Atmospheric operation of small craft, incorrect assumptions

[hdan]

If a pilot was stupid enough to go for hypersonic reentry, yes. However, with the ability to negate gravity, you can enter the atmosphere at 1 mph if you wanted.

There have been some threads here regarding why this doesn't work out so well in practice, especially in any system where you have lots of things in orbit to collide with. But that's certainly a consideration.

BTW - I didn't say no streamlining, I'm talking about no lifting surfaces (airframe). A 20 ton launch has better streamlining (reduced drag) than something with a lifting surface (induced drag), parasitic drag being equal.

Maybe the problem then is the rules' choice of words. If we go back to "first principles", I believe that the rules say a hull with fins or other atmospheric control surfaces will be more maneuverable in an atmosphere than one without those surfaces, and that a hull with no streamlining at all cannot enter an atmosphere without great difficulty.

And if I understand your other posts, you disagree with this assessment for hulls that have gravitic drives, right? Or maybe it would be more accurate to say that you disagree that a "standard" hull with a gravity drive should be less maneuverable than a non-gravitic "streamlined" hull?

 

[far-trader]

However, the fastest would probably have the more general advantage because they are more likely to be able to evade missiles and other weapons fire...

You can't outrun the missile. You might be able to out maneuver based on flight envelopes. The grav craft has the clear advantage in this.

The hovering grav craft? Again, you seem to be imagining an instant change from hover (zero velocity) to full supersonic speed. Ain't gonna happen. And you have almost no maneuvering capability from hover to dodge a missile.

I'm pretty confident, the way grav drives seem to operate (to me anyway), most pilots would take the supersonic aircraft over the grav drive craft any day of the week. Given equal thrust performance, and even equal top speed performance, the aircraft is still going to be more maneuverable, quicker to change its position, than the grav drive craft with no lifting surfaces to act in the atmosphere. And that's at speed. If you're hovering you lose the edge speed gives you.

Your hovering ability will mean squat in most combat situations. The one place I can think of where it might give you an edge would be in pop-up/shoot-down scenarios where you surprise the supersonic aircraft. And even there counter measures against your missiles will give the ss aircraft a chance. And if it lives you're, quite literally, a sitting duck for his riposte attack run.

 

[rust]

Again, you seem to be imagining an instant change from hover (zero velocity) to full supersonic speed.

Just to make sure: Is there any reason to assume that a Traveller grav
drive is an inertialess drive, which would indeed be new to me ?

 

[DFW]

ok, but the control fins only provide a minimum of lift? and it still doesn't explain how you will evade a proximity fused high manoeuvrability missile unless your aircraft has near equal manoeuvrability to said missile... yes?

While in level flight almost all the lift is supplied by the "fin" surfaces. Maneuverability is how quickly you can change your direction. ALL craft using wings for lift have to maintain minimum forward speed or stall and fall. Because of this the missile can't "turn on a dime". Therefore, by definition, one of those missiles is less maneuverable than a craft that can stop, turn, all without regard to lift.

 

[DFW]

But YOU said Bernoulli would be the basics.

And so it is. If you studied it, you already know that. If you didn't go look t up.

 

[barnest2]

While in level flight almost all the lift is supplied by the "fin" surfaces. Maneuverability is how quickly you can change your direction. ALL craft using wings for lift have to maintain minimum forward speed or stall and fall. Because of this the missile can't "turn on a dime". Therefore, by definition, one of those missiles is less maneuverable than a craft that can stop, turn, all without regard to lift.

aye, but as said above, you cant go from standing to full speed so even an AIM-9 would probably catch a hovering grav vehicle, cos those things are damn turny

 

[barnest2]

Of course an AIM-9 would be less effective on a grav vehicle in some situations... know that i realise that...

 

[DFW]

Again, you seem to be imagining an instant change from hover (zero velocity) to full supersonic speed.

No, never said such a thing. reread what I wrote.

 

[barnest2]

Again, you seem to be imagining an instant change from hover (zero velocity) to full supersonic speed.

No, never said such a thing. reread what I wrote.

Then how else would you get out of a hypersonic missiles flight envelope from a standing start?

 

[DFW]

aye, but as said above, you cant go from standing to full speed so even an AIM-9 would probably catch a hovering grav vehicle, cos those things are damn turny

An AIM-9 WOULD be damn tricky to pull out of its envelope due to its thrust vectoring. Pretty much impossible for a fighter air craft. Only slightly less difficult for a grav vehicle depending on the approach vector and reletive speed. Wouldn't want to be in that position.

 

[far-trader]

Again, you seem to be imagining an instant change from hover (zero velocity) to full supersonic speed.

Just to make sure: Is there any reason to assume that a Traveller grav
drive is an inertialess drive, which would indeed be new to me ?

...I was gonna say no. Then half way through replying I suddenly wasn't so sure. I've never played it that way but now you've got me questioning just how a reactionless thruster/grav drive would have to interact and behave and a deep part of my brain got a cold shiver that it might just have to be inertia free. And that would mean it would be an instant effect. But then acceleration (as in Gs of thrust, the way the rules use it) would be meaningless. I need to think on this a bit...

...or a lot.

 

[DFW]

Then how else would you get out of a hypersonic missiles flight envelope from a standing start?

The key is "hypersonic" as opposed to the AIM-9. Once you see its launched (as per the stated scenario earlier) you start your run. The missile burns and doesn't slow, thus at hypersonic speed its maneuverability is low (not as much compared to clumsy modern fighter planes). As it gets close enough you drop like a stone (the missile isn't designed to counteract that characteristic) You would have a chance if exceeding its maneuverability.

 

[barnest2]

Then how else would you get out of a hypersonic missiles flight envelope from a standing start?

The key is "hypersonic" as opposed to the AIM-9. Once you see its launched (as per the stated scenario earlier) you start your run. The missile burns and doesn't slow, thus at hypersonic speed its maneuverability is low (not as much compared to clumsy modern fighter planes). As it gets close enough you drop like a stone (the missile isn't designed to counteract that characteristic) You would have a chance if exceeding its maneuverability.

Ok, in that situation i have no idea what would happen, i dont think any of us would... but define close enough... if your far enough outside of its fuse range it will follow you, and if you leave it too late you'll get thumped with a fistful of shrapnel...you would have to know exactly what you were doing at exactly what moment, especially at those speeds... i.e... get a computer to do it...

 

[DFW]

There have been some threads here regarding why this doesn't work out so well in practice, especially in any system where you have lots of things in orbit to collide with. But that's certainly a consideration.

Once you get to an altitude with barely ANY atmosphere you are below all orbiting craft. At that point you slow to hover and descend. Very simple.

I believe that the rules say a hull with fins or other atmospheric control surfaces will be more maneuverable in an atmosphere than one without those surfaces, and that a hull with no streamlining at all cannot enter an atmosphere without great difficulty.

And if I understand your other posts, you disagree with this assessment for hulls that have gravitic drives, right?

Correct, and for no streamlining, see comment about entering at 1 mph.

 

[DFW]

you would have to know exactly what you were doing at exactly what moment, especially at those speeds... i.e... get a computer to do it...

Yes, of course. Similar knowledge fighter pilots get regarding the missiles they will face. IT would take lots of knowledge AND skill.

 

[far-trader]

...As it gets close enough you drop like a stone (the missile isn't designed to counteract that characteristic) You would have a chance if exceeding its maneuverability.

I'm pretty sure that maneuver is going to be much slower/less drastic a change than an airframe could produce in a full burn turn. The missile is a darned sight more likely to be able to track your 1G (local gravity, whatever it is) drop (as you still move forward at whatever speed you have managed to get up) than it can an airframe full turn burn. And missiles ARE designed to track and counteract just such maneuvers. The dicey bit of the game is timing. If you can wait long enough, but not too long, you may be able to turn inside the missile. I don't think you can as easily cut your grav lift and expect to be able to drop inside the missile's own maneuvering.

 

[far-trader]

...for no streamlining, see comment about entering at 1 mph.

Relative to what? The ground? Ignoring very high speed upper atmosphere winds as inconsequential? At your peril :twisted:

All the reality aside of why such a maneuver would be ill advised there is simply the fact that the rules state no streamlining = no atmosphere entry. There is an implied whole host of reasons. From lack of landing gear meaning once down what do you do? To all kinds of wind shear effects twisting you out of a proper flight configuration causing a loss of control and a crash.

 

[DFW]

The dicey bit of the game is timing. If you can wait long enough, but not too long, you may be able to turn inside the missile. I don't think you can as easily cut your grav lift and expect to be able to drop inside the missile's own maneuvering.

No kidding! It would be hairy.

 

[rust]

And missiles ARE designed to track and counteract just such maneuvers.

Besides, there is a very high chance that the missile will have a proximity
fuse, and unless one knows to what distance this is set, precise timing is
very much a lottery game.

 

[far-trader]

Some interesting thoughts coming out of this But I have to get back to work, and noodle on that inertia question (curse you rust for kicking my brain ).