Problems with Laythe Spaceplane

[jost]

Hello,

 

I'm trying to construct a Laythe spaceplane for my Jool5. It works somehow: It's able to make orbit on Kerbin thus it should be able to orbit on Laythe too. 

When I try do land from Kerbin or Laythe orbit at some point it flips over. I tried to follow the Basic aircraft construction tutorial but I must missed something or can't pilot.

Any ideas folks?

Craft file: https://drive.google.com/open?id=1V7NJG_05gW_7XHkl9rJnanHxgVKVC-lU 

[18Watt]

The most common cause is your center of mass has shifted rear-wards as you burned fuel.  The craft was stable with full fuel, but as you burned fuel the center of mass moved aft.

There are several ways to deal with this.  One is to design a ship (plane) in which the center of mass doesn’t move.  In other words, the center of mass stays in the same location wether the ship has full fuel, or is completely empty.  Keeping most of the fuel in the ‘middle’ of the ship, or centered around the center of mass is helpful.

Another way to overcome that issue is to move fuel once you are in orbit.  Before entering the atmosphere, move some fuel from the rear tanks to the front tanks.  How much?  Good question.  If you enter the atmosphere, and still lose control, you didn’t move enough fuel forward.

On the other hand, if you move too much fuel forward, the ship can become too nose-heavy to control with the elevator.

Start by looking at your center of mass and center of lift in the SPH.  Then take most of the fuel out of the craft, and look again.

[Foxster]

The craft looks stable regarding fuel. The dry CoM is actually forward of the wet. 

First guess: the airbrakes are forward of the CoL and close to the CoM. That might cause some stability problems when deployed. 

I'll have a fly and see what happens...

I think it's draggy at the front. That blunt front end, the RCS, ladder, canards and Divertless Supersonic Intake are all adding to the drag at the front end. 

You will also find it flies better if you move the tailfin back, plus turn off roll and pitch on it. Similarly on the canards and flaps if you turn off yaw.  

Questions: 

What is the Whiplash for? 

Why so many intakes?

Update:

Yup, I'd say it was too draggy at the front. I tweaked a few things to streamline it, plus a few more bits and pieces, and it flies fine now...

Craft file: https://www.dropbox.com/s/owm2lxjf3mqrdkg/LaythePlaneMk1 Fox 2.craft?dl=0

 

Edited July 22, 2019 by Foxster

[Aegolius13]

19 hours ago, Foxster said:

I think it's draggy at the front. That blunt front end, the RCS, ladder, canards and Divertless Supersonic Intake are all adding to the drag at the front end. 

I've also noticed the Science Jr. is very draggy as of late, whether it's open or closed.  Almost wonder if it's a bug.  But the placement of said part could be contributing to the drag issue.  Putting it near the back as in @Foxster's revamp, should improve stability.

[jost]

On 7/22/2019 at 10:50 AM, Foxster said:

The craft looks stable regarding fuel. The dry CoM is actually forward of the wet. 

First guess: the airbrakes are forward of the CoL and close to the CoM. That might cause some stability problems when deployed. 

I'll have a fly and see what happens...

I think it's draggy at the front. That blunt front end, the RCS, ladder, canards and Divertless Supersonic Intake are all adding to the drag at the front end. 

You will also find it flies better if you move the tailfin back, plus turn off roll and pitch on it. Similarly on the canards and flaps if you turn off yaw.  

Questions: 

What is the Whiplash for? 

Why so many intakes?

Update:

Yup, I'd say it was too draggy at the front. I tweaked a few things to streamline it, plus a few more bits and pieces, and it flies fine now...

Craft file: https://www.dropbox.com/s/owm2lxjf3mqrdkg/LaythePlaneMk1 Fox 2.craft?dl=0

 

Didn't had any time to play Kerbal due to real life. I tried to load your craft but Kerbal said: "missing part modules: ModuleCrewRequirement ModuleCrewAssignment PartTemperatureState"

[AHHans]

The center-of-lift / center-of-drag of a plane actually changes at different airspeed / air pressure combinations.

At low airspeed and high pressure, the non-lifting-surface parts of you plane have comparatively little drag. So the point where the combined aero-forces push on your plane is mostly given by the center-of-lift of the actual  lifting-surfaces (you wings). This is what is actually shown in the editor. But at high (hypersonic) airspeed all the parts have high drag, while low air pressure means that the lift forces on the lifting-surfaces are low. That means that the aero-forces on your plane are dominated by drag. So if you have a plane with lots of non-lifting-surface parts in the front and fewer, but heavier parts in the back (e.g. engines ) then the center-of-lift / center-of-drag will be further in the front of your plane during re-entry.(*) If your plane is sturdy enough then you can just let it tumble until it becomes sub-sonic. Or, if you have some fuel left, you can pump all fuel as far to the front as possible (and pump it back if the plane becomes too nose-heavy at low speeds).

P.S. (*) Or during the later stages of the ascent of your spaceplane. My first spaceplane SSTOs tended to flip out of control at around the time in the ascent when I switched from air-breathing engines to rockets.

[jost]

On 8/11/2019 at 7:46 PM, jost said:

Didn't had any time to play Kerbal due to real life. I tried to load your craft but Kerbal said: "missing part modules: ModuleCrewRequirement ModuleCrewAssignment PartTemperatureState"

@Foxster Which mod did you use which led to this error message?

[jost]

I tried to use the screenshot of Foxsters Revamp to do some changes to my construction.  After several tries I ended with a craft which is able to land on Laythe and return to orbit. 

Thanks to @Foxster for the inspiration.
I uploaded my craft (note the 13, it's the number of  returns to the drawing board after failure ) If some of you like to do a  trip to Laythe.
Craft file: https://drive.google.com/open?id=1NM_m_wezd1JOpNXlsaepN6RujGLrC_vF

It consists of an deorbit stage and the actual plane. Action groups:

1. Toggle engine of rapiers
2. Switch mode of rapiers
3. Toggle intakes
4. Collect science data to science box (hidden in service bay together with several experiments and a RTG)
5. Cut drogues
6. Cut main chutes

A good pilot propably don't need the chutes, I'm none. Even with chutes I needed several tries to land safe
If you  wonder about the ladder: I used a mod to add a crew hatch to the passenger cabin.  The ladder is to provide easy access from the cabin to the chutes for repacking and the material science  bay for restoring  

Screenie: https://imgur.com/a/jodzbU4 

 

Edited August 15, 2019 by jost