Final Assembly

October 22 - 25, 2015

	Tail feathers installed!.
Wing trailing edge (TE) offset bracket mount. The TE is dropped down from the original on-boom location 3-1/2" to achieve a positive wing incidence of 2.75 degrees. This will cause the boom to fly at a more level "angle of attack" compared to OEM, thus raising the tail and making the stabilizer more effective since it will be at an effective -2.75 degree incidence to the wing. Notice the unused hole in the boom to the left. This was the original rear bolt hole for the bracket, but due to a miscalculation, it had to be moved forward 2-3/4". So, the front hole became the rear and a new forward hole drilled.	Wing leading edge (LE) bracket attached using the rear engine mounting bracket bolt location. The front bolt is 6" forward with the front fuselage braces mounted mid-way between.
	Wing (primer only) installed and rigged for 5.5 degrees dihedral (tips higher than root) and 3.5 degrees of wing tip washout (twist). Washout was engineered into the wing, but the built-in twist still has to be supported by the correct lengths of the front and rear wing struts on each side. Yep, that thin, flexible root rib sure looks nasty after being contorted and warped under tension of the shrunk fabric. I'll probably cover the gap with thin plexiglass or lexan held on with velcro strips.
Well, all of the above is the good news. The bad news is she fails weight and balance big time! I anticipated this would be the case, because I didn't know how far back to move the new wing. I moved it 6" aft in the digital 3D design and in this build. As shown, the Center of Gravity (CG) is 41% of the wing's Mean Aerodynamic Chord (MAC). My desired CG is 30%. This means she's VERY tail heavy... unstably so. The fix? Three things. Move the engine forward. I have almost 2" on the engine mounting bracket available to do so. However, moving it forward this amount only moves the CG forward 1%.   Move the tail forward... that is, shorten the boom. Due to the tail redesign, in which I added several lengths of tubing when adding the upper vertical stabilizer, splitting the horizontal stabilizer in half so it could fold up vertically for transport, and adding the required bracing tubes and support members, the added weight probably comes to 5 - 7 pounds over the OEM tail group. Moving the tail group forward moves the weight of the tail forward (and thus CG) and more on to the nose wheel where it needs to be. I'm easily able to shorten the boom by drilling out the boom splice rivets (see Main Boom), sliding the tail section boom off the inner splice tube, cutting 6" (to start) off the tail boom, and placing it back on the splice. If the resulting new W&B fails, I'll cut another 3" off. However, I will not cut off more than 12" total. If  W&B fails at a 12" reduction in length, then step 3 will have to be performed.   Move the wing backwards. Currently the CG is too far back in relation to the wing (41% of the distance back from the front of the middle of the wing). CG needs to be 30% back for proper in-flight stability. If the CG can't be moved far enough forward using steps 1 and 2, then the wing has to be moved backward (towards the tail) to align its 30% MAC location to where the CG is. How much? That's a moving target! Moving the wing ALSO moves the CG, so it will be a trial and error procedure. For now, I can simply move the TE bracket 2-3/4"back to this original location and move the wing's LE bracket aft an equal amount. Hopefully this amount, in conjunction with the other two steps above will align the wing with the GC AND place the CG a few more inches in front of the main landing gear axle so that the plane becomes stable on the ground as well. Right now the GC is less than 1-1/2" in front of the axle when it should be around 9".

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October 26 - November 6, 2015

I opted to perform ALL THREE options above! Move the engine forward, move the tail forward, move the axle backward, and move the wing backward.

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.	Weight and balance set up. Moment arm measurements are referenced to the front of the propeller hub. Weights are taken with pilot in seat and a full tank (5 gallons) of gas.
For reference, this is the original location of the wing leading edge bracket and front fuselage brace tubes, resulting in a CG location of 41% MAC. This location was arbitrarily selected based on the OEM wing LE being located at the front engine mount bracket bolt, seen here in front of the Front Brace tube.	For reference, this is the original location of the wing trailing edge brackets and seat back/tank support tubes. The empty hole shown was miscalculated as being the rear bolt location for the extension drop down plates. The front hole, 2-3/4" in front of it, became the extension's rear bolt hole.
This is where everything had to move in order to put the CG at 30% MAC. As you can see, the wing's LE brackets are now located on the boom, instead of the motor mount. Moving the wing also involved moving the main axle and every tube connected to it. The front fuselage brace tube was moved 4" aft on the motor mount.	I used thin metal straps that looped over the boom to temporarily hold the wing mounting brackets, allowing me to move the entire wing as needed. TE brackets are shown here using these straps, along with a C-clamp to hold it in place.
Wing LE brackets at their new location on the boom, 11-3/4" farther back than the original, motor mount location.	Wing LE brackets with new saddle blocks installed, after drilling a new 5/16" hole in the boom. Because these brackets were bent and drilled for the OEM wing, with a 16 degree sweep, the brackets had to be modified for the new wing's 12.5 degree sweep. This was done by cutting the holes off the bracket and drilling new holes to match the ones in the LE spar.
TE bracket drop down extension remounted 11-3/4" aft of its original location. Anchors for the four-point harness shoulder straps added.	After moving the main axle 4" back, the seat back/tank support tubes now occupy the vacated TE extension's rear mounting hole. This view also shows that the rivets for the boom splice have yet to be drilled in the tail section, after 6" of the boom was cut off to bring the tail group closer to the wing.
To recap: Original position of the wing, axle, and tail boom length created a failed W&B of 41% MAC with only 20 pounds on the nose wheel. Not documented above was moving the wing 2-3/4" aft so that the TE extension returned to its original "miscalculated" position. 6" was cut off the tail section of the boom at the boom splice. The engine was moved 2" forward. Steps 2, 3, and 4 changed CG to 35% MAC, and added 4 pounds to the nose wheel. The axle was then moved back 4" (and thus the entire cockpit -- seat, tank, front fuselage braces, and nose wheel). Then the seat and bottom of the tank/seat back tubes were moved 4" forward, to compensate. Even though more weight was put on the nose wheel, the resulting CG returned to 41% MAC. The wing was moved back 9 additional inches to it's current and final 3rd position. With everything moved per above, CG is now at 29% MAC. When the plane is fully loaded, there's 70 pounds on the nose wheel.  Next on the list to be done is to rivet the tail boom back on to the boom splice; measure, cut, and drill new wing struts; cut and remount the windshield; and cut the elevator push rod and rudder cables to their new, shorter lengths.

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November 27, 2015

I initially set the wing dihedral angle to 5.5 degrees using a construction angle finder gauge. It turns out that the gauge was inaccurate by about 1.5 degrees on the "negative" side of the zero mark, compared to the "positive" side. I did not discover this until after measuring, cutting, and drilling the wing struts. ARGH! Time to execute Plan B... use the time tested alternative... string, trigonometry, and a laterally and longitudinally LEVEL plane! To measure and set dihedral using this method: Block up the vehicle so it's not sitting on its tires, where tire pressure and overall weight distribution affects level. Prop the wings up at the tips with an adjustable stand to your desired dihedral angle using an angle finder gauge (even if inaccurate).  Stretch a string between the wing tips and securely attach them to the top surface of the wing.  Mark the wing and string where the two touch.

Remove the string, fold it in half (the two end marks brought together), and mark the fold, which is the exact center.\ Put the string back in place on the wing tips.  Drop a very light "plumb bob" (such as a nut on a string) from the center mark down to the boom. Adjust the heights of the wing tip supports until the bob hangs the calculated height (step 11) over the center of the boom (if one wing tip goes up 1/4", then the other goes down 1/4") The string and plumb bob form right triangles.  The height of the short side of the triangles = hypotenuse x tangent of dihedral angle.  In this case, the length of the TE spar is the hypotenuse, which is 168". I decided to increase the dihedral to 6 degrees, thus the tangent of 6 = 0.105. So, 168 x 0.105 = 17.64", the height of the string above the boom.

As you can see here, the plumb bob is centered over the boom. This indicates that both wings have the same upward angle. If not, the bob would be off center one side or the other. Since the bob's weight, though miniscule, causes the string to sag, it needs held up to take the weight off the string when measuring the height of the string above the boom. The wings are held up with tripod utility light stands. Their telescopic design allows incremental height adjustments to evenly set the dihedral... in this case, until the string was 17.5" above the boom.

Due to not having any virgin stock to cut new, longer wing struts, I used the existing struts, cutting off the drilled holes at the wing end, adding a 4" long inner splice tube (7/8" OD x 0.065"), and an extension section. Each splice is secured with 12, 1/8" aluminum pop rivets and two 1/4" bolts, guaranteeing that the joint is stronger than the tube itself. Two holes are drilled in the tang and wing strut, in case I want redundant bolt connections. For now, I'm using one bolt to secure the struts, per OEM.

UPDATE 08/2018: I replaced the wing struts with new, one-piece tubes and replaced longer AN4-17 bolts [1.5" grip] and nylock nuts with shorter, drilled, AN4-13 bolts [15/16" grip], castle nuts, and cowling pins. A regular thin nut was soldered to each castle nut to lengthen it, so that when finger tightened to contact the strut, the hole in the shank aligns deeply with the castle notches, allowing the cowling pin to positively engage and lock the nut. Why change from nylock to castle nuts? To shorten assembly time and nylock nut wear out after repeated use. Why are the bolts 15/16" grip when the tubes are 1" OD? Because the tangs that slide in to the tubes are a smidge larger than the tube's ID, thus the tube must be squashed down 1/16" in order to make them slightly oval.

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November 28, 2015 (updates in red starting Jan 28, 2016)

Here's the maiden flight! The air was about 7-10 mph at 300 AGL, so it was a little bumpy and "swayey" so I purposely kept her low. Remember, it's been 5 years since I last flew, so I wasn't comfortable being jiggled around up there.



Observations:

Take off: ~ 45 mph
Cruise: ~50 mph @ 5,500 rpm
Stall: unknown, untested, but expect it to be around 35 mph. √ Confirmed to be 30 mph.
Handling: I was being conservative on this first flight around the pattern and so I was varying the throttle to find out how she responded. I found that she needs about 500 more rpm than her previous incarnation as a Weedhopper to maintain altitude. Anything less and she started to sink. She also required significant up elevator. Letting the stick go to neutral resulted in a nose dive.

Update: With all the changes in red below, especially the lexan gap seal and finish paint, this plane is now a dream to fly! No ill handling, LOTS of lift, trimmed for hands-off level cruise of 50 mph @ 5,200 rpm, climbs like a rocket at WOT (6,100 rpm) take off, and nose dive is minimal on power off.

What's Next?

1. 
   Drop the LE of the horizontal stabilizer down 2" for a 4.27 deg neg. incidence, in order for the stabilizer to generate more negative lift, so that the elevator returns to a more stick-neutral (elevator level) position.
   √ Completed. I put the LE in the middle, 1" down hole. After further flights I discovered that it was the spring tensioner on the elevator push rod that was causing the issue of having to apply constant forward stick pressure. I didn't realize such a small amount of tension would do that.
    
2. 
   Paint the finish coat on the wings. The fabric pores were not 100% sealed, thus possibly reducing lift a little bit. I will be using 3 coats of olive drab semi-gloss exterior latex house paint on the top and 4 coats of yellow on the bottom.  Sopwith Camel top sides were actually brown (due to the UV protecting pigments yellow iron oxide and carbon black or soot), while the undersides were plain, non-pigmented varnish that tinted the white linen yellow.
   √ Completed (started Dec. 28 and finished Jan. 21) 
    
3. Install a "gap seal" between the wing root sections, in order to recover a few percent of lift being lost by the flow of air off the top of the wing and down into the gap.
   √ Completed using scrap lexan and 3/8" wide velcro tape.
   
   Update: The industrial strength velcro wasn't very industrial. The very strong backing adhesive wasn't the problem; it was the fuzzy loops themselves that broke more and more after each removal of the gap seal, to the point that air, pushing up on the gap seal from underneath, caused the weakening velcro loops to separate from the velcro hooks on the wings, allowing the seal to bulge up several inches.
   
   The velcro was removed and a new system installed. It consists of several plastic hooks screwed to each root rib and corresponding rings riveted to the underside of the gap seal. Paracord zig-zags between the hooks and rings, firmly securing the gap seal to the wing. Attaching and detaching the seal is quick and easy, because the paracord remains permanently attached to the gap seal as they pass through their respective sets of rings. All I have to do is pull down on the cord and slip it under each hook, causing the cord to become tauter and tighter, until the last hook clinches it all together.
    
4. Fix a downward droop in the front of the boom caused by not adequately supporting the boom when I disconnected the front fuselage braces from the motor mount brackets in order to move the axle back a few inches when correcting CG. The weight of the engine unknowingly "bent" the boom down as I redrilled the holes for the front braces, "locking" this droop in place when I reattached them.
   √ Completed by drilling new holes in the motor mount angle brackets after the boom was "unsprung." I subsequently made entirely new angle bracket motor mounts, because all those trial and error holes looked bad.
    
5. #4 means I will have to make new front fuselage braces a couple inches longer to put the braces back to the original holes that have more stability.
   √ Completed
    
6. Pitch the 65" Powerfin Model B prop a degree or so more to see if a smidge more thrust can be obtained at a little lower rpm.
   √ Completed
    
7. 
   Build wing carriers for my 5x8 plane transportation utility trailer per this design...
   √ Completed