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Okay, here's my first try at a build thread. Be kind.
Always hazardous to suggest something is really new. These are features of this helicopter that I think are either new or at least uncommonly used:
1. Size. Certainly not the largest ever launched, but I think it is bigger than anything you can buy in the store at the moment.
2. Integrated Rotor-Fin (the component that functions as a fin for stability in boost phase is an actual functioning part of the rotor on descent.) This has been used on the FlisKits Tiddlywink, otherwise I have not seen it.
3. Reinforced floss/tape hinges. Double tape hinge has been in use for a while. I first found it on a QCR flopwing glider (I think.) Sewing the hinges in with dental floss is something I haven’t seen elsewhere. (Other types of thread will probably work as well and might be lighter.) Sewing it in makes it a lot stronger with what I think is negligible weight penalty.
4. The flop-rotor design with the Standoff Hinge.
5. The “burn band” motor retention system with “Burn Chamber” and “Blow-Out Assist” deployment of the rotors.
6. Pyramid Nose Cone
Goal was to create a flop-rotor helicopter with at least a 10 foot rotor cone diameter, and keep it within the realm of low power engines. Note I had actually hoped for a 12 foot rotor cone but early on felt the weight would be prohibited by low power engines (at least in this prototype level)
Also was hoping for a model with engine retention rather than my typical engine eject models—mainly because while engine ejection is accepted with sport models and most people probably wouldn’t whine too much about getting conked with an A, B, or C engine, and maaaaybeee a D, dumping an E casing from 300 or 400 feet didn’t sound very smart.
Decision for 4 rotors rather than 3 had to do with weight. To create a continuous “fuselage” of balsa around the engine mount, you can use less balsa with 4 “sides” than with 3. (The smallest square you can draw around a circle has smaller total circumferential diameter than the smallest triangle you can draw.) Tim Van Milligan tells me that you also get more DRAG during launch with 4 blades, but I felt that in my case launch weight was more critical. Also, my engine retention method used here works much easier with 4 than 3 rotor-fins.
Understand before this I had never launched anything greater than a D, and basically I thought D was pretty high. At 4 bucks an engine at Hobby Lobby WITH the 40% off coupon, going up to the E9-4 was a stretch for me.
Biggest challenge on a Flop Rotor of this sort, with a single elastic actuator which operates BOTH the central hub hinge and the flop hinge, was getting the central rotor blade to be stiff enough NOT to flex. Finally figured I'd try 1/4 inch balsa-- which was CERTAINLY stiff enough but obviously presented weight issues.
Note for reference from here on out I will name these rotors according to their position during the BOOST phase. Since the central rotor is on the OUTSIDE of the rocket in boost, I call it the OUTER-ROTOR. The peripheral rotor is on the INSIDE during boost, so it is the INNER-ROTOR. When these two are attached, they are referred to as the Rotor-Fin.
I am writing this as if I was telling you how to build it. I found the grammar easier to keep up with that way.
Parts:
Parts:
one sheet of 36" x 6" x 1/4" balsa
two sheets of 36" x 6" x 3/32" balsa
Duct Tape
Dental Floss
Kevlar Thread (for pull strings and nose dowel loops)
2 small paper clips to make s-hooks.
3/8 inch dowel 3 feet long.
BT-50 body tube
BT-50 nose cone (just about ANY shape nose cone will work)
Mylar Tape
Thrust Ring for D engine BT-50
E size engine hook recommended
4 short (1 cm) carbon fiber strips, 1/4" thick or less.
4 short (6 cm) carbon fiber rods, 1/8" is fine
Lots of #16 [2.5” x 1/16” rubber bands (you can get a 1 Lb bag at Office Depot for $5.29. I don’t know how many are in a pound, but it is a lot. https://www.officedepot.com/a/product...bber-Bands-16/.) The rocket uses 24 for pull strings, which are re-usable (haven't had to replace them after 7 launches), and two "burn bands" are consumed at each launch.
Qualified Competition Rockets ejection protecting "plugs" for D-engine rockets for centering "rings" for the dowel. Note you can make centering rings out of lots of different materials, I just happened to have some of these.
Large Crochet Hook
3/16 inch launch lug, can cut them from a 1 inch segment.
Small piece of heavy card stock for centering squares.
Always hazardous to suggest something is really new. These are features of this helicopter that I think are either new or at least uncommonly used:
1. Size. Certainly not the largest ever launched, but I think it is bigger than anything you can buy in the store at the moment.
2. Integrated Rotor-Fin (the component that functions as a fin for stability in boost phase is an actual functioning part of the rotor on descent.) This has been used on the FlisKits Tiddlywink, otherwise I have not seen it.
3. Reinforced floss/tape hinges. Double tape hinge has been in use for a while. I first found it on a QCR flopwing glider (I think.) Sewing the hinges in with dental floss is something I haven’t seen elsewhere. (Other types of thread will probably work as well and might be lighter.) Sewing it in makes it a lot stronger with what I think is negligible weight penalty.
4. The flop-rotor design with the Standoff Hinge.
5. The “burn band” motor retention system with “Burn Chamber” and “Blow-Out Assist” deployment of the rotors.
6. Pyramid Nose Cone
Goal was to create a flop-rotor helicopter with at least a 10 foot rotor cone diameter, and keep it within the realm of low power engines. Note I had actually hoped for a 12 foot rotor cone but early on felt the weight would be prohibited by low power engines (at least in this prototype level)
Also was hoping for a model with engine retention rather than my typical engine eject models—mainly because while engine ejection is accepted with sport models and most people probably wouldn’t whine too much about getting conked with an A, B, or C engine, and maaaaybeee a D, dumping an E casing from 300 or 400 feet didn’t sound very smart.
Decision for 4 rotors rather than 3 had to do with weight. To create a continuous “fuselage” of balsa around the engine mount, you can use less balsa with 4 “sides” than with 3. (The smallest square you can draw around a circle has smaller total circumferential diameter than the smallest triangle you can draw.) Tim Van Milligan tells me that you also get more DRAG during launch with 4 blades, but I felt that in my case launch weight was more critical. Also, my engine retention method used here works much easier with 4 than 3 rotor-fins.
Understand before this I had never launched anything greater than a D, and basically I thought D was pretty high. At 4 bucks an engine at Hobby Lobby WITH the 40% off coupon, going up to the E9-4 was a stretch for me.
Biggest challenge on a Flop Rotor of this sort, with a single elastic actuator which operates BOTH the central hub hinge and the flop hinge, was getting the central rotor blade to be stiff enough NOT to flex. Finally figured I'd try 1/4 inch balsa-- which was CERTAINLY stiff enough but obviously presented weight issues.
Note for reference from here on out I will name these rotors according to their position during the BOOST phase. Since the central rotor is on the OUTSIDE of the rocket in boost, I call it the OUTER-ROTOR. The peripheral rotor is on the INSIDE during boost, so it is the INNER-ROTOR. When these two are attached, they are referred to as the Rotor-Fin.
I am writing this as if I was telling you how to build it. I found the grammar easier to keep up with that way.
Parts:
Parts:
one sheet of 36" x 6" x 1/4" balsa
two sheets of 36" x 6" x 3/32" balsa
Duct Tape
Dental Floss
Kevlar Thread (for pull strings and nose dowel loops)
2 small paper clips to make s-hooks.
3/8 inch dowel 3 feet long.
BT-50 body tube
BT-50 nose cone (just about ANY shape nose cone will work)
Mylar Tape
Thrust Ring for D engine BT-50
E size engine hook recommended
4 short (1 cm) carbon fiber strips, 1/4" thick or less.
4 short (6 cm) carbon fiber rods, 1/8" is fine
Lots of #16 [2.5” x 1/16” rubber bands (you can get a 1 Lb bag at Office Depot for $5.29. I don’t know how many are in a pound, but it is a lot. https://www.officedepot.com/a/product...bber-Bands-16/.) The rocket uses 24 for pull strings, which are re-usable (haven't had to replace them after 7 launches), and two "burn bands" are consumed at each launch.
Qualified Competition Rockets ejection protecting "plugs" for D-engine rockets for centering "rings" for the dowel. Note you can make centering rings out of lots of different materials, I just happened to have some of these.
Large Crochet Hook
3/16 inch launch lug, can cut them from a 1 inch segment.
Small piece of heavy card stock for centering squares.
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