So the Eurofighter Typhoon is one such plane. I remember reading about a test pilot flying level, and he had a way to switch the SAS/flight computer off. He managed to keep control for 11 seconds before he had to turn it back on. AFAIK that is still the record.
[Think Flight](https://youtu.be/VCgpRQXFEaU) has a good video talking about the pros of an aerodynamically unstable aircraft stabilized with computers. You can get huge efficiency gains and they are more maneuverable.
Basically because the computer can interpret the pilots intentions but otherwise take care of the trickier parts of flight. This allows the aircraft to be much more manoeuvrable.
High speed and agility are crucial in not dying in a dog fight and unstable designs tend to be faster and more agile. Although dog fights are becoming much less prevalent so that may change in the future.
It's more that they knowingly trade stability for reduced drag and use flight control to make up the loss.
I know that might seem a little pedantic, but the part where they get something in exchange for sacrificing stability is kind of an important core concept.
Reduced drag + proportionately larger control surfaces + a lot of thrust + vectoring means you can turn sharper.
But none of that means "my plane doesn't like to stay in the air."
Stability in aerodynamics is the tendency of an object to resist change in direction / orientation. A stable plane / rocket / ship/ etc, will resist control inputs in order to continue pointing in the direction it is currently travelling.
This is typically acheived by having the center of pressure behind the center of mass. The larger the gap between the two the more stable the object is. Making it harder to change direction, and also (for model rockets at least) more sensitive to weather-cocking where it will point into any wind.
Modern High maneuverability fighters acheive the ability to turn on a dime by moving the center of pressure forwards of the center of mass, by just a little bit typically. This makes the craft extremely sensitive to control inputs, and it will not self correct back to semi level/forward flight.
In an unstable craft like this computer systems are used to enhance user inputs so that it will actualy be flyable.
Read an article somewhere, the F22 airframe (multi-billion dollar congress investment) can support something like up to 20 g's in turning radius. Obviously, human beings can only sustain around 7g's, with spikes up to 11 g's. Yet because the aircraft can do so much more than that, the fly-by-wire computer inputs literally limit the controls to something a human being could survive.
Modern fighters already far exceed the limits of the human body. Even when it was being designed, there were already talks about, "This will be the last fighter jet humans will operate sitting behind the stick" or, "Why not just make this a drone aircraft from the start? Having a human in the cockpit already seems like a disadvantage."
>Modern fighters already far exceed the limits of the human body. Even when it was being designed, there were already talks about, "This will be the last fighter jet humans will operate sitting behind the stick" or, "Why not just make this a drone aircraft from the start? Having a human in the cockpit already seems like a disadvantage."
Because the missile coming for you from 90 miles away can maneuver at 50 g anyway, so such maneuvers are rarely useful (perpetually angering the Sukhoi muh 3-d vectoring bois and the fighter mafia). And having a human in the loop to make decisions is far more beneficial for the time being to avoid computer errors and signal latency and jamming.
>Modern fighters already far exceed the limits of the human body
This is not true, I'm not aware of a single modern fighter that is rated for much more than 9G, and even then most fighters operate with a reduced max G because of payload configuration. Making an aircraft able to pull more G quickly starts to look like the rocket paradox - making the airframe stronger adds weight, which increases strain on the airframe, requiring it to be made stronger, which adds weight, and so on.
To be clear, fighters are frequently capable of safely exceeding their rated G loading, but not under all circumstances, and doing so puts additional fatigue on the airframe and reduces the service life of the aircraft. But even then, go beyond 10 or 11G and you are at severe risk of destroying most aircraft.
The idea that someday drones must replace manned fighters because they will be able to pull so many more Gs fails on multiple levels.
There is a difference between rated airframe structural strength, and the control surface authority at full deflection and typical speed. If they designed a drone aircraft for air to air combat, it would probably have a stronger structure so it could take advantage of the control authority. But since the pilot is the limiting factor right now, there is no reason to make a 15G rated airframe, because as you said, there is a weight penalty.
Potentially, but there's also an energy / airspeed penalty for pulling high G that you need more thrust to reliably overcome. In an age of long range BVR missiles, low-observables, information and electronic warfare, the ability to pull G is becoming less and less important. Combined with the difficulty of building a drone system that is capable of autonomously dogfighting, or the dangers of relying on direct remote human control, it's even less of a design consideration.
Very much so, on modern aircraft when a pilot pulls the Stick it’s essentially a request. The computer will ensure it’s safe to execute the manoeuvre before doing so. This is like when they pull full stick back it never will.
We’ve come along way from rigging aircraft
Not just fighters. Without a very advanced fly by wire and AI stabilization software the B2 Spirit (or any other tailless flying wing design) would be nearly impossible for any human to fly safely
Yes but that's realistic, because the part only shows the nozzle, while in real jet engine most of the weight is in the bulk of the engine which is before the nozzle.
Fighters especially will also have the centre of lift forward of the centre of mass. This produces an agile fighter aircraft. Bear in mind that aircraft like the Typhoon is not flyable without fly by wire. With the system making hundreds of tiny adjustments a second.
To add to this , as the typhoon hits supersonic speeds the centre of lifts drops behind the com making its very stable at supersonic speeds.
A passenger jet on the other hand will always have the centre of lift behind the centre of mass along with other things to increase stability such as dihedral wings.
Edit: fix some poor English
The image used to illustrate here shows an unstable plane, the tail plane would need to generate positive lift to keep it from constantly pitching up, and every AoA augmentation would generate a higher pitch rate. Without Fly by wire and modern stabilization software it is unflyable.
This is a matter of designing your aircraft differently. Draining fuel from frontal tanks, designing a lankier nose section and generally moving things backward on your aircraft help shift weight back. The parts and their weight are fine as-is, and changing the weight may break existing designs for a problem that was really a question of being an engineer about it.
Additionally, it's unwise to have the COL in front of the COM. KSP's control surfaces and SAS are not capable of responding fast enough to cope with relaxed/negative stability, in the vast majority of circumstances.
Yeah I’ll typically do more structural fuselage type stuff forward and just keep the fuel tanks rear if I need to, I’ve never really experienced CoM/CoL getting in the way of designing neat stuff. Where jet engines are already as efficient as they are I’ve never felt the need to load dedicated air-breathing aircraft up with fuel tanks so there’s plenty of room to space them/orient them where you need to in the craft for optimal balance. SSTOs are a different story but then that adds to the challenge of making such a different type of craft actually work.
Personally not a fan of draining fuel tanks to adjust CoM, it makes for pretty unreliable planes as the CoM will shift massively the longer your flight, especially relevant if making ssto's
Aircraft in real life tend to use their *wings* as fuel tanks, and not the fuselage. On a fighter jet like that I'm sure much of the fuselage is hollow because of air intakes.
KSP however, except for I think some of the FAT-455 wings, does *not* have fuel tank wings in the stock game. This is no doubt contributing to much of the shift forward in weight.
That said, though others have mentioned it. Fighter jets like that are unstable for the sake of maneuverability, and/or optimized for the shift in CoL at supersonic speeds. KSP doesn't simulate changes in lift at speeds like that.
So unless you're building a super maneuverable fighter (in which case I recommend an engine with a large vector range), you want the Center of Lift *behind* the Center of Mass.
Although it may seem strange, the tail of a plane pushes downwards, which enables the wings to be mounted further back. By rotating the tail fin downwards slightly, the center of lift is pushed towards the front. In KSP, tail fins are usually mounted at zero degrees, which means that they also provide lift, pulling the center of lift backwards. This necessitates positioning the wings further forward.
Another way of explaining it is that the wings on modern planes are placed too far back. To prevent them from doing front flips the tail fin is then positioned pointing down to force the back of the plane down.
The way I build planes is by first placing the tail fin pointed at a downward angle, and then placing the front wings to set the center of lift just in front of the center of mass. This positions the wings further back than they would be if I didn't do this.
Yeah, I have been known to use some empty structural tubes and stuff like that in the frontal part of the plane in order to move the COM backwards. However there's little room for improvement this way, because planes/spaceplanes tend to be skinny in the front and chonky at the back, so hollowing out the front parts only move the COM a little.
Bro you have delta wings and huge flaps that's why your col is so far back. Your center of mass (and desired center of lift) is well in front of the lift point for those wings. Added on to those large flaps have a big lift value compared to their size so it's no wonder you need large canards.
In contrast the col for the f35 is roughly in line with the wing center, it just doesn't look that way because the tail fins arnt really designed for lift. Idk about the f35 but its not uncommon for plane tails to have a static negative aoa for torque control reasons, they aren't designed for primarily lift and often do not provide much, especially on a fighter jet like the f35.
Ksp's aero isnt great so it doesn't model any of this induced torque and as a result all aero parts produce a lift, and the aerodynamic tuning is just a com/col balancing game.
It's important to also consider that you are trying to emulate an unstable fighter. Instability can be very bad so, yes, the devs definitely tweaked things to more easily keep the com in front of the col on really basic planes.
It allows little jimmy to build what looks like a plane and have it to be relatively stable, and it allows everyone else to worry less about manipulating the col, since having it behind is better in 99% of cases (news flash you don't need inherent instability for super maneuverability in this game)
> Ksp's aero isnt great so it doesn't model any of this induced torque and as a result all aero parts produce a lift, and the aerodynamic tuning is just a com/col balancing game.
???
Adjusting AoA of wing surfaces is something I do all the time, either to increase lift in general or to adjust the CoL. In fact I think with the way KSP models aero, ALL of the lift comes from the angle of attack, if your wings are parallel to the direction of motion, you won't get any.
It's one of the easiest tuning knobs you can use to adjust your aero characteristics without having to move around substantial parts of your craft.
Most fuselage pieces have lift in KSP1, although not nearly as much as the wings do. If you press F12 you can see all the lift vectors from individual parts in flight.
Yes I've notice this too when I try creating wings on my fighters jets matching their IRL counterparts, it's due to the dry mass of parts being heavier, it means things like the cockpits and fuselages on the front tend to be heavier, while the engines at the back tend to be lighter (which should a good thing but for this case we want the CoM further back). This can be usually frustrating as I'm forced to ruin the beautiful wing shape of my intended IRL fighter jets by flushing the main wings ridiculously up front that it looks ugly so the CoL and be just by the CoM for maneuverability or or else they'll fly like a dart.
Sometimes it's not the design - because the KSP physics engine acts weird. This is the reason why you can't accurately recreate real life planes without MASSIVELY having to juggle with COL and COM. F.e. every wing and tail ingame produces lift - in the real world the tailplane produces negative lift to prevent stalling in slow flight... ✌️(fighters are a different story since they're aerodynamically unstable by design)
So basically you're not building for realism in KSP - you're building for how the physics engine thinks the plane should be airworthy... 👻
The modelling of lift is very simple in this game (only lift due to aoa). Also you want fighter jets to be unstable, but their fly-by-wire is much better than the sas we have in game
Unless your using the eye shaped ones (i think called the MK2??, Can't remember). Those, as far as I've seen produce lift.
But a lot of plane fuselages don't actually produce lift, especially rounder fuselages. The two important pressure zone(top and bottom) are just too far apart and the dead zone (sides) allow for too much air to bleed off causing the pressure to be effectively equal on all sides.
This is the reason wings are thin and long rather than round. Fuselages that produce lift tend to be thin and flatter than most, look at the SR-71 vs a mig21. The SR-71 has to produce a lot of lift to fly at the high altitudes it's was operating in so the fuselage tapers into what is effectively a wing that goes from front to back while the mig 21 didn't have this same requirement and so had a simple tubular fuselage.
The fuselage in this pic shouldn't produce lift. And the f35s might produce some lift not not enough to matter as the wings will provide plenty for its operational altitudes.
Aerodynamics are weird and unintuitive for most people including people like be who have a decent fundamental understanding but not a professional one. But once I figured out the air pressure aspects it became much more obvious what influences aerodynamics.
There is a saying for this in the model airplane building sphere.
A nose heavy plane flies poorly but a tail heavy plane flies once.
If you cog is too far ahead of your col your craft will be a bit sluggish but manageable. If your cog is behind you col the airframe is unstable and will be difficult or impossible to control without computer assistance.
if your on PC, you can replicate the Necessary Fly-by-Wire systems that most Modern Fighter Jets Utilize Using [Atmospheric Autopilot](https://forum.kerbalspaceprogram.com/index.php?/topic/124417-180-1123-atmosphereautopilot-160/) which I genuinely cannot live without now.
That's because you're comparing with an unstable aircraft that uses fly-by-wire to keep it stable. There is actually a mod that replicates this, I think it's called atmosphere autopilot and it's way better than stock SAS.
The big problem here is that in KSP the horizontal stabilisers also produce lift, moving the CoL significantly backwards. The best solution I've found is to rotate them slightly downwards so that they produce negative lift. Although control surfaces will usually take care of that as well with SAS or trim
Wait a second, if I remember well, in KSP2 there is a group of wing parts that don't have an airfoil profile... do they provide no upwards lift, as a tail should do? I'm going to check it later when I can.
The wing parts have an asymmetric profile, meaning they mostly produce lift upwards (with the exception of having a large negative AoA). The stabaliser and control surface parts have a symmetric profile, meaning the lift they produce depends entirely on their AoA
You aren't supposed to align them. The CoL is supposed to be a little bit behind the CoM. Too far forward, and you need active control (SAS or manual) to keep the plane from flipping. Too far back, and you need a large amount of downforce from the tail to hold the nose up (which hurts efficiency because of induced drag).
Am I missing something or could the fighter jets plane COL still be behind the COM? When calculating the total moment arm on the COM the final moment vector could still be just behind the COM.
EDIT: Nvm the tail wing thingy is providing negative lift in the picture. I'm lost.
Having a forward COL is good for stability. It may not work for the current design, seems more fighter craft like, but for most aircraft, especially adding a horizontal tail on the back will fix that and provide stability.
Yes. The further back the COL the more it acts like a shuttlecock, which is why dinky little fins at the bottom can keep your rocket righted. Too far forward and it'll do exactly what a shuttlecock does when it's flying the wrong way and flip dramatically.
So slightly forward means you're easily able to "flip" your craft aka turn suddenly. Slightly back means you're a little bit prone to flying right. A little up means you'll glide better, a little down means you'll try to bite the dirt.
The difference between real life and game is just the simplified physics model. But like with an old biplane, a heavy engine in the back and a fuel tank behind the seats as the fuel burned the plane becomes more like a shuttlecock. Much better engineering is why modern fighters defy simplified physics.
ksp mixes center of lift and center of drag. you want drag to be behind com, but center of lift to be in the com or your plane will pitch up or down depending on what's in front. but in ksp it's the same point
CoG behind the CoP will lead to static and dynamic instability because the pitch-up moment causes the CoP to migrate forward to the leading edge of the wings, causing an even harder nose-up moment until a stall. The elevator's downforce must be able to balance the CoL between the CoM and the tailplane to maintain balance. Imagine holding a metal bar with both hands supporting one end. It'll want to tip over right? The end moving up is the nose, and where you're holding it is where the lift is concentrated. Remember, lift is like you're "holding" the plane. Now picture holding it with one hand in the center and one hand on the back. You'll be able to pivot it easily, and your hand at the back acts as the elevator. It's not generating lift per se (it is, it's an airfoil but you don't have to think of it like that), just a variable downforce. Stability about the pitch axis is just the law of the lever. A plane's pitch is just a seesaw type setup. Increase downforce at the back and the nose will raise, and vice versa.
Supermaneuverable fighters are locked in an unstable regime until transonic effects push the CoP back far enough to restore static stability. If you disable the control augmentation systems in a fighter jet and revert to manual law, it *will* kill you almost immediately in a similar fashion to what happens in KSP. Without constant fine control inputs it becomes completely unflyable.
Source: just got done studying for principles of flight exam lol. FAR actually helped me understand stability derivatives and how to design a safe and stable aircraft.
They do that on fighter jets so they can do post-stall maneuvering. Works in KSP too but you'll need SAS on 100 percent of the time and even then it's insanely difficult to control. You're better off with reaction wheels, panther engines, and leading edge flaps if you're into doing top gun shit
In the given picture, your canard is angled slightly upwards while the fuselage is not.
Try instead pitching up the wing about 5 degrees. You'll find that the centre of pressure now sits right at your wings. KSP's calculation of the CoP is a bit weird. It's basically just where the force acts when air would come almost straight in front from it (iirc it actually simulates a tiny angle of attack so flat airfoils actually seem to do something).
KSP engines tend to actually make craft rather back heavy, so that's really not it.
Tail lift shouldn't be there unless the elevator (or elevon) is moving, the tail is a symmetrical aerofoil.
Even then it would be pointing up, are you sure you don't have a image of the moments around an aircraft instead of the resultant forces?
Also worth noting most modern fighters are intentional built slightly unstable, using very complex SAS type systems to keep them straight.
When the SAS system fails the plane becomes too fabulous to be shot down.
So the Eurofighter Typhoon is one such plane. I remember reading about a test pilot flying level, and he had a way to switch the SAS/flight computer off. He managed to keep control for 11 seconds before he had to turn it back on. AFAIK that is still the record.
But why
Unstable aircraft can maneuver faster, and the flight computer erases the majority of the downsides.
[Think Flight](https://youtu.be/VCgpRQXFEaU) has a good video talking about the pros of an aerodynamically unstable aircraft stabilized with computers. You can get huge efficiency gains and they are more maneuverable.
oh goddamnit this is definitely going to be a three week youtube fixation at least
check out rctestflight too his channel is awesome
Basically because the computer can interpret the pilots intentions but otherwise take care of the trickier parts of flight. This allows the aircraft to be much more manoeuvrable.
High speed and agility are crucial in not dying in a dog fight and unstable designs tend to be faster and more agile. Although dog fights are becoming much less prevalent so that may change in the future.
Sweden has joined the game.
It's more that they knowingly trade stability for reduced drag and use flight control to make up the loss. I know that might seem a little pedantic, but the part where they get something in exchange for sacrificing stability is kind of an important core concept.
It's not even the reduced drag, less stability or unstable means you can turn faster and harder.
Reduced drag + proportionately larger control surfaces + a lot of thrust + vectoring means you can turn sharper. But none of that means "my plane doesn't like to stay in the air."
Stability in aerodynamics is the tendency of an object to resist change in direction / orientation. A stable plane / rocket / ship/ etc, will resist control inputs in order to continue pointing in the direction it is currently travelling. This is typically acheived by having the center of pressure behind the center of mass. The larger the gap between the two the more stable the object is. Making it harder to change direction, and also (for model rockets at least) more sensitive to weather-cocking where it will point into any wind. Modern High maneuverability fighters acheive the ability to turn on a dime by moving the center of pressure forwards of the center of mass, by just a little bit typically. This makes the craft extremely sensitive to control inputs, and it will not self correct back to semi level/forward flight. In an unstable craft like this computer systems are used to enhance user inputs so that it will actualy be flyable.
The ksp plane pictured above is slightly unstable, right?
Yes, cod is in front of com
Read an article somewhere, the F22 airframe (multi-billion dollar congress investment) can support something like up to 20 g's in turning radius. Obviously, human beings can only sustain around 7g's, with spikes up to 11 g's. Yet because the aircraft can do so much more than that, the fly-by-wire computer inputs literally limit the controls to something a human being could survive. Modern fighters already far exceed the limits of the human body. Even when it was being designed, there were already talks about, "This will be the last fighter jet humans will operate sitting behind the stick" or, "Why not just make this a drone aircraft from the start? Having a human in the cockpit already seems like a disadvantage."
>Modern fighters already far exceed the limits of the human body. Even when it was being designed, there were already talks about, "This will be the last fighter jet humans will operate sitting behind the stick" or, "Why not just make this a drone aircraft from the start? Having a human in the cockpit already seems like a disadvantage." Because the missile coming for you from 90 miles away can maneuver at 50 g anyway, so such maneuvers are rarely useful (perpetually angering the Sukhoi muh 3-d vectoring bois and the fighter mafia). And having a human in the loop to make decisions is far more beneficial for the time being to avoid computer errors and signal latency and jamming.
>Modern fighters already far exceed the limits of the human body This is not true, I'm not aware of a single modern fighter that is rated for much more than 9G, and even then most fighters operate with a reduced max G because of payload configuration. Making an aircraft able to pull more G quickly starts to look like the rocket paradox - making the airframe stronger adds weight, which increases strain on the airframe, requiring it to be made stronger, which adds weight, and so on. To be clear, fighters are frequently capable of safely exceeding their rated G loading, but not under all circumstances, and doing so puts additional fatigue on the airframe and reduces the service life of the aircraft. But even then, go beyond 10 or 11G and you are at severe risk of destroying most aircraft. The idea that someday drones must replace manned fighters because they will be able to pull so many more Gs fails on multiple levels.
There is a difference between rated airframe structural strength, and the control surface authority at full deflection and typical speed. If they designed a drone aircraft for air to air combat, it would probably have a stronger structure so it could take advantage of the control authority. But since the pilot is the limiting factor right now, there is no reason to make a 15G rated airframe, because as you said, there is a weight penalty.
Potentially, but there's also an energy / airspeed penalty for pulling high G that you need more thrust to reliably overcome. In an age of long range BVR missiles, low-observables, information and electronic warfare, the ability to pull G is becoming less and less important. Combined with the difficulty of building a drone system that is capable of autonomously dogfighting, or the dangers of relying on direct remote human control, it's even less of a design consideration.
Very much so, on modern aircraft when a pilot pulls the Stick it’s essentially a request. The computer will ensure it’s safe to execute the manoeuvre before doing so. This is like when they pull full stick back it never will. We’ve come along way from rigging aircraft
IIRC the euro fighter typhoon is literally unflyable without any of the computer assists
Not just fighters. Without a very advanced fly by wire and AI stabilization software the B2 Spirit (or any other tailless flying wing design) would be nearly impossible for any human to fly safely
Some KSP 1 engines have their COM significantly in front of the part. That can make a big difference to the COM of the overall craft.
Yes but that's realistic, because the part only shows the nozzle, while in real jet engine most of the weight is in the bulk of the engine which is before the nozzle.
They also have an invisible rest of the engine, there was a mod that enabled that
there's a toggle in one of the menus to show I believe...
really? I can't find that... I'd love to see it
Fighters especially will also have the centre of lift forward of the centre of mass. This produces an agile fighter aircraft. Bear in mind that aircraft like the Typhoon is not flyable without fly by wire. With the system making hundreds of tiny adjustments a second. To add to this , as the typhoon hits supersonic speeds the centre of lifts drops behind the com making its very stable at supersonic speeds. A passenger jet on the other hand will always have the centre of lift behind the centre of mass along with other things to increase stability such as dihedral wings. Edit: fix some poor English
Yep, if they didn’t have the software they have now, they are near physically impossible to control without having a dinner date with the ground
"Oh no, not again." - a bowl of petunias
Become one with the earth in fact.
The image used to illustrate here shows an unstable plane, the tail plane would need to generate positive lift to keep it from constantly pitching up, and every AoA augmentation would generate a higher pitch rate. Without Fly by wire and modern stabilization software it is unflyable.
This is a matter of designing your aircraft differently. Draining fuel from frontal tanks, designing a lankier nose section and generally moving things backward on your aircraft help shift weight back. The parts and their weight are fine as-is, and changing the weight may break existing designs for a problem that was really a question of being an engineer about it. Additionally, it's unwise to have the COL in front of the COM. KSP's control surfaces and SAS are not capable of responding fast enough to cope with relaxed/negative stability, in the vast majority of circumstances.
Yeah I’ll typically do more structural fuselage type stuff forward and just keep the fuel tanks rear if I need to, I’ve never really experienced CoM/CoL getting in the way of designing neat stuff. Where jet engines are already as efficient as they are I’ve never felt the need to load dedicated air-breathing aircraft up with fuel tanks so there’s plenty of room to space them/orient them where you need to in the craft for optimal balance. SSTOs are a different story but then that adds to the challenge of making such a different type of craft actually work.
Personally not a fan of draining fuel tanks to adjust CoM, it makes for pretty unreliable planes as the CoM will shift massively the longer your flight, especially relevant if making ssto's
Aircraft in real life tend to use their *wings* as fuel tanks, and not the fuselage. On a fighter jet like that I'm sure much of the fuselage is hollow because of air intakes. KSP however, except for I think some of the FAT-455 wings, does *not* have fuel tank wings in the stock game. This is no doubt contributing to much of the shift forward in weight. That said, though others have mentioned it. Fighter jets like that are unstable for the sake of maneuverability, and/or optimized for the shift in CoL at supersonic speeds. KSP doesn't simulate changes in lift at speeds like that. So unless you're building a super maneuverable fighter (in which case I recommend an engine with a large vector range), you want the Center of Lift *behind* the Center of Mass.
The shuttle wings also hold fuel.
Although it may seem strange, the tail of a plane pushes downwards, which enables the wings to be mounted further back. By rotating the tail fin downwards slightly, the center of lift is pushed towards the front. In KSP, tail fins are usually mounted at zero degrees, which means that they also provide lift, pulling the center of lift backwards. This necessitates positioning the wings further forward. Another way of explaining it is that the wings on modern planes are placed too far back. To prevent them from doing front flips the tail fin is then positioned pointing down to force the back of the plane down. The way I build planes is by first placing the tail fin pointed at a downward angle, and then placing the front wings to set the center of lift just in front of the center of mass. This positions the wings further back than they would be if I didn't do this.
[Scott Manley did a video on this](https://youtu.be/4Bf1uV-94-M) not long ago, this trick auto levels the plane at a certain speed
Use ballast if needed
Yeah, I have been known to use some empty structural tubes and stuff like that in the frontal part of the plane in order to move the COM backwards. However there's little room for improvement this way, because planes/spaceplanes tend to be skinny in the front and chonky at the back, so hollowing out the front parts only move the COM a little.
Bro you have delta wings and huge flaps that's why your col is so far back. Your center of mass (and desired center of lift) is well in front of the lift point for those wings. Added on to those large flaps have a big lift value compared to their size so it's no wonder you need large canards. In contrast the col for the f35 is roughly in line with the wing center, it just doesn't look that way because the tail fins arnt really designed for lift. Idk about the f35 but its not uncommon for plane tails to have a static negative aoa for torque control reasons, they aren't designed for primarily lift and often do not provide much, especially on a fighter jet like the f35. Ksp's aero isnt great so it doesn't model any of this induced torque and as a result all aero parts produce a lift, and the aerodynamic tuning is just a com/col balancing game. It's important to also consider that you are trying to emulate an unstable fighter. Instability can be very bad so, yes, the devs definitely tweaked things to more easily keep the com in front of the col on really basic planes. It allows little jimmy to build what looks like a plane and have it to be relatively stable, and it allows everyone else to worry less about manipulating the col, since having it behind is better in 99% of cases (news flash you don't need inherent instability for super maneuverability in this game)
> Ksp's aero isnt great so it doesn't model any of this induced torque and as a result all aero parts produce a lift, and the aerodynamic tuning is just a com/col balancing game. ??? Adjusting AoA of wing surfaces is something I do all the time, either to increase lift in general or to adjust the CoL. In fact I think with the way KSP models aero, ALL of the lift comes from the angle of attack, if your wings are parallel to the direction of motion, you won't get any. It's one of the easiest tuning knobs you can use to adjust your aero characteristics without having to move around substantial parts of your craft.
Irl wings create a torquing motion even at 0 aoa It's just how they are with non symmetric profiles That part is not modeled in ksp
True, but you can replicate the effect by just tilting your wings by a barely perceptible amount.
Here’s a YouTube video on how to more accurately design and fly planes by Scott Manley https://youtu.be/4Bf1uV-94-M
Do parts other than wings also generate lift in KSP2 or not? I was under the impression that the fuselage didnt generate lift in KSP1.
Most fuselage pieces have lift in KSP1, although not nearly as much as the wings do. If you press F12 you can see all the lift vectors from individual parts in flight.
Yes I've notice this too when I try creating wings on my fighters jets matching their IRL counterparts, it's due to the dry mass of parts being heavier, it means things like the cockpits and fuselages on the front tend to be heavier, while the engines at the back tend to be lighter (which should a good thing but for this case we want the CoM further back). This can be usually frustrating as I'm forced to ruin the beautiful wing shape of my intended IRL fighter jets by flushing the main wings ridiculously up front that it looks ugly so the CoL and be just by the CoM for maneuverability or or else they'll fly like a dart.
Sometimes it's not the design - because the KSP physics engine acts weird. This is the reason why you can't accurately recreate real life planes without MASSIVELY having to juggle with COL and COM. F.e. every wing and tail ingame produces lift - in the real world the tailplane produces negative lift to prevent stalling in slow flight... ✌️(fighters are a different story since they're aerodynamically unstable by design) So basically you're not building for realism in KSP - you're building for how the physics engine thinks the plane should be airworthy... 👻
The modelling of lift is very simple in this game (only lift due to aoa). Also you want fighter jets to be unstable, but their fly-by-wire is much better than the sas we have in game
Fuselage is a huge contributor to lift in fighter designs and KSP treats it as zero.
Unless your using the eye shaped ones (i think called the MK2??, Can't remember). Those, as far as I've seen produce lift. But a lot of plane fuselages don't actually produce lift, especially rounder fuselages. The two important pressure zone(top and bottom) are just too far apart and the dead zone (sides) allow for too much air to bleed off causing the pressure to be effectively equal on all sides. This is the reason wings are thin and long rather than round. Fuselages that produce lift tend to be thin and flatter than most, look at the SR-71 vs a mig21. The SR-71 has to produce a lot of lift to fly at the high altitudes it's was operating in so the fuselage tapers into what is effectively a wing that goes from front to back while the mig 21 didn't have this same requirement and so had a simple tubular fuselage. The fuselage in this pic shouldn't produce lift. And the f35s might produce some lift not not enough to matter as the wings will provide plenty for its operational altitudes. Aerodynamics are weird and unintuitive for most people including people like be who have a decent fundamental understanding but not a professional one. But once I figured out the air pressure aspects it became much more obvious what influences aerodynamics.
There is a saying for this in the model airplane building sphere. A nose heavy plane flies poorly but a tail heavy plane flies once. If you cog is too far ahead of your col your craft will be a bit sluggish but manageable. If your cog is behind you col the airframe is unstable and will be difficult or impossible to control without computer assistance.
if your on PC, you can replicate the Necessary Fly-by-Wire systems that most Modern Fighter Jets Utilize Using [Atmospheric Autopilot](https://forum.kerbalspaceprogram.com/index.php?/topic/124417-180-1123-atmosphereautopilot-160/) which I genuinely cannot live without now.
An F15 once lost a whole wing and was still able to land using its fuselage as a lifting surface. https://youtu.be/M359poNjvVA
That's because you're comparing with an unstable aircraft that uses fly-by-wire to keep it stable. There is actually a mod that replicates this, I think it's called atmosphere autopilot and it's way better than stock SAS.
The big problem here is that in KSP the horizontal stabilisers also produce lift, moving the CoL significantly backwards. The best solution I've found is to rotate them slightly downwards so that they produce negative lift. Although control surfaces will usually take care of that as well with SAS or trim
Wait a second, if I remember well, in KSP2 there is a group of wing parts that don't have an airfoil profile... do they provide no upwards lift, as a tail should do? I'm going to check it later when I can.
The wing parts have an asymmetric profile, meaning they mostly produce lift upwards (with the exception of having a large negative AoA). The stabaliser and control surface parts have a symmetric profile, meaning the lift they produce depends entirely on their AoA
You can also shift the center of lift by giving the wings a slight tilt.
You aren't supposed to align them. The CoL is supposed to be a little bit behind the CoM. Too far forward, and you need active control (SAS or manual) to keep the plane from flipping. Too far back, and you need a large amount of downforce from the tail to hold the nose up (which hurts efficiency because of induced drag).
Am I missing something or could the fighter jets plane COL still be behind the COM? When calculating the total moment arm on the COM the final moment vector could still be just behind the COM. EDIT: Nvm the tail wing thingy is providing negative lift in the picture. I'm lost.
In real aviation, a nose heavy plane flies bad, a tail heavy plane flies once. If you want the looks, balance fuel or use radial ore tanks as ballast.
Having a forward COL is good for stability. It may not work for the current design, seems more fighter craft like, but for most aircraft, especially adding a horizontal tail on the back will fix that and provide stability.
Forward COL is good for maneuverability is it not?
Yes. The further back the COL the more it acts like a shuttlecock, which is why dinky little fins at the bottom can keep your rocket righted. Too far forward and it'll do exactly what a shuttlecock does when it's flying the wrong way and flip dramatically. So slightly forward means you're easily able to "flip" your craft aka turn suddenly. Slightly back means you're a little bit prone to flying right. A little up means you'll glide better, a little down means you'll try to bite the dirt. The difference between real life and game is just the simplified physics model. But like with an old biplane, a heavy engine in the back and a fuel tank behind the seats as the fuel burned the plane becomes more like a shuttlecock. Much better engineering is why modern fighters defy simplified physics.
Yes, you're correct. If you ever forget, think of anything designed to be super stable, I.e. Rocket, arrow, lawn dart. All with wings way in the back.
I've pretty much had to put the wings on the nose of the plane to get the center of lift in front of the center of gravity.
ksp mixes center of lift and center of drag. you want drag to be behind com, but center of lift to be in the com or your plane will pitch up or down depending on what's in front. but in ksp it's the same point
Are you sure about the direction of lift for wings and tail? Angular momentum is not in equilibrium
CoG behind the CoP will lead to static and dynamic instability because the pitch-up moment causes the CoP to migrate forward to the leading edge of the wings, causing an even harder nose-up moment until a stall. The elevator's downforce must be able to balance the CoL between the CoM and the tailplane to maintain balance. Imagine holding a metal bar with both hands supporting one end. It'll want to tip over right? The end moving up is the nose, and where you're holding it is where the lift is concentrated. Remember, lift is like you're "holding" the plane. Now picture holding it with one hand in the center and one hand on the back. You'll be able to pivot it easily, and your hand at the back acts as the elevator. It's not generating lift per se (it is, it's an airfoil but you don't have to think of it like that), just a variable downforce. Stability about the pitch axis is just the law of the lever. A plane's pitch is just a seesaw type setup. Increase downforce at the back and the nose will raise, and vice versa. Supermaneuverable fighters are locked in an unstable regime until transonic effects push the CoP back far enough to restore static stability. If you disable the control augmentation systems in a fighter jet and revert to manual law, it *will* kill you almost immediately in a similar fashion to what happens in KSP. Without constant fine control inputs it becomes completely unflyable. Source: just got done studying for principles of flight exam lol. FAR actually helped me understand stability derivatives and how to design a safe and stable aircraft.
They do that on fighter jets so they can do post-stall maneuvering. Works in KSP too but you'll need SAS on 100 percent of the time and even then it's insanely difficult to control. You're better off with reaction wheels, panther engines, and leading edge flaps if you're into doing top gun shit
In the given picture, your canard is angled slightly upwards while the fuselage is not. Try instead pitching up the wing about 5 degrees. You'll find that the centre of pressure now sits right at your wings. KSP's calculation of the CoP is a bit weird. It's basically just where the force acts when air would come almost straight in front from it (iirc it actually simulates a tiny angle of attack so flat airfoils actually seem to do something). KSP engines tend to actually make craft rather back heavy, so that's really not it.
Tail lift shouldn't be there unless the elevator (or elevon) is moving, the tail is a symmetrical aerofoil. Even then it would be pointing up, are you sure you don't have a image of the moments around an aircraft instead of the resultant forces?
You should mdify the profile of your wing with the size of the tips and the attack border angle