goduranus

Guide for building competitive BD Armory jet fighters

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Gained some insight into building fighters with BD Armory lately, so I'm making a post of what I learned. Some of the content is from posts I made in the 1.2 Dogfight thread.

How to build a competitive jet fighter for BD Armory:

 

AI Pilot and Weapon Manager settings

Let's start with AI settings, which is an often neglected aspect that has a decisive impact on the outcome of the dogfights. Your plane will be slow if its AI Pilot is not told to make use of its maneuverability, and your weapons will be inaccurate if the Weapon Manager is not told to use them properly. The default values are no where near good enough for a fighter so you'll have to change them.

AI Pilot settings is meant to achieve good maneuverability through rapid steering response and kinetic energy management. Through experimentation, I've found some reasonably good values that work well with any ~10 ton fighter that has center of lift close to center of mass:

  • Steer Factor: 12 , this increases control sensitivity so steering commands are executed faster
  • Steer Dampening: 6, this increases stability, which you'll need because with CoL very close to CoM there is very little dampening force in the craft itself
  • Min Combat Speed:100, you need to keep your speed up, which means you have more kinetic energy, which means your kinetic energy can be converted to rotational energy faster
  • Idle Speed: 200, again this keeps your speed high before Guard Mode is activated, so you have more kinetic energy work with at the start of a match
  • Max G: 25, this tells the plane to maneuver hard at high speed, by setting G-limit to max, so that it will turn hard when it has lots of kinetic energy to spare.
  • Max AoA: 10-15, tells the plane to not maneuver too hard at low speeds, so that it doesn't bleed speed when kinetic energy is already low. You generally turn faster in a gentle turn by keeping the kinetic energy up. Don't set it to more than 20 as an abrupt turn will be fast initially but become sluggish as kinetic energy is bled away. See reference https://www.youtube.com/watch?v=EfZdUnGJkZU

Note* Propeller planes built with Airplane Plus are different, you should make them turn sharper, and at slower speeds than jets. This is because propellers' powercurve maxes out between 40-100m/s, where as jets max out at 600-900m/s. So depending on the propeller engine you're using, you can turn as sharply as you want as long as it doesn't make the plane drop below the speed where it generates 80%-90% of its maximum power (power=thrust*speed, which you can check by right clicking on the engine.) This means you can usually go whild on your steer factor and AoA settings, as well as set Min Combat Speed to something 60 and below.

 

Weapon Manager settings controls missile tactics, with these settings, you can already win against untuned planes. For standard 8km competition mode, the best settings seem to be:

  • Firing Interval:5, you want to space your missiles close enough such that there is always at least one AMRAAM in active seeker range of the enemy, which force them onto evasive maneuvers, which in turn cause them to lose energy and become easier targets. At the same time, missiles have to be spaced far enough apart so that you maximize the duration of the suppression to keep the enemy always on the defensive.
  • Gun Range:1000, reduce the gun range because missiles are also much more accurate at close range, you want to encourage the AI to use missiles right down to the point where guns can't miss.
  • Missiles/Target:4, you need several missiles in flight so that when the leading AMRAAM passes the target, the next AMRAAM's active seeker is already engaged, to suppress the enemy non-stop missile warnings.
  • Spread:300, you want your fighters to spread out the minimize the chance that all of you team can be caught in the active seeker cone of a single AMRAAM
  • Lag: 100, again, this is to spread your fighters out, which also encourages them to pick different missile targets

Note* With In absence of missiles you want to set your gun range to the maximum that the tournament you're in allows.

 

Munition choices

There are several missiles and guns to choose from, I've seen that Sidewinders and 50cal Browning arrays to be quite popular, but they are a no-no if you want to win the fight 

Missiles:

  • Use only AMRAAMs in missiles. AMRAAM has active radar, which gives out radar warnings to all enemy crafts within a cone in front of it, so you can suppress several enemy fighters with a single AMRAAM. 
  • Sidewinders are bad because they won't work if the enemy has even one decoy flare, so don't use them if you don't have to.
  • PAC-3 is terrible, because it requires constant radar lock for guidance, which meant it will miss if the enemy has ECM or if you have to do evasive maneuvers
  • HARM and others simply won't work against aircraft

Guns:

  • Use only GAU for your gun whenever possible. GAU has the highest dps/ton, because GAU fires explosive shells producing splash damage and nearly constant damage output independent of range.
  • Vulcan are bad because it only works very well at short range, at 500m and above the bullets lose damage which negates its high rate of fire.
  • Brownings are terrible, while light, they do very little damage at long range, and also has slowest bullet velocity which make them harder to aim.

Munition settings

With BDArmory 0.212 you can right click on individual gun and missile parts to change their range settings, doing you usually gives you an advantage

AMRAAMs :

  • Set the Detonation Radius to 20m to reduce the chance of a near miss at the target, since the AMRAAM's blast radius is 20m
  • Use forward ejection, which although slightly unsafe, adds to the missile's velocity and makes it reach the target faster.
  • If your plane is stealthy, you can reduce the max range of your AMRAAMs to as low as 6km to conserve them for when your up close, and you can lower the Fire Interval setting in your Weapons Manager to compensate and achieve a higher salvo density
  • To avoid exploding your planes by your own missiles, set ejection speed to max and set drop time to zero.

Sidewinders:

  • Set the Detonation Radius to 10m to reduce the chance of a near miss at the target, since the sidewinder's blast radius is 15m, but you can only adjust in increments of 10m.
  • Although easily distracted by flares, Sidewinders are useful in that it forces the enemy to temporarily shut down afterburners.
  • If you are forced to use sidewinders due to tournament rules, it's best to limit their max range to 1km above your gun range, which I recommend to be 2km, so that your plane fires a Sidewinder just before it goes in guns blazing
  • The point to doing this is to make the enemy shut down afterburners, lose speed, and become an easier target.
  • Also, to avoid exploding your planes by your own missiles, set ejection speed to max and set drop time to zero.

Guns:

  • Not much, except to set the gun range to 1km if you have missiles, so that gun aiming won't get in the way of missile lockon. If you have no missiles, set gun range to max
  • If you have more than one gun, setting Barrage to false seems to make the AI fire the guns faster.

 

Stealth, ECM and countermeasures

BD Armory calculates radar cross section by counting how many pixels of the sky your plane blocks out from the perspective of a radar. Below a certain threshold, and the radar won't be able to see your plane. Radar sensitivity is further reduced by active ECM pods the target has on board. A small plane with ECMs can reduce the range of enemy AMRAAMs' active seeker to about 2.5km, from 6km active seeker lock-on range for typical fighters without ECM, which means your plane spends considerably less time being force into evasive maneuvers, and some AMRAAMs may not lock onto you at all. 

For this to happen the ECM pods need to be activated before the enemy missiles engage their active seekers. So you need to bind the ECMs to the "Stage(Space Bar)" action group. ECMs take alot of electricity, so you'll need about 3000 electric charge in batteries. Alternatively, put on a tiny amount of oxidizer and a Fuel Cell Array, and make sure to also activate it with the"Stage(Space Bar)" action group. ECM seems to work better the smaller your plane is, if your plane's frontal profile is bigger than Mk-2 space plane fuselage, ECMs seem to stop working against AMRAAMs. ECMs have a diminishing return, so more than 2 ECM pods is ineffective, more than 4 ECM pods is completely useless.

Note that because of how airplanes maneuver by pitching up, enemy radars generally come from the bottom. So you'll want to reduce your aircraft's profile when viewed from 20-30 degrees below direct front. This means you'll generally want to mount your missiles on the top of your craft so the missiles' tails don't stick out and increase your radar profile.

You'll also want to put chaff and flares on the craft, right now 1 of each is sufficient, maybe put 2 of each just to be sure.

 

Aircraft construction

 

Moving Center of Lift with Elevators:

With regards to center of mass vs center for lift for optimum maneuverability. Mount all the wings and control surfaces except your elevators(the ones that control pitch), and make sure the center of lift with everything except the elevators is a good distance in front of the center of mass. Then mount the elevators in such a way that it pulls the center of lift slightly behind the center of mass, usually by placing elevators as far back as possible. Then set the elevator authority limit such that at full deflection is near the desired pitching AoA for the craft, which imo is 10-15 degrees.

What this allows you to do is turn much faster by shifting the center of lift back and forth, in front and behind the center of mass, by changing the elevator angle. When the elevator is at full deflection during a turn, it is nearly parallel to the airflow and don't contribute to the center of lift, so center of lift moves in front of the center of mass, and the aerodynamics force on your main wings contributes to your manevuerability. When the turn is finished, the elevator centers, moving the center of lift behind the center of mass, and your craft stabilizes.

 

Reducing adverse yaw from Ailerons:

With stock game not taking airflow direction into account, the ailerons will produce a yaw force when the craft is rolling while pitching. This is because aileron on one side is deflected against the airflow, while the other side is deflected into the airflow. For example, while pitching up and rolling right, the airflow is coming from below, so the ailerons produce a yaw left, because the left aileron is deflected against the airflow while the right aileron is deflected parallel to the airflow. I think the solution is to either mount the ailerons to exert a partial yaw force to counteract this,(swept forward for ailerons behind CoM, swept back for ailerons in front of CoM) or to just make sure the ailerons aren't too big, and mounted as far to the sides as possible for leverage. See explanation https://youtu.be/Y6RcTtGfG3E?t=9m50s

 

 

 

Don't use Canards:

Canards are bad in stock, because their orientation don't depend on direction of airflow, so what you get is basically a reversed elevator that's worse than an elevator because they generate much for drag when in use. This is because while pitching, the canard turns opposite to the airflow while the elevator turns into the airflow. With FAR, you can set canards to follow the airflow and they become much more useful for assisting with stability, see video https://www.youtube.com/watch?v=EBuQvZvBdto

 

Put enough but not too many Wings:

Make sure you have enough wings that your craft can maneuver at a relatively shallow AoA, as this is efficient for retaining kinetic energy during a turn. Although don't put too many wings as doing so causes your plane lose a lot of kinetic energy from drag. You seem to need at least 2 unit of wing area for every 10 ton in craft mass to fly, preferably 4 units of wing area per 10 tons of craft or more, but no more than 10.

 

Use rudders:

I've seen people not put rudders on, which puts them at a disadvantage in gun fights. While the bulk of the maneuvers are carried out by ailerons, rudders are still useful for fine adjustments.
 

Weight Distribution:

You want your center of mass to not move very much as you expend fuel and munitions, so build the craft with all fuel tanks empty. Then add fuel back bit by bit while keeping the CoM in the same spot. For this to be possible you should have fuel tanks both in front and behind the CoM, or on the CoM itself. After you get the desired amount of fuel, add missiles and ammo while keeping the CoM in the same spot. Note that you should have heavier components/munitions near the center of mass and lighter components/munitions further but still as close as possible from center of mass to minimize the moment of inertia, which gives you a higher angular acceleration.

 

 

I'd love it if someone builds a plane using these tips and send it to TAPE gaming, because I think all the crappy planes he gets sent deserve some major curbstomping, muahaha:cool:

https://www.youtube.com/watch?v=ZB_PdO9SFwQ&t=19s

 

Here's a new craft demonstrating the content of this thread, built for BDArmory 0.212

https://kerbalx.com/goduranus/F-18C-Hornet

6VjICJG.jpg

Edited by goduranus

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I think so, other than the missile settings part. Gun range should be set to max in that case, and you'd need to change the speed settings depending on the performance of the engines you're using.

Edited by goduranus

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On 7/13/2017 at 2:56 AM, goduranus said:

all the crappy planes he gets sent

I think many people prefer making their fighters look cool and somewhat realistic, rather making little solid-lifting bodies that use cheap tactics to suppress and then destroy aircraft.

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On 7/22/2017 at 5:34 AM, Deathpuff12 said:

I think many people prefer making their fighters look cool and somewhat realistic, rather making little solid-lifting bodies that use cheap tactics to suppress and then destroy aircraft.

Cheap tactic! Wut man! Suppressing the enemy with radar missiles to prevent them from getting an angle on you is a staple of 4th generation fighter tactic. Not doing this would be very unrealistic.

 

Edited by goduranus

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Yes, it is a tactic used in real life, but people submit their planes to things like TAPE's fighter jet showdown to be show off their designs and to have fun. In that kind of a "competition," ultra-competitive jets WOULD curbstomp most other jets, and it would be no fun for the people watching, or for the people getting their jets stomped on.

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Yeah, but building a decent looking hull is easy, only takes 10 minutes to do that. I feel that the real fun of building KSP fighters is in fine tuning the complicated stuff, like minimizing moment of inertia, finding a way to preserve kinetic energy through a turn, optimizing the shift in center of lift depending on angle of attack and control input, and optimizing radar profile, etc.

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Maybe you're right. I just find it more rewarding to build a really good-looking plane that flies decently. I've never really been into optimizing things for combat (in fact, I never really thought about energy fighting), and I know that many other people aren't as well (as you can see in TAPE's fighter showdown). Maybe I'll give this guide a try.

 

(PS, sorry for being so snarky in that first post. I was just tired and the comment about the crappy planes irritated me a little more than it should have.)

 

Edit: I'm using your E2-F2 to test against, and I noticed that it's quite vulnerable when attacked from above (my jet's minimum and default altitudes are 1000m and 2500m, respectively). You may want to consider raising the default altitude and adding chaff. Also, its gun is set to engage ground only.

Edited by Deathpuff12

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On 7/14/2017 at 3:33 AM, SpaceBadger007 said:

Would this guide still be usefull with slower ww2 aircraft?

Just tested WW2 crafts some, and it seems that my previous advice was wrong.

Since WW2 propellers in the Airplane Plus mod provide more thrust at low speeds, it's actually better to make your plane turn really hard in order to lose enough speed such that your engine provides more thrust. So AoA limit should be at least 25-30 degrees. 

I don't know whether this is completely true but I think the aim is to tune your plane so when it turns, it  spend most of its turn going at or slightly below the speed where your engines provides the greatest thrust power(Kinetic energy gained by your plane per second=kNs of thrust * plane's air speed)

Edited by goduranus

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On 7/13/2017 at 3:56 AM, goduranus said:

because I think all the crappy planes he gets sent deserve some major curbstomping, muahaha:cool:

As with @Deathpuff12, I think there's really a line between "competitive" fighters and "aesthetic" ones, the first group belonging in stuff like the ASC we got a while ago and the second in Hatbat's Kethane Station or similar series. I think Tape's videos really lie in the aesthetic side where people don't care about performance and just strap on a flight computer directly, since from what I've seen in his latest video, their performance is really excrementsty even for turn rate, not to mention choosing the ramjet engines for no apparent reason.

Any fighter with some wits put in it could beat them down, but again it would remove the fun from the not-so fighter hardcore community of KSP, aka most of the players.

 

Edited by NotAnAimbot

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But Tape does end up praising the better performing planes, so I assume he wants more competitive planes sent to him.

Edited by goduranus

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I found out the technical term for yaw instability created by ailerons at high AoA, which is actually "Adverse Yaw". Turns out my idea of swept ailerons was over-complicated, and the solution to Adverse Yaw is pretty simple: If you have any rudders on the bottom of your plane, just set them be roll enabled. And be sure to disable roll for rudders on the top, or that'll make it worse.

Video explaining Adverse Yaw, the F-4 Phantom apparently suffered badly from this problem.

 

Edited by goduranus

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wew...  just to know that the default for you is 12 in the steer factor makes my planes look weak... guess imma d e l e t e  and make new ones

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i made a modified tomcat thats really maneuverable and has decent speed, but if the enemy has a gau 8 then it'll have a run for its money. so i made a pak fa that had WAYY too many wing parts but was REAALLY maneuverable, but it was slow, trying to improve it right now too. (i wish this was revived.)

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On 8/8/2018 at 12:42 AM, Xd the great said:

Anyone have insights into other bdac AI settings?

I know a lot about the AI, and I've been thinking on making a post about what I have learned so far about the AI and plane designing. Ill announce it in the air superiority thread if I make it.

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30 minutes ago, dundun92 said:

I know a lot about the AI, and I've been thinking on making a post about what I have learned so far about the AI and plane designing. Ill announce it in the air superiority thread if I make it.

Thanks.

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The neat thing with a particular plane I am building is that the Max G absolute limit is 10. However, my plane can do 11-13 G sustained, and the AI is turning less than 10 G. How do I work around it that it turns hard but not too hard while keeping Max G to 10?

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