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

[tetryds]

@everybody: Stock engines were not touched this time, their curves fit that of REAL jet engines.

So, yes, better hold the foot on the thrust there.

Also, remember that fairings which are larger than the rocket body are VERY UNSTABLE, that is one of the reasons why gimbal was buffed 1.5x.

Small tail fins will not fix your problem as much as before.

Just try to keep your rocket as streamlined as possible.

@Horus: whoops.

Well, Blitz has the landing gear retracted because it was so much of a pain to area rule a straight wing design that I forgot to open them, haha.

Will try to remember to fix it for the next release, thanks.

Also, protip: it's optimal low altitude flight speed is Mach 0.7~0.8, it pulls some sick g's.

@prog: Airbreaks use stock code for now, they are a bit overpowered but work well enough.

With a simple single stack ship I set my periapsis to 30k to airbreak and ended with more apoapsis than when I started. Now I'm lost.

Are both your AP AND PE higher than before, and are you sure you just did not bounce up on the atmosphere?

Which craft are you using?

Screenshots (of the orbits)?

Mods?

Please answer these questions so that I can check it out here and if it's really a bug I will annoy ferram to death until he fixes it

Edited May 9, 2015 by tetryds

[jrandom]

Feel like a noob asking this, but what exactly is area ruling? (I'm assuming it's to do with wing area vs. lift at different speed regions, but is there an actual description somewhere?)

[tetryds]

Feel like a noob asking this, but what exactly is area ruling? (I'm assuming it's to do with wing area vs. lift at different speed regions, but is there an actual description somewhere?)

Don't feel like a noob asking this, it's quite complicated and even requires calculus to really grasp the maths of it.

And even the simplest explanations can be quite confusing (most of stuff you find on the internet is historical or a pure description of what it means/what it's for, and don't even tell how it works).

If you slice your airplane, you get a cross-sectional cut (for example, Mk2 spaceplane parts cross-section cut is the Mk2 connection shape).

Throughout the airplane, the area of these slices must vary smoothly, so if it's increasing it must continue to increase at the same rate, same for if it's straight or decreasing.

The trick here is to balance it, so that that you don't get abrupt changes in area, and that can be achieved by positioning things right and adding area on the right spots.

The green line is the area, so that you can see what is going on, the yellow line is how smooth the area is, and you want that one as close to zero as possible.

Edited May 9, 2015 by tetryds

[atomicfury]

Feel like a noob asking this, but what exactly is area ruling? (I'm assuming it's to do with wing area vs. lift at different speed regions, but is there an actual description somewhere?)

I had that exact same question and found this: http://en.wikipedia.org/wiki/Area_rule

Basically keep the way cross-sectional area changes smooth across your plane design.

[Dnoe]

I guess we need to go for swept wings.

my first nuFAR design

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Quite fast...

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Thanks ferram for the awesome mod /!\

[Mipe]

Okay, now that I took the nuFAR for a spin, starting a new career specifically for this... A couple observations:

a) The first command pod has a rather wild yellow curve. If you add that "Flea" booster to it, it gets even wilder, touching VAB walls on both sides.

The first launch I do is always with pod, 2x goo canisters, parachude and "Flea" booster set to low fuel and thrust for 10 sec "hover" above launchpad, so I can collect low altitude flight data as well. Well, turns out the parachute can't save you there once the "Flea" is burnt out and you drop from 50-100m altitude... I've lost Jeb to this.

c) When I toggle debug vertex drawing on, my somwehat decent rig (i5, Radeon 280X)starts crawling and squeaking for mercy. Guess I better leave that thing toggled off.

[ferram4]

@Azimech: If the body is closed, FAR will treat it as a closed shape. If not, it'll treat it as hollow.

No, building airfoils doesn't work, and the wing code is still legacy code.

@Wanderfound: I'm not nerfing the engine parameters because thrust does not need nerfs. Instead, engines need code for catastrophic failures from heat and overspeed, which Squad never bothered to implement.

@UnanimousCoward: For one, I recall RoverDude saying something about pulling FAR support for all his stuff once 1.0 hit because it wasn't necessary anymore. For two, if the CoL isn't a dot and is instead a vector, it means that FAR is not functioning properly, as FAR removes the vector from the CoL because it is confusing; in any case, something is very wrong there.

@Ravien: I can look into that, but those values should be saved whenever changing from the Space Center scene to another seen. If you made a change and then ALT-F4'd, then they won't take.

@Iasus: Not a bug. You have a giant rocket and tiny fins, of course the rocket is going to have a greater effect on the CoL than the fins.

@JohnFX: Sounds like stupid_chris needs to send an event when he updates chute sizes. Maybe he already is, but is doing it at the wrong time?

@prog: Yep, work perfectly fine.

@cttw: Need reproduction steps that include a perfectly non-lifting vehicle engaging in an aerobrake. If not, I'm assuming that's just body lift raising your apoapsis.

@Mipe: Yes, blunt objects have poor transonic characteristics. This is expected, and the little pod + flea is a blunt as hell rocket.

[blu3wolf]

Okay, now that I took the nuFAR for a spin, starting a new career specifically for this... A couple observations:

a) The first command pod has a rather wild yellow curve. If you add that "Flea" booster to it, it gets even wilder, touching VAB walls on both sides.

The first launch I do is always with pod, 2x goo canisters, parachude and "Flea" booster set to low fuel and thrust for 10 sec "hover" above launchpad, so I can collect low altitude flight data as well. Well, turns out the parachute can't save you there once the "Flea" is burnt out and you drop from 50-100m altitude... I've lost Jeb to this.

c) When I toggle debug vertex drawing on, my somwehat decent rig (i5, Radeon 280X)starts crawling and squeaking for mercy. Guess I better leave that thing toggled off.

It should be clarified that parachutes have a safe operation envelope. Rare (and expensive) is the real life parachutes which are 'zero-zero' chutes that work down to 0 altitude, 0 airspeed.

You need to have more altitude when you pop that chute. Try it from a kilometer.

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@cttw: Need reproduction steps that include a perfectly non-lifting vehicle engaging in an aerobrake. If not, I'm assuming that's just body lift raising your apoapsis.

Im not the expert on this topic around here... but shouldnt atmospheric drag cause a net reduction in orbital energy?

body lift is going to put either a radial or normal force on the vehicle... dont you need a prograde force to raise apoapsis?

By all means, someone correct me if Im wrong, Im intrigued here.

[ferram4]

Yes, it must reduce energy. However, removing body lift turns it from requiring a "how much energy was removed" calculation involving Ap and Pe to a simple, "did Ap lower? Then it's fine."

[Hodo]

@Ferram4

What exactly is the Critical Mach Number? Is that the speed at which the airflow over the wings goes supersonic?

And what is considered a good number for say a high performance fighter vs a Concord type aircraft?

[tetryds]

@Ferram4

What exactly is the Critical Mach Number? Is that the speed at which the airflow over the wings goes supersonic?

And what is considered a good number for say a high performance fighter vs a Concord type aircraft?

Yes and no, it's the mach number where the airflow (usually) above the wing's speed is Mach1, not higher.

A good value depends on the total area, but a decent wave drag area for a transonic fighter on KSP is usually 0.75m² or less.

[Dinokin]

@Ferram4

What exactly is the Critical Mach Number? Is that the speed at which the airflow over the wings goes supersonic?

And what is considered a good number for say a high performance fighter vs a Concord type aircraft?

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

[taniwha]

blu3wolf: You can raise you Ap (within limits) while lowering your orbital energy... by lowering your Pe even further. It is the semi-major axis that matters when it comes to orbital energy:

(energy is per kg, thus no m term)

E_p = -μ/r

E_k = v²/2

E_t = E_k + E_p (always negative for closed orbits)

a pile of math later (pm me if you want details):

a = -μ/(2E_t) and e² = 1 + 2E_th²/μ²

where a is the semi-major axis (body radius + (Ap+Pe)/2), e is the eccentricity, and h is the angular momentum |r x v| (ie, h² = (r x v) . (r x v))

(Ap = a(1 + e) - R, Pe = a(1 - e) - R, R is body radius)

Edited May 9, 2015 by taniwha

[Pyromaniacal]

Ahh, looking forward to seeing if that SSTO is functional with nuFAR, or if I should stick to old fashioned shenanigans. Still, I hope it works!

[Gfurst]

With FAR installed, it's virtually impossible to get the CoL low enough on one of RoverDude's sounding rockets to make it stable, and tilted fins seem to impart zero spin to the rocket.

Even adding about 10 of these fins doesn't help. I'd just like to ask if this is reasonable/realistic. If you say it is, then that's fine - I'll play around with the lift on the fins and see if that helps.

Like ferram said, last time I've checked there were no FAR module for them fins, making them useless, strapping on the stock small fin works well.

@ another note.

I've quickly tested nuFAR before the release, it seems drag is bit too low at sub-sonic speeds. It handles great at trans to super sonic speeds, but drag seems still too low.

I've reported this back in 0.25 I think, seems to still apply, for high, non delta wings, the plane still just glides level with engines off, barely loosing speed. In the recent it seems a bit harder however to maintain control a lower speeds.

In my test I was going a bit ~120m/s before loosing control and stalling, thats is way too fast. coming in for a landing on that speed is nearly impossible, specially with the level runway.

So pretty much a plane designed for sub-sonic is going super-sonic way too fast and handling flight very well.

If you so desire, I can run designated test and report back on findings.

[ferram4]

Then here are the tests I want you to do:

Find data on a real life plane. Build a replica of said plane. Test plane in flight, compare Cd values from FAR to stated data. When I have data to work with, then I can fix any actual discrepancies. I can't code feelings.

Last I heard from NathanKell, subsonic drag was too high because he couldn't get a Bonanza up to its rated top speed. This is also consistent with my findings given that I've tended to allow slightly higher subsonic drag on planes in order to achieve proper subsonic performance on command pods.

[jrandom]

When I have data to work with, then I can fix any actual discrepancies. I can't code feelings.

This is one of the greatest quotes ever.

[eddiew]

Streamlined you say? Swept wings? Smooth curves?

All I see is a need for poowwweeeeerrrrrr!

(Honestly I'm amazed this flew. Only minor tweaks to a nuStock plane required. It was oddly easier to land than to take up, it behaves really well when all the fuel is spent.)

[Mipe]

Huh. I'm trying to cobble together a low tech plane (up to Aviation, the bare minimum), but no matter what I do, it keeps veering to the right. In flight, there's those yellow arrows pointing to the right. I'm at a loss as of to what could cause this, since the plane is perfectly symmetric in every aspect. I don't see much sense in providing a screenshot, since I've redone the plane like ten times now and the issue persists.

Any ideas?

Edit: eh, figured it out, I'm an idiot... I placed mystery goo canister inside storage bay off-center to the right, which shifted the CoM a little bit to the right. I was eyeballing the placement and it seemed "centered" to me, but it obviously wasn't.

Edit2: what the hell, after placing the goo canister into strict center, the plane still veers to the right! I'm totally lost now.

Edited May 9, 2015 by Mipe

[Wanderfound]

Huh. I'm trying to cobble together a low tech plane (up to Aviation, the bare minimum), but no matter what I do, it keeps veering to the right. In flight, there's those yellow arrows pointing to the right. I'm at a loss as of to what could cause this, since the plane is perfectly symmetric in every aspect. I don't see much sense in providing a screenshot, since I've redone the plane like ten times now and the issue persists.

Any ideas?

First suspect: asymmetric thrust if it's multi-engine. Second suspect: a broken fuel hose causing asymmetric fuel use. Third suspect: broken strut causing asymmetric flexing. Fourth suspect: control surfaces placed with radial instead of mirror symmetry, causing all sorts of weirdness.

But, really, we do need the screenshots, if only to rule out what isn't causing it.

[MiltiTrace]

Finally! Thanks Ferram!)

[taniel0401]

It might be a bug... but the action groups assigned to control surfaces don't seem to be working

[Mipe]

First suspect: asymmetric thrust if it's multi-engine. Second suspect: a broken fuel hose causing asymmetric fuel use. Third suspect: broken strut causing asymmetric flexing. Fourth suspect: control surfaces placed with radial instead of mirror symmetry, causing all sorts of weirdness.

But, really, we do need the screenshots, if only to rule out what isn't causing it.

It's a tad bit unbalanced, keeps lifting the nose and stalls easily... also keeps veering to the right a bit, as you can see by those yellow arrows.

I know duck all about plane building, I just wanted a little something I could do biome hopping with.

[ferram4]

@Mipe: Yellow arrows are moment arrows, which signify the direction a torque rotates around. Odds are the cause is just the vehicle flexing, like always happens. Unless it's on the runway, in which case, that's because landing gear.

Edit: with picture, the problem is that you have no yaw authority because your plane has no length to put the vertical tail behind the CoM.

@taniel0401: Need reproduction steps, they work perfectly fine for me so long as you configure the control surfaces.

[Hodo]

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

It's a tad bit unbalanced, keeps lifting the nose and stalls easily... also keeps veering to the right a bit, as you can see by those yellow arrows.

I know duck all about plane building, I just wanted a little something I could do biome hopping with.

I can give you the simple answer.

None of your YAW control surfaces are far enough away from the CoM of the craft to have ANY affect on it one way or another.

If you made the aircraft longer and placed your vertical stabilizer further back away from your CoM you would have a far more stable craft when it comes to your yaw issue.