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

[capi3101]

Yeah - red numbers are bad as a rule, and you've got a pair of particularly bad ones. Mw in the red means your plane has nose-up tendencies, and red Nß means you've got yaw instabilities for the speed indicated (Mach 0.35 in this case). Translates to A) your aerodynamic center is too close to the center of mass (might even be ahead of the center of mass), and B) you need more vertical stabilizer. Try moving your main wings further back, move some weight forward, and building up your fin a bit.

If you'd like something a bit more visual about what those numbers actually mean, try this page here. If nothing else it may teach you how to use the dynamic simulation graphs.

Edited September 13, 2016 by capi3101

[UltraJohn]

11 minutes ago, capi3101 said:

Yeah - red numbers are bad as a rule, and you've got a pair of particularly bad ones. Mw in the red means your plane has nose-up tendencies, and red Nß means you've got yaw instabilities for the speed indicated (Mach 0.35 in this case). Translates to A) your aerodynamic center is too close to the center of mass (might even be ahead of the center of mass), and B) you need more vertical stabilizer. Try moving your main wings further back, move some weight forward, and building up your fin a bit.

If you'd like something a bit more visual about what those numbers actually mean, try this page here. If nothing else it may teach you how to use the dynamic simulation graphs.

Ah thanks, but I don't understand what you mean by aerodynamic center? Does it mean that my CoL is too close to CoM? And by vertical stabilizer, I assume you mean i need more/bigger vertical fins than just the 2 at the back?

[softweir]

45 minutes ago, John007qwe said:

Ah thanks, but I don't understand what you mean by aerodynamic center? Does it mean that my CoL is too close to CoM? And by vertical stabilizer, I assume you mean i need more/bigger vertical fins than just the 2 at the back?

FAR removes the CoL and replaces it with an aerodynamic centre, which is similar but displayed without the meaningless arrow. (It also calculates its position differently to the stock CoL.) But yes, he means they are too close. And yes, the vertical fins are vertical stabilisers and you need more.

Happy flying!

[UltraJohn]

Thank you for the help!

[softweir]

You're very welcome!

[raxo2222]

I wonder if there could be some sort of calculator, that could pick best pith setting, altitude and speed for our aircraft, so we can know how high, how far and how long it could possibly fly.

 

[nablabla]

hi, does anybody have an idea where this weired behaviour can originate from?

http://imgur.com/a/a06wx

I have a very strong lift sideways on all parts. Or is it caused by the procedural parts?

It also happens after restart

I basically installed Realism Overhaul / RP-0, not much else.

 

Best regards

[blowfish]

@nablabla Does it happen if you're perfectly prograde?  Does the magnitude scale with how much AoA you have?  It's expected to have some lift force if you're not perfectly prograde.

[nablabla]

okay, sorry, of course you cannot see all of that form the picture >_<

- I am lifting of 0° straigt upwards

- the lift force seems to be relative to (wind) speed

- and orthogonal to the flight direction

- also if I am flying perfectly prograde

- it is insanely high, it will disintegrate my vessel

- drag (red arrows) seems to be correct

- the winglets seem not to be affected

I am not shure whether or not it only affects these procedural tanks, there is a probe core in the upper part of the rocket, I am not shure if the lift indicators belong to them or not

 

Edit  +And it is not the first rocket I built in this install, and did not change anything

 

 

Edited September 14, 2016 by nablabla

[blowfish]

You don't appear to be perfectly prograde in either of your screenshots where the navball is visible.  Could you open the FAR GUI and check your AoA and sideslip?  Even as small deviation will produce some lift force.

[nablabla]

yeah well it is impossible to hold to prograde, the force gets so strong

[Nansuchao]

1 hour ago, nablabla said:

okay, sorry, of course you cannot see all of that form the picture >_<

- I am lifting of 0° straigt upwards

- the lift force seems to be relative to (wind) speed

- and orthogonal to the flight direction

- also if I am flying perfectly prograde

- it is insanely high, it will disintegrate my vessel

- drag (red arrows) seems to be correct

- the winglets seem not to be affected

I am not shure whether or not it only affects these procedural tanks, there is a probe core in the upper part of the rocket, I am not shure if the lift indicators belong to them or not

 

Edit  +And it is not the first rocket I built in this install, and did not change anything

 

 

I noticed from the KER window and from your speed that your TWR is too high. This doesn't help maintaining stability in low atmosphere, cause every command you send to the rocket is too strong to maintain stability.

[ferram4]

@nablabla: Check in the VAB if the cross-section graph is properly aligned with the vehicle.  If it is, then I concur with everyone else that it's a general instability / too much TWR combination.  If it isn't, I need the craft file.

[cantab]

10 hours ago, raxo2222 said:

I wonder if there could be some sort of calculator, that could pick best pith setting, altitude and speed for our aircraft, so we can know how high, how far and how long it could possibly fly.

 

FAR offers quite a lot of in flight data, which should be enough for what you want.

http://www.eaa1000.av.org/technicl/perfspds/perfspds.htm#How_Do_I

This appears to assume a constant engine efficiency, which is not always exactly the case in KSP but it's often pretty close; keep an eye on your engine Isp.

Basically to maximise range on your fuel, find the angle of attack that gives maximum L/D ratio - which you can do in the SPH analysis tools before takeoff - and then in flight find the engine power needed to maintain level flight at that AoA.

[SpannerMonkey(smce)]

On 23/08/2016 at 1:03 PM, PTGFlyer said:

So this mod doesn't work with FAR.

 

And they know that. Do you guys know if that problem's on your end?

As Ferram says , it's not 100% clear what is actually going on, the most likely culprit is the connection between the chute and the Kerbal, as it isn't( wasn't) rigid as in 100% on or off, and not a connection the game likes.  The proof of this is that the chutes work perfectly well in a FAR environment when not attached to a kerbal, theres a post with images and FAR readout to prove.  As we're still in the 1.2 confusion period, in which anything can happen, we'll have to wait and see if it's fixed or alleviated at least. As an aside, the chutes are not the only part module that goes nuts when you attach it to a Kerbal, I've tried most and most end  badly.

[nablabla]

30t

atmo twr is 2.26

I have a little experience with RO rockets, its definitively wrong behaviour

my craft file: https://uploadfiles.io/f6532

(my other rocket is not affected)

Edited September 14, 2016 by nablabla

[capi3101]

23 minutes ago, nablabla said:

30t

atmo twr is 2.26

!!!!!!!!!!

Yeah - if it's 2.26 at launch, your TWR is too high. Ideally you want it somewhere around 1.3 on the pad, tops. Have you tried throttling back to see if the problem still exists then?

[nablabla]

yes i reduced it. But is is not getting that fast when the problem happens. Eventually this lift-force is taking it apart.

okay, I guess my craft file was corrupt. I just rebuilt the craft, with about exactly the same numbers and it kicks ass.

Edited September 14, 2016 by nablabla

[nablabla]

about the same craft with no problems: https://ufile.io/c0109

[raxo2222]

1 hour ago, cantab said:

FAR offers quite a lot of in flight data, which should be enough for what you want.

http://www.eaa1000.av.org/technicl/perfspds/perfspds.htm#How_Do_I

This appears to assume a constant engine efficiency, which is not always exactly the case in KSP but it's often pretty close; keep an eye on your engine Isp.

Basically to maximise range on your fuel, find the angle of attack that gives maximum L/D ratio - which you can do in the SPH analysis tools before takeoff - and then in flight find the engine power needed to maintain level flight at that AoA.

Hmmm so also we can get optimal altitude of flight - get autopilot and pick pith equal to optimal AOA. It will fly higher and higher until AOA equalizes with pith.

With AJE there are 3 engines with constant ISP: slower turbojet engine at 12000 (for subsonic aircraft), white-ish turbojet at 4000, that can go very fast too - for hypersonic aircraft.

And there is RAPIER with even higher max speed.

With RAPIER I could fly at 6 mach.

 

Edited September 14, 2016 by raxo2222

[blowfish]

@raxo2222 Uhh, nothing in AJE has constant I_sp though I think the RAPIER varies less than traditional jets.

[ferram4]

@nablabla: Standard RO install?  What part packs?

[nablabla]

3 minutes ago, ferram4 said:

@nablabla: Standard RO install?  What part packs?

RP-0, I think you know that? No other part mods

Spoiler

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}

 

 

[ferram4]

Well, I just tried, and I cannot see any issues.  It flies straight unless it goes far off prograde.  Some funky voxelization related to the second stage engine, but I don't think that's the cause here.  I'll still have to look at that though.

[raxo2222]

9 hours ago, blowfish said:

@raxo2222 Uhh, nothing in AJE has constant I_sp though I think the RAPIER varies less than traditional jets.

Weird then my AJE didn't install properly, because some of jet engines have constant ISP.