The 5th Generation Fighter challenge [FAR]

[tetryds]

Okay guys, every single plane I make in FAR porpoises when I turn. If you guys know what I mean... the nose bounces up and down...

and then the plane disassembles itself.

*sigh*

Indeed, you are stalling.

The reason why you are stalling? Those canards.

You have way too much deflection on the canards, when flying straight they are fully effective, pitching up generates a lot of pitch momentum.

Then, they stall, at a certain AoA, this creates even more momentum.

That increases your AoA a lot, and that makes your main wings and horizontal stabilizer also stall.

But the stall of the wings and horizontal stabilizers together is very strong, that pulls your nose down violently.

Then your AoA decreases and stall is gone, your canards become effective again and you keep bouncing forever.

Your canards will stall at a very low AoA, and they generate a positive feedback loop.

Their deflection will hardly ever be above 7 degrees, I recommend setting it to something between 4 and 6 degrees.

But be careful, when your canards do not stall they are extremely effective, which may cause disassembles.

After you set your canards right, use this to set your elevators: http://forum.kerbalspaceprogram.com/threads/121176-Official-FAR-Craft-Repository?p=2060785&viewfull=1#post2060785

...let me add these to my sig now.

[Hodo]

So I added canard to try to help. It didn't.

Here's the design.

http://i.imgur.com/KANTasG.png

Holding W...

http://i.imgur.com/ARlRsY1.png

Still holding W...

http://i.imgur.com/6j9rNbP.png

I like it better this way.

http://i.imgur.com/JSZkRKP.png

http://i.imgur.com/oEuBGMt.png

I'm not very good with all this aerodynamic-y stuff. I usually just do what looks like it'll fly.

Ok I can start with some of the obvious issues I am seeing.

You have to much control authority. Canards AND elevators are a bit of an overkill on such a small design. If you are going to have both reduce the control authority to about 7.5-10 on the canards and 12-14 on the elevators. This will help reduce some of the oscillations you are experiencing.

Also you have a bit to much wing for an aircraft that small, you are generating a lot of lift for a light aircraft. You could actually get away with a smaller wing area. This will help reduce your wave drag form making the craft faster. The other option is to extend the body of the craft a bit, add another section to it behind the mk2 adapter and it will lengthen the craft giving the air more area to travel over and smooth out.

Last but not least.

Relax your flying style, gentle key inputs will help the aircraft perform better. Hammering down on W will make anything stall and flip out. You should see how my Mig-21 SSTO knock-off flies... that 21deg AoA limit on the real Mig-21, that is a REAL thing on my SSTO.

[Halsfury]

@ Darth Lazarus:

I found out some problems with your aircraft, one of which is that wing sections D an E are defective in terms of rigidity, in stock KSP any kind of control surface attached to them invariably ends up with virtually no authority.

If I were you I'd go with procedural wings, the stock ones just don't like to conform to the shape you want

EDIT:

@Crisk, I'm sorry but in relation to your X-32 you need to calculate your own score with relevant proof shots, I don't want to have to download all your mod dependancies and test your aircraft when you probably have a better computer for it.

Edited July 11, 2015 by Halsfury

[CrisK]

@Crisk, I'm sorry but in relation to your X-32 you need to calculate your own score with relevant proof shots, I don't want to have to download all your mod dependancies and test your aircraft when you probably have a better computer for it.

Will do!

[Halsfury]

Also what's the best 1.0.4 compatible procedural wings mod? I'm looking for a simple extrusion based wing, not one with basically an editable config in a GUI

[RocketTurtle]

Indeed, you are stalling.

The reason why you are stalling? Those canards.

You have way too much deflection on the canards, when flying straight they are fully effective, pitching up generates a lot of pitch momentum.

Then, they stall, at a certain AoA, this creates even more momentum.

That increases your AoA a lot, and that makes your main wings and horizontal stabilizer also stall.

But the stall of the wings and horizontal stabilizers together is very strong, that pulls your nose down violently.

Then your AoA decreases and stall is gone, your canards become effective again and you keep bouncing forever.

Your canards will stall at a very low AoA, and they generate a positive feedback loop.

Their deflection will hardly ever be above 7 degrees, I recommend setting it to something between 4 and 6 degrees.

But be careful, when your canards do not stall they are extremely effective, which may cause disassembles.

After you set your canards right, use this to set your elevators: http://forum.kerbalspaceprogram.com/threads/121176-Official-FAR-Craft-Repository?p=2060785&viewfull=1#post2060785

...let me add these to my sig now.

Ok I can start with some of the obvious issues I am seeing.

You have to much control authority. Canards AND elevators are a bit of an overkill on such a small design. If you are going to have both reduce the control authority to about 7.5-10 on the canards and 12-14 on the elevators. This will help reduce some of the oscillations you are experiencing.

Also you have a bit to much wing for an aircraft that small, you are generating a lot of lift for a light aircraft. You could actually get away with a smaller wing area. This will help reduce your wave drag form making the craft faster. The other option is to extend the body of the craft a bit, add another section to it behind the mk2 adapter and it will lengthen the craft giving the air more area to travel over and smooth out.

Last but not least.

Relax your flying style, gentle key inputs will help the aircraft perform better. Hammering down on W will make anything stall and flip out. You should see how my Mig-21 SSTO knock-off flies... that 21deg AoA limit on the real Mig-21, that is a REAL thing on my SSTO.

I added the canards to see if it helped, however it does the same without them. I'll try the other suggestions though.

[tetryds]

I added the canards to see if it helped, however it does the same without them. I'll try the other suggestions though.

Then it's just too much deflection on the elevators, your main wings may be too far forward or your deflection is set too high, or both.

[Hodo]

Also what's the best 1.0.4 compatible procedural wings mod? I'm looking for a simple extrusion based wing, not one with basically an editable config in a GUI

B9Procedural wings is what I and many others are using now. It is honestly one of the best right now. And the only one that lets you place fuel in your procedural wing.

[CrisK]

Also what's the best 1.0.4 compatible procedural wings mod? I'm looking for a simple extrusion based wing, not one with basically an editable config in a GUI

The B9 wings require a lot of configuration, but on the plus side they require very little memory. You can replace all of the Squad stock wing parts with the 4 B9 procedural wings. This is great for people like me who run KSP on an inexpensive Macbook Air.

PS: I don't know if I've written this yet, but thanks for coming up with this challenge.

[Halsfury]

The B9 wings require a lot of configuration, but on the plus side they require very little memory. You can replace all of the Squad stock wing parts with the 4 B9 procedural wings. This is great for people like me who run KSP on an inexpensive Macbook Air.

PS: I don't know if I've written this yet, but thanks for coming up with this challenge.

You run KSP on a macbook air? I'm using a 2012 macbook pro and I'm concerned about heat generation

Thanks for the help with the wings and you're welcome in regards to the challenge. I got the idea at first because of the F-35 and just how bad and compromised it is. At first I wanted the challenge to be something along the lines of build a better aircraft than Boeing can.

But then I increased the difficulty by insisting that you build a real 5th gen fighter

[Hodo]

You run KSP on a macbook air? I'm using a 2012 macbook pro and I'm concerned about heat generation

Thanks for the help with the wings and you're welcome in regards to the challenge. I got the idea at first because of the F-35 and just how bad and compromised it is. At first I wanted the challenge to be something along the lines of build a better aircraft than Boeing can.

But then I increased the difficulty by insisting that you build a real 5th gen fighter

The F-35 is a compromise for an aircraft. It is a single engine fighter, with S/VTOL capabilities mach 2 capable and still supercruise. All this and still be stealthy and agile for dogfighting oh and still be cheap to purchase. Much like my XF-149B1, it is just that kind of fighter. Most everyone is going to build a WAY better fighter than that craft, but out of all of them it is one that is most like the F-35 in many ways. I actually love it for that reason.

I built it and the XF-150A in my career mode, because I have a budget in that and I like to build on a budget. I actually have since graduated the XF-150A and the XF-149B1 from X status to full F status. I used my XF-150A just yesterday to complete a military contract, which required it to destroy several ground targets on the island airfield. It did it without taking damage and returned to base.

[Halsfury]

Also Darth I fixed your YF-17, I'll post the link sometime today

It was really those little wing sections which have weird qualities, either they flex or they are aerodynamically ugly in some other way but after redesigning the wing without them the roll authority is great, the aircraft snaps from side to side in turns and it can accelerate to mach 4 at 10km

- - - Updated - - -

The F-35 is a compromise for an aircraft. It is a single engine fighter, with S/VTOL capabilities mach 2 capable and still supercruise. All this and still be stealthy and agile for dogfighting oh and still be cheap to purchase. Much like my XF-149B1, it is just that kind of fighter. Most everyone is going to build a WAY better fighter than that craft, but out of all of them it is one that is most like the F-35 in many ways. I actually love it for that reason.

I built it and the XF-150A in my career mode, because I have a budget in that and I like to build on a budget. I actually have since graduated the XF-150A and the XF-149B1 from X status to full F status. I used my XF-150A just yesterday to complete a military contract, which required it to destroy several ground targets on the island airfield. It did it without taking damage and returned to base.

Wow there's a military contracts mod?

I know that the F-35 is a compromise, and in the past similar design philosophies have produced great planes but in our current conditions it probably won't be as useful as intended, that being said it probably won't be so deficient as to cost anyone their lives

EDIT:

I do love the futuristic F-35B though, VTOL's are amazing feats

Edited July 11, 2015 by Halsfury

[Darth Lazarus]

realy those little wingsection? wow ... very strange. Squad realy should rebalance such smaller parts

thanks a lot for your work. can't wait to see your improvments to the YF-17!

[RocketTurtle]

Then it's just too much deflection on the elevators, your main wings may be too far forward or your deflection is set too high, or both.

So I did everything you recommended, and it turns stable now, however I was only able to obtain 9.4 G's for a short moment.

I'm thinking I should scrap the design.

Also, are there any tutorials that explain all this aerodynamic stuff as if you know nothing about it? I know the basics but... well yeah. Lol.

[tetryds]

So I did everything you recommended, and it turns stable now, however I was only able to obtain 9.4 G's for a short moment.

I'm thinking I should scrap the design.

Also, are there any tutorials that explain all this aerodynamic stuff as if you know nothing about it? I know the basics but... well yeah. Lol.

I am making those, I have the scripts and everything ready, just need plenty of time to make the videos

Wanderfound has some tutorials, but I don't remember where you can find them.

[Hodo]

Also Darth I fixed your YF-17, I'll post the link sometime today

It was really those little wing sections which have weird qualities, either they flex or they are aerodynamically ugly in some other way but after redesigning the wing without them the roll authority is great, the aircraft snaps from side to side in turns and it can accelerate to mach 4 at 10km

- - - Updated - - -

Wow there's a military contracts mod?

I know that the F-35 is a compromise, and in the past similar design philosophies have produced great planes but in our current conditions it probably won't be as useful as intended, that being said it probably won't be so deficient as to cost anyone their lives

EDIT:

I do love the futuristic F-35B though, VTOL's are amazing feats

Here is the military contract pack.

5dim Military contracts

And you need this to install those.

Contract Config

[FourGreenFields]

So I did everything you recommended, and it turns stable now, however I was only able to obtain 9.4 G's for a short moment.

I'm thinking I should scrap the design.

Also, are there any tutorials that explain all this aerodynamic stuff as if you know nothing about it? I know the basics but... well yeah. Lol.

I usually did the high-G tests during, or just after dives btw. Nobody ever said it had to be in level flight speed (although I prob could reach that speed, but if I'm up at 10km for some other test, I might just as well dive and test max G load).

Anyway, a guide on subsonic stuff: Basic Aircraft Design - Explained Simply, With Pictures

That's a guide from 0.90 FAR, but physics still apply. CoL is less importand, but still helps explain stuff.

For transsonic, keep your cross section area something like this: https://de.wikipedia.org/wiki/Fl%C3%A4chenregel#/media/File:Sears-Haack.png

For hypersonic you should try to stay within a cone beginning at your nose (size of the cone varies with speed, just calculate Cd and check if it is ridiculously high), and avoid any bumps (so nothing that would decrease cross section if you'd only look at that very small part of the plane) (If I am not mistaken that helps avoid more shockwaves). Basicly what tetryds said earlier this thread.

[RocketTurtle]

I usually did the high-G tests during, or just after dives btw. Nobody ever said it had to be in level flight speed (although I prob could reach that speed, but if I'm up at 10km for some other test, I might just as well dive and test max G load).

Anyway, a guide on subsonic stuff: Basic Aircraft Design - Explained Simply, With Pictures

That's a guide from 0.90 FAR, but physics still apply. CoL is less importand, but still helps explain stuff.

For transsonic, keep your cross section area something like this: https://de.wikipedia.org/wiki/Fl%C3%A4chenregel#/media/File:Sears-Haack.png

For hypersonic you should try to stay within a cone beginning at your nose (size of the cone varies with speed, just calculate Cd and check if it is ridiculously high), and avoid any bumps (so nothing that would decrease cross section if you'd only look at that very small part of the plane) (If I am not mistaken that helps avoid more shockwaves). Basicly what tetryds said earlier this thread.

Can you elaborate on the last part? I'm not very familiar with those terms. (Cd, cross section (that one's fairly self explanatory though)... etc.)

[Hodo]

Can you elaborate on the last part? I'm not very familiar with those terms. (Cd, cross section (that one's fairly self explanatory though)... etc.)

Here is two videos for you. I watched both of them and they help explain a lot in simplest forms.

Edited July 11, 2015 by Hodo

[RocketTurtle]

Here is two videos for you. I watched both of them and they help explain a lot in simplest forms.

https://www.youtube.com/watch?v=atItRcfFwg

The first video doesn't seem to work for me, however the second was interesting and helpful. Thanks.

[FourGreenFields]

Can you elaborate on the last part? I'm not very familiar with those terms. (Cd, cross section (that one's fairly self explanatory though)... etc.)

Cd is drag coefficient or something like that. The higher, the more drag (note that it is not drag, and flying at higher speed with lower Cd usually still means higher drag - it is merely something along the lines of "drag, with speed and alt not taken into consideration").

Shockwaves, etc. are most likely explained in the vids, but can't currently watch them, due to bad internet connection.

[Halsfury]

@ Darth

This is how I finally found an aesthetically pleasing solution, it does make the wingtips more pointed so lower speed turns can result in wingtip drops.

It's been area ruled to .89m^2 wave drag area and has a pretty nice flying character overall

[Hodo]

Lets see if this works

[Halsfury]

realy those little wingsection? wow ... very strange. Squad realy should rebalance such smaller parts

thanks a lot for your work. can't wait to see your improvments to the YF-17!

Also here it is in flight, look at the G meter

It has a low tolerance for stalls under 200m/s but true to a 4th generation fighter it is liable to spin in a friendly, recoverable way

I didn't get a screenshot but it went right up to mach 4.2 at 10km, then it exploded, not just into bits, but violently and into dust particles

EDIT:

Also I changed the elevons to reflect your original choice, no loss in ability was recorded

Edited July 11, 2015 by Halsfury
Thought my first post didn't go through

[RocketTurtle]

Lets see if this works

Yes, that works. Thanks.