Bill --
Your recent post and about radial balance and your paper at Reaction Research Society: Static Balancing of a Payload were very interesting.
I am a recent REBAR -- I used to fly rockets in the 1990s with an axial accelerometer and a pressure sensor.
In the old days. I analysed what data I could but I was only seeing events and effects in one dimension.
I left the hobby in 2000 and just recently returned and the newest flight computers and simulators are a whole new world for me.
I've got a lot to learn, relearn and unlearn.
Something I would like to learn more about is the importance of balancing the masses in the rocket, both radially as well as longitudinally,
I was once long ago a 'cable monkey' for a very talented engineer who ran a vibration analyser on rotating equipment and I understand how important radial balance can be in rotating systems.
For example a turbine engine needs to be balanced about the roll axis, otherwise it will fail catastrophically in short order.
The tires on my car need to be rotationally balanced or they will fail prematurely and so on.
You mentioned that a bullet deliberately out of balance will cone.
But each if these systems are already rolling.
My skills are not at the same 'stage' as @JimJarvis50 and his flights with active guidance ( see I could use just a little guidance for an amazing thread ) where Jim has successfully controlled tilt and roll via active guidance.
I do try to eliminate roll due to unbalanced aerodynamic forces in my rockets as much as possible by installing the fins straight and by making the airfoils as consistent as possible and other than rail giudes, I also try to avoid any 'warts' on my airframes which might introduce an imbalanced aero forces.
But in addition to aero forces, something I always wondered but that I was never able to put my finger on are the effects of radial mass imbalances along the axis of the rocket that might affect tilt and roll.
This is why your recent post was interesting to me and it reminded me of some very old questions I've wondered about.
I understand why a statically stable rocket flying off-vertical will do a gravity turn ( tilt ) -- gravity acts down thru the CG toward the center of the earth and the aero forces act in more-or-less the opposite direction, normal to the axis of the rocket thru the CP causing the ever-increasing turn as the rocket is flying.
But I don't have a feel for the other non-aero roll forces ...
If I launch a rocket that is aerodynamically radially symmetrical, which has no inherent tendency to roll due to aero forces, but the rocket's mass is radially imbalanced, will the rocket naturally tend to roll due to the radial mass imbalance ?
If not, then does radial mass balance matter ?
If so, then once roll is introduced, I can see where coning would follow.
Other than parachutes, shock cords and dog barf, my payload is an AV-Bay.
These days the electronics are very small and lightweight and LiPo Batteries weigh 'nothing' compared to the batteries from the old days.
None-the-less, the mass of the AV-Bay payload can be significant, especially in a small rocket.
I do try to locate the (x,y) plane of the accelerometer and gyro along a longitudinal center plane of the rocket ( usually purpendicular to the launch rail ).
But that is more for the quality of my data than for any other reason.
I've wondered this: Should I also try to locate my AV-Bay near the longitudinal center of gravity of the rocket ?
That point along the rockets length is a 'moving target' so maybe it should be located at the CG after burnout where the rocket spends most of it's flight time ?
But then if I fly motors with different burnout masses, that pursuit becomes impossible so I've settled on locating the AV-Bay where dual deployment works best.
But does it matter ?
I am running out of time this morning before work ... more to come ( I hope ) !
Thanks Bill !
-- kjh
EDIT: I 'lost' this post but then found it and I accidentially re-posted it ... sorry
Your recent post and about radial balance and your paper at Reaction Research Society: Static Balancing of a Payload were very interesting.
I am a recent REBAR -- I used to fly rockets in the 1990s with an axial accelerometer and a pressure sensor.
In the old days. I analysed what data I could but I was only seeing events and effects in one dimension.
I left the hobby in 2000 and just recently returned and the newest flight computers and simulators are a whole new world for me.
I've got a lot to learn, relearn and unlearn.
Something I would like to learn more about is the importance of balancing the masses in the rocket, both radially as well as longitudinally,
I was once long ago a 'cable monkey' for a very talented engineer who ran a vibration analyser on rotating equipment and I understand how important radial balance can be in rotating systems.
For example a turbine engine needs to be balanced about the roll axis, otherwise it will fail catastrophically in short order.
The tires on my car need to be rotationally balanced or they will fail prematurely and so on.
You mentioned that a bullet deliberately out of balance will cone.
But each if these systems are already rolling.
My skills are not at the same 'stage' as @JimJarvis50 and his flights with active guidance ( see I could use just a little guidance for an amazing thread ) where Jim has successfully controlled tilt and roll via active guidance.
I do try to eliminate roll due to unbalanced aerodynamic forces in my rockets as much as possible by installing the fins straight and by making the airfoils as consistent as possible and other than rail giudes, I also try to avoid any 'warts' on my airframes which might introduce an imbalanced aero forces.
But in addition to aero forces, something I always wondered but that I was never able to put my finger on are the effects of radial mass imbalances along the axis of the rocket that might affect tilt and roll.
This is why your recent post was interesting to me and it reminded me of some very old questions I've wondered about.
I understand why a statically stable rocket flying off-vertical will do a gravity turn ( tilt ) -- gravity acts down thru the CG toward the center of the earth and the aero forces act in more-or-less the opposite direction, normal to the axis of the rocket thru the CP causing the ever-increasing turn as the rocket is flying.
But I don't have a feel for the other non-aero roll forces ...
If I launch a rocket that is aerodynamically radially symmetrical, which has no inherent tendency to roll due to aero forces, but the rocket's mass is radially imbalanced, will the rocket naturally tend to roll due to the radial mass imbalance ?
If not, then does radial mass balance matter ?
If so, then once roll is introduced, I can see where coning would follow.
Other than parachutes, shock cords and dog barf, my payload is an AV-Bay.
These days the electronics are very small and lightweight and LiPo Batteries weigh 'nothing' compared to the batteries from the old days.
None-the-less, the mass of the AV-Bay payload can be significant, especially in a small rocket.
I do try to locate the (x,y) plane of the accelerometer and gyro along a longitudinal center plane of the rocket ( usually purpendicular to the launch rail ).
But that is more for the quality of my data than for any other reason.
I've wondered this: Should I also try to locate my AV-Bay near the longitudinal center of gravity of the rocket ?
That point along the rockets length is a 'moving target' so maybe it should be located at the CG after burnout where the rocket spends most of it's flight time ?
But then if I fly motors with different burnout masses, that pursuit becomes impossible so I've settled on locating the AV-Bay where dual deployment works best.
But does it matter ?
I am running out of time this morning before work ... more to come ( I hope ) !
Thanks Bill !
-- kjh
EDIT: I 'lost' this post but then found it and I accidentially re-posted it ... sorry
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