Unstable mk3 shuttle

[foamyesque]

1 hour ago, Geonovast said:

Your CoM and CoL@MysticTURBO are significantly close than his, and your screenshots are only showing re-entry at roughly mach 3.5.  That's not the same as gliding down to land.

 

That just means theirs would be even more stable.

 

And you want pictures from other flight regimes?

Fine by me, as I took some on my way up to Mach 3.5 (wasn't re-entry: was an infinite-fuel powered takeoff, wherein my aerodynamic stability was sufficient to overcome a massive thrust offset):

 

 

Maybe let's try something with a CoM *way* ahead of the CoP?

 

You may note the continued lack of flipping. This is so trivially observable, both IRL and in KSP, that I have no idea where you're getting the idea that a CoP well behind a CoM will lead to flips.

Edited February 7, 2018 by foamyesque

[Geonovast]

6 minutes ago, foamyesque said:

I have no idea where you're getting the idea that a CoP well behind a CoM will lead to flips.

Personal experience in the game of planes nosediving and flipping with a CoL too far back.

 

6 minutes ago, foamyesque said:

This is so trivially observable, both IRL and in KSP,

Makes you wonder why all real life aircraft don't put their wings at the very back then.

 

You might notice that I requested is craft so I could specifically see if my concern was actually an issue.  I don't understand why you're so vigilant to prove how right you are.  You're telling me something different than I've seen personally and mentioned many times over, so I simply wanted to check to see if it really was a problem.

[foamyesque]

17 minutes ago, Geonovast said:

Makes you wonder why all real life aircraft don't put their wings at the very back then.

 

There's multiple reasons why not to, starting with the fact that a plane needs to do more than just follow its nose into the ground like a dart or arrow would. I would be very interested in seeing the craft that you claim flip with CoPs well behind their CoMs; I have produced planes that will execute loops by aggressively inclining the tail fins and getting an angled lift vector as a result, but OP's wings are flat.

[Geonovast]

3 minutes ago, foamyesque said:

I would be very interested in seeing the craft that you claim flip with CoPs well behind their CoMs;

If it happens again, I'll try to remember to show it to ya.  I don't remember their exact configuration, I just remember fixing the flipping problem by sliding the CoL forward.

[Mr. Peabody]

2 hours ago, foamyesque said:

 

That just means theirs would be even more stable.

 

And you want pictures from other flight regimes?

Fine by me, as I took some on my way up to Mach 3.5 (wasn't re-entry: was an infinite-fuel powered takeoff, wherein my aerodynamic stability was sufficient to overcome a massive thrust offset):

 

 

Maybe let's try something with a CoM *way* ahead of the CoP?

 

You may note the continued lack of flipping. This is so trivially observable, both IRL and in KSP, that I have no idea where you're getting the idea that a CoP well behind a CoM will lead to flips.

Ah, but the center of thrust is compensating for the fact that the centers of mass and lift are far apart. Note the engines mounted exactly on the center of mass.

[Geonovast]

35 minutes ago, The Dunatian said:

Ah, but the center of thrust is compensating for the fact that the centers of mass and lift are far apart. Note the engines mounted exactly on the center of mass.

The throttle is at zero though, and KER is reporting 0 thrust.

[foamyesque]

1 hour ago, The Dunatian said:

Ah, but the center of thrust is compensating for the fact that the centers of mass and lift are far apart. Note the engines mounted exactly on the center of mass.

 

Uh, 1. I intentionally took all the screenshots at zero thrust (well, almost zero -- the Junos take a bit to wind down); 2. The engines on the shuttle have a massive pre-built gimbal, so the thrust vector does not go through the CoM, and so required the aerodynamic stability to fly at all; 3. The Juno engines aren't mounted on the CoM either, they're somewhat below it. You can see that because with just the tiny bit of thrust left, KER is still reporting thrust torques.

Edited February 8, 2018 by foamyesque

[Kuskejens]

On ‎08‎-‎02‎-‎2018 at 1:52 AM, foamyesque said:

 

Uh, 1. I intentionally took all the screenshots at zero thrust (well, almost zero -- the Junos take a bit to wind down); 2. The engines on the shuttle have a massive pre-built gimbal, so the thrust vector does not go through the CoM, and so required the aerodynamic stability to fly at all; 3. The Juno engines aren't mounted on the CoM either, they're somewhat below it. You can see that because with just the tiny bit of thrust left, KER is still reporting thrust torques.

Good example, I agree with you.

This guide has helped me a lot when I struggled with how to put together a stable spaceplane. I'm by no means good at it yet, but the concepts are sound.

Just take a look at the first part that covers balance, where the author writes:
"Basically, CoL in front of CoM = flip happy. CoL too far behind CoM = lawn dart." 

[Capt. Hunt]

the thing you should know is that Mk3 was designed for the looks, they weren't really designed to be balanced when assembled as a shuttle.

[ajburges]

On 2/7/2018 at 1:28 PM, Geonovast said:

Personal experience in the game of planes nosediving and flipping with a CoL too far back.

Flipping and nose dives are caused by opposite problems. A marginally stable craft could flip from tans-sonic CoL migration and be stable sub-sonic, but any control surfaces should have sufficient authority to avoid lawn darting.

The only time a CoL that far back would produce torque off prograde is if there was wing incidence.