Right

Wing Lift & Wing Lift to Drag Ratio Charts

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I have experimentally determined the lift curve and the lift to drag ratio for given AoAs. Please note that these reflect ONLY the values for wings.

ua5Tl9Y.png

  • Each marker represents a data collection point.
  • Don't read too much into the trend line, its just a visual aid.
  • Low speed measurements taken at 72m altitude, high speed measurements taken at 65,000m altitude.
  • High speed measurement is mach 7.027 (Adjusted for orbital velocity & air density).
  • The right side Y-Axis is associated with the red high speed line. Values are smaller than low speed measurements due to altitude.
  • Lifting force measurement is per 10 units of lift area.

Just for clarity, that is two overlapping lines. This graph tells us two things:

1.) The relationship curve between AoA and Lift remains the same at all speeds and altitutes,

2.) Maximum lift generation is achieved at 30°. If you're on a fatal trajectory like heading for the ground or the VAB, get to 30°. Only go above this if you're intent is to slow down (E.g.; flare for landing).

q3XxxLH.png

Design Methodology Inference:

Crafts optimized for low speed flight should have their wings pre-tilted to 2° while crafts optimized for high speed flight should have their wings pre-tilted to 5°.

Piloting Methodology Inference:

None - This graph does not account for non-wing (body) drag. AoA L/D ratios will vary from craft to craft.

  • Mods used: MechJeb, AeroGUI, BetterTimeWarp, Part Angle Display.
  • Measurements were first taken of both test crafts without wings to offset any affects the body had.
  • For each speed, measurements were taken precisely at wing AoAs: 0°-5°, 10°, 15°, 20°, 22.5°, 25°, 27.5°, 30°, 32.5°, 35°, & 40°. Vessel body AoA remained at 0°...

wWN3Iph.png

  • Wing AoA was set in the SPH using Part Angle Display...

FCkkGjX.png

I know its not groundbreaking or anything, but I've been assembling this post for a few weeks, so it is as precise and appropriate as I can currently conceive. Please do post critiques if you see a possible issue or way to improve, or just have a question. For more detailed information and additional graphs, download and open excel document (Google viewer is weird).

TL;DR Summary:

Before attaching wings to your spaceplane, its generally a good idea to press shift+"S" once to tilt your wings to 5°.

Edited by Right

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Odd, i have actually experimented with the AoA quite a bit and ive come to a different conclusion. Anything above ~3 degrees seems to give me major flight problems. For one, drag seems to skyrocket when i go above 3 degrees (which is very very bad for efficiency), and two, if you have a highish AoA, your plane is not very consistent with its flight vector, at low speeds it doesnt have enough lift, and at higher speeds (500-800), you dont fly straight either as too much lift.

I may be wrong and will defenetely experiment with this, but at least for my designs that most have extremely low TWR, and SSTL capabilities (single stage to laythe, and above 7000dV in LKO), ive found 2-3 degrees to be the best, any less, and your body drag makes it impossible to break mach1, and more, and your wing drag makes it impossible to break mach1 (not to mention that it gives a very non straight flight, sometimes you need to angle nose very high, other times you need to angle nose down to fly straight, leading to more body drag).

I know my results are not universal (you dont see many people designing 40 ton fighters that can carry 2 tons of missiles and get 7000dV in LKO, capable of landing on laythe, bop and pol in one trip and returning to kerbin with 0 refueling), and that most likely more conventional planes might benefit from higher angles, but sofar my testing has shown that you want to be between 2 and 3 degrees, and if you are lifting too much, decrease number of wings, and too little, increase wings or cut mass.

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Odd, i have actually experimented with the AoA quite a bit and ive come to a different conclusion. Anything above ~3 degrees seems to give me major flight problems. For one, drag seems to skyrocket when i go above 3 degrees (which is very very bad for efficiency), and two, if you have a highish AoA, your plane is not very consistent with its flight vector, at low speeds it doesnt have enough lift, and at higher speeds (500-800), you dont fly straight either as too much lift.

These reports correspond to wings only. Because they don't include the body, the results don't really recommend any particular methodology during piloting, rather they recommend a methodology for wing inclination placement during construction. Did your AoA drag tests include the body?

These figures only recommend high AoAs (30°, first graph) if you're in an emergency. Otherwise, they recommend shallow AoAs for efficiency (2° to 5° depending on speed and altitude). Of course you don't always need the extra lift, but then you're typically better served cutting out a bit of wing and saving the mass and drag.

ive found 2-3 degrees to be the best, any less, and your body drag makes it impossible to break mach1, and more, and your wing drag makes it impossible to break mach1 (not to mention that it gives a very non straight flight, sometimes you need to angle nose very high, other times you need to angle nose down to fly straight, leading to more body drag).

Hmm, wouldn't a decrease in AoA (say from 3° to 1°) decrease your body drag? Also, a refined and efficient ascent profile will deviate from 0° AoA as little as possible (in both amount and frequency). Some planes can deviate as little as 2° throughout their ascent.

I know my results are not universal (you dont see many people designing 40 ton fighters that can carry 2 tons of missiles and get 7000dV in LKO, capable of landing on laythe, bop and pol in one trip and returning to kerbin with 0 refueling)

If you're going to place a flag on laythe, you're going to need missiles right? LOL

...and that most likely more conventional planes might benefit from higher angles, but sofar my testing has shown that you want to be between 2 and 3 degrees, and if you are lifting too much, decrease number of wings, and too little, increase wings or cut mass.

The idea is that these figures be universally applicable. Thats why the data was sadly limited to just wings (rather than the whole plane, which would be more practical but much more variable).

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I tend to fly a particular AoA rather than particular pitch angle - AoA being the difference between the orange -W- symbol and the yellow prograde marker. AoA below target, more back pressure on stick, above target, less back stick. Airspeed comes out at whatever it comes out at, based on altitude and weight. I try to avoid the sound barrier however, and will pitch up to 10 AoA to postpone exceeding 240 as long as possible,then pitch down to 2 AoA to accelerate through to 380+ ASAP. Pitch angle will vary with TWR and AoA, but I never pay any attention to it. I only target AoA.

Good to know what the optimums are, OP !

Going hands off, with SAS and trim, I've noticed that my airplanes also tend towards a constant AoA, but the flight path is **NOT** constant, settling into a gentle phugoid oscillation with a period of about a minute. Real aircraft do that too, so it's a win for the game's physics.

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I try to avoid the sound barrier however, and will pitch up to 10 AoA to postpone exceeding 240 as long as possible...

Thats interesting. I haven't looked too much into this yet, but I've seen a variety of opinions on this. Some prefer to go at slower speeds to avoid unnecessary drag. Other seem to operate as if the losses of accelerating to Mach 1.1+ are made up for by being able to ascend steeper and with higher TWR. Not to mention rear drag (Sideflow drag/laminar flow stand in) falls off fast at Mach 1.

I9OpiAe.png

X axis is Mach, Y Axis is rear drag factor

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On 11/6/2015, 2:58:30, Right said:

Thats interesting. I haven't looked too much into this yet, but I've seen a variety of opinions on this. Some prefer to go at slower speeds to avoid unnecessary drag. Other seem to operate as if the losses of accelerating to Mach 1.1+ are made up for by being able to ascend steeper and with higher TWR. Not to mention rear drag (Sideflow drag/laminar flow stand in) falls off fast at Mach 1.

I9OpiAe.png

X axis is Mach, Y Axis is rear drag factor

Aha! If I understand this correctly, this explains why I saw negligible effect from removing the Rapierspikes from my Payload Fraction Challenge entry.

I go fast at sea level and climb at a shallow angle. I reach approximately 1000 m/s at 5 km, ~1400 m/s at 10 km, ~1500 m/s at 15 km, and ~1600 m/s at 22 km, where I switch to Closed Cycle.

Which means I pretty much only benefitted from the Rapierspikes during the first 2 minutes, until I passed Mach 1. And the weight saved was more benefit to payload fraction.

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There is an argument for angling wing past the efficient 5% L/D The more Lift your craft is creating the less wing you need.  Half your dV comes from atmospheric acceleration and 1/2 from spaceish acceleration.  Weight of the craft is probably closer to 25%/75% so you could argue paying a little more now in drag will pay off later in LFO mode.  I have not done the actual math but the charts will help with the calculations. Thanks

On 12/3/2015 at 7:48 PM, Val said:

Aha! If I understand this correctly, this explains why I saw negligible effect from removing the Rapierspikes from my Payload Fraction Challenge entry.

I go fast at sea level and climb at a shallow angle. I reach approximately 1000 m/s at 5 km, ~1400 m/s at 10 km, ~1500 m/s at 15 km, and ~1600 m/s at 22 km, where I switch to Closed Cycle.

Which means I pretty much only benefitted from the Rapierspikes during the first 2 minutes, until I passed Mach 1. And the weight saved was more benefit to payload fraction.

My biggest problem with slow to 10km or 15km is you need a lot of wing or AOA to get up there and stay up there.  Wing hurts you on the next 1000 m/s and I have had craft that couldn't brake the sound barrier at 10km because of too much AOA and not enough thrust but could at sea level.

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