gear pin slop.

Make a snag list and clear it at the workshop. Wait one week before flight 3 and review all the flight parameters and data. Briefing with the spotters.Modify the dual rate/ control throws if required. Modify the CG if required.

 

Flight 3, gear retraction and stall speeds: 

Make this flight when the previous snag list is clear.

Configuration: variable, gear down then up, takeoff flaps then landing flaps.

Program: 

Takeoff,

One pattern to retract the gear in front of you

One pattern to confirm the new CG behavior with gear up.

Extend landing flaps.

One pattern to confirm the new CG behavior with gear up.

Climb and stall at comfortable altitude. Record stall speed, implement 1.3 vs that is the approach speed ( spotter's job ) with the gear up.

Come back for landing.

Extend the gear.

Landing and full stop.

This flight takes typically 4 to 5 minutes.

Post flight verifications: Steering servo, brakes wear, tire wear, gear components, turbine parameters, battery consumption, fuel consumption, air trap air quantity ( should be full ) internal components fastening, servos fastening, servo arm, pushrod, control horn, fuel system, flight controls slop, gear slop, bearing and gear pin slop.

Make a snag list and clear it at the workshop. Wait one week before flight 4 and review all the flight parameters and data. Briefing with the spotters. Modify the dual rate/ control throws if required. Modify the CG if required.

 

Flight 4, flaps retraction and stall speed ( do not push the speed ): 

Configuration: variable, gear down then up, takeoff flaps then clean, then landing flaps.

Make this flight when the previous snag list is clear.

Program: 

Takeoff,

One pattern to retract the gear in front of you

One to two patterns to retract the flaps and trim.

One to two patterns to check CG behavior.

Climb and stall at comfortable altitude. Record stall speed, implement 1.3 vs that is the stall  speed protection ( spotter's job ) with flaps up.

Come back for landing.

Extend gear and landing flaps.

Landing and full stop.

This flight takes typically 5 to 6 minutes.

Post flight verifications: Steering servo, brakes wear, tire wear, gear components, turbine parameters, battery consumption, fuel consumption, air trap air quantity ( should be full ) internal components fastening, servos fastening, servo arm, pushrod, control horn, fuel system, flight controls slop, gear slop, bearing and gear pin slop.

Make a snag list and clear it at the workshop. Wait one week before flight 5 and review all the flight parameters and data. Briefing with the spotters. Modify the dual rate/ control throws if required. Modify the CG if required.

 

 

Flight 5, flap up CG validation with inverted flight ( do not push the speed ): 

Configuration: variable, gear down then up, takeoff flaps then clean, then landing flaps.

Make this flight when the previous snag list is clear.

Program: 

Takeoff,

One pattern to retract the gear in front of you

One to two patterns to retract the flaps and trim.

One to two patterns to check CG behavior:

Climb at 45 degrees and invert the plane. Once the plane is climbing stable on its back, release the elevator pushing action. Let the plane fly alone. Note the behavior. If the nose is dropping heavily: too nose heavy. If the plane is dropping the nose slightly: good CG. If the plane is climbing more ( nose going up ): too aft CG.

Come back for landing.

Extend gear and landing flaps.

Landing and full stop.

This flight takes typically 5 to 6 minutes.

Post flight verifications: Steering servo, brakes wear, tire wear, gear components, turbine parameters, battery consumption, fuel consumption, air trap air quantity ( should be full ) internal components fastening, servos fastening, servo arm, pushrod, control horn, fuel system, flight controls slop, gear slop, bearing and gear pin slop.

Make a snag list and clear it at the workshop. Wait one week before flight 6 and review all the flight parameters and data. Briefing with the spotters. Modify the dual rate/ control throws if required. Modify the CG if required.

 

Flight 6, flap up CG validation with inverted flight ( do not push the speed ): 

Configuration: variable, gear down then up, takeoff flaps then clean, then landing flaps.

Make this flight when the previous snag list is clear.

Program: 

Takeoff,

One pattern to retract the gear in front of you

One to two patterns to retract the flaps and trim.

Two patterns to check the new CG behavior:

Climb at 45 degrees and invert the plane. Once the plane is climbing stable on its back, release the elevator pushing action. Let the plane fly alone. Note the behavior. 

If the CG is good, come back for an inverted flight in front of you ( if the airframe permits it ). Note how much elevator stick pushing is required. 

Come back for landing.

Extend gear and landing flaps.

Landing and full stop.

This flight takes typically 5 to 6 minutes.

Post flight verifications: Steering servo, brakes wear, tire wear, gear components, turbine parameters, battery consumption, fuel consumption, air trap air quantity ( should be full ) internal components fastening, servos fastening, servo arm, pushrod, control horn, fuel system, flight controls slop, gear slop, bearing and gear pin slop.

Make a snag list and clear it at the workshop. Wait one week before flight 7 and review all the flight parameters and data. Briefing with the spotters. Modify the dual rate/ control throws if required. Modify the CG if required: if too much pushing is required when inverted, get the CG aft. If to light on the stick push, get the CG forward.

 

Repeat flight 7 program till the CG is set to your preference.

 

Subsequent flights:

Gradually push the speed to the maximum allowed speed and check the airframe.

Start introducing aerobatic maneuvers if the plane is capable of it. Start with low G's maneuvers ( rolls ) then high g's maneuvers ( loop based maneuvers ).

The last maneuver to perform will be the snap stall if the airframe is capable of it.

Verify: no signs of flutter, no cracks on the spars, skin, control horns...

Once the test program is fully completed, the plane can be flow with confidence in meetings and competitions. Note that the airframe will gradually age and once the early failure rate is eliminated, will slowly get more reliable.