Atmospheric operation of small craft, incorrect assumptions

[rust]

Just enter the aircraft's speed on entering the turn and the stall speed
into the spreadsheet behind the link and then play with the bank angle
value until the calculation results in a 12 G load, and you have the time
it takes to make a 180° turn as well as the radius of the turn.

Edit.:
With a speed of 800 mph, a stall speed of 200 mph and a turn bank angle
of 85° for a G load of 11.4 my result would be 10.2 seconds for a turn of
180°.

 

[DFW]

I still think the turning plane would win. It retains its speed through the turn and is already travelling when it come out of the turn.

In a dog fight it is about getting behind your opponent for a shot. put an F-16 and the grav vehicle side by side. Now, you have to get the f-16 BEHIND the grav vehicle to get off the missile.

The maximum instantenous turn rate of an F-16 is: 26 degrees/second. That means under OPTIMUM conditions and speed it takes 7 seconds to do a 180. In the mean time the F-16 has long ago flown past (now in front of the grav vehicle which is decelerating MUCH faster) and the grav vehicle already shot the F-16 down before it completes the turn.

Done deal. :lol:

 

[rust]

Ishmael's question was this one:

"I guess that in the end, the real question is whether a plane that can pull a 12-g turn can change direction and facing faster than a ship than can do 6-g straightline accelerations ( decelerate to a stop then accelerate at 6-g's in the opposite direction vs. a 12-g turn whose radius is set by the limit of 12-g's )"

And the answer seems to be that a jet fighter can indeed change direction
and facing faster than a Traveller grav vehicle.

 

[DFW]

I've not seen any real description of the hypothetical grav plane's performance characteristics, nor any real discussion of its hypothetical opponent's performance, nor any real discussion of aerodynamics.

Then you should read through all the posts. :roll:

 

[barnest2]

In a dog fight it is about getting behind your opponent for a shot. put an F-16 and the grav vehicle side by side. Now, you have to get the f-16 BEHIND the grav vehicle to get off the missile.

The maximum instantenous turn rate of an F-16 is: 26 degrees/second. That means under OPTIMUM conditions and speed it takes 7 seconds to do a 180. In the mean time the F-16 has long ago flown past (now in front of the grav vehicle which is decelerating MUCH faster) and the grav vehicle already shot the F-16 down before it completes the turn.

Done deal. :lol:

Well the F-16 simply appears to be more manoeuvrable. And as the tech level increases, it will only get more manoeuvrable (thrust vectoring etc), and should be able to maintain a better attack position then the slower to turn grav vehicle...

 

[Ishmael]

sigh
seriously DFW

You have given no info about any of your grav plane's aerodynamic characteristics and I am just assuming it can accel at 6g and is stressed for +-6 g .
You have given no direct descriptions of the aero jet fighter and its just assumed ( so far ) that its an f-16 which is not even state of the art for today much less the same tech level of the grav plane. And you refuse to discuss aerodynamics in detail as you seem to think Bernoulli is beyond our comprehension.
Given how you described the capabilities of an AIM-9L ( or whatever variant you used ) .........

How about if you design a grav fighter that does not use aerodynamic lift or controls using the rules, and present it for analysis?

 

[DFW]

When would a spacecraft ever be able to 'feel' accelerations greater than its own engines can produce unless it runs into something or is hit by something?

While skimming a gas giant at speed. You could pull a lot of Gs at high speed in a turbulent GG atmosphere. I guess it's a good thing you aren't a ships architect for the imperial navy! :wink:

 

[barnest2]

How about we go with this
DFW: put up the stats of a streamlined grav vehicle with no flight controls or lift etc
Somebody else: put up stats of an equal tech level (lets keep it at 10?) air superiority fighter, i would but i am away from books (moving).
Compare the two, etc etc...
would this help solve arguments?

 

[Ishmael]

When would a spacecraft ever be able to 'feel' accelerations greater than its own engines can produce unless it runs into something or is hit by something?

While skimming a gas giant at speed. You could pull a lot of Gs at high speed in a turbulent GG atmosphere. I guess it's a good thing you aren't a ships architect for the imperial navy! :wink:

I could also argue that gas giant skimming as described by Traveller isn't even possible. Have you even figured out the skin temps for such maneuvers at the speeds required to maintain escape velocity? IIRC, grav drives aren't strong enough to overcome a GG's gravity well on there own, thus skimming is done at speed.

And in any case, I feel that any ship that is expected to skim would have to be stressed for the forces that a pure spacecraft would never feel.

Please design the hypothetical grav plane and present it for analysis.

 

[rust]

When would a spacecraft ever be able to 'feel' accelerations greater than its own engines can produce unless it runs into something or is hit by something?

While skimming a gas giant at speed. You could pull a lot of Gs at high speed in a turbulent GG atmosphere. I guess it's a good thing you aren't a ships architect for the imperial navy! :wink:

I think you should read entire posts before making derisive remarks, be-
cause the post you quoted also states:

"Naturally those ships intended to operate in atmosphere may indeed have structure rated for higher accelerations."

Apart from this, I am now finally back to working on my setting. From my
point of view the important questions seem to be answered, and this de-
bate is moving in circles and spirals with no more results in sight.

 

[GJD]

I gave up on reading the whole thread after about page 6, but I'm an avid reader of aviation litrature (one reccomendation for all - Fate is the Hunter by Earnest K Gann) and have been flown and taken flying lessons - if I could afford it I would certainly be a qualified pilot, but flying is an expensive hobby.

The key things in an aircraft that i have gleaned from talking to pilots and reading aviation books seem to be:

Agility
Speed
Stability
Reliability

Each pilot seems to place one above the other and obviously they have different priorities for different jobs (stable bombers, agile fighters, reliable transports and so on).

I don't see that how those categories are met, be it by thrusters, grav drives, wings, rotors, ducted fans, magic beans or the voices of angels - a good ship needs a combination of all four.

A grav drive does not automatically make a ship maneauverable, it just removes the need for wings that generate lift. My understanding of a grav drive is that it negates the mass of a vessel, and the thruster plates or some form of drives do the actuall moving around.

Wings do not automatically make a ship slower or less maneauverable - look at the pitts aerobatic planes or UCAV drones that can pull stupid ammounts of + and - G's.

A grav drive does allow the ship to hover, but you still WANT to maneauver - winning the fight is about hitting the other guy and not getting hit yourself - the best way to do that is to move fast enough that he can't track you, be it by moving outside of a missile engagement envelope, or changing the intercept angle or whatever. Sitting still and blazing away at each other is for battleships and tanks, not fighters and interceptors.

Just my thoughts.

G.

 

[Jeff Hopper]

I always thought that the ponderous maneuvering had to do with the small craft being less aerodynamic than a similar sized winged aircraft, and that they were thus more severely affected by weather conditions while in flight. YMMV.

No, a small craft in the shape of a cylinder rounded on the front without wings is like a missile. More aerodynamic than a regular aircraft, less drag.

Agreed, but it is also bigger than a missile - more surface area for wind to affect when in level flight.

 

[DFW]

Agreed, but it is also bigger than a missile - more surface area for wind to affect when in level flight.

Yes, it does. However, a craft that has lift surfaces will be effected even more than the "fat" missile. So, point stands.

Ever go to where planes are parked in the open and notice the spoilers placed on the wings? ...

 

[alex_greene]

Grav would not eliminate the actual mass of the supported vehicle - only the influence of the local natural gravitational field. The M-drive would provide both lift and propulsion, and if it is designed for atmospheric flight at least part of the propulsion system would be designed to operate off-axis.

Flight surfaces would only be needed if the drive were failing, because without the drive the vessel would simply drop out of the sky without a supplementary source of lift to permit a controlled glide down.

Of course, if the drive fails on a vacuum world even atmospheric control surfaces would be of no use at all ...

 

[Jeff Hopper]

Agreed, but it is also bigger than a missile - more surface area for wind to affect when in level flight.

Yes, it does. However, a craft that has lift surfaces will be effected even more than the "fat" missile. So, point stands.

Ever go to where planes are parked in the open and notice the spoilers placed on the wings? ...

I grew up around Air Force bases and served on a Navy carrier. Yes, I am familiar with aircraft and their operation, even when parked.

 

[Ishmael]

on the hypothetical grav craft, what is its mass, frontal x-sectional area and what is the fuselage's fineness ratio? (assumes 6g total thrust...I'll figure out forward thrust later..1g goes to vertical thrust to maintain altitude so I can talk about level flight )

Then I can get a pretty good ball park figure of its top speed in an atmosphere at least.
( after I dig out my aero-design notes anyways )

 

[rinku]

Actually, the maneuver drive doesn't cancel the gravity vector. That's what the contra-grav does. You can assume all of the ship's thrust is available for acceleration.

All seems a bit pointless though; any spacecraft capable of acheiving orbit (even the space shuttle) will leave any fighter jet in its dust...

Power to weight ratings (cf. wiki):
(edit: this should read Thrust to weight. Oops)

F-15C = 1.06 (loaded), 1.6 (light, full afterburner)
F-22 = 1.14 (loaded)
Space Shuttle = 1.5 (takeoff), 3 (peak)

As Gs equate directly to thrust/weight, a 6G vessel will have thrust equal to 6 x vessel mass. Top speed in an atmosphere? Whatever it wants up to escape velocity - it's a hypersonic vehicle by definition or it couldn't acheive orbit.

And while an F-22 is clearly more agile than the space shuttle, the same could be said about a P-51 Mustang vs a jet fighter.

 

[Ishmael]

Actually, the maneuver drive doesn't cancel the gravity vector. That's what the contra-grav does. You can assume all of the ship's thrust is available for acceleration.

Only if the ship in question has both, which is not always given.

Top speed in an atmosphere? Whatever it wants up to escape velocity - it's a hypersonic vehicle by definition or it couldn't acheive orbit.

Not really
Its a pity that there ended up being no discussion about actual aerodynamics.....
oh well

no sense in hanging about after all

 

[rinku]

Only if the ship in question has both, which is not always given.

Well, since the discussion was about standard small craft, in this case it is.

no sense in hanging about after all

As you still haven't backed yourself up with any figures, you are finally correct.

 

[rust]

All seems a bit pointless though; any spacecraft capable of acheiving orbit (even the space shuttle) will leave any fighter jet in its dust...

You should tell that to the people over at Steve Jackson Games, because
their stats for their GURPS Traveller standard small craft all include a ma-
ximum atmospheric speed (the speed at which the craft can still maneu-
ver instead of flying in a straight line only) based upon the atmospheric
drag of the craft, and these speeds are in the 1,700 to 3,000 mph range,
with the pinnace (which has wings) as the fastest and the ship's boat the
slowest. None of the standard small craft with a calculated atmospheric
drag and atmospheric speed, but without wings, could leave a modern
jet fighter in the dust, except in a straight line race - which is not the si-
tuation we discussed, I think.