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Breaking Ground Propellers Help Needed


I am in need of a tutorial on the Breaking Ground Propellers for the Complete Moron. I mean I have been playing around with these but I don't know drek on how to get these <CENSORED> to work and it is really <CENSORED> me off.

Where do I start? How do I get something that will power an aircraft and allow me to fly? What do I need to accomplish this?

I'm completely clueless and getting pretty angry over it. KSP community, you are my only hope...

Edited by thesmokindeist
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IMHO, the reason propellers are so difficult to work with in KSP is due to the designers' attempt to mimic the main physical forces to some level of integrity, which not only is very difficult given the resources available to do so, but is frustrating because it tends to amplify one area of force over others (a similar example is vessels that ignore surface friction and slide all over planet surfaces).

So first, recognize that while the implementation is trying to be 'honest' about the forces involved, it accounts for some forces and not so much others - in reality, an incomplete list of physical forces on/caused by a real propeller include torque, pitch, power and thrust, slipstream effect, p-factor, interference drag, blade-tip speed, ascending/descending blade effects and so on.

Second, again attempting to enforce the "pure" physics of the simulation requires the user's attention to each and every aspect they DO program into the simulation - nothing can be taken for granted. So that's the why.

The how, unfortunately, requires one to delve into many of these forces and the interactions between those forces; @king of nowhere begins to list these but also acknowledges that there are a lot of if's, and's and but's because of the way propellers are implemented in KSP and @Echo__3 has some good videos but due to the breadth of the topic presents a LOT of good information that may or may not be 'absorbed' by the casual viewer.

Like any post addressing a 'simple' topic that is actually complex, I'll try to delineate the likely missteps most folks make with propellers based on what I read as well as my own 'A-ha!' moments...

  1. Propellers need to be thought of as rotating wings
  2. Default placement of propellers does not make them very functional; the default orientation places them at a 90° angle on the motor hub but it should be 0° which can be easily done by pressing the W key prior to left-click placement. This so that when you next select the Deploy button and move the Deploy Angle slider to 0°, now the 0° Deploy Angle coincides with a 0.0 kN thrust in operation.




  3. Default motor configuration is also not very functional and the motor Action Groups should also be changed: Select the Actions tab/button to access the Action Groups and left-click on the motor.
  4. Select the <Brakes Action Group, then click on the motor's Brake  > Group Action to remove it (it will 'jump' to the Selection column and be unassigned).
  5. While the motor is still selected/highlighted, select the <Main Throttle Action Group and then click on the motor's Torque Limit%  > in the Selection column to move it to the Group Actions column.
  6. While still having Action Groups open, click on the <Translate F/B Action Group, then click on one of the propellers, then click on the Deploy Angle  > in the Selection column to place it in the Group Actions. Translate Forward/Backward is normally used to control the RCS system, but because most planes do not have this, it correlates nicely with creating more thrust or less thrust - you can choose any axis group that seems logical to you. My suggestion simply assigns the H key to increasing propeller pitch and N to decreasing propeller pitch. You COULD and likely WILL place a KAL-1000 controller on your airplane to control this function but here I try to focus only on what makes the propellers 'do their thing' and not how to program the KAL-1000 to make life easier. Save this configuration and head out to the runway!!
  7. On the runway, Set your Brakes to keep from rolling away. If we had not unassigned the motor brake in Step 4, we would be scratching our heads during the next step as to why the propeller won't turn...
  8. Right-click on the propeller while it is stationary to open its PAW so you can watch the results of the rest of this mini-tutorial. Opening the motor's PAW is optional but allows you to monitor the Torque Limit with changes in throttle.
  9. Press SHIFT a few times to get the propeller turning (remember how we linked Torque Limit to Main Throttle back in Step 5?) and note that even with the motor turning the propeller, while the Deploy Angle of the propeller is 0° no thrust is produced although the effect of torque IS apparent if you accelerate the propeller too quickly with the main throttle as it will cause your airplane to rotate somewhat.
  10. Tap the H key once and note the change in Deploy Angle as well as the increase in thrust. You now see how the propeller needs to be both powered and angled properly to produce thrust - from here on its just a few nuances that relate back to treating a propeller as a wing.
  11. Intuitively one might think that the more you increase motor torque and deploy angle the more thrust you will produce but this is only partially correct. If you experiment around a little, you will find that when you are static (not moving with brakes set) increasing deploy angle up to around 9° keeps increasing thrust but then beyond that, the thrust begins to drop - this is because, like a wing, you can increase lift by increasing it's angle UP TO the point where it begins to stall and results in less lifting force. ~9° seems to be the magic number for KSP propellers. So NOW you think you've got it wired... set the angle to 9°, you release the brakes, accelerate for takeoff... and the thrust begins to decrease!!



  12. This decrease in thrust happens because while the primary speed of the propeller "wing" is the motor torque, as your airspeed increases, the actual angle that the propeller 'bites' into the air is being reduced due to the forward motion! So as you accelerate, to maintain that ~9° angle, you actually need to INCREASE the Deploy Angle - and this is reflected in the propeller's PAW under that label (Angle of Attack); you will see that the actual deploy angle to maintain an optimal angle of attack varies with your airspeed. Keep in mind that the opposite of this is true as well, i.e. after being at cruise speed/high deploy angle, you will lose propeller efficiency and thrust ability as you slow if you don't also reduce your deploy angle as the blade will be stalled at slower speeds with high deploy angle. [BTW, THIS is the reason you would incorporate a KAL-1000 into your airplane so that you can easily change pitch with throttle... but that's for another diatribe, er, I mean mini-tutorial!]

Hope the descriptions help. Good luck!

Edited by Wobbly Av8r
Always clarifying and refining... NOW with images!
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I've made extensive use of them, but they are quite complex. you need to do 3 main things

. first thing to discuss is angle of attack. if your propeller blades are flat, you won't get any propulsion. in fact, they need to be angled just right, and the right angle changes with air speed. for this, you need to tie your blade angles to a KAL controller, and move the controller to change the blade angle during flight.

i guess you'll also need instructions on the KAL controller... it's easier to do than to say it. You place the KAL anywhere on your vehicle, then you select it and open the editor. Now from the editor you go in the actions menu, and you select the blades. you select the angle of attack, and you put the two extreme values you want (you will have to experiment with those, they depend on how you made the propellers). Now you can open the KAL and mode the bar on it, and it will move all the propellers. Use f12 to activate aerodinamics show during flight, it will show you a bunch of blue, red and purple lines; you are looking at the purple ones, you want them to point forward. move the KAL to make them do so. if they always point backwards, you got the angle inverted.

- Also, one propeller will cause your plane to spin. You need two propellers rotating in opposite directions, so their momentum will cancel

- to accelerate the propellers with the normal accelerator, you have to go in the action menu, under "main accelerator", and select the propellers and their torque.

I don't feel like i'm doing a good job of explaining. It's easier done than said. unforrtunately, very few people in this forum understand propellers, so not many to explain. feel free to ask clarifications

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On 12/24/2020 at 1:39 AM, thesmokindeist said:

Where do I start? How do I get something that will power an aircraft and allow me to fly? What do I need to accomplish this?

How about this?

Extremely detailed, well written tutorial with illustrations and so forth.

My own observations, boiled down to a few easy bullet points:

  • Propellers work better if you have short blades on a wide hub.  Use the wide-hub version of rotors, not the narrow-hub, it makes a huge difference.  And I find that the props work better if the blade length is smaller relative to the hub diameter-- for example, I get excellent results with the "fan blades" instead of "propeller blades", because they are shorter relative to their amount of lift.
  • Propellers need different blade pitch at different speeds.  The faster the aircraft goes, the steeper the blade pitch needs to be.  You don't need to muck with this if you just want a very basic aircraft that flies at fairly low speeds, but if you're wondering "why won't my plane go faster than 100 m/s" or the like, this is why.
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