Lost in the Sun and Spiral Dive

Debrief on RC incident 20090419-1-C-B

Event

• Spiral Dive from 150 feet.

Date/Time

• UU April 2009 10:30:00 (exact time to be determined)
  

Location

• Secondary flying location - UUU
  

Weather

• Very windy, with gusts exceeding 19 knots, changing direction from westerly to, at times, easterly
  

Aircraft

• Make model and type of A/C to be determined
  

Details of Aircraft

• All up weight 398g
  
• New brushless motor just installed (outrunner)
• Make and model and specification of motor to be determined
• Pitch and diameter of propeller to be determined
  
• Net thrust > 500g
• Slightly (incidental) off centre thrust - about 5 degrees to the left
  
• Weight and balance modified, tail wait of approximately 15g installed forward of vertical stabiliser
• C of G 25mm aft of leading edge (within limits)
  
• 11.1v LiPo fully charged
• Radio gear - digital 2.4GHz - DX6
  

Owner

• Mr UU-heli-man
  

Pilot in Command

• Mr UU-aero-man-not-too-windy
  

Other Mitigating Circumstances

• Little G was running around, creating a landing hazard which required the PIC to need to look out top and bottom
  

Description Prior to Event

• Aero configured in hangar
• New brushless and brushless ESC installed - checked out okay
• Motor held onto balsa with drilled screw
  
• Thrust slightly to the left (5 degrees) due to over pushing the motor onto balsa rod
  
• C of G moved aft by the application of plasticine weight fore of v. stab.
• Ground check okay
• Controls correct and proper movement
• Controls visually centred
  

Launch

• Full throttle, count "1-2-3-go"
  
• A/C hand launched by assistant - straight and level launch
  
• A/C airborne without too much trouble
• The A/C was difficult to handle in the fluky winds, with excessive aileron roll requiring constant correction
• Positioning the A/C was difficult - it was fairly constantly choosing its own path to fly
• Keeping altitude was easy - as excess thrust allowed it to climb near vertical, limited only by the ability to maintain the A/C attitude
• After around 3 minutes, the pilot considered attempting to try and get enough control to check the balancing of the A/C
  

Description of Event

• at T-10 seconds, the pilot attempted to initiate a down-wind (right to left (east to west)) pass, needing to turn the A/C 180 degrees to initiate the run
• the A/C was at about 100 feet and climbing - on initially 1/2 power
• at T-8 seconds the turn commenced, and additional power was applied (to full power) as the A/C became unmanageable
• the A/C climb at around 45 deg angle of climb to an altitude of around 300 feet at T-5 seconds
• the PIC was aware of the near vertical sun which was full (no clouds obscuring) - and was unable to bring the A/C under any control as it approached the suns direction at about T-4 seconds
• the PIC sheltered one eye and closed the other in order to try and keep visual on the A/C, and be able to pick it up post pass as soon as possible
• the A/C passed over the sun at T-3 seconds, also achieving maximum altitude of 350 feet as power was cut
• at T-2.5 seconds the PIC regained visual on the A/C which was proceeding to the northern outer permitter in with an attitude that was not initially determined
• at T-2.0 seconds the aircraft adopted a nose done, proceeding to vertical nose down attitude, with the PIC still not having positive control
• at T-1.5 seconds the A/C was nose down vertical, accelerating, and exactly on the edge of the boundry, although it appeared to be slightly beyond
• at T-1.0 seconds - at this point the PIC applied full back stick (elevator) - instintively - which only increase the speed - the A/C was in a tight near vertical spiral dive, estimated speed was at least 20 meters per second (70 km/h)
  
• the actual speed of rotation was not conciously realised until a few seconds later, but it was around two rotations per second
• again, the instinctive maneover to level the wings and pull back - was countered by the knowledge that this had a 50 percent chance of taking the A/C beyond the boundry - as a result - no action was taken
• at T-0.5 seconds - some control action was being applied, but with no response - the A/C's wings were perhaps stalling or some other type of control problem
• at time "T" (-0.0 seconds), the A/C impacted the ground nose first vertical, 5 cm into the boundary (short plants), remaining vertical after impact due to leaning on those same short plants - some 150 meters distant from the PIC

Post Event

• the throttle remained closed, and the controls were still responsive (rudder, elevator) the ailerons were obviously jamming and did not have much movement
• the A/C initially appeared mostly intact despite the impact speed; however
• on closer inspection, the nose was considerable damaged and bent, and the wings were displaced
• the battery was disconnected
• video of the damage was taken
  

Post Event Analysis

• The A/C was prepared sufficiently and to the best knowledge available
  
• The flight should not have taken place due to the nature and speed of the winds
• There should have not been extra people on the field during the test flight
• Being a test flight - the Sun's position in the sky was a factor, before sunrise would be preferable - or during overcoast (nil wind day)
• The aircraft's top speed was quite high, allowing the aircraft to get a long way downrange very quickly - perhaps different propping could improve this situation
  This meant the orientation and attitude of the aircraft became ambiguous at difficult to determine quite frequently
• It is quite possible the PIC's eyesight "ain't what it used to be" or it is just that the model was faster than what he was used to
  
• The PIC was unfamiliar with A/C of type - and needed at least extra simulator training before hand
• Incorrect recovery technique was applied, however the mitagating circumstances of loss of control in general, and exceed boundary were an issue
  

Outcome

• The model could probably be repaired, with a fair amount of effort
• Rebuild nose mount, and fairing
• Re-set wing position
• Strengthen and straighten bent structural parts

Precautions for Re-flight

• Paint or indicate on wings unique colours the enable simpler attitute and orientation perception
• Experiment with pitch and prop size to "gear down" the motor, which means greater low speed thrust, at the expense of top speed (which was too fast for the area) - trials and calculations required to do this
  
• Rebalance and correct control deflections on newly rebuilt model
• Airfield to be large and unobstructed
• No extra personnel or observers on airfield
  
• Nil wind conditions
• Series of planned exercises to ensure the model is flying correctly
• Initiate landing sequence early, then re-launch
• Low - or clouded Sun if possible
  

Things to Learn

• Gusty winds not the best for initial flight of a model (including changed setups)
• Practice, train, simulate, and stay current
• More diverse training worthwhile
• If it is your model, don't let some talk you into flying it in gusty wind - they don't know what they are talking about :-)

Terms

• RC - Remote Control
• A/C - Aircraft
• PIC - Pilot in Command
• attitude - the direction the aircraft is pointing (e.g. nose high)
• orientation - the exact relative position of the aircraft with repect to the PIC - e.g. closer (left) wing down, far wing up
  
• altitude - the height above the ground
• ESC - Electronic Speed Controller
• brushless - no brushes to the commutator
  
• outrunner - the outside of the motor rotates
• propping - the configuration of the propeller - pitch and diameter
• propeller pitch - how "deep" the cut into the air is, measured in inches