Briefing: Aerotow

Introduction

Aim: You will learn how to fly the areotow launch, keeping yourself and the tug pilot safe

What do we know?
  • Who here has flown an aerotow?
  • What skills do you think are pre-requisites?
  • Where is your focus during the flight?
  • What is the risk to you?
  • What is the risk to the tug pilot?
Pre-requisite skills

Upper Launch
  • Ability to fly straight:
    • indicates an ability to detect and correct small angles of bank
Ground Run and Lower Launch
  • Ability to pat head and rub tummy: independent use of ailerons and rudder, while controlling elevator
  • Ability to maintain position behind the tug
Upper Launch

Vertical Positioning

Positioning is relative to the Tug’s Slipstream:

Method to maintain vertical position

  • Establish the slipstream’s location (buffet)
  • Move vertically, to just above, or below the slipstream.
  • Fix the tug’s position in the canopy as the attitude datum.
  • Adjust elevator to keep the tug on the datum:
    • If the Tug is High in the canopy, use Up elevator to place it on the datum.
    • If the Tug is Low in the canopy, use Down elevator to place it on the datum.
    • There is no need to aim higher or lower.
    • The glider will home in on the desired position if the datum is held.
Low Tow Position

  • Beneath the tug’s slipstream
  • Rarely used in the UK
    • Cross-country retrieves
    • Dual tows
Normal (High) Tow Position
  • Above the tug’s slipstream (just)
Lateral Positioning

Physics wants to keep the Tug and Glider in line

Gliders with a Nose Hook will tend to ‘follow’ more readily than those using a CG hook.

Positioning datum: the Tug’s wings (Angle of Bank)

Method to follow the Tug

Match the angle of bank to follow the tug.

Straight flight: glider is directly behind the tug, wings level.

Deviation: if the angle of bank is not matched, the glider will move off-line, in the direction of its ‘lower’ wing.

Correction: match the Tug’s angle of bank to keep the wings parallel to the tug. Allow the rope to pull you back in line.

Notes:

  • In still air, corrections are minor.
  • Aileron must always be coordinated with Rudder.
  • Compared to normal flight, the Rudder will feel heavier and Adverse Yaw will be worse.
Divergent Oscillation

The result of over-correction:

  • The tow rope exerts a strong centralising force.
  • Over-correction therefore leads to over-shooting the desired position.
  • Further over-correction makes things worse – potentially leading to a rope break.

When out of position, match the tug’s angle of bank and allow the glider to settle.

Boxing the Slipstream

  • This exercise demonstrates a range of positions to which the glider may reasonably go.
  • It will be performed at a later stage in your training.
  • It typically involves:
    • dropping below the slipstream
    • moving half a wingspan laterally, and holding that position
    • Climbing above the slipstream
    • Moving back to the normal towing position.
Turning

During turns, the glider is not directly behind the tug

To fly the same path:

  • The glider must point outside the turn (laterally).

If pointing at the tug:

  • The glider will fall inside the turn,
  • creating slack in the rope.
Method to maintain position in Turns

Match the angle of bank.

In shallow turns:

  • The glider will be pointing at the tug’s outer wingtip.

In steeper turns:

  • The glider will point further out.
Slack (Bows) in the Rope

Small bows:

  • Will be taken out by the tug’s pull
  • Do nothing… don’t make it worse!

Large bows:

  • An experienced pilot may use minimal airbrakes or sideslip to remove the bow. This must be removed before the rope tightens.
  • To release the cable in this situation:
    • Wait for the rope to tighten
    • Release just before it goes taught
  • Releasing with a large bow is to be avoided: it can cause the rings to come back towards you, or wrap around the glider.
Releasing from Tow
  • Confirm you are holding the (yellow) release control.
  • If possible, confirm the location of the Airfield.
  • Lookout
    • Check the Tug
    • Look for other gliders, hazards, clouds, before releasing the rope.
  • Release the rope under tension:
    • confirmed by it rippling away from you.
  • Confirm it is clear to manoeuvre, and the rope has released:
    • Raise the nose to maximise the separation
    • Make a climbing turn in the opposite direction to the tug.
      • Local rules may vary in terms of the direction.
  • Monitor airspeed as the glider slows – avoid stalling.
  • Confirm the location of the airfield – watch the tug.
  • Configure for flight.
Descending on Tow

  • May be necessary to avoid
    • cloud
    • airspace
  • Cross country retrieve
  • Inability to release

Low Tow position is less tiring and safer.

Use airbrakes to avoid climbing above the tug.

Emergency Signals

Tug

Tug Waggles Rudder

The glider has a problem

Check your Airbrakes (or braking parachute)

Tug Rocks Wings: The Emergency Wave Off

The tug (or combination) has a problem

Glider must Release Immediately

In rough air, watch the tug’s ailerons:

  • Moving after a roll: responding to a gust
  • Moving before a roll: signalling
Glider

The only problem the tug pilot wants to know about is if you can’t release…

  • Try the Radio.
  • Fly to the Left of the tug, and waggle your wings
    • Forward enough to be visible
    • Roll left first
    • (Almost no right roll is required)
    • May need some Airbrake to keep the rope taught.
      • Beware airbrakes snatching open at towing speed.

The tug pilot will take you back to the airfield, then release the tow rope.

Ground Operations
Glider Positioning

Align with the tug’s intended direction of take-off

The tug often takes up position after the glider is in place

Pre-Flight Checks
  • Glider lined up, with no obstacles ahead
  • Cushion usage: Confor
  • Pre-flight Checks: ABCDE, CBSIFTBEC
  • Min and Max safe aerotow speeds
  • Wind direction
  • Cloud base
  • Where to go? Tell the tug pilot

Establish Radio contact

Tug pilot may want your details for the log

Will need to know where you want to go

Set the Volume for the (noisy) tow

Know who is in control of the launch

Club procedures vary:

  • Who is calling “Take up slack” and “All out”?
Position of controls

Read the glider’s Flight Manual

  • Trim for Aerotow speed
  • Flap setting as recommended
  • Stick Fore / Aft / Neutral as recommended, to get the glider to balance on its mainwheel for the ground run. Typical recommendations:
    • Glider sits on its nose: Stick Aft.
    • Glider sits on its tail: Stick Neutral.
  • Anticipate prop-wash

Once hooked on, your left hand stays on the cable release until you release from the tow.

Wing Drop

More common with aerotows than winch (but initially slower):

  • Initial forward movement is slow
  • Prop-wash
  • Wing runner
  • Water Ballast

Immediate Action: Release

Ground Run, Take-Off and Climb
Ground Run

  • The objective is to follow in line with the tug:
    • Independent use of
      • Aileron: wings level
      • Rudder: track along the ground
      • Elevator: raising the nose / tail, to get the glider to balance on the mainwheel – allowing maximum acceleration.
      • Flaps: as recommended
  • If you cannot keep the wings level, release.
  • Stick position depends on the type of glider (nose/tail heavy).
  • Lift-off just above stalling speed.
Factors Affecting the Ground Run
  • Tug performance & Glider weight
  • Wind direction (headwind or cross wind?)
  • Wind variability
  • Surface and condition
  • Runway length

Crosswind considerations on the Ground Run
  • Initially: Downwind rudder to prevent yaw
  • Initially: Use the elevator to help maintain track while airspeed builds

Take-Off and Climb

  • Lift-off just above stalling speed.
  • Ease the stick back, very gently, if the glider does not lift-off.
  • Maintain height of 6-10 feet: your vertical datum.
  • Take extreme care not to climb any higher: this is critical for the tug pilot’s safety.
    • If the climb is uncontrollable – release immediately.
    • If you lose sight of the tug – release immediately.
Crosswind considerations after take-off

  • yaw or bank to prevent drift while the tug is on the ground
  • wings level, string central after the correction
  • the glider will be crabbing over the ground
When the tug lifts off

  • it may not climb much initially,
  • it may accelerate and hence climb more quickly
  • fly the glider to keep the tug at the desired datum
Wind Gradient

  • Climbing into a wind gradient may initially increase your airspeed:
    • More lift
    • Control responsiveness
    • Heavy rudder
Launch Failures

Ground Run:

  • Know where you will pull off if not airborne.

Airborne:

  • Options to land ahead from a low failure are often limited
  • Do not turn back unless sufficient height has been gained
  • Turning back low down is undesirable:
    • Stall / Spin
    • Downwind drift
    • Downwind landing
  • Identify the land ahead options before launching
    • On the airfield
    • In an overshoot area
    • Beyond the airfield
  • Consider a controlled crash:
    • into a clear space
    • fly onto the ground
    • ground loop, at the slowest speed possible
  • Retain the tow rope.
Tug Upsets

Tug upsets kill tug pilots.

Caused by the glider climbing too high: the Slingshot

Keep your left hand on the release and your attention on the tug.

If you lose sight of the tug, Release

If getting high uncontrollably, Release

Risk Factors associated with Tug Upsets

  • Light Pilot(s), close to minimum weight
  • Inexperienced Pilot
  • Belly or CG Hook
  • All-flying tailplane (light elevator forces)
  • Short Rope
  • Significant Cross-wind component
  • Turbulent conditions
  • Rough Ground
  • Light-weight glider, low wing loading
Recap

  • How do you keep the tug pilot safe?
  • How do you position the tug in your ‘sights’?
  • What is the Emergency Release signal?
  • What other signals are there?
  • How do you hold your position?
  • What factors do you consider before launching?
  • What tasks are permissible during a launch / tow?
TEM

Risk of Tug Upset
  • Low experience of glider and/or tug pilot
  • Gliders fitted with C of G hook only
  • Glider’s C of G towards the aft limit
  • Turbulent air in the take-off area
  • Rough ground in the take-off area
  • Significant cross-wind component
  • Short rope
  • Light-weight glider, low wing loading
  • Loss of concentration and focus

Ground Loop Risk Factors
  • Long, Low wings
  • Flapped Glider
  • Cross-wind
  • Prop-wash
  • Wing Runner
Low Launch Failure
  • Plan to land ahead
  • Turn Back only if safe to do so (height and speed)

BGA’s Safe Aerotowing Advice