Kerbal University: Wings - Magic and Mundane

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In this episode of Kerbal University, we will take a deep dive into the mechanics of lift in KSP, looking at each of the 3 sources of lift: wing lift, body lift, and capsule lift.
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TIMESTAMPS
00:00 Intro
02:26 Wing Lift
06:14 Wing Incidence
09:49 Body Lift + Capsule Lift
11:21 Magic Wings

[@rocketology1105]

This is the first KSP plane tutorial I have seen that uses angle of incidence - everyone always asks why my planes fly so well, and this is one of the main reasons.

[@lt_duckweed]

It's such a powerful tool, its a shame everyone treats it like it's some kind of super advanced voodoo not to be used by the average player.

[@rocketology1105]

@@lt_duckweed AoI with balanced CoM/ CoL, proper gear placement, and control surfaces set correctly goes such a long way. I am so happy this isn't just another "as long as CoL is behind CoM you are good to go!" videos. Well done!

[@maximpikalev9538]

oh my GOD my EYES HAVE BEEN OPENED

[@NoSTs123]

Ah! this will help me to refine my medium sized SSTO's. I am so grateful for channels that take their time to explain the maths and inner workings of this game, like Mike Abben and yours. Thank you for all this info.

[@Spashium]

Just skipped to the wing incidence testing section because it seemed so interesting, the results are insane! I've always liked to experiment with stuff in KSP, but I never got around to wing incidence. Great video!

[@lt_duckweed]

Yeah, I always say that wing incidence is the single most powerful tool a ssto builder can use! It almost always makes a craft far more efficient, and much easier to fly, since you can just slap prograde hold on it and it will practically fly itself!

[@anthonybury8446]

So very underrated, I love this

[@Tr0lliPop]

Two things about 8:15 Barrel roll is the wrong term. The maneuver you performed there is an Aileron roll. Second of all, how does an aileron roll affect vertical velocity? And what part of the vertical velocity needs to be _managed?_

[@lt_duckweed]

Because the plane is flying hold prograde with wing incidence, lift is always directed upwards from a plane centric frame of reference. By rolling the craft I redirect the lift vector away from surface centric vertical. The reason I do this is to allow gravity to reduce vertical speed, and while the craft is inverted, to have the lift vector contribute to this, reducing vertical speed even faster. The reason I want to manage vertical speed is that if I don't, the craft will pick up a large phugiod en.m.wikipedia.org/wiki/Phugoid For a given designed wing loading for a plane with wing incidence, for any altitude there will be a single airspeed that causes lift to balance gravity. Going faster than this will cause you to begin to gain vertical velocity and the craft, following prograde, starts to nose up. You will continue to gain vertical speed until you climb to you ideal altitude for your current speed, but all the built up vertical velocity causes you to shoot right past you ideal altitude into thinner air that doesn't provide enough lift, eventually causing your vertical speed to drop negative and cause you to lose altitude, with the eventual result of dropping right past your ideal altitude again, leading to a cycle of bobbing up and down. So the overall goal is to moderate and manage the rate of climb so that you stay as close to your ideal altitude as possible, as both you and it slowly climb as you gain airspeed.

[@lt_duckweed]

Putting this all together, a typical efficient ssto will have an ideal altitude of about 0 at around Mach 1, meaning that until you reach Mach one you have to nose up above prograde to get enough lift toaintain level flight, even at sea level. As you pass Mach 1, you can transition to prograde hold and your ideal altitude starts rising. However, this is about the time that the rapier really kicks it into high gear, so your airspeed and thus ideal altitude start rising fast, but your vertical velocity, and thus actual altitude, takes time to build up, so idea altitude runs away from you and the plane will continuously gain vertical speed, usually reaching a peak climb angle of 20-30 degrees. Actual altitude won't catch up to ideal altitude untill you are around 10-12km, at which point you have built up several hundred m/s of vertical velocity, and you overshoot by something like 5-6km, entering a massive phugiod cycle. A single well timed roll during the initial high angle climb will clip off most of this excess vertical velocity right before you finally catch up to you ideal altitude, so that you reach it with a much more sedate rate of climb that more closely matches the rate of climb of the ideal altitude.

[@Tr0lliPop]

@@lt_duckweed Ohh, I see. And I'm assuming the other way of lowering vertical velocity, pitching down, is not recommended because of drag?

[@XHU524-OFSET5]

This disserves more attention, that is so interesting, i dit D not know i could save so much Delta V just by a minute change to wings.

[@KnightofSaintJohn]

If you continue like this, anytime I build another high-performance spacecraft, I'll be able to just come back to one of your videos instead of trying to find some old, and probably long lost, website with the information I need.

[@wxb200]

Breh. You are detailed as ferk! Keep up the good work! Holy Sh*t!

[@proxima_fish]

Epic video

[@IdRatherNotHaveAHandleThankYou]

Thank you for the video! Very easy to understand! Could you perhaps do a video on flag part physics and properties one day? I've seen Stratzenblitz use them in all sorts of ways, and it'd be useful to know exactly what they're capable of.

[@JYF921]

Well done! This channel is underrated

[@dextruax4903]

Great Info as always! Can you do a tutorial on how to get rid of drag with fairings?

[@lt_duckweed]

You are in luck! I don't have an exact eta, but my next video will cover fairings!

[@NickBDesigns]

Great work as always Thanks for getting into the maths for us I still can’t get over the 1000m/s difference in dv

[@lt_duckweed]

It was actually 1000m/s total, for a difference of ~700m/s Still, nothing to sneeze at, especially for doing nothing but use the rotation tool on a couple of parts!

[@NickBDesigns]

@@lt_duckweed ah, thanks for the correction, Between school, work, and family my time on ksp is far and few between but I love learning about all the game has to offer

[@dsdy1205]

Ironically, this might be the final push I need to explore Ferram

[@losttale1]

Why did you put the nose cones inside a fairing instead of a fuel tank?

[@adamlancaster2]

Hey there! Could you go into how the "wing area" is computed for Body Lift parts? You mention that it's drag cube face area times psuedo drag coefficient, but how does that work? Thanks for an informative video!

[@lt_duckweed]

As far as I can recall, it is simply the result of that calculation for each face, with each face then calculating body lift on its own based on the angle of each face, then summing for the body lift of the whole part.

[@JYF921]

Also how do flag wings work?

[@lt_duckweed]

The way flag wings work is rather interesting. In 1.10 and 1.11, flags had drag cubes, but the drag portion of the drag cube was forcibly disabled, which meant that only the body lift component was left. So they had only lift, and no drag at all. In 1.12, they were changed, and now they have no lift or drag.

[@JYF921]

@@lt_duckweed thanks! Now I don’t have to worry about spamming flags on my plane. It might be good idea to mention how there’s no airfoil in ksp so the only lift you get is the air deflected downwards and not because air flows faster below the wing creating an indifference in pressure

[@danieldc8841]

Hi, can I ask for the source for all these curves? I'd like to have a go at making a curve for ideal AoA for a given mach number, then use KOS and a lookup table to control the wings with motors. Any idea what the drag is like on the rotors? I wouldn't be against turning it off alltogether.

[@lt_duckweed]

All the lift and drag curves are stored as sets of key value pairs in physics.cfg in the base folder of your KSP install

[@martijn9568]

Hmm, wasn't expecting these parts to still have a stall modeled since they seemed effective way past the critical AoA for most real life airfoils. By the way, how did you get all this data. I'm guessing you plotted the curves that can be found in the part data. Is that correct?

[@lt_duckweed]

While stall is modeled, it's what you might refer to as a "soft" stall, in that the lift drops of fairly slowly, whereas irl, when you stall, you STALL. And yep, I pulled the info from the physics.cfg file, and there is a spesific set of equations that you use to plot the curves, called cubic hermite splines.

[@martijn9568]

@@lt_duckweed I guess irl you could make a wing design that doesn't have a hard stall, but it probably wouldn't look anything like we have in KSP.

[@bingusbongus9807]

do heat shield wings still work like this as of the current version?

[@lt_duckweed]

as far as I am aware, yep

[@bingusbongus9807]

@@lt_duckweed YAY!! im kinda glad the updates on the game have stalled since it means information isnt going out of date! also thats for the reply so quick!!!