Openrocket fin question

[TRFfan]

Is the "airfoil" setting in openrocket a full airfoil or is it just a bevel?

 

[K'Tesh]

Is the "airfoil" setting in openrocket a full airfoil or is it just a bevel?

I don't know, I suspect it's a full airfoil.

 

[TRFfan]

I don't know, I suspect it's a full airfoil.

Yeah, that's what I though too but i wanted to be sure.

I just wanted to know if there is any way you can get the aerodynamic qualities for a beveled fin since there are only airfoiled, rounded, and square options.

 

[K'Tesh]

Yeah, that's what I though too but i wanted to be sure.

I just wanted to know if there is any way you can get the aerodynamic qualities for a beveled fin since there are only airfoiled, rounded, and square options.

To my knowledge, there isn't.

 

[Peter Olivola]

This seems like yet another thread trying to find a level of precision that is rendered pointless by the variation in motor performance. OR is a hobby tool, not something to bet your life on. With a reasonable experience level it's useful in getting much closer to an optimum design than most kits provide, but, like any such tool, it requires test verification. That, in turn, builds experience. If you're looking for a "book" approach to model rocketry you'll miss a substantial amount of the pure joy of the hobby.

 

[tim cubbedge]

Yeah, that's what I though too but i wanted to be sure.

I just wanted to know if there is any way you can get the aerodynamic qualities for a beveled fin since there are only airfoiled, rounded, and square options.

Try RASaero II

 

[Steve Shannon]

This seems like yet another thread trying to find a level of precision that is rendered pointless by the variation in motor performance. OR is a hobby tool, not something to bet your life on. With a reasonable experience level it's useful in getting much closer to an optimum design than most kits provide, but, like any such tool, it requires test verification. That, in turn, builds experience. If you're looking for a "book" approach to model rocketry you'll miss a substantial amount of the pure joy of the hobby.

Or their approach is just one additional way to find joy in this hobby. Different strokes...

 

[Peter Olivola]

As long as motor performance is such a big variable, such an effort isn't going to produce the kind of satisfaction you seem to be suggesting is achievable by this method.

Or their approach is just one additional way to find joy in this hobby. Different strokes...

 

[markkoelsch]

As long as motor performance is such a big variable, such an effort isn't going to produce the kind of satisfaction you seem to be suggesting is achievable by this method.

While what you are saying is true there is no reason to not be accurate with the file. Make it the best you can.

That said, people should realize that due to a variety of variables if they can get within 5-7% difference between reality/altimeter and sim they are doing about as good as they can expect.

 

[SpaceManMat]

While what you are saying is true there is no reason to not be accurate with the file. Make it the best you can.

That said, people should realize that due to a variety of variables if they can get within 5-7% difference between reality/altimeter and sim they are doing about as good as they can expect.

Totally agree if your sim is out by 10% and your motors can vary by 10%, then fixing my sim can half my error and in my opinion that's worth trying. It also seems a lot of people agree. Not t sure why the negativity about people wanting to improve, it's what scientist always strive for. Not your thing? that's fine, just don't stop those who do want to.

 

[Peter Olivola]

Your negativity is reality in the real world.

Totally agree if your sim is out by 10% and your motors can vary by 10%, then fixing my sim can half my error and in my opinion that's worth trying. It also seems a lot of people agree. Not t sure why the negativity about people wanting to improve, it's what scientist always strive for. Not your thing? that's fine, just don't stop those who do want to.

 

[markkoelsch]

Gents, you are making this personal, and it should not be.

 

[Steve Shannon]

As long as motor performance is such a big variable, such an effort isn't going to produce the kind of satisfaction you seem to be suggesting is achievable by this method.

Peter,
I can't say what will cause them satisfaction and frankly neither can you. But some people simply derive pleasure from the journey rather than basing it all on the result. Who are we to tell them they are wasting their time.

 

[Chuck Rogers]

With careful measurements of the rocket external geometry, weighing the rocket before launch, and using mostly certified motors for which there is static test thrust curve data available, RASAero typically predicts about 40% of the rockets to within +/- 5%, and about 75% of the rockets to within +/- 10%. (The actual figures are 42.4% of the flights within +/- 5%, 78.8% of the flights within +/- 10%, for 33 rockets compared.) The average RASAero altitude prediction error is 3.38%
An altitude prediction comparison table showing the RASAero altitude prediction errors for rockets up to 121,000 ft is on the RASAero web site at;

https://www.rasaero.com/comparisons-alt.htm

A graphical summary of the accuracy of the RASAero altitude prediction results is attached.

View attachment RASAero Altitude Prediction Accuracy.pdf

RASAero handles the fin airfoils which are attached below. For supersonic rockets the fin airfoil, in addition to the fin leading edge sweep, have significant effects on the supersonic drag of the rocket.

View attachment RASAero Fin Airfoils.pdf


Chuck Rogers
Rogers Aeroscience

 

[Peter Olivola]

The pursuit of perfection is, at best, destined to be frustrating. Understanding why you can't get there is enlightenment.

Peter,
I can't say what will cause them satisfaction and frankly neither can you. But some people simply derive pleasure from the journey rather than basing it all on the result. Who are we to tell them they are wasting their time.

 

[Buckeye]

With careful measurements of the rocket external geometry, weighing the rocket before launch, and using mostly certified motors for which there is static test thrust curve data available, RASAero typically predicts about 40% of the rockets to within +/- 5%, and about 75% of the rockets to within +/- 10%. (The actual figures are 42.4% of the flights within +/- 5%, 78.8% of the flights within +/- 10%, for 33 rockets compared.) The average RASAero altitude prediction error is 3.38%
An altitude prediction comparison table showing the RASAero altitude prediction errors for rockets up to 121,000 ft is on the RASAero web site at;

https://www.rasaero.com/comparisons-alt.htm

A graphical summary of the accuracy of the RASAero altitude prediction results is attached.

View attachment 308465


Chuck Rogers
Rogers Aeroscience

This is a great example showing the variation in flight measurements and the danger in assuming any one measurement is always "real world." Five different measurement techniques are used in this data, each with its own caveats.

Reading my Raven manual, it says that the Standard Atmosphere model is used without temperature correction, possibly inducing 10% errors in barometric measurements. The sims like RS, OR, and RA at least give the option to adjust the atmosphere model by local weather conditions, attempting to be more real world.

 

[Chuck Rogers]

Five different measurement techniques are used in this data, each with its own caveats.

That's why I make sure to list the data types with the altitudes listed in the table. Based on the data type, the reader can make his own assessment of the data.

One interesting flight, the A-601 P4935 motor flight, had three different types of altitude measurements (GPS, barometric altimeter, integrated accelerometer). Additionally, there were two different barometric altimeters from two different manufacturers. The altitudes are below.


A-601 Rocket P4935 Motor

Note 5: Altitude based on GPS data. Rocket also carried two barometric altimeters and an accelerometer. Altitudes from the different onboard instrumentation were the following:

GPS 42,771 ft
Adept 42,231 ft (barometric altitude)
ARTS II 40,113 ft (barometric altitude)
ARTS II 44,924 ft (integrated accelerometer altitude)

The rocket had a very vertical flight, and landed only 2 miles from the launch site.


For this rocket the altitude I compared the RASAero altitude prediction to was the GPS altitude. The RASAero altitude prediction was 41,086 ft, a -3.94% error compared to the 42,771 ft GPS altitude.



Other interesting rockets were the Violent Agreement, and the Violent Agreement SS Sustainer, where balloon atmospheric pressure data was used to adjust the barometric altimeter data.

Note 6: Altitude from barometric altimeter, with the altitude data adjusted based on balloon-referenced atmospheric pressure data, from a balloon launched prior to flight.



Chuck Rogers
Rogers Aeroscience

 

[Steve Shannon]

The pursuit of perfection is, at best, destined to be frustrating. Understanding why you can't get there is enlightenment.

It can be frustrating, but as long as a person does as much as possible correctly and understands the sources and ranges of magnitude of error, a person can generate a simulation with results that can be useful. The results will have a range rather than a pat answer, but that's okay.

 

[Peter Olivola]

Range being the key word and experience being the means to interpret it.

It can be frustrating, but as long as a person does as much as possible correctly and understands the sources and ranges of magnitude of error, a person can generate a simulation with results that can be useful. The results will have a range rather than a pat answer, but that's okay.

 

[tmacklin]

I'll have you gentlemen know that accuracy is my motto and I mever nake mistakes!

 

[Steve Shannon]

Range being the key word and experience being the means to interpret it.

Agreed


Steve Shannon

 

[TRFfan]

That's why I make sure to list the data types with the altitudes listed in the table. Based on the data type, the reader can make his own assessment of the data.

One interesting flight, the A-601 P4935 motor flight, had three different types of altitude measurements (GPS, barometric altimeter, integrated accelerometer). Additionally, there were two different barometric altimeters from two different manufacturers. The altitudes are below.


A-601 Rocket P4935 Motor

Note 5: Altitude based on GPS data. Rocket also carried two barometric altimeters and an accelerometer. Altitudes from the different onboard instrumentation were the following:

GPS 42,771 ft
Adept 42,231 ft (barometric altitude)
ARTS II 40,113 ft (barometric altitude)
ARTS II 44,924 ft (integrated accelerometer altitude)

The rocket had a very vertical flight, and landed only 2 miles from the launch site.


For this rocket the altitude I compared the RASAero altitude prediction to was the GPS altitude. The RASAero altitude prediction was 41,086 ft, a -3.94% error compared to the 42,771 ft GPS altitude.



Other interesting rockets were the Violent Agreement, and the Violent Agreement SS Sustainer, where balloon atmospheric pressure data was used to adjust the barometric altimeter data.

Note 6: Altitude from barometric altimeter, with the altitude data adjusted based on balloon-referenced atmospheric pressure data, from a balloon launched prior to flight.



Chuck Rogers
Rogers Aeroscience

Thanks.

Is htere any way to transfer a OR file to RASAero?

 

[TRFfan]

This seems like yet another thread trying to find a level of precision that is rendered pointless by the variation in motor performance. OR is a hobby tool, not something to bet your life on. With a reasonable experience level it's useful in getting much closer to an optimum design than most kits provide, but, like any such tool, it requires test verification. That, in turn, builds experience. If you're looking for a "book" approach to model rocketry you'll miss a substantial amount of the pure joy of the hobby.

Not really. I put a lot of effort in this project, and i want it to fly the way i want to. A few extra minutes of time on the computer isnt really going to hurt, and probably will save a ton of time in the future. I dont want to spend time flying the rocket over and over to get nearly the same results that i get on a computer. If you ask me, it isnt worth it.

 

[Peter Olivola]

I wish you luck and a motor/motors that are an accurate reflection of the data used in OR. Both would be best.

Not really. I put a lot of effort in this project, and i want it to fly the way i want to. A few extra minutes of time on the computer isnt really going to hurt, and probably will save a ton of time in the future. I dont want to spend time flying the rocket over and over to get nearly the same results that i get on a computer. If you ask me, it isnt worth it.

 

[Chuck Rogers]

Is there any way to transfer a OR file to RASAero?

In OpenRocket save the file as a RockSim (.RKT) file. Then import the RockSim file into RASAero II. Importing RockSim files into RASAero II is covered starting on Page 39 in the RASAero II Users Manual.

Note that after importing the RockSim file, it is important to check the Fin Airfoil inputs and the Rail Guide or Launch Shoe inputs. RASAero II has additional Fin Airfoil inputs and Rail Guide and Launch Shoe inputs which are not included in RockSim. As an example, if the rocket has a Hexagonal (beveled) Fin Airfoil, that Fin Airfoil is not available in RockSim. In the Open Rocket file, or the RockSim file, the User may have just entered "Airfoiled" (NACA Airfoil in the RASAero II Fin Airfoil inputs). After importing the file, RASAero II will transfer over the Airfoiled/NACA Airfoil inputs. The User will have to go in and enter the Hexagonal Fin Airfoil inputs.

Same with Rail Guide and Launch Shoe inputs. The Rail Guides or Launch Shoes may have been approximated by using a Launch Lug, or left off the rocket altogether. Again, for a Rail Guide approximated as a Launch Lug, importing the RockSim file into RASAero II will transfer over the Launch Lug input. The User will have to go in and remove the Launch Lug input, and add the Rail Guide input.


Chuck Rogers
Rogers Aeroscience

 

[TRFfan]

In OpenRocket save the file as a RockSim (.RKT) file. Then import the RockSim file into RASAero II. Importing RockSim files into RASAero II is covered starting on Page 39 in the RASAero II Users Manual.

Note that after importing the RockSim file, it is important to check the Fin Airfoil inputs and the Rail Guide or Launch Shoe inputs. RASAero II has additional Fin Airfoil inputs and Rail Guide and Launch Shoe inputs which are not included in RockSim. As an example, if the rocket has a Hexagonal (beveled) Fin Airfoil, that Fin Airfoil is not available in RockSim. In the Open Rocket file, or the RockSim file, the User may have just entered "Airfoiled" (NACA Airfoil in the RASAero II Fin Airfoil inputs). After importing the file, RASAero II will transfer over the Airfoiled/NACA Airfoil inputs. The User will have to go in and enter the Hexagonal Fin Airfoil inputs.

Same with Rail Guide and Launch Shoe inputs. The Rail Guides or Launch Shoes may have been approximated by using a Launch Lug, or left off the rocket altogether. Again, for a Rail Guide approximated as a Launch Lug, importing the RockSim file into RASAero II will transfer over the Launch Lug input. The User will have to go in and remove the Launch Lug input, and add the Rail Guide input.


Chuck Rogers
Rogers Aeroscience

Thanks.

 

[TRFfan]

I wish you luck and a motor/motors that are an accurate reflection of the data used in OR. Both would be best.

Yea, the G150's motor data (from CTI) is pretty similar to the openrocket version so i think i would be fine.

 

[Peter Olivola]

That isn't the issue. Whether or not the motor you have matches the CTI and/or OR data is.

Yea, the G150's motor data (from CTI) is pretty similar to the openrocket version so i think i would be fine.

 

[TRFfan]

That isn't the issue. Whether or not the motor you have matches the CTI and/or OR data is.

I think the perdictions would come pretty close (probably around 1 newton/sec) for the average thrust and impulse. CTI uses actual test data for their motor files.

 

[Peter Olivola]

Look at the certification requirements for TRA/NAR/etc. The acceptable range is significant. The certification test only sees a very small number of motors.

I think the perdictions would come pretty close (probably around 1 newton/sec) for the average thrust and impulse. CTI uses actual test data for their motor files.