flaps and their effects

bomber
Posts: 1379
Joined: Mon Nov 30, 2015 3:40 pm

flaps and their effects

Postby bomber » Mon Jul 13, 2020 7:16 pm

Here's the code for it..

Code: Select all

            <function name="aero/coefficient/CDwbh">
                <description>Drag_due_to_alpha</description>
                <product>
                    <property>aero/qbar-psf</property>
                    <property>metrics/Sw-sqft</property>
                    <property>aero/function/kCDge</property>
                    <table>
                        <independentVar lookup="row">aero/alpha-rad</independentVar>
                        <independentVar lookup="column">fcs/flap-pos-deg</independentVar>
                        <tableData>
                                         0        10       20       30
                             -0.0873   0.0041   0        0.0005    0.0014
                             -0.0698   0.0013   0.0004   0.0025    0.0041
                             -0.0524   0.0001   0.0023   0.0059    0.0084
                             -0.0349   0.0003   0.0057   0.0108    0.0141
                             -0.0175   0.002    0.0105   0.0172    0.0212
                             0.0000    0.0052   0.0168   0.0251    0.0299
                             0.0175    0.0099   0.0248   0.0346    0.0402
                             0.0349    0.0162   0.0342   0.0457    0.0521
                             0.0524    0.024    0.0452   0.0583    0.0655
                             0.0698    0.0334   0.0577   0.0724    0.0804
                             0.0873    0.0442   0.0718   0.0881    0.0968
                             0.1047    0.0566   0.0874   0.1053    0.1148
                             0.1222    0.0706   0.1045   0.124     0.1343
                             0.1396    0.086    0.1232   0.1442    0.1554
                             0.1571    0.0962   0.1353   0.1573    0.169
                             0.1745    0.1069   0.1479   0.1708    0.183
                             0.1920    0.118    0.161    0.1849    0.1975
                             0.2094    0.1298   0.1746   0.1995    0.2126
                             0.2269    0.1424   0.1892   0.2151    0.2286
                             0.2443    0.1565   0.2054   0.2323    0.2464
                             0.3491    0.2537   0.3298   0.3755    0.3983
                             0.5236    0.45     0.585    0.666     0.7065
                             0.6981    0.7      0.91     1.036     1.099
                             0.8727    1        1.3      1.48      1.57
                             1.0472    1.35     1.755    1.998     2.1195
                             1.2217    1.5      1.95     2.22      2.355
                             1.3963    1.57     2.041    2.3236    2.4649
                             1.5710    1.6      2.08     2.368     2.512
                          </tableData>
                    </table>
                    <property>gear/drag-coef[1]</property>
                    <property>gear/drag-coef[2]</property>
                    <property>gear/drag-coef[3]</property>
                    <property>gear/drag-coef[4]</property>
                    <property>gear/drag-coef[5]</property>
                    <property>gear/drag-coef[6]</property> <!-- Amphibious gear extended -->
                </product>
            </function>


On first inspection it doesn't look that bad... but look at this last line

1.5710 1.6 2.08 2.368 2.512

With a full flap defection at 90 degs AoA it's offering more drag than with no flaps deflected... that can't be as in that angle it's actually offering less surface area which mean that the coefficient should come down to reflect this.

But also consider this... if you're flying at zero AoA when applying flaps and the speed remains constant to get the same lift the AoA would have to reduce by 3 or so degrees to -3 degs.... Whereas the table is completely the other way around hardly any fidelity on the -ve angles of attack and all in the +ve...

This is wrong

Simon
"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

Richard
Posts: 114
Joined: Sun Sep 11, 2016 5:57 pm

Re: flaps and their effects

Postby Richard » Mon Jul 13, 2020 8:26 pm

bomber wrote:1.5710 1.6 2.08 2.368 2.512

This is wrong


Quite possibly. Raise an issue on their github.


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