Vehicle Speed vs. Aerodynamics

[phavoc]

The G/bike is rated for speed 7 (500-800km/hr). But the problem is that it's not enclosed and a human body couldn't take the pounding. That windscreen won't be enough for the wind sheer effect. An open bike like that is going to be practically limited to about 200 kph due to buffeting.

If you enclosed it fully then you could get up to speed 7, but not like it's now. Assuming you wore say enclosed combat armor, you'd still suffer the effects of buffeting and have your head and movement affected by air flow.

The air/raft is going to suffer from the same effects, especially with any passengers who have none of the direct protection of the windscreen.

 

[MongooseMatt]

Well, the question here is whether we want Jet Bikes or not

 

[Rikki Tikki Traveller]

YES we do. But they also have to "practical".

The Jet Bike is the knockoff of the Speeders from Star Wars, we can admit that here - or they are "inspired" by the Speeders.

For the Core Rulebook, have an open-framed unit with a 200 kph limit (Speed Medium (4). In CSC or the Vehicle book, you have the enclose Rocket-Bike that is basically a flying tear-drop and can go up to Speed Very Fast/7.

Not sure what the design rules have, but if you lower the top speed, you can probably add to the Agility or lower the size down to 1 Dton.

ALSO, as I was writing this and reviewing the G-Bike, I noticed that the picture only has 1 seat, but the stats say it can carry a passenger... Need a double-seat on that baby.

 

[-Daniel-]

ALSO, as I was writing this and reviewing the G-Bike, I noticed that the picture only has 1 seat, but the stats say it can carry a passenger... Need a double-seat on that baby.

Yes, I saw that as well but because I will always thing of this as the Grav Bike, it didn't bug me.
http://orig08.deviantart.net/15b6/f/2011/076/8/9/scout_bike_by_arcass-d3bu0x8.jpg

I have always love this image, a true "crotch rocket". I thought of them as super cool, fast replacements for todays street bikes.

 

[phavoc]

Well, the question here is whether we want Jet Bikes or not

Yes we do!

And how do we want to arm them?

Grenade launchers! Lasers!! Rockets!!!

I'd like the option to hang stubby little wings off to mount additional weapons, please. Oh, and don't forget the center console comm jammer. Never know when a princess will need one in the woods.

But seriously, they are VERY cool, and you can have lots of fun zipping around and fighting in them. Just not at the speeds listed. A few hundred KPH is more than sufficient for a flying crotch rocket.

 

[-Daniel-]

But seriously, they are VERY cool, and you can have lots of fun zipping around and fighting in them. Just not at the speeds listed. A few hundred KPH is more than sufficient for a flying crotch rocket.

I agree, modern street bikes top out around 250 to 300 kl/hr. Of course they are dealing with roads, but still, I would expect the limit will be on the driver/pilot not the bike. I would drop the Grav Bike down to "Fast" band 6 max. This would reflect their speeds comparable to modern street racing bikes.

 

[Infojunky]

I would like to point out that in previous editions of Traveller, Grav vehicles had a limited speed in Nape of the Earth operations. generally topping out at around 200kph.

 

[-Daniel-]

I would like to point out that in previous editions of Traveller, Grav vehicles had a limited speed in Nape of the Earth operations. generally topping out at around 200kph.

There you go, that makes sense. But even given that, I would drop the G-Bike down to Fast anyway. :mrgreen:

 

[Rikki Tikki Traveller]

I would make the speed limit part of the Open Vehicle trait, so the machine can go faster, but the people can't...

 

[MongooseMatt]

I'll drop it to Fast for now - in the Vehicle Handbook we'll have something about being in sealed suits/armour allowing you to go faster...

 

[phavoc]

Unless it's powered armor thar you lock the head in place and have augmented abilities, it's just not possible to do that sort of thing at those kinds of speeds. The airflow will be banging you around too much.

If the pilot or passengers are exposed to the air they shouldn't be allowed to travel at those speeds and operate the crafts. If you do want to do that then you need to enclose the craft. Not pressurize it, just fully enclose it.

 

[MongooseMatt]

Unless it's powered armor thar you lock the head in place and have augmented abilities, it's just not possible to do that sort of thing at those kinds of speeds. The airflow will be banging you around too much.

Not an aerodynamics expert, but would it not be possible to shape the front fairing to push most of the airflow over and past the rider?

 

[Condottiere]

I'm thinking rocket bikes are mentioned in Logan's Run.

 

[MongooseMatt]

There is also the thought that we should include them because, well, Rocket Bikes

However, if we can at least nod to how they actually work, I would be happier.

 

[phavoc]

Unless it's powered armor thar you lock the head in place and have augmented abilities, it's just not possible to do that sort of thing at those kinds of speeds. The airflow will be banging you around too much.

Not an aerodynamics expert, but would it not be possible to shape the front fairing to push most of the airflow over and past the rider?

You could put a fairing of pretty good size in front, but even then the air passing over and around the fairing is going to create negative drag (i.e. sucking power) on the driver. Without a way to totally block out that airflow you are going to experience this, to a greater or lesser degree. A simple suit isn't enough because it doesn't enhance your strength to deal with the buffeting. If you look at formula one drivers the only thing they have exposed at high speeds is their helmet. The airflow goes over and around them, and anything coming inside their little safety bathtub they sit in has equal pressure - the airflow coming in pushes down on the airflow that wants to be sucked out, thus more or less equalizing it. A flying machine would be all to the rear, thus it would be constantly pulling on the driver and their extremities.

You can still have crotch rockets in the sky, but the speed needs to be dialed back to a reasonable level in order to make it somewhat plausible. Hurtling through the sky at 200mph is going to seem pretty damn fast to anyone.

 

[-Daniel-]

Hurtling through the sky at 200mph is going to seem pretty damn fast to anyone.

Hurling down the road at 200mph seems pretty damn fast too. :wink:

 

[Infojunky]

Hurtling through the sky at 200mph is going to seem pretty damn fast to anyone.

Hurling down the road at 200mph seems pretty damn fast too. :wink:

Take it from me, its seems a lot faster the closer to the ground you are..... Four words "Grand Prix Sidecar Racing"

 

[Condottiere]

 

[Libris]

Without a faring of some sort 200kph is about the maximum you could handle but with clever aerodynamics it would be quite possible to get a lot more out of it; it's all about diverting the airflow around the rider and diffusing the base drag. 300kph? Easy. Modern street legal road bikes can get to that (just) and they have the added disadvantage of actually having to stay on the road.

 

[phavoc]

Without a faring of some sort 200kph is about the maximum you could handle but with clever aerodynamics it would be quite possible to get a lot more out of it; it's all about diverting the airflow around the rider and diffusing the base drag. 300kph? Easy. Modern street legal road bikes can get to that (just) and they have the added disadvantage of actually having to stay on the road.

That's true. Diverting the inbound airflow around the pilot provides for some protection. And that's when you'll start getting negative air pressure on the backside of your fairing, which will also cause pull on the driver/rider, though in a different direction. The faster you go, the more the negative pressure. It won't be nearly the same impact as forward-facing pressure, but it will be strong nonetheless, and if you provide air bleed inside that will get sucked out too.

Depending on how you design it, the less aerodynamic it becomes the more power you need to apply, and the stronger the materials need to become, which changes the flow and you have to start over again. With lots of power and super-strong materials you can overcome a lot. But at some point you no longer have a crotch rocket, you have a nearly fully encapsulated craft. So you might as well fully encapsulate it and gain much more speed and protection for the occupants.

But crotch rockets are all about feeling the air whipping in your face and laughing at the danger of riding something so fast with so little protection. Only wussies are gonna go with full protection!