Official FAR Craft Repository

[Kitspace]

What I see is exactly the same as on your pictures.

According to the statics page on the second screenshot your plane stalls at about 16 degrees AoA with Cl 1.1

However the derivatives page on the first screenshot clearly claims the plane is stalled at Cl as low as 0.754

That is quite a large discrepancy. So there is a speed range for which the derivatives page does not want to work for some reason.

What happens if you increase the speed just to the bare minimum at which it shows meaningful numbers?

[Van Disaster]

If one part of that panel is garbage ( like the out-of-bounds AoA ) then I wouldn't trust any of it.

This is as slow as it will fly with those flap settings ( actually flies slower with no flaps, I don't remember what I was doing there ). Cl is way below maximum possible because it doesn't need any more lift to stay level at that altitude.

At 8km it's a bit different - I think that is actually the stall speed given a fraction above it gives a lot of control back.

This would be the lowest usable speed I guess:

Edited September 2, 2017 by Van Disaster

[kcs123]

Keep in mind that graph shows AoA needed for level flight. On landing, you don't need level flight, it is actualy desireable that you plane fall down slightly, -1 to -5 m/s that will allow you to maintain horizontal speed. Plane would be perfectly controlable with lower AoA and flaps like shown on pictures. Due to tail clearance, you don't want more than 10 - 15 degree of AoA on landing. Judging from provided pictures, it would be easy to land this plane with engine shut off.

Nice design, Van Disaster.

[Kitspace]

As I understand it the critical angle of attack in level flight is the measure of stall speed. The fact that a plane does not need its maximum lift coefficient to stay level to me means that it CAN go slower. If it is not yet stalling at that speed then what would keep it from slowing down further?

What do you mean by as slow as it will fly?

It seems right on the pictures at 8 km. It becomes pretty much uncontrollable at the critical angle of attack and at about maximum Cl and looses lift if pulled harder.

From my observations with actual flying all the crafts behave according to the statics page and stall where the graphs show. At least at low altitude it happens at a slower speed than the derivatives page predicts. I sometimes have it claim the craft stalls at angles of attack as low as 5 degrees while it actually stalls at 20.

Do you seriously suspect the calculations on that panel are broken?

[Van Disaster]

Well, two things. 1) the aerofoil profile is a NACA supersonic profile, so it's not optimised for slow flight. 2) You'll have to ask Ferram for more because I don't actually use the panels all that much, I tend to just build things & only look at the numbers when there's a gross handling problem - but the graph has no altitude so I suspect it's under best possible conditions. At sea level my craft is hitting flow separation issues at 37m/s & 4 deg AoA, that seems reasonable to me given the wing profile. If we had the wing profile of a glider it would be less so.

This is the slowest flying aircraft I can find, and again around 4 deg AoA in level flight is it's sea-level minimum. The wings are similar but not quite the same shape & I think this one has more incidence.

Edited September 3, 2017 by Van Disaster

[capi3101]

On 9/2/2017 at 1:44 PM, Kitspace said:

Here are the pictures with the center of mass and controls

https://imgur.com/a/ohfRg

Been gone over the weekend; just now looking at this.

Okay...so, first thing I see is that your Mass-Strength multipliers are in the 0.6-1 range. In my experience, you're okay with putting those at 0.5; the fin you can sometimes get away with 0.4. Lowering the mass-strength multipliers would move your CoM aft slightly, so maybe limit any changes to the surfaces on the main wing

Also, do you have your standard controls zeroed out for the various flap parts? Just checking. I might take the outboard set and change them to spoilers (bumping the deflection up to full, of course), since I'm not seeing airbrakes on the design anywhere. Then again, that's just me. 

Getting back to your original problem, my suggestion would be to increase the area of the horizontal stabilizer - It struck me as a little small for the size of the aircraft initially but I wanted to see if there was any other issue I could identify first. I couldn't tell from any of your screenies if you had a degree of dihedral going on with your stabilizer or not; if you do, try zeroing that out, and if you can get the stabilizer up on the fuselage any higher, do that too. All three of those things should increase your pitch authority.

[Kitspace]

On 5 сентября 2017 г. at 6:12 AM, capi3101 said:

Been gone over the weekend; just now looking at this.

Okay...so, first thing I see is that your Mass-Strength multipliers are in the 0.6-1 range. In my experience, you're okay with putting those at 0.5; the fin you can sometimes get away with 0.4. Lowering the mass-strength multipliers would move your CoM aft slightly, so maybe limit any changes to the surfaces on the main wing

Also, do you have your standard controls zeroed out for the various flap parts? Just checking. I might take the outboard set and change them to spoilers (bumping the deflection up to full, of course), since I'm not seeing airbrakes on the design anywhere. Then again, that's just me. 

Getting back to your original problem, my suggestion would be to increase the area of the horizontal stabilizer - It struck me as a little small for the size of the aircraft initially but I wanted to see if there was any other issue I could identify first. I couldn't tell from any of your screenies if you had a degree of dihedral going on with your stabilizer or not; if you do, try zeroing that out, and if you can get the stabilizer up on the fuselage any higher, do that too. All three of those things should increase your pitch authority.

Hello again!

I would be happy to rearrange the center of mass relative to the wing if not for the main landing gear. Even the way they are now it hesitates a bit before settling on the nose gear when it spawns.

Yes, I do have the standard control inputs all zeroed on all of the flaps parts. Also there are no speed brakes indeed. Should probably add them anyways. Every time I build something I hope the craft would be able to descend at least somehow if not that quickly without them. But it seems that all planes are just too aerodynamically perfect when it comes to subsonic drag in FAR.

The dihedral on the stabilizer is zero however its angle of incidence is different on some of the pictures. Regarding increasing the area of the stabilizer, would that not be helpful only if the stabilizer itself was movable in flight? I have tried both increasing and decreasing it but it seems that the effect is negligible even if it is twice the original size. Does FAR have a problem with tweakscaled parts? That would explain why it did not work then. I always thought that in real life the control authority is defined as sufficient if the maximum deflection corresponds to flying at the critical angle of attack when landing. I just feel that the sweep of the wing gives it way too much static stability to achieve this. For some reason with kerbal planes in general I often find that the wing has to go further forward than I would expect when comparing to the real life planes. Same with this one. Why would that be the case actually?

[Van Disaster]

14 hours ago, Kitspace said:

 For some reason with kerbal planes in general I often find that the wing has to go further forward than I would expect when comparing to the real life planes. Same with this one. Why would that be the case actually?

"Cockpits are heavy" - because the mass distribution of kerbal parts is not like real ones. Drag-wise, don't forget Kerbin's atmosphere stops at 70km so it is all compressed vertically. Tweakscale at times has caused chaos, but generally it's been fixed eventually - you'll have to go check the mod threads.

As for control authority, defining it only by the part of the envelope you find yourself in a normal landing *at sea level* is pretty restrictive - supersonic flight might need more authority than that, given the CL shift rearwards. CL shifts fore-aft in subsonic flight, too.

Edited September 9, 2017 by Van Disaster

[Schwarz]

As you can probably tell I'm still new to KSP and FAR.
I'm having low speed maneuverability issues with my recreated fictional fighter, the ADF-01 Falken.

#Important Note:
Because the original is such a massive plane yet light compared to its size, I had to trade strength for weight(0.5 for the less important parts, 0.6~0.7 for wings and such) along with Kerbal Joint Reinforcement installed. I have aerodynamic failures turned off in FAR, and I have no idea how quickly would the plane rip itself apart if it's turned on.

Quick overview of the plane itself:
Just found out I forgot the engineer's report window. The plane has a length of 23.5m, and a wingspan of 16.9m. Yes, Even larger than a Sukhoi and about 5 tons heavier when empty.

CoL versus CoM, Air Superiority setup(AIM-9x2, AIM-120x6, ~1200U LF)

Dry tank CoM, missiles removed

Frontal view. 

Engine layout. Gimbal on the Sabre has been locked, while it's free on the two F119s.

Internal weapons bay at the back housing 4 AMRAAMs. Not the best place I suppose. Note that there's an AN/AAQ-28 pod mounted on the inside of the left engine nacelle. 

Dynamic Deflection setup.  The airbrakes also act as ailerons.

 

Right now the fighter's maneuverability deteriorates quickly with decreases in speed, as presented in this rather inaccurate sustainted turn rate chart:

Two AMRAAMs were expended from the internal weapons bay before testing to simulate 2 AMRAAMs fired at BVR ranges before engaging in close range combat.

While modern jet fighters turn quicker at lower speeds, this one is the exact opposite, pulling 14~15Gs at around Mach 0.9 while struggling to turn its head around at even Mach 0.6. This result has left me confused.
It also disagrees with thrust vectoring at low speeds, if I want to pull back on the stick I have to disabled it, otherwise it would start oscillating or worse, stall. Leaving it on would require care with the stick(not yanking it all the way to 100%, I have to simulate it by continuously tapping S, don't have my flight stick with me atm) or careful regulation of thrust. This made me even more confused as real life sustained turn rates are tested with full afterburner even at low speeds, while I have to put the throttle to 1/4 or less at Mach 0.4 when I have TVC.
Such a big difference combined with the weird turning behavior has led me to believe there are some serious design flaws, but so far I haven't been able to identify any by asking Google.

Experiments with different canard setups are also largely failures. Why are canards so sensitive to slight changes compared to other parts of an airplane?

If you need the craft file, here it is:
https://drive.google.com/open?id=0B8bJl5w55aiQbEJudWVOX2QyS0U
List of mods required(KSP 1.3):
FAR(obviously)
B9 Aerospace & B9 Procedural Wings 
BDArmory                                                  
Dynamic Deflection                                
KerbalJointReinforcement                    
MasterTechWeapons
Surface Mounted Stock-Alike Lights for Self-Illumination

Action groups are quite messy and hard to understand by looking at the list, so I'll list them here as well:
Group 1: Switch weapons   2:Turn off all engines     3.F119 Afterburner         4/5. Open/close internal weapons bay        6/7 extend/retract forward vertical stabilizer    
8/9  Reveal/hide airborne laser("splits" the nose apart to reveal the hidden laser unit)
6/7/8/9 are just there to replicate designs found on the original. 10 is currently empty, I haven't assigned flaps to it yet.

Thanks in advance for any help that might come

And a screenshot of it pulling off the Cobra. Who doesn't love Cobra? The fact it can supermaneuver AND suck at low speeds at the same time is just amusing

Edited September 10, 2017 by Schwarz
Missed out the engineer's report window.

[Van Disaster]

I can't look at it in game right now, but it might simply need lower wing loading - the advantage real aircraft have is they can shape fuselage areas to properly act as lifting bodies, and we can't really even if FAR could pay attention properly ( fuselage stuff is part of voxel-FAR so presumably it could in theory - that doesn't change that we can't sculpt our fuselages ). If you make it light enough you can pull extreme G even with low structural strength, ( a rather old example ) but I doubt you're going to manage that with two heavy engines

[AeroGav]

@Schwartz  Real air superiority fighters are limited to 9G (at the very most) as they are flown by humans.     Turn rate is basically speed divided by acceleration in Gs,  so the lowest speed at which the fighter can reach 9g is the one at which it does its best turn rate.   In KSP that's not a factor so peak is at higher speeds.

The ability to pull sustained Gs is all about lift vs weight.   The trick is to get more lift without making the plane draggy and have a low top speed.

What your plane has - supermaneuverability - is more to do with control authority, and the ability to command extreme pitch angles and generate high roll rates - not the same thing !

In my last experiment with FAR,  I was trying to develop a utility aircraft that could supercruise, fly to the polar biome and back, and also have a low landing speed.I managed to cram quite a bit of wing area in while keeping low wave drag.   It could fly pretty slow for an FAR aircraft,  and was quite good at sustained turns (4g at 100 m/s), but roll authority was weak,  and couldn't command much more than 20 degrees AoA :

 

Spoiler

 

 

Despite having a "low wave drag" number however, it needed to go to very high altitude to go supersonic, and was only barely so.   It failed in its goal of supercruising, because at such high altitude the engine had too little power.    I could probably make it a twinjet and overcome that lack of power at altitude, but this wing design was very complex with lots of different segments and i found that making a tiny change in one place had huge knock-on effects.  I just couldn't face that redesign.    

In contrast, this thing  had a worse wave drag area, but as you'd expect with the tiny stub wings, was much faster and would go sonic right on the deck.   Of course, it was also a widowmaker,  with insane landing speeds.  It's wave drag numbers were also less sensitive so it was an easier plane to modify.  Just couldn't land it...

[Schwarz]

15 hours ago, Van Disaster said:

I can't look at it in game right now, but it might simply need lower wing loading - the advantage real aircraft have is they can shape fuselage areas to properly act as lifting bodies, and we can't really even if FAR could pay attention properly ( fuselage stuff is part of voxel-FAR so presumably it could in theory - that doesn't change that we can't sculpt our fuselages ). If you make it light enough you can pull extreme G even with low structural strength, ( a rather old example ) but I doubt you're going to manage that with two heavy engines

Since I'm basically piecing the plane together with procedural wings, supposedly I can put some work into reshaping some parts(such as the engine nacelles) to make them create more lift?
It does feel like it needs lower wing loading. Last time I enlarged the main wing by a little bit, handling did improve by a small factor. 
Oh, and make that three engines. I have a sabre underneath the cockpit
I kept the size and weight as identical to the original as I can, now it seems like I should try to lighten it more. It's going to be hard though.

15 hours ago, AeroGav said:

@Schwartz  Real air superiority fighters are limited to 9G (at the very most) as they are flown by humans.     Turn rate is basically speed divided by acceleration in Gs,  so the lowest speed at which the fighter can reach 9g is the one at which it does its best turn rate.   In KSP that's not a factor so peak is at higher speeds.

Makes sense. Didn't realize that "turns slower at high speeds" is only true when load factor is the same.
 

15 hours ago, AeroGav said:

The ability to pull sustained Gs is all about lift vs weight.   The trick is to get more lift without making the plane draggy and have a low top speed.

So basically it means at low speeds my plane is not generating enough lift(not enough airflow going over the wings?) compared to its weight, I would have to either make it lighter or somehow squeeze more lift out of the current design, or both.
 

15 hours ago, AeroGav said:

What your plane has - supermaneuverability - is more to do with control authority, and the ability to command extreme pitch angles and generate high roll rates - not the same thing !

According to this, I assume TVC and high TWR is much more important than how the plane handles a stall? That I can simply brute force it with enough thrust and being able to vector it?
How the Russians did it with the Flanker without TVC seems a myth.

 

15 hours ago, AeroGav said:

In my last experiment with FAR,  I was trying to develop a utility aircraft that could supercruise, fly to the polar biome and back, and also have a low landing speed.I managed to cram quite a bit of wing area in while keeping low wave drag.   It could fly pretty slow for an FAR aircraft,  and was quite good at sustained turns (4g at 100 m/s), but roll authority was weak,  and couldn't command much more than 20 degrees AoA :

Nice plane BTW. Those complex wings can be a nightmare to design and optimize. 
"Tries rotating the wing tip by 5 deg"
"plane flips over every time pilot touches the stick"

About lifting bodies - I recalling reading somewhere the F-15 has a very flat underbelly, thus the fuselage has some lifting capabiilites. 
Maybe I can try replicating that?
 

[AeroGav]

1 hour ago, Schwarz said:

According to this, I assume TVC and high TWR is much more important than how the plane handles a stall? That I can simply brute force it with enough thrust and being able to vector it?
How the Russians did it with the Flanker without TVC seems a myth.

If anyone could chime in here i'd appreciate it, because I'm still unclear what "supermaneuverability" is myself.     My understanding is that it involves being able to point the nose well past stall angle.

With pure aerodynamic control in stock aero (where all surfaces stall at 30 degrees) this is impossible - an aerodynamically stable craft has more lifting surface behind CoM than in front of it.    The only way you can get the nose up is to give the surfaces ahead of CoM more angle of attack than those at the back.   In a canard you do that by pitching the canard up so it's got more AoA than the main wing,  in a tailplane the elevator surface pitches down so the main wing has a higher AoA than it.    When the angle of attack of the whole aircraft nears the stall, the surfaces at the front will stall first as they were  at the highest AoA to begin with so the front end looses lift and the nose slams down no matter how hard you keep pulling.        In an aircraft with negative stability,  rather than the nose slamming down when a critical AoA is reached, instead the aircraft will pitch up uncontrollably despite you correcting with full nose down and you'll end up going backwards/flat spinning.

Now i think FAR does allow things like drooping leading edge devices,  to modify the stall angle as does the shape of the lifting surface, but i can't see how that allows control past the stall.

What does work is 

a) having some non-aerodynamic means to point the nose (TVC, reaction wheels, RCS)

b) keeping CoM and CoL close together .reduces the forces your non-aerodynamic system needs to generate

c) paying close attention to the layout of fuel and ordinance so that CoM moves as little as possible between full and empty helps with b)

Even then I think post-stall manuvers only happen at low dynamic pressure - ie.  fast and high or low and slow,  when the plane can only pull 2 or 3g aerodynamically without stalling anyway.    If you're going 450knots on the deck the aero forces are just too strong and you're not pointing the nose 60 degrees off prograde.

Real airplanes use TVC but in KSP remember we also have magic reaction wheels and I imagine some Vernor thrusters right on the nose and wingtips will do good too - they'll be nice and far from CoM so they'll have plenty leverage.    Not sure high TWR is actually necessary in itself,  though generally a good idea on a fighter for other reasons.

[AeroGav]

2 hours ago, Schwarz said:

About lifting bodies - I recalling reading somewhere the F-15 has a very flat underbelly, thus the fuselage has some lifting capabiilites. 
Maybe I can try replicating that?

Su-57   PAK-FA     ...mmm

Also notice on the front of the strakes / LERXs  are what appear to be "elevons".    They call them LEVCONs (leading edge vortex controller).  King of the LERX was of course the F-18,  which enabled part of the main wing to remain unstalled to 60 AoA.        

[Van Disaster]

2 hours ago, Schwarz said:

Since I'm basically piecing the plane together with procedural wings, supposedly I can put some work into reshaping some parts(such as the engine nacelles) to make them create more lift?
It does feel like it needs lower wing loading. Last time I enlarged the main wing by a little bit, handling did improve by a small factor. 
Oh, and make that three engines. I have a sabre underneath the cockpit
I kept the size and weight as identical to the original as I can, now it seems like I should try to lighten it more. It's going to be hard though.
[..]
About lifting bodies - I recalling reading somewhere the F-15 has a very flat underbelly, thus the fuselage has some lifting capabiilites. 
Maybe I can try replicating that?

FAR does handle body lift - but I don't think you can make an aerofoil shape out of body parts ( ask in the main FAR thread how sophisticated body lift is, I don't know the details ). Easiest thing to do is just have longer proc wings & clip the roots into the fuselage. If you want to build a full replica of something at a structural level try X-plane.

Supermaneuverability is having full control of the aircraft post-stall. I don't know the details of how they do other than thrust vectoring, but presumably there's still use of control surfaces for differential drag. That we can't really do unless you differentially unstall a surface, I think. KSP vectoring engines are strong enough to build a working aircraft.

Sticking AoA into leading edges works to delay stall of the wing surface. Other things to do are mixing AoA into control surfaces so they stay unstalled.

Edited September 10, 2017 by Van Disaster

[capi3101]

On 9/8/2017 at 5:14 PM, Kitspace said:

Hello again!

I would be happy to rearrange the center of mass relative to the wing if not for the main landing gear. Even the way they are now it hesitates a bit before settling on the nose gear when it spawns.

Yes, I do have the standard control inputs all zeroed on all of the flaps parts. Also there are no speed brakes indeed. Should probably add them anyways. Every time I build something I hope the craft would be able to descend at least somehow if not that quickly without them. But it seems that all planes are just too aerodynamically perfect when it comes to subsonic drag in FAR.

The dihedral on the stabilizer is zero however its angle of incidence is different on some of the pictures. Regarding increasing the area of the stabilizer, would that not be helpful only if the stabilizer itself was movable in flight? I have tried both increasing and decreasing it but it seems that the effect is negligible even if it is twice the original size. Does FAR have a problem with tweakscaled parts? That would explain why it did not work then. I always thought that in real life the control authority is defined as sufficient if the maximum deflection corresponds to flying at the critical angle of attack when landing. I just feel that the sweep of the wing gives it way too much static stability to achieve this. For some reason with kerbal planes in general I often find that the wing has to go further forward than I would expect when comparing to the real life planes. Same with this one. Why would that be the case actually?

I had originally assumed from looking at your craft that the full horizontal stabilizer was movable; my apologies there. Making the whole thing one movable surface would increase your pitch authority, though; I can speak from personal experience on that one, and it's particularly true as your plane approaches the transonic regime (Mach 0.8-1.3 or thereabouts).

Spoilers can save you a lot of headaches/heartaches on approach. I always include them in my designs even after I have access to AIRBRAKE parts.

To my knowledge, FAR has no problems with tweak-scaled parts. I use B9 Procedural Wing parts my own self.

Van Disaster has pretty well covered the answer to your final question; I have nothing else to add there.

I'm trying to think what else you could do to try to improve the plane's pitch authority. Comes down to either moving the CoM aft or moving the CoL forward. I'd suggest canards on a low mass-strength ratio (0.3-0.35, perhaps) but I think that would totally throw off the aesthetic you're trying to achieve with this craft. Might have to play around with it my own self - would you object to making the craft file available? Only mods you're using with this craft are Tweakscale and FAR, right?
 

@Schwarz, I'll have to find time to jump in with the discussion of your aircraft later. Quick question: are you also using a fly-by-wire mod? I can't imagine a successful supermaneuverable craft without having one installed - definitely not with the stock SAS system. If you're not using one, I'll humbly suggest Atmosphere Autopilot; for me, that mod changed flying in KSP from an annoying chore into to a real joy (comes in handy for docking too, incidentally).

[Schwarz]

17 hours ago, capi3101 said:

@Schwarz, I'll have to find time to jump in with the discussion of your aircraft later. Quick question: are you also using a fly-by-wire mod? I can't imagine a successful supermaneuverable craft without having one installed - definitely not with the stock SAS system. If you're not using one, I'll humbly suggest Atmosphere Autopilot; for me, that mod changed flying in KSP from an annoying chore into to a real joy (comes in handy for docking too, incidentally).

Unfortunately no, but I'll give it a try, thanks for mentioning it. Hopefully it would make the craft more manageable.
Actually I'm reworking major parts (ditched the sabre engine and some other stuff for 6 ton weight loss, adjustments to wings, CoL now touching CoM), the aircraft might behave differently, although preliminary testing shows that even with a much lower wing loading(30->24 tons with the same area, powered by 2 F119s), it still turns sluggishly at sow speeds. Really can't understand what's going on here.....I'll have to try some different configurations with the wings.

[kcs123]

First and foremost, you have to understand that how fast you point aircraft nose in some direction is not same as changing velocity direction or turning craft in new desired heading. With highly responsive control surfaces, engine gimbals and in some cases RCS you can turn craft nose faster, you can get higher AoA, but whole aircraft does not necessary be able to change direction of movement.

Have to remind yourself what sir Isaac Newton told to us. Only his first two laws are needed here for further observations.

• In an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force.
• In an inertial reference frame, the vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = ma. (It is assumed here that the mass m is constant)

Now, what turning aircraft means ? It is acceleration that is perpendicular to velocity vector, or better said sum of all acceleration vectors and their perpendicular fractions to velocity vector and turn direction that we observe.

From second Newton's law we know that accelerations formula is a = F / m

But, you where that force that turn aircraft comes from ? If we disregard gravity for a moment, that force might come from only two surces: aircraft engine or wings. In most cases, you only get fraction of available thrust force trough engine gimbals, it can help to turn aircraft nose faster in desired direction, can help in stabilization, but usually it does not provide enough force to change direction of velocity vector.

Only significant source of force that can rapidly change velocity vector comes from wings. And I'm talking about main wings here, not control surfaces that just point craft nose in one direction or another. You need enough wing surface area (can be combined with fuselage body area) to be able for fast turn rate of aircraft. Large wing surface area also helps in flight stability at low subsonic speeds.

In conclusion, you were cuting off wing area to reduce mass as much as possible, but you were also cutting down main force source that have significant role in turning aircraft. That is art of successful craft designs, because it is fine line between enough wing surface area, craft mass, benefits that large wing surface area provide and consequences of large wings due to higher drag and increased craft mass because of it. It is not uncommon that trough craft design you are focused on one thing, to reduce wing surface area and mass but you forgot about positive effects of it at same time.

[Schwarz]

20 hours ago, kcs123 said:

First and foremost, you have to understand that how fast you point aircraft nose in some direction is not same as changing velocity direction or turning craft in new desired heading. With highly responsive control surfaces, engine gimbals and in some cases RCS you can turn craft nose faster, you can get higher AoA, but whole aircraft does not necessary be able to change direction of movement.

If i want to turn quickly, I would have to 1.be able to point the nose in a new direction quickly and 2.do that while maintaining low AoA, is that correct?
Supposedly I can delay the stall on the wings to a higher AoA, would that result in a quicker turn?
 

 

20 hours ago, kcs123 said:

In conclusion, you were cuting off wing area to reduce mass as much as possible, but you were also cutting down main force source that have significant role in turning aircraft. That is art of successful craft designs, because it is fine line between enough wing surface area, craft mass, benefits that large wing surface area provide and consequences of large wings due to higher drag and increased craft mass because of it. It is not uncommon that trough craft design you are focused on one thing, to reduce wing surface area and mass but you forgot about positive effects of it at same time.

If I retain the same wing area and reduce mass at the same time, that in theory would have positive effects towards turn performance, am I correct? Less mass means it has less inertia, and easier for the same force to change it's direction.
Also, instead of an all-moving small main wing(if it even exists), would I actually turn faster with a larger wing but with smaller control surfaces? 

[Schwarz]

New airframe is ready to roll out, although I'm afraid that even it went through a major 6 ton weight loss program while having about the same wing area, it only improved a little bit in terms of maneuverability. 
Craft file:
https://drive.google.com/open?id=0B8bJl5w55aiQcUZNd3ZjZUV3TkU

Changes:
1.Sabre engine under the cockpit has been removed; total weight is down by six tons.
2.main wings are about the same size but control surfaces are now much smaller.
3.Nose has been shortened and now pointing downwards at a shallower degree.
4.Highlighted part is now parallel with the main wing, instead of pointing downwards.
5.CoL moved backwards ever so slightly while CoM was moved forwards.
6.F119s have been upscaled from 1.25m to 1.375 meters, Tweakscale is now needed!
7.numerous cosmetic changes, mainly new cockpit underslung and engine exhaust ports.

I found out the old nose produced quite a lot of negative lift; if there wasn't enough pitch authority on the canards, at supersonic speeds the nose would pitch down quickly until the plane flipped over. The new nose produces much less negative lift now.

@capi3101, the FBW mod you suggested was really good, can absolutely see just how many more micro adjustments it can make in a second compared to stock SAS. Flying this plane over long distances used be very annoying because of the pitch instability, I had to regularly steer the plane back on path. Quick question: The standard FBW seems to automatically roll the plane keep the plane horizontal(does not happen with pitch controls), was that meant as a function, or am I missing something? Because sometimes banking and turning can be hard to execute with the plane constantly rolling in the other direction, and I don't have my stick with me to test if this was a keyboard problem or so.

Edited September 12, 2017 by Schwarz
More changes done to the airframe.

[AeroGav]

8 hours ago, Schwarz said:

Supposedly I can delay the stall on the wings to a higher AoA, would that result in a quicker turn?

Yes because lift = airspeed x air density (altitude) x aoa x wing area

however,  increasing aoa produces a lot of drag, so you need to consider if you have enough engine power to maintain airspeed while turning at maximum rate.

This is what sustained turn performance means.  If you fitted leading edge devices to your wings that droop at high AoA and enable you to pull another 10 degrees of AoA,  the extra lift would certainly improve your instantaneous turn rate.     But if your engines can't maintain the airspeed at this higher AoA and after a couple of seconds you've slowest down such that you're pulling fewer Gs. this means your sustained turn rate has not improved.

[Schwarz]

15 hours ago, AeroGav said:

Yes because lift = airspeed x air density (altitude) x aoa x wing area

however,  increasing aoa produces a lot of drag, so you need to consider if you have enough engine power to maintain airspeed while turning at maximum rate.

This is what sustained turn performance means.  If you fitted leading edge devices to your wings that droop at high AoA and enable you to pull another 10 degrees of AoA,  the extra lift would certainly improve your instantaneous turn rate.     But if your engines can't maintain the airspeed at this higher AoA and after a couple of seconds you've slowest down such that you're pulling fewer Gs. this means your sustained turn rate has not improved.

I do have one leading edge slat that would always match the AoA. If I have more control surfaces that will react to the present AoA(not necessarily match it),  then the main wing would only stall at an even higher AoA, right?
As of now I do have some excess thrust at low speeds, especially when engaging afterburners. If the above hypothesis is true, supposedly I would be able to utilize some of that excess power.

[AeroGav]

3 minutes ago, Schwarz said:

I do have one leading edge slat that would always match the AoA. If I have more control surfaces that will react to the present AoA(not necessarily match it),  then the main wing would only stall at an even higher AoA, right?
As of now I do have some excess thrust at low speeds, especially when engaging afterburners. If the above hypothesis is true, supposedly I would be able to utilize some of that excess power.

What is your stall AoA BTW?  Leading edge droops enable the wing they are attached to to reach a higher AoA without stalling, but don't increase lift by themselves.   Trailing edge devices don't increase stall AoA (if anything, they slightly decrease it) but they increase lift at same AoA.

The airplane above is actually two wings - that horizontal black band parallel to the cockpit is the dividing line.   The forward wing is basically a canard but has a thin sliver of a fixed wing with broad, full span leading and trailing edge flaps.   This controls pitch - I find with an all-moving surface as the canard, the lack of leading edge device makes it stall at quite a low AoA and prevent you pulling much AoA - since the canard's AoA is equal to the airplane's AoA plus the angle of control surface deflection, it is very prone to stalling first.

The above airplane could get over 40 deg AoA with minor stalling on the front wing , but this wasn't much use for it's mission - I wanted a supercruising STOL science plane.  That high AoA let it fly slowly but would obviously cause tail strikes on landing.

The inboard sections of the main wing didn't seem to need any leading edge device - maybe because the front wing acts as a leading edge device for the main wing, or maybe the low aspect ratio of the inner section allows higher AoA.   Also swept back wings tend to stall at the tips first.    But the outermost section - the relatively thin, tapering wing tips - do have leading edge droops to prevent tip stall.

Does your fighter have full span droops and combat flaps?  Real airplanes like the F16 and F18 do, they deflect automatically at high AoA.

Looking at this plan view  I wonder if you could get away with a longer wing span if you increased the sweep angle?    Or how about increasing the chord at the wing root?  Would be a lot of work though to re-optimise everything...

[Schwarz]

15 hours ago, AeroGav said:

What is your stall AoA BTW?  Leading edge droops enable the wing they are attached to to reach a higher AoA without stalling, but don't increase lift by themselves.   Trailing edge devices don't increase stall AoA (if anything, they slightly decrease it) but they increase lift at same AoA.

Right now it stalls at an abysmal 16 deg, or whenever I actuate the massive airbrakes(not a problem though).

15 hours ago, AeroGav said:

The inboard sections of the main wing didn't seem to need any leading edge device - maybe because the front wing acts as a leading edge device for the main wing, or maybe the low aspect ratio of the inner section allows higher AoA.   Also swept back wings tend to stall at the tips first.    But the outermost section - the relatively thin, tapering wing tips - do have leading edge droops to prevent tip stall.

I didn't notice the thickness was different across the wing....that is certainly some brilliant design.

15 hours ago, AeroGav said:

Does your fighter have full span droops and combat flaps?  Real airplanes like the F16 and F18 do, they deflect automatically at high AoA.

hmm, I think I'm wrong about calling this a slat, since it's rotating not extending it should be a droop. Right now this is the only one and I'm considering adding more, including the angled one close to the fuselage.


Combat flaps? No, I don't think I know how to set them up to extend at a certain AoA. Or actually you can't and you have to manually deploy/retract them with an action group?

 

 

15 hours ago, AeroGav said:

Looking at this plan view  I wonder if you could get away with a longer wing span if you increased the sweep angle?    Or how about increasing the chord at the wing root?  Would be a lot of work though to re-optimise everything...

I can do both but not a big change, since I'm trying to recreate I'll do my best to stick to the original without deviating too much.
This is the fifth model you're looking at, first two failed to fly, third one was real bad and the fourth one was the 3 engine one I started this query with. I've already spent about 150~200 hours across all models, and I plan to recreate the attacker variant too, so I guess a couple dozen hours wouldn't matter too much.
 

 

15 hours ago, AeroGav said:

Leading edge droops enable the wing they are attached to to reach a higher AoA without stalling, but don't increase lift by themselves.

No wonder the I used to have no luck on leading edge droops. They were massive before I reworked the wing, I was losing a lot of lift without me even knowing.

[AeroGav]

13 minutes ago, Schwarz said:

I didn't notice the thickness was different across the wing....that is certainly some brilliant design.

What i mean is "aspect ratio" - the outboard sections have a much higher aspect ratio than the inboard section.    High aspect ratio wings have better l/d ratio but stall at lower aoa, so i was worried about my wing tips.    Stalls progress backward along the sweep of the wing, so again on a swept back design you got to worry about tip stall.   On your swept forward design the roots should stall first.

Stall AoA increases with sweep angle too.   I wonder if the game is handling swept forward wings correctly?

 

19 minutes ago, Schwarz said:

Combat flaps? No, I don't think I know how to set them up to extend at a certain AoA. Or actually you can't and you have to manually deploy/retract them with an action group?

Could you just have them deploy with AoA like that slider in screenshot?   If the plane is at a larger AoA than 5 degrees it's probably not in cruising flight.    In fact above 5 degrees AoA, you'd probably get lower drag with trailing edge drooping since that increases lift and reduces the AoA needed?  The drag reduction from AoA reduction probably outweighs that from the flaps themselves at larger AoA