Fun with Rockets (When the Weather Improves)

My RocketCopter arrived a week ago, but the weather has not been cooperative enough for a launch. EDIT: I had a chance to launch on Friday and the video is here. It's a helicopter-recovery model rocket designed for "A" type motors. Theoretically, the rotor blades should flutter out on hinges when the rocket begins its descent to Earth. The launch lugs are sized for a 1/8" launch rod. The versions pictured below are in Royal Blue Strong & Flexible and White Strong & Flexible.



The hinges are loose enough that gusts of wind will make them flutter on the launch pad. I don't anticipate a problem with the blades deploying after acceleration ends.



This project is to make up for a failing 8th-grade rocketry project. My 8th-grade self decided that form was more important than function for model rockets, and I made mine look like a fighter jet. It looked amazing, but was horribly non-aerodynamic. It twirled, flaming, into the gathered crowd of my fellow students. My teacher generously gave me a D for the project.

Awesome design, I love it. Can't wait to see it in action.

SOOOO COOOL!

Feature this dude, I don't even care if it flies or falls. Epic idea that looks very cool.

This does look awesome, but have you done a drop test? Looks like your center of gravity may be fairly high. In my uneducated opinion (not a rocket scientist) it will want to nose dive. If the center of gravity is lower than the center point, that should be less of a concern.

I'd be interested in learning what happens with a drop test as well once you have an expended motor in there.
I'm not a rocket scientist either, but I think you'll have a fairly stable descent since your lifting surface is above your center of gravity.

Regardless, this is an awesome idea and a great execution!

Remember to wear safety goggles so you don't take an eye out!

Thanks, everyone. It doesn't nosedive during a drop test, but I don't know if the rotors will provide enough resistance to slow the descent. No work tomorrow and the forecast is for sun and low wind. And MrNib, I will certainly be wearing safety goggles.

Oh man, I'm going to have to see this!! What an amazing idea. Be sure to show your 8th grade too

Looks like a great idea, but I have a couple of aerodynamic concerns.

1) the CG is SUPPOSED to be high (toward the nose) for rockets, at least the model kind. That keeps a deflection of the nose from overpowering the fins.

2) I'm concerned about the rotors for two reasons. First, I'm not sure they're big enough. It MIGHT be that if they don't slow the drop enough, you could try 3 rotor blades with twice (or even more, through overlapping...) the area. (or, a double layer of blades, one hinged about an inch above the other...) Second, it looks like you're depending on the engine ejection charge to deploy the rotors. My worry there (particularly after your comment about them fluttering on the launch stand...) is that you'll still have enough forward movement to collapse them again, and might not get them to re-open. Is there some kind of latch to keep the blades deployed? Ot perhaps you could use some very light elastic of some kind at the top to open them as your airspeed drops. Very light, because you don't want it opening the blades before then. Or maybe the motor mount could be designed to slide a bit when the ejection charge goes off, unlatching the lower/outer end of the blades and letting a stronger spring deploy them?

(Dad was an aero engineer, and I launched a lot of Estes rockets as a kid.)

(Didja put a screamer whistle in the engine nacelles?)

I managed a few test flights on Friday and the video is here. I apologize for the videography. I lost track of the rocket each time between the launch pad and where it hit the ground. Even with the highest-power engines, the rocket did not fully deploy the rotors. It started to rotate and stabilize shortly before landing on most launches. I think it might need more altitude to fully helicopter as intended. Also, the wind knocked the rocket sideways as soon as thrust ended. Some things I learned:

1. WSF is more resilient than I thought. Each of the two rockets survived four test flights each. However, it becomes quite malleable when exposed to the heat of the engine and the rocket needs to cool before launching again. The last launch on the video (the one that goes all squirrely) was probably hindered because I didn't allow the WSF to cool and stiffen between flights.

2. I need to design a way for the rotors to remain flush with the barrel of the rocket while under thrust. I think rotor flutter reduced the altitude the rocket achieved.

3. I need to move somewhere less windy. We're going to have a constant 10-20mph wind in Michigan for the next four months. Any suggestions? Arizona maybe?

@TrainThingz: No, there is no latch to keep the blades deployed. I'm pondering what sort of system of elastic bands, string, or latches would keep the blades flush under thrust and deployed after thrust. This is something I'll have to chew on a bit. Thank you for the advice and suggestions, they will be helpful when I make changes to the design.

@bartv: My 8th-grade rocket is still in my parents' attic somewhere. The RocketCopter isn't perfect yet, but it's 1000% better than the aeronautical monstrosity I unleashed back then.

Some modifications/ideas you might consider for your next effort...

1) I'd consider making the fins a bit larger... maybe increasing their area as much as 25%, to make them more effective.

2) Either cant the fins slightly (only a degree or two) or make one side of the fin curved (like an airfoil, it should spin TOWARDS the curved surface) to put rotation on the rocket in flight. This will help in several ways.
a) The rocket will be more stable and less likely to "weathercock" like the last flight in the video.
b) The rotation will help the rotor blades deploy when they're released. (centripetal force)
c) The rocket won't depend on the blades to begin rotation, it will already be established, This will PROBABLY help you to get the thing spinning and slowing the drop sooner.

3) Make the motor mount slide back when the ejection charges fires. This will move the CG of the rocket rearward, and you can use this movement to release the blades if you make latches on the mount that hold the tips of the blades.

4) Use some kind of spring(s) or rubber band(s) inside the rocket body at the top to pull hooks on the tops of the blades to the center when they're released. This will be a kind of "booster" to get the rotors deployed without having to rely on it falling tail-first, and air doing the job. If necessary, increase the diameter of the rocket body around the point where the rotors are hinged... there are any number of real and model rockets whose diameter just below the nose cone is significantly larger than the rest of the body.

You might try some drop tests with the rockets you have, too... stick an expended engine in them. rig the rotors with thread or tape to hold them open, and try dropping it tail-first out of a second or third story window. Give it a little spin to get it started, too. That will help you verify that the rotors actually will do what you want them to.

I REALLY want to see this thing working right!

@TrainThingz: I have updated the model with thicker walls near the base for added weight and greater structural integrity. I am also going to follow your suggestions #1 and #2 to modify the fins. I will test it with these changes and modify it further if necessary. Thanks for the advice!