The 5th Generation Fighter challenge [FAR]

[tetryds]

Wing strenght and deflection angles depend a lot on the design.

I am starting to think I should put the explanations I gave on my sig...

I also typed a long text explaining how to optimize for high g maneuvers but I did not have time to fix it before posting, will do tomorrow.

[Skyentist]

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Craft File

I believe I can claim 21 points:

Supercruise: +.1, 1 point

Top Speed: +.9, 18 points

Vertical Climb: Yes, 1 point

Drop Tank: 72 Fuel Units, 1 point

[Halsfury]

So many interesting things just happened and I left this page alone for only a day!

I should get to work on another fighter

Also Darth Lazarus, that's a really cool F-18. If the Area ruling gives you trouble try using the long tail connector parts to cut down on the fuselage where the wings are. Clip them into each other with 1 running back and another running forwards

- - - Updated - - -

I've started working on a new yet to be named design.

I managed to lower its wave drag area to about .65, and it's now able to supercruise at M2.4 @10000m, and go past M2 on afterburner at 3000m (further than M3-4 and it tends to rip itself apart). Fuel tanks are quite straightforward and I have plenty of fuel to spare in the internal tanks - range is excellent.

http://i.imgur.com/DQeFV3b.jpg

Right now TWR is the problem - it tends to exceed 2 in horizontal flight but I have been unable to test in the vertical because it seems to have lost pitch authority over the course of its versions - Pulling GS and sometimes taking off can be quite difficult. I'll try bringing the CoL and CoG closer together.

By the way, any recommended values for mass/strength and deflection angle on control surfaces ?

If you want more deflection on the control surfaces, there's a point where the surfaces will cause flow separation and will act like a large brake, it's a trial and error thing mostly, just scale up the values until you find the limit, if you go past the limit, you'll know it by the fact that upward pitch will stop working and it will crash

[Darth Lazarus]

so, new news on the F-18 (YF-17, while i work on it ...). I rebuilded the body of the fighter so i could decrease the negative things on the tail with the engines. Like Halsfury said, tailconnectors are great for smoothing out the shape! still not happy .. BUT i'm getting there. And an Antenna on the Nose is fantastic to decrease wave drag ...

next i will work on the air-intake area, cockpit neck and final adjustments on the engines. maybe some minor tweeking for the wings too ...

and then i need to reinforce the body and wings. still i need help because i don't know how to withstand the G-loads without braking apart

oh and did i mention, that this is my very first plane in FAR?

download:

-> YF-17 (F-18 Prototype) <-

(it needs adjustable landinggear mod! -> click me <- )

edit: link fixed.

Edited July 8, 2015 by Darth Lazarus

[Halsfury]

Yeah I see your problem with wave drag, you just need more volume behind the cockpit and behind the wings, I downloaded it so I'll try to work it out

EDIT: You used a mod for the F-18 which I don't have, what was it?

Edited July 8, 2015 by Halsfury

[Darth Lazarus]

Yeah I see your problem with wave drag, you just need more volume behind the cockpit and behind the wings, I downloaded it so I'll try to work it out

EDIT: You used a mod for the F-18 which I don't have, what was it?

Adjustable landing gear mod

-> click me <-

[tetryds]

my second question is: how to make the jet withstand high G-loads without braking apart? struting the hell out of it don't work

Good question, this is one that I have never seen people asking before.

One of the most important things when designing towards being able to pull high G loads is placing your wings efficiently on your craft.

Your main wings are meant to sustain the craft, their lift should be very close to the center of mass, or slightly ahead of it.

If you place the wings too far behind, you will have to generate a lot of extra force on your elevators, and that overloads the wings.

Placing them right on the center or slightly ahead of it makes it behave like a fulcrum placed on the center of mass, you can easily tilt it up and down with a very small force on the elevators.

Another thing is setting your control surface deflection to be as efficient as possible, you can do that using the method I mentioned on the official FAR craft repository.

If you place your main wings correctly the drag on the elevators will be close to negligible, you will not need to worry about them stalling.

There are a lot of ways to pull high g turns, but it depends on the size of your craft and at which speed you want to fly.

A solution that works often is having a lot of lift, but you will get a lot of drag from that, and extra weight, they can also make it more complicated to area rule.

So, you will usually want a low aspect ratio profile, as a plus you gain resistance to stall at the expense of lift, so you will be able to pull much higher AoA before stalling.

Thus, while subsonic you need control to keep such higher angles of attack, and stability.

The major stability concerns when doing this is roll, wing flexing should give you some extra dihedral, but be careful with uneven flexing.

Transonic is a problem here, if you go supersonic you have reduced lift, and need higher deflection on your elevators, but subsonic gives you a much greater lift.

What happens here is that if you bleed too much speed while turning when barely supersonic you will get subsonic and your wing lift will skyrocket together with the cloud of debris.

There are some not yet implemented transonic effects, so my advice is just stay away from this region if you can.

When at supersonic what you want is to have as much lift as you can with as little AoA as possible, this way dynamic pressure does not kill you but you can still pull relatively tight turns.

But if you fly supersonic at high altitudes, you will need that extra deflection again.

You see, there is a problem here, for every situation you will need the control surfaces to deflect differently, that makes it complicated to design a craft that behaves well on all cases without using control mods.

It ends up that if you want to make a good plane, not just for pulling high G turns, you need to focus on a certain speed and altitude range.

There are many other things I did not mention here, and the closest you get to the optimal point, the more tradeoffs you will have to make.

Edit: about wing strenght/weight, you always want them to be as light as possible, but enough so that they can keep up with the turns.

The heavier they are relative to the rest of your craft, the lighter you need to make them, to the point that you can pull insane g turns with a 0.675m drone with your wings close to the minimum weight possible.

Edited July 11, 2015 by tetryds

[Hodo]

Keeping a craft together is a trick much like Tetryds said. I am a huge fan of delta wing designs, I use them above all others for several reasons. Most of which are the same reasons why some of the most successful high speed fighters of all time used them. They are strong, when placed properly you wont have to deal with the wing loads that you would with a more conventional straight wing design. There is a downside to the delta wing, you often sacrifice lower speed agility and stability, but you gain high speed agility.

The thing that is often the cause of a structural failure on most planes in this is to much load on the main body of the craft and not on the wings. You will see the nose flex down or up and it will "worm" its way through the air. This flex is not good for a combat craft or any craft that is expected to perform at high speeds. Sometimes strategically placed struts will fix this. Other times it requires a complete redesign.

This craft suffers from that flex issue, two sections behind the cockpit, the wings will flex up and down instead of staying straight. This will cause an oscillation that only gets worse with speed and increase atmospheric pressure till the craft explodes.

I fixed it by placing two struts, one on top and one under the wing at the leading edge attached to the body of the craft, and then hid them inside of the wing by increasing its thickness. This gave the craft a "box" frame for the strength.

[CrisK]

Tetryds's advice is worth following. To give a visual illustration, this is my plane before and after I adjusted it to consider area ruling. The parts are the same, but I shifted the wings, adjusted thicknesses, etc. The strength of the wings is set to 1.

Before:

After:

[Cinocal]

Engine swap just to see.

[Halsfury]

While we were on the discussion about various forms of aerodynamic oscillation and snaking I thought I might share this short clip of some of the nastier side of flutter

[RocketTurtle]

See, I look at all these awesome designs but I can't for the life of me make a good one. It always just ends up as a Mk 1 cockpit, with some fuel, 2 engines, some ram intakes, a generic tail, and delta wings. It literally couldn't be more generic.

I haven't played in a few months, so I probably just need to learn all the new parts, and how I can use them.

[FourGreenFields]

Engine swap just to see.

Am I right to assume that this was done using a new FAR version with ducted area ruling taken into consideration?

@Halsfury: Did my design get overlooked, or did the community decide it doesn't fit their definition of beauty?

[Cinocal]

Am I right to assume that this was done using a new FAR version with ducted area ruling taken into consideration?

Negative. Not using Dev build, using Garabedian or whatever its called.

[FourGreenFields]

Negative. Not using Dev build, using Garabedian or whatever its called.

Then how did you manage to keep the wave drag low enough, despite the inside of the basic jets not being modelled?

[Cinocal]

Then how did you manage to keep the wave drag low enough, despite the inside of the basic jets not being modelled?

So that's why my drag went to .... when I put on the basic jets! I just made it longer and tweaked things, it wouldn't go as low as with the Rams but I got it down to .47.

And it still looks cool.

[tetryds]

I am starting to think about better ways to measure how good a fighter is.

I feel that right now it's a "who is the fastest" competition rather than traits that are important for combat.

And that is something very complicated to define, I will see what I can come up with.

[FourGreenFields]

So that's why my drag went to .... when I put on the basic jets! I just made it longer and tweaked things, it wouldn't go as low as with the Rams but I got it down to .47.

And it still looks cool.

Mine looks cool too In it's own way. Unusual aerodynamic configurations always look good imo (if they fly properly).

Anyway... someone mind telling me why you manage to reach Mach 2 at more than twice the wave drag area I need? Is the Mach cone or whatever it's called already that narrow that my wings produce more drag? Or am I missing something else here?

I am starting to think about better ways to measure how good a fighter is.

I feel that right now it's a "who is the fastest" competition rather than traits that are important for combat.

And that is something very complicated to define, I will see what I can come up with.

Atm it feels more like "who can supercruise with the biggest droptanks" to me.

It would basicly end in completely overhauling the challenge though.

Three thoughts (might think of more stuff later on):

- Internal fuel tanks need to be worth WAY more points, and droptanks should not grant points if they're bigger than the internal fuel reserve (else you couldn't rtb on long range missions if you had to drop the droptank).

- It might be worth considering to grant points for being able to land on and take off from short runways (like lift-off before the end of the old airfield).

- Roll rate could be measured as well

Edited July 9, 2015 by FourGreenFields

[Halsfury]

@Halsfury: Did my design get overlooked, or did the community decide it doesn't fit their definition of beauty?

Which one do you mean, I thought I put your score up on the main page, the P 13 shrike. I thought you weren't making another entry so it just became fodder for the general conversation, my mistake, which post was it again?

- - - Updated - - -

Mine looks cool too In it's own way. Unusual aerodynamic configurations always look good imo (if they fly properly).

Anyway... someone mind telling me why you manage to reach Mach 2 at more than twice the wave drag area I need? Is the Mach cone or whatever it's called already that narrow that my wings produce more drag? Or am I missing something else here?

Atm it feels more like "who can supercruise with the biggest droptanks" to me.

It would basicly end in completely overhauling the challenge though.

Three thoughts (might think of more stuff later on):

- Internal fuel tanks need to be worth WAY more points, and droptanks should not grant points if they're bigger than the internal fuel reserve (else you couldn't rtb on long range missions if you had to drop the droptank).

- It might be worth considering to grant points for being able to land on and take off from short runways (like lift-off before the end of the old airfield).

- Roll rate could be measured as well

How about how long does it take to arrive in the same flight position at a given altitude, say that you must fly by the SPH tower and time how long until you fly by it again? That's an easy turn time calculation

[FourGreenFields]

Which one do you mean, I thought I put your score up on the main page, the P 13 shrike. I thought you weren't making another entry so it just became fodder for the general conversation, my mistake, which post was it again?

The P 12 "Flying Pencil". Basic jet.

I suppose it'll soon be obsolete, due to ducted area ruling, but for now it works.

And she's alive! Aliiiiiiiiiiiiiiiive!

Craft file on KerbalX

http://imgur.com/a/d0N9C

43.27 points. And as long as she is called "Flying Pencil" she looks good

(And btw: it might be a good idea to link either an album, or, if no album was published, an image of the planes on the leaderboard, on the leaderboard.)

EDIT: And btw the 2.: It's P 13 "Shrike". "" indicating a nickname, and although the 'Muricans used P-XX for "Pursuit" (I think) = fighter planes, I use it for "Projekt" = project, as good ol' Willy Messerschmitt did. And, like he did, without a "-". Minor things, I know. But if I'm going to have several designs on the leaderboard, I'd like that to be correct.

[Emilio]

Atm it feels more like "who can supercruise with the biggest droptanks" to me.

And that's exactly what I'm struggling with. The thing is, I'm not sure there are any aircraft IRL that can keep supercruising with additional tanks- unless you count conformal fuel tanks, but those aren't meant to be dropped.

In other news, sixth attempt and still no success... I might be taking a small break . TWR is still impossible to meet, I need to find the turbojet's best performance area.

[Hodo]

And that's exactly what I'm struggling with. The thing is, I'm not sure there are any aircraft IRL that can keep supercruising with additional tanks- unless you count conformal fuel tanks, but those aren't meant to be dropped.

In other news, sixth attempt and still no success... I might be taking a small break . TWR is still impossible to meet, I need to find the turbojet's best performance area.

Turbojets best power range is just over the speed of sound. Depending on altitude/pressure the power will peak at different speeds. Like my 149B it doesn't reach 1:1 till mach 1.25 at 10km.

So far I agree with the others. While some of the entries are great looking fighters others are just racers and are not even armed or capable of being armed. I look forward to seeing if anyone else posts a dl for their entry. I will be posting my newest one later tonight along with the XF-149B.

[tetryds]

Anyway... someone mind telling me why you manage to reach Mach 2 at more than twice the wave drag area I need? Is the Mach cone or whatever it's called already that narrow that my wings produce more drag? Or am I missing something else here?

Yes there is, you forgot one detail, area rule is for transonic drag, right now FAR measures supersonic drag by a composition of hypersonic and transonic drag (may/will change).

You can imagine hypersonic drag as being generated by a raycast, your large thin wings and bumps on the craft will not be hypersonic drag friendly.

That is the reason why I did not add a single anti-shock body on my craft and it can easily make it to much faster than Mach 4.2 even though it has around 0.60 m² of transonic wave drag area.

Area ruling blinded you to the other effects, it happens, don't worry.

Atm it feels more like "who can supercruise with the biggest droptanks" to me.

It would basicly end in completely overhauling the challenge though.

Well, yes, kind of.

The idea I am having is not overhauling the challenge, but making a second version of it, or a completely new one.

But I don't want to kill this challenge, this second version would come later, there is still a lot to happen here, and we also need to see what people come up with.

Now we know what works and what doesn't, and we also know how far we can pull it and still have people to submit crafts.

So, what I am coming up with so far is something totally different, so different that it may end up not even interfering with this challenge.

The first idea is to have a few possible roles, likely three, each with it's specific requirements.

More than one role can be fulfilled by a craft, which would compete on them at the same time.

Filling all of the roles would be extremely hard, and by doing so your craft competes on the special multirole aircraft category.

Specific role combos can be set, but that would only happen if we had a very big amount of submissions.

About mods, I don't think there should be a distinction between modded and stock aircraft, this challenge showed us that there is no problem with that.

But of course some mods like FAR itself would have to be enforced, I was thinking about AJE just for the realism boost, it's not hard to move to it since stock improved so much.

Engine choice would not be a problem, you should be able to pick any that you wish.

If the requirements are set right the engine choice will be just a design decision, some categories will fit certain engine types better, naturally.

For scoring, I am still unsure, but I am thinking about dropping a point score system and using something else.

I also think that the player skill can count, it's a challenge afterall, but it's very hard to get subjective judgment like this.

It could be that I could fly all of them myself, but that wears out quickly, and something like this is very complicated to judge.

The last one I made where I had to fix the crafts myself had to be put on hold simply because I did not have time to work on all of them.

Halsfury suggested challenges, but amount of completed challenges gives preference to people with more playtime.

A possible solution would be having two or three scenarios per role, and instead of having a better craft completing the missions are just extra requirements.

We would end up having lists of capable airplanes, without defining which is better or worse.

But this is something that still needs a lot of thought.

The idea is to start simple, and as more people submit their crafts more roles can be added, it would be cool to include propeller fighters, bombers, etc. on the future.

Or make new challenges for them.

[Hodo]

Here is the XF-149B download

XF-149 Download

And here is the XF-150A download.

XF-150A Download

Edited July 9, 2015 by Hodo

[FourGreenFields]

Yes there is, you forgot one detail, area rule is for transonic drag, right now FAR measures supersonic drag by a composition of hypersonic and transonic drag (may/will change).

You can imagine hypersonic drag as being generated by a raycast, your large thin wings and bumps on the craft will not be hypersonic drag friendly.

That is the reason why I did not add a single anti-shock body on my craft and it can easily make it to much faster than Mach 4.2 even though it has around 0.60 m² of transonic wave drag area.

Area ruling blinded you to the other effects, it happens, don't worry.

I wasn't blinded, I just hadn't heard of it until now.

Am I right to guess that that average pressure blue graph is for hypersonic drag? Or will I have to rely completely on the old fationed calculation of drag at a given speed and alt?