#### KerryQuinn

##### Well-Known Member

- Joined
- May 5, 2009

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I built the "4 Square" rocket from Newway Spacemodels.

This rocket uses a 1.375"x1.375" square body tube, a pyramid nose "cone", and four square tube fins. I don't know if this is something that can be anaylzed in Rocksim or not...? (I don't have Rocksim.)

Instead, I tried to use WRASP 2.1... but you have to enter a body tube "diameter" and a drag coefficient.

The square tube "width" is 1.375"

The square tube diagonal is 1.94"

I also used the average of these two which is 1.66"

The rocket weighs 2.93 oz without an engine.

I also flew it with the QuEST how-high altimeter which adds 0.25 oz.

With the altimeter, I measured an altitude of 194 feet.

I ran simulations between drag coeff of 0.75 and 1.25.

Analysis using a QuEST B6-4 engine showed best agreement at:

WITH altimeter:

drag coeff of 0.9 and 1.66" diameter gives a prediction of 199 feet

Without altimeter it would have been lighter and gone to...

With NO altimeter:

drag coeff of 0.9 and 1.375" diameter gives a prediction of 243 feet

drag coeff of 0.9 and 1.66" diameter gives a prediction of 220 feet

drag coeff of 0.9 and 1.94" diameter gives a prediction of 197 feet

I don't have a wind tunnel so I don't know if the estimate of 0.9 is good or not for this rocket. It makes sense to me that the average diameter would give the answer closest to my measured altitude. I have also looked at drag coefficients for standard nose cones vs pyramids with an aspect ration near the "4 square" - seems that they are not that different.

Anyone out there able to shed more "science" on my method?

This rocket uses a 1.375"x1.375" square body tube, a pyramid nose "cone", and four square tube fins. I don't know if this is something that can be anaylzed in Rocksim or not...? (I don't have Rocksim.)

Instead, I tried to use WRASP 2.1... but you have to enter a body tube "diameter" and a drag coefficient.

The square tube "width" is 1.375"

The square tube diagonal is 1.94"

I also used the average of these two which is 1.66"

The rocket weighs 2.93 oz without an engine.

I also flew it with the QuEST how-high altimeter which adds 0.25 oz.

With the altimeter, I measured an altitude of 194 feet.

I ran simulations between drag coeff of 0.75 and 1.25.

Analysis using a QuEST B6-4 engine showed best agreement at:

WITH altimeter:

drag coeff of 0.9 and 1.66" diameter gives a prediction of 199 feet

Without altimeter it would have been lighter and gone to...

With NO altimeter:

drag coeff of 0.9 and 1.375" diameter gives a prediction of 243 feet

drag coeff of 0.9 and 1.66" diameter gives a prediction of 220 feet

drag coeff of 0.9 and 1.94" diameter gives a prediction of 197 feet

I don't have a wind tunnel so I don't know if the estimate of 0.9 is good or not for this rocket. It makes sense to me that the average diameter would give the answer closest to my measured altitude. I have also looked at drag coefficients for standard nose cones vs pyramids with an aspect ration near the "4 square" - seems that they are not that different.

Anyone out there able to shed more "science" on my method?