Original Posted By: "Christian Bobka"
Here is Chris Bobka's report on the first flights:The first flight report of the Pietenpol is as follows:2:40 was flown in five flights this morning and afternoon. Wind was 1/2 to fullquartering right headwind at a steady 10 kts. Field conditions were dry grass.Location was Stanton Field, near Northfield, Minnesota. The ship has spokedmotorcycle wheels and tyres rolling on bronze bushings with no brakes anda tail skid. A straight axle and wrapped bungies provided suspension. The firstflight was 45 minutes, second flight was about 20 minutes, third flight wasabout 25 minutes, fourth flight was 25 minutes and the fifth flight was 45 minutes.A few years ago I wrote a long dissertation on how to select the proper axle locationwith the 1929 style wooden gear legs installed on the long "Corvair" fuselage.I was right on the money in the analysis because at the aft CG loadingthat we had, the ship would perform flawlessly on the grass. Travelling 90degrees to the 10 knot wind, I could turn into the wind by stick aft, windwardrudder, and a burst of power and I could turn away from the wind by stick forward,lee rudder, and a burst of power. I was comfortable taxiing next to buildingsand other aircraft with very little practice.I weigh 220 lbs and Greg computed that we needed 100 lbs of ballast in the forwardbag compartment (aft of firewall above passenger's feet) to get loaded CGat .5" forward of arbitrary aft CG limit (greg will have to give you the datumand the CG range, etc.)The ship is powered by an A-65 freshly overhauled with a homemade wood prop thatwas made using a duplicating machine copying an old Sensenich W72C42 blade fromabout 50 years ago.The motor mount as originally made had TONS of down thrust and TONS of right thrustwelded into it: like 1" in each direction over the length of the crank.The angle would be arctan(1/24) . This looked so far out that spools were fabricatedand used to shim the motor back until it had "a little" right thrust and"a little" down thrust.On takeoff, a pronounced and uncomfortable tendency to turn left was observed whichrequired a constant input of 1/2 right rudder at cruise settings and 3/4right rudder at full power and climb speed. To let up on the rudder would invitea rapid yaw induced roll to the left. This kept me making almost all theturns into the rudder (to the right for those of you in Rio Linda). The aircraftis equipped with the highly calibrated Johnson wind vane type of airspeedindicator and it showed about 35-40 mph in the climb and about 55-60 flat out.The engine rpm in a moderate climb was 2100 indicated and the flat out rpmin level flight was 2220 rpm. The tach has not been calibrated. The rpms soundedright for 2150 or so in cruise and 2300 rpm (the correct number we want)level flat out. The left turning tendency is mitigated when power is broughtback to idle. This fact identifies the problem to be a deficiency of right thrustat the motor mount and/or left offset of the vertical stabiliser. The aircraftflew well in the 1900 rpm range. I did not feel that much was gained byrunning the power up above 2100 rpm.Anyway, Greg and Dale's initial fix for this vicious left turning tendency willbe first to offest the vertical stabiliser to the left to the maximum degreewe can move it which is about 5/8" at the leading edge of the vertical stab. This fix will be instituted prior to the next flight. Then the spool spacer onthe motor mount will be adjusted to take out the rest of the left turning tendencythat we find remaining. Those of you still building, plan to allow foradjustment at the vertical stabiliser leading edge, a little to the right anda whole lot to the left.The A-65 equipped Piet is said to have increased vertical surface forward of theCG which offsets vertical surface aft of the CG. This is destabilizing in thevertical axis and appeares to be present with the aircraft reluctant to returnto straight ahead after a yaw is induced. I will investigate this characteristicafter the aircraf tis trimmed for hands and feet free flight. I wouldrecommend that future Piet builders who plan to use an A-65 increase the sizeof their vertical stabilizer to help offset the increased vertical area forwardof the CG with the A-65 installations. A little extra way aft has quite aneffect.....Another tendency the ship displayed was a severe nosedropping tendency. This requireda tiring constant pull on the stick of more than 6 lbs or so. Lettingo of the stick would hang me on the straps as the nose pitched over.This could be attributed to engine downthrust or to aerodynamics and needed furtherinvestigation. I found that the pull on the stick was independent of thrustproduced. It is an aerodynamic issue that needs to be cured by either loweringthe leading edge of the horizontal stabiliser or raising its trailing edge.This is difficult to do in practise as the Vi Kapler rudder hinges are reluctantto move up or down the rudder spar. Again, current builders, allow forthe ability to raise or lower the leading edge of the horizontal stab by usingshims at the forward attach point only. You may also need a space to existbetween the bottom of the vertical stabilser and the centerline of the horizontalstab to allow for a slot where vertical positioning of the horizontal stabcan be made. Just give some thought as to how you will allow the leading edgeto be raised or lowered 1/2" or maybe even more after the ship is asssembled.Knowing that we had 100 lbs of ballast in the forward bag compartment, we removed40 lbs of it and that relieved maybe 1/4 of the 6 lb pull on the stick. Gregwas concerned that would put the ship aft of the arbitrary CG aft limit. However,poweroff stalls were performed both with 100 lbs and 60 lbs of ballastand in both cases the ship had no difficulty in lowering the nose to unstalledflight upon the slightest easing of aft stick pressure. When the stick washeld full aft, gingerly use of the rudder could hold the ship in a falling leafbut you had to stay right on it with a good horizon.There was also a left wing heaviness that was mostly mitigated by shortening theleft front strut by 1-1/2 turns and lengthening the right front strut by thesame amount.As test flights go, the ship was moderately difficult to fly as it needed continuoussubstantial input in all three axes, gobs of right rudder, a lot of aftstick, and a bit of right stick. I tried taking pictures but gave up after threebecause I could not take pictures and fly at the same time.We will work through each item until the ship flies properly. Ideas, comments,and insights are welcome.Chris________________________________________________________________________________