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

[undercoveryankee]

Sorry, no not exactly. This is what i meant.

http://i.imgur.com/wbv2LIr.jpg

To explain: the "spoiler" setting on a control surface tries to deflect the control surface upward to kill lift and push the aircraft down onto the runway. Generating drag is only a side effect.

If a control surface is exactly vertical, it's a toss-up which direction FAR will decide is "up," and there's a good chance that two vertical spoilers in basically the same place will decide to go the same direction. Rotating each surface by one notch so it has an unambiguous "up" direction allows you to control what it does and trick it into serving a purpose it wasn't meant to do.

- - - Updated - - -

I checked, and it was off. Just to be sure, I toggled it, and the isShielded remains.

-Duxwing

If you're still getting the isShielded indicator with FAR set not to display shielding, that's a problem. FAR is either failing to write its settings file or failing to honor the setting. Would anyone who's seeing this mind sharing a Unity log of a KSP session where you toggled the setting?

[Dermeister]

To explain: the "spoiler" setting on a control surface tries to deflect the control surface upward to kill lift and push the aircraft down onto the runway. Generating drag is only a side effect.

If a control surface is exactly vertical, it's a toss-up which direction FAR will decide is "up," and there's a good chance that two vertical spoilers in basically the same place will decide to go the same direction. Rotating each surface by one notch so it has an unambiguous "up" direction allows you to control what it does and trick it into serving a purpose it wasn't meant to do.

- - - Updated - - -

If you're still getting the isShielded indicator with FAR set not to display shielding, that's a problem. FAR is either failing to write its settings file or failing to honor the setting. Would anyone who's seeing this mind sharing a Unity log of a KSP session where you toggled the setting?

NIceeeeeeee now I see what you mean I shall try this

[cantab]

So, I've been looking into flying wings. According to Wikipedia, "Sweeping the wing leading edge back, either as a swept wing or delta wing, and reducing the angle of incidence of the outer wing section allows the outer wing to act like a conventional tailplane stabiliser." But I've found that changing the angle of incidence isn't needed - just sweeping the wing enough will obtain longitudinal stability. For example, this infinite-fuel-powered flying wing:

Static stability: https://flic.kr/p/qMrjjd

Derivs: https://flic.kr/p/qMxpKv

Is FAR simply assuming that change in incidence (ie "washout"), is Wikipedia wrong, or is something else going on?

(And yes, I know my flying wing has yaw stability/control issues. I'm just looking at pitch first.)

Edited February 6, 2015 by cantab

[bartekkru99]

My figter doesn't seem to roll at higher AoAs! HALPH MY!!!11111111111111

Edit: Looks like my vertical stabilisers stall when doing it...

Edited February 6, 2015 by bartekkru99

[thaflya]

I copy my own post the second time cause it got lost amd i still didnt get a proper answer.

One question, i tested it several times and it seems that it does not matter for drag if air intakes are open or closed while using FAR. Is this intended or a bug?

I tested it with the FAR airstats window opened, and the values for BC and Cd didnt changed at all (I guess Reference Area didnt changed too). The speed or acceleration didnt changed too.

I tested it again, and i didnt recognize any influence on speed, drag or acceleration when intakes are closed or open.

[bartekkru99]

I copy my own post the second time cause it got lost amd i still didnt get a proper answer.

One question, i tested it several times and it seems that it does not matter for drag if air intakes are open or closed while using FAR. Is this intended or a bug?

I tested it with the FAR airstats window opened, and the values for BC and Cd didnt changed at all (I guess Reference Area didnt changed too). The speed or acceleration didnt changed too.

I tested it again, and i didnt recognize any influence on speed, drag or acceleration when intakes are closed or open.

Propably in real life it would also not matter... But i don't know is it intended...

[JackGruff]

https://twitter.com/KerbalSpaceP/status/563862958942334976

Hopefully this implies ferram won't have much of a problem with FAR working in 1.0.

[ferram4]

@cantab: So it is stable and flies with positive lift without any pitch-up input at all, then? Because if it needs pitch up input, then the effect of deflecting the elevons is the same as the lowered angle of incidence on the outer span.

@bartekkru99: Yes, stalled ailerons don't roll very well. Common problem, don't stall them.

@thaflya: Intended behavior; actually, intakes should make more drag when closed, simply because the air that was passing through them now needs to pass around them. So not quite intended behavior, since it's too beneficial.

[bartekkru99]

@bartekkru99: Yes, stalled ailerons don't roll very well. Common problem, don't stall them.

Only vertical stabilisers were stalled, ailerons weren't

[cantab]

@cantab: So it is stable and flies with positive lift without any pitch-up input at all, then? Because if it needs pitch up input, then the effect of deflecting the elevons is the same as the lowered angle of incidence on the outer span.

Fair point. I made a variant though, adding a reaction wheel and removing the elevons and increasing the sweep of the wings by 10 degrees to get the CoL just behind the CoM. That showed one red number in the longitudinal stability (bottom left), but was stable and controllable in flight just as the one with elevons was.

[HoneyFox]

This is a fly-wing aircraft i designed several days earlier.

With brake-rudders and modified FAR Yaw stability enhancer (actually i changed that from a pure Yaw Damper to a PD controller with an AoA-based Roll-to-Yaw command converter which works as ARI IMO), it can be flown with no big trouble unless I pull the AoA too much and stall it.

Edited February 8, 2015 by HoneyFox

[blowfish]

Has anyone had any success creating spaceplanes that manage to keep Cd low at high mach numbers (say <0.1 at mach 3-4)? Large amounts of high mach drag seem to be keeping me from putting reasonably-sized spaceplanes into space.

On a possibly unrelated note, I seem to occasionally be experiencing aero failures on shielded parts. If the issue persists I'll provide more info.

[kcs123]

Has anyone had any success creating spaceplanes that manage to keep Cd low at high mach numbers (say <0.1 at mach 3-4)? Large amounts of high mach drag seem to be keeping me from putting reasonably-sized spaceplanes into space.

On a possibly unrelated note, I seem to occasionally be experiencing aero failures on shielded parts. If the issue persists I'll provide more info.

You need to climb above 18km to be able to reach mach 3. For speeds above mach 3 up to 4 you need to climb at 23km. For mach 5 and higher you will need 27 km or more.

Just expirience from test flights. Following those rules I'm able to put unreasonably sized craft in space

Drag is 0.073 for 3.23 mach @19km, no wories, large wings don't produce so much drag as you may think. Of course, drag is increased as you accelerate, so when you do, you need to climb higher and have stable plane on those altitudes.

Drag is 0.086 for 3.57 mach @22km even on this large plane

[blowfish]

I should mention that I'm using AJE, so the usual trick of minimizing dynamic pressure by climbing steeply doesn't work - I need to stay close to the high dynamic pressure boundary to maintain thrust.

[kcs123]

I should mention that I'm using AJE, so the usual trick of minimizing dynamic pressure by climbing steeply doesn't work - I need to stay close to the high dynamic pressure boundary to maintain thrust.

I didn't have time to rebuild my planes for AJE in V0.90, probably next step on to do list. Check my test flight gallery, I didn't used steep ascent path to reach high altitude.

You need to find sweet spot for accelerating and climbing rate. In V0.25 my only trouble with AJE is that I have to put more fuel in plane to compensate afterburner effect.

Payload is also slightly lowered, but fundamental principles are the same. Difference in AJE is that you need to go faster to be able to go faster.

Like I said, you need to find sweet spot for altitude, speed and amount of air intakes that will provide enough air without too much drag.

[m1sz]

Hi guys!, I'm having a little problem with drags in one of my planes. Is there any way to check what parts are generating the drag, apart from the aero viz? I need to know some numbers, as I'm getting massive drag without any obvious source.

Here are two pictures of two planes. The first one, we can see a Cd=0.257 at his terminal speed, about 230m/s, which is very slow considering the TWR of 2. Also, the Cl=0.129.

On the second picture, the Cd=0.017 and the Cl=0.004, at the terminal speed, about 1000m/s, with a little bit more TWR (RAM engine so it's about 2 at 230m/s).

I'm not sure if it's a compatibility issue with OPT mod, or if this would be better posted there.

And here's an album of what the aero viz shows when flying the "bad" plane:

Javascript is disabled. View full album

[kcs123]

Hi guys!, I'm having a little problem with drags in one of my planes. Is there any way to check what parts are generating the drag, apart from the aero viz? I need to know some numbers, as I'm getting massive drag without any obvious source.

Here are two pictures of two planes. The first one, we can see a Cd=0.257 at his terminal speed, about 230m/s, which is very slow considering the TWR of 2. Also, the Cl=0.129.

On the second picture, the Cd=0.017 and the Cl=0.004, at the terminal speed, about 1000m/s, with a little bit more TWR (RAM engine so it's about 2 at 230m/s).

I'm not sure if it's a compatibility issue with OPT mod, or if this would be better posted there.

http://i.imgur.com/3Im3EGx.jpg

http://i.imgur.com/A3k7dI7.jpg

And here's an album of what the aero viz shows when flying the "bad" plane:

http://imgur.com/a/0S9cf

While you are at Kerbal space center open FAR, there is debug option to provide more info on surfaces.

Now, when you are in flight when you right click on craft part you will see current lift and drag for that part.

Quick look at pictures, seems that you have placed neutral pitching moment too close to zero AoA. Because of it, your plane provides little to none lift most of times.

Check links in my signature for more info if you are confused what I'm talking about.

[m1sz]

While you are at Kerbal space center open FAR, there is debug option to provide more info on surfaces.

Now, when you are in flight when you right click on craft part you will see current lift and drag for that part.

Quick look at pictures, seems that you have placed neutral pitching moment too close to zero AoA. Because of it, your plane provides little to none lift most of times.

Check links in my signature for more info if you are confused what I'm talking about.

I am a little bit confused about that "pitching moment too close to zero AoA" thing. I know what a momentum is, and also what AoA is, but I don't get what that means. I'll check your signature links and see what I can do. Also, I'll check that debug options you said about FAR!, thanks !!

[cantab]

With brake-rudders and modified FAR Yaw stability enhancer (actually i changed that from a pure Yaw Damper to a PD controller with an AoA-based Roll-to-Yaw command converter which works as ARI IMO), it can be flown with no big trouble unless I pull the AoA too much and stall it.

Nice design. Were you able to link the yaw control to A/D correctly, or did you have to work around it somehow?

[m1sz]

While you are at Kerbal space center open FAR, there is debug option to provide more info on surfaces.

Now, when you are in flight when you right click on craft part you will see current lift and drag for that part.

Quick look at pictures, seems that you have placed neutral pitching moment too close to zero AoA. Because of it, your plane provides little to none lift most of times.

Check links in my signature for more info if you are confused what I'm talking about.

Ok I read everything you put in your guide, and checked my graphs. They look wonderful, plane flies very nice, all derivatives are good, is stable at low and high speeds..., The thing is, the engine mount is generating as much drag as the cockpit. That doesn't seem very realistic, might be a problem OPT and FAR. What do you guys think?, if it looks like that, I'll post it in the OPT forum thread. Thanks a lot!

Here are the screens in an album:

Javascript is disabled. View full album

[kcs123]

Ok I read everything you put in your guide, and checked my graphs. They look wonderful, plane flies very nice, all derivatives are good, is stable at low and high speeds..., The thing is, the engine mount is generating as much drag as the cockpit. That doesn't seem very realistic, might be a problem OPT and FAR. What do you guys think?, if it looks like that, I'll post it in the OPT forum thread. Thanks a lot!

Here are the screens in an album:

http://imgur.com/a/En8XD

Just as I suspected, you plane will always have low L/D ratio, only when you activly pitching up, you will have L/D ratio over "1". Not entirely bad thing, depends what you expect from your plane, for small fighter a like agile craft it is OK, although not very effective.

Now, for your problem. It is pretty much "normal" for FAR to calculate drag at engine mount like in picture. Don't know exactly how much of realism FAR caluclates, but it is not entierly unrealistic. When any body travels fast in fluid it leaves area with low preasure in rear area. That low preasure creates forces that pulling back that body - that is why it is called drag.

Not only surfaces in front, but surface area at back is equaly important when comes to drag. You will find more info and better explanation on wikipedia for this than I am able to provide.

Perhaps ferram can give more insight what is calculated and what not in FAR.

Please note that you are near mach 1 at only 1.3 km, almost sea level flight. Aerodynamic forces at that altitudes are realy high. Nothing strange about it.

EDIT:

Second look at pictures, it is J to Mk2 adapter from OPT mod. FAR calculates lift/drag based on frontal cross section of mesh over lenghth of part.

Engine mounts adds some more frontal cross section area than standard MK2 to Mk1 adapter. That is another reason why you have slightly more drag than usual MK2 adapter.

Edited February 8, 2015 by kcs123

[tetryds]

@m1sz: try to activate a decoupler before taking off, if nothing changes that is expected behaviour/issue with mod parts.

[cantab]

Does anyone have a FAR config for these grid fins? forum.kerbalspaceprogram.com/threads/66502-Kerbonov-Kn-2-Cockpit-Module Can FAR even work with grid fins, or can it only work with aerodynamic surfaces all aligned on the same plane?

Related to this old comment, what will happen if I try and use the grid fins - or any control surface really - without a FAR configuration and with FAR installed? Will they work as stock control surfaces with all the attendant AoA/infiniglide issues? Will they do nothing at all? Something else?

[blowfish]

I didn't have time to rebuild my planes for AJE in V0.90, probably next step on to do list. Check my test flight gallery, I didn't used steep ascent path to reach high altitude.

You need to find sweet spot for accelerating and climbing rate. In V0.25 my only trouble with AJE is that I have to put more fuel in plane to compensate afterburner effect.

Payload is also slightly lowered, but fundamental principles are the same. Difference in AJE is that you need to go faster to be able to go faster.

Like I said, you need to find sweet spot for altitude, speed and amount of air intakes that will provide enough air without too much drag.

So it looks like I may have discovered a bug in AJE which was capping the thrust of the Sabre M much lower than it should be.

Still though, it's worth asking. Reaction Engines Limited has a simulation of the Skylon's ascent trajectory (xls file), which suggests that the Skylon manages to keep Cd low even at Mach 5 with very high dynamic pressure. Are they not accounting for skin drag, or is there something fundamentally different about the assumptions they're making vs the assumptions that FAR is making?

Also it looks like the Cd value given in the FAR editor doesn't always match what's given in flight under the same conditions. At high mach numbers, the in-flight Cd value is much higher than what's given in the editor. Does the editor analysis not account for skin drag?

Edited February 9, 2015 by blowfish

[m1sz]

@m1sz: try to activate a decoupler before taking off, if nothing changes that is expected behaviour/issue with mod parts.

I tried this, but nothing changed ^^