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Taming the Baby Blender - Wings with Dihedral

#1
To help tame a Baby Blender, add dihedral to the wings.

I built and test flew a Baby Blender V2 and, while I generally liked the plane, others and I found it to be a bit squirrelly in the air.

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With short, stubby, flat wings, it had no self-centering capabilities. I thought adding a little dihedral to the wings might help settle down the BB V2.

After viewing the Flitetest FT Spitfire Build video, I decided on building the Baby Blender with 5 degrees of dihedral to both the upper and lower wings. However, I realized that it would be difficult to mount the lower wing to the fuselage with an angle so I decided to have a 4 inch flat center section with the remaining 10 inches on the wings on either side angled upward. I purposefully did not crease the wing at where the fuselage joins the wing but 5/8 inch outside (2 inches off center) because of my concerns for ease of mounting the wing and strength.

I used the stock BB V2 spar template for measurements for the ½ inch high spar. I drew out a 4 inch long, ½ inch high center section. Then, at 2 inches off center, I drew the spar bottom line at a 5° angle using a compass, out to 10 inches on either side of the 4 inch center section. I then used the compass to mark 90° off the spar bottom line and drew a perpendicular line of ½ inch high, the height of the spar. I connected the two marks to draw out the top of the ½ inch spar for each of the 10 inch, upward angled portions of the wings. I next drew in the 1 inch tabs to fit into the wings at the stock 5 inches in from wing tip (5 inches from wingtip + 1 inch tab + 4 inches to dihedral break + 2 inches to center = 12 inches each side). I repeated this 3 times to make 4 spars, and, after cutting out the 4 spars, glued 2 spars together for each wing. By using a one-piece spar, I hope it will give me greater strength than joining 2 or 3 sections together.

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Since the lower wing is the more difficult to prepare, I first prepared the stock lower wing. I had to increase the cutout section between the ailerons by a ½ inch on both sides to match the dihedral break (A 4 inch cutout instead of a 3 inch cutout.) and added clear packing tape to the leading edge for added strength. To allow for the dihedral, at 2 inches off center on each side, I creased the inside portion of the bottom of the lower wing and cut through the top portion of the lower wing (Marked with barbeque skewers on the photo.).

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To assemble the lower wing, after dry-fitting everything to make sure it all fit, I decided it would be easier to fit the center section first, the outer wings sections after that. To make sure everything lines up, I drew 2 parallel lines connecting the 2 holes in the wings for the spar tabs. I hot-glued in the center section, making sure it fit within the parallel lines and matched the break in the wing where the dihedral begins. I then hot-glued in the side spars, one side at a time. The dihedral is now beginning to be formed.

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After securing the spar, it was time to build the top of the wing. I first folded over and hot-glued one of the 10 inch sides, followed by folding over and securing the other 10 inch side. This left the 4 inch center section the last to be fitted.

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Because of the angle, the space on top for the center section is actually slightly less than the 4 inch bottom. I test fitted the center section and found that I could force it into the opening without trimming the sides but it was a very tight fit. This tight fit should give the wing added strength. You may need to trim or sand the sides to fit, especially if your angle is greater than 5°. To add more strength to the joint, I ran a bead of hot-glue down the 2 seams where the outer wings join the center section, squeegeeing off the excess.

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I repeated the same procedure for the upper wing, including increasing the rear center cutout to 4 inches at the forward edge to fit the dihedral break in the wing. Because the upper wing does not have the fuselage rail cutouts in the center section like the lower wing top, the center section was almost too tight to fit. Again, I recommend test fitting the center section after constructing the wing ends and trimming or sanding slightly, if necessary.

After painting the wings and wing struts, I assembled the wings just like one assembles the stock BB V2 wings. Although not readily visible, there is a slight dihedral to both the upper and lower wings.

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I then mounted the wings to the fuselage, set the control surfaces and checked the throws.

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FLIGHT REPORT

So, did the dihedral help tame the squirrelly nature of the Baby Blender? In a word: Somewhat.

It was a relatively calm morning on the test flight. After trimming out the BB V2, I noted that it was less squirrelly and more stable in flight with the wing with dihedral. Because the wings are short and stubby, it is still a handful in the air and not a sedate trainer. However, with the dihedral in the wing, it is just not as much of a handful. Also, the dihedral wing did not adversely affect the BB V2’s ability to do loops or snap (and I do mean “snap”) rolls.

By the third battery, winds had kicked up to around 7-10 mph. While the Baby Blender is not a big fan of winds, the BB V2 handled better the winds with the wing with dihedral than with a flat wing.

As noted above, I added 5° of dihedral on each side. A greater angle may add more stability but you also start loosing lift.

Now time to print out USAAC “Star and Ball” roundels for the new wings to finish her.

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#2
Awesome, I have the same problem. Very squirrely I the air. So much that it I need to build a new one. I am going to add the dihedral as you did. Thank You for the build tip, pics and explanation.