What Are Some Good Techniques For Building Maneuverable Planes That Don't Lose Too Much Speed?

[KidWithTheHands]

I have tried many ideas for fighter aircraft but most of them are junk and lose speed in turns. Anyway I can fix that with the right flaps?

[Fueniker S.]

Hello, glad for you to join us on the forum! To answer your question visit this link : 

I've used this post multiple times when creating my atmospheric vehicles, one of my most maneuverable planes was born not long after reading through it (pulled a constant 80g, made another that got ~300g from pulling out of a nose dive). Hope it helps! 

[Geschosskopf]

17 hours ago, KidWithTheHands said:

I have tried many ideas for fighter aircraft but most of them are junk and lose speed in turns. Anyway I can fix that with the right flaps?

Edit:  WHOOPS, I misspoke something....  Fixing it now.

For a more thorough dissertation on the principles below, see Robert Shaw's Fighter Combat:  Tactics and Maneuvering, which is THE BIBLE of air combat amongst real-life fighter pilots.  Shaw was a Top Gun instructor.  I'm lucky enough to have an autographed copy .  Anyway....

All planes lose speed in turns.  it's unavoidable, because the turning process necessary increases drag while it's happening due to increasing AoA, yaw, and control surface deflection, all of which increase the plane's effective frontal area.  And the change in AoA and/or yaw also points the engine off the direction of travel so you have less thrust than before going to maintaining your previous speed.  Thus, you're going to lose speed during a turn and all you can do is try to minimize this.  To minimize the speed loss during turns, you need to fly the thing so as to minimize the AoA and/or yaw relative to your current direction of travel, which essentially means not turning so hard.  But the faster you're going, the wider the turn radius, and the less hard you turn, the larget the turn radius, which goes against maneuverability.  So what do you do?

EDIT (added):  First off, you need to define maneuverability.  There are 2 things about turning that are important:  turn RADIUS (how tight the turn is) and turn RATE (how fast the turn is in degrees/second).  Turn RADIUS is pretty much entirely a function of speed.  The faster you're going, the wider you turn due basically to the vector addition nature of the process.  Turn RATE, OTOH, varies.  It is highest at "corner velocity", which is a function of the plane's design, and is usually not much above the plane's accelerated stall speed (like in a hard turn), which is considerably higher than the plane's normal, level, low-speed stall speed.

Turn RATE is generally more important for the opening and mid-game stages of the fight because it's what lets you change directions quickly to gain the advantage.  Turn RADIUS, OTOH, is usually only important in the final stages of the fight when you're going for or trying to avoid the kill shot.  By this point, at least one of the planes will have bled energy through repeated maneuvering to be below its corner speed.

Anyway, to get good turn rates and radii, there are 2 pretty much mutually exclusive approaches.  One is to make the plane a "turn-fighter", the other is to make it an "energy-fighter" (or E-fighter).  The difference between them is plane in which they turn.  Turn-fighters work mostly in the horizontal plane, E-fighters turn in the vertical plane.  Thus, they need rather different design characteristics.  I'll discuss turn-fighters first because they're more intuitive.

When doing ANY turn (horizontal or vertical),, the main turning force comes not from the control surfaces (or engine gimbal) but the lift vector of the wing.  You roll the plane to point the lift vector in the direction you want to turn, then use the elevator to increase the AoA of the wing so that it makes more lift, which pulls the plane around in the desired direction.  And for the best sustained turn, you want to be doing this while maintaining a specific speed called "corner velocity", which is the speed at which the plane has the highest turn rate and a reasonably small turn radius.  At higher speeds, you have a bigger turn radius due to momentum and reaching G limits, and a lower turn rate due to not being able to pull so hard around.  At lower speeds, you have to ease off on the turning to prevent stalling but have a smaller turn radius due to lower speed.  To maintain corner velocity through a series of turns, such as doing a horizontal scissors with the enemy, you have to be in a slight dive, so that the speed gained from falling counters the speed lost by turning.

So, for a turn-fighter, wing area is more important than thrust.  The more wing area for the plane's weight (IOW, the lower its wing loading), the lower its corner velocity.  The lower its corner velocity, the tighter its best turn radius will be, and the less altitude it has to lose to maintain speed through the turn.  In WW2, the early Zeros, Spitfires, and Bf-109s were like this.  Problem is, more wing area means more drag which means lower top speed.  And the lower the corner velocity, the lower top speed you want so you're always close to your corner velocity when you need it.  All of this limits the plane's performance in the vertical.  To try to work around this, you can use flaps very sparingly.  The purpose of these flaps is to increase wing area slightly without adding much drag, so you can have a higher top speed between turns.  The WW2 P-51, P-38, and N1K1 (among others) had such flaps.

And then there's the E-fighter.  This plane's turns are done in the vertical plane so it needs high TWR and high speed, which means less wing area and higher wing loading.  The F-104 is the quintessential E-fighter.  Such planes can't turn very well at all in the horizontal plane but can zoom vertically quite well.  As they go up, they slow down.  At the top of their zooms, they're going slow enough that they can flip over like in a tight loop and start back down.  As they dive back down, they regain most of the speed they lost during the zoom.  They also roll while pointing vertically downward to align their lift vectors with the target's future position, then pull out to intercept it.  The whole vertical maneuver has a very large turn radius in the vertical plane, but the projection of the maneuver into the horizontal plane has a very tight turn radius.  It's therefore possible for an E-fighter to have an effectively tighter or at least equal turn radius in the horizontal plane than a turn-fighter.  However, the E-fighter is still losing speed each turn so can only do this a few times before losing so much speed that it can no longer zoom effectively.  And when that happens, the turn-fighter will be all over it.

I personally prefer E-fighters because they're inherently faster and fly higher than turn-fighters.  This enables them to dictate the terms of the fight or whether it happens at all.  Then, if they don't win after a few passes, they're still moving faster than the turn-fighter so can disengage at will, go off somewhere safe, regain their energy, and come back for a rematch ,

Edited February 22, 2016 by Geschosskopf

[Geschosskopf]

Edited my last.  It's been a while since I did any serious dogfighting so I forgot the distinction between turn RATE and turn RADIUS, and misdefined corner velocity as a result.  So I went back up and fixed that.

[RizzoTheRat]

Cracking writeup @Geschosskopf

One thing you don't really mention much there, which is relatively new, is thrust vectoring and post stall manouvering.  Not sure if any KSP mods give you full 2D thrust vectoring but it potentially allows an aircraft to temporarily face in a drastically different direction to it's velocity vector in order to lock weapons to a target, but at the cost of a lot of momentum.  With modern targeting systems and all aspect missiles I'm not entirely convinced how useful that is, but it looks good and in KSP where you don't have fancy radars and capable missiles it could be of more use.

The obvious examples being the Cobra and Kulbit manoeuvres https://www.youtube.com/watch?v=dZg0jZfI6Cg

 

Edited February 23, 2016 by RizzoTheRat

[Val]

34 minutes ago, RizzoTheRat said:

The obvious examples being the Cobra and Kulbit manoeuvres https://www.youtube.com/watch?v=dZg0jZfI6Cg

Great clip and there's an awesome comment: "Screw your western physics".

Though I would have phrased it: "Screw your western aerodynamics"

[RizzoTheRat]

I saw him do it practice week for the Farnborough Airshow that year.  A whole bunch of aero engineers standing in the carpark open mouthed asking each other if it had just done what we thought it had.

Our car park was also right under where the Mig 29 always did his tail slide.  That always looked impressive from underneath until you remembered Paris '89...

[Geschosskopf]

1 hour ago, RizzoTheRat said:f

One thing you don't really mention much there, which is relatively new, is thrust vectoring and post stall manouvering. 

I didn't mention this because they have no practical value outside airshows.  The main thing to avoid in air combat is running out of airspeed, altitude, and ideas all at once, which is exactly the situation you're in if you're doing a Cobra or some such thing.  If you're slow enough for such moves, you're a sitting duck for every incoming weapon.

Where thrust-vectoring has proven to be useful was to tighten conventional dogfighting turns.  This was shown back in the Falklands War by the Harrier, which has hardly any wing so isn't built like a turn-fighter, yet it was turning inside A-4s, which were so maneuverable the Blue Angles kept using them long after they were obsolete on the front line.

[RizzoTheRat]

2 minutes ago, Geschosskopf said:

they have no practical value outside airshows

That's my view as well, but I can't help thinking if so many people are spending so much money on supermanouvrability that they must know something I don't.

Interestingly I don't recall any mention of "VIFFing" (which again would result in losing a lot of speed) in "Sharkey" Wards book on the Falklands, despite it often being mentioned as a capability of the Harrier, so I wonder if that was another manoeuvre which sounded good on paper but never really had any use in combat.  Mind you it was a long time ago I read it.  I'd not heard of using a small amount of vectoring to tighten the turn though, that makes a fair bit more sense.

[Geschosskopf]

1 hour ago, RizzoTheRat said:

That's my view as well, but I can't help thinking if so many people are spending so much money on supermanouvrability that they must know something I don't.

From what I understand, the main use of this isn't for sustained use in dogfighting but for quick sidesteps to avoid a weapon or get off a snapshot.  But dodging gun runs and incoming missiles isn't done by sitting essentially in 1 place and rotating.

1 hour ago, RizzoTheRat said:

Interestingly I don't recall any mention of "VIFFing" (which again would result in losing a lot of speed) in "Sharkey" Wards book on the Falklands, despite it often being mentioned as a capability of the Harrier, so I wonder if that was another manoeuvre which sounded good on paper but never really had any use in combat.  Mind you it was a long time ago I read it.  I'd not heard of using a small amount of vectoring to tighten the turn though, that makes a fair bit more sense.

Well, in truth, there really wasn't a whole lot of dogfighting going on in the Falklands.  The Brit fleet was right at the extreme range of the Argentine attack planes so the latter didn't have enough few to divert much from the straight run there and back.  But I do recall it being mentioned a lot at the time (i was in the process of deploying to the war so was paying lots of attention to events ).  What wasn't mentioned so much, but which was definitely a major factor, was that this was the 1st major use of all-aspect IR missiles, and defensive tactics hadn't caught up with that yet.

[Hodo]

On 2/22/2016 at 7:48 PM, KidWithTheHands said:

I have tried many ideas for fighter aircraft but most of them are junk and lose speed in turns. Anyway I can fix that with the right flaps?

 

As Geschosskopf said, all fighters lose speed or energy when turning.  In a short version everything works on math, even cars.  If you want to turn you have to devote energy to that, energy = speed.   How hard you turn will depend on how much energy you are willing to spend to do it.  Now this is in the simplest terms.  

 

I think it went something like Altitude = Energy = Speed = Altitude.   This is why Dicta boelcke still holds true to this day.

Altitude: From the advantage of flying above his opponent, a pilot had more control over how and where the fight takes place. He could dive upon his opponent, gaining a sizable speed advantage for a hit and run attack. Or, if the enemy had too many advantages- numbers for instance- a pilot could fly away with a good head start. At best, World War I aircraft climbed very slowly compared with later types. Altitude was a hard earned 'potential energy' store not to be given away capriciously.

[Nothalogh]

On 2/22/2016 at 7:48 PM, KidWithTheHands said:

What Are Some Good Techniques For Building Maneuverable Planes That Don't Lose Too Much Speed?

Higher TWR