Reference / Paper · 2015
Peak of Flight #398: The Effect of Blade Twist on Helicopter Descent
Apogee Components' Peak of Flight newsletter, issue 398 (2015-08-25).
- peak-of-flight
- apogee-components
- model-rocketry
Reference / Paper · 2015
Apogee Components' Peak of Flight newsletter, issue 398 (2015-08-25).
Apogee Components' Peak of Flight newsletter, issue 398 (2015-08-25).
In This Issue The Effect of Twisting Helicopter Blades at an Angle On Duration Cover Photo: The redisgned SR-99 Hyperswift rocket kit from North Coast Rocketry Get yours at: www.apogeerockets.com/Rocket_Kits/Skill_Level_3_ Kits/SR-99_HyperSwift Apogee Components, Inc. — Your Source For Rocket Supplies That Will Take You To The “Peak-of-Flight” 3355 Fillmore Ridge Heights Colorado Springs, Colorado 80907-9024 USA www.ApogeeRockets.com e-mail: [email protected] Phone: 719-535-9335 Fax: 719-534-9050 ISSUE 398 AUGUST 25, 2015 The Effect of Twisting Helicopter Blades at an Angle On Duration By Allison Van Milligan The Objective of the Work 1.26” wide 13” long I am trying to create the most effective helicopter blades possible. I will use data from my sisters R&D report and then conduct my experiment. I will be evaluating blade twist to see if that increases the descent time. The Approach Taken Tapered shape chosen that would fit into a FAI style body tube. Step 1: I chose all the different helicopter blade shapes and angles I was going to test based on my sister Ashley’s R&D project. I decided to test the best three blade shapes. I would test a twisted and non-twisted version of each shape. The shapes I used were the optimum blade that I created last year, https://www.apogeerockets.com/education/ downloads/Newsletter381.pdf a blade that was rectangular, and finally a rectangular shape with a tapered end. I The different blade shapes used in this experiment Allison’s Optimized Blade from 2014 Rectangular Blade Shape Image 2: Tapered shape chosen that would fit into an FAI style body tube. a rectangular blade that would fit in an FAI body tube. The only difference with this blade compared to the rectangular blade is it tapered on both the leading and trailing edge of the blade to fit inside the tube (see Image 1). The blade that I created last year had a wider point at the root and then it got thinner more steadily as it went to the tip of the blade. This is the blade I found to be the most effective shape last year. Step 2: I had to figure out how I was going to twist the blades. 0.3268” 1 inch Tapered Blade Shape Image 1: The different blade shapes used in this experiment. tested all three of these shapes twisted and not twisted. The rectangular blade was just a rectangle. I used this blade to create a baseline so that I would have something to compare the other blades to. The only problem with this blade is it does not fit into a 40mm FAI body tube (see Image 2). My sister Ashley Van Milligan tested all of these blades for her R&D to find the best angle of attack, and I was going to use her results and find out if a twist made it better. She built them the same way as I, and I tested them the same way she did (see newsletter https://www.apogeerockets.com/education/downloads/Newsletter397.pdf ). I was going to make the blades twist at 5 degrees starting from the root of the blade and then curving out. The objective was to make the tip at 0° angle of attack and the root at -5° angle of attack. I started the process by drawing straight black lines down a 4 inch PVC pipe that has an outside diameter of 4.5 inches. Then my Dad and I did the math to figure out how much 5° measured. I created a tapered blade because I wanted to have Continued on page 3 About this Newsletter Newsletter Staff You can subscribe to receive this e-zine FREE at the Apogee Components web site (www.ApogeeRockets.com), or by sending an e-mail to: [email protected] with “SUBSCRIBE” as the subject line of the message. Page 2 Writer: Allison Van Milligan Layout / Cover Artist: Chris Duran Proofreader: Michelle Mason ISSUE 398 AUGUST 25, 2015 Continued from page 2 Effect of Twisting Helicopter Blades at an Angle On Duration each blade 0.19 inches away (see Image 3). To create the curvature and twist on each blade I had to wrap them around the PVC pipe at the angle of .19 inches. Because the wood is brittle, I sprayed each blade with an ammonia/water mix to make the wood flexible. Step 1: Draw blade chord at 0° Angle-of-Attack on the PVC Pipe. This will be the tip cross section Step 2: Rotate the chord 5°. This will be the root cross section. Then I taped the root trailing edge corner of the blade on the red line and the tip trailing edge corner along the black line (see image 4). I did this for the 3 shapes that were twisted. I also had 3 sets of the same shapes that were untwisted. For the untwisted blades, they were oriented so the trailing edge was along the black line. After all the blades were taped on the PVC pipe I wrapped an old sheet around them so it would hold the blades to the curvature of the tube while they were drying. I set the blades out in the sun for about 4 hours to dry. Step 3: Measure the distance between the edges. This will be the rotation distance when wrapping the blades on the PVC pipe. Image 5: Wrapped tightly in cloth and allowed to dry. Image 3: Diagram layout for wrapping the blades on the PVC pipe. Step 3: Reinforcing the blade attachment slots We found out that each blade needed to be rotated 0.19 inches from the trailing edge. Along side of each black line on the PVC pipe I drew a straight red line to the left of Once the blades were curved I had to put a mesh-like material (called skyloft) over the slot hole on the blade. I needed to do this because this prevents the slot hole from tearing and I needed to create these blades like I would for my actual rockets. To put the Skyloft mesh on, I cut pieces about 1 inch wide and 2 inches long. They weren’t always the exact same they just needed to be big enough to cover the slot holes. I then set the Skyloft over the hole and put thin super glue over all of it. Image 4: Blade rotated 0.19” to create twist. Continued on page 4 www.apogeerockets.com/Team_America_Challenge ISSUE 398 AUGUST 25, 2015 Page 3 Continued from page 3 Effect of Twisting Helicopter Blades at an Angle On Duration Once it was dry, if any mesh went over the edge of the blade I cut it off with a hobby knife, and cut out the piece in the slot hole. FAI helicopter weighs. Once that was done I had to balance the hub with the blades. I did this by putting a string through the hub and Step 4: Preparing the blades to drop I needed all the blades to be the exact same when I dropped them. In each different set of blades I weighed each of the three blades and found the one which had the greatest mass. Then I added enough clay to the other two blades of the set so that all three blades had the same mass. Then I found the balancing spot of the heaviest blade and used it to mark where the other blades needed to balance. I bal- Image 6: Each blade is balanced so both the weight and the CG position are the same for the entire 3-blade set. anced these blades in the same spot by adjusting the spot the clay was placed on the blade. I repeated this step for each blade set. I needed all three of the blades and the drop test fixture to have a total mass of 20g. They need to be 20g because each blade set has to have the same mass, and 20g is about how much a typical Image 7: After the blades are attached to the drop fixture, clay is added or removed from the bucket so that it weighs 20 grams. Image 8: Close-up view of the hub used on the drop fixture. pulling it straight. I spun the blades and marked the blade that landed on the bottom. I spun it again and if it was the same blade I moved some of the clay around to make that side lighter. I did this until it was perfectly balanced. Step 5: Drop tests Now it was time to test the blades. My Dad and I went to this “historic” bridge that was 32 feet and 2 inches above the ground. We had to go at dusk since it was since it was under construction. I went to the top of the bridge and my Dad went down underneath it. I counted down 3..2..1..Drop and then I dropped the blades while my Dad was timing it. Once the blade got to the bottom my Dad would pick it up while I threw a string Continued on page 5 www.apogeerockets.com/Rocket_Kits/Scale_Rockets Page 4 ISSUE 398 AUGUST 25, 2015 Continued from page 4 Effect of Twisting Helicopter Blades at an Angle On Duration 5. Tapered Not Twisted 6. Rectangular Twisted My data shows that the only way to have a rectangular blade work is to have it not twisted. I’m not a 100% sure this is accurate because my sister found it to perform poorly. Either way it doesn’t affect me that much because I cannot use this blade anyway since it won’t fit in the tube. Image 9: Drop test from bridge. with a paper clip on the end over the bridge. My Dad attached the blade set to it so I could pull the blades back up and drop them again. My Dad recorded the times for each test. I repeated this 3 times for each set of blades. Once it was time to change blade sets my dad put the next blades on the hubs and added the extra weight if needed. My Dad and I repeated this until all 6 blade sets had been tested. List of Any R&D Reports Previously Entered By Me “The Effect of Blade Curvature and Angle-of-Attack on Helicopter Descent” NARAM-57 R&D report By: Ashley Van Milligan, 2015 “Finding the Best Gyrocopter Blade Shape and Best Place to Attach the Blade” NARAM-56 R&D report By: Allison Van Milligan, 2014 The Results Obtained The optimum shape I created last year still showed to be the best blade shape overall. And it is even better when the blade is twisted. I did discover when actually building the rockets that the new configuration of blades would not fit into the body tube. Since the blade is not centered on the mounting arm (it is attached at a point 0.3268” from the trailing edge), it would deform the tube. And then the nose cone would not fit on the rocket. I tried to move the blade attachment point to the middle of the blade, like it was for the rectangular and Image 10: Tube deformithe tapered blades. ty due to blade shape. As my chart shows the order from best to worst: 1. Rectangular Not Twisted 2. Allison’s Optimum Twisted 3. Tapered Twisted 4. Allison’s Optimum Not Twisted FREE Rocket Construction Videos A new Apogee video every two weeks to help you become a better modeler! www.ApogeeRockets.com Image 11: Drop time results bar graph. Continued on page 6 Join Tripoli.org Mention Apogee Components ISSUE 387 AUGUST 25, 2015 Page 5 Continued from page 5 Effect of Twisting Helicopter Blades at an Angle On Duration However, when I did a drop test to see how well it spun, it didn’t spin at all. It was just like the rectangular blade. My dad came up with the solution to move the mounting arm on the hub so that it was off-center. This way the blade could be centered in the tube, and it would still be mounted at the correct angle. Flight tests performed on July 19 showed that the blades and the new hub configuration performed well. The second flight thermaled away after 2 minutes on an A3-4T motor. The Conclusion Drawn My conclusions are that twisting helicopter blades increases the descent time unless it is a straight rectangular blade. The optimum blade that I created last year still has proven to be one of the best shapes. For my FAI gyrocopter rockets I will twist my optimum shape. I will be testing out how well they work in competition on Saturday at the FAI tryouts. Further Work that Would Clarify or Extend Results If I had more time and money I would’ve liked to have done more drop tests, more actual flight tests, and tried testing different degrees of twisting the blades. Blade Shape Twisted Y or N Drop Height Drop Weight Drop Time 1 Drop Time 2 Drop Time 3 Notes Avg. Drop Time Rectangular Yes 32ft 2in 20g 3.47s 5.94s 5.34s None to Slow Rotation 4.917s Tapered Yes 32ft 2in 20g 7.22s 5.13s 5.9s Worked Okay 6.83s Allison’s Optimum Yes 32ft 2in 20g 8.22s 8.25s 6.37s Worked Good 7.613s Rectangular No 32ft 2in 20g 9.78s 5.12s 8.19s Tapered No 32ft 2in 20g 6.28s 4.25s 5.94s First & Second Test Slow to Start Rotating; Third Hit Bridge 5.49s Allison’s Optimum No 32ft 2in 20g 6.29s 5.56s 6.38s Unbalanced 6.077s Image 12: Drop test chart results. Minimum Diameter Motor Retainers! Apogee is your one stop shop for your minimum diameter rockets projects! • Fly High • Fly Fast We Have: • Minimum Diameter Retainers • Motor Extenders • Threaded Forward Closures • Adapters for • Impress Your Cesaroni Cases Friends! RockSim Version 9! Great for High-Power Rockets Design It. Smooth Surface - No Spirals Super Strong and Tough Launch It. Easy to Paint www.RockSim.com Waterproof For further information, call Apogee Components at: 719-535-9335. Centering Rings Bulkhead Disks Fin Stock www.ApogeeRockets.com/ProLine_Composites Page 6 ISSUE 398 AUGUST 25, 2015 www.ApogeeRockets.com Build Rock-SolidYour Rockets Cool Rocket Designs So Much Better In With FiberglassLook Parts Fiberglass Tubes Nose Cones Couplers First Test hit Bridge; 7.697s Inconsistent