Rotor Kites as Alternatives to Parachutes

[shynung]

After reading a Wikipedia article on Autogyros and Rotor kites, and observing landing space capsules via KSP, I was struck with an idea.

Real-world space capsules use parachutes to slow their descent. Due to limitations inherent from using parachutes on touchdown speed, the capsules either have to splash down on water (Apollo), or use landing rockets (Soyuz). While satisfactory, these methods give little control of where the spacecraft ultimately lands, beyond aerodynamic adjustments during reentry.

I propose embedding helicopter rotors into the capsule. When not in use, these rotors fold flush with the capsule's outer shell, probably on the conic section of the vehicle. After reentry, the blades pop open to its full length, and assumes a negative angle-of-attack. This is done to convert some of the velocity of the capsule to either store raw kinetic energy within the rotating blades, or use the rotor as an input to a generator to charge a battery. During final landing approach, the negative AoA is changed to a positive AoA, using the stored kinetic/electric energy stored from freefall-charging phase, effectively turning the space capsule into a helicopter, enabling precise control over the final position of the landing capsule.

I'd like to hear your opinions on this.

[MBobrik]

would a rotor of the size needed not be much heavier than a equivalent parachute ? I don't know, I am just asking ...

[deadshot462]

Not too crazy an idea, NASA actually considered it for their Orion capsule:

http://www.americaspace.com/?p=27214

To me, parachutes seem safer with fewer failure points, but maybe it's worth testing.

[Pockrtplanesairways]

There actually was a test of the pre-production Soyuz where they added rotors to slow it down.

[Sillychris]

This is a really good idea. My suggestion would be to store the rotor energy on a flywheel which can later be dumped into spinning the rotors on final landing. Only downside is complexity.

[shynung]

I think, since parachutes are lightweight anyway, we can pack both a chute and a rotor assembly in one capsule. The rotor is used as the primary descent device, the parachute taking the backup role.

And yes, I am aware of the possible weight penalties and mechanical complexities. But I think it is justifiable for the end result: ability to land softly on practically anywhere, with complete control from the pilot inside.

[DaveofDefeat]

Well, from what I know about auto rotation in helicopters when the engine cuts out, it is not a soft landing, nor is it incredibly steerable.

[shynung]

It's not completely autorotation, at least not on final approach. One could store the energy via battery or flywheel, to be used on final approach. There's also the lack of a tail rotor, which could be an issue.

[Armchair Rocket Scientist]

Well, from what I know about auto rotation in helicopters when the engine cuts out, it is not a soft landing, nor is it incredibly steerable.

Looks pretty soft (and steerable) to me.

Definitely better than a parachute if it works right, but seems rather heavy and complicated. I'd be a little uneasy about reliability.

I'm not sure what advantages it would have over a parafoil though.

[shynung]

I'm not sure what advantages it would have over a parafoil though.

Parafoils need horizontal speed in order to get any lift; they're practically fabric wings. If used on a lifting-body spaceplane design, it could be useful for final approach. Capsules are designed for vertical landings, not horizontal ones, barring a significant redesign.

[Tommygun]

You might find this interesting from the Rotary Rocket Company.

They basically took it a few steps farther.

http://en.wikipedia.org/wiki/Rotary_Rocket

[Kerbin Dallas Multipass]

My question is: what is the benefit?

100+ points for being cooler and more controllable. But on a scale of a space project there are some questions:

-Can the vehicle land at pre-defined bases after return from orbit. The whole concept of shooting wings into orbit is that you don't have to do all the expensive search and rescue stuff usually involved in parachute landings.

-Is it worth the payload? Parachutes are like 20 or so kg each. I'll have three please, just because I can. Rotor system is probably not competitive.

-How is this all controlled? Do we need a whole helicopter avionics system (manual and robotic) and re-entry proof sensors and all of that to make it happen?

-What is our backup system? What about parachutes?

-Is it scalable to higher payloads? (it's even worse than parachutes isn't it?)

I don't buy it but I demand more artists impressions.

[Duxwing]

And yes, I am aware of the possible weight penalties and mechanical complexities. But I think it is justifiable for the end result: ability to land softly on practically anywhere, with complete control from the pilot inside.

That capability is unnecessary because astronauts can instead tolerate the rare and brief discomfort of hard-landing.

-Duxwing

Edited April 10, 2014 by Duxwing

[shynung]

snip;

Indeed. The concept of rotor blades as descent controllers has been tried before. Unfortunately, they came out in the wrong place at the wrong time, and got shelved because of it.

What I proposed was a foldable rotor system stuffed to the conic section of the reentry vehicle, which carries a compact onboard energy storage system. The Roton rocket used tipjets, which could complicate the system in small reentry vehicles.

[shynung]

My question is: what is the benefit?

Controllability, to the point of predictable soft landings.

-Can the vehicle land at pre-defined bases after return from orbit?.

Yes. In comparison to wings, it could be as little as 1/5 the weight for the same payload, and does not need a runway. It is able to land practically anywhere, even on ships, given a skilled pilot.

-Is it worth the payload?

Only if it was very sensitive to mechanical shock. Manned payloads, too.

-How is this all controlled? Do we need a whole helicopter avionics system (manual and robotic) and re-entry proof sensors and all of that to make it happen?

Yes, unfortunately. Though a basic one would suffice for the short time the rotor system works, in theory.

-What is our backup system? What about parachutes?

Parachutes could be used as backups, in an emergency situation.

-Is it scalable to higher payloads?

Use more rotor blades, or/and a bigger rotor. Skycranes for lifting heavy objects often have 6 to 8 blades on one rotor.

[Mattasmack]

Indeed. The concept of rotor blades as descent controllers has been tried before. Unfortunately, they came out in the wrong place at the wrong time, and got shelved because of it.

What I proposed was a foldable rotor system stuffed to the conic section of the reentry vehicle, which carries a compact onboard energy storage system. The Roton rocket used tipjets, which could complicate the system in small reentry vehicles.

But if you put torque on the rotors, either to charge up the energy storage system or to drive the rotors from that system, then you need another system on the vehicle to counteract that torque. Likely that would be rockets, unless you envision a tail rotor popping out of the vehicle as well. Why not just put the rockets on the rotor tips and skip the whole energy storage system? Should be simpler and lighter that way.

Can you flesh out your idea with some numbers to get an idea of whether it would make sense? Choose a vehicle as a starting point. How long a rotor blade could fit on it? How fast would they have to spin for their lift to counteract the vehicle's weight? Does that speed make sense from a strength of materials standpoint? How much power would be required to descend at your desired rate? (The power required to decelerate to that descent rate will be at least that high...) How much energy would have to be stored? (Related to how long you want to descend at that rate...) Those numbers would allow you to make a stab at how much each system (rotors, motor, energy storage) must weigh.

[magnemoe]

Not too crazy an idea, NASA actually considered it for their Orion capsule:

http://www.americaspace.com/?p=27214

To me, parachutes seem safer with fewer failure points, but maybe it's worth testing.

Some SSTO idea also used rotor for landing, this however was powered by rocket engines at the tip. Probably makes more sense in this setting as you have the long rocket body to keep the rotor at and the ssto would be to large to land with parachutes anyway.

[shynung]

Can you flesh out your idea with some numbers to get an idea of whether it would make sense? Choose a vehicle as a starting point. How long a rotor blade could fit on it? How fast would they have to spin for their lift to counteract the vehicle's weight? Does that speed make sense from a strength of materials standpoint? How much power would be required to descend at your desired rate? (The power required to decelerate to that descent rate will be at least that high...) How much energy would have to be stored? (Related to how long you want to descend at that rate...) Those numbers would allow you to make a stab at how much each system (rotors, motor, energy storage) must weigh.

Unfortunately, I don't have enough data with me to do a more comprehensive analysis. I'm merely describing a basic concept here, so I doesn't have much of a clear picture, besides some data of the Roton rocket. (which happened to be here, in case you're wondering:http://www.spaceandtech.com/spacedata/rlvs/rotary_specs.shtml)

[Kerbin Dallas Multipass]

How much power would be required to descend at your desired rate? (The power required to decelerate to that descent rate will be at least that high...) How much energy would have to be stored? (Related to how long you want to descend at that rate...) Those numbers would allow you to make a stab at how much each system (rotors, motor, energy storage) must weigh.

The thing is, every helicopter can perform an unpowered autorotation landing in case of an engine failure. I guess it would be possible to design a landing system without any power source or energy storage.

[Mattasmack]

Unfortunately, I don't have enough data with me to do a more comprehensive analysis. I'm merely describing a basic concept here, so I doesn't have much of a clear picture, besides some data of the Roton rocket. (which happened to be here, in case you're wondering:http://www.spaceandtech.com/spacedata/rlvs/rotary_specs.shtml)

Well, the Roton was pretty tall, which helped make room for its rotors. Applying this to something shaped like the Orion or other capsules limits you to much shorter rotors, and their diameter when deployed won't be all that much greater than the diameter of the capsule itself. That will certainly change its behavior.

It's an interesting concept, but it might be nonsense -- you (or someone) would need to do some basic high-level analysis to find out.

The thing is, every helicopter can perform an unpowered autorotation landing in case of an engine failure. I guess it would be possible to design a landing system without any power source or energy storage.

The thing is, that's a different concept from what the OP is talking about. Helicopters also need forward velocity to autorotate and that doesn't go very well with something capsule-shaped. I think a purely vertical autorotation is possible, with the right shape of the rotor blades, but descent might be pretty fast.

[Kerbin Dallas Multipass]

Helicopters also need forward velocity to autorotate and that doesn't go very well with something capsule-shaped. I think a purely vertical autorotation is possible, with the right shape of the rotor blades, but descent might be pretty fast.

Seems to work without forward motion as long as there is enough altitude

[Technical Ben]

It's not completely autorotation, at least not on final approach. One could store the energy via battery or flywheel, to be used on final approach. There's also the lack of a tail rotor, which could be an issue.

It can be done. It's a trick some model copter pilots use. They adjust the pitch of the blade, after it's built up speed from the descent. But this is somewhat tricky, and less safe than a powered landing. Also possibly less safe than a parachute. So it would be useful more so if mixed with powered and directed landings, as parachutes are more prone to the wind etc.

[Mattasmack]

Seems to work without forward motion as long as there is enough altitude

http://upload.wikimedia.org/wikipedia/en/4/48/Hvcurve.png

That proves my point. The reason you need altitude if you lack forward motion, is that you use that altitude to gain the forward motion! Inside the red area on the left you don't have enough height to get up to the autorotation airspeed, and you just fall out of the sky.

[Kerbin Dallas Multipass]

That proves my point. The reason you need altitude if you lack forward motion, is that you use that altitude to gain the forward motion! Inside the red area on the left you don't have enough height to get up to the autorotation airspeed, and you just fall out of the sky.

I'm not convinced but I know too little

[Mattasmack]

I'm not convinced but I know too little

That image you included comes from the Wikipedia article 'Height-Velocity Diagram'. Try looking at the two external links at the bottom of the article, especially the first one. A helicopter in autorotation is essentially gliding forwards; if its engine quits while hovering (or moving slowly) it needs to be high enough above the ground to have room to 'dive' to gain that forward speed.

(The article mentioned an interesting case of an experimental helicopter with weights built into its rotor. The weights give the rotor high enough inertia that the 'dead man's curve' (the shaded portion on the left of that diagram) doesn't exist -- the rotors have enough inertia to keep spinning long enough to let the helicopter land even if the engine quits while flying low and slow. But there are disadvantages to making the rotors heavier, and the helicopter never went into production.)

Interestingly, a link from that page discusses the aerodynamics of autorotation (http://www.copters.com/aero/autorotation.html), and it starts with the case of vertical autorotation. So I guess it is possible, after all. But the vertical speed is higher than in the forward autorotation case -- too high -- which is why the 'dead man's curve' exists.

For something like an Orion capsule with rotors, the fact that the rotors wouldn't extend much past the body of the capsule itself (i.e. the capsule would block most of the 'driving region' of the rotors) is an additional problem for vertical autorotation.