Powered soft landing?

Has anyone ever successfully flown and landed a model with powered descent using a rocket engine, much like many of NASA's probes?

:surprised:

Julian
NAR 95955

Not to my knowlege, and it would most likely violate CAR/NAR rules (or they would be dead set against such a thing), plus the fire departments would have an issue with this.

I'm half asleep...but there was a model rocket that had a motor in the nose....lit by a fuse for this purpose....I'm at a loss for a name....

There was/is a company that had a rocket designed for a retro burn before landing. I can't remember what it was called. As I recall, it used a fuse to light the second motor and you had to get the timing just right. Also, it used the motor to brake but not land.

JAL3 said:

There was/is a company that had a rocket designed for a retro burn before landing. I can't remember what it was called. As I recall, it used a fuse to light the second motor and you had to get the timing just right. Also, it used the motor to brake but not land.

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https://store.heavenlyhobbies.com/01-024-0001.html

WillMarchant said:

https://store.heavenlyhobbies.com/01-024-0001.html

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That rocket is just berzerk...I'm going to have to think on that one:eyepop:

WillMarchant said:

https://store.heavenlyhobbies.com/01-024-0001.html

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That's the one.

I remember seeing these a couple of years ago; are they still available?

It seems to me that using an altimeter system you could ignite that “retro-rocket” without the need of a fuse. Much less trying to “Time it correctly”.

Just program the altimeter to fire what would otherwise be the main chute deployment charge, at say 400 feet and Boom, Bobs you uncle.

The charge in the retro-motor would then be used to deploy the “Landing Chute”.

My guess is no responsible club would let you fly it; though if you are launching from a vast field of plowed dirt the likelihood of a fire would marginal.

The problem with a retro-rocket landing is that commercially available rocket motors burn for a very short period of time. This makes timing very critical and essentially impractical for use in landing. Also, you have no control over thrust unlike NASA which could shutdown the system once you landed. Even the Backdraft rocket mentioned above does not use the rocket to land; just to slow it down to deploy a chute at low level.

im not sure if it counts as a model rocket but there was a novice space competition and the challenge was to make a rocket that flew up, hovered for 60 seconds, and then landed again using the rocket.
I remember the winner was a sputnik shaped craft with 4 landing legs, it was hollow and was filled with liquid fuel, it ascended, hovered, and descended.
Perfect flight!

Nothing that could be even remotely described as a "model rocket" could do that.


The "Backdraft" model linked above looks interesting, but I foresee a possible source of major problems if the rocket on its descent trajectory is pointed even a few degrees off the vertical: instead of acting as a direct "retrorocket," the secondary motor would propel the model off on a completely new flight path at a lateral angle to the original track.

So even some side winds of a couple mph which could cause the rocket to weathercock, pitch or yaw out of the vertical would result in the rocket veering off in a new direction. Probably not an insurmountable problem if you have a huge launch field in every direction, but the rocket could end up someplace entirely different than you planned at liftoff (and maybe even during descent).

JStarStar said:

Nothing that could be even remotely described as a "model rocket" could do that.


The "Backdraft" model linked above looks interesting, but I foresee a possible source of major problems if the rocket on its descent trajectory is pointed even a few degrees off the vertical: instead of acting as a direct "retrorocket," the secondary motor would propel the model off on a completely new flight path at a lateral angle to the original track.

So even some side winds of a couple mph which could cause the rocket to weathercock, pitch or yaw out of the vertical would result in the rocket veering off in a new direction. Probably not an insurmountable problem if you have a huge launch field in every direction, but the rocket could end up someplace entirely different than you planned at liftoff (and maybe even during descent).

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Not really...

The rocket is powered by a motor which accelerates it up to max velocity, and then burns out... the rocket then coasts upwards to apogee, at which point it's flying at it's lowest velocity (and that speed is dependent on the amount of weathercocking and how vertical the flight is, or how much it deviates from vertical). At any rate, once the rocket follows its ballistic path through apogee and starts falling back to Earth, it accelerates under the influence of gravity until it reaches its terminal velocity (where aerodynamic drag and the acceleration of gravity balance, in essence). The rocket then falls back toward the ground, and a second model rocket motor is ignited FACING FORWARD, in the DIRECTION OF FLIGHT. So long as that motor's thrust centerline is passing through the rocket's center of gravity (CG) the actual orientation of the rocket is irrelevant... (and it should be falling pretty darn close to straight down by that point anyway). The motor is ignited and thrusts AGAINST the direction of flight, acting as a BRAKING ROCKET-- it merely slows the rocket down from (optimistically or desirably) from the terminal velocity (or whatever velocity it happens to be falling at under the acceleration of gravity that is below the terminal velocity) down to a point as close to zero as possible... if the motor burned longer, it would attempt to accelerate the rocket in the opposite direction it was falling after stopping it, with the fins at the "wrong end" it would merely pinwheel unstably... The rocket should then eject the parachute for a gentle landing as close to zero velocity as possible, and at a low altitude just sufficient to give the parachute time to deploy properly and slow the rocket down to landing speed, with as little drift as possible...

I agree that an altimeter would be the perfect thing for a rocket like this... merely pre-program it for the desired ignition altitude of the "braking motor" so that the rocket decelerates as close to zero as possible and then deploys the chute as soon as the motor burns out. Basically such a rocket could use simple booster motors, with no delay or ejection charge of their own... the main booster motor should be sized to loft the rocket with the weight of the additional braking motor and whatever payload you want to launch. The braking motor should be sized to decelerate the rocket back to as close to zero (hovering) as possible (which is desirable but essentially impossible to achieve in practice) figuring the weight of the rocket at apogee (liftoff weight minus the launch motor propellant weight). Basically, you want to IMMEDIATELY deploy the chute when the braking motor burns out, since that will then be THE lowest speed that the rocket achieves after firing the braking motor-- gravity will begin to accelerate it again at 32.2 ft/sec/sec for every second (1 g) after burnout of the braking motor. This should occur at a high enough altitude that the parachute, after deployment, has time to open and decelerate the rocket to the parachute's descent rate before impacting the ground (landing).

Later! OL JR

luke strawwalker said:

Not really...

The rocket is powered by a motor which accelerates it up to max velocity, and then burns out... the rocket then coasts upwards to apogee, at which point it's flying at it's lowest velocity (and that speed is dependent on the amount of weathercocking and how vertical the flight is, or how much it deviates from vertical). At any rate, once the rocket follows its ballistic path through apogee and starts falling back to Earth, it accelerates under the influence of gravity until it reaches its terminal velocity (where aerodynamic drag and the acceleration of gravity balance, in essence). The rocket then falls back toward the ground, and a second model rocket motor is ignited FACING FORWARD, in the DIRECTION OF FLIGHT. So long as that motor's thrust centerline is passing through the rocket's center of gravity (CG) the actual orientation of the rocket is irrelevant... (and it should be falling pretty darn close to straight down by that point anyway). The motor is ignited and thrusts AGAINST the direction of flight, acting as a BRAKING ROCKET-- it merely slows the rocket down from (optimistically or desirably) from the terminal velocity (or whatever velocity it happens to be falling at under the acceleration of gravity that is below the terminal velocity) down to a point as close to zero as possible... if the motor burned longer, it would attempt to accelerate the rocket in the opposite direction it was falling after stopping it, with the fins at the "wrong end" it would merely pinwheel unstably... The rocket should then eject the parachute for a gentle landing as close to zero velocity as possible, and at a low altitude just sufficient to give the parachute time to deploy properly and slow the rocket down to landing speed, with as little drift as possible...

I agree that an altimeter would be the perfect thing for a rocket like this... merely pre-program it for the desired ignition altitude of the "braking motor" so that the rocket decelerates as close to zero as possible and then deploys the chute as soon as the motor burns out. Basically such a rocket could use simple booster motors, with no delay or ejection charge of their own... the main booster motor should be sized to loft the rocket with the weight of the additional braking motor and whatever payload you want to launch. The braking motor should be sized to decelerate the rocket back to as close to zero (hovering) as possible (which is desirable but essentially impossible to achieve in practice) figuring the weight of the rocket at apogee (liftoff weight minus the launch motor propellant weight). Basically, you want to IMMEDIATELY deploy the chute when the braking motor burns out, since that will then be THE lowest speed that the rocket achieves after firing the braking motor-- gravity will begin to accelerate it again at 32.2 ft/sec/sec for every second (1 g) after burnout of the braking motor. This should occur at a high enough altitude that the parachute, after deployment, has time to open and decelerate the rocket to the parachute's descent rate before impacting the ground (landing).

Later! OL JR

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I suspect the highlighted assumption may not always be dependable, nor the assumption the braking motor thrust centerline will pass directly through the lateral CG of the model.

In conventional staging, we presume upper-stage ignition will always take place in an orientation within a couple degrees of vertical. As we all know from experience sometimes that does not occur according to plan.

Has anyone actually built a "Backdraft?" How do they fly?

EMRR's review page indicates mixed results.

https://www.rocketreviews.com/backdraft---heavenly-hobbies.html

Fascinating idea but I don't see it as very practical in our hobby at the current stage. I don't think the one above is exactly what you are trying to describe.

You may be thinking more in line of the Space X Grasshopper?

Or you could consider going Soviet style and eject a small parachute/drogue at apogee with a downward facing cluster of three or four BP motors arranged in a conical configuration at or near the point where the shroud lines are attached to the shock cord. Near the downward pointing motor end of the rocket would be an ultrasonic distance sensor like that used in hobby robots. Just prior to impact, the sensor would fire the BP motors for braking. Got the idea from this:

https://www.youtube.com/watch?v=4uGfOppQD_g

Of course, this is not a practical way for hobbyists to recover rockets, if done would be done just for demo purposes, and definitely would need to be done only over a landing area where there is zero fire hazard. Also, I'm not sure what NAR rules and fire regulations it might violate.

JStarStar said:

I suspect the highlighted assumption may not always be dependable, nor the assumption the braking motor thrust centerline will pass directly through the lateral CG of the model.

In conventional staging, we presume upper-stage ignition will always take place in an orientation within a couple degrees of vertical. As we all know from experience sometimes that does not occur according to plan.

Has anyone actually built a "Backdraft?" How do they fly?

EMRR's review page indicates mixed results.

https://www.rocketreviews.com/backdraft---heavenly-hobbies.html

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When a rocket lawn darts, it pretty much falls straight down... it might be a few degrees off vertical, but if it's falling from altitude, say if the nosecone simply didn't pop off for whatever reason and it goes ballistic, it's going to be falling almost vertically-- certainly as close as any two-stager would be to vertical at staging...

Now if you're talking about an underpowered flight or something that weathercocked EXTREMELY badly at liftoff, and basically took off at a 45 degree angle as soon as it cleared the rod, and flew a flat ballistic trajectory, then yeah, those will come back in at close to a 45 degree angle. BUT, that's NOT the kind of flight path we expect here...

And, even if it was, again, it makes little difference as to the gravitational force vector compared to the vehicles flight path vector and the thrust vector of the braking motor... so long as the thrust vector is opposite the flight vector (IOW, the rocket "streamlining" in falling nose-first with the fins behind it, IE, flying stably, just nose-down, like a lawn dart) and the braking motor thrust vector/centerline passing through the vehicle centerline/CG which it certainly should-- it's no harder than making a motor mount that's true and aligned with the centerline of the rocket-- which we do on every rocket we build anyway, otherwise they'd ALL corkscrew and flop around the sky... So long as the thrust is opposite the direction of flight and the CG intersects with the thrust vector line (IE the braking motor isn't cocked to one side) the braking motor thrust will slow the rocket down... the rocket it still flying FORWARD, so the fins are providing stability, but the thrust is slowing it down... in fact, at that point, with the added weight of the braking motor up front, the rocket is MORE STABLE than when it lifted off, since the burnoff of the booster motor propellant has lightened up the aft end of the rocket, and thus shifted the CG of the rocket forward... as the braking motor propellant burns off, the CG will shift aft again, however... As the rocket slows down from the braking thrust of the braking motor, and the airspeed decreases, the CP will shift forward somewhat, meaning the rocket will have less and less stability control from the fins as the velocity approaches zero, where the fins essentially 'stall' and have NO stabilizing effect, since there is insufficient airflow over them-- basically just exactly what we see on a good, straight flight where the rocket gets to apogee and "tailslides", falling backward straight down until there's enough airflow over the fins to "flip the rocket over" nose down again, it wobbles side to side a few times until the airspeed increases enough to stabilize the rocket nose-down, hopefully the parachute is ejected before that, because the speed is increasing under gravity every second the parachute doesn't pop.

It's at this point that the braking motor should burn out, with the rocket's freefall speed bled off by the counterthrust of the braking motor, achieving as close to a zero airspeed as possible... getting it at/below the normal parachute deployment speed is in fact "good enough", at which point you want the parachute to IMMEDIATELY deploy-- IE NO time delay-- eject the chute, at enough altitude to give it time to unfurl and deploy as the rocket continues to fall, plus a second or two for the parachute drag to slow the rocket down to its normal descent rate...

Now, if the airspeed gets TOO low, if the braking motor has TOO much thrust/duration, then the rocket will slow to a stop in midair, and try to "fly backwards" as the braking motor thrust tries to push the rocket's mass the other way. It will go unstable and flip, since it would be like trying to launch a "normal" rocket with the fins on the front end of the body tube! It would thrash around the sky as it fell toward the ground, until the motor burned out and the parachute (hopefully) deployed... but you wouldn't want to choose a braking motor with more impulse than the booster motor that launched it anyway... that would be foolish.

It's kind of a hard concept to grasp, but if you think and visualize how the thing is SUPPOSED to work, you'll get the idea...

Later! OL JR

I know at our launches it would never be allowed. I would think it would be a very good way to start some nasty fires. Our recovery area is tall dry grass so I am sure a fire would start very easy away form the launch area.
GP

Has anyone actually built one and launched it? Is there any video of one? Did it actually do what it is supposed to do or when the second engine fires does it go into a hissy fit until the chute pops.

I won't try one but maybe some of you more adventurous rocketeers might try it.

See ya,
Rod

crossfire said:

I know at our launches it would never be allowed. I would think it would be a very good way to start some nasty fires. Our recovery area is tall dry grass so I am sure a fire would start very easy away form the launch area.
GP

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If you're talking about soft landing via powered descent to the surface, yes... but igniting a second motor at several hundred feet altitude-- no problem-- at least no more than a multistage rocket...

We've sorta strayed from the original topic of an actual powered descent and soft landing via propulsion versus parachute or whatever... the "backdraft" style deceleration and parachute deployment is the most feasible method of actual propulsive recovery. Using an actual landing engine (meaning a liquid engine) is beyond the purview of hobby rocketry... and using a solid landing motor would be extremely difficult if it could be done at all, due to the throttling requirements and the solid motors inability to be throttled.
I suppose if one really wanted to an extremely advanced type of propulsive landing, it could be done with enough electronics to maintain stability and operate throttling valves for a cold-propellant type landing engine... doing it with an actual combustion engine, either liquid or solid, would violate the MRSC on several levels and of course would pose a huge fire danger unless performed strictly in the middle of the desert or on bare plowed ground.

IOW, the Backdraft idea is as close as you can get to propulsive landing in "standard" model rocketry..

LateR! OL JR