Propeller-Plane on Eve is rolling independently

[Jubo_KSP]

Hi everyone,

Build a prop-plane (coaxial) for Eve. Tested in flight at Kerbin, everything worked smoothly and stable there. After landing on Eve, the plane seems to have torque along the longitudinal axis, like from the rotors. But no parts were destroyed during entry and landing. I can cancel the torque by having different rpm  for my two rotors. While testing on Kerbin, there was no torque. 

 

Edit: I found that, with lower torque(33%), the rpm of one of the rotors is not at maximum and is decreasing with higher blade angle. So I can fly stable, when I limit the rpm and have the rpm of the rotors at a certain ratio while also limiting the blade angle... but all that was not present at Kerbin. I'm certain it has something to do with altitude or atmospheric pressure, since stability varies at certain altitudes.

 

Can anybody make sense of this or is it just bugged?

 

 

Edited May 30, 2022 by Jubo_KSP
Gained additional information on the problem

[Lt_Duckweed]

8 hours ago, Jubo_KSP said:

After I first encountered the rolling issue. I tested the same Aircraft on Kerbin and no issue.  This made me think, "ok, seems to be bugged". However, the interesting part was that the effect was in fact inconsistent. It is the biggest with greater angles of attack (of rotor blades) and decreases with altitude. With greater angle of attack, the rev. speed of the rotors is forcefully lowered, for both but more so in the front.

....

But normally, if a plane is stable and flys on Kerbin, it should also (more easily) on Eve, because of it's much denser atmosphere?

This is actually the issue.

Deeper in the atmosphere = higher atmospheric density
Eve = higher pressure, CO₂, both mean higher atmospheric density
Eve = higher gravity, meaning you need more lift to fly, so for a given speed you must fly in denser air than on Kerbin

 

Eve has 70% more gravity than Kerbin, so you need 70% more lift, which means, with the same plane, roughly 70% more drag.

This means 70% more thrust, which means 70% more torque needed.  If the torque needed is higher than the rotors can supply, the rpm starts to bog own.

The inconsistencies of KSP building can mean that the two rotors have different torque to thrust ratios, so one bogs down slightly earlier

Edited May 31, 2022 by Lt_Duckweed

[Vanamonde]

I'm having difficulty visualizing the issue. Can you share pics of your craft? 

[king of nowhere]

On 5/30/2022 at 12:01 AM, Jubo_KSP said:

Hi everyone,

Build a prop-plane (coaxial) for Eve. Tested in flight at Kerbin, everything worked smoothly and stable there. After landing on Eve, the plane seems to have torque along the longitudinal axis, like from the rotors. But no parts were destroyed during entry and landing. I can cancel the torque by having different rpm  for my two rotors. While testing on Kerbin, there was no torque. 

 

Edit: I found that, with lower torque(33%), the rpm of one of the rotors is not at maximum and is decreasing with higher blade angle. So I can fly stable, when I limit the rpm and have the rpm of the rotors at a certain ratio while also limiting the blade angle... but all that was not present at Kerbin. I'm certain it has something to do with altitude or atmospheric pressure, since stability varies at certain altitudes.

 

Can anybody make sense of this or is it just bugged?

assuming there are no construction mistakes or power shortages or anything like that, there are a lot of glitches with propellers. they can get bent in a variety of situations, like being exposed to the harsh aerodinamic conditions of an eve descent, or being accidentally turned on in space. If that happened, then your rotors would behave differently, and this could cause torque

[Jubo_KSP]

5 hours ago, Vanamonde said:

I'm having difficulty visualizing the issue. Can you share pics of your craft? 

https://imgur.io/gallery/ydnspZM

Made pictures from different angles.

[Vanamonde]

Interesting design.

Is the effect consistent? If you have a joystick, make sure it's calibrated and centered. 

[Jubo_KSP]

Thank you.

I'm using a controller (since I'm one of those weird console players).

After I first encountered the rolling issue. I tested the same Aircraft on Kerbin and no issue.  This made me think, "ok, seems to be bugged". However, the interesting part was that the effect was in fact inconsistent. It is the biggest with greater angles of attack (of rotor blades) and decreases with altitude. With greater angle of attack, the rev. speed of the rotors is forcefully lowered, for both but more so in the front.

The issue didn't make the craft unusable though , it flys stable at around 12500 m (over sea level) with blade authority at 57% , front/clockwise rotor at 437rpm and rear/CCW ROTOR at 326rpm with a speed of ~110m/s. I did quite some tweaking and testing...

After all, this craft, despite or because of the issue, provided me quite some fun hours.

I just wanted to check here in the forum, if it's typical for EVE, since it's my first prop-plane or if it's bug or potential damage on the plane. I have to admit, the additional time I spent to design the plane, was saved during the creation of my decent "vehicle".

But normally, if a plane is stable and flys on Kerbin, it should also (more easily) on Eve, because of it's much denser atmosphere?

I also think, it has something to to do with the coaxial rotor design. So will test with a second craft with differently arranged rotors.

[Vanamonde]

I have not encountered this. It sure sounds like a bug. 

[Jubo_KSP]

15 hours ago, Lt_Duckweed said:

This is actually the issue.

Deeper in the atmosphere = higher atmospheric density
Eve = higher pressure, CO₂, both mean higher atmospheric density
Eve = higher gravity, meaning you need more lift to fly, so for a given speed you must fly in denser air than on Kerbin

 

Eve has 70% more gravity than Kerbin, so you need 70% more lift, which means, with the same plane, roughly 70% more drag.

This means 70% more thrust, which means 70% more torque needed.  If the torque needed is higher than the rotors can supply, the rpm starts to bog own.

The inconsistencies of KSP building can mean that the two rotors have different torque to thrust ratios, so one bogs down slightly earlier

Thanks for the detailed explanation, very insightful. I didn't think about the gravity difference...

Will consider this for future missions.