Grav vehicle dogfighting tactics?
- Thread starter HG_B
- Start date
I'm not familiar with " Col. Boyd's Energy-Maneuverability theory for lift dependent craft". Could you summarize it, or point me to it?
I have given some thought to Grav vehicle maneuvering and dog fighting but specifics probably depend on how Grav works IYTU or in the particular version of Traveller. However I chime in if I know a bit more about what you're looking for.
[Edit] Eh... maybe I just had a blonde moment but are you refering to the real life Col. Boyd of the "Boyd Loop" fame, because I read it first as a Traveller reference to "Lift" craft
I have given some thought to Grav vehicle maneuvering and dog fighting but specifics probably depend on how Grav works IYTU or in the particular version of Traveller. However I chime in if I know a bit more about what you're looking for.
[Edit] Eh... maybe I just had a blonde moment but are you refering to the real life Col. Boyd of the "Boyd Loop" fame, because I read it first as a Traveller reference to "Lift" craft
You can start here but it probably would require a bit more work if you have no aeronautics background.
Basics: If you have a grav vehicle that has 2G's worth of anti-grav available and you are on a 1G world, you use 1G to negate the planets grav and a net 1G of force to apply to movement in any direction and, you can orient the craft as you please (upside down, straight up, down, etc.)
Okay so assuming your Grav drive can "apply to movement in any direction" your fighter's nose can be pointed in any direction allowing you to target your opponent with bore sight weapons. I'm thinking this influences dogfight tactics in a similar way to modern thrust vectoring, but without the need to return to a conventional flight profile to sustain lift.
Effectively you have Thrust of 1G. Your craft is still going to be subject to Drag . While you don't need to generate Lift it might still be a good idea to design your Grav fighter with lift generating surfaces to gain any advantage possible in maneuverability in atmosphere.
Of course you can't talk dogfighting tactics based on thrust medium alone. Other things you have to take account of are:
Of course there's a whole other argument about why would you ever get into dogfighting range, when you have both over the horizon and from orbit capabilities.
Effectively you have Thrust of 1G. Your craft is still going to be subject to Drag . While you don't need to generate Lift it might still be a good idea to design your Grav fighter with lift generating surfaces to gain any advantage possible in maneuverability in atmosphere.
Of course you can't talk dogfighting tactics based on thrust medium alone. Other things you have to take account of are:
- Weapons systems
- Pilot limitations (unmaned Grav fighters would withstand sudden cahanges in g better)
- Range and Endurance (Grav fighters are likely to have much great range and endurance affecting where, when and how you engauge)
- Sensors and electronics (if you can point your nose anywhere, where should you point your Mk1 Eyeball?)
Of course there's a whole other argument about why would you ever get into dogfighting range, when you have both over the horizon and from orbit capabilities.
Yeah, you'd want the normal profile to not have any induced drag and any control surfaces to have lift only when used. That would leave only parasitic drag during high speed flight. Probably a thin, symmetrical disk so it can be put into vertical for quick deceleration yet be able to go supersonic.
OTH radar is better for early warning and not so good for targeting due to aperture width, back-scatter, etc.
mike wightman
SOC-14 10K
The hull shape will probably look like a small slimmed down submarine. You'll want to have everything inside the hull to reduce drag.
With acceleration compensators you don't need to worry about centripetal "g" from pulling really tight turns.
With acceleration compensators you don't need to worry about centripetal "g" from pulling really tight turns.
You might have to take it into account when firing weapons. Detachable weapons such as missiles or rockets will be subject to g forces when ejected from the compensation envelope and bullets slugs and plasma weapons will need sight correction when firing during high g maneuvers.
Thinking about this, you may have more than 1G to play with. Since you don't need to generate Lift you can climb to altitude at 2G and descend at 3G (am I right just adding vectors, I know I'm not accounting for drag). By trading height you can add velocity, go ballistic and use your full 2G as thrust.
The idea of using 1G to negate the planet's gravity and using the surplus thrust is akin to a helicopter generating lift and thrust with its rotor, but as long as you don't mind falling I can see Grav vehicles switch from helicopter like flight to being more like a Trapeze Artist. I'm not sure if you can model this in Traveller though.
if you have 2g grav, in order to do manuvers of greater than 2g's, you'll be using aerodynamics to pull more g's than that. If that's the case, then grav is simply a different source of thrust which can be used to hover. If that's not the case, then a jet can out-turn a grav vehicle ( turn radius related to g's pulled ).
As a result, I'd say that grav tend to bounce tactics and use the vertical plane more often, whereas jets used more turning.
Either way, as in real-life, a lot will depend upon who sees who first. Most aircraft that have been shot down never saw the attacker until it was too late.
If you have 2G's of total grav on a 1G planet, you can only climb at 1G
Correct. That's why I said to make it a disk shape. Stand it in the vertical to create air resistance to slow down/reverse course. Another plus. A disk Grav fighter can spin in any direction while at full speed, which a jet can't. So even without using regular control surfaces, a jet will get its clock cleaned every time. But, that is obvious.
Rigel Stardin
SOC-13
HG_B: a disc shape is fine for forward, backward and left and right in the atmosphere, but if it tries to go vertical up or down at those speeds, it will tear itself apart. So it has to take some aerodynamic flight characteristic while in denser part of the atmosphere. In space however, it one mean mother....
Nope. No more than an F-22 going vertical at those speeds. You have a misunderstanding of what "aerodynamic flight characteristic" means. A disk shape would be much stronger than an attached wing configuration also.
Rigel Stardin
SOC-13
HG_B: You lost all aerodynamics when you go upward or down. The surface area of the disc will cause the ship to wobble through the atmosphere. Yes the Grav engines are still able to keep it aloft, but the violent shaking from the wobble is bound to pop a rivet or two.
Then there is the issue the lost of stability, which will reduce the chance of any gunner hitting his target.
Then there is the issue the lost of stability, which will reduce the chance of any gunner hitting his target.
Sorry, it would be controllable enough using control surfaces. And NO, rivets will not be popping off. You have insufficient data or, outdated info on modern aircraft construction. You would not be shooting in the short time you did that maneuver. It is simply to rapidly kill forward velocity.
Rigel Stardin
SOC-13
It's just one of those things my mind can't wrap itself around. I can't envision the control surfaces that would allow such a thing to take place.
that is not correct.
Changes in orientation are not instantaneous. As soon as you begin to change the orientation of your disc-craft, you will be changing its aerodynamic characteristics, namely the drag and lift caused by the new airflows over the surface. Depending on the speed of the airflows, the resulting lift may easily be much greater than the grav tech's ability to compensate. If the structure of your disc-craft has not been built to withstand many G's of acceleration ( in modern planes, 10 or more G's dynamic load ), then it will break up into little pieces.
of course, comparing real-world equipment's performance to fantasy-world equipment is not really that productive or accurate.
and again, unless inertialess propulsion is envisioned, changes in direction/vector will be limited to the grav's thrust...2 G's in the original example? whereas a modern jet can change its vector with 10 or more G's from lift.
The grav ship will be better in the vertical ( sustained climb, although a 2 g craft may lose out briefly to a jet's zoom climb before passing the jet again ) and perhaps top speed, but not in a simple turning fight; without its own aero controls, it won't be able to pull as many G's in a manuver, being limited to only 2G's of thrust.
oh...and keep in mind any energy budgets and consider changes from kinetic energy to potential energy as altitude increases.
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They are right a disc has its own aerodynamic properties and Grav drive does not mean that there is no airflow over the craft surfaces.
A disc fighter may well be able to spin in any direction at full speed but if it needs to depress or elevate a weapon located along its edge then in doing so it will change its angle of attack.
Its not so obvious that the jet will get its clock cleaned every time. If the form of its airframe gives it sensors with a bigger cross section allowing it to fire first. There are many more factors which influence the outcome of a dogfight than just maneuverability. And most air-to-air engagements won't get to the point where a dogfight ensues.
Hi,
I seem to recall reading somewhere that a shorter fatter submarine shape is actually better than a longer thinner shape aero/hydro dynamically. I believe that similar principles applied to airship design, with short/fat zeppelins and blimps having some advantages over longer/thinner ones at least in terms of drag (if I am recalling correctly)
Backwards, at least for subs and boats. Longer/thinner is faster for a given displacement. Shorter and wider is more stable, however.
Hi,
Here is a quote from "US Nuclear Submarines: The Fast Attack" ( http://books.google.com/books?id=91...AEwAg#v=onepage&q=short fat submarine&f=false ) that notes, in a discussion of the Skipjack class that;
"The short, fat hull shape combined with a smooth outer surface made the boat very fast indeed, with a speed over 25 knots (it as even faster than the design group had hoped.)"
Additionally, the paper "Some Aspects of Submarine Design Part 1. Hydrodynamics" ( www.dsto.defence.gov.au/publications/3442/DSTO-TR-1622.pdf ) also notes that;
"The second kind of drag, the skin friction drag is proportional to the wetted surface, so a long skinny submarine would have more wetted surface than a short fat one of the same displacement. The variation of the two kinds of drag and their summation when plotted against the L:B ratio for constant volume is shown in Figure 11.
"There is clearly a minimum in total drag at an L:B ratio of about 7 but the curve is flat in this region. There is no precise minimum."
and
'In his 1983 paper, R.J.Daniel, Managing Director Warship Building, British Shipbuilders [16], states “for a solid-of-revolution form, zero parallel middle body is associated with minimum residual drag and the effect of reducing the length:diameter ratio is to decrease surface area and hence skin friction resistance down to the optimal ratio of about 6, with a prismatic coefficient Cp of about 0.6.”"
and
"A second parameter, which influences resistance of the streamlined body, is the prismatic coefficient, Cp. This parameter describes the amount of volume in the ends of the hull. Collins for example would have a coefficient at the high end of the scale (estimated as greater than 0.8). Albacore had a Cp of about 0.65."
Looking at some modern submarines you get the following info;
(L D -- L/D)
USS Nautilus 320 x ~ 28 -- 11.1
USS Seawolf 350 x ~28 -- 12.5
USS Skate 267 x ~25 -- 10.68
USS Skipjack 251.7 x 31.5 -- 7.99
USS Triton 447.5 x ~37 -- 12.09
USS Halibut 350 x 29 -- 12.07
USS Thresher/Permit 278.42 x 31.58 -- 8.82
USS Tullibee 273 x 23.58 -- 11.58
USS Sturgeon 292.25 x 31.67 -- 9.23
USS Los Angeles 362 x 33 -- 10.97
USS Seawolf (SSN21) 353 x 40 -- 8.83
USS Virginia 377 x 34 -- 11.09
HMS Dreadnought 265.7 x 31.2 -- 8.52
HMS Valiant 285 x 33.25 -- 8.57
HMS Churchill 285.1 x 33.1 -- 8.61
HMS Swiftsure 272 x 32 -- 8.50
HMS Trafalgar 280 x 32 -- 8.75
HMS Astute 323 x 37 -- 8.73
HMAS Collins 254 x 26 -- 9.77
HMCS Victoria 230.5 x 24.92 -- 9.25
Soryu Class 275.58 x 29.83 -- 9.24
Type 212 183.7 x 22.96 -- 8.00
So, from the quotes provided and the limited sampling of subs above it looks like the suggested optimum for a submarine would be on the shorter/fatter lower end of current submarine practice.
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