Estimating Masses of SW vehicles

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MKSheppard
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Estimating Masses of SW vehicles

Post by MKSheppard » 2018-06-06 05:22pm

The Millennium Falcon (as of ESB) has 7 landing gear leg pads configured in a (1 x 3 forward) and (2 x 2 aft) configuration.

Image
Red is ANH landing gear. Blue is gear added by ESB

Scaling off a decent bottom view of the Falcon gives me dimensions of 137 x 133 cm for each landing gear, or about 1.821 m2 per landing gear, for a total "on ground" contact area of 12.747 m2.

Example Ground Pressures in are:

Human (16 PSI) 11,249 kg/m2
Threshold for Soft Ground Mobility (25 PSI) 17,577 kg/m2
Passenger Car (30 PSI) 21,092 kg/m2
Mountain Bike (40 PSI) 28,123 kg/m2
Motorized Cherry Picker Lift (150 PSI) 105,460 kg/m2

The thing about Star Wars mobility is that they don't play by "normal" rules due to the existence of repulsorlifts, which allow for easy vertical takeoffs, as shown by the Falcon repeatedly during the movies; so I would say that the Falcon could go as high as 50 PSI ground loading, because it doesn't have to "fight" the ground to start moving -- i.e. it doesn't have to overcome rolling resistance.

That being said, there are inherent limitations, because if you have too high a ground pressure, the Falcon sinks all the way to it's belly in muck; and the entrance ramp can't open.

At 50 PSI loading, the falcon's maximum mass for "unimproved planetary landings" is 448.1 metric tons.

Interestingly; in ANH, the Falcon had a different landing gear configuration; with just 5 landing gear legs arranged in a (1 x 1 forward) and (2 x 2 aft) configuration, for a total contact area of 9.105m2. At 50 PSI loading, that comes out to 320 metric tons.

If we hold the Falcon's landing mass constant at 320 metric tons; the ground pressure of the Falcon comes out to:

ANH: 49.98 PSI (35,145 kg/m2)
ESB: 35.7 PSI (25,103 kg/m2)

One possible reason for the difference is that before the events of A New Hope, Solo basically flew the Falcon out of spaceports, with the occasional side jaunt to impromptu landing strips that were carefully chosen for smuggling, whereas when he started working with the Rebellion after the events of A New Hope, he needed to go to places really off the beaten path with little prep time available; so he added the landing gear to reduce his ground pressure.

Yes, I know, you could always just use repulsorlifts to reduce your ground pressure, the technology is shown as being reliable enough for mid-air floating landing platforms in Attack of the Clones on Coruscant; but that would consume energy (bad for tramp freighters $$$) and create a energy signature much more detectable (bad for smugglers) if it had to be kept on all the time to keep the Falcon from collapsing/sinking into the ground under its own weight.

Doing some more refining on the falcon's volume:

**********

"Claws" -- Triangle 9 m long by 6 m wide and 1.25m thick (33.75m3 per claw, 67.5m3 for both)

***********

Saucer (1513.08 m3)
Top -- 5.8m top radius, 12m bottom radius, 1.83m long conical frustrum (473.80m3)

Middle -- 12m radius, 1.25m thick cylinder (565.48 m3)
Bottom

Bottom -- 5.8m top radius, 12m bottom radius, 1.83m long conical frustrum (473.80m3)

*******

Cockpit (49.87 m3)
1.86m radius and 3.4m long cylinder (36.95m3)
plus
0.77m top radius, 1.86m bottom radius, 2.25m long conical frustrum (12.92m3)

*********

Total Volume: 1,630.45 m3

Estimated Density at 50 PSI landing leg pressure (448.1 metric tons) in ESB configuration -- 274.83 kg/m3

That's fully loaded though. Throughout the RPGs the Falcon has always carried about 100 metric tons of cargo. In unloaded configuration, she's 213.49 kg/m3.

Another method for estimation of space warship mass is tanks:

M1A1: 19.7 m3 armored volume, 61,300 kg: 3,111.67 kg/m3.

T-80B: 11.8 m3 armored volume, 42,500 kg: 3,601.69 kg/m3.

T-90A: 11.04 m3 armored volume, 46,500 kg: 4,211.95 kg/m3.
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Re: Estimating Masses of SW vehicles

Post by MKSheppard » 2018-06-06 06:30pm

Per Curtis Saxton's old site:

http://www.theforce.net/swtc/walkers.html

Saxton estimated the AT-AT as 22.6±0.8m high; ~26m long; ~7.9m wide (hull).

Using some blueprints (LINK) via using his 22.6m height estimate to scale it, I estimate AT-AT foot diameter is about 3.85m (11.64m2), and because of the way AT-AT's walk, three legs are in contact at any one time (34.92 m2).

Using a 20 PSI (14,061 kg/m2) rule for mobility -- a little bit heavier than a human's 16 PSI, but lighter than the 25 PSI threshold for wheeled ground vehicle mobility -- the AT-AT masses about 491,010 kg.

(The high end estimate -- if you assume all 4 legs are in contact with the ground -- ends up at 654,680 kg)

This...actually starts to explain things:

A.) How it was able to crush the snowspeeder.
B.) Shrug off blasters

Since it weighs about as much as a YT-1300 light freighter!

Scaling off the blueprints:

Head: (83.495m3)
601 x 267 x 423 cm (67.87m3) (Head)
251 x 250 x 250 cm (15.625m3) (Neck)

Hull: (594.63m3)
Front: 444 x 571 cm by 617 cm wide
Middle: 608 x 710 cm by 617 cm wide
Aft: 501 x 556 cm by 617 cm wide

Drive Shaft under Hull (135.13 m3)
668 x 264 x 239 cm (Front section) (42.14m3)
515 x 158 x 625 cm (center section) (50.85m3)
668 x 264 x 239 cm (rear section) (42.14m3)

Foot: (24.61m3 per foot, 98.44m3 for all 4)
385 cm diameter, 175cm height - (20.37m3)
214 cm diameter, 118cm height - (4.24m3)

Leg: (8.416m3 per leg, 33.664 m3 for all 4)
205 x 1173 x 35 cm = 8.416m3

Total Volume: 945.359 m3
Density: 519.39 kg/m3 (high end estimate 692.52 kg/m3)

So the AT-AT appears to be a bit more than twice as dense as the Millenium Falcon; but far below the density of modern tanks (3,100 to 4,200 kg/m3); due to that enormous "hump".

Looking at the ICS cutaway:

LINK

The density/efficiency of the AT-AT could be greatly improved if it was reduced from 40 troops (2 decks) to 20 (1 deck) and the power cells moved into the speeder bike garage.
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Re: Estimating Masses of SW vehicles

Post by Captain Seafort » 2018-06-06 06:40pm

MKSheppard wrote:
2018-06-06 06:30pm
So the AT-AT appears to be a bit more than twice as dense as the Millenium Falcon; but far below the density of modern tanks (3,100 to 4,200 kg/m3); due to that enormous "hump".
How does AT-AT density compare to an AS-90, Warrior or StuG, given that they're closer to its combat role?
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Re: Estimating Masses of SW vehicles

Post by MKSheppard » 2018-06-06 06:46pm

Captain Seafort wrote:
2018-06-06 06:40pm
How does AT-AT density compare to an AS-90, Warrior or StuG, given that they're closer to its combat role?
I think you mean the M2 Bradley :D

A quick estimate off blueprints and known dimensions give me a volume of about 20 to 21.5 m3 for the Bradley.

At the 34,200 kg combat weight of the M2A3 (circa 2000), that's 1,590 to 1,710 kg/m3 density for the Bradley.

One thing that might be skewing this is possibly Imperial requirements that the AT-AT be a sealed environment vessel, supporting 40 men for however long in total gas/lava/whatever environments, forcing a fairly large life support system and large internal volume so people can eat/sleep/shit in comfort for a long period of time, as opposed to sleeping outside of the APC.
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Re: Estimating Masses of SW vehicles

Post by MKSheppard » 2018-06-06 07:22pm

There are two (maybe three) other vehicles that we can estimate masses for:

X-Wing and Y-Wing, due to them being on landing skids in the Rebel Temple Base in ANH, and then Luke's X-Wing in ESB/ROTJ.

Rebel Transport, due to this scene Link

Scaling off the old Essential Guide to Vessels, gives a landing gear pad size of 2.07 x 1.42m (2.93m2) for each landing gear pad on the Rebel Transport.

Link shows there are four gear pads for a total of 11.757m2 of space.

If we assume it's got the following ground pressures:

50 PSI (35,153 kg/m3): 413.31 metric tonnes
100 PSI (70,306.88 kg/m3): 826.64 metric tonnes
150 PSI (105,460 kg/m3): 1,239.96 metric tonnes

I'm inclined to go with 150 PSI, because that's within the weight limits of a specially prepared surface -- because these ships are big enough to need specialized equipment to load in a reasonable amount of time -- but small enough that they have to be economical enough to operate from low end surfaces -- as in typical concrete a few inches thick, not massive 6 foot thick reinforced concrete.
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Re: Estimating Masses of SW vehicles

Post by madd0ct0r » 2018-06-07 11:56am

Treating them more as a pad footing then a vehicle (because unlike a track or wheel, we don't need the soil to hold under the horizontal shear of the vehicle dragging itself forward)


50 PSI is 244kN/m2

The presumed bearing value table in the link below: puts that somewhat below loose sand.
http://environment.uwe.ac.uk/geocal/fou ... unbear.htm


I'm trying to figure out wether the landing legs of the falcon should be considered dynamic compensators. Ie if they land on a bit of a slope, and the top level of soil slips, will the foot rotate around to return to level to prevent further load concentration and return the foot to the more stable deeper soil?

Soil ain't quicksand, even if fails you won't sink indefiently. Just unitl the weight of the soil on the slip surface is enough to stop further slippage.
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Re: Estimating Masses of SW vehicles

Post by fractalsponge1 » 2018-06-07 12:00pm

Do repulsorlifts even take power once their height setting is fixed? This is for hover (or I guess landed state), not movement.

My read on landing legs (at least at ship rather than fighter level) is that they are more for stability (maybe with their own small repulsorlift plates to fine tune the main system response) than any serious load bearing.

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Re: Estimating Masses of SW vehicles

Post by MKSheppard » 2018-06-07 08:07pm

Regarding this segment by me:
I'm inclined to go with 150 PSI, because that's within the weight limits of a specially prepared surface -- because these ships are big enough to need specialized equipment to load in a reasonable amount of time -- but small enough that they have to be economical enough to operate from low end surfaces -- as in typical concrete a few inches thick, not massive 6 foot thick reinforced concrete.
The original XB/YB-36 had a massive 110" diameter, 46" wide single tire on each landing gear, which required a 22.5" thick runway and limited it to just three fields in the entire world.

The B-36A had four 56" diameter, 16" wide tires on each landing gear, which reduced it to a 13.5" thick runway, allowing the use of 20+ airfields around the globe; published figures put the ground pressure of this "standard" gear as being 156 PSI.

They experimented with caterpillar track gear on the XB-36 which lowered ground pressure to 57 PSI, allowing the use of "unimproved" runways -- read -- dirt and grass, because they were worried about nuclear exchanges destroying B-36 airfields.
Treating them more as a pad footing then a vehicle (because unlike a track or wheel, we don't need the soil to hold under the horizontal shear of the vehicle dragging itself forward)
Repulsorlift controlled takeoffs still have some forward motion for takeoff/landings. Plus you don't want to sink too deeply into the soil, because then you have to face suction issues and damage to your landing gear.

But anyway, pad footing...according to this:

https://www.pole-barn.info/soil-bearing-capacity.html

http://civilblog.org/2015/09/22/safe-be ... ils-rocks/

The soil bearing capacity of various types of soil (dry) are:

Hard Rock (Granite): 478.6 PSI
Laminated Rock (Sandstone/Limestone): 239.3 PSI
Shattered Bedrock: 130.5 PSI
Gravel/Sand mixture: 65.2 PSI
Sand: 20.8 PSI
Clay: 13.8 PSI

Of course, you add water and all bets are off.
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Re: Estimating Masses of SW vehicles

Post by MKSheppard » 2018-06-07 09:24pm

http://nl.starwars.wikia.com/wiki/Besta ... Hangar.jpg

Scaling off the length (12.5m) in Canon....

Front landing gear skid
70 x 26 cm (0.182 m2)

Rear Landing Gear skid(s) (0.429 m2)
65 x 33 cm (0.2145 m2)

Total landing skid area: (0.611 m2)

At the 50 PSI (35,153 kg/m2) limit (remember, the X-Wing in ESB was capable of sitting on heavily waterlogged soil in Dagobah without sinking appreciably once Yoda had removed it from the lake) a T-65 X-Wing is 21,478.48 kg.

If you assume that all three skids are the same size as the nose skid (easier to see the nose skid vs the rear skids), the surface skid area changes to 0.546 m2, and a mass of 19,193.54 kg

Given that various semi-canon sources say the X-Wing weighs 10 metric tons.....I'd say that it massing about 20 metric tons is about right; since that's closer to "reality" -- 10 metric tons is basically a F-16 Fighting Falcon in weight.

For volume, I said "fcuk it" and went here

http://www.st-v-sw.net/STSWvolumetrics.html

and got a 27m3 volume for a X-Wing.

Assuming a median mass of 20,336 kg; the X-Wing has a density of 753.185 kg/m3.

*******

His site gives 615m3 volume for an AT-AT; and using that gives us a density of 798.39 kg/m3 (three leg) or 1,064.52 kg/m3 (four leg).

***

Also a TIE fighter's volume is given as 7.8 m3. If we assume it's the same density (750 kg/m3) as a X-Wing, that results in a mass of 5.85 metric tons.
"If scientists and inventors who develop disease cures and useful technologies don't get lifetime royalties, I'd like to know what fucking rationale you have for some guy getting lifetime royalties for writing an episode of Full House." - Mike Wong

"The present air situation in the Pacific is entirely the result of fighting a fifth rate air power." - U.S. Navy Memo - 24 July 1944

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