[1.3.1] Ferram Aerospace Research: v0.15.9.1 "Liepmann" 4/2/18

[Wanderfound]

There seems to be enough weirdness with the CoL marker (which, as mentioned upthread, is not actually representing CoL now) that I'm pretty much ignoring it. So long as your stability numbers are green and your yellow lines are sloping down in the AoA sweep, you're all good.

[jrandom]

Is it possible to update the CoL marker to show a general average center of lift? The stability numbers are great and all, but it's super handy to have a simple visual guide when roughing out the initial shape of the craft. It's faster when iterating over various design possibilities.

Maybe show two markers: average CoL at level flight for subsonic, and another for supersonic. That would be ridiculously handy.

[blowfish]

Is it possible to update the CoL marker to show a general average center of lift? The stability numbers are great and all, but it's super handy to have a simple visual guide when roughing out the initial shape of the craft. It's faster when iterating over various design possibilities.

Maybe show two markers: average CoL at level flight for subsonic, and another for supersonic. That would be ridiculously handy.

The problem is that it changes with AoA.

[jrandom]

The problem is that it changes with AoA.

Right, which is why I specifically mentioned "level flight" or maybe at say 5 degrees incline. Some mostly-level orientation. Or heck, just make a simple slider control in its own floating window that lets you adjust the AoA for what you want used in the CoL location. Having to constantly pop up the derivatives window and run an analysis greatly slows down initial craft creation when you're still playing around with the design. It's great for fine-tuning, though.

[NathanKell]

Here's some actual numbers, using the Beech Bonanza as reference.

S = 16.815m^2

Cd0 = 0.0192

Mass at Vmax = 998kg

downforce = 998*9.80665

lift = 998*9.80665 = 9787N

93.88m/s Vmax

Cl = 9787 / (.5 * 1.225 * 93.88^2 * 16.815)

Cl = 0.108

AR = 6.2

Cdi = 0.108^2 / (pi * e * AR)

Cdi ~= 0.0006

Cd at Vmax ~= 0.0199

Drag force = 0.5 * 1.225 * 93.88^2 * 0.0199 * 16.815 = 1806.4N

Ingame, the Cd is about 1.3x as high as it should be at Vmax and Cl is more like 1.72x as high as it should be. That leads me to believe that subsonic, M<0.3 drag should be about .8x what it is now, and lift should be about 0.58x what it is now.

Note that for testing I removed the wing landing gear to not have excess drag on the wings. Pics are from .90 and oldfar, too lazy to upload a new album, but the numbers cited above are from nuFAR Fenno. S is correct, cross-section is as correct as I can make it.

Javascript is disabled. View full album

Edited May 11, 2015 by NathanKell
Stupidity

[Gfurst]

@NathanKell, nicely done, how the hell did you get that bonanza in KSP?

And for everyone else, is there a nice working procedural wing mod yet?

[jrandom]

And for everyone else, is there a nice working procedural wing mod yet?

I've heard tell that B9 Procedural Wings (with patch) works, although I haven't tested it out much myself yet. Apparently there's an issue on 64-bit linux if either the root or the tip have a length of 0.

[Pyromaniacal]

I am having the absolute worst luck trying to pass about 20km altitude. I have tried speeds between 1.0 and 3.5 mach, but I always run in to odd yaw forces at the transition from the middle atmosphere to the upper (Medium blue to dark blue on the altitude gage).

Here's an example of the ship I used. Included is the stability data for the altitude and airspeed that the plane suffered loss of roll control, followed by a stall and flatspin. (Sorry, can't figure out how to embed a slideshow, the embed codes were crap.)

http://imgur.com/a/CDk9D

Additionally, reading back, I saw something about sudden changes in cross section, so I stripped a plane that I had down to a fuselage, wings, and rudder, and was presented with this:

I am so confused. I have read the design process information on the Github page, but it isn't helping in the slightest, as all of the numbers in the example craft are green for the failure point. What is it that I'm doing wrong? How gradual do I need to build these wings and maintain a decent ship length? What is a proper flight path and airspeed breakdown for FAR?

[pjf]

(This is only required if you've installed Euler via the CKAN and can't upgrade. New FAR users, and users of older releases won't need this.)

Upgrading from Euler to Fanno via the CKAN

1. Shift-right-click on the folder containing ckan.exe icon and choose "open command prompt here"

2. Type 'ckan update' and hit enter. This will fetch the updated metadata. It might take a moment.

3. Type 'ckan upgrade FerramAerospaceResearch=v0.15.1_Fanno' and hit enter. Capitalisation matters. This will upgrade to Fanno.

4. Rejoice! You're done!

Edited May 12, 2015 by pjf
Capitalisation matters. Oops.

[Gfurst]

I am having the absolute worst luck trying to pass about 20km altitude. I have tried speeds between 1.0 and 3.5 mach, but I always run in to odd yaw forces at the transition from the middle atmosphere to the upper (Medium blue to dark blue on the altitude gage).

Isn't it only a turbo jet engine? I'm guessing that around 25km and above its too thin even for turbo jets... Anyway , in the thinner atmosphere you get less and lesser lift on your wings and control surfaces, eventually having to transition to RCS reaction wheels, but by then I'm sure the jet engine will burn out.

[Pyromaniacal]

There are twin turbojets and an LV-N engine on the imgur link example spaceplane. The fuselage and wings were me asking for help with the cross sectional thingy involving that yellow squiggly line. I am good at wording.

Should I assume that there's no real fuel efficient way to get an SSTO out of atmosphere without the RAPIER engines?

[NathanKell]

Gfurst: thanks! Lack's SXT comes with the fuselage parts, then I wrote Realism Overhaul configs for the size and mass to be correct and an AJE config for the IO-550 to be correct. The wings are B9 proc wings (download from the Addon Dev forum, then go to the last page in the thread for Crzyrndm's patch). I've actually made a bunch of replicas, stretching back to .24. They were to tune engine performance so I could figure out how all these creations would perform. I have yet to try anything but the Bonanza with nuFAR however, and AJE props aren't quite all there in 1.0 yet.

[Goddess Bhavani]

Ok my mistake, you managed to include proper flaps and I didn't take note until I flew it the way it was intended. And yes now it flies well...

One thing though. Why do you have a negative angle of attack? The nose of the plane is pointing down by 5 to 10 degrees but it stays level. I've been trying to achieve this with some of my SSTO's but so far the best I've done is manage to get a zero AoA at say 20km altitude vs yours which literally points slightly down and still doesn't descend. I'm going to do some more research into this. The nose of the plane destroyed itself on initial lift off but I'm unsure as to why.

So yes a good design. =) I try base my designs off the SR71 or there about. To me the SR71 is a bullet proof design at even mach 6. Now that the game has friction heat (deadly re-entry) I probably won't be doing all the magical cool stuff that I could achieve before. I'll have to try new techniques. Not to mention that the B9 Sabre M engine will probably vanish in v6 of B9 pack.

Edit:

@pandoras kitten

One issue also was that your plane tends to explode at >700km/h at low altitude. If I drop flaps (key: 2,2) before takeoff and just get upto 500km/h then lift off. Not long after the plane blows up. I'm not sure if it's just me or what.

Edit 2:

I just realised that enabling SAS causes dramas because stability assist tries to level the plane based on prograde. So SAS flips the plane upside down.

No worries at all, the use of negative flaps as initial rotation boost is not a usual craft design technique.

I'm alright with the inability to go supersonic at low level as I intended the plane to be a typical Cold War era interceptor. In its intended use it will act like an English Electric Lightning, streak up to high altitude in less than a minute and vector under ground control, intercept target and run for home.

You could try reinforcing the wings to make them survive higher dynamic pressure but I was trying to keep the weight similar to a real life lightweight fighter jet.

As for the nose down attitude, observe that the cockpit is angled downwards, both for better IVA visibility and to match the original shape of the plane in the Captain Scarlet TV show.

[jrandom]

Designing with the area rule in mind from the start is interesting!. Kept the curves visible for the entire design so I could watch how my changes affected potential wave drag.

(Haven't actually flown this one yet. I'm about to.)

Edited May 12, 2015 by jrandom

[tempsgk]

I think that would be pretty fast, I created a plane with similar lines and went 1300 m/s in thick kerbin atmosphere lol. So far I feel like new FAR plane designs reward more middle Centre of Mass planes instead of the Centre Of mass being at the rear that favours delta shaped planes. So Skylone shaped planes would be the best for speed.

Edited May 12, 2015 by tempsgk

[jrandom]

Well, it flies (using turbofans, not turbojets), but since I don't have RSS/RO/AJE installed, I have no idea if this is flying well or not. (Wings are full of 600 units of liquid fuel each, so the thing's got mass at present -- 28 tons or so.)

Edited May 12, 2015 by jrandom

[Amram]

Additionally, reading back, I saw something about sudden changes in cross section, so I stripped a plane that I had down to a fuselage, wings, and rudder, and was presented with this:

I am so confused.

I'll just touch on area ruling as I understand things...I may as well lay it out there, I'm either right and I can help, or I'm not and we'll both get it from someone that does know more.

Your constraining your focus too much, its not about gradual changes in the wing, its gradual changes in everything plus an avoidance in changes of the whole. More confused yet?

First a visual, this is a cross section of a human, top down. Note that it starts small at the head, suddenly increases at the shoulders, then becomes three shapes when its torso and arms, then two when it is both legs, and again suddenly changes at the feet. That is the cross sectional shape of that particular human. For our purposes here, that is his cross sectional area at each point along the way and when its multiple shapes, they are combined for the total, so torso plus arms,or both legs, or just the head, etc. Avoid what happens at the shoulders and feet, as those are sudden and significant changes in area.

Now imagine if you took your plane and did the same thing from nose to tail. You'd start off good, things would increase at a fairly steady rate, and then you'd hit the end of those canards, and suddenly the area drops, because its not fuselage plus canards anymore, now its just fuselage. But then things are good again, its all fuselage until the wings start, but they start slowly and things vary a bit but tolerable. Then we get to the end of the wings, and they just stop.

The problem is this. We go from all this area the wings occupy, plus tail, plus fuselage, to just tail and fuselage, magnified even more by the fuselage thinning as well. That change is area is what's getting you.

Give this image a view.

As soon as they start their wings, they slim the fuselage, and its thinnest when the wings are thickest and nearly at their widest. As the wings begin the thin to the rear, the tail begins, and the fuselage slowly widens out again, so that the overall area remains nearly if not exactly the same. Then, rather than abruptly end their wings, they use a diamond shaped delta, tapering back into the fuselage to prevent a sudden change in area, and allow the fuselage some room to expand smoothly to account for it. Then, once the wings have ended, the tail is still getting bigger, so the fuselage again resumes shrinking, so that the area remains as close to constant as possible. Of course, they also have to slim down for the end, since ordinary drag doesn't agree with dragging around flat areas perpendicular to the flow.

The T-38 really exemplifies it.

The short version is that when you have to make something bigger, you make something else smaller at that same point, by that same amount. They initially increase to a certain point that is a useful minimum size and then try to stay at that point and no bigger/smaller until they have to reduce to a minimum at the end of the aircraft. So when the wings need to get wider and or thicker, the fuselage gets smaller and vice versa.

The entire goal, is to do this, note that the wing in the image is thinning as it reaches the end which helps to offset the sudden change, KSP's wing panels don't.

This would be worth a read, its not real long, doesn't get into math, its just area rule for the beginner.

It is a bit more involved than that, but thats enough to get reasonable lines fairly consistently. Procedural parts will make designing it a whole lot simpler since you can scale to whatever you need at that spot.

[Hektos]

I'll just touch on area ruling as I understand things...I may as well lay it out there, I'm either right and I can help, or I'm not and we'll both get it from someone that does know more.

Your constraining your focus too much, its not about gradual changes in the wing, its gradual changes in everything plus an avoidance in changes of the whole. More confused yet?

First a visual, this is a cross section of a human, top down. Note that it starts small at the head, suddenly increases at the shoulders, then becomes three shapes when its torso and arms, then two when it is both legs, and again suddenly changes at the feet. That is the cross sectional shape of that particular human. For our purposes here, that is his cross sectional area at each point along the way and when its multiple shapes, they are combined for the total, so torso plus arms,or both legs, or just the head, etc. Avoid what happens at the shoulders and feet, as those are sudden and significant changes in area.

Now imagine if you took your plane and did the same thing from nose to tail. You'd start off good, things would increase at a fairly steady rate, and then you'd hit the end of those canards, and suddenly the area drops, because its not fuselage plus canards anymore, now its just fuselage. But then things are good again, its all fuselage until the wings start, but they start slowly and things vary a bit but tolerable. Then we get to the end of the wings, and they just stop.

The problem is this. We go from all this area the wings occupy, plus tail, plus fuselage, to just tail and fuselage, magnified even more by the fuselage thinning as well. That change is area is what's getting you.

Give this image a view.

As soon as they start their wings, they slim the fuselage, and its thinnest when the wings are thickest and nearly at their widest. As the wings begin the thin to the rear, the tail begins, and the fuselage slowly widens out again, so that the overall area remains nearly if not exactly the same. Then, rather than abruptly end their wings, they use a diamond shaped delta, tapering back into the fuselage to prevent a sudden change in area, and allow the fuselage some room to expand smoothly to account for it. Then, once the wings have ended, the tail is still getting bigger, so the fuselage again resumes shrinking, so that the area remains as close to constant as possible. Of course, they also have to slim down for the end, since ordinary drag doesn't agree with dragging around flat areas perpendicular to the flow.

The T-38 really exemplifies it.

The short version is that when you have to make something bigger, you make something else smaller at that same point, by that same amount. They initially increase to a certain point that is a useful minimum size and then try to stay at that point and no bigger/smaller until they have to reduce to a minimum at the end of the aircraft. So when the wings need to get wider and or thicker, the fuselage gets smaller and vice versa.

The entire goal, is to do this, note that the wing in the image is thinning as it reaches the end which helps to offset the sudden change, KSP's wing panels don't.

This would be worth a read, its not real long, doesn't get into math, its just area rule for the beginner.

It is a bit more involved than that, but thats enough to get reasonable lines fairly consistently. Procedural parts will make designing it a whole lot simpler since you can scale to whatever you need at that spot.

WOW this was all so very helpful! Thanks for taking the time to make this post. I have come to the realization that the stock KSP parts are quite limiting at my point in the career for the endeavor I am trying to undertake.

[Pyromaniacal]

That does help a fair amount, actually. I can see on my fuselage where I should start tapering it off, and I'm questioning if I should have those canards at all. Additionally, stock parts are just about useless for spaceplane design with FAR installed. Is that close to the mark? I keep seeing B9 P-wings mentioned a lot, after work today I'll have to give those a look. That explanation told me what, when, and where I should be looking at.

Wow, spaceplanes are hard...

[Hektos]

That does help a fair amount, actually. I can see on my fuselage where I should start tapering it off, and I'm questioning if I should have those canards at all. Additionally, stock parts are just about useless for spaceplane design with FAR installed. Is that close to the mark? I keep seeing B9 P-wings mentioned a lot, after work today I'll have to give those a look. That explanation told me what, when, and where I should be looking at.

Wow, spaceplanes are hard...

Spaceplanes? I just want to get a normal jet going fast

I think I just need to consign to the fact that my current selection of parts are just too weak to make a sufficiently smooth curve without a mile long plane

[Kitspace]

Hello!

The planes handle wonderfully with the new voxel system!

If I actually recall that correctly it used to be somehow possible to have different travel limits in different directions for the control surfaces like in most real planes. Is it currently possible and was it ever really possible?

Is it possible to set a hard limit for the control surface so it would not go beyond that instead of just deflecting to a sum of the control and flap inputs? Like if a control surface deflects with the flaps it uses some of its downward travel range for that not just adds more?

Also I have noticed something that could be a bug but I do not know for sure.

The indicated airspeed and the equivalent airspeed shown are significantly higher than the stock game groundspeed.

As far as I know there is no wind in the game so groundspeed equals the true airspeed.

So the real indicated airspeed should be approximately equal to the groundspeed at sea level and less than that at a higher altitude.

Does my logic seem correct?

I could not think of a physical explanation to what happens in the game so I am in doubt if that is intended and what it means or it is a bug.

But it seems like it is an indication only issue and does not affect the handling of the planes.

Not quite sure on that yet also.

Thank you!

[B15HOP_xmen]

No worries at all, the use of negative flaps as initial rotation boost is not a usual craft design technique.

I'm alright with the inability to go supersonic at low level as I intended the plane to be a typical Cold War era interceptor. In its intended use it will act like an English Electric Lightning, streak up to high altitude in less than a minute and vector under ground control, intercept target and run for home.

You could try reinforcing the wings to make them survive higher dynamic pressure but I was trying to keep the weight similar to a real life lightweight fighter jet.

As for the nose down attitude, observe that the cockpit is angled downwards, both for better IVA visibility and to match the original shape of the plane in the Captain Scarlet TV show.

Yeah I gave it a test flight from inside the IVA and it's definitely much easier to fly with the nose slightly down. I might reinforce the wings to see what happens. I am also curious about the way you did the wheels. I have a tool to align wheels to be dead straight. But what makes me like your plane is that the faster it goes down the runway, the less the steering impacts the craft. Exactly what is needed because smaller adjustments are better at higher speeds. I'm not sure if you did that deliberately or you just fluked it.

[blu3wolf]

without wind, the ground speed GS is equal to the true airspeed TAS.

The indicated airspeed IAS is roughly the TAS at sea level, but accumulates error at higher altitudes. Basically the IAS is the result of imperfect instrumentation.

The equivalent airspeed EAS is the IAS after calibration to correct the imperfections (and that makes it TAS again), and after correction for compressibility (which is where it becomes EAS).

I havent really wrapped my head around EAS properly, but the way it works (I believe) is that EAS will be significantly lower than TAS, as it gives you the effective airspeed you are travelling at, with respect to the amount of air going over the wings.

At least, thats the way it works in Falcon. Problem there is that that speed is CAS which should not have the compressibilty correction.

Im sure someone here can set us both straight with how it works in FAR

[balu0]

without wind, the ground speed GS is equal to the true airspeed TAS.

The indicated airspeed IAS is roughly the TAS at sea level, but accumulates error at higher altitudes. Basically the IAS is the result of imperfect instrumentation.

The equivalent airspeed EAS is the IAS after calibration to correct the imperfections (and that makes it TAS again), and after correction for compressibility (which is where it becomes EAS).

I havent really wrapped my head around EAS properly, but the way it works (I believe) is that EAS will be significantly lower than TAS, as it gives you the effective airspeed you are travelling at, with respect to the amount of air going over the wings.

At least, thats the way it works in Falcon. Problem there is that that speed is CAS which should not have the compressibilty correction.

Im sure someone here can set us both straight with how it works in FAR

IAS is Indicated air speed. In real life every speed meter on the plane show this value and for aerodynamic purpose it is the one that matters. For example, if your stall speed is 100 knots on sea level in IAS it will be 100 knots IAS at 10000m as well. 100 knots IAS will produce the same amount of lift on every altitude.

If you just fly you use IAS.

On the other hand EAS is about dynamic pressure, this is useful when building the plane to go supersonic.

http://en.wikipedia.org/wiki/Airspeed

[B15HOP_xmen]

RE ...area drag...

This is all well and good. But the whole principle of area drag goes against maintaining a cargo in centre of mass. Especially with a SSTO with a huge cargo mass. If anything you want most of the mass of the plane in the middle of the craft. So shrinking the fuselage right where it needs to be heaviest is almost counteracting the point of carrying a reasonable sized mass. I can see the point of area drag being useful in terms of low altitude supersonic speeds. Yet the point of a SSTO is to get above the atmosphere anyway... So really, this isn't as much of an issue for a SSTO. In practice you get much less drag by climbing above 25km altitude anyway which makes the area drag less important. I instead focus on a strong glide angle (lift to drag ratio) while still having a TWR of over 1.5 at the very least. Also if you have plenty of thrust, drag is less of an issue anyway. So for me it was a matter of climbing high enough with some kind of jet engine before powering up rockets.

Notice here with My Jumbo sized Rockomax 64 which I think weighs over 30 tonne. Right smack dab in the middle of the centre of mass of the plane. So once the mass is removed, the SSTO acts almost exactly the same.

@Ferram4

Do the engines count as part of the area wave drag? It wouldn't seem right if they did because the engine would be creating a vacuum right in front of the engine nose cones? I don't know much about air flow dynamics. But I guess that higher speeds a vacuum would not be present once going supersonic. The air wouldn't be able to move fast enough to counter the sudden air pressure changes in front of the engines. I could imagine an engine stalling say a vacuum bubble was created in front of the engine too... I'm unsure if nuFAR can account for this though?

Edited May 12, 2015 by B15HOP_xmen