VSP AERO Actuator Disk Setup Instructions
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Bill Fredericks
Sep 13, 2018, 5:50:37 PM9/13/18
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Hi Rob,
Would you please tell me, and the rest of the community, some of the basic instructions on how to use the Actuator Disks in VSP Aero properly.
I have performed the following steps thus far:
1) I have built a VSP model and I have added "Disk" to the model to locate where the propeller(s) will go.
2) I have opened the VSP Aero window from the tool bar and specificed the settings as required on the Overview and Advanced tabs.
3) On the Rotor tab, I see the actuator disks listed.
Now I need some help and have the following questions:
1) How do I calculate what I should input for CT and CP?
For example, say we were trying to model a Tecnam P2006 with the props blowing over the wing. We know the prop diameter is 5 feet 10 inches in diameter and prop RPM is around 2,400 and each engine is 100 hp . How do we compute CT and CP?
I have found the following equations on an MIT website:
where
v velocity
D diameter
n revolutions per second
rho density of air
P power
T thrust
This should answer how to compute CP. How does one estimate what the thrust will be to compute CT?
Follow up question, clearly props are not 100% efficient, so when computing CP would the input be 80 hp assuming 80% propeller efficiency?
Thank you,
Bill
Rob McDonald
Sep 14, 2018, 12:00:57 PM9/14/18
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Bill,
Since this is an actuator disk model, we don't have to worry about any details of the prop -- its pitch, number of blades, chord, etc. This is just a disk that absorbs power and produces thrust.
The P in the Cp equation is shaft power absorbed by the propeller. So, you don't need to use 80hp in the way you describe.
You'll need two more equations to approach this the way I normally would.
Advance Ratio:
J = V / (n D)
Propeller Efficiency:
eta = J CT/CP
Start with your flight condition and propeller parameters -- V (ft/s), rho (slug/ft^3), D (ft), n (rev/s).
Choose a desired thrust, T (lbf).
Assume Prop Efficiency, eta
Calculate CT, from the definition you gave.
Calculate J from my equation
Re-arrange the efficiency equation for CP
CP = J CT / eta
Solve for the CP that corresponds to your Thrust, efficiency, and advance (i.e. this flight condition).
Done. Feed that CT, CP, n into VSPAERO.
I've discussed this actuator disk model in this group a few times. You need to know that it only has one-way interaction between the disk and the aircraft. The disk induces a flow field -- that flow field influences the aircraft -- not the other way around. So, it will probably do a good job of modeling a propeller on a wing at cruise. It won't do a good job for a configuration with strong slipstream deflection -- or for a VTOL aircraft in transition or hover.
Hope this helps,
Rob
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Bill Fredericks
Sep 14, 2018, 1:11:56 PM9/14/18
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Great. Thank you.
Bill Fredericks
Sep 14, 2018, 10:10:46 PM9/14/18
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Follow up question. It appears that it doesn't save the Rotor Disk input data (hub diam, RPM, CT, CP) after making changes to the model and reopening VSP AERO. For designs with DEP, this makes for a lot of retyping input data for each rotor. Is their a way to save the data? and/or is their a way to like the data to multiple rotors, so you only have to type it in for one prop?
Bill
Rob McDonald
Sep 14, 2018, 10:58:15 PM9/14/18
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Bill,
What version of OpenVSP are you running? I suspect you're running something pretty old as there were many improvements made to the VSPAERO GUI in the last few versions.
When I do it -- I put in a Disk component to set the position and diameter of the prop. Then, I use the 'Rotor' tab to adjust the values for each one. They save just fine for me in the model.
Bill Fredericks
Sep 14, 2018, 11:36:43 PM9/14/18
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I'm using OpenVSP 3.16.1
I have always had a uncanny ability to break stuff...
Could you add a feature in VSP Aero for linking Rotor data on the Rotor Tab? This way you can specify the data once and it uses it for all the rotors that you select.
Cell: 757-727-3326
w.j.fre...@advancedaircraftcompany.com
w.j.fre...@advancedaircraftcompany.com
Peninsula Technology Incubator
1100 Exploration Way Suite 302S Hampton, VA 23666-6264
“In chaos comes opportunity” –old Marine Corps quote
On Fri, Sep 14, 2018 at 10:58 PM, Rob McDonald <rob.a.m...@gmail.com> wrote:
Bill,What version of OpenVSP are you running? I suspect you're running something pretty old as there were many improvements made to the VSPAERO GUI in the last few versions.When I do it -- I put in a Disk component to set the position and diameter of the prop. Then, I use the 'Rotor' tab to adjust the values for each one. They save just fine for me in the model.
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Rob McDonald
Sep 15, 2018, 1:56:57 PM9/15/18
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Is there anything unusual about your file that won't save actuator disk information?
My expectation of the behavior is this:
Launch OpenVSP
Open your model that already has Disk components in it
Open VSPAERO GUI
Go to Rotor Tab
Enter desired CT, CP, RPM for every rotor
Save these changes to your *.vsp3 file.
Quit OpenVSP
Launch OpenVSP
Open your model
Open VSPAERO GUI
Go to Rotor Tab
Things should be as you left them.
If this does not match your experience, I would appreciate a detailed description of what really does happen...
I understand your request for a way to change rotor information as a group. It is unlikely that I will have time to make that kind of change any time soon. I get very little time to work on OpenVSP that isn't work related.
BTW, you can change a prop's rotation by using negative RPM.
Rob
On Fri, Sep 14, 2018 at 8:36 PM Bill Fredericks <w.j.fre...@advancedaircraftcompany.com> wrote:
I'm using OpenVSP 3.16.1I have always had a uncanny ability to break stuff...Could you add a feature in VSP Aero for linking Rotor data on the Rotor Tab? This way you can specify the data once and it uses it for all the rotors that you select.
Cell: 757-727-3326
w.j.fre...@advancedaircraftcompany.comPeninsula Technology Incubator1100 Exploration Way Suite 302S Hampton, VA 23666-6264“In chaos comes opportunity” –old Marine Corps quote
On Fri, Sep 14, 2018 at 10:58 PM, Rob McDonald <rob.a.m...@gmail.com> wrote:
Bill,What version of OpenVSP are you running? I suspect you're running something pretty old as there were many improvements made to the VSPAERO GUI in the last few versions.When I do it -- I put in a Disk component to set the position and diameter of the prop. Then, I use the 'Rotor' tab to adjust the values for each one. They save just fine for me in the model.
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Bill Fredericks
Sep 20, 2018, 12:04:16 PM9/20/18
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I think I know were the bug may be now.
I have multiple sets in the model that I'm using for VSP Aero. One set has actuator disks, and the other set does not. I wanted to quantify the difference with power on vs off.
If I use the set that has this disks, and save it, that works fine. Then I run the set without the disks, that works fine. Then I run the set with the disks again and the values of RPM, CT, CP, etc are no longer saved from before.
I'm running VSP version 3.16.1 on a PC.
“In chaos comes opportunity” –old Marine Corps quote
On Fri, Sep 14, 2018 at 10:58 PM, Rob McDonald <rob.a.m...@gmail.com> wrote:
Bill,What version of OpenVSP are you running? I suspect you're running something pretty old as there were many improvements made to the VSPAERO GUI in the last few versions.When I do it -- I put in a Disk component to set the position and diameter of the prop. Then, I use the 'Rotor' tab to adjust the values for each one. They save just fine for me in the model.
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