Propellers-the hows (i already have the whys)

[Jacob Kerman]

Okay. so im...mildly familiar with propellers in KSP,  and its for the obvious reason- hitting things with them. why else would we have them? but now i want to do the unthinkable- LEAVE THE GROUND! after your done reeling from that suprise plot twist, could someone explain to me...how to do that?

[Kryxal]

First thing to ask is, do you want lift generated by fixed or moving (relative to CoM) surfaces.  That is, plane or helicopter?

[Jacob Kerman]

3 hours ago, Kryxal said:

First thing to ask is, do you want lift generated by fixed or moving (relative to CoM) surfaces.  That is, plane or helicopter?

preferably plane, my good sir

 

like, i was thinking ducted fan behind a plane kinda propeller science

 

[king of nowhere]

5 hours ago, Jacob Kerman said:

preferably plane, my good sir

 

like, i was thinking ducted fan behind a plane kinda propeller science

 

where to start... take a rotor, put some ducted fans on it. for rotor size and blade size and number, go by trial and error: you obviously want the rotor to be as light as possible, but if it can't push the propellers at 460 rounds per minute in the conditions you want to achieve, then it's too small.

the hard thing is blade angle. make sure angle of attack is activated on the blades. put a KAL controller on the plane. use it to control blade angle.

the thing is, propellers generate thrust only with proper blade angle, which changes with speed (and possibly a bunch of other factors that aviation nerds will be able to tell at lenght, I'm not a plane guru). your blade inclination must also change with speed, hence the kal controller to do it in real time.

You also need to keep the aerodinamic interface open, as you see in the image (also featuring beautiful Neidon from the OPM pack). the number you want is total drag, because thrust from the propellers is displayed as negative drag. So in that image I have -22 kN drag, which means that propeller thrust minus actual drag totals -22 kN. And with the kal controller I slide the bar to change the inclination of the propellers, and I watch the drag number, trying to get it as negative as possible. 

Some people prefer to link blade angle to the main accelerator, but all my planes are rocket planes, I prefer to reserve the main accelerator for the rockets. on a purely atmospheric plane it could be easier, though.

How to set the blade angle in the fist place? I go by trial and error. I place the blades, set the angle, then test the plane and see which way thrust is produced. I fiddle with the blade orientation until I get thrust in the right direction. Controller generally goes from 90 to 45 degrees, a 45° arc is more than enough for what you need and gives more fine control.

 

I'm sure the greater experts use more refined means, but my method is robust to be used by someone who doesn't really know the details. All you need to know is to set up the kal controller to change the blade angles, everything else you can figure out with trial and error.

 

[18Watt]

https://xl-logic.com/KSP/Tutorial/UTEM_271.pdf

 

Oh, here's one from me:

 

[Jacob Kerman]

thank ye, and thank ya