Open Rocket and elliptical boattails

[shockie]

According to this thread, up to about mach 0.39, an elliptical nose cone has the lowest drag:

https://www.rocketryforum.com/threads/elliptical-nose-cones-in-openrocket.174284/
This got me to thinking, would the same be true for an elliptical boat tail versus a conical taper or a cut off parabola.

I've read that angle of the boattail , a 5-6degree angle for a conical taper is generally good.

Does OR have the ability to choose the boat tail shape?

I did find this online;
Models, 7 calibers long, with a variety of conical, ogival convex and concave boattails were free-flight tested at M 1.70, for drag and other aerodynamic characteristics. The total drag decreases monotonically for boattails longer than 0.5 calibers. For shorter boattails, the drag is higher than that of the square based body. For boattail lengths between 0.5 and 1.5 calibers, conical boattails have lower drag than either the ogival or concave configurations. The base pressure decreases with boattail length but increases with the boattail angle at the base. Among other aerodynamic characteristics, the boattailing appears to cause the most significant change in the Magnus torque coefficient. For certain boattails, this change may be sufficiently large to make the configuration dynamically unstable.

 

[SolarYellow]

There's a paper out there that tests a variety of conical and parabolic boat tail projectiles and determines that a conical angle of 4.5 degrees per side is optimal. The parabolic boat tails with the same length and percent reduction in diameter all had a final angle of 9 degrees per side. They were roughly equivalent. Some radius at the transition from straight to taper is desireable to avoid triggering flow separation at that point.

If by elliptical, you mean something with a 90-degree angle at the minor diameter, that would surely have flow separation at some prior point, making the separation turbulent and messy, effectively making the minor diameter larger. Possibly worse than no boat tail. If you mean to trim the ellipse before it turns all the way to 90 degrees, I'm not sure how that would really be much different than a cone, ogive, or parabolic.

 

[lakeroadster]

Does OR have the ability to choose the boat tail shape?

Yes. The "Shape Parameter" can be selected during optimization.

 

[neil_w]

Any transition (including at the tail end) can be set to any of the same shapes as nose cones.

 

[shockie]

Yes. The "Shape Parameter" can be selected during optimization.

View attachment 571350

Fantastic

 

[shockie]

There's a paper out there that tests a variety of conical and parabolic boat tail projectiles and determines that a conical angle of 4.5 degrees per side is optimal. The parabolic boat tails with the same length and percent reduction in diameter all had a final angle of 9 degrees per side. They were roughly equivalent. Some radius at the transition from straight to taper is desireable to avoid triggering flow separation at that point.

If by elliptical, you mean something with a 90-degree angle at the minor diameter, that would surely have flow separation at some prior point, making the separation turbulent and messy, effectively making the minor diameter larger. Possibly worse than no boat tail. If you mean to trim the ellipse before it turns all the way to 90 degrees, I'm not sure how that would really be much different than a cone, ogive, or parabolic.

Solar yellow: you wouldn't happen to have a url?

 

[SolarYellow]

Solar yellow: you wouldn't happen to have a url?

NASA TR R-100 posted by Joe Pfeiffer in the thread you linked in your OP. p. 17

 

[lakeroadster]

@shockie you might like this thread also..

https://www.rocketryforum.com/threads/supersonic-tailcones-in-simulators.42095/#post-401872