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  1. #1
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    Question Openrocket fin question

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

    trffan has been retired

  2. #2
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    Quote Originally Posted by TRFfan View Post
    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.

    Dreaming of making the rockets I dreamed of as a kid (and then some).


    NAR L1 Cert flight: Sheridan, Oregon, USA. Sept. 19, 2015. Flew Deep Space OFFl on an I357T-14A Blue Thunder

  3. #3
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    Quote Originally Posted by K'Tesh View Post
    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.
    trffan has been retired

  4. #4
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    Quote Originally Posted by TRFfan View Post
    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.
    Dreaming of making the rockets I dreamed of as a kid (and then some).


    NAR L1 Cert flight: Sheridan, Oregon, USA. Sept. 19, 2015. Flew Deep Space OFFl on an I357T-14A Blue Thunder

  5. #5
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    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.
    Peter Olivola

  6. #6
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    Quote Originally Posted by TRFfan View Post
    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
    Tim
    L3 NAR 98225

  7. #7
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    Quote Originally Posted by Peter Olivola View Post
    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...
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  8. #8
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    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.

    Quote Originally Posted by Steve Shannon View Post
    Or their approach is just one additional way to find joy in this hobby. Different strokes...
    Peter Olivola

  9. #9
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    Quote Originally Posted by Peter Olivola View Post
    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.
    Mark Koelsch
    Tripoli 6155 L2
    Owner of http://www.rocketryfiles.com/
    Editor of http://www.thrustcurve.org/
    Keeper of the motor files
    Former Moderator of Rocketry Planet -R.I.P.

  10. #10
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    Quote Originally Posted by markkoelsch View Post
    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.
    QRS: 124
    AMRS: 32 L2
    Highest Altitude: 10,849 feet
    Largest Motor: CTI 1115J530 IM
    Current Projects:
    Purple Parrot, X Wing


  11. #11
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    Your negativity is reality in the real world.

    Quote Originally Posted by SpaceManMat View Post
    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

  12. #12
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    Gents, you are making this personal, and it should not be.
    Mark Koelsch
    Tripoli 6155 L2
    Owner of http://www.rocketryfiles.com/
    Editor of http://www.thrustcurve.org/
    Keeper of the motor files
    Former Moderator of Rocketry Planet -R.I.P.

  13. #13
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    Quote Originally Posted by Peter Olivola View Post
    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.
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  14. #14
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    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;

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

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

    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.

    RASAero Fin Airfoils.pdf


    Chuck Rogers
    Rogers Aeroscience
    Last edited by Chuck Rogers; 3rd January 2017 at 10:18 PM.

  15. #15
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    The pursuit of perfection is, at best, destined to be frustrating. Understanding why you can't get there is enlightenment.

    Quote Originally Posted by Steve Shannon View Post
    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.
    Peter Olivola

  16. #16
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    Quote Originally Posted by Chuck Rogers View Post
    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;

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

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

    RASAero Altitude Prediction Accuracy.pdf


    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.

  17. #17
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    Quote Originally Posted by Buckeye View Post
    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
    Last edited by Chuck Rogers; 6th January 2017 at 12:13 AM.

  18. #18
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    Quote Originally Posted by Peter Olivola View Post
    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.
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  19. #19
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    Range being the key word and experience being the means to interpret it.

    Quote Originally Posted by Steve Shannon View Post
    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

  20. #20
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    I'll have you gentlemen know that accuracy is my motto and I mever nake mistakes!
    http://www.macklinmissileworks.com/

    Making Guillotines Great Again

  21. #21
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    Quote Originally Posted by Peter Olivola View Post
    Range being the key word and experience being the means to interpret it.
    Agreed


    Steve Shannon
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  22. #22
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    Quote Originally Posted by Chuck Rogers View Post
    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 has been retired

  23. #23
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    Quote Originally Posted by Peter Olivola View Post
    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.
    trffan has been retired

  24. #24
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    I wish you luck and a motor/motors that are an accurate reflection of the data used in OR. Both would be best.

    Quote Originally Posted by TRFfan View Post
    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

  25. #25
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    Quote Originally Posted by TRFfan View Post
    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

  26. #26
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    Quote Originally Posted by Chuck Rogers View Post
    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 has been retired

  27. #27
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    Quote Originally Posted by Peter Olivola View Post
    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.
    trffan has been retired

  28. #28
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    That isn't the issue. Whether or not the motor you have matches the CTI and/or OR data is.

    Quote Originally Posted by TRFfan View Post
    Yea, the G150's motor data (from CTI) is pretty similar to the openrocket version so i think i would be fine.
    Peter Olivola

  29. #29
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    Quote Originally Posted by Peter Olivola View Post
    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.
    trffan has been retired

  30. #30
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    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.

    Quote Originally Posted by TRFfan View Post
    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

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