Speed, Lift & Gravity on the Moon.

[ckatt]

Hello
Just curious if anyone had some knowledge to share. Here's the scenario
Here on Earth, race cars often use a spoiler to improve traction of the rear wheels. But I suspect this would have no effect if operating someplace with no atmosphere. And this got me wondering about lift. If you were travelling at high speeds on the moon (currently the top speed reached seems to be about 17 kph but I'm thinking closer to 300 kph). would lift become a problem due to the low gravity? What other consideration might there be? Going over a bump at that speed might produce significant air time. Still, you'd have to be going over 8000kph to actually escape the moon's gravity. so if we did take a race car to the moon, how different might the driving experience be?

 

[Wayne Mack]

On the moon, aerodynamics would become unimportant, but tire tread on contact surface would be more significant. To state the obvious, the internal combustion engine is not a starter. Heat dissipation may become an issue; radiant heat would seem to be the only cooling technique. Banked turns for tracks would also become more important. Rollover may become more of an issue with a conflict between having a low center of balance and having high clearance for the lunar surface. Braking would also be a concern and chutes would be kind of pointless for dragsters.

I could see lunar racecars having large, deep treaded tractor tires, but having the car body hung below the axle. Electric engines would be a given and I would expect to have a heavy duty reverse gear to be used to stop the car at the end of the race.

 

[ckatt]

@Wayne Mack
Hey, those are some good points. Yeah, I wasn't imagining combustion engines. Either electric or some as yet to be developed means of locomotion.
What makes me most curious is what new problems come to light when aerodynamics are out of the picture(like a spacecraft) But you are still driving on dirt and have to worry about traction where there is a lack of gravity.

 

[Swank]

Couple of thoughts:

You could probably make internal combustion work if you wanted to - the fact that you're in a vacuum opens up the possibility of radiated cooling via white hot vanes that would have combusted in oxygen - like a bulb filament. Or develop a racing fuel that is endothermic and run it parallel to the exothermic stuff.

You don't have air to provide downdraft, but you do have fine dust - which is much heavier than air. You could use the dust and sand the tires kick up to push straight down on the car by ejecting it straight up. Think snowblower. Of course, you could have a separate rocket thruster just for downforce.

And you can always add mass to the car. A 6000 kg car should ride similarly to a 1000 kg car here, with the exception of turning or changing speed. Inertia remains the same.

The absence of wind resistance means that you could use large tires to decrease rolling resistance - even putting the car inside a huge wire mesh wheel.

With an active suspension (using radar), there really is no upper limit to your top speed, except to corner and avoid running into something much bigger than the wheels.

Given the lack of wind resistance, breaking contact with the ground would only preserve your velocity. So bumps aren't a bad thing unless you're accelerating or turning.

 

[Wayne Mack]

One option to recreate a spoiler effect would be to allow the use of small jet engines or thrusters. There would like have to be some sort of rule set, otherwise, the race would become rocket ship racing. In an airless environment, drafting would be pointless, but if thrusters are allowed, a trailing racer could utilize the lead car's thruster exhaust to provide downward push without using its own thrusters; i.e., preserve a constrained resource for later in the race. Likewise, if the lead car positioned itself properly, its thrust could also force a trailing car upwards.

On a social note, in an airless world, it might seem extremely wasteful to expel gasses into space merely for sport and entertainment.

 

[Swank]

One option to recreate a spoiler effect would be to allow the use of small jet engines or thrusters. There would like have to be some sort of rule set, otherwise, the race would become rocket ship racing. In an airless environment, drafting would be pointless, but if thrusters are allowed, a trailing racer could utilize the lead car's thruster exhaust to provide downward push without using its own thrusters; i.e., preserve a constrained resource for later in the race. Likewise, if the lead car positioned itself properly, its thrust could also force a trailing car upwards.

On a social note, in an airless world, it might seem extremely wasteful to expel gasses into space merely for sport and entertainment.

How do you use jets in space?

If the rockets or thrusters are allowed solely for downthrust rather than propulsion, it would be a simple enough rule to have them pointed straight up, only. Hard to gather thruster exhaust that is coming out of the top of a car. But even if it was coming out of the back, AND hadn't dispersed in the vacuum, gather the exhaust of the car ahead of you is just adding drag to your car, limiting speed.

 

[Cthulhu.Science]

@Swank wrote "And you can always add mass to the car. A 6000 kg car should ride similarly to a 1000 kg car here, with the exception of turning or changing speed. Inertia remains the same."

I'm curious how mass vs "weight" (gravitational pull) affects performance of said vehicle. Using traditional definitions of the two.
All of my experience with vehicles has been on a planet where mass & weight are the same.

For example, given a vehicle of 3,000 kg mass...
1 Will each bump result in a more eccentric reaction on the moon? (less gravitational resistance to the redirected movement of the mass)
2. Turning becomes much more interesting as well. Less gravitational pull and no atmosphere.
3. Essentially traction is dropped significantly...
3a. the lower weight reduces friction between the wheels and the soil
3b. Atmosphere contributes significantly to vehicle stability (or lack of ) particularly at higher speeds.

I know this is the base topic, but that's me trying to work out the basics on my own.

This is all fascinating and way outside my bailiwick.
Great thread!

 

[Elckerlyc]

It is fascinating. Can't wait till the first race!

 

[Wayne Mack]

Rockets and thrusters are existing technologies used in space. Oxygen + fuel + ignition is a slightly more complex design, but would provide a constant level of thrust. Compressed gas would be a simpler design, but the thrust level would decay with the decrease of pressure and volume in the tank.

Downward thrust is useful in providing addition cohesion for the wheels, but vertical thrust would also have strategic advantages. It could provide an additional burst at the finish, at the start to establish a lead position, or throughout to pass. The thrust could also be used to force trailing cars either upward to the side. This would restore the need for aerodynamics in cars to convert the leading exhaust into downward pressure and minimize the drag. This might allow a trailing car to maintain thruster capacity with the trade-off of using more engine capacity. The lead car might also use selective blasts to force a trailing airborne (need a better term for this) car higher or direct a trailing car to the side. If the race course has hills and moguls, ala motocross, it may be advantageous to use a slight downward thrust to go from crest to crest rather than lose momentum through impact with an incline.

End of race stopping and mid-race pitstops may also pose some interesting challenges.

 

[Wayne Mack]

Adding mass would directly increase momentum. Additional force would be required to start the car in motion and also to cause the car to turn. It would be more difficult to grab the lead position at the start and the car would be less maneuverable and responsive than a lighter car.

 

[ckatt]

Super interesting input folks.
So all along I've been picturing a three-wheeled vehicle with two large wheels at the front.
Now if you put a thruster at the back would it be possible to operate without the need for a rear wheel?
Another thought I'd had would be a tread on the back. As the lunar dust can be fine, I thought it might be traversable on a snowmobile-like vehicle.
I'd imagine most of the weight would be in the rear then, so what effect would that have on steering? The front skis on a snowmobile work a bit like a rudder to redirect the motion. Wheels need traction. But perhaps if they are big enough, the contact patches would be sufficient?

 

[Swank]

Super interesting input folks.
So all along I've been picturing a three-wheeled vehicle with two large wheels at the front.
Now if you put a thruster at the back would it be possible to operate without the need for a rear wheel?
Another thought I'd had would be a tread on the back. As the lunar dust can be fine, I thought it might be traversable on a snowmobile-like vehicle.
I'd imagine most of the weight would be in the rear then, so what effect would that have on steering? The front skis on a snowmobile work a bit like a rudder to redirect the motion. Wheels need traction. But perhaps if they are big enough, the contact patches would be sufficient?

Snow is slippery. I doubt moon dust is. Beach buggies don't use skis, for instance.

As I mentioned earlier you could do everything with one wheel and the chassis dangling inside it.

 

[ckatt]

Snow is slippery. I doubt moon dust is. Beach buggies don't use skis, for instance.

This is true. That's why I envision front wheels rather than skis. But getting traction in sand can be difficult. So rather than nobby tires, a tread might be a good option. Still, a front-wheel drive system might be better...


I've seen designs of such one-wheel bikes before, think they used them in one of the Men in Black movies. Steering would become a very different problem to solve then, wouldn't it? I expect sharp turns would be nearly impossible on a flat area.

 

[Swank]

This is true. That's why I envision front wheels rather than skis. But getting traction in sand can be difficult. So rather than nobby tires, a tread might be a good option. Still, a front-wheel drive system might be better...


I've seen designs of such one-wheel bikes before, think they used them in one of the Men in Black movies. Steering would become a very different problem to solve then, wouldn't it? I expect sharp turns would be nearly impossible on a flat area.

It would steer like a motorcycle.

 

[Wayne Mack]

As I mentioned earlier you could do everything with one wheel and the chassis dangling inside it.

Interesting idea. I'm trying to picture how to get the torque to turn the wheels as opposed to the internal compartment. I guess it is safe to assume that the mass of the engine would be much greater than the mass of the wheel, so that should probably work. I'd guess the engine would hang down from the axle and keep the center of gravity low and probably the pilot would sit above the axle.

I'd likewise have concerns about turning. The spinning tire would tend to hold the craft upright. Remember, in motorcycle racing, the center of gravity from the engine and rider is quite high and above the wheel axles. This gives more of a lever arm to exert force than I guess would be experienced when the center of mass and the shifted weight lies inside the spinning wheel. Probably need to do some calculations or tests to resolve this concern.

I assume that starting and stopping would require some sort of 'landing gear' to be extended out either side of the craft.

I would also assume that the pilot would require some sort of heads up display driven by a pair of cameras mounted outside the tire.

Once other concern would be the stability in a crash. Two cars touching tires could send them both spinning out of control.

 

[Swank]

Interesting idea. I'm trying to picture how to get the torque to turn the wheels as opposed to the internal compartment. I guess it is safe to assume that the mass of the engine would be much greater than the mass of the wheel, so that should probably work. I'd guess the engine would hang down from the axle and keep the center of gravity low and probably the pilot would sit above the axle.

I'd likewise have concerns about turning. The spinning tire would tend to hold the craft upright. Remember, in motorcycle racing, the center of gravity from the engine and rider is quite high and above the wheel axles. This gives more of a lever arm to exert force than I guess would be experienced when the center of mass and the shifted weight lies inside the spinning wheel. Probably need to do some calculations or tests to resolve this concern.

I assume that starting and stopping would require some sort of 'landing gear' to be extended out either side of the craft.

I would also assume that the pilot would require some sort of heads up display driven by a pair of cameras mounted outside the tire.

Once other concern would be the stability in a crash. Two cars touching tires could send them both spinning out of control.

 

[ckatt]

Here's the movie I was thinking of

And I guess this is the real thing. I'm not sure if it would make the best moon car though.

 

[Cthulhu.Science]

1869

 

[Cthulhu.Science]

Or better a video of the improved version - perfect for the moon.

1932 Dynasphere at British Pathe

 

[msstice]

(10 min mark). First I thought I had seen this in Space 1999, then in Joe 90, turns out it's Capt. Scarlet.