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Spemble

Jet Aerodynamics

Question

Well, after hours of testing, reading, and testing again, I am still having a really hard time understanding the aerodynamics.

Previous post:

Even though my previous post was ironically the only ground drag issue that came into the equation with trying to make a stable jet, I'm still trying to build a stable jet. Rather, understanding how to make one that is.

I know CoM, CoT, and CoL, but I don't understand their results. There are numerous claims that if the CoL is behind the CoM, then the rocket will be stable.

KSP wiki:

http://wiki.kerbalspaceprogram.com/wiki/Center_of_lift#Flight_characteristics

Quote

Flight characteristics

Different flight characteristics are desired in different craft. If the COL or the lift vector is positioned or pointing off-center left-to-right, the craft will turn. If the COL is positioned too far toward the bottom of the craft, it will want to roll over. Assuming the COL is centered side-to-side, and possibly top-to-bottom, performance is basically as follows:

  • COL ahead of COM → Flips or turns uncontrollably
  • COL inside COM → Excessively maneuverable; needs constant course correction
  • COL closely behind of COM → More maneuverable
  • COL further behind of COM → More stable
  • COL very far behind of COM → Very hard to correct course; likely to flip up or nosedive

foamyesque:

Quote

"pull the pull the CoM ahead of the CoL again, making the plane stable.

But my mind is vehemently refusing to accept this. Don't you guys mean the "center of drag"? I feel like this is very similar to the CoL, but is still different. You could have a ship with two wings in the front and then a bunch of random parts on the back, and would fly with the drag-inducing parts in the back like an arrow with feathers. Yet, the CoL would be right between the two wings, because they are the only things providing lift. I've had planes where the CoL is significantly behind the CoM, but it still wants to flip at high speeds, or at least doesn't want to just go straight.

And this flows into my second question.

You know, let's make a list. Welcome to the buffet of questions for all your answering needs:

  1. Is the CoL the same thing as the "Center of Drag"?
  2. If not, is there a good way to find how far the CoD (center of drag) is behind the CoM?
    1. I've been shooting my crafts way up in the atmosphere and then letting them fall to see if the CoD is behind the CoM. Kinda time-consuming.
  3. If all parts create lift (KSP wiki quote below), why don't they change the CoL in-game?
    Quote

    As of version 1.0, all parts generate some lift as well as drag; however the lift-to-drag ratio is much higher from aerodynamic parts such as wings, control surfaces, etc. KSP also models drag created as a consequence of lifting force.

    1. KSP wiki: http://wiki.kerbalspaceprogram.com/wiki/Lift#Dynamics
  4. The wings are symmetrical. Do they still produce vertical lift in ksp if they are not given any angle of attack?
  5. Are there specific wings that do/don't produce vertical lift at 0° angle of attack?

I'm really sorry I'm asking the same question that everyone always asks, but this is a little different.

Thank you so much for taking the time :D

- Spemble

Edited by Spemble

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1 hour ago, Spemble said:

Well, after hours of testing, reading, and testing again, I am still having a really hard time understanding the aerodynamics.

Don't give up. You'll get there. But KSP airplane design is just as steep a learning curve as rocket design.

Quote

I know CoM, CoT, and CoL, but I don't understand their results. There are numerous claims that if the CoL is behind the CoM, then the rocket will be stable.

Not exactly a claim. More a rule of thumb. It depends on where your control surfaces are. You want the CoL pretty close to the CoM, so that most of the weight of the plane is lifted by the wings. Then the control surfaces can balance out the rest -- if you have enough of them in the right places. It tends to be easier to have the CoL behind the CoM, because then the failure mode is for the nose to drop -- which might actually be recoverable. If you have it the other way, then the nose rises, and the plane stalls and flips -- which is often not recoverable.

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But my mind is vehemently refusing to accept this. Don't you guys mean the "center of drag"? I feel like this is very similar to the CoL, but is still different.

Yes, it is indeed. But KSP does not (can not really) show you the center of drag. So you have to guess from the CoL -- they are usually close to each other. But not always. You have to look at the plane and know where the draggiest bits are. Including the nose of the plane, which doesn't look draggy but tends to have the most drag of all.

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  1. Is the CoL the same thing as the "Center of Drag"?

Not quite, see above.

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 2. If not, is there a good way to find how far the CoD (center of drag) is behind the CoM?

Kentucky windage. Oh, wait, you said a good way.

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2.1 I've been shooting my crafts way up in the atmosphere and then letting them fall to see if the CoD is behind the CoM. Kinda time-consuming.

The game is time consuming, yes. Engineering PhDs take years to earn. But you have a clever method here. You may figure out a faster way of lobbing them into the air to do your testing. All you have to do is get them moving at a reasonable speed and then turn off SAS.

Quote

3. If all parts create lift (KSP wiki quote below), why don't they change the CoL in-game?

They don't all create lift -- except in the sense that if you are falling straight down, then drag and lift are the same thing. Parts that have straight sides can crate a small amount of "body lift". But that's almost always a small side-effect.

Quote

4. The wings are symmetrical. Do they still produce vertical lift in ksp if they are not given any angle of attack?

No. But if you fly the plane with an AoA, then that gives an AoA to every part on the plane.

Quote

Are there specific wings that do/don't produce vertical lift at 0° angle of attack?

Nope. All the wings (except one which is worse) are identical. The only difference is lifting area and aesthetics (and money, and tech level).

Quote

I'm really sorry I'm asking the same question that everyone always asks, but this is a little different.

Actually, I think you asked this one differently than anyone has asked it before, AFAIK. :D

Edited by bewing

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16 minutes ago, Spemble said:

You know, let's make a list. Welcome to the buffet of questions for all your answering needs:

  1. Is the CoL the same thing as the "Center of Drag"?

No, they are different, and can be in very different places depending on the shape of the plane.  There has been much discussion of this and many requests that we get a "CoD" marker.  I myself have never seen the need for a "CoD" marker, however.

 

16 minutes ago, Spemble said:
  1. If not, is there a good way to find how far the CoD (center of drag) is behind the CoM?
    1. I've been shooting my crafts way up in the atmosphere and then letting them fall to see if the CoD is behind the CoM. Kinda time-consuming.

Like I said, I've never seen the need for a CoD marker so have never really worried about it.  The advice you quoted eariler in your post about the relationship between CoM and CoL, and their effects on plane stability and handling, are all you really need.

The deal is, CoD is highly variable so will change position by large amounts as you fly.  The biggest factor is AoA changes because that has the largest increase in the effective frontal area of the plane.  Thus, having a marker for it in the SPH really won't do you any good because because it usually won't be at that point in flight.

 

16 minutes ago, Spemble said:
  1. If all parts create lift (KSP wiki quote below), why don't they change the CoL in-game?

They do change the CoL.  It's just that most folks build the fuselage first, then attach wings, then turn on the CoL marker and slide the wings forward and backwards to get the CoL in the right spot relative to the CoM, so they don't see the CoL changes caused by the fuselage parts.

You can do a simple experiment.  Make a long fuselage of 1.25m cylindrical parts and see where the CoiL is.  Then swap out one of these parts for a Mk2 tank and you'll see the CoL move.

 

16 minutes ago, Spemble said:
  • The wings are symmetrical. Do they still produce vertical lift in ksp if they are not given any angle of attack?
  • Are there specific wings that do/don't produce vertical lift at 0° angle of attack?

AFAIK, all wings produce upwards lift at 0^ AoA whether rightside up or upside down.

Really, you're totally overthinking this whole subject.  KSP has very, very simplified aerodynamics that have only a superficial resemblance to the real world.  There are only a few things you have to do to make a stable airplane.

1.  Give it enough thrust and wing area to fly at all.

2.  Build it so the CoM doesn't move much or at all as the fuel burns.

3.  Build it so the CoL is slightly behind the CoM.

4.  Turn on SAS.

SAS is what makes planes stable.  KSP planes are inherently unstable no matter how you build them so SAS is essential.  Long, long ago, SAS worked differently and planes were sometimes more stable without it, but that changed well before even the big change in the atmosphere.  

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I just made this as a joke, to test the wings

8jNpepK.png

It flopped around like a dead fish around the Space Center (and broke the front landing gear), but then left the computer to come back to it half way around kerbin, skipping across the top of the atmosphere. ._. "Stable rocket" like a slap in the face. Thanks KSP. <3

4 minutes ago, Geschosskopf said:

1.  Give it enough thrust and wing area to fly at all.

2.  Build it so the CoM doesn't move much or at all as the fuel burns.

3.  Build it so the CoL is slightly behind the CoM.

4.  Turn on SAS.

I have done this countless times, but sometimes the plane flips around anyways, even with SAS. I'd really like to understand how KSP models it so I can build crafts that will reliable, and thus know how to fix things in the future, if another problem presents itself.

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If the planes flip around anyways, then you don't have enough control surfaces, or they aren't big enough, or they aren't placed quite right. The control surfaces need to be a long way from the CoM, in order to give them leverage to force your plane back into alignment if it deviates.

For your control surfaces, you can have a tail that controls yaw negatively. You can have canards at the front that control pitch and yaw positively, and they can also control roll. Rear stabilizers can control pitch negatively, and roll. Elevons can control pitch negatively, and roll. Stick more of them on. :)

And it is possible to build a passively stable plane in KSP. But your CoM also has to be significantly below your CoL. So you need to move your wings up on the body.

Edited by bewing

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@Spemble: Technically, yes, passive drag from non-wing parts also contributes to aerodynamic stability (or lack thereof). In most circumstances, though, the forces from wing and stabilizer angle of attacks will vastly outstrip anything else, particularly with planes. The major exception is when tail-heavy rockets get enough nose drag to overwhelm rear fins.

 

Lots of people will tell you the solution to control problems is to add more control surfaces. Personally, I regard this as a bit of a failure when I have to resort to it; unless your craft is large enough that the control surfaces will bend the craft instead of turning it, you should only ever need one set per axis for control purposes. Leverage and careful balancing maximize the oomph, and it honestly doesn't take much to move a plane if you've done so. (EDIT: In fact, I often design my spaceplanes such that they are actually not stable, so I can maintain high AoAs during reentry. SAS can handle these surprisingly well).

Of course, it's also kind of fiddly to do so and tends to require a fair number of trials to get the exact balances I want.

Edited by foamyesque

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5 hours ago, Geschosskopf said:

AFAIK, all wings produce upwards lift at 0^ AoA whether rightside up or upside down.

No. KSP wings produce no lift unless they have AoA.

Even real life wings do not produce enough lift to fly unless they have AoA, which is why most real life aircraft have the wings mounted with built-in-AoA, called Angle of Incidence.

Quote

Wings are typically mounted at a small positive angle of incidence, to allow the fuselage to have a low angle with the airflow in cruising flight. Angles of incidence of about 6° are common on most general aviation designs.

Source: Wikipedia

piper-9a.jpg

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@Spemble

There is a mod called CorrectCoL that improves the SPH CoL indicator to take account of body lift on parts that don't explicitly generate it (the stock one takes account of mk2 fuselage lift rating, but not body lift from other stuff).  It's got a static stability analysis graph too ,  that plots the nose up/down tendency the plane has across the aoa range.  It does the same for yaw too.

I think people are conflating  control surface with stabilizer and talking at cross purposes.

Ie.  Vertical stabilizer is just a wing panel mounted vertically at the back of the ship, giving passive stability.   Control surface is the part you can move with the rudder controls.  In career games, when part count limited,  I sometimes omit the rudder and just have  a passive rudder.  

20161114211344_1_zpsr4qjynyl.jpg 

Yaw stability is just a case of "more the better".  Obviously at some point, there is a performance penalty for putting an outsized vertical stabilizer on a plane, but 0 degrees of sideslip is always the ideal.

With pitch, we need to be able to move the plane off prograde to generate lift, and move it further off prograde to pull stunt maneuvers, so too much stability requires excess forces to hold the nose up.   

In  a tailplane design, where you are getting the nose up by pushing the tail down, the elevons are creating drag in the process of making this downforce, and that downforce increases the amount of lift the main wings have to generate to keep the plane in the air , so you  pay for it twice.     Worst case scenario, you end up with this failed space shuttle i made -

20161102203800_1_zpsc11fwfaq.jpg

What makes it worse is that the elevons are quite close to the centre of mass, so they only have a short lever arm to work with.  As a result, you need even more downforce to get the same nose up torque.  And even worse still, these elevons have a max deflection angle of 30 degrees and are close to maxing out just maintaining level flight.  Just as with wings,  you get your best lift:drag ratio at 7 degrees to prograde.  Deflecting them over 15 degrees  creates a lot more drag for not much more lift.

If you are using a canard, the lift at the front end to get the nose up is at least helping to support the whole ship, so the penalty for very aft CoL is not as bad.       Control surfaces and wings have the same lift:drag ratio at the same mach number and AoA.  The only difference in their performance is that control surfaces are twice as heavy for the same wing area (lift rating) as a passive wing part.    

Again , if your canard is undersized, it will be at greater AoA than the main wing.  Too much of this pushes it into the draggy near-stalled condition.   A larger canard will operate at a less extreme angle and give less drag while maintaining level flight, but remember that fitting a larger one adds lift to the front end and moves CoL forward.   In any case, having the canard at a greater AoA than the main wing is good for stability, because in the event of a disturbance that raises the craft's AoA, the main wing will gain lift quicker than the canard , which is getting into diminishing returns, and this creates a nose down tendency that helps return you to level flight.   And of course,  it becomes impossible to stall the main wing because the canard runs out of lift first and can push the nose up no further.

Of course, if you are fitting control surfaces that are larger than strictly necessary in the name of low trim drag, you can get a plane that is twitchy and hard to make small adjustments on.   What I do is right click the surface and "limit authority" so i can have the benefit of large control surfaces (low deflection angles in normal flight, low drag) without having it pull a 30G turn if the pilot sneezes.

20161106073606_1_zpsekq1jshp.jpg

Despite appearances, this fighter cannot stall and has pretty good low speed handling.  https://kerbalx.com/AeroGav/Silver-Gryphon

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On 12/1/2016 at 10:44 PM, Spemble said:

I have done this countless times, but sometimes the plane flips around anyways, even with SAS. I'd really like to understand how KSP models it so I can build crafts that will reliable, and thus know how to fix things in the future, if another problem presents itself.

Besides the 3 main points I listed in my 1st post, I should have added 2 more that are VERY important:  DISABLE ENGINE GIMBAL and TWEAK CONTROL SURFACES..

Seriously, engine gimbal is total poison except in 2 very specific cases:  Dogfighting and the bottom stage of a lifter that lacks tail fins.  In all other cases, you're trying to go in an essentially straight line so don't want any off-axis thrust.

As to control surfaces, they default to being active for all axes, which is usually quite inappropriate.  So disable yaw for everything that's not a dedicated rudder, and disable roll for nearly everything else.  You don't need (or want) very much aileron authority but you need a lot of pitch authority.  Also, it helps to put rudders on the wingtips so they don't introduce unwanted roll when used, but this isn't critical. 

But anyway, build the plane so the CoM doesn't move, put the CoL right behind hit, and turn on SAS.  Add extra SAS if necessary.

Don't over-think this.  KSP aerodynamics are a minimal rule set that only loosely approximate real life.  Most of the things real airplane designers have to deal with simply don't exist in KSP, and trying to chase them usually causes more problems than it solves.

 

On 12/2/2016 at 4:10 AM, Val said:

No. KSP wings produce no lift unless they have AoA.

Even real life wings do not produce enough lift to fly unless they have AoA, which is why most real life aircraft have the wings mounted with built-in-AoA, called Angle of Incidence.

Um, no.  KSP is not real life.  KSP wings produce lift regardless of AoA.  They just produce more lift with a positive AoA.  Think about it.  If KSP wings required a positive AoA to produce lift, then as soon as your pitch inputs created an AoA of zero or less, the plane would fall like a brick because the wings would instantly quit working.

---------------------------------

Anyway, back to @Spemble

To illustrate the severe simplicity of KSP aerodynamics, consider the following aircraft, which I call the Bowtie.  I actually designed this plane back in 0.24, LONG before the atmosphere changed in 0.9 and 1.x,  It flew quite well then and, with the necessary adjustments for different parts, flies even better today.  You can download it here:  https://www.dropbox.com/s/yzth4xst2nyll42/Bowtie STOCK.craft?dl=0 (action group 2 works the ladders, 0 works the airbrakes).

I built this plane simply to show how weird you could make things that still fly perfectly fine in KSP.  It looks like this:

Bowtie 3-View

 

Despite this weird shape (note also that the forward wings are upside down to get the forward sweep), it flies superbly because the CoM doesn't move and the CoL is right behind it.

Bowtie Markers

 

You can also see that the 4 rudders are on the wingtips symmetrically above and below the centerline, so don't produce unwanted roll.  Finally, the CoM doesn't move.  In the pic below, I tweaked the fuel out of one of the rear tanks, so the red full CoM" moved forward of the red "empty CoM" markers, as shown by the wonderful mod RCS Build Aid.  With that tank full, the full and empty CoMs are in the same place, as shown in the pic above.  Also note the extra SAS in the cargo bay.  The torque of the cockpit alone is usually insufficient so all my planes have more.

Bowtie Secrets

 

 

 

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3 hours ago, Geschosskopf said:

If KSP wings required a positive AoA to produce lift, then as soon as your pitch inputs created an AoA of zero or less, the plane would fall like a brick because the wings would instantly quit working.

And that is exactly what happens. When the wings have 0° AoA, they start falling. But as soon as they fall, they no longer have 0° AoA. Which is why a craft with 0° AoI ALWAYS has to fly with the nose pointing a few degrees above prograde, to climb or even maintain altitude.

Edit: @Right did some experiments last year in 1.0.5. How lift works has not been changed since.

Zero lift at 0° AoA.

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Yeah. If you have negative pitch (or 0), you don't have lift; you can readily see it in the aero overlay (or the aero GUI from alt-F12). Alternatively, you can lock-prograde and watch a 0 AoI plane lawndart.

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Here's a video, I made last night, that demonstrates what @foamyesque said.

It shows no appreciable lift until AoA is significant.

The craft is built with a special nose gear that can deploy, to change AoA while on the runway. (But makes it really bouncy)

After takeoff ballistic flights with close to 0° AoA is attempted a few times, before landing again.

Another takeoff run (2:30), this time just using elevator inputs to show lift changes on main wing, and another 0° AoA ballistic flight, before landing and crashing. :0.0:

 

 

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6 hours ago, Palaceviking said:

All of this fantastic info and no-one has mentioned dihedral stability? 

 

@bewing sort of did. It's not really a huge factor, though I'll put a bit of it on my wingtips from time to time if I have a CoM that's well above my CoL otherwise. Having enough yaw stability to counteract adverse yaw from rolling is a much larger design consideration IME.

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31 minutes ago, foamyesque said:

 

@bewing sort of did. It's not really a huge factor, though I'll put a bit of it on my wingtips from time to time if I have a CoM that's well above my CoL otherwise. Having enough yaw stability to counteract adverse yaw from rolling is a much larger design consideration IME.

Do you understand the "distance from center" of mass thing for roll authority surfaces?

ie; next to the fuselage or out on the wing tips?

Summoning.

Edited by Palaceviking

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32 minutes ago, Palaceviking said:

Do you understand the "distance from center" of mass thing for roll authority surfaces?

ie; next to the fuselage or out on the wing tips?

Summoning.

What, that you have more lever arm to work with, and consequently you can get more roll from the same deflection, thereby (somewhat) reducing adverse yaw? Of course. Is there more to it I'm unaware of?

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1 hour ago, foamyesque said:

 

@bewing sort of did. It's not really a huge factor, though I'll put a bit of it on my wingtips from time to time if I have a CoM that's well above my CoL otherwise. Having enough yaw stability to counteract adverse yaw from rolling is a much larger design consideration IME.

Dihedral can stop your craft rolling but it requires perfect yaw stability, because i think dihedral can increase the tendency to roll into a yaw.   In practice i've found that no matter how much rudder area you add, there's always some yaw going on which means roll stability won't be there either, despite dihedral.

The only aircraft which truly fly straight are the ones that have angled wings to make lift on prograde,  are being flown on prograde, and that have dihedral.

I've found that once i get above 10km they track perfectly straight and don't need roll/heading corrections.   I suspect that's because the Prograde assist is keeping sideslip and yaw to zero actively. Prograde assist doesn't care about roll and won't try correct it, but the dihedral is able to do so thanks to the lack of yaw.

Note, even with these aircraft, there is some wandering at low altitudes.  I suspect that's just a product of the chronic Phugoid tendency they exhibit down low when flown on Prograde - the nose is constantly rising and falling which seems to introduce rolls too.

11 minutes ago, foamyesque said:

What, that you have more lever arm to work with, and consequently you can get more roll from the same deflection, thereby (somewhat) reducing adverse yaw? Of course. Is there more to it I'm unaware of?

Not sure it's that easy.

If your aileron is out near the wing tip, it has more lever arm to roll the aircraft.  Unfortunately, this also means it has more lever arm to make adverse yaw.

What might help is using really big ailerons then tweaking their control authority way down.  If you're flying one wing low and need 5kn to pick it up (for example),  you could deflect the smallest aileron to 30 degrees or  a much bigger one to 5 degrees to get that force.    The thing is, after 10 degrees angle to the airflow, drag starts to rise exponentially while lift tails off,  so the bigger aileron will achieve the effect for less adverse yaw.  

Also having really big vertical stabilizers - passive yaw stability - might help.    Ultimately, i've found it's best if i'm flying on prograde lock. since that automatically makes rudder inputs to correct yaw for you.     Stability Assist is useless for this, it just tries to hold the same heading with yaw inputs , so it actually causes sideslip to get worse the longer it is left on.

 

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10 hours ago, Palaceviking said:

All of this fantastic info and no-one has mentioned dihedral stability? 

The way dihedral mostly works IRL is that real wings lose lift with increasing dihedral angle. So in a roll, one wing is gaining angle and losing lift, and the other wing's dihedral angle is decreasing, so it is gaining lift. Yes, there is also a small effect from raising the CoL above the CoM IRL from dihedral, but it's a small effect.

But KSP does not model the decrease in wing lift from dihedral angle. So it's really a totally worthless thing to do in KSP. All dihedral does in KSP is cause your wings to fight each other, by creating "lift" forces in opposite directions. In KSP, the only roll-stability effect you get from wings is the effect from having your CoL above your CoM. Other than that, you should always make your wings level. You can make a biplane if you like, but dihedral is worthless.

 

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6 hours ago, bewing said:

The way dihedral mostly works IRL is that real wings lose lift with increasing dihedral angle. So in a roll, one wing is gaining angle and losing lift, and the other wing's dihedral angle is decreasing, so it is gaining lift. Yes, there is also a small effect from raising the CoL above the CoM IRL from dihedral, but it's a small effect.

But KSP does not model the decrease in wing lift from dihedral angle. So it's really a totally worthless thing to do in KSP. All dihedral does in KSP is cause your wings to fight each other, by creating "lift" forces in opposite directions. In KSP, the only roll-stability effect you get from wings is the effect from having your CoL above your CoM. Other than that, you should always make your wings level. You can make a biplane if you like, but dihedral is worthless.

This doesn't sound right to me.

6 hours ago, bewing said:

KSP does not model the decrease in wing lift from dihedral angle.

Are you saying KSP wings produce the same lift no matter the dihedral angle? What if I make a craft with 45° dihedral? Or 90°? Will it still fly if both wings are pointing straight up like a vertical stabilizer?

What you said doesn't make sense. Lift has to decrease with dihedral in KSP, otherwise a craft would keep flying straight no matter the angle of roll, because if there's no change in wing lift with dihedral, then there'd be no change with roll either.

I don't disagree that dihedral seems much less effective in KSP, than RL, though.

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8 minutes ago, Val said:

Are you saying KSP wings produce the same lift no matter the dihedral angle? What if I make a craft with 45° dihedral? Or 90°? Will it still fly if both wings are pointing straight up like a vertical stabilizer?

If your KSP wing is mounted at 90 degrees, and it has 5 degrees of AoA from front to back, it will produce the same amount of "lift" sideways as it would if it were mounted horizontally (same AoA), and producing that same amount of lift up. That is, the lifting force of the wing is always normal to the plane of the wing, of course.

Whereas, a wing mounted at 90 degrees IRL will produce a lot less sideways lift that one mounted horizontally with the same AoA.

 

Edited by bewing

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29 minutes ago, bewing said:

Whereas, a wing mounted at 90 degrees IRL will produce a lot less sideways lift that one mounted horizontally with the same AoA.

No. That is wrong.

If that was true then a propeller blade would produce different amount of thrust, depending on where it was in it's circling of the propeller axis. And I'm very sure that's not the case.

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Dihedral based roll stability IRL works through a sideslip-AoA interaction, and KSP does model those forces, so it does, in fact, contribute to stable flight. It also raises the CoP for the same wing root placement.

Edited by foamyesque

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16 hours ago, Val said:

No. That is wrong.

If that was true then a propeller blade would produce different amount of thrust, depending on where it was in it's circling of the propeller axis. And I'm very sure that's not the case.

Not sure if this is the same thing you guys are talking about, but propellers actually do produce uneven thrust at nonzero angles of attack.

ap2Or.jpg

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On 07/12/2016 at 3:12 AM, KevinW42 said:

Not sure if this is the same thing you guys are talking about, but propellers actually do produce uneven thrust at nonzero angles of attack.

ap2Or.jpg

It is not the same. The picture shows uneven thrust due to different AoA of the propeller blades on each side, caused by a craft flying with the fuselage at high AoAEdit: It's know as P-factor. More info here.

My statement was that no matter how the wing/propeller blade is oriented, a specific AoA always creates the same lift/thrust.

Edited by Val
Grammar

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