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  1. I present to you fine spaceplane enthusiasts... the Kerbal Wind Tunnel mod! We all build spaceplanes to fly faster and higher, but how do you know how fast or how high your current design can go? In the real world of aircraft design, engineers calculate the flight envelope for their aircraft before the first test flight rolls out. This mod runs your spaceplane through a virtual wind tunnel while still in the SPH and predicts its engine and flight performance at every speed and altitude. It also gives you a readout of various performance curves, plotting against angle of attack: ... and velocity: Try it out and start building even better spaceplanes today! You can even output the data to a CSV file to incorporate knowledge of the performance data into a KOS script or the like! Check out this Imgur album for more details on these images and more: https://imgur.com/a/D2i4Fge Download it from GitHub: https://github.com/DBooots/KerbalWindTunnel/releases Or SpaceDock: https://spacedock.info/mod/1927/Kerbal Wind Tunnel Source: https://github.com/DBooots/KerbalWindTunnel Released under the MIT License (with sub-components under their own license). P.S. This mod incorporates a pretty sweet graph-drawing library I made. If anyone's interested in super-simple graphing of data, hit me up.
  2. Applies to KSP versions: 1.0.4 and newer. TL/DR: Among other things, this post explains why your reentering Space Shuttle replica and other winged craft can be unstable even though you built it with Center of Lift (CoL) behind Center of Mass (CoM). It also explains how you can improve general stability of any winged craft with Angle of Incidence (AoI), while at the same time making the craft very SAS friendly, and able to fly straight without SAS. The difference between CoL and Aerodynamic Center Longitudinal Stability, the ability of the aircraft to self stabilize, is attained by having the Aerodynamic Center+ behind CoM. +) The wikipedia explanation for how to calculate the Aerodynamic Center for an aircraft is in the spoiler below. I find it useful to imagine the Aerodynamic Center as an arrow that pulls backward in your craft, relative to it's movement, while the CoL pulls perpendicular to the direction of movement. Lift influences the Aerodynamic Center because, among other things, lift creates drag, but it is only a dominant part while the craft is pointed near prograde. When the craft points away from prograde other types of drag become dominant. CoL actually has less effect on stability, than either Center of Drag and Aerodynamic Center. The CoL actually needs to move to be able to control the craft. To pitch down it needs to move behind CoM. To pitch up the CoL needs to be moved in front CoM. Left and right for roll. And that is exactly what control surfaces do*. You can see this in action in the SPH. Create a simple aircraft mockup, with a handful of structural fuselage. Select the root part and Shift+S, to give it a little AoA, because that's needed for the wings to create lift. Add a couple of small wing panels with control surfaces in mirror symmetry as elevators, either at the front or back. Turn on CoM and CoL and add a couple of larger wing panels with control surfaces in 2x radial symmetry, and place them so CoL is on top of CoM. Using the Rotate Gizmo you can now directly see what really happens to the CoL, when control surfaces move, by rotating them slightly up or down. *) I'll ignore yaw for now. It doesn't contribute to CoL in the same way, because it's a vertical surface. In the SPH yaw is shown as a rotation of the CoL marker. As long as the Aerodynamic Center stays behind CoM, designing your craft with CoL in front or behind of CoM doesn't change aircraft stability much, even in KSP, it just changes how much control input you need to apply, to fly straight. And keeping the Aerodynamic Center behind CoM is the hard part. We can't see the Aerodynamic Center, and for many designs it is close enough to CoL, because large control authority can move the CoL to CoM, so that the CoL works OK as a stand-in for Aerodynamic Center, during design. But the closer then CoM is to the rear of the craft, the worse it gets. The Aerodynamic Center is now significatly in front of CoL. So even if CoL at design time is behind CoM, the Aerodynamic Center might be right on top of CoM or in front of it. This is why most people believe CoL needs to be behind CoM. And with the available information it is the right thing to do. Except it's not always enough. This is also one of the reasons why Shuttles in KSP are so hard to get stable, even when the CoL is far behind CoM. If the Shuttle isn't built to account for the invisible Aerodynamic Center, the mass and wings are often concentrated in the back, but that long fuselage, with lots of drag, pulls the Aerodynamic Center in front of CoM. The result is a lawn darting shuttle, because of CoL too far back, which at the same time spins out of control, because of Aerodynamic Centre being in front of CoM. This has led people to accuse the aerodynamics or the cargo bays of being bugged. Which is understandable given the information available at design time. Angle of Incidence (AoI) Most of us were taught how lift works with pictures like this. Pictures showing lift from cambered wing profiles without Angle of Attack. It's not completely wrong, but it's missing a big part. Most of the lift comes from Angle of Attack, not from the cambered shape. But because of how we were taught, we all have a tendency to imagine wings mounted parallel to the fuselage. On top of that KSP defaults to wings mounted that way. When really we shouldn't. And to make things even worse, KSP does not model wings as cambered profiles. Which means: Wings in KSP always need Angle of Attack to provide lift. By giving the wings "built-in AoA", Angle of Incidence, the craft can be pointed prograde while still creating lift. That reduces fuselage drag greatly. If you mount wings with no Angle of Incidence, then the fuselage has to point away from prograde (the direction of movement) in order to get the wings to create lift. This creates a lot of drag. Even in real life, wings are mounted with incidence. For the same reason: Less drag from fuselage. There is no one AoI that works for everything and it isn't necessarily most optimal to have the fuselage pointed directly prograde, because the fuselage can also contribute to lift (not just Mk2). But in my experience it is always better to have at least 1° AoI than none. Personally I use between 1-5° Angle of Incidence on my designs. I don't have any set rules, but fast craft and/or big wings, needs smaller AoI, and high altitude needs bigger AoI. For SSTO spaceplanes, I've had good experiences with designs that can fly at 0° pitch, without losing or gaining altitude near sea level at 350-400 m/s. That also means the fuselage is close to 0° AoA at the critical phase just above supersonic where drag is highest and the engines haven't reached maximum performance yet. My Solutions Until KSP is able to show the Aerodynamic Center, I use the rule of thumb, that CoM of the craft needs to be as close as possible to midway between nose and tail, and never closer than 2/3 of the craft length towards the tail. Not a very accurate solution and doesn't work for all designs, but it has worked OK for me. Additionally, I design my crafts so the forward most wing has more Angle of Incidence than those behind it. That works effectively as if the elevator has built in pitch, which you can use to move the CoL on top of CoM, without compromising stability. Here are some examples. A stable conventional design (craft file) The conventional straight wing design with CoM forward of the middle. It's a breeze to get stable with CoL on top of CoM, because the Aerodynamic Center is most often behind CoL. Nonetheless, this design has 2° AoI on the main wing to reduce fuselage drag, and no AoI on the tail plane. A stable canard design (craft file) Canard designs, the most prevalent type in KSP, probably due to the way engines are massed in KSP for the LEGO™-modularity and gameplay balance. CoM is often way behind the midpoint, which means the Aerodynamic Center will most likely be in front of CoL. If the CoM isn't too far behind, you might get away with initially designing it with CoL a good bit behind CoM, using CoL as a stand-in for Aerodynamic Center. Once you've tested that it flies stable, you can then add a little more** AoI to the Canard than the main wing, to move CoL up to CoM. If the CoM is far behind the midpoint, see the Shuttle designs. It will now be possible to fly the craft without you or the SAS having to constantly apply pitch-up. It won't reduce drag, but it will make it easier for you or an autopilot to control the craft. The shown craft has a fixed canard with 4° AoI and the main wing has 2° AoI. **) Only very rarely will it be required to have more than 2° difference between main wings and tailplane/canards in KSP. An unstable shuttle design A stable deltawing design (craft file) Shuttles and other pure deltawing designs, are the hardest to balance and require great care taken during design to make sure the CoM doesn't fall too far back. If the CoM is far behind the midpoint, you may be forced to redesign it. It might not be possible to stabilize it without adding dummy weights near the cockpit. Moving the fuel tanks forward might help initially, but instability could re-emerge when the fuel is spent. If the CoM isn't too far behind, you might be able to do something similar as with a Canard designs, by initially designing it with CoL a good bit behind CoM, using CoL as a stand-in for Aerodynamic Center. Again, once you've tested that it flies stable, you can then use the Rotate Gizmo to prebake the elevons with some pitch up, to move CoL up to CoM, to get the craft to fly without you or the SAS having to constantly apply pitch-up. The deltawing jet shown here, has 2° AoI om the main wing and the elevons have been angled up 2° from their default attachment angle. Additionally, the big wing strake has also been angled up 1° more than the rest of the wing. Test showing increased stability with AoI Edit 2016-03-01: Fixed some grammar and clarified a few sentences. Edit 2016-11-03: Added applicable KSP version. Edit 2016-12-01: Added AoI image. (source) Edit 2020-10-21: Format fixes as the new forum software made it apparant, that lots of old style formattings have been mixed over many, many edits.
  3. Assume a rocket is standing on the ground with mass = 1000 kg, and near the top of rocket we apply a force of 100 N for say 1 sec,now assume that this is sufficient to tip rocket over/start tipping over. If the rocket is mid air and accelerating at 30 m/s^2, then likewise how much force would be required to tilt it pi/180 rad or change its trajectory by some degree, please neglect the change of mass due to consumption of fuel because the value calculated with this assumption is going to be a a value higher than required, so that is not an issue. Will the force required mid air be the same as the force required on the ground with no acceleration ?
  4. My suggestion in a fly-by wire avionics system, and I'm not referring to SAS. It could be implemented into stock or made into a mod. This way an aircraft with, say, a broken elevator or missing canard, could fly. Heck, if the system were properly implemented, you could fly an aircraft that is facing backward without the control surfaces going the wrong way, or even fly an inherently unstable aircraft! Some background info (especially for those who don't know what an actual fly-by wire system is): From Wikipedia TL;DR: Instead of the aircraft responding to the stick being pulled (or in this case [ S ] being held) by deploying elevators, the aircraft just calculates what control surface movements would actually accomplish this pitch up. Here's a hypothetical situation to demonstrate what I mean: You're flying an F-16, but (oh no!) your right stabilator isn't moving, no matter what you do. Now, whenever you try to pitch up, it also rolls the aircraft left. A fly-by wire system would accommodate this by also using the ailerons to stop the roll before it even happens. Another example: you're flying an Aeris 3A (modified to be supermanueverable), and now after pitching up to vertical, you have stalled, but your attitude is still nose straight up. You try to pitch back, and the canards face leading-edge up and the elevators face trailing-edge up. When flying normally, this would do the right thing. But because you are falling backward, it causes a new pitch down. Similarly, roll is also reversed! To simplify it further, the fly-by wire system makes it so that the aircraft does what it thinks you want, instead of what you asked for. KSP could gain so much from a fly-by wire system. Even if you don't fly aircraft, it'd still be useful. Vertically landing rockets would be so much easier because you wouldn't have to fiddle with a negative authority limiter on control surfaces.s2
  5. Hello guys i need answers for very important thing for me and many people. I need to remove or decrease to 0 the lifting of B9 Procuderal wings. Because i want to use them us structural parts. I tried to decrease deflection lift coeff to 0 but its not worked. How to remove or decrease to 0 the lifting of B9 Pwings ?
  6. All I wanted was to figure out how much excess thrust I had for my spaceplane along its ascent profile. And then I wanted to know the lift curve slope and level flight AoA so I could program my kOS spaceplane autopilot better. Next thing you know, I'm writing a mod to work in the Spaceplane hangar to calculate flight envelopes, alpha curves, and so much more. And it works, sort of totally! Check out the release thread here: https://forum.kerbalspaceprogram.com/index.php?/topic/177302-ksp-142-kerbal-wind-tunnel/ This shows that the Aeris 4A has a ceiling of about 22km and a max speed at sea level of about 790m/s and a max overall speed of about 1360m/s at around 14km using its air-breathing engines. Then, at 15km and at 964m/s its level-flight AoA is 2.8 degrees and it has 365kN of excess thrust. Great! But now I want to freshen up the GUI (thanks @TriggerAu, but this was clearly designed for Transfer Window Planner ) and add in Lift, Drag, and L/D curves for a given altitude and mach number. I also want to move to using background threads for calculating (right now, I either hang the program for 20 seconds while it calculates that graph or put up with artifacts from my non-thread-safe implementation on the BackgroundWorker, as you can see). First, some credits: Thanks to @linuxgurugamer and @Boris-Barboris. I learned a ton about the aerodynamics model from your Correct COL mod. Also your method of drawing line graphs is coming in handy for the lift curves I'm working on drawing. Thanks to @TriggerAu. I learned a ton about making the graph from your Transfer Window Planner. And thanks to the MechJeb team. I'm using a lot of your tricks to make things more thread-safe.
  7. Hey guys, I've been searching the internet, but haven't been able to find the answer to this. Maybe I'm using the wrong keywords or something, but then I remembered the well informed people on this forum, so I thought I'd ask here. Why do the R-7 family of rockets have their liquid boosters inset? What I mean is, most other rockets I see with boosters just strap cylindrical boosters to a cylindrical core, but R-7/Soyuz have a tapering core that has the boosters far closer together. I assume this makes it more aerodynamic, but how much difference does it actually make, and are there other considerations I don't know about? Thanks!
  8. So I made a plane and I pointed some wing parts downward and upwards and the CoL pointed a bit backwards, what are the effects?
  9. This is a tale of two aircraft. The kerballed version has a flimsy mark 1 cockpit and crew cabin. Both have FAT455 airliner wings, which as you know are made of white chocolate. The kerballed version weighs 30 tons and has a lift rating of 25. This unmanned probe launcher has 10 tons less weight and the lift rating is just 2 less. I have taken screenshots during 2 different launches in the kerballed version, capturing altitude and mach numbers and the verified non exploded status of the airplane. Some data points Alt 24km Mach 4.33 Alt 25km Mach 4.52 Alt 27km Mach 4.65 Alt 30km Mach 4.82 Alt 32km Mach 5.18 Alt 36km Mach 5.71 Alt 40km Mach 5.97 Alt 43km Mach 6.28 Alt 47km Mach 6.67 The second ship, by comparison, is an absolute nightmare. I could not exceed 3.75 mach on the Rapier airbreathing without blowing up. Heat levels remained horrendous even when closed cycle. There was some weird effect where allowing the angle of attack to decrease below a critical value (18 degrees) would make kerbal engineer's critical thermal percentage increase 30% in less than 3 seconds. If i was fast enough to the S key, they'd instantly drop as soon as i nosed up , but obviously there were occasions (10 in fact) where I was not and found myself starting over. The critical part was always the wings, it must have been related to skin temperature because everything changed so quick, and obviously at 43km altitude, raising the nose from 16 to 18 degrees does not produce much of a change in speed or altitude within the space of 2 seconds. I was forced to fly a very inefficient profile with a hugely draggy AoA, massive cosine losses and could not exceed mach 5 till over 50km. Why is one set of wings so much more durable than the other? Are they being shielded by the manned aircraft's longer nose or its forward strakes? I had no idea the thermal model was that sophisticated !
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