Community > Forum > Official Armadillo Aerospace Forum > Landing legs

Landing legs

Posted by: JamesHughes - Mon Oct 24, 2005 12:47 pm
Post new topic Reply to topic
 [ 79 posts ] 
Go to page Previous  1, 2, 3, 4, 5, 6  Next
Landing legs 
Author Message
Space Walker
Space Walker
avatar
Joined: Sat Jun 26, 2004 2:00 pm
Posts: 213
Post    Posted on: Mon Oct 31, 2005 1:02 pm
I think this is pretty cool!

Interview transcript:
http://www.hobbyspace.com/AAdmin/archiv ... atani.html
http://www.spacefuture.com/archive/flig ... cles.shtml

Image
Image


Back to top
Profile
Space Station Commander
Space Station Commander
avatar
Joined: Thu Oct 27, 2005 7:44 am
Posts: 707
Location: Haarlem, The Netherlands
Post    Posted on: Mon Oct 31, 2005 1:16 pm
Supershuki: That doesn't change the fact that a machine with a computer and a lot of moving parts and retractable landing gear is still less reliable than a machine with a computer and a lot of moving parts :).

Whether a seized up leg is a problem depends on how far the legs splay and how high up the center of gravity is. Let's assume that the vehicle has four landing legs, and that the two of them on the left splay, and the two on the right get stuck. If the center of gravity is high enough to go beyond the end of the splayed legs, the vehicle will topple.

The farther the legs splay, the farther the vehicle will lean over, but also the farther the CG will have to go to go beyond them. Unfortunately, when the legs are attached close to the ground, the CG moves outward more than the legs when the splaying angle is increased. Another way of looking at this is that when the legs are attached close to the ground, they become a lot shorter vertically when you move their tips outward a useful distance, thus causing a big difference between the splayed and the stuck legs.

Attaching the legs up higher would make the whole thing more stable, because the splaying angle to reach a certain "wheel base" is less, thus causing a smaller leaning angle when a leg fails to splay. A small splaying angle also has the advantage of making the mechanism I drew above thinner, and because of less sideways forces, less likely to jam. The disadvantage is obviously the extra weight of the longer legs.

How heavy would a metre of aluminium tube strong enough to carry a quarter rocket be?


Back to top
Profile
Moon Mission Member
Moon Mission Member
User avatar
Joined: Tue Oct 05, 2004 5:38 pm
Posts: 1361
Location: Austin, Texas
Post    Posted on: Mon Oct 31, 2005 2:31 pm
koxinga wrote:
:D That is WAY COOL! A Japanese Armadillo! No, it uses LIQUID HYDROGEN, it is a Japanese DC-X! Next step, Kankoh-Maru!


Back to top
Profile WWW
Space Walker
Space Walker
User avatar
Joined: Thu Jun 17, 2004 3:01 am
Posts: 173
Location: Dallas, TX
Post Re: KISS   Posted on: Mon Oct 31, 2005 3:44 pm
SuperShuki wrote:
It's also got alot of . . . like . . . what shall we call them . . . moving parts!


Maybe it's a glass half full/empty kind of thing, but I'd hardly say it has a lot of moving parts. Let's see, two ball valves, four solenoids, two gimbals... I think that's it.


Back to top
Profile WWW
Space Station Commander
Space Station Commander
User avatar
Joined: Mon May 31, 2004 9:47 pm
Posts: 814
Location: Yerushalayim (Jerusalem) - capital of Israel!
Post Re: KISS   Posted on: Tue Nov 01, 2005 3:53 am
Matthew Ross wrote:
SuperShuki wrote:
It's also got alot of . . . like . . . what shall we call them . . . moving parts!


Maybe it's a glass half full/empty kind of thing, but I'd hardly say it has a lot of moving parts. Let's see, two ball valves, four solenoids, two gimbals... I think that's it.


Well if the vehicle doesn't move, what's the point?
:lol:

_________________
“Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.”
-Anonymous


Back to top
Profile WWW
Space Station Commander
Space Station Commander
avatar
Joined: Thu Oct 27, 2005 7:44 am
Posts: 707
Location: Haarlem, The Netherlands
Post    Posted on: Tue Nov 01, 2005 9:13 am
Yeah and what about the telemetry bits?

Anyway, I've just looked up some data about the coefficient of friction between metal and concrete, and while I couldn't find any definitive numbers, and it's become clear to me that you can't say anything definitive without doing experiments, it seems that if you want your legs to splay because of the weight of the vehicle pushing down on them, you'd better have a wheel on the bottom of the leg so it can ride rather than slide outwards.Or make a teflon landing pad :).

The static coefficient of friction of wood on concrete is about 0.62. Metal is a bit harder than wood, but let's take a value of 0.6 for the moment. If there is 2.5kN of weight on the leg, you'd need a sideways force of 1.5kN to slide the leg outwards along the concrete. I'm afraid that would overload my little aluminium rail, especially because that 1.5kN has to be delivered to the end of the leg. The sideways forces on the rail, which is near the centre of rotation, would be much larger, perhaps ten times as large.

Other materials might help, carbon legs on a steel landing plate would give a friction coefficient of about 0.14, requiring a force of 350N at the end of the legs, but that would still put 3.5kN on the rail. Carbon legs could be lighter though.

Having a wheel on the leg would reduce the coefficient of friction by a lot, probably down to about 0.001. This would lower the required force to 2.5N (25N on the rail), and allow lighter construction of the rail. Of course, the wheel would be extra weight, about 12 lbs per wheel or so (from here).

Maybe it would be a better idea to have a simple fixed gear as they have now, and just not land in muddy fields?


Back to top
Profile
Space Station Commander
Space Station Commander
User avatar
Joined: Mon May 31, 2004 9:47 pm
Posts: 814
Location: Yerushalayim (Jerusalem) - capital of Israel!
Post    Posted on: Wed Nov 02, 2005 3:51 am
Lourens wrote:
Maybe it would be a better idea to have a simple fixed gear as they have now, and just not land in muddy fields?


The problem is that no matter where you land, those stubby little verticle legs are unstable. What happens when a passenger decides to vomit, and throws his/her weight all over the place? What if weight shifts for some other unforseen reason?
I really don't see why the landing legs have to be so complicated. Take a bunch of hollow, metal tubes a little bit shorter than the length of the vehicle. Put a hinge on one end, weld the hinge to the top of the vehicle; attach a rod to each leg, attach the other end of the rod to a rotating cylinder in the vehicle [e.g. like a bank lock, or an airlock], and presto! We have liftoff!
What's the worst that can happen? :roll:

_________________
“Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.”
-Anonymous


Back to top
Profile WWW
Spaceflight Trainee
Spaceflight Trainee
avatar
Joined: Mon Aug 30, 2004 6:28 am
Posts: 43
Post    Posted on: Wed Nov 02, 2005 9:34 am
...


Last edited by whonos on Thu Jun 07, 2007 7:18 pm, edited 1 time in total.



Back to top
Profile
Space Station Member
Space Station Member
avatar
Joined: Tue Dec 07, 2004 6:50 am
Posts: 265
Location: UK
Post Vehicle modifications   Posted on: Wed Nov 02, 2005 10:49 am
The problem with the La Cruces landing was primarily due to the control code not handling landing very gracefully with a gimballed engine. That could be fixed in a number of ways without involving the legs themselves E.g. using differentially throttled engines, or more marginally by gimballing the nozzle about its far extremity rather than above the chamber. Reducing the thrust much more rapidly and diminishing or eliminating the purge thrust spike.

However there isn't something fundamentally wrong with the vehicle itself, it only just managed to fall over and it was obviously doing something wrong - it just needs to learn from the experience and behave a bit differently. Having the control code recognise when part of the vehicle is touching the ground and responding accordingly should not be overly-hard.


Back to top
Profile
Moon Mission Member
Moon Mission Member
avatar
Joined: Tue Feb 10, 2004 2:56 am
Posts: 1104
Location: Georgia Tech, Atlanta, GA
Post    Posted on: Wed Nov 02, 2005 5:02 pm
whonos wrote:
Falling over is easily remedied in a orbital VTVL because your going to have a bank of horizontal thrusters for the reaction control system (most likely one set near the top and one near the bottom for complete attitude control), so when you land all you have to do is fire a couple quick bursts from the top set to stabilize the vehicle.


Interesting thought; but keep in mind that the RCS is not designed to fight gravity.

_________________
American Institute of Aeronautics and Astronautics
Daniel Guggenheim School of Aerospace Engineering

In Memoriam...
Apollo I - Soyuz I - Soyuz XI - STS-51L - STS-107


Back to top
Profile
Space Station Commander
Space Station Commander
User avatar
Joined: Mon May 31, 2004 9:47 pm
Posts: 814
Location: Yerushalayim (Jerusalem) - capital of Israel!
Post Re: Vehicle modifications   Posted on: Thu Nov 03, 2005 6:22 am
nihiladrem wrote:
However there isn't something fundamentally wrong with the vehicle itself


I agree. However, I also don't think the landing legs are fundamental to the vehicle. Sure, the vehicle could land the way it is - but wouldn't it be better to land with those extra legs for a safety measure? Not only that, but it increases the variety of landing areas available. Again, what's the loss?

About the RCS: Besides gravity, they also cost fuel.

_________________
“Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.”
-Anonymous


Back to top
Profile WWW
Spaceflight Trainee
Spaceflight Trainee
avatar
Joined: Mon Aug 30, 2004 6:28 am
Posts: 43
Post    Posted on: Thu Nov 03, 2005 9:22 am
...


Last edited by whonos on Thu Jun 07, 2007 7:17 pm, edited 2 times in total.



Back to top
Profile
Space Station Commander
Space Station Commander
User avatar
Joined: Wed Aug 18, 2004 8:47 am
Posts: 521
Location: Science Park, Cambridge, UK
Post    Posted on: Thu Nov 03, 2005 1:26 pm
Why bother with the complexities of RCS to aid landing, when just having wide legs for landing prevents all possibilitiies of falling over?

In any case, RCS would not have helped with the fall at XPC, as when they turned off it would have fallen over anyway, because the CoG was outside the leg/ground contact point.

A Lunar hopper would need wide legs as you cannot predict the surface you will land on, and you dont want to keep engines running just the stay upright.

James


Back to top
Profile
Moon Mission Member
Moon Mission Member
User avatar
Joined: Tue Oct 05, 2004 5:38 pm
Posts: 1361
Location: Austin, Texas
Post    Posted on: Thu Nov 03, 2005 1:57 pm
JamesHughes wrote:
A Lunar hopper would need wide legs as you cannot predict the surface you will land on, and you dont want to keep engines running just the stay upright.
And a Lunar hopper will not encounter any air drag. Air drag is the reason Armadillo has made all their legs narrow.


Back to top
Profile WWW
Spaceflight Trainee
Spaceflight Trainee
avatar
Joined: Mon Aug 30, 2004 6:28 am
Posts: 43
Post    Posted on: Thu Nov 03, 2005 2:17 pm
...


Last edited by whonos on Thu Jun 07, 2007 7:20 pm, edited 1 time in total.



Back to top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 79 posts ] 
Go to page Previous  1, 2, 3, 4, 5, 6  Next

Who is online 

Users browsing this forum: No registered users and 9 guests


© 2014 The International Space Fellowship, developed by Gabitasoft Interactive. All Rights Reserved.  Privacy Policy | Terms of Use