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hornet driver

hornet driver

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Let me preface this by saying I mainly use it to determine engine size and get a close guestimation on altitude and such, since most of my designs cannot be completely inputted--shape and all--sorrta like comparing a stick figure with a real human--it gets me close enough.First question--I was running some sims on the "Waith" and realized the mass was off by about 80g. This is mainly because of the added structure around the ship that I could'nt simulate. Should I add this in on top of the CG or the CP or somewhere in between? Second question has to do with printing. As I roll the design 90 deg I can still only print the original side profile. Is there a way around this. Thanks
 
After completion, the best way I've found to deal with weight and CG is to set all component weights to 0. Then, after weighing the rocket and determining CG without a motor installed but with a complete recovery system in place, I measure the distance from the front of the main body tube to the CG point. Enter the total weight in the override section for that component along with the CG position.

The effect will be to set a correct weight and CG for the rocket without motors so that when you run sims you'll be using the most accurate lift off weight and stability calculations.
 
Peter Olivola said:
After completion, the best way I've found to deal with weight and CG is to set all component weights to 0. Then, after weighing the rocket and determining CG without a motor installed but with a complete recovery system in place, I measure the distance from the front of the main body tube to the CG point. Enter the total weight in the override section for that component along with the CG position.

The effect will be to set a correct weight and CG for the rocket without motors so that when you run sims you'll be using the most accurate lift off weight and stability calculations.
Click to expand...

That makes sense to me -- I was adding the extra weight on top of the CG with engines installed. I guess that presupossed the CG was correct to begin with. Fact is ,it's pretty darn close. I'll try it both ways but yours sounds smarter
 
Last edited:
Hi,

Peter Olivola said:
After completion, the best way I've found to deal with weight and CG is to set all component weights to 0. Then, after weighing the rocket and determining CG without a motor installed but with a complete recovery system in place, I measure the distance from the front of the main body tube to the CG point. Enter the total weight in the override section for that component along with the CG position.
Click to expand...

You should use the override CG/mass for the stage component. That overrides the CG/mass for the entire stage, without the need for setting other component masses to zero. The problem with setting individual component masses to zero is that OR will compute that component's moment of inertia to be zero as well.

The best way is to use the correct materials so each component is computed approximately correctly. (Or if you have the patience, you can weigh each component and override their mass individually, though this is largely unnecessary.) Then when the design is ready, measure its weight and CG and override those on the stage component.

This will give you the correct CG and mass, but also a very good estimate for the moments of inertia. The moments are automatically corrected for the overridden mass/CG. The moments of inertia are not very critical in the simulations, so its quite sufficient to have them computed automatically as long as the individual component weights are in the correct ballpark.


Regards,
Sampo N.
 
Thanks, Sampo. I hadn't found that feature, yet.

Sampo said:
Hi,



You should use the override CG/mass for the stage component. That overrides the CG/mass for the entire stage, without the need for setting other component masses to zero. The problem with setting individual component masses to zero is that OR will compute that component's moment of inertia to be zero as well.

The best way is to use the correct materials so each component is computed approximately correctly. (Or if you have the patience, you can weigh each component and override their mass individually, though this is largely unnecessary.) Then when the design is ready, measure its weight and CG and override those on the stage component.

This will give you the correct CG and mass, but also a very good estimate for the moments of inertia. The moments are automatically corrected for the overridden mass/CG. The moments of inertia are not very critical in the simulations, so its quite sufficient to have them computed automatically as long as the individual component weights are in the correct ballpark.


Regards,
Sampo N.
Click to expand...
 
hornet driver said:
Second question has to do with printing. As I roll the design 90 deg I can still only print the original side profile. Is there a way around this. Thanks
Click to expand...

This is a limitation in the current design report and something I noticed as well. It should be fairly trivial to use the same rotation angle for printing as in the displayed rocket figure. I'll implement the fix in the next day or two.

Cheers,
Doug
 
I checked in the code to honor the rotation angle of the main rocket figure in the printed figure. Will be available in the next release (or you can pull the latest source and compile it.)

Cheers,
Doug
 

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