Atmospheric Flight feels weird

[DragonHalo99]

is it just me or is atmospheric flight a bit strange. my aircraft fly decently it's just turning seems completly off for an aircraft and I can never seem to level out aircraft is always losing or gaining altitude.

[herbal space program]

Less lift, less drag than before. That will have all sorts of effects. I had to slap around 1.33X wing area on my planes to make them fly like before. Up high, things drop off faster now as well.

[Xavven]

What do you mean by "off"? As for your altitude gain and loss, that's just phugoid oscillation and is completely normal in real life aircraft unless an autopilot mode is engaged. https://en.wikipedia.org/wiki/Phugoid

[BebopRebop]

Are you using a joystick?

Flying in KSP feels really wonky because apparently joysticks have an issue with input lag, which I could see causing oscillations and difficulty turning. The advanced fly-by-wire mod worked to fix this for me, but tends to crash KSP when I try to tweak its settings.

[G'th]

Its mainly because aeronautics is more or less tacked on, only possible because it can rely on whats required to simulate the rockets during ascent. We lack a lot of the things that would make flying both more realistic and enjoyable, namely better controls and more details on the actual numbers behind the performance of the aircraft (which is something rockets also lack, but they're affected to a much lesser degree)

But it can also be due to the fact that unlike real life planes, KSP planes unless designed extremely well (super tedious and potentially impossible in stock, still super tedious with FAR, mitigated with FAR combined with Dynamic Deflection) will fly weird. 

[DragonHalo99]

Hey guys sorry it took me so long to reply I am running a walmart load to fort worth texas got 172 miles to go. What I mean about aircraft feeling wierd is that its heck getting aircraft to turn in my career. I am only using kerbal engineer redux atm. I started a new career for 1.1.2 so far I am in the 90 science section of the tech tree. I have all aircraft parts up to mark 2.

Is it normal to have to fly in atmosphere with sas on? I also wonder if maybe sas is making turning hard. I have been flying all my aircraft with sas on. I also want to link the aircraft design that I am using for you guys to give me some tips to refine the design. How do I link the aircraft?

I am getting back on the freeway so I will reply in a few hours

Edited May 28, 2016 by DragonHalo99
spelling corrections

[ZooNamedGames]

Use FAR

[OrbitalBuzzsaw]

3 hours ago, G'th said:

Its mainly because aeronautics is more or less tacked on, only possible because it can rely on whats required to simulate the rockets during ascent. We lack a lot of the things that would make flying both more realistic and enjoyable, namely better controls and more details on the actual numbers behind the performance of the aircraft (which is something rockets also lack, but they're affected to a much lesser degree)

But it can also be due to the fact that unlike real life planes, KSP planes unless designed extremely well (super tedious and potentially impossible in stock, still super tedious with FAR, mitigated with FAR combined with Dynamic Deflection) will fly weird. 

That is not true. Consider the use of SSTOs. And stop hating on stock aero. It's actually a lot like older FAR. Also, planes in stock aero usually fly well if you aren't being a DumbS. I really don't understand what's so great about FAR - As far as I can tell, it's not that different from Stock Aero Model. It also broke my KSP (Installed correctly and no CKAN) the one time I tried to try it...

[G'th]

^ Not really sure what you're saying isn't true.

And as for FAR, its very different from stock aero in that it simulates what stock aero is faking, while also introducing the things stock aero doesn't simulate. And I highly doubt it was installed correctly if it broke your game. Or you're attributing the issue to FAR when its something else.

[DragonHalo99]

Only mods I have installed is kerbal Engineer redux and mcjeb which I have yet to actually use. How would I got about linking the aircraft ive been using? I want some input on it. I have never heard of Far though. Honestly I want to keep my current playthrough as mod free as possible until I complete everything possible. Though I have heard that you can unlock nearly the entire tech tree from just kerbin the mun and minmus. My problem with mun landings is I can't seem to nail having the right amount of fuel for the return and 95% of the time I lose the landing gear and the engine or the rocket tips over on me and I lose the engine...

[MaxPeck]

From a pilot's perspective, I can tell you there are two things you're experiencing that make it feel weird.  Stock/FAR arguments aside, and mathematical proofs notwithstanding, there are two things that dramatically impact aircraft performance:

1. Speed is indicated in a scale you're not used to, and wholly unrealistic.  We typically don't measure our forward (or vertical) velocity in m/s.  We measure them in knots and feet/second.  Most aircraft under 18,000' MSL operate at 250kts or less, even those sexy fighter planes and airliners.  That's a mere 128m/s.  The slowest useable approach speed for most aircraft in KSP, even propeller-driven light aircraft using firespitter and KAX is around 65m/s.  That's a blistering 126 knots, faster than the level cruise speed for most piston-driven light aircraft.  For contrast, the recommended approach speed of a Boeing 757 is 132 knots, which is only 68 m/s.  Keep that in mind next time you're trying to land a cessna mockup in KSP at 125 m/s.  Also, as a result of this, most KSP aircraft cruise at entirely absurd speeds.  A propeller-driven airplane cruising at 150m/s is blasting along at 291 knots, which would appear to be a blatant violation of FAR 91.117(a).  Except it's not, because our altitude expectations are also wonky.  We're used to measuring altitude in feet, not meters.  The upper limit of most non-turbocharged piston aircraft is around 12,000' MSL, which is only 3,658 meters.  10,000 meters is about 32,000 feet MSL.  20,000 meters is pretty much in the stratosphere.  And that's on Earth, Kerbin probably has smaller atmospheric layers.

2. There is zero turn coordination in KSP, unless you do it yourself (or use a mod).  When you bank a real airplane, centrifugal force will try to push the airplane to the outside of the turn unless you apply yaw correction in the direction of the turn.  The aircraft will still turn in the direction of the bank due to asymmetric lift, but the turn will be very inefficient, as you see in KSP.  A properly coordinated turn requires both rudder into the turn, as well as slight back pressure on the controls to keep the nose from dropping. In KSP, we tend to just bank the wings and hope for the best, whereas in properly controlled flight, a turn requires adjustments along all three axis, and possibly power adjustments as well. Also, going back to point #1, because we're flying at 90% of ludicrous speed all the time, there's a fair amount of inertial coupling going on as well, so your control surfaces either have to be cartoonishly large or are ineffective outside of the small subsonic sweet spot that real aircraft operate in.

[Green Baron]

pls. let me add to jje64 (had a ppl myself over 10 years), that once an aircraft is trimmed to a certain speed it holds that speed. I'm not talking about any sort of axis-stability or lability, which apparently is not modeled in ksp, just the power of the engine or the aoa. If trimmed, when you change engine power, a real aircraft sinks or climbs but it holds the speed. In ksp it changes the speed, the altitude stays the same. Furthermore, a real aircraft, once you change the trim (aoa), it changes the speed, higher aoa meaning lower airspeed. Well, if you pull it will certainly climb a bit but speed will drop, you'll have to pay that climb back after a few seconds. Or you change the engine power.

Yes, the aircraft flies straight while kerbin is a ball. So after a while it "climbs". Or Kerbin disappears. I find that weird too. Furthermore no, an aircraft has no sas. Some instruments have gyro to stabilize, e.g. the artificial horizon.

Hope that helps :-)

(I last flew ksp-aircraft in 1.0.5, stock, maybe there has changed something now)

Edit: Just fpr completeness: once in level flight you "trim all forces away" from the controls so that if you let go the aircraft just flies level without any autopilot. I never achieved this in ksp, but i must admit i'm more into rockets than planes.

Cheers

 

Edited May 28, 2016 by Green Baron
Typos

[DragonHalo99]

The plane I made Flies at 501ms cruise speed when 1/4 of the fuel is left. when it does that the whole aircraft is glowing red and the engines are close to overheating but never overheat completly.

Edited May 28, 2016 by DragonHalo99
Fixing post

[Padishar]

44 minutes ago, DragonHalo99 said:

How do I delete the post above? It wouldn't let me cancel what I was typing.

Edit the post, click on the bit where it says the time and author of the quote and then hit the delete key.

[KerikBalm]

1 hour ago, JJE64 said:

From a pilot's perspective,

...

The slowest useable approach speed for most aircraft in KSP, even propeller-driven light aircraft using firespitter and KAX is around 65m/s.  That's a blistering 126 knots, faster than the level cruise speed for most piston-driven light aircraft.  For contrast, the recommended approach speed of a Boeing 757 is 132 knots, which is only 68 m/s.  Keep that in mind next time you're trying to land a cessna mockup in KSP at 125 m/s.

...

2. There is zero turn coordination in KSP, unless you do it yourself (or use a mod).  When you bank a real airplane, centrifugal force will try to push the airplane to the outside of the turn unless you apply yaw correction in the direction of the turn.  The aircraft will still turn in the direction of the bank due to asymmetric lift, but the turn will be very inefficient,

...

there's a fair amount of inertial coupling going on as well, so your control surfaces either have to be cartoonishly large or are ineffective outside of the small subsonic sweet spot that real aircraft operate in.

#1) You can design planesto land at far slower than 68 m/s... I have SSTOs landing slower than that (after a mission ,with nearly empty tanks)

From another thread:

#2) Your explanation of turn co-ordination is really bad.

"centrifugal force will try to push the airplane to the outside of the turn" - No

"The aircraft will still turn in the direction of the bank due to asymmetric lift," - No

It turns because the lift vector has changed... it can do this while still being asymetrical. Unless you've got sideslip going on and dihedral, in KSP, it will still be symetrical.

A lot of it has to do with the face that we're building planes out of lego parts. No washout in almost every plane, for example

Another issue is the ridiculous OP reaction wheels which can have your nose pointing in ways that can't be sustained... flying with reaction wheels disabled tends to be much smoother IMO.

Them of course, there's the binary input of a keyboard (unless you use a joystick) which will make things not smooth at all

#3) "here's a fair amount of inertial coupling going on "

Indeed, KSP stuff is generally quite heavy, and they have a lot of roll/pitch/yaw inertia. I find the SAS can often make things worse as you end up fighting it... I miss the old mode where it just tried to stop all rotation, but not hold any heading... its been gone since... 0.21 I think? I used to use that mode a lot on landers. I want it back

 

[Pecan]

4 hours ago, DragonHalo99 said:

...Is it normal to have to fly in atmosphere with sas on? I also wonder if maybe sas is making turning hard. I have been flying all my aircraft with sas on. I also want to link the aircraft design that I am using for you guys to give me some tips to refine the design. How do I link the aircraft?...

You have pilots' comments on real aircraft so I'll address your specific questions about KSP.

1. It is not desirable to depend on SAS for stability but it probably is normal for most people.  Better by far (pun intended) to use trim: <mod>+WASDQE (<mod> is the 'modifier' key; alt in Windows, Option on mac, right-shift in Linux.)  I'm also assuming that you'll be using 'fine' controls; toggle between coarse controls (pitch/yaw/roll input indicators at bottom-left of the screen are red) and fine (indicators are blue) by pressing caps-lock.  Pressing alt-S, for instance, increases the 'hands-off' position of the pitch controls so without you touching anything tthe vehicle has more tendency to pitch-up.  Trim on all three axis can be cancelled/zeroed by pressing alt-X,  It is quite possible that you will still want to engage SAS just so you don't have to fiddle with trim all the time (eg; as your fuel burns and the natural balance/trim of the vehicle changes) but ...
2. ... The whole point of SAS is to keep the vehicle pointing the same way so, yes it WILL make turning hard(er).  Assuming you are using it for a bit of 'auto-trim' as above then before any deliberate manoeuvre you should turn it off, then back on again once you're back in straight (but not necessarily level) flight.  The full sequence for a turn to the right, for instance, is therefore: disengage SAS (T), roll right (E), co-ordinate with yaw-right (D) and keep the nose up by pulling the stick back (S), return to wings-level on the new heading and re-engage SAS (T).
3. Now consider what will happen to a vehicle nicely-trimmed for straight and level flight when you disengage SAS (which is just trying for 'straight').  In theory - not much.  In practice - maintaining a fixed altitude around the world is not straight.  Therefore the longer you've been using SAS the higher and higher it has been pitching you - straight to Mun if you set it up right! - so when you disengage it and the vehicle settles back to its trim settings the nose is very likely to drop quite a bit and there are likely to be 'disturbances' along the other axis too.  So - if you want hands-off level flight you should disengage and re-engage SAS every now and again anyway (and adjust trim), just to reset it to current conditions.  This is also the RL case with any gyro-stabilised system (depending on how cleverly they are built).
4. LINKS!  A screenshot (F1) of a vehicle, preferably in the VAB/SPH with CoM and CoL displayed (buttons bottom-left of the screen when in those buildings) will usually tell the cognoscenti here enough to diagnose the more usual things.  Otherwise the craft file itself is just a text file stored in your KSP_win\saves\<save game name>\ships\SPH or \VAB folder (If you're not on Windows change the 'KSP_win' as required).  It's called a craft file because it has the extension of '.craft. so "My Plane" will be stored as "My Plane.craft".  In order to post either of those to the forums you will need to use a file-sharing web site such as imgur (for pictures) or dropbox (for any files). and post/embed the link here.

[Green Baron]

31 minutes ago, KerikBalm said:

#1) You can design planesto land at far slower than 68 m/s... I have SSTOs landing slower than that (after a mission ,with nearly empty tanks)

From another thread:#2) Your explanation of turn co-ordination is really bad.

"centrifugal force will try to push the airplane to the outside of the turn" - No

"The aircraft will still turn in the direction of the bank due to asymmetric lift," - No

It turns because the lift vector has changed... it can do this while still being asymetrical. Unless you've got sideslip going on and dihedral, in KSP, it will still be symetrical.

 

 

#1: These things would never fly IRL. jje64 was talking about about real aircrafts.

#2: His explanation is near perfect. The lower(inner) wing is slower than the higher one when turning, so Yes and Yes. Sorry. And the lift counters the centrifugal force. It wouldn't turn from the lift alone, you have to ccordinate that with rudder (sorry, i mean yaw, not that perfect in english ...) and elevators. Sorry about that.

 

Edit: turn: assuming not too much v-shaped or anti-v-shaped wings of course ;-)

Edited May 28, 2016 by Green Baron
Added sth., plane = wing

[KerikBalm]

#1) It was claimed that KSP aircraft land much much faster than real aircraft... KSP aircraft can fly much slower than he claimed, countering his complaint (and yes, stuff very similar to them count fly IRL)

#2) the radius of most turns relative to the wingspan is so much greater that a speed differential doesn't cause any noticable asymetry in lift. There's nothin with centrifugal force and yawing here. The yawing it to prevent sideslip. Its not needed if the aircraft has sufficient yaw stability.

It turns in the direction of the bank due to the lift vector not being vertical... well the craft's velocity vector moves to the side anyway. The sideslide that results will impart a yaw moment if it is yaw stable, which will cause the nose to point in the direction of the turn.

The case of lift asymmetry and a need to counter with yawinput only occurs when a roll is initiated.. due ot a higher and lower effective AoA of the wings, causing adverse yaw

https://en.wikipedia.org/wiki/Adverse_yaw

Thats not applicable to a "steady state" bank... merely a response to a roll input

[DragonHalo99]

http://imgur.com/6b6Typ4

This is the Aircraft in question.

Hmm maybe 2 engines was enough. That TWR is really high with 4.....

[klesh]

Take the top 2 engines off and your center of mass will shift forward.   Your center of lift is too far behind the center of mass  Alternatively, should you want to keep the engines, slide them wings forward a bit.   

[Death Engineering]

Make sure you have Claw's 'Stock Bug Fixes' installed. 1.1.x 'broke' lifting body mechanics which makes planes feel weird.

[cantab]

9 hours ago, DragonHalo99 said:

Is it normal to have to fly in atmosphere with sas on? I also wonder if maybe sas is making turning hard. I have been flying all my aircraft with sas on.

Lots of people do fly planes with SAS, but it is indeed what's making turning weird. SAS attempts to hold the craft in a particular orientation in space. That means that if you bank your aircraft, SAS fights the turn and puts you into a slip, the plane flying slightly sideways through the air. You have to wrench the plane around with manual control inputs to turn effectively when SAS is on.

I prefer to fly stable planes without SAS, and instead use trim, which is set by Alt+WASDQE, or RShift+WASDQE on Linux. This sets a constant control input, which you can see in the bottom left when SAS is off and you aren't making manual inputs. I use pitch trim to maintain level flight (or a climb or descent as desired). I hit Caps Lock to enable fine controls, the markers in the bottom left turn blue, which smooths out direct control inputs. I find many planes in KSP don't really need rudder input when banking, the turns are good enough anyway. I only enable SAS if the plane starts misbehaving, in particular in the upper atmosphere where it can get very "floaty".

Setting up a joypad or flightstick can let you fly more smoothly, but simple flights on Kerbin or spaceplanes to orbit are doable with the keyboard.

Your plane design above looks basically fine, though I agree it would probably do better with two engines.

[The_Rocketeer]

@DragonHalo99 my advice based on your description and SPH screen:

1. the CoL is too far behind the CoM. This will cause pitch down that is never completely corrected by SAS alone (SAS isn't sensitive enough, so all rounding errors are consistently on the 'not quite enough' side. Trim will help better but will require constant manual adjustment.

2. the CoT/thrust vector is out of alignment with the CoM. This will also cause pitch down that gets worse the harder you're working the throttle, and if those engines are shut down it will cause pitch up due to asymmetrical drag.

3. the Tail Fins you're using for control surfaces provide tremendous amounts of steering torque - really far too much for light aircraft (for this reason I never use them except when messing around). I would swap them for static tail wings and control surfaces like those you're using for ailerons (which will help with the CoL/CoM problem too).

4. flying with SAS on will prevent your aircraft from sideslipping during a banking manoeuvre because the yaw input corrects it too effectively (see 3.). Turning it off will cause you to pitch down due to the reasons above. Trim would be better than SAS (but see 1).

5. Adjusting CoM/CoL/CoT issues is the best solution and would produce better aerodynamic stability all round.

Edit:

6. user controls aren't precise enough to maintain constant altitude at all, and since mass is always decreasing trim will also become inaccurate. RL aircraft have autopilots for this same reason. So, in all seriousness, the best solution for perfectly straight and level flight is to install an autopilot mod (I recommend Pilot Assistant) which will react much faster than a human player can to these gradual changes.

Edited May 28, 2016 by The_Rocketeer

[DragonHalo99]

ok so I took what you guys said to change into consideration and I gotta say this aircraft is performing twice as better it even got 3x farther than it could reach before. Tell me what you think!

http://imgur.com/a/6f91R

What I am really impressed by is it was cruising at 601ms at mach 1.78. All of my earlier designs can't hold a candle to this plane. I got rid of the chutes and moved the science experiments into a service bay to cut aerodynamic drag. I ended up sticking the 2nd pair of engines back on to drag the com back to where it would line up perfectly with the col. the cot is in line with everything else. Makes me wonder what I can accomplish when I get better parts later on. turning is much better and using precision controls made flying a breeze. Thanks for the advice guys!

[The_Rocketeer]

Yes, much better those adjustments have got you a much more stable aircraft.

Here's a quick pic of an aircraft of similar size and tech level that I built. This craft is slower (it only has 2 engines, the fastest I've gone is about 600m/s) (Edit: Misread your post! Speed seems comparable despite having fewer engines - I guess less mass/drag.) but still capable of a round trip to the North Pole in under 90 minutes, and with higher tech engines could of course be faster and more efficient.

However, the real point of putting this here is to show you how I've arranged my fuel around the CoM (see the small tanks at the base of the wings?). This means that as the fuel drains, the CoM stays in roughly the same place, whereas if the fuel is mostly in front or behind the CoM, then after a while you start to find stability issues creeping in again because the CoM has moved. If the CoM -has- to move (for reasons of practicality) it is better to have it move forwards than backwards, because this is more stable for gliders. (and if you run out of fuel, guess what you are! )

Spoiler

Edit: Oh yes, one thing I remembered after reading my post again - those Tail Fin parts are also very draggy compared to other winglets! That could also be part of your stability issues

Edited May 29, 2016 by The_Rocketeer