The Hurricane Helicopter Blade Twisting Device

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Ray King

I have been building and studying helicopter recovery rockets for the last couple years. I have read a number of R&D reports as well as attended a number of NARCON presentations on how to improve performance. One of the key areas identified is blade twist. Blades should be twisted at steep angle of incidence near the rocket body and flatten out toward the tip. This device will allow you to twist 14" blades at varying angles to optimize the rotor blade performance.

Here is the material required:

• 1 - 1" x 6" x 16" (Adjust this dimension to change blade length) - Frame Base
• 2 - 1" x 6" x 10" - Frame Sides
• 2 - 1"x 5" x 5" (Actual Dimensions) - Pivot Sides
• 2 - 1.5"x 4.25" x 2.875" (Actual Dimensions) - Pivot Clamps
• 2 - 1.5" x 2.0" Hinges
• 2 - Draw Hasps
• 2 - 5/16" x 2" carriage bolts, washers and nuts.
• 2 - ¼" X 2" bolts
• 10 - #8 X1.25" Drywall screws

Construction:

Starting from the inside and working out.

Clamps:

To make the clamps first draw a line from corner to corner diagonally to mark the center. Draw another set of lines through the center point marking the center of each side. Now cut the 1.5"x 4.25" x 2.875" in half opposite the grain (see picture right)

Next mount a hinge on one side and the hasp on opposite side of the wood clamp. Repeat for the other end. These will be used to clamp the blades during the twisting process. In order to clamp the blade cut the blade shape into the top clamp using a Dremel tool or what ever you feel is best (I am still perfecting this).

Clamp pivots:

Now on the 1"x 5" x 5" clamp pivot mark the center by drawing diagonal lines and the perpendicular lines in both directions through the center. Drill a 5/16" hole through center. Now countersink 1 side so the head for the carriage bolt is flush or slightly below flush. Drill a ¼" hole - .5" from the top on the center line. Do this to each clamp pivot (see picture left)

Attaching the clamps and clamp pivot:

Mount the bottom portion of the clamp using 2 drywall screws so that the center of the closed clamp is on the center line of the pivot (see pictures below).

Frame:

The next step is the construction of the frame. Mark a hole in the center from side to side (3") and 3-5/8" from the top on each frame side. Using a protractor draw a line at 80, 70, 60, 50, 40, 30, 20, and 10 degrees from the center line (see picture below left). Now, drill a 5/16" hole on the centerline marks. Now mount the clamp pivots using the 5/16 carriage bolts, washer and wing nuts. Tighten until snug. Align the horizontal line on the clamp pivot with the first mark (10 degrees from horizontal) (See picture below right). Now drill a ¼" hole thru the top hole in the center of the clamp pivot and the frame. Do your best to use the clamp pivot hole as a guide without enlarging it. Now repeat for all the rest of the lines.

Finally, screw the sides and frame base together using the drywall screws.

Using the Hurricane:

Using the Hurricane is very simple. Soak the balsa wood blade in a mixture of warm water and ammonia for roughly 2 hours. Then place the blade into the clamps. Lock one clamp pivot with the bolt. Twist the pivot block to the desired angle and lock in place using the hole in the center of the pivot block. I leave blades in the Hurricane for 24 hours and then repeat for each blade.

I hope this device helps you improve your performance of your helicopter rockets. Feel free to offer any improvements - this is a work in process.

GUEST's OPINION:
04/09 - "Thanks G.A.R. Send EMRR some pictures of your modification and ask them to add them to this tip page. It sounds like a nice improvement. I would like to see this improvement as well as some pictures of your rocket... e-mail me off the Who's/Who page. Thanks." (R.K.)

GUEST's OPINION:
03/09 - "Got to try my 1/8A HD for first time yesterday. The blades were "twisted" with this jig. Even though I didn't get much height, my first attempt @ an HD, the blades rotated flawlessly. Everyone @ launch impressed. This is a new class this year and quite challenging. With the help of the "Hurricane," I'm sure the height will come and the recovery will work fine. I did make a change though. Instead of a "fixed base," I mounted each side to a 4" base. Then I permanently fixed one side to 16" base. The other side I drilled 2 holes about 1" in from inside edge. I then marked the large base in 1 " increments. Screwed it to 16" base thru holes I drilled. Now its adjustable." (G.A.R.)

GUEST's OPINION:
12/08 - "Ingenious! Do u have any other tips for "helicopter recovery?" (G.R.)

1. Fins
   One of the "pain in the a---s" is making/sanding the correct angle on the blades for "Helicopter Recovery." The other is trying to hold the blade, while sanding. I found an old book, (one you no longer want), and has a plastic cover. Or cover the book in plastic or wax paper. **Cover shouldn't move**. Lay one edge of your helicopter blade along edge of book. Most people mark the blade with a line down the middle in pencil. Then draw another line down the middle of Half of the blade. So you have the blade divided in "half" and one half divided again or 1/3. Take some masking tape, I use painters tape, and run a long piece with the edge along "middle" pencil line. You're now protecting 1/2 the blade and exposing "trailing edge of blade. Take a few more pieces of masking tape and go over end of the masking tape, **being sure not to cover blade,** Use your finger nail and press down tape so it's secure. Take a very long sanding block, (tile float, with sand paper attached works), longer than blade. Hold on slight angle and sand edge ‘til you start to sand "masking tape." Once you r satisfied with "trailing edge," remove tape. Repeat by turning blade 180 degrees and taping middle of 2nd half of blade to book edge. (only 1/3 of blade exposed). Sand till satisfied with "leading edge." This works well and is relatively fast, if you’re making multiple blades. - G.R. (PA)