Quantcast

Propulsive Landing

The Rocketry Forum

Help Support The Rocketry Forum:

switalab

New Member
Joined
Nov 26, 2020
Messages
1
Reaction score
0
Hi,

I'm totally new to this forum. I used to make model rockets with my dad ... just simple Estes kits. Usually they wound up in trees.

Circumstances have prompted me to reconsider model rocketry. I'm wondering if it's feasible to propulsively land a model rocket.

Basic idea: solid motors launch rocket --> at top of flight, a timer deploys grid fins --> at some time during descent, a second timer ignites a second batch of solid motors (smaller) for landing --> third timer deploys landing legs (wider the base the better).

I don't think I could get the landing burn down exactly right, but I'm hoping I could get it sort of close.

A more advanced version would include an altimeter and computer to more precisely time the landing burn and leg deployment.

Any pointers that would help me get this started? I've never made a scratchbuilt rocket. At one point in my life I knew enough electronics (undergrad CS with hearty dose of EE) to get the controls down, although maybe not the onboard igniter.


Thanks! I hope you enjoyed reading about my idea.
Ben
 

OverTheTop

Well-Known Member
TRF Supporter
Joined
Jul 10, 2007
Messages
4,621
Reaction score
1,877
Location
Melbourne Australia
Hi switlab. Welcome to the forum. Lots to see and learn here.

You are not the first to ask this question! I guess the technology for making this happen is getting closer and closer. Look at the TVC system from BPS Aerospace as an example, which can stabilise a flight without having static stability due to the airframe.

The biggest problems with propulsive landings being able to throttle the thrust, and also the inherent fire risk. A normal flight has the motor actually quite cool before landing, compared to a propulsive landing where you torch whatever you are landing on.

It is a nice thought experiment but I wouldn't want to be the one to set fire to some land somewhere causing rocket privileges to be taken away from regular flyers.
 

Zeus-cat

Well-Known Member
Joined
Mar 14, 2009
Messages
4,543
Reaction score
735
I see several issues:

1) Timing. Most model rocket motors burn 2 to 3 seconds. So getting the motor to fire at the right time and slow the rocket down for a safe landing seems implausible.

2) Orientation. For your idea to work you need the rocket to be pointing up as it comes in for a landing. To do that you need some sort of recovery system other than your second motor. Which sort of defeats your idea.

3) Stability. Using a motor to land the rocket means it has to be moving very slowly just as it lands. This runs counter to model rocket design and safety code. You need the rocket to be moving fast so that the fins keep the rocket oriented properly for safety reasons. This seems to be a fatal issue.
 

SDramstad

Well-Known Member
TRF Supporter
Joined
Jun 26, 2014
Messages
735
Reaction score
579
We have enough of a problem with grass fires as it is. Intentionally landing with an engine burning seems like a cool but still really bad idea.
 

Jeff Lassahn

Well-Known Member
TRF Supporter
Joined
Jul 5, 2020
Messages
255
Reaction score
278
Location
Portland OR
First off, I agree with everyone else about the concern with grass fires on landing. Don't attempt this unless you've got a flying range where you're clear of vegetation and other flammables even if things go waaaay off course.

Beyond that, I think all the individual pieces of what you're trying to do are well within known model rocket technology, but the design is going to be quite tricky to get right.

About the electronics, there are several available electronics packages that include barometric altimeters, accelerometers, timers etc so there may be something off the shelf you can use. Be aware that the size of battery you need to do motor ignition might be bigger than you expect -- this is probably a mid-power design, bigger than a typical Estes kit.

If you haven't done much with mid-power, flight electronics, scratch building, etc before, you should definitely get some experience with these things in some simpler rockets before tackling the design you're talking about. Maybe start with a mid-power two stage rocket to get a feel for using the electronics and air starting engines first.
 

neil_w

Marginally Stable
TRF Supporter
Joined
Jul 14, 2015
Messages
10,577
Reaction score
3,562
Location
Northern NJ
It's an incredibly difficult challenge with solid propellant motors, where you can't control the thrust. I'm impressed he's gotten as close as he has, and it wouldn't surprise me if he nails it one of these times. It also wouldn't surprise me if he never gets it. The attempt is glorious either way.
 

aerostadt

Lifetime Supporter
TRF Lifetime Supporter
Joined
Oct 27, 2009
Messages
3,273
Reaction score
242
Location
Brigham City, UT
Sometimes local fire departments will seek out who started a grass fire and charge them the bill for putting out the fire. Such bills have reported to be in the hundred of thousands of dollars or more. There is also the safety consideration of a firing rocket coming down in the midst of people.
 
Top