what a hack; it mostly works, but there are edge cases.

OpenRa.Game/Traits/Activities/Fly.cs

@@ -7,10 +7,10 @@ namespace OpenRa.Game.Traits.Activities
 {
 	class Fly : IActivity
 	{
-		readonly int2 Cell;
+		readonly float2 Pos;
 		bool isCanceled;
 
-		public Fly(int2 cell) { Cell = cell; }
+		public Fly(float2 pos) { Pos = pos; }
 
 		public IActivity NextActivity { get; set; }
 
@@ -20,7 +20,7 @@ namespace OpenRa.Game.Traits.Activities
 		{
 			if (isCanceled) return NextActivity;
 
-			var d = Util.CenterOfCell(Cell) - self.CenterLocation;
+			var d = Pos - self.CenterLocation;
 			if (d.LengthSquared < 50)		/* close enough */
 				return NextActivity;
 
@@ -44,12 +44,49 @@ namespace OpenRa.Game.Traits.Activities
 		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
 
+	class Land : IActivity
+	{
+		readonly float2 Pos;
+		bool isCanceled;
+
+		public Land(float2 pos) { Pos = pos; }
+
+		public IActivity NextActivity { get; set; }
+
+		public IActivity Tick(Actor self)
+		{
+			if (isCanceled) return NextActivity;
+
+			var d = Pos - self.CenterLocation;
+			if (d.LengthSquared < 50)		/* close enough */
+				return NextActivity;
+
+			var unit = self.traits.Get<Unit>();
+
+			if (unit.Altitude > 0)
+				--unit.Altitude;
+
+			var desiredFacing = Util.GetFacing(d, unit.Facing);
+				Util.TickFacing(ref unit.Facing, desiredFacing, self.Info.ROT);
+			var speed = .2f * Util.GetEffectiveSpeed(self);
+			var angle = unit.Facing / 128f * Math.PI;
+
+			self.CenterLocation += speed * -float2.FromAngle((float)angle);
+			self.Location = ((1 / 24f) * self.CenterLocation).ToInt2();
+
+			return null;
+		}
+
+		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
+	}
+
 	class FlyTimed : IActivity
 	{
 		public IActivity NextActivity { get; set; }
 		int remainingTicks;
+		int targetAltitude;
 
-		public FlyTimed(int ticks) { remainingTicks = ticks; }
+		public FlyTimed(int ticks, int targetAltitude) { remainingTicks = ticks; this.targetAltitude = targetAltitude; }
 		
 		public IActivity Tick(Actor self)
 		{
@@ -65,6 +102,7 @@ namespace OpenRa.Game.Traits.Activities
 			self.CenterLocation += speed * -float2.FromAngle((float)angle);
 			self.Location = ((1 / 24f) * self.CenterLocation).ToInt2();
 
+			unit.Altitude += Math.Sign(targetAltitude - unit.Altitude);
 			return null;
 		}
 
@@ -82,10 +120,11 @@ namespace OpenRa.Game.Traits.Activities
 		public IActivity Tick(Actor self)
 		{
 			if (isCanceled) return NextActivity;
-			return new Fly(Cell)
+			var unit = self.traits.Get<Unit>();
+			return new Fly(Util.CenterOfCell(Cell))
 			{
 				NextActivity =
-					new FlyTimed(50)
+					new FlyTimed(50, 20)
 					{
 						NextActivity = this
 					}
@@ -94,4 +133,67 @@ namespace OpenRa.Game.Traits.Activities
 
 		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
 	}
+
+	class ReturnToBase : IActivity
+	{
+		public IActivity NextActivity { get; set; }
+		bool isCanceled;
+
+		readonly float2 w1, w2, w3;	/* tangent points to turn circles */
+		readonly float2 landPoint;
+
+		public ReturnToBase(Actor self, float2 landPos)
+		{
+			var unit = self.traits.Get<Unit>();
+			var speed = .2f * Util.GetEffectiveSpeed(self);
+			var approachStart = landPos - new float2(unit.Altitude * speed, 0);
+			var turnRadius = (128f / self.Info.ROT) * speed / (float)Math.PI;
+
+			/* work out the center points */
+			var fwd = -float2.FromAngle(unit.Facing / 128f * (float)Math.PI);
+			var side = new float2(-fwd.Y, fwd.X);		/* rotate */
+			var sideTowardBase = new [] { side, -side }
+				.OrderBy( a => float2.Dot( a, self.CenterLocation - approachStart ) )
+				.First();
+
+			var c1 = self.CenterLocation + turnRadius * sideTowardBase;
+			var c2 = approachStart + new float2(0, 
+				turnRadius * Math.Sign( self.CenterLocation.Y - approachStart.Y ));		// above or below start point
+
+			/* work out tangent points */
+			var d = c2 - c1;
+			var e = (turnRadius / d.Length) * d;
+			var f = new float2(-e.Y, e.X);		/* rotate */
+
+			/* todo: support internal tangents, too! */
+
+			if (f.X > 0) f = -f;
+
+			w1 = c1 + f;
+			w2 = c2 + f;
+			w3 = approachStart;
+			landPoint = landPos;
+
+			var rup = self.traits.Get<RenderUnitPlane>();
+			rup.wps = new[] { self.CenterLocation, w1, w2, w3, landPoint, c1, c2 };
+		}
+
+		public IActivity Tick(Actor self)
+		{
+			if (isCanceled) return NextActivity;
+			var unit = self.traits.Get<Unit>();
+			return new Fly(w1)
+			{
+				NextActivity = new Fly(w2)
+				{
+					NextActivity = new Fly(w3)
+					{
+						NextActivity = new Land(landPoint)
+					}
+				}
+			};
+		}
+
+		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
+	}
 }

OpenRa.Game/Traits/Plane.cs

@@ -17,6 +17,8 @@ namespace OpenRa.Game.Traits
 			if (mi.Button == MouseButton.Left) return null;
 			if (underCursor == null)
 				return Order.Move(self, xy);
+			if (underCursor.Info == Rules.UnitInfo["AFLD"])
+				return Order.DeliverOre(self, underCursor);		/* brutal hack */
 			return null;
 		}
 
@@ -27,6 +29,12 @@ namespace OpenRa.Game.Traits
 				self.CancelActivity();
 				self.QueueActivity(new Circle(order.TargetLocation));
 			}
+
+			if (order.OrderString == "DeliverOre")
+			{
+				self.CancelActivity();
+				self.QueueActivity(new ReturnToBase(self, order.TargetActor.CenterLocation));
+			}
 		}
 	}
 }

OpenRa.Game/Traits/RenderUnitPlane.cs

@@ -3,13 +3,17 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using OpenRa.Game.Graphics;
+using OpenRa.Game.Traits.Activities;
 
 namespace OpenRa.Game.Traits
 {
 	class RenderUnitPlane : RenderUnit
 	{
+		Animation debug = new Animation("litning");
+		public float2[] wps;
+
 		public RenderUnitPlane(Actor self)
-			: base(self) {}
+			: base(self) { debug.PlayRepeating("bright"); debug.Tick(); }
 
 		public override IEnumerable<Tuple<Sprite, float2, int>> Render(Actor self)
 		{
@@ -18,6 +22,10 @@ namespace OpenRa.Game.Traits
 			yield return Util.CenteredShadow(self, anim.Image, self.CenterLocation);
 			var p = self.CenterLocation - new float2(0, unit.Altitude);
 			yield return Util.Centered(self, anim.Image, p);
+
+			if (wps != null)
+				foreach (var w in wps)
+					yield return Tuple.New(debug.Image, w - .5f * debug.Image.size, 0);
 		}
 	}
 }

units.ini

@@ -670,6 +670,8 @@ ImpactSound=kaboom15
 OreChance=.02
 LowPowerSlowdown=3
 
+
+
 [VoiceTypes]
 GenericVoice
 VehicleVoice
@@ -683,6 +685,7 @@ CivilianMaleVoice
 CivilianFemaleVoice
 EinsteinVoice
 
+;; explicit extension on voice clips overrides the normal `variants` mechanism
 [GenericVoice]
 SovietVariants=.r01,.r03
 AlliedVariants=.v01,.v03
@@ -699,12 +702,12 @@ Move=ackno,affirm1
 [EngineerVoice]
 Select=eengin1,eyessir1
 Move=eaffirm1,emovout1
-Die=dedman1.aud,dedman2.aud,dedman3.aud,dedman4.aud,dedman5.aud,dedman6.aud,dedman7.aud,dedman8.aud,dedman10.aud
+Die=dedman1,dedman2,dedman3,dedman4,dedman5,dedman6,dedman7,dedman8,dedman10
 
 [MedicVoice]
 Select=mrespon1,myessir1
 Move=maffirm1,mmovout1
-Die=dedman1.aud,dedman2.aud,dedman3.aud,dedman4.aud,dedman5.aud,dedman6.aud,dedman7.aud,dedman8.aud,dedman10.aud
+Die=dedman1,dedman2,dedman3,dedman4,dedman5,dedman6,dedman7,dedman8,dedman10
 
 [TanyaVoice]
 Select=yo1,yes1,yeah1
@@ -722,12 +725,12 @@ Die=dogw5,dogw6,dogw7
 Select=syessir1,scomnd1
 Move=sonway1,sindeed1
 Attack=sking1
-Die=dedman1.aud,dedman2.aud,dedman3.aud,dedman4.aud,dedman5.aud,dedman6.aud,dedman7.aud,dedman8.aud,dedman10.aud
+Die=dedman1,dedman2,dedman3,dedman4,dedman5,dedman6,dedman7,dedman8,dedman10
 
 [ThiefVoice]
 Select=swhat1,syeah1
 Move=saffirm1,smout1,sokay1
-Die=dedman1.aud,dedman2.aud,dedman3.aud,dedman4.aud,dedman5.aud,dedman6.aud,dedman7.aud,dedman8.aud,dedman10.aud
+Die=dedman1,dedman2,dedman3,dedman4,dedman5,dedman6,dedman7,dedman8,dedman10
 
 [CivilianMaleVoice]
 Select=guyyeah1