New Free RASAero II Software Released

To All:

The new free RASAero II software has been released! It is available for download from the RASAero web site at www.rasaero.com , click on the RASAero II Software and RASAero II Users Manual buttons to access the web pages to download the software and the users manual.

The big new features are new and improved supersonic Center of Pressure (CP) models, the ability to run multi-stage rockets, and the ability to import RockSim files. There are many other improved models, including improved boattail drag models, and other new features listed below.

For those who have run RASAero, running RASAero II is pretty intuitive. One change is the location of the motor selection, weight, CG, and nozzle exit diameter inputs; see pages 75-80 of the users manual.

As always the RASAero II authors, Chuck Rogers and David "Coop" Cooper, are always looking for flight data to compare the RASAero II altitude predictions against to further develop and improve the RASAero II aerodynamic prediction and altitude prediction models.


Chuck Rogers
Rogers Aeroscience



RASAero II

Version 1.0.0.0 – Release Date September 12, 2015


New and improved models and capabilities compared to the RASAero software:


New and improved supersonic Center of Pressure (CP) models. Rocket supersonic CP typically moved forward approximately 1 caliber compared to previous RASAero models. For supersonic stability should run RASAero II software rather than RASAero software.

New multi-stage capability for aerodynamic predictions and for flight simulations. RASAero II software can run rockets with up to 3 stages.

User-specified booster separation delay and upper stage ignition delay for delayed staging, or coast before ignition of upper stage.

Ability to import RockSim .rkt rocket files directly into RASAero II.

New and improved dynamic stability models.

New and improved transonic CD models.

New and improved supersonic boattail wave drag and base drag models for increased altitude prediction accuracy for rockets with boattails.

For very steep or very short boattails, new flight data-based boattail wave drag and base drag models which eliminate unrealistically high altitude predictions for very steep or very short boattails.

Added power law, LV-Haack, parabolic and elliptical nose cones, including subsonic, supersonic, and hypersonic CD, Cnalpha and CP models for the new nose cones.

Added the capability for 5, 6, 7 and 8 fins, to the existing 3 and 4 fins.

Added improved viscous crossflow models to the Rogers Modified Barrowman Method and the supersonic body CP methods for improved predictions for the forward movement of the rocket CP with angle of attack.

Added improved, increased accuracy launch shoe subsonic, supersonic, and hypersonic CD models.

Added new and improved square airfoil leading edge wave drag model.

Made corrections to square airfoil and rounded airfoil friction drag models for all turbulent flow.

Rocket reference area changed from base area of the nose cone to the maximum cross-sectional area of the rocket body.

Updated the rasp.eng motor database file with new motor data for TRA/NAR/CAR certified motors.

Some amazing stuff here, thanks Chuck!

Thanks Chuck. Look forward to using RASAero II!

Bob

Some RASAero II Useful Tips:


1) For two stage N motor to M motor rockets, where the upper stage approaches and/or exceeds Mach 3, or for high thrust N motor minimum diameter rockets which also approach and/or exceed Mach 3, select All Turbulent Flow and a Surface Finish of Rough Camouflage Paint, see pages 34-35 and pages 37-39 in the RASAero II users manual. Rockets of this type have come back with aerodynamic heating damage resulting in "scuffing" of the paint, increasing surface roughness and tripping the flow to turbulent. For these types of rockets RASAero II will have more accurate altitude predictions using the All Turbulent Flow and Surface Finish - Rough Camouflage Paint settings.


2) When importing a RockSim file, be sure to check the Fin Airfoil inputs and the Rail Guide/Launch Shoe inputs once the file has been imported into RASAero II. See pages 39-42 in the RASAero II users manual. RockSim only has Square, Rounded, and Airfoiled Fin Airfoils. RASAero II has 6 Fin Airfoils available which are detailed on pages 13-15 of the RASAero II users manual. If an airfoil, say an Hexagonal airfoil, was approximated in RockSim as Airfoiled (a NACA airfoil in RASAero II), then RASAero II will load this as a NACA airfoil. The RASAero II software has no way of knowing whether the airfoil entered into RockSim was the actual airfoil, or an approximation for the airfoil. The same goes for rail guides or launch shoes, in RockSim they are either modeled as launch lugs, or left off altogether. Most Users appear to just leave the rail guides or launch shoes off the rocket in RockSim. So again the User will have to add the rail guides or launch shoes the rocket actually has into the RASAero II inputs.


3) RASAero II has new and improved supersonic Center of Pressure (CP) models, which are more conservative and have a more forward Mach 2-3 CP than the previous RASAero models. Run the RASAero II Flight Simulation and take a look at the rocket's maximum Mach number, which for some rockets is approaching or exceeding Mach 3. Use the RASAero II Aero Plots feature to make the CP versus Mach number plot shown below, and look up the Angle of Attack 0-4 degrees CP. (Average CP for Angle of Attack 0 deg to 4 deg, CP is moved forward.)

Have at least 2.0 calibers of stability margin on the Mach 3 (or maximum Mach number) CP value. If the stability margin falls below 1.0 caliber, at Mach 2-3 there may be coning, and/or pitch-roll coupling, and other undesirable effects. The additional 1.0 caliber is additional stability margin, to make sure the stability margin never falls below 1.0 caliber. As an example, a rocket might have a stability margin at Mach 3 of 1.25 calibers, but there might be an error in the CP prediction of 0.25 caliber, lowering the stability margin below 1.0 caliber into the coning/pitch-roll coupling potential danger area.


Chuck Rogers
Rogers Aeroscience

Cant wait to use it.

Awesome tool. Easy to use. Well-supported. Thank you very much.

You guys are my heroes!!! By far my favorite rocket simulator.

Though when is the 6-DOF version coming out...

Chuck Rogers said:

Some RASAero II Useful Tips:


1) For two stage N motor to M motor rockets, where the upper stage approaches and/or exceeds Mach 3, or for high thrust N motor minimum diameter rockets which also approach and/or exceed Mach 3, select All Turbulent Flow and a Surface Finish of Rough Camouflage Paint, see pages 34-35 and pages 37-39 in the RASAero II users manual. Rockets of this type have come back with aerodynamic heating damage resulting in "scuffing" of the paint, increasing surface roughness and tripping the flow to turbulent. For these types of rockets RASAero II will have more accurate altitude predictions using the All Turbulent Flow and Surface Finish - Rough Camouflage Paint settings.


2) When importing a RockSim file, be sure to check the Fin Airfoil inputs and the Rail Guide/Launch Shoe inputs once the file has been imported into RASAero II. See pages 39-42 in the RASAero II users manual. RockSim only has Square, Rounded, and Airfoiled Fin Airfoils. RASAero II has 6 Fin Airfoils available which are detailed on pages 13-15 of the RASAero II users manual. If an airfoil, say an Hexagonal airfoil, was approximated in RockSim as Airfoiled (a NACA airfoil in RASAero II), then RASAero II will load this as a NACA airfoil. The RASAero II software has no way of knowing whether the airfoil entered into RockSim was the actual airfoil, or an approximation for the airfoil. The same goes for rail guides or launch shoes, in RockSim they are either modeled as launch lugs, or left off altogether. Most Users appear to just leave the rail guides or launch shoes off the rocket in RockSim. So again the User will have to add the rail guides or launch shoes the rocket actually has into the RASAero II inputs.


3) RASAero II has new and improved supersonic Center of Pressure (CP) models, which are more conservative and have a more forward Mach 2-3 CP than the previous RASAero models. Run the RASAero II Flight Simulation and take a look at the rocket's maximum Mach number, which for some rockets is approaching or exceeding Mach 3. Use the RASAero II Aero Plots feature to make the CP versus Mach number plot shown below, and look up the Angle of Attack 0-4 degrees CP. (Average CP for Angle of Attack 0 deg to 4 deg, CP is moved forward.)

Have at least 2.0 calibers of stability margin on the Mach 3 (or maximum Mach number) CP value. If the stability margin falls below 1.0 caliber, at Mach 2-3 there may be coning, and/or pitch-roll coupling, and other undesirable effects. The additional 1.0 caliber is additional stability margin, to make sure the stability margin never falls below 1.0 caliber. As an example, a rocket might have a stability margin at Mach 3 of 1.25 calibers, but there might be an error in the CP prediction of 0.25 caliber, lowering the stability margin below 1.0 caliber into the coning/pitch-roll coupling potential danger area.


Chuck Rogers
Rogers Aeroscience

Click to expand...

So I am planning a Mach 3 flight for Balls (two-stage 4" to 3"). In terms of the 2 caliber statement I had a question... By the time the sustainer is traveling in the Mach 2+ range it will have consumed ~50% of its propellant. In addition, according to Aerotech, the M685 maintains its CG location during the burn (not sure if I totally believe this). Thus my stability margin has greatly improved due to the burned propellant by the time I'm screaming along. So as long as we start the burn off with 1.5 calibers we should be fine? Is my logic right here?

Kip_Daugirdas said:

So I am planning a Mach 3 flight for Balls (two-stage 4" to 3"). In terms of the 2 caliber statement I had a question... By the time the sustainer is traveling in the Mach 2+ range it will have consumed ~50% of its propellant. In addition, according to Aerotech, the M685 maintains its CG location during the burn (not sure if I totally believe this). Thus my stability margin has greatly improved due to the burned propellant by the time I'm screaming along. So as long as we start the burn off with 1.5 calibers we should be fine? Is my logic right here?

Click to expand...

You can check by looking at the RASAero II CG and CP plot, shown below. Also, RASAero II will display an error message, also shown below, if the stability margin falls below 2.0 calibers at any point in the flight. If the stability margin falls below 2.0 calibers, the Flight Simulation still runs to completion, it just notifies the User with the warning message. If the rocket goes unstable, RASAero II stops the Flight Simulation at the point the rocket went unstable, and plots the trajectory data up to that point.


Chuck Rogers
Rogers Aeroscience

Sweet!

I am seriously stoked to hear this and can't wait to start playing around with it.

Huge thanks for your efforts in making this available.

Sweet!
I will have to try it out

I want to thank the authors, Chuck Rogers and David "Coop" Cooper for RASAero and now RASAero II. I love the programs. I simulate my rocket kits or scratch rockets before I build and launch them. I haven’t built many but enjoy simulating as part of the design process. So I was delighted to see that RASAero II supported 2-stage rockets. I am finalizing my design for a 2-stage before cutting tubes and fins.

I simulated launching one of my designs and received the message “Rocket was stable, but Stability Margin less than recommended during flight. Rocket should have a Positive Stability margin of at least 2.0 Calibers for all Mach Numbers during the flight. .. Etc.” Ok, so I take a risk if I leave the design as is. Up to now I had believed if the rocket stability margin was 1+ caliber it would fly ok. Subsonic it probably would. And I’ve not flown a Mach 2+ rocket to have found out the hard way.

I then started exploring CP without launching. Please see the attached PDF for the results.

I tried attaching the Excel file but it wouldn’t open during my test. RASAero II file types are not allowed at this time. And, I can’t get RASAero I file to load with data. So I’m not much help with the actual files except RockSim.

I don’t understand why the CP differences are as large as they are between RASAero II and RASAero I or RockSim. Can someone help?
Thanks,
StanO

StanO said:

I want to thank the authors, Chuck Rogers and David "Coop" Cooper for RASAero and now RASAero II. I love the programs. I simulate my rocket kits or scratch rockets before I build and launch them. I haven’t built many but enjoy simulating as part of the design process. So I was delighted to see that RASAero II supported 2-stage rockets. I am finalizing my design for a 2-stage before cutting tubes and fins.

I simulated launching one of my designs and received the message “Rocket was stable, but Stability Margin less than recommended during flight. Rocket should have a Positive Stability margin of at least 2.0 Calibers for all Mach Numbers during the flight. .. Etc.” Ok, so I take a risk if I leave the design as is. Up to now I had believed if the rocket stability margin was 1+ caliber it would fly ok. Subsonic it probably would. And I’ve not flown a Mach 2+ rocket to have found out the hard way.

I then started exploring CP without launching. Please see the attached PDF for the results.

I tried attaching the Excel file but it wouldn’t open during my test. RASAero II file types are not allowed at this time. And, I can’t get RASAero I file to load with data. So I’m not much help with the actual files except RockSim.

I don’t understand why the CP differences are as large as they are between RASAero II and RASAero I or RockSim. Can someone help?
Thanks,
StanO

Click to expand...

What he said! RASAero II is awesome!

StanO said:

I want to thank the authors, Chuck Rogers and David "Coop" Cooper for RASAero and now RASAero II. I love the programs. I simulate my rocket kits or scratch rockets before I build and launch them. I haven’t built many but enjoy simulating as part of the design process. So I was delighted to see that RASAero II supported 2-stage rockets. I am finalizing my design for a 2-stage before cutting tubes and fins.

I simulated launching one of my designs and received the message “Rocket was stable, but Stability Margin less than recommended during flight. Rocket should have a Positive Stability margin of at least 2.0 Calibers for all Mach Numbers during the flight. .. Etc.” Ok, so I take a risk if I leave the design as is. Up to now I had believed if the rocket stability margin was 1+ caliber it would fly ok. Subsonic it probably would. And I’ve not flown a Mach 2+ rocket to have found out the hard way.

I then started exploring CP without launching. Please see the attached PDF for the results.

I tried attaching the Excel file but it wouldn’t open during my test. RASAero II file types are not allowed at this time. And, I can’t get RASAero I file to load with data. So I’m not much help with the actual files except RockSim.

I don’t understand why the CP differences are as large as they are between RASAero II and RASAero I or RockSim. Can someone help?
Thanks,
StanO

Click to expand...

New, more realistic and accurate models of the CP forward shift at higher Mach numbers have been implemented in RASAero II. Please read Chuck's posts in this thread, past TRF threads, and the RASAero II manual that you can download when you downloaded the program, for more details.

Bob

bobkrech said:

New, more realistic and accurate models of the CP forward shift at higher Mach numbers have been implemented in RASAero II. Please read Chuck's posts in this thread, past TRF threads, and the RASAero II manual that you can download when you downloaded the program, for more details.

Bob

Click to expand...

Yes, I understand that Mach affects CP in flight per posts and documentation, but I'm interested to know why it changed significantly at Mach=0 prior to launch from RASAero I. Could it be they implemented an offset at Mach=0? Just trying to understand why it's so much different.

Thanks,
StanO

StanO said:

Yes, I understand that Mach affects CP in flight per posts and documentation, but I'm interested to know why it changed significantly at Mach=0 prior to launch from RASAero I. Could it be they implemented an offset at Mach=0? Just trying to understand why it's so much different.

Click to expand...

StanO:

From RASAero to RASAero II there was an update to the Nose Cone-Cylinder CP model in the Rogers Modified Barrowman Method. Actually, looking over the RASAero II model update list on the RASAero web site, we forgot to include this model update in the list of improved models in RASAero II.


Chuck Rogers
Rogers Aeroscience

Thanks Chuck! I like conservative.

StanO

Chuck Rogers said:

For those who have run RASAero, running RASAero II is pretty intuitive. One change is the location of the motor selection, weight, CG, and nozzle exit diameter inputs; see pages 75-80 of the users manual.

Click to expand...

If I am doing this correctly, then this is a HUGE change and and not a good one, IMO. In all simulation software (including RASAERO I), the user provides the mass and CG of the rocket WITHOUT motor. When the motor is selected from database, the software reads the mass info in the motor file and adjusts the mass and CG of the rocket in liftoff-ready condition. This makes it very easy to swap out motors for analysis.

In RASAERO II, the user must supply the mass and CG of the rocket with motor installed in liftoff mode?? This is fine if you have a motor assembled and rocket prepped for flight, but very difficult to do if you are just running sims without rocket/motor in hand. You would have to manually find the mass of each motor and add it to the total mass and make some further calculations to figure out the CG with motor loaded. Ugh.

I see no place in the GUI to provide a "dry weight", nor does the liftoff mass/CG change when different motors are selected. Am I missing something?

Thanks for the cool software, but I am running into a usability issue, here.

Buckeye said:

If I am doing this correctly, then this is a HUGE change and and not a good one, IMO. In all simulation software (including RASAERO I), the user provides the mass and CG of the rocket WITHOUT motor. When the motor is selected from database, the software reads the mass info in the motor file and adjusts the mass and CG of the rocket in liftoff-ready condition. This makes it very easy to swap out motors for analysis.

In RASAERO II, the user must supply the mass and CG of the rocket with motor installed in liftoff mode?? This is fine if you have a motor assembled and rocket prepped for flight, but very difficult to do if you are just running sims without rocket/motor in hand. You would have to manually find the mass of each motor and add it to the total mass and make some further calculations to figure out the CG with motor loaded. Ugh.

I see no place in the GUI to provide a "dry weight", nor does the liftoff mass/CG change when different motors are selected. Am I missing something?

Thanks for the cool software, but I am running into a usability issue, here.

Click to expand...

Buckeye:

In RASAero the CG is varied during flight from the User-entered liftoff CG based on the motor selected, but the liftoff CG has always been manually entered, and in RASAero the liftoff CG is not changed when you change the motor selection. When running RASAero most Users have calculated and entered one liftoff CG, and then not bothered to vary it as the motor selection was changed, only changing the liftoff CG when a final motor was selected.

The Motor Selection/Liftoff Weight/No Motor Weight feature from RASAero was not included in RASAero II when multi-stage capability was added, due to some issues with the FlightDataEntry screen GUI, and limited development time. A lot of development time went into the new, more accurate models, so we had to drop adding some additional features to RASAero II.

RASAero II accurately varies weight and CG for each stage, but you have to enter the liftoff/initial weight and CG for each stage.

For quick trade studies many of the initial RASAero II Users take a look at the subsonic CP's on the Scale Rocket Drawing first page, enter CG's a little over 2.0 calibers ahead of the CP's, run the rocket and wait for the stability margin less than 2.0 caliber warning message, if it occurs (CP moved too far forward supersonic), they adjust the CG's. After they make a final motor selection (or selections for multi-stage), then they go back and adjust the CG's to the final values.

As noted you do have to manually add the motor loaded weight to your rocket no motor weight to get the liftoff weight.

Adding the Motor Selection/Liftoff Weight/No Motor Weight feature to individual stages in RASAero II is something we'll be considering in the future.


Chuck Rogers
Rogers Aeroscience

Well, OK. Thanks. This approach is just not the way I think about doing simulations. I can't imagine prepping a 3-stage rocket with motors and all before running a simulation on it. Otherwise, I need to build a design+motor in RockSim or OpenRocket prior to using RASAero. Or, do some hand calculations of CG with motor. Or, nuclear option, only use RASAero for 1D flights and not worry about CG.

If the code varies the CG during flight simulation (I assume by using propellant mass and motor length values found in the rasp.eng file), then why can't it compute the motor CG contribution before it leaves the pad and thus leaving it up to the user to provide the simpler "dry weight?" As always, the user can override the calculated values.

Buckeye said:

Well, OK. Thanks. This approach is just not the way I think about doing simulations. I can't imagine prepping a 3-stage rocket with motors and all before running a simulation on it. Otherwise, I need to build a design+motor in RockSim or OpenRocket prior to using RASAero. Or, do some hand calculations of CG with motor. Or, nuclear option, only use RASAero for 1D flights and not worry about CG.

If the code varies the CG during flight simulation (I assume by using propellant mass and motor length values found in the rasp.eng file), then why can't it compute the motor CG contribution before it leaves the pad and thus leaving it up to the user to provide the simpler "dry weight?" As always, the user can override the calculated values.

Click to expand...

Again, limited development time. With Motor Selection, Liftoff (Initial) Weight, No Motor (Empty) Weight; one is fixed (constant/same), one is changed, then there is a resulting change in the third. With three stages, 9 different combinations. Each succeeding stage adds to the stages before it. It was simpler for RASAero when it was just for a single stage. Just having the No Motor (Empty) Weight input only has drawbacks, for post-flight comparisons of the altitude prediction with the actual rocket altitude (which I do a lot of), you have the actual Liftoff (Initial) Weight, and would have to do the calculations in reverse to get the No Motor (Empty) Weight inputs.

Using Liftoff (Initial) Weight and Liftoff (Initial) CG for each stage combination (Stages 1 and 2 and 3, Stages 2 and 3, Stage 3) seemed the more direct approach. For documentation purposes and comparisons with flight data, it's clear what the rocket inputs were. But again, this is something we're considering changing in the future.

You are correct, we use the propellant mass and the motor length values from the rasp.eng file to adjust the rocket CG during flight.

Many rocketeers do the initial rocket design in RockSim or Open Rocket where the rocket internal and external components are included, but then run the rocket on RASAero (and now RASAero II) to refine the design and get a more accurate prediction for the performance of the rocket. With RASAero II the RockSim rocket external geometry can now be imported directly into the software, although as I have noted in other posts the User needs to check the fin airfoil inputs and the rail guide/launch shoe inputs.

For quick trade studies (basic rocket size, basic selection of motors for each stage), you can use generic empty weights and rough CG's, the quick run CG-CP approach from an earlier post I made to this thread, and yes, you'll have to do some hand calculations. Which is why we'll be considering changing this in RASAero II in the future.


Chuck Rogers
Rogers Aeroscience