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On 19.3.2016 at 9:53 AM, ss8913 said:

There's a lot of people that understand all of the actual numbers and what they mean; I'm in the process of learning this myself.  However that's the *science* of it.  What you really need to know is the *engineering* perspective of it.  Here's the quick guide to FAR plane design:

1. Go into the FAR menu in SPH and open the static analysis.  Click 'run analysis' and make sure there are no red numbers at 0.35 and 1.35 mach.

2. Lower the 0.35 until red numbers appear.  Never go below this mach # when flying.  (make sure to have the FAR window open in flight - also set your airspeed indication to indicated knots EAS.   This is what real aircraft use and is critical to knowing how much lift you're getting.  Your surface speed is pretty much irrelevant when you want to know your V speeds and stall speeds).

3. Now open the transonic design.  click the middle radio button for the yellow line.  The flatter it is the less mach buffeting you will get in the transonic zone (0.80 to 1.20 mach), and the less likely you are to have serious aerodynamic issues at high speed.

4. Are you using adjustable landing gear?  If not get it immediately.  This part isn't really FAR related but if you can't get the plane off the runway, FAR doesn't matter.  Use adjustable landing gear and never touch stock gear again.  ALG gives you an alignment indicator.  Make sure your wheels are not aligned to point away from the craft centerline.  If they are, use the rotation tool to fix that - about 1 degree of "toe in" towards the centerline will make the craft stable on the runway.  This does not apply to the nose gear.  Leave that alone as far as rotational alignment, but make sure it's shorter than the mains - you want 1 to 5 degrees of pitch down when sitting on the runway.  Set your spring and dampers to almost max on all gear.  Set main gear brake torque to between 60-100 depending on craft weight, and set the brake torque on the nose wheel to half of what you've set on the mains.  Turn shielding on for all gear.  Now FAR is relevant because you won't crash on takeoff or on your landing rollout :)

5. Use the FAR yaw stability helper when flying in atmosphere, even if you're using an autopilot.  This is like the yaw damper on real jets.  It helps.

6. Mechjeb even with the FAR helper module is not that great.  Kramax autopilot is a million times better than mechjeb for flying within atmosphere.  It is however completely useless in space, so I use both MJ2 and Kramax.

7. Kramax likes triangle shaped planes.  It can't follow a glideslope worth a **** if you have a plane with horizontal stabilizers and wings placed like on a commercial airliner.  Especially if you 1. have flaps and 2. use the flaps.  So you may need to control pitch yourself unless you have a triangle shaped plane (like the US space shuttle, with no independent elevators).


Follow the above tips and you too can have a fun and stable SSTO spaceplane that can land safely back on the KSC runway.  I also recommend KSP Interstellar Extended, because who *doesn't* like antimatter-powered thermonuclear hybrid turbojet/rocket engines giving you 80k dV in a Mark3 spaceplane?  I know I do :)

Here's a picture of one of my most successful designs.  This shape works well, and at about 25% fuel has a stall speed well under 200kts EAS, making it easy to land.  It's also got ATILLA arcjet VTOL engines with enough thrust to do a VTOL landing *anywhere*, even Eve.  The engines are also from KSPIE.  If you make a spaceplane using this layout (modify to suit), you'll have good results aerodynamically.

1. I've run into problems at different speeds in the past. One layout for my planes would reliably cause significantly lower stability at exactly 0.9M (+-0.05M or so). So I calculate at stall-speed (see 2.) and just above, 0.9M, and in 0.1 steps to about 1.5M, and/or whatever top speed it's designed for.

2. That's stall speed - don't check when red numbers appear, but check when the AoA is exactly 0 (or >0 or something, no longer XX.whatever AoA). If red numbers appear earlier check which numbers are red - some make the plane unflyable, some hard to fly, some don't seem to do much at all. Having the plane get unstable just below intendet landing speed can ruin your day pretty good, so avoid that.

4. You can set rotation mode to absolute (some key like "F", I forgot), and with angle snap can be used to help aligning. Also, nose down when on the runway depends on how the plane is intendet to take off. I usually aim for just barely above 0 AoA (yes, for spaceplanes as well). Also test if you can use full breaks at the highest speed on the runway (may cause significant craft wobble, although I haven't tried the 1° toe-in yet). And I can usually set nose gear break torque a good bit higher than half the main gear's torque.

5. Needs to be set-up properly though. Ran into problems with it in the past. Works great for artificial stability though.

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The Beluga.

 

Its 800 tons and it flies. Amazingly. Landing however is impossibly difficult. Apprach and landing speeds are too high and I cannot bring the plane to a stop after touchdown. I need to be able to fly at slower speeds here. So flaps and spoilers I imagine are the key. The ones I have now just either rip off the plane or just act more as airbrakes then anything. So as far as placement and size goes whats a good place to start? I notice in real pictures most flaps are placed on the rear of the wings. I cannot do this because If I put flaps so far behind my CoM the craft just dive bombs. So I need to put them onto the CoM or atleast I think.

The tail pitch control is also an issue. That is an all-moving B9proc part. I cannot make a regular aileron large enough. That thing works, but it flexes hard which I cant imagine helps with controllability. So if anyone knows any larger ( like really large ) ailerons I can get that'd help. Other then that... is there anything here that is just a big red flag? Again it flies, but I feel it can be so much better. I'm sure that if I opened up kerbal constructions, extended the runway ( probably going to do this anyway ) and sat here for an hour I could land it. But I feel like I could make this easier on myself someone. Any tips?

 

 

 

 

Edited by Motokid600
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9 hours ago, Motokid600 said:

I notice in real pictures most flaps are placed on the rear of the wings. I cannot do this because If I put flaps so far behind my CoM the craft just dive bombs. So I need to put them onto the CoM or atleast I think.

Real flaps also cause pitch movement unless they've been built to be very balanced in that regard (like the Focke-Wulf Fw 190). The way you seem to have placed them, they are placed like airbrakes often are (like on the Junkers Ju 87 for example). You could try to counter that by adding canards that deflect up when the flaps go down, or stuff like that.

9 hours ago, Motokid600 said:

The tail pitch control is also an issue. That is an all-moving B9proc part. I cannot make a regular aileron large enough. That thing works, but it flexes hard which I cant imagine helps with controllability. So if anyone knows any larger ( like really large ) ailerons I can get that'd help. Other then that... is there anything here that is just a big red flag? Again it flies, but I feel it can be so much better. I'm sure that if I opened up kerbal constructions, extended the runway ( probably going to do this anyway ) and sat here for an hour I could land it. But I feel like I could make this easier on myself someone. Any tips?

B9 Procedural Wings. I still have some "unofficial" B9 PW mod (original is no longer supported I think), and found similar stuff with a quick search.

Edited by FourGreenFields
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2 hours ago, FourGreenFields said:

Real flaps also cause pitch movement unless they've been built to be very balanced in that regard (like the Focke-Wulf Fw 190). The way you seem to have placed them, they are placed like airbrakes often are (like on the Junkers Ju 87 for example). You could try to counter that by adding canards that deflect up when the flaps go down, or stuff like that.

B9 Procedural Wings. I still have some "unofficial" B9 PW mod (original is no longer supported I think), and found similar stuff with a quick search.

Interesting. I'm already using B9Proc wings, but that there can make it so I can build larger wings and ailerons? I just hope the "May conflict with FAR" part isn't an issue.

Other then that is there anything you see here in general that you'd do differently design wise?

Edited by Motokid600
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46 minutes ago, Motokid600 said:

Other then that is there anything you see here in general that you'd do differently design wise?

I wouldn't build as big.

I'd probably also check if lower aspect ratio would reduce hypersonic drag (keep in mind that reference area/wing loading should stay roughly the same). Gear replaced with Adjustable Landing Gear, so I can fully retract it, and further reduce drag (ALG can be pretty big). Less struts (Kerbal Joint Reinforcement might be necessary for that). Would check if artificial yaw stability could reduce hypersonic drag. Possibly recoverable takeoff-boosters, and some kind of bad-ass airbrake for landing (spoilers along the entire span of the wing, landing chutes, or stuff like that).

Difficult to say without the design itself, and tbh I don't think my toaster could even handle that beast.

Edited by FourGreenFields
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Just incase when you mention hypersonic drag. This isn't an ssto orbital craft ( I'm sure it could be ). I just need to to haul a very large amount of fuel from a mining depot in the mountains ( I put down a large airstrip with Kerbal Constructs ) back to the KSC. Its so large because I don't want to have to make multiple trips per mission to fuel my rockets.

"Gear replaced with Adjustable Landing Gear"

The reason I did that with the gear is because I need that wide profile. I need to spread its weight over as many landing wheels as possible. If I used adjustable landing gear I'd have to do the same thing more or less. Need that wide wheel base. 

"Less struts (Kerbal Joint Reinforcement might be necessary for that)"

I am using KJR and it still needs the struts that's how heavy this thing is. 

"Would check if artificial yaw stability could reduce hypersonic drag."

What's artificial yaw? Because this plane will never be hypersonic.

"Possibly recoverable takeoff-boosters, and some kind of bad-ass airbrake for landing (spoilers along the entire span of the wing, landing chutes, or stuff like that)."

Taking off isn't an issue. But for landing I'm going to have to pull out all the stops ( pun intended ). Maybe even some jato rockets :P Thanks for the input I appreciate it.

 

Edited by Motokid600
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13 hours ago, Motokid600 said:

I am using KJR and it still needs the struts that's how heavy this thing is.

And that's exactly why I don't build as big.

 

13 hours ago, Motokid600 said:

What's artificial yaw? Because this plane will never be hypersonic.

FAR yaw-stability assist, tweaked to provide yaw stability, as on my P 21 "Lanner Falcon". Could also build a smaller tail-fin, that doesn't make it stable, and set the rudder to deflect when encountering an AoA.

Drag-reduction is probably not as big when subsonic though.

Edited by FourGreenFields
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I've been meaning to ask this for a while now, and I suppose this would be the place to ask, since it pertains less to FAR and more to designing craft.

Does anyone have some information on the equations and calculations FAR makes? I've tried to look through the github source, but I'm not too familiar with programming, and certain shorthands throw me off a bit. I'd like to know because I'd prefer to design a plane from scratch based on the actual math behind aeronautics, instead of going through a protracted stage of trial-and-error. As such, a post containing the equations Ferram's derived for FAR would be very useful (although I know that with the use of voxelization, certain calculations would be difficult to carry out on paper, but seeing as wing design is half or more of aeronautic engineering, and that FAR uses the voxelized model to find certain parameters, then there must be some equations using these derived parameters).

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  • 2 weeks later...

@Chickenshark: that sort of question is best asked in the actual FAR thread, or even directly to Ferram. This one's generally been about actual craft rather than FAR itself.

Because Tetryds' BAD-T got me building ever odder 40's era craft, I rolled this out:

26145015520_9d20125916_c.jpg
26325470862_73a83e4286_c.jpg
26145015930_a57c1580b1_c.jpg

Which is sort-of a WW2 era Focke-Wolf Ta283 ( which obviously wasn't ever built, or we'd definitely have noticed! ). 40 years after the Wright Bros, and we were working on *that*.

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More early jets. This one kinda happened by accident, I just swapped the Jumo in for the piston engine on an existing craft & noticed it looked quite a bit like a DeHavilland Vampire. It still only looks quite like a DH Vampire but it also has to be an actual combat craft, so it's an evolutionary work.

26480130392_5a215bf5a5_b.jpg
26546344116_dc1fd69e2b_b.jpg

 

Some actual combat, please excuse the sound. Turned labels off to better appreciate the craft which makes opponents somewhat hard to see, but hey, still nice to watch.

https://www.youtube.com/watch?v=StEFChaN6uc

 

Edited by Van Disaster
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@Van Disaster you can fix the cockpit color problem by making the nosecone slightly larger and connecting it to the body right behind it, like this:

qC3LLGz.png

Works wonderfully well!

 

I made this monster: 

N6goQtK.png

I should destroy it for being too good, it's hypermaneuverable, goes supersonic with 5% thrust (maybe less) and all that stuff.

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Hmm, yeah, that's an idea. I'm still getting used to things you can do with voxelFAR even now!

Well, it'd definitely work but maybe not for this particular one - could do with some cockpit detail & now the blasted cannon look even more daft :P

25987807853_3408cf620a_b.jpg

Edited by Van Disaster
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3 hours ago, Van Disaster said:

Hmm, yeah, that's an idea. I'm still getting used to things you can do with voxelFAR even now!

Well, it'd definitely work but maybe not for this particular one - could do with some cockpit detail & now the blasted cannon look even more daft :P

25987807853_3408cf620a_b.jpg

Is it procedural parts for the frame ?

Also why do yo need angle display ?

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On 23/04/2016 at 11:49 PM, RevanCorana said:

Ok any updates on the BD armory challenge by the way ?

Didn't we decide to wait for FAR's new wing system? either way I'd not suggest starting any new contests until 1.1 & mods have settled down.

Does anyone have some secret to making triangular section fuselages? I tried various combinations of B9 PW but everything basically looked worse than just not having it :P

 

 

Edited by Van Disaster
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Mmh? no idea bu dynamic deflection and bdarmory are up to date. What is this new wing system and when is it released approximately and how is it better than b9 wings ?

 

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19 hours ago, RevanCorana said:

Mmh? no idea bu dynamic deflection and bdarmory are up to date. What is this new wing system and when is it released approximately and how is it better than b9 wings ?

 

Ferram is redesigning FAR again to better simulate wings. No ETA been hearing about it for over 6 months now. Has nothing to do with part mods :)

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I thought I'd turn to this thread for some help with a plane I built. I've been using FAR for years and I've run into a problem where my plane is unstable in pitch, wanting to backflip/frontflip as soon as it has any positive/negative AoA after taking off. We've all seen this before. However I don't understand why, all derivatives suggests it's stable as does the static analysis. Moving the main wing back helps ofcourse, but I shouldn't have to right? Any ideas?

 

Edited by ThorBeorn
imgur fail
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