An Airspeed Indicator for my GN-1 Aircamper

I've decided on an airspeed indicator for my GN-1 instrument panel. The airspeed indicator will be centred in the instrument panel so I've chosen a larger 80mm diameter instrument.

The indicator is a Winter model 6 FMS item number 6403. This indicator has a measuring range of 0 - 100 knots and a 510 degree dial design.

Check out the full range of Winter instruments here: http://www.winter-instruments.de/english/home.html

GN-1 Aircamper Stall Speed at Maximum Weight

The graph on the right shows a theoretical solution for the maximum lift coefficient and corresponding stall speed at 1100 lbs - the quoted gross weight for the GN-1 Aircamper.

The red curve is the line of best fit for calculated maximum lift coefficients for the GN-1 Aircamper airfoil obtained using Xfoil.

The black curve shows the results obtained for the lift coefficient (Cl) using the following equation for Lift (straight and level flight):

L = 0.5 x (density) x (velocity)^2 x (S) x (Cl)

Where:

L = lift force = weight = 1100 lbs (at the stall)

density = density of air = 0.00238 slug/ft^3 (at sea level on a standard day)

velocity = free air velocity at the stall in ft / sec

S = wing surface area = 145 sq.ft

Cl = calculated maximum lift coefficient at the stall

The results obtained suggest that the power off stall speed for the GN-1 Aircamper at 1100 lbs maximum gross weight is approximately 64 ft / sec or 38 knots. The calculated maximum lift coefficient at this stall speed is 1.56.

Question:

Does anyone has some actual flight performance data on the stall speed of the GN-1 Aircamper at maximum gross weight ?

XFOIL Version 6.96 Analysis GN-1 Aircamper Airfoil at Stall Speed

XFOIL Version 6.96 was used to produce aerodynamic characteristics of the GN-1 Aircamper airfoil at the quoted stall speed, i.e. 22 knots (25 mph). The Reynolds number equating to this free air velocity at sea level is approximately Re = 1,164,000.

It turns out that the maximum calculated lift coefficient at a free air velocity of 22 knots for the GN-1 Aircamper airfoil is Clmax = 1.45.

XFOIL Blended Airfoil Ordinates

XFOIL is an interactive program for the design and analysis of subsonic isolated airfoils. You can download the program for free here:

http://web.mit.edu/drela/Public/web/xfoil/

The airfoil ordinates developed in an earlier post were imported into the program and smoothed for analysis. Listed below is the set of smoothed ordinates for the GN-1 Aircamper airfoil exported from XFOIL.

Station Ordinate

1.000000 0.000000 Trailing Edge
0.995458 0.002617
0.985912 0.004412
0.973799 0.006650
0.959737 0.009487
0.945087 0.012411
0.931205 0.015248
0.918239 0.017484
0.905565 0.020025
0.892297 0.022460
0.878142 0.024934
0.863962 0.027360
0.850022 0.030137
0.836368 0.033145
0.823039 0.035827
0.809479 0.038974
0.795025 0.042144
0.780086 0.045437
0.765333 0.048731
0.751259 0.052049
0.738329 0.054578
0.725063 0.056931
0.710941 0.059771
0.696988 0.062622
0.683810 0.064975
0.670980 0.067389
0.657872 0.069677
0.643413 0.071704
0.628784 0.073968
0.614423 0.076145
0.600793 0.077814
0.587284 0.079823
0.573197 0.081621
0.558362 0.083107
0.543550 0.084621
0.529738 0.085882
0.516418 0.086943
0.502864 0.088254
0.488469 0.089318
0.473897 0.090295
0.459318 0.091324
0.444603 0.092324
0.430040 0.093058
0.415755 0.093947
0.400947 0.094484
0.385791 0.094816
0.370599 0.095003
0.355583 0.095108
0.340917 0.094947
0.327098 0.094818
0.314110 0.094200
0.301045 0.093836
0.287482 0.093208
0.273490 0.092509
0.259287 0.091452
0.244656 0.090365
0.229684 0.089036
0.214571 0.087695
0.200100 0.086078
0.185700 0.084244
0.171981 0.082222
0.158938 0.079673
0.146567 0.077330
0.134939 0.074470
0.122274 0.070638
0.109174 0.066541
0.096151 0.061788
0.083023 0.056509
0.071195 0.050981
0.058951 0.044323
0.046658 0.037427
0.035322 0.030658
0.025649 0.024600
0.018679 0.019902
0.013693 0.016249
0.009812 0.013557
0.006855 0.011425
0.004770 0.009292
0.002991 0.007376
0.001684 0.005514
0.000891 0.003505
0.000272 0.001669
0.000000 -0.000000 Leading Edge
0.000173 -0.001728
0.000538 -0.003644
0.001204 -0.005625
0.002625 -0.007538
0.004564 -0.009519
0.006998 -0.011641
0.010068 -0.013705
0.014217 -0.015353
0.019770 -0.016842
0.026835 -0.017986
0.036264 -0.018552
0.048253 -0.018997
0.061042 -0.019644
0.074066 -0.019970
0.087424 -0.020641
0.101523 -0.020989
0.116385 -0.020974
0.130914 -0.021020
0.144181 -0.020818
0.157469 -0.020118
0.170648 -0.019361
0.183733 -0.018452
0.197259 -0.017715
0.211833 -0.016576
0.227231 -0.015433
0.242874 -0.014262
0.258414 -0.013071
0.273674 -0.011918
0.288368 -0.010907
0.303392 -0.010190
0.318757 -0.009422
0.333827 -0.008644
0.348762 -0.008213
0.364235 -0.008019
0.379602 -0.007794
0.395040 -0.007403
0.410408 -0.007004
0.425403 -0.006780
0.440444 -0.006810
0.455780 -0.006887
0.471219 -0.006888
0.486270 -0.006863
0.500485 -0.007015
0.514560 -0.007298
0.528756 -0.007570
0.543152 -0.007815
0.558013 -0.008128
0.573517 -0.008522
0.589137 -0.008918
0.604395 -0.009248
0.619648 -0.009435
0.634893 -0.009519
0.650464 -0.009505
0.665926 -0.009506
0.681317 -0.009282
0.697116 -0.008918
0.713133 -0.008545
0.729139 -0.008174
0.745152 -0.007801
0.761181 -0.007427
0.777211 -0.007054
0.793241 -0.006681
0.809272 -0.006308
0.825302 -0.005935
0.841329 -0.005561
0.857353 -0.005189
0.873370 -0.004816
0.889354 -0.004441
0.905287 -0.004076
0.921158 -0.003714
0.936706 -0.003312
0.951585 -0.002972
0.965834 -0.002804
0.978600 -0.002431
0.988583 -0.001875
0.996204 -0.002120
1.000000 0.000000 Trailing Edge

AeroFoil Vesion 2.1 Analysis at Stall Speed

Following on from the airfoil data created in the previous post, I thought it might be interesting to import the data into an airfoil design program and get a feel for the performance of the airfoil near the quoted stall speed for the GN-1 Aircamper, i.e 25 mph.

AreoFoil Version 2.1 is a 2-dimensional airfoil design and analysis program written and distributed by Mr Donald L Reid P.E.

You can download Mr Reid's program here: http://aerofoilengineering.com/

Below is a summary of airfoil coefficients for angles of attack ranging from -4.5 degrees to 16.5 degrees at a free stream air velocity of 25 mph using Areofoil Version 2.1. The numbers obtained for the lift coefficients look far too low and I'm not sure why ? Any feedback would be appreciated.

Airfoil Ordinates GN-1 Aircamper

Spent a good part of today generating a set of airfoil ordinates for the GN-1 Aircamper.

The method used was to lay out the full size rib drawing and scribe the chord line between the leading and trailing edges. I then marked and measured nominal stations and corresponding ordinates from the trailing edge around the upper surface to the leading edge and then back around the lower surface to the trailing edge.

The stations and ordinates are given in percent of airfoil chord and are dimensionless. The leading edge is taken as the origin.

Here they are :

Station Ordinate

1.000000 0.000000 TRAILING EDGE
0.998088 0.001967
0.993881 0.002951
0.981150 0.005246
0.967762 0.007869
0.954703 0.010492
0.941643 0.013115
0.928584 0.015738
0.915197 0.018033
0.902465 0.020656
0.889405 0.022951
0.876346 0.025246
0.862959 0.027541
0.849899 0.030164
0.836512 0.033115
0.823452 0.035738
0.810721 0.038689
0.797334 0.041639
0.783946 0.044590
0.770559 0.047541
0.757827 0.050492
0.744768 0.053443
0.731381 0.055738
0.717993 0.058361
0.704934 0.060984
0.691874 0.063607
0.678487 0.065902
0.665100 0.068525
0.652040 0.070492
0.638325 0.072459
0.625921 0.074426
0.612534 0.076393
0.599147 0.078033
0.586087 0.080000
0.573028 0.081639
0.559968 0.082951
0.546909 0.084262
0.533849 0.085574
0.520462 0.086557
0.507403 0.087869
0.494671 0.088852
0.481284 0.089836
0.468224 0.090656
0.455165 0.091639
0.442105 0.092459
0.429046 0.093115
0.415987 0.093934
0.402927 0.094426
0.389868 0.094754
0.376808 0.094918
0.364077 0.095082
0.351345 0.095082
0.337958 0.094918
0.324898 0.094754
0.311839 0.094098
0.298779 0.093770
0.285720 0.093115
0.272660 0.092459
0.259601 0.091475
0.246214 0.090492
0.233154 0.089344
0.220095 0.088197
0.206707 0.086885
0.193648 0.085246
0.180916 0.083607
0.167857 0.081475
0.154798 0.078852
0.141410 0.076230
0.128351 0.072459
0.115291 0.068525
0.102232 0.064098
0.089172 0.059016
0.076113 0.053443
0.062726 0.046393
0.049994 0.039344
0.036935 0.031639
0.023875 0.023443
0.018357 0.019672
0.010871 0.014262
0.005680 0.010328
0.004096 0.008525
0.002184 0.006393
0.000928 0.003607
0.000000 0.000000 LEADING EDGE
0.000344 -0.002623
0.001016 -0.005246
0.002344 -0.007213
0.005639 -0.010492
0.009590 -0.013443
0.015508 -0.015738
0.022410 -0.017377
0.035541 -0.018525
0.048672 -0.019016
0.061803 -0.019672
0.074934 -0.020000
0.087738 -0.020656
0.100869 -0.020984
0.114000 -0.020984
0.127016 -0.020984
0.139984 -0.020984
0.152951 -0.020328
0.166410 -0.019672
0.179377 -0.018689
0.192508 -0.018033
0.205639 -0.017049
0.218770 -0.016066
0.231902 -0.015082
0.245033 -0.014098
0.257836 -0.013115
0.270967 -0.012131
0.284098 -0.011148
0.297230 -0.010492
0.310361 -0.009836
0.323492 -0.009180
0.336623 -0.008525
0.349754 -0.008197
0.362885 -0.008033
0.376016 -0.007869
0.389475 -0.007541
0.402607 -0.007213
0.415738 -0.006885
0.455098 -0.006885
0.468230 -0.006885
0.481689 -0.006885
0.494820 -0.006885
0.507951 -0.007213
0.521082 -0.007377
0.534213 -0.007705
0.547344 -0.007869
0.560475 -0.008197
0.573607 -0.008525
0.586738 -0.008852
0.599869 -0.009180
0.613000 -0.009344
0.626459 -0.009508
0.639590 -0.009508
0.652721 -0.009508
0.665525 -0.009508
0.993738 -0.001967
0.998016 -0.001967
1.000000 0.000000 TRAILING EDGE