Propeller-Stabilized Rocket!

[UpsilonAerospace]

So, apparently, many rockets use these jutting-out-bits, made out of some sort of wood or plastic. These bits are placed near the bottom of the rocket, and they make the rocket fly straighter. And get this: They're called 'fins'. Who knew?

You know, there are only a few types of fins out there, compared with the incredibly wide variety of other fiddly bits that make rockets special. Sure, there are interesting variations on fin design, such as tube fins and ring fins. For the most part, though, they're not very interesting compared with the remainder of the rocket.

So, as I was just about to go to sleep, it hit me: Propellers mounted on the end of dowels would make really great fins! They have auto-gyro-stabilization. They would continue to provide lift after burnout, resulting in interesting-looking boosts. They're unconventional and cool-looking. Hey, they could even help a little with slowing the rocket for recovery!

Okay. Maybe this is one of the top worst inventions that was ever forced into the rocket community. Maybe the fins will just shear off, despite the amount of epoxy glommed on. Maybe I'll finally manage to be banned from my rocketry club. But it's worth a try! I'll start out with a little 18mm motor powered contraption and work my way up.

Here's a concept picture:



Wish me luck!

 

[shrox]

So, apparently, many rockets use these jutting-out-bits, made out of some sort of wood or plastic. These bits are placed near the bottom of the rocket, and they make the rocket fly straighter. And get this: They're called 'fins'. Who knew?

You know, there are only a few types of fins out there, compared with the incredibly wide variety of other fiddly bits that make rockets special. Sure, there are interesting variations on fin design, such as tube fins and ring fins. For the most part, though, they're not very interesting compared with the remainder of the rocket.

So, as I was just about to go to sleep, it hit me: Propellers mounted on the end of dowels would make really great fins! They have auto-gyro-stabilization. They would continue to provide lift after burnout, resulting in interesting-looking boosts. They're unconventional and cool-looking. Hey, they could even help a little with slowing the rocket for recovery!

Okay. Maybe this is one of the top worst inventions that was ever forced into the rocket community. Maybe the fins will just shear off, despite the amount of epoxy glommed on. Maybe I'll finally manage to be banned from my rocketry club. But it's worth a try! I'll start out with a little 18mm motor powered contraption and work my way up.

Here's a concept picture:

View attachment 156680

Wish me luck!

Well, actually the propellers will slow the rocket after burnout, they are a source of drag like any surface is. They would work as a heli kind of recovery.

 

[aerostadt]

The sidewinder missile had rollerons housed in the aft fins that provided a gyroscopic action to reduce spinning of the rocket.

 

[fyrwrxz]

With the addition of a few rubber bands, these could assist with lift off! Hmmmm.....

 

[luke strawwalker]

The sidewinder missile had rollerons housed in the aft fins that provided a gyroscopic action to reduce spinning of the rocket.

Good point... I was going to post that... couldn't recall what they were called exactly til I read your post though...

Chaparral had them too...

Later! OL JR

 

[K'Tesh]

The sidewinder missile had rollerons housed in the aft fins that provided a gyroscopic action to reduce spinning of the rocket.

but those are rotating in line with the length of the rocket. The design seen in the OP however isn't. I'm worried about how much drag those rotors would generate. I'm betting that they'd never get to the speed needed to gyro stabilize the rocket.

 

[Salvage-1]

They would definitely act as a drag stabilizer, once they are turning and 'up to speed'. The problem that I see is that they will take a short while to 'spin' up, and may not be providing enough drag during the first 1/2 second of motor burn.

 

[Daddyisabar]

Build it and see how it works. Low and slow?

 

[TopRamen]

The sidewinder missile had rollerons housed in the aft fins that provided a gyroscopic action to reduce spinning of the rocket.

So that's what those Rollerons are for! I knew they had something to do with the way the Fins worked inflight, but not what it was exactly.
The first time I saw them I thought they were for if you could'nt find the right amout of Folks to lift the Missile, you could just roll it around on its Rollerons like a Wheelbarrow by lifting the Nose, but then I realized that that was a Dumb Thought, and that they surely must provide some greater Purpose.

 

[TopRamen]

With the addition of a few rubber bands, these could assist with lift off! Hmmmm.....

Or, the Bands could "Spool Up" during lift Then, the Rocket would arc over Ballistic, and the Bands would then be under Tension, providing Thust downward on the Descent to slow the Rocket. No Chute needed.
Like those Guillows Balsa Planes I used to fly as a Kid, with that Red Propeller and the super long rubbery Rubbebands. I remember sometimes the Prop would slip during winding and really put a "Smartin" on a Thumb:y:. That, or else you would wind the band so tight the Model would collapse under the Tension.

 

[ThirstyBarbarian]

Hide behind something when you push the button.

 

[gpoehlein]

My hunch is that he will be ok - remember that the struts out to the prop bubs are going to act as fins (albeit, very short fins), and just the drag from the props will add to the stabilizing factor whether they are spinning or not. My guess is that they won't add much more, if any, drag when spinning. If you build this, though, I would vent the ejection and use a booster motor (B6-0 or C6-0). My guess is that the three props will autogyro during descent. Definitely let us know how it works - you may be on to something for helicopter recovery models!

 

[blackbrandt]

OOOOH!!



Try putting a small servo or solenoid on each propeller. These would be activated on the way down. The rocket would come in nose first. The rocket would slow down a ton!

 

[Micromeister]

My hunch is that he will be ok - remember that the struts out to the prop bubs are going to act as fins (albeit, very short fins), and just the drag from the props will add to the stabilizing factor whether they are spinning or not. My guess is that they won't add much more, if any, drag when spinning. If you build this, though, I would vent the ejection and use a booster motor (B6-0 or C6-0). My guess is that the three props will autogyro during descent. Definitely let us know how it works - you may be on to something for helicopter recovery models!

Agree with Greg On this one;
With this exception: Your struts will have to be reinforced to take the bending stress placed on them under thrust. Adding Gussets to the Struts in the form of a Triangle above each with about 1/3 to 1/2 the span should do it...OH and then these Gussets BECOME Fins as well LOL! Those Spinning props will just be Altitude Limiting Drag fins. Your achieved altitude will likely be in the range much like that of the fixed airfoiled Rotors on the Tasmanian Devil helicopter recovery model. Up or down scale the Tas 1/8A to C6 powered all get about the same 45-50ft max altitude.
One more observation those Propellers WILL NOT provide lift after burnout. They will Rapidly DECREASE the forward momentum of the Bird to zero in short order. They Will as other have also mentioned provide Auto-Gyro slowing on the way down depending on the Prop diameter being used relative to the models mass.

Can this Odd-Roc Scheme work? Not Likely as drawn: but if you Heavy up your strut Diameter using Hardwood (Oak, Maple or Hickory) dowel not Pine and add gussets with epoxy fillets it will stay together and should fly a short way
For Sure BUILD one and update us on how it works.

 

[BABAR]

They would definitely act as a drag stabilizer, once they are turning and 'up to speed'. The problem that I see is that they will take a short while to 'spin' up, and may not be providing enough drag during the first 1/2 second of motor burn.

Not sure if I agree with this one. I believe the drag they cause will be the same whether they are spinning or not.

Until they are spinning they will not provide much gyrostabilization. Given their mass, doubt they will provide much gyrostabilization even AFTER they are spinning.

The drag IS likely to slow this puppy down in a hurry after burnout. Recommend a SHORT delay.

Good luck! Should be an interesting flight one way (or 50 or 60 ways:wink or another!

 

[Coop]

I'd like to see the flight--particularly the recovery sequence.


Later!

--Coop

 

[UpsilonAerospace]

Wow! This idea attracted a surprising amount of attention!

Time to give a quick description of the craft so far (it's coming together in my basement):

Because of the rotor-induced drag, I've decided to make the airframe rather streamlined. I'm just using a standard 29mm body tube for the airframe, with an 18mm motor mount. I'm probably going to vent the ejection, as suggested by gpoehlein, and thus I've drilled a couple small vent holes near the top of the airframe tube.

I'm using four 1/4" dowels for the propeller mounts, each about three and a quarter inches long. These dowels will be mounted TTW, and they'll be coated in a little epoxy for maximum stability. The propellers I've decided on are 5" in diameter, and are made of tough plastic. When the propellers are mounted, two of them will rotate one way and two will rotate the other, allowing for minimal spin during descent.

I hope that this brief summary helps you visualize the rocket, and any further suggestions on its construction are welcome.

 

[Daddyisabar]

Get it done because this weekend is looking good to launch. Calm weather with little fire danger, perfect for the oddroc crowd.

 

[jeffgeraci]

It should work fine, but it won't be a straight flight. I imagine it's going to wobble on the way up, but I'd be more concerned about the prop shafts breaking under stress. The props themselves won't serve any purpose on the way up, and even on the way down I doubt they'll spin because your rocket is probably going to tumble on the way down unless you have a chute. Question: Are the propeller tips clear of the exhaust path? Are prop shafts made of carbon, or are they at least single-piece construction? I'm not slamming your idea by any stretch here, I wanna see a video of the flight... I really really wanna see.

 

[UpsilonAerospace]

It has been flown!

The rocket was launched on a B6-0. It went fairly straight on the way up, although it did tip to the side as the propellers began to spin. The boost showed signs of serious drag, with the rocket slowing down immediately after boost was complete. The rocket vented its ejection charge through its vent holes, and then started downwards.

I overlooked one important factor of the design: The propellers have to spin the opposite way to produce lift on the descent. In the video, you can clearly see the propellers slow and then begin to spin the other way during descent, though they didn't pick up enough speed to significantly slow the craft down before it landed. The rocket crashed sideways into the ground, dislodging the nose cone and breaking two of the propeller struts off of the body tube. This damage is fixable with a little epoxy but I'm thinking of building another, slightly bigger one instead. Maybe. Then again, the RSO will probably never forgive me for this launch.

The much-requested video!

[video=youtube_share;zO1GlQIXg1I]https://youtu.be/zO1GlQIXg1I[/video]

Let me know if you have any questions...?

 

[Salvage-1]

excellent flight. You will need a chute or something though as the propellers will not be giving you any 'lift' at all during any part of the flight. To provide 'lift', the props have to spin in such a way as to force air forwards over the body in a direction from tail to nose. As it is, the props are being spun by the air flowing the other way, due to the thrust of the rocket motor. When the rocket turns at apogee, and goes nose down, the airflow is still front front to back, and will keep the props rotating that way.

They are there for drag induced stabilization.

 

[Daddyisabar]

I think some higher power, rear eject - long streamer action would be cool. The props are a good visual effect and you can hear them chop through the air as well.

 

[John Beans]

Not to nitpick (here comes a nitpick, right?), but there's nothing "gyroscopic" about this, since the propellers don't weigh that much compared to the drag that they experience. Since their mass is so low, they just spin due to the relative wind, and pretty much stop as soon as the rocket slows.

The better analogy would be: This is like launching a rocket with the parachute already open.

Also, I think the contribution of propellers to stability may not be as strong as you think. Fins work because when the rocket begins to rotate around the center of gravity, the fins present more and more surface area to the relative wind and thus torque that resists turning. Also, they have the advantage of having very low drag when moving straight. I'm guessing a propeller with a fixed axle presents "less and less" resistance to rotation (drag) as you turn the rocket (not more and more), thus not providing a strong "central tendency" towards stability.

If your RSO will let you launch this, best to make sure the center of gravity is WELL ahead of the propellers (extra stability margin). Add weight to the nose if necessary. Also, maybe put a swivel to connect the propellers so that they stay perpendicular to the wind and maintain maximum drag if the rocket starts to rotate. Not as good as fins (when resistance to rotation increases during rotation), but staying the same is better than a decrease.

It would be cool you could hold (or fold) those props up underneath fins and release them at ejection.

 

[jadebox]

I overlooked one important factor of the design: The propellers have to spin the opposite way to produce lift on the descent. In the video, you can clearly see the propellers slow and then begin to spin the other way during descent...

The propellers don't actually change spin direction since the rocket is moving through the air nose-first the entire time. They only appear to stop and spin in the opposite direction because of the "wagon wheel" effect.

The props don't seem to be large enough to slow the rocket enough for a safe, damage-free recovery. Perhaps you could implement a more traditional helicopter recovery with larger vanes deployed at apogee.

Although it's surely not the most effective way to stabilize and recovery a rocket, I think what you've done is pretty cool. Experimentation is one of the things that keeps our hobby exciting and interesting!

-- Roger

 

[BABAR]

Not to nitpick (here comes a nitpick, right?), but there's nothing "gyroscopic" about this, since the propellers don't weigh that much compared to the drag that they experience. Since their mass is so low, they just spin due to the relative wind, and pretty much stop as soon as the rocket slows.

The better analogy would be: This is like launching a rocket with the parachute already open.

Also, I think the contribution of propellers to stability may not be as strong as you think. Fins work because when the rocket begins to rotate around the center of gravity, the fins present more and more surface area to the relative wind and thus torque that resists turning. Also, they have the advantage of having very low drag when moving straight. I'm guessing a propeller with a fixed axle presents "less and less" resistance to rotation (drag) as you turn the rocket (not more and more), thus not providing a strong "central tendency" towards stability.

If your RSO will let you launch this, best to make sure the center of gravity is WELL ahead of the propellers (extra stability margin). Add weight to the nose if necessary. Also, maybe put a swivel to connect the propellers so that they stay perpendicular to the wind and maintain maximum drag if the rocket starts to rotate. Not as good as fins (when resistance to rotation increases during rotation), but staying the same is better than a decrease.

It would be cool you could hold (or fold) those props up underneath fins and release them at ejection.

Agree with above. You are trying to use the same structure to provide stability on boost (when you are supposed to be accellerating) AND to slow descent on recovery (when you are supposed to be DEcellerating.) Perhaps similar in a multirotor way to the Tasmanian Devil

https://www.rocketryforum.com/showthread.php?9940-Upscale-Tasmanian-Devil&highlight=tasmanian+devil

The Taz's rotors however have a LOT more surface area.

You would get a similar effect if you replaced the rotors with flat disks of surface area equivalent to the rotors. But would lose the "neato factor"

Also agree that mass of rotors probably is not providing any significant gyrostabilization.

I also agree with Jadebox, it IS a cool way of stabilizing a rocket (essentially tail drag with spinning rotors), but not sufficient (by itself) for safe recovery. I liked it!

Looking forward to the "more to come"!

Tom

 

[bugwubber]

A possible solution for your recovery system. Take the guts, motors and props from a micro quadcopter and install on your rocket in place of your unpowered props. Setup system to turn on from the ejection charge. Autopilot fuctions could be programmed to land gently.

 

[BABAR]

A possible solution for your recovery system. Take the guts, motors and props from a micro quadcopter and install on your rocket in place of your unpowered props. Setup system to turn on from the ejection charge. Autopilot fuctions could be programmed to land gently.

Interesting thought. Do you think the micros would have enough oomph to land a rocket?

 

[bugwubber]

Well not the finger sized one..

All you need is enough to slow descent- doesnt have to hover unless you want to play with people's mind and program it to hover at 5ft.