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

Wing Loading GN-1 Aircamper

The wing loading is another useful aircraft design ratio and is the gross weight of the aircraft divided by the wing area.

For a GN-1 Aircamper having a gross weight (Wo) of 1100 lbs and a wing area (S) of 145 square feet, the wing loading (W/S) = 1100 / 145 = 7.59 lb per square foot (psf).

Power Loading GN-1 Aircamper

The power loading is a useful aircraft design ratio and is simply the ratio of the gross weight of the aircraft (Wo) to the aircraft's available engine power (hp).

Power loadings for home built aircraft typically range from 10 to 15 lb per horsepower.

Using a TMX O-200 engine, the power loading for my GN-1 Aircamper will be approximately 1100 / 100 = 11 lb/hp.

Comparatively, the power loading for a KR-2 (shown below) is 11.2 lb/hp. Although I'm sure my Aircamper will be nowhere near as fast !

An Engine for my GN-1 Aircamper

I've decided on an engine for my GN-1 Aircamper. The engine I've selected is a TMX O-200 experimental engine manufactured by Teledyne Mattituck Services Inc.

Here's the link to their site... http://www.mattituck.com/

Whilst it's not the cheapest option on the market I like the reduced risk offered by a proven powerplant constructed to a certified ISO 9001 quality system.

The TMX O-200 engine drives a fixed pitch propeller and delivers 100 HP. The engine weighs approximately 215 lbs. Overall dimensions are 23"x 31"x 28".

Aspect Ratio GN-1 Aircamper

Let's have a look at the aspect ratio of the GN-1 Aircamper wing.

First a definition... "Aspect ratio is defined as the ratio of the span squared to the wing area, which reduces to the ratio of the span to the chord in the case of a rectangular wing."

The GN-1 Aircamper has a rectangular wing with a span of 29 ' (348") and a cord of 60". Giving a wing area (S) of 29 x 5 = 145 ft^2.

The aspect ratio (A) of the GN-1 Aircamper wing is therefore 348/60 = 5.8.

This is a relatively lower aspect ratio compared to the wing of a Cessna 150 (pictured right) which has an aspect ratio of approximately 6.95.

Here's some more info on the effect of the wing aspect ratio...

(1) As the angle of attack is increased, the corresponding lift that can be produced by a wing progressively increases as the aspect ratio is increased.

(2) Marked reductions in drag occur at higher lift coefficients as the aspect ratio is increased.

(3) A lower-aspect-ratio wing will stall at a higher angle of attack than a higher-aspect-ratio-wing.

Design Specifications GN-1 Aircamper

Design specifications for the GN-1 Aircamper are provided below (as stated on Plans Set No. 3582AC).

Span 29' (8839 mm)

Chord 60" (1524 mm)

Length 18' 1" (5512 mm)

Height 6' 8" (2032 mm)

Engine Power 65 - 85 hp

Maximum Speed 115 mph (99.9 knots)

Cruise Speed 87 mph (75.6 knots)

Stall 25 mph (21.7 knots)

Take Off Run 300' (91.44 m)

Rate of Climb 500 fpm

Gross Weight 1100 lbs (499 kg)

History of the GN-1 Aircamper

Reproduced below is an excellent account of the origins of the GN-1 Aircamper.

"Early in 1958, John W. Grega, EAA 3808, embarked on the Pietenpol Project, the object of which was to modernize the excellent 1933 Model A Ford powered version, to a Continental A-65 powered two-seat "fun plane" with good small field capabilities, using modern straight forward construction methods.

With engineering know-how available to him from his then EAA Chapter 5, located at the old Welcome Airport in Northfield Centre Township in Ohio, John Grega enlisted the aid of a fellow member to run a preliminary weight and balance on the 65 hp version of the Pietenpol Aircamper.

Armed with this data, John Grega, an experienced woodworker, proceeded to design a new fuselage structure employing Piper J-3 motor mount, landing gear, control assembly, and tail wheel assembly. Using a GN modified clip wing off a J-3 Cub, for which the original fuselage designed was intended. Along with the use of a J-3 wing, an improved and modernized version of the original Pietenpol Aircamper wing was initiated, lending versatility to the design. The original airfoil was redesigned with a more rounded leading edge for better stall characteristics, the truss was improved for more strength, and spars were relocated for greater depth and in keeping with modern designed parameters. Construction of the GN-1 prototype was immediately started after the original drawings were completed. This was to the be the J-3 wing version. John Grega finished and was flying his GN-1 prototype, N4705G, in 1963.

Selling plans on the GN-1 Aircamper was the furthest thing from John Grega's mind, until a small article appeared in the June 1960 issue of Sport Aviation, regarding the fact that the GN-1 was under construction. From that time on, the amount of mail received by John Grega was overwhelming, all letters expressing the desire to purchase plans for the GN-1, if and when available. Most requested parts were drawn up and sent out so construction could start. All sketches, doodles, and bits and pieces of construction were correlated into a set of drawings, first pencil tracings, and as construction problems arose, they were resolved and incorporated into a finished set of drawings. The finished set being officially copyrighted in 1992, by John W. Grega."

Source: http://www.pilotfriend.com/experimental/acft3/55.htm

Every Journey has a Beginning

Ever since I was a young lad I have wanted to fly. And few years ago a burning desire took hold to build my own aircraft.

Hence, this project was born... To study the design and construct a GN-1 Aircamper.

I have created this blog to share my experiences.

Friends are very welcome and both questions and criticisms will be warmly received.