If you are seasonal R/C hobby flyer i'm sure you know where to setup the proper CG (Center Gravity) for your plane and keep the plane well balance not too nose heavy or tail heavy either. This ensure balance, save and linear flight. For any high or low winds may it be bi-wings or delta jet CG always basically at 1/3 from the front leading edge of the wings and keep the fuselage horizontally stable.
Some CG setup goes to FPV/UAV planes too but with slightly nose heavy.
Why we need a "slightly" nose heavy plane? How do we know our airframe need to be "at this" nose weight?
There are hundreds or maybe thousands type of flyable airframe available around the world that are FPV/UAV capable but non have the exact proper generic formula to guess the proper setup but the common feature all of these airframe have is that they all have wings. Wings help to keep the platform afloat and constant airflow required around the wings to maintain lift.....so what does it have to do with nose weight?
Earth gravity pull everything down, that includes winged platform such as planes. Its mother nature's natural downwards thrust. Before i proceed with my discussion try pondering out my CG setup below:
My setup:
Flying platform type: ES Drifter Ultralight, P-51D Mustang, Pitts Special, Coota Sea plane, Tristania 3D, Sky Surfer glider and AXN Cloud fly glider
Center Gravity point: 1/3 length from the leading front edge of the wings.
Nose degree tilt (pivoted from CG): 5 degree pointing down from horizontal 0. (Slightly nose heavy causing it to point 5 degree down angle)
Let get better picture what we are taking about here by looking some sample of scenario as shown below:
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Scenario example #1:
Assume i'm flying FPV glider around the skies and something happens..."Brown-out" (no power at all probably temporary BEC overheated) . Below are example of chronology of events:
Your setup is:
Flying platform type: Glider
Center Gravity point: 1/3 length from the leading front edge of the wings.
Nose degree tilt (pivoted from CG): Perfect 0 degree horizontal. Flat leveled
- Flying..then suddenly "Brown-out". A sudden power cut off to all main flight control including motor but you still can see and hear what going since FPV live video are on separate power supply but the pan-tilt was not moving.
- The plane slows down due to absent from motor thrust.
- Then plane suddenly losing speed. Due to perfect flat CG the wind started to toss your plane around randomly.
- The wings started to sink on the right side. Slip into wing " Washout"...slowly it bank hard ....spins and spiral down.
- The heavy wind started to rush along right side of the wing instead of front leading edge where airfoil shape of the wings should have provide lift but no.
- You plane plummet speed become increasingly fast in side spiral manner.
- You can hear from FPV earphone that your ESC started to 'beep' indicating motor initialization. BEC is recovering from overheating issues.
- You got your servo control and motor back...but too late you are already at minimum altitude to bail out. Bam! Crash.
You wish the plane didn't bank/roll instead. Ah you crash into someone's property. That's bad.
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Scenario example #2:
Assume i'm flying FPV glider around the skies and something happens..."Brown-out" (no power at all probably temporary BEC overheated) . Below are example of chronology of events:
Your setup is:
Flying platform type: Glider
Center Gravity point: 1/3 length from the leading front edge of the wings.
Nose degree tilt (pivoted from CG): 5 degree pointing down from horizontal 0. (Slightly nose heavy causing it to point 5 degree down angle)
- Flying..then suddenly "Brown-out". A sudden power cut off to all main flight control including motor but you still can see and hear what going since FPV live video are on separate power supply but the pan-tilt was not moving.
- The plane slows down due to absent from motor thrust.
- Due to nose heavy by 5 degree angle pivoted from CG point the plane started to dive downwards forward assisted by earth gravity pull.
- The dive speed increase steadily, each side of the wings receive airflow from the front causing balance lift on each side of the wing prevent rolling and spiraling.
- The wind started to get rough in all direction pushing the plane in all direction, but the gravity chooses the heaviest point of the plane ( the nose) to pull it down/to tilt the plane forward. Because its nose heavy at 5 degree down the plane receive slight horizontal forwards stability as it dive or sink down like paper plane going down in linear manner.
- You can hear from FPV earphone that your ESC started to 'beep' indicating motor initialization. BEC is recovering from overheating issues.
- You got your servo control and motor back. Your plane slightly downwards but stable in all axis. You gain control, pull elevator and push throttle thrust.....zooom!!.. You recovered! Hooray!
You got your plane back in one piece.
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Based on above scenario you get all overall picture why "slightly" nose heavy is crucial for FPV flight especial in fail situation. A slight nose heavy is something of a must "fail safe". How do you know how much nose heavy needed to get things right? Easy, just add some weight on the nose until the nose bow down about 5 degree down angle from horizontal 0 (zero degree) pivoted from main CG point.
Being nose heavy not only helps during power-loss/surface control loss but also allow user to determine if he/she flying to high AOA (Angle Of Attack) to avoid stall. In panic situation, by releasing the stick elevator to neutral position the plane dive slightly down to allow pilot to regain "Horizon" consciousness for FPV /UAV plane that lost sense of neutral horizon level or orientation especially inside the clouds, fog or live video feed black out. Plane that is not euipped with AHI (Artificial Horizon Indicator) on their OSD (On Screen Display) FPV display may benefit this setup.