[1.7.3] [Stock/DLC] Flying propellor aircraft etc.

[fulgur]

This guide is based around the propeller parts - specifically, variable pitch propellers. In @Brikoleur's guide to helicopters, he recommended using servos to change the pitch of the rotors, therefore changing the lift and allowing the helicopter to change vertical speed. The new propellers have built in servos. However I have found them a little hard to understand, so I created this guide.

Here is the craft we will be using:

The Lux aircraft is not a very good plane, but it is simple. It has 2 counter-rotating propellers. You can make planes with 1 propeller, but the torque from the propeller will cause the aircraft to roll, which makes it hard to control and also sometimes causes the wings to hit the ground and explode. Either you can use two rotors as I have done, which allows this plane to get up to 200m/s, or you can use a freewheeling servo as described in Brikoleur's guide. My craft has been set up so that [ I ] and [ K ] change the authority limiter of the propellers, changing their pitch.

Now let's look at the craft pre-launch.

Here you can see the propeller blades. The blade is deployed, but the Authority Limiter is at 0. This means that the blade will be at the limiter I set. At the moment, it is 0 - the propeller is perpendicular to how it will rotate. It will therefore cause no lift, but lots of drag. The throttle is also at 0. As I used Axis Groups to tie the turboshaft engines to the throttle, the propellers are not rotating.

You can see that as the propellers rotate, they are producing only drag. This is because they are perpendicular to rotation. However, when I press [K]...

While the propellers are not yet in the optimum position, they have rotated a lot. They are producing little drag, and the yellow and purple lines (representing lift) are long. (You cannot see the yellow lines from the rear propellers as they are inside the body). This lift moves the plane forwards. The plane is accelerating slowly as the propellers are not in the optimum position, however it can get up to 100m/s in around ten seconds as this particular plane is very light for the number of engines.

I have now rotated the propellors into (currently) optimum position. There is little drag and a lot of lift.

You can see here that the lift has decreased. This always happens - I think it is because we are reaching the limit of the props deployed as they are. You can also see that the red drag lines have increased in length as I rotate the blades. There is a balance to be struck between lift and drag, which determines the speed of the aircraft. Often (but not always) decreasing the Authority Limiter will increase speed and drag.

There are a few different (and annoying) things which can happen with your aircraft when flying. Firstly, the propellers can rotate past 90 degrees, and cause increased drag (like at authority 0) or even for the plane to start flying backwards. Secondly, the lift from different rotors can cancel each other out if you set the axis groups wrong. Finally, it is very difficult to set the propellers exactly and this can mean that your plane has some unwanted behaviour.

However, there are advantages to propeller planes. Without a specialised engine like the Wheesley, you can reverse thrust and land quickly. As well as this, the engines are very efficient, and even the electric motors do not draw much power. Finally, they are the fastest (if not the cheapest) option for exploring Eve, Duna and any other modded planets (such as Tekto in OPM) with a non-oxygen atmosphere.

I hope this guide is useful and allows some more people to build their own propeller aircraft. Please do not copy the above aircraft, as it is not very stable and a pain to land. Copy this much better aircraft instead! Link to KerbalX.

Edited April 17, 2020 by fulgur
Apparently [I] makes stuff italic.