If your center of mass is low, your rocket basically becomes a giant lever, requiring only minor force on the top to cause big changes to the entire thing. But for any case goes: The lower your center of lift on your rocket, the more stable it flies, at least to my experience.
+shune84 Oh yeah that is correct when I started this game i was thinking of a building which would be stable when the center of mass is at the bottom, but I found out the hard way it's the other way around on a rocket as the rocket rotates around the center of mass so having it higher on the rocket means that the aerodynamic drag Willoughby the back of the rocket in line with the direction you are traveling meaning it will auto correct which way the rocket is pointing 😎
Why do you not use the SAS prograde lock? Also, how many of those overlays are stock KSP and how many are mods? Can you say the keyboard shortcut in the future?
+Marc Stollmeyer I do use prograde for the gravity turn during launch but as this was an experiment for center of mass and flipping out so didn't use it to eliminate the variable from the experiment ;) The overlay is stock the key is F12 sorry I've mentioned it in a couple of videos so you tend to forget to mention it for new viewers
The number one reason for rockets flipping is the fairing glitch. In 1.0 the drag from the fairing is calculated wrong. You can see with the overlay that its much higher then the fairing itself. In 1.1 it's been fixed and it's much easier to launch rockets with large payloads without flipping.
There is no experiment to do.. The center of mass has to be as high on the rocket as possible. This is to prevent the drag from having a stronger push on top of the rocket. If you have your center of mass low, you are just begging for your rocket to flip around. Remove the fins and you will see that fins are not necessary as long as you keep the mass high. I actually make my first orbit just by locking the upper fuel tanks to prevent fuel to change the mass to the lower part of the rocket, fins are not necessary.
+Ozone Grif That's correct. Most of my rockets don't even have/need fins. (I like Ares 1 style rockets so the COM is high up) This increases the distance between the rocket's natural center of pressure or lift, and the CoM. = More stable rocket more resistant to flipping.
From what I see and understand, if the center of mass is low, the rocket will flip when you turn a little(because of the air flow going now in a different direction than the rocket and pushing on it), if the CoM is very high, the air flow will push too on the rocket, but the surface under the center of mass being much wider, it will tend to prevent the rocket from flipping, making the turn harder. But if the CoM was in the middle, the forces on both sizes would be equal and there would be no resistance/flip when turning. But I guess we also have to consider what you said about the distance between the center of lift/center of mass for the stability. Maybe a point between the top and the middle?
The high CoM doesn't do anything to the drag (Center of Pressure). A better way to think about it is that the center of mass is pretty much going to be where it ends up; there're very few (but not none) things you can do about it. What you CAN do very easily is move the CoP lower with fins. No matter what you do, the CoP is probably going to end up in the capsule at the top; it's about the only thing the air is going to push on to start flipping things out, and when it turns sideways, there's more stuff in the top than in the bottom to push against and make it worse. Spam the bottom stage with fins and you're set. (Or make a very careful ascent keeping inside the prograde marker.)
+Joe Not quite. If you designed your rocket as perfectly as NASA does then you could probably get away with that, but for those amateurs of us we usually have to keep the nose up slightly so the prograde markers doesn't dip down too fast. Getting that center of mass vs. center of lift/drag vs. center of thrust thing just right is tricky, I mean it is rocket science after all. I have yet to design a rocket that could fly itself into orbit, even using MechJeb.
The main problem when flying a rocket, your center of Thrust, Mass and velocity vector have to be aligned. So turns must be executed very slowlyor at slower speeds before reaccelerating. Your expreriment did made me understand why the Space Y heavy lifters mod give rockets that always flip over. Fairings are very big, generated insane drag and the very big booster stages make the CoM very low. Saturn V had a very low TWR at launch so drag was not that high.
+Simas A. The best advise I can give is add control parts to the rocket like reaction wheels, rcs thrusters and winglets at the bottom of the rocket, the more control you have the more you can correct to stop flipping
Turn on advanced tweakables in settings, it will let you pick what tanks drain in what order, so you can make your rocket drain bottom up. Makes it very easy to keep the weight forward
I think you got it right with your experiment this time. I know it's fun to test (it's the most important thing right? ;) ) but you shouldn't base all your conclusions on what you THINK you see. the proof is that you've had wrong conclusions because you didn't realize what was actually going on (flipping due to the fact that your fairing adds a lot of drag to the front). from what I know and my experience with ksp, you should make a difference between having a stable vehicle and a stable flight path. in your case the cause of instability is the angle of attack (angle between your flight direction and your prograde vector). the solution is what you show at the end : a zero lift turn aka a zero AoA turn. with this technique you can even make unstable rockets fly! :) until you reach the thinner upper atmosphere where you can afford some reasonable AoA without flipping. this game is awesome because you learn more everyday! :) keep having fun! :)
+Raphael Taormina Thanks for the awesome comment :) I didn't associate the center of lift with center of mass though I did know the rocket would pivot on the center of mass and center of lift will effect an object like a dart, but it was cool that people corrected me in my flipping rocket video and also I was surprised that the Apollo rocket didnt have a high center of mass this goes to show you need to point prograde as you said to stop flipping and preform a slow turn for your gravity turn and any rocket will get into orbit :D
You are still voice recording while you are playing. Play first, fix a drink, and voice over your recording while not doing anything else. We can absolutely tell you are busy talking because your gameplay sucks, and we can tell you are busy playing because your narration sucks 2:00 "Oh what is that thing called". Separate the tasks, improve your videos.
If your center of mass is low, your rocket basically becomes a giant lever, requiring only minor force on the top to cause big changes to the entire thing. But for any case goes: The lower your center of lift on your rocket, the more stable it flies, at least to my experience.
so weight at the top and thrust at the bottom and less aerodynamic drag from the top some winglets on the bottom for control and should be good?
+shune84 Oh yeah that is correct when I started this game i was thinking of a building which would be stable when the center of mass is at the bottom, but I found out the hard way it's the other way around on a rocket as the rocket rotates around the center of mass so having it higher on the rocket means that the aerodynamic drag Willoughby the back of the rocket in line with the direction you are traveling meaning it will auto correct which way the rocket is pointing 😎
Why do you not use the SAS prograde lock?
Also, how many of those overlays are stock KSP and how many are mods? Can you say the keyboard shortcut in the future?
+Marc Stollmeyer I do use prograde for the gravity turn during launch but as this was an experiment for center of mass and flipping out so didn't use it to eliminate the variable from the experiment ;)
The overlay is stock the key is F12 sorry I've mentioned it in a couple of videos so you tend to forget to mention it for new viewers
+Orb8Ter Thanks!
The number one reason for rockets flipping is the fairing glitch. In 1.0 the drag from the fairing is calculated wrong. You can see with the overlay that its much higher then the fairing itself. In 1.1 it's been fixed and it's much easier to launch rockets with large payloads without flipping.
+Caine Sloan Yeah I didn't realise that at first, I had a lot of comments stating their rockets flipped that's why I made these videos.
There is no experiment to do.. The center of mass has to be as high on the rocket as possible. This is to prevent the drag from having a stronger push on top of the rocket. If you have your center of mass low, you are just begging for your rocket to flip around.
Remove the fins and you will see that fins are not necessary as long as you keep the mass high. I actually make my first orbit just by locking the upper fuel tanks to prevent fuel to change the mass to the lower part of the rocket, fins are not necessary.
+Ozone Grif That's correct. Most of my rockets don't even have/need fins. (I like Ares 1 style rockets so the COM is high up) This increases the distance between the rocket's natural center of pressure or lift, and the CoM. = More stable rocket more resistant to flipping.
From what I see and understand, if the center of mass is low, the rocket will flip when you turn a little(because of the air flow going now in a different direction than the rocket and pushing on it), if the CoM is very high, the air flow will push too on the rocket, but the surface under the center of mass being much wider, it will tend to prevent the rocket from flipping, making the turn harder.
But if the CoM was in the middle, the forces on both sizes would be equal and there would be no resistance/flip when turning.
But I guess we also have to consider what you said about the distance between the center of lift/center of mass for the stability. Maybe a point between the top and the middle?
A year-ish late. But how do you keep COM as high as possible when the heaviest parts are the engines and fuel tanks?
The high CoM doesn't do anything to the drag (Center of Pressure). A better way to think about it is that the center of mass is pretty much going to be where it ends up; there're very few (but not none) things you can do about it. What you CAN do very easily is move the CoP lower with fins. No matter what you do, the CoP is probably going to end up in the capsule at the top; it's about the only thing the air is going to push on to start flipping things out, and when it turns sideways, there's more stuff in the top than in the bottom to push against and make it worse. Spam the bottom stage with fins and you're set. (Or make a very careful ascent keeping inside the prograde marker.)
Why don't you just use the rocket guiding system to stay prograde? Just start the tilt then turn it on right?
+Joe This was a center of mass experiment to see were to place the weight far a more stable rocket.
+Joe
Not quite. If you designed your rocket as perfectly as NASA does then you could probably get away with that, but for those amateurs of us we usually have to keep the nose up slightly so the prograde markers doesn't dip down too fast. Getting that center of mass vs. center of lift/drag vs. center of thrust thing just right is tricky, I mean it is rocket science after all. I have yet to design a rocket that could fly itself into orbit, even using MechJeb.
AaronAlso lol at that, I let mech Jeb fly almost all my rockets into orbit...
+Joe I qualify any mods like mechjeb and kerbal engineer as cheating. CHEATER!
The main problem when flying a rocket, your center of Thrust, Mass and velocity vector have to be aligned. So turns must be executed very slowlyor at slower speeds before reaccelerating.
Your expreriment did made me understand why the Space Y heavy lifters mod give rockets that always flip over. Fairings are very big, generated insane drag and the very big booster stages make the CoM very low. Saturn V had a very low TWR at launch so drag was not that high.
Fun video. Thanks again.
+Jaarbahd Saberhaigen Cheers I enjoy experiments especially in games ;)
No matter what I do the rocket still flips out.
+Simas A. The best advise I can give is add control parts to the rocket like reaction wheels, rcs thrusters and winglets at the bottom of the rocket, the more control you have the more you can correct to stop flipping
Simas A. Try building long rockets and not wide
Turn on advanced tweakables in settings, it will let you pick what tanks drain in what order, so you can make your rocket drain bottom up. Makes it very easy to keep the weight forward
I think you got it right with your experiment this time. I know it's fun to test (it's the most important thing right? ;) ) but you shouldn't base all your conclusions on what you THINK you see. the proof is that you've had wrong conclusions because you didn't realize what was actually going on (flipping due to the fact that your fairing adds a lot of drag to the front). from what I know and my experience with ksp, you should make a difference between having a stable vehicle and a stable flight path. in your case the cause of instability is the angle of attack (angle between your flight direction and your prograde vector). the solution is what you show at the end : a zero lift turn aka a zero AoA turn. with this technique you can even make unstable rockets fly! :) until you reach the thinner upper atmosphere where you can afford some reasonable AoA without flipping. this game is awesome because you learn more everyday! :) keep having fun! :)
+Raphael Taormina Thanks for the awesome comment :) I didn't associate the center of lift with center of mass though I did know the rocket would pivot on the center of mass and center of lift will effect an object like a dart, but it was cool that people corrected me in my flipping rocket video and also I was surprised that the Apollo rocket didnt have a high center of mass this goes to show you need to point prograde as you said to stop flipping and preform a slow turn for your gravity turn and any rocket will get into orbit :D
You're an engineer ? really ? wow ... you could have fooled me ... damn
You are still voice recording while you are playing. Play first, fix a drink, and voice over your recording while not doing anything else. We can absolutely tell you are busy talking because your gameplay sucks, and we can tell you are busy playing because your narration sucks 2:00 "Oh what is that thing called". Separate the tasks, improve your videos.