New rules for hull configuration and re-entry

[Murdoc]

I've been working on this project for a while now, trying to make them more realistic without getting bogged down. Most of the rules are just for dealing with fringe cases anyway, since most ships should be able to make it to the surface of a planet in about half an hour, completely safely (not two days). Let me know what you think!

http://www.travellerrpg.com/CotI/Discuss/showthread.php?p=449003#post449003

 

[esampson]

Huh. Black hole must have eaten my post.

I only had time to skim the PDF but it looks pretty good. I would probably reclassify your 'hypersonic airframe' as a lifting body. Technically the flying wing is a lifting body as well, but if you are creating grades of airframes then you might as well create grades of lifting bodies, so it's more a changing of terms than ideas.

The one thing I noticed was your formula for calculating thrust for a ship that has to use its engines directly against gravity is overly simplistic. (S²-P²)^.5 is a pretty easy formula and would do a much more accurate job of modelling using a portion of the ship's thrust to counteract gravity (S is the thrust of the ship in G's and P is the force of the planet's gravity).

 

[Murdoc]

Huh. Black hole must have eaten my post.

I only had time to skim the PDF but it looks pretty good. I would probably reclassify your 'hypersonic airframe' as a lifting body. Technically the flying wing is a lifting body as well, but if you are creating grades of airframes then you might as well create grades of lifting bodies, so it's more a changing of terms than ideas.

So a hypersonic airframe would be basically a lifting body with wings then? Then we run into what I said in the notes about the subsonic airframe being basically 'streamlined with wings', I'd have to put the extra stats somewhere.
And yes, the flying wing is a lot like a lifting body, just it is all-wing instead of all-body. Yeah, just definitions, but I think it is different enough to keep its name. I do like your idea of creating different grades of l.b. though, I'll have to think on it.

The one thing I noticed was your formula for calculating thrust for a ship that has to use its engines directly against gravity is overly simplistic. (S²-P²)^.5 is a pretty easy formula and would do a much more accurate job of modelling using a portion of the ship's thrust to counteract gravity (S is the thrust of the ship in G's and P is the force of the planet's gravity).

Really? I was a little unsure about that section of the rules, but not that specific part. Why is that formula more accurate? I assume that it is just replacing the part before taking into consideration the lift factor, right?

 

[esampson]

. . . Really? I was a little unsure about that section of the rules, but not that specific part. Why is that formula more accurate? I assume that it is just replacing the part before taking into consideration the lift factor, right?

It's more accurate because you are dealing with vectors and Pythagorean theorem.

Since a² + b² = c² then c² - a² = a² or (c² - a²)^.5 = b.

In this case c is the length of the vector (the thrust from the ship), a is the portion of that vector that has to be used to fight gravity and b is the portion that is used for velocity.

This only applies to objects that lack lifting surfaces (body and wings). In the case of an object that does have lifting surfaces you can reduce a by the amount of lift, but that's going to get awful headachy because the amount of lift will vary by the angle the object is at as well as its speed (this, however, is why planes that are flying slowly have to fly with their nose up and why they have minimum air speeds).

 

[Murdoc]

It's more accurate because you are dealing with vectors and Pythagorean theorem.

Since a² + b² = c² then c² - a² = a² or (c² - a²)^.5 = b.

In this case c is the length of the vector (the thrust from the ship), a is the portion of that vector that has to be used to fight gravity and b is the portion that is used for velocity.

Ah, I see now, thanks. I never even thought of using that that way before. Ok, that fits. That's one of the reasons I like to post stuff like this on here, because sometimes others will see ways to improve them I hadn't thought of.

This only applies to objects that lack lifting surfaces (body and wings). In the case of an object that does have lifting surfaces you can reduce a by the amount of lift, but that's going to get awful headachy because the amount of lift will vary by the angle the object is at as well as its speed (this, however, is why planes that are flying slowly have to fly with their nose up and why they have minimum air speeds).

I know, which is why I was just keeping it simple. Really, the entire Lift rules are only there to justify the "Accel" column of the Hull Config chart. Add lifters to your ship and you can ignore them entirely; they're just for fringe cases and aero-heads like me. But if anyone does have ideas to make them more accurate too, I'm open to them.