Ferram Aerospace Research vs Stock

[CoriW]

Pretty much exactly what the title says, I'm wondering about what's really better, the FAR plugin or Stock aerodynamics?

The reason I say this is because, I originally got FAR when I wanted my re-entries to be more realistic and for nose cones on rockets to actually work, that being said I had only ever really done stuff with rockets and not spaceplanes. Now recently I went ahead and decided to look into spaceplanes a bit, and after much research on how to build a functional spaceplane and many hours of building and testing I found that it was literally impossible for me to create an SSTO using FAR, every single time I tried a design it would work perfectly up until about 15,000m where I would always end up encountering an un-recoverable stall.

So that's the problem I'm having with FAR, is that it seems to work perfectly with rockets, but not with spaceplanes. Why?

At this point the only reason I'm keeping FAR is for rockets, I'll just have to avoid doing spaceplanes unless I can figure out why I'm having these issues. It's a shame really, I think I would of liked spaceplanes.

[leax256]

well without pics it could be impossible to determine the problem, the biggest thing people don't realise is that you need 2 pivit points, or put simplier, you need a wing and a tail.

[fcdrifter13]

Pretty much exactly what the title says, I'm wondering about what's really better, the FAR plugin or Stock aerodynamics?

The reason I say this is because, I originally got FAR when I wanted my re-entries to be more realistic and for nose cones on rockets to actually work, that being said I had only ever really done stuff with rockets and not spaceplanes. Now recently I went ahead and decided to look into spaceplanes a bit, and after much research on how to build a functional spaceplane and many hours of building and testing I found that it was literally impossible for me to create an SSTO using FAR, every single time I tried a design it would work perfectly up until about 15,000m where I would always end up encountering an un-recoverable stall.

So that's the problem I'm having with FAR, is that it seems to work perfectly with rockets, but not with spaceplanes. Why?

At this point the only reason I'm keeping FAR is for rockets, I'll just have to avoid doing spaceplanes unless I can figure out why I'm having these issues. It's a shame really, I think I would of liked spaceplanes.

I love FAR when launching rockets and recently I loved it when I was building spaceplanes, until today. Every tried and true design I have just started going nuts. And I found out that it was me and not the mod, I was not going fast enough higher up to generate lift so I would get a flat spin, fixed that by adding moar boosters. I literally cussed for an hour because I switch back and forth between a copy with and without and forgot I was using far. I usually want to be at 1000m/s surface before I go above 15k.

[CoriW]

well without pics it could be impossible to determine the problem, the biggest thing people don't realise is that you need 2 pivit points, or put simplier, you need a wing and a tail.

Hold on, by tail do you mean the vertical tail fin or like a second smaller "wing" near the tail of the plane like on real planes? If the latter, then that's probably part of my issue.

I love FAR when launching rockets and recently I loved it when I was building spaceplanes, until today. Every tried and true design I have just started going nuts. And I found out that it was me and not the mod, I was not going fast enough higher up to generate lift so I would get a flat spin, fixed that by adding moar boosters. I literally cussed for an hour because I switch back and forth between a copy with and without and forgot I was using far. I usually want to be at 1000m/s surface before I go above 15k.

Hmm, 1000m/s at 15,000m? That could be why, I'm only typically at around 500m/s at 15,000m.

[zzz]

I'm wondering about what's really better, the FAR plugin or Stock aerodynamics?

Stock aerodynamics is not aerodynamics at all.

FAR aerodynamics at least use some aerodynamic principles in simulation with more or less correct results.

If you need aerodynamics then FAR if you not care about aerodynamics then stock. This what this question about.

with FAR, is that it seems to work perfectly with rockets, but not with spaceplanes. Why

Usually I see opposite impression and problems.

Everything is nice with planes in FAR, it's just you doing something wrong,

[asmi]

So that's the problem I'm having with FAR, is that it seems to work perfectly with rockets, but not with spaceplanes. Why?

It works just fine with spaceplanes, just as with rockets. Infact it's primary purpose is to make planes work like they actually fly in the air, not in weird fluid. If you can't do that, you need to learn how to do it, not assume that it's FAR's fault - this mod is pretty solid at the moment, and if you go through FAR thread, you'll see plenty of accusations like your, and almost all of them turned out to be design issues with vessels, not with the mod.

There recently was a big thread on SSTO designs with FAR, so I'm far from being alone in making it happen. If you want, you can go through that thread and maybe it will give you some clues as to how to do that properly. And if you want to get some help, please post screenshots of your vessel - there are many knowledgeable people over here, and I'm sure they'll be able to figure out what is wrong with your designs.

[CoriW]

I'm sorry, it seems that I've come across as saying it's FAR's fault, which wasn't my intention.

My intention was more of asking why I may be having these problems, which I didn't really state clearly, my apologies.

[asmi]

I'm sorry, it seems that I've come across as saying it's FAR's fault, which wasn't my intention.

My intention was more of asking why I may be having these problems, which I didn't really state clearly, my apologies.

As I've said, it's hard to suggest anything useful without seeing your craft. With FAR, shape is everything.

[CoriW]

As I've said, it's hard to suggest anything useful without seeing your craft. With FAR, shape is everything.

Alright well, here it is.

Pheonix SSTO KP Mk5

EDIT: Oh and it uses Procedural Dynamics, almost forgot to mention that.

Edited September 25, 2013 by CoriW

[ferram4]

Possible problems:

CoM movement rearward causes loss of pitch stability.

Lack of dynamic pressure due to excessive climb rate causes engine flameout, initiating flat spin.

Lack of dynamic pressure due to excessive climb rate causes loss of lift; pilot compensates with increased angle of attack, causing stall.

Plane is only marginally stable at low supersonic speeds; acceleration to hypersonic velocities causes loss of stability.

Stalling decreases stability of aircraft.

These might help, but pictures will help narrow down the problems.

Edit: It also has MechJeb, Kerbal Engineer, and probably a bunch of other mods that I don't have installed; this is why I tend to ask for pictures, not the craft itself. Diagnosis will have to wait for a bit.

Edited September 25, 2013 by ferram4

[CoriW]

Possible problems:

CoM movement rearward causes loss of pitch stability.

Lack of dynamic pressure due to excessive climb rate causes engine flameout, initiating flat spin.

Lack of dynamic pressure due to excessive climb rate causes loss of lift; pilot compensates with increased angle of attack, causing stall.

Plane is only marginally stable at low supersonic speeds; acceleration to hypersonic velocities causes loss of stability.

Stalling decreases stability of aircraft.

These might help, but pictures will help narrow down the problems.

Edit: It also has MechJeb, Kerbal Engineer, and probably a bunch of other mods that I don't have installed; this is why I tend to ask for pictures, not the craft itself.

Actually I have all those other mods build into my command pods, the only mod that is actually a part on the craft is Procedural Dynamics.

Although to help find a solution to the problem I'll go ahead and load up KSP to get a screenshot, I'll edit this post with said screenshot in a few minutes.

EDIT: Here's the screenshot.

Edited September 25, 2013 by CoriW

[ferram4]

Alright, here are the many problems:

You don't have a separate horizontal tail / forward canard for pitch control and stability; this means that any pitching motion on your plane will take a long time to damp out, as well as making its stall characteristics worse. It would probably also benefit from having the wings swept a bit to reduce drag at low angles of attack and at high Mach numbers. If fuel is draining from the central tank to the outboard tanks then it will also become less stable as the CoM moves backwards; I don't think you actually need that much fuel for the jets alone either. It would probably benefit from a slightly larger vertical tail as well. I'd also get rid of the engine nacelles entirely, since they are incredibly inefficient weight-wise, intake-wise and drag-wise; they're just bad to have in general and they are likely making your plane less stable.

[CoriW]

Alright, here are the many problems:

You don't have a separate horizontal tail / forward canard for pitch control and stability; this means that any pitching motion on your plane will take a long time to damp out, as well as making its stall characteristics worse. It would probably also benefit from having the wings swept a bit to reduce drag at low angles of attack and at high Mach numbers. If fuel is draining from the central tank to the outboard tanks then it will also become less stable as the CoM moves backwards; I don't think you actually need that much fuel for the jets alone either. It would probably benefit from a slightly larger vertical tail as well. I'd also get rid of the engine nacelles entirely, since they are incredibly inefficient weight-wise, intake-wise and drag-wise; they're just bad to have in general and they are likely making your plane less stable.

Alright, thanks for all the insights ferram, I've been working on the design since my last post and the first thing I did was add a horizontal tail, which is helping the stability a ton. I'll try fixing all the things you've mentioned and hopefully I'll be in orbit in no time.

EDIT: Thanks for the help! I removed half the jet fuel and replaced that with rocket fuel, then centered the mass, dry mass, and center of lift all directly on top of each other, as well as swapped the nacelles with XM-G50 Radial Air Intakes. With that I got to orbit with 66 units of rocket fuel left (36 of which I used to de-orbit) and when I finally landed back on the runway at KSC I had 212 units of jet fuel left. (You were really right about too much jet fuel)

Edited September 25, 2013 by CoriW

[rakutenshi]

The only reason most aircraft are built the conventional way now is because that's what people are used to seeing and (esp. regarding passenger aircraft) feel more comfortable with. A full moving canard design with a swept aft mounted main wing - especially for super/hypersonic designs typically offers superior controllability, with the canards being ahead of the main shock, they tend to have better control authority, and as stated before, the swept wing reduces drag significantly at higher speeds when your aircraft is flying near straight rather than at the 2-5 degrees positive AoA of lower speed flight.

However FAR seems to have issues with the shock front calculations over the wing surface, where a delta wing with a longer root cord should improve control authority over a purely swept wing design at mach 1+ (the SR-71, STS, Concord, and Tu-144 all have deltas for this reason).

Compound the effects of Mach Tuck with a center of gravity that may not be shifting the way you'd like it to, and you're likely to end up with an aircraft that hits about mach .85 or so, decides space is scary and it wants to get back down to safe altitudes, and refuses to pull up no matter how hard to press the S key or pull back on your joystick.

To maintain manouverability at trans/supersonic speeds, many modern fighter aircraft are built with the Center of Pressure forward of the average center of mass, as well as other features that reduce the inherent stability of a design. The drawback is that these aircraft almost by necessity must be controlled by a FCC or similar Fly -by -wire system, that constantly makes very minor adjustments to the control surfaces.

We don't really have that option in KSP so we're left to deal with aircraft that may perform wonderfully at low speeds, but generally become very stubborn flaming darts at high speeds.

At least that's what i've arrived at through my own research and wonder what this does.

[Dooz]

If you want realism Ferram i tried ferram and it messed up all my rockets but plane controls are awesome in ferram

Yeah im on stocks side

[Captain Sierra]

FAR is very accurate, moreso than most KSP players are ready for. I have flown jet flight sims. The FAR flight modeling is very good. I suggest doing some researh on realistic hypersonic aircraft designs and making something that would theoretically work in real life (Keep in mind, space planes need to hit speeds 5x higher than kerbal to make orbit, you only need to hit around 2,000m/s and 25km max).

[Van Disaster]

However FAR seems to have issues with the shock front calculations over the wing surface, where a delta wing with a longer root cord should improve control authority over a purely swept wing design at mach 1+ (the SR-71, STS, Concord, and Tu-144 all have deltas for this reason).

IIRC one of the benefits of a delta for supersonic flight is a large wing area with a small span - that makes a smaller cone and less drag without loss of lift ( depending how much FAR is checking sweep either it's not being accurate or the drag loss is less than I'm imagining though ). Add the high AoA possible so they don't have to land at extreme speeds, and that makes it a bit of a no-brainer choice ( and I suspect there's also longditudinal stability bonuses with those size deltas ). Canards offer positive lift all the time, but there's issues in stalls and the interaction with the main wing so it's not just about being unconventional ( and then again there's airflow benefits for some types of canards too, but I suspect anything that close to the wing won't be much use as a control surface ).

I've built a working unstable canard design - the latest SAS can actually handle that, it appears.

As for rockets: oh no, people have to actually design proper rockets, FAR can't be right there

Edited September 25, 2013 by Van Disaster

[Hodo]

Here is how a SSTO/Space plane design should look roughly. This is my SP-103 Jackal.

Notice how the center of lift is just behind the center of balance.

Also notice how the center of thrust is inline with the center of balance.

These are things that help greatly with a space plane design.

[zzz]

{post deleted}

Edited September 27, 2013 by zzz

[Hodo]

Also notice intake abuse

LOL actually it's not that bad, only 5 intakes for 4 air breathing engines. I have seen FAR worse. And the one directly under the nose was so the nose gear was slightly lower, or give it a bit more of a positive AoA while sitting on the runway.

[zzz]

I have seen FAR worse.

I'm too, this is more or les resonable design in comparsion, this is why decide do not nitpick and to delete my post.

[Hodo]

I'm too, this is more or les resonable design in comparsion, this is why decide do not nitpick and to delete my post.

I was not offended, not in the slightest. And I found it actually kind of funny, because I did build a air hog design in FAR and it flew like a brick with all those intakes open. So much drag it was useless. So I went back to a simple design concept, go to the local airport and military airfield and look at planes and how they are designed. Then load up my FreeFalcon 5.0 and look at the modern fighters. Then do some other research. I found at most you have a 3:1 ratio of intake to engines design. So that is my MAX for all of my aircraft. Now I do have some stupid fun ones that have something like 20 intakes on them... but they also have 12 air breathing engines and go just around the speed of thought.

[Van Disaster]

That's not really what I'd call "just behind the centre of mass" - CoL is going to move a fair bit going supersonic with that size chord, you could put the CoL ball right inside the CoM ball & it'd be less stable for takeoff ( which is good for rotating ) and then become a bit more stable at high speed. Well that's how I attempt it anyway, although I'm experimenting with aerocentre in front of CoM at the moment - if your mass shifts forwards with fuel use so it gets in front of the aerocentre by the time you want to land, it seems to work given some stability assists and canard layout.

[rakutenshi]

Regarding spaceplane/hypersonic aircraft designs.. Most of them use a lifting body delta design, the poster child of this theory seems to be the X-43C of the Hyper-X project.

As far as inherent instability, I had quite a bit of luck with a forward swept gull wing design. It was very unstable and I had to use mechjeb to fly it just because otherwise it would somersault on takeoff rotation. It did perform very very well, and initial testing had it cross the transsonic threshold with minimal (negligible) mach tuck effects. I had used the CoM stacked on top of the CoP approach. I'm going to do some experimenting with using flaps possibly to move the center of lift a little further back during takeoff and initial acceleration, then as speed increases, raising the flaps should allow the CoP to move forward slightly to counteract the effects of trans sonic flight.

That's the hope anyway.

Jeb is loving this research... screaming in terror is very bad when it's jeb doing it.

... after some testing. Flaps only served to move the CoP forward when deployed. .. will have to fiddle more .

Edited September 28, 2013 by rakutenshi

[Van Disaster]

Well, real life spaceplanes have to deal with going considerably faster than ours...

I turned all the reaction wheels off, pulled it off the runway & nosed up by hand, hit T & it just sat in the same attitude climbing, no noticeable control surface deflection. Up at 19km it wanted to pitch up regardless of SAS but it wasn't uncontrollable, I just used SmartASS at that point because my hand was getting tired

The indicator bugs don't help much for this sort of thing, unfortunately.