Retry
10/27/14 01:51 AM
76.7.225.145
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So I was playing this one game that lots of semi-realistic WWII aircraft. One of the most notable things about them is that they all fly incredibly different, and many have unique quirks. Energy retention, stall characteristics, turn radius and rate, climb rate, acceleration, top speed, diving capabilities, and many more factors differ substantially between many different aircraft.
While messing around with the aircraft, I began to realize that aerospace fighters in Battletech, despite their differing fluff, are identical in regards to flight performance.
In space, of course, there is no air or fluid to move through and so aerodynamics wouldn't need to be considered and probably wouldn't even affect the aerocraft at all. The ability to vector the engine thrust, the weight of the aerocraft, and the thrust the engines can produce would be some of the most important factors in the performance of the aircraft in space. So to some extent, they should fly very identically here.
The same doesn't hold true elsewhere. An aerocraft moving near a large mass will be affected by at least two forces. In addition to thrust, the aerocraft will have to deal with the force of gravity that the nearby planetary body exerts on it. If an atmosphere exists around said planetary body, they will have to deal with two additional forces related to movement through air:Lift and Drag. Aerodynamics in general would begin to greatly matter in atmospheric operations. Less clean aircraft with more drag will have a lower top speed than an otherwise similar airframe. Wing loading (Weight of the aircraft divided by the area of the lift-producing wings) becomes a factor in stall speeds, climb rate, overall turning performance(although vectoring thrust can cancel this out to an extent).
Amazingly(from a physics perspective anyways), every single aerospace fighter in the Battletech universe behaves identically in an atmosphere.
Take for example three aerospace fighters: The Xerxes, the Striga, and the Simurgh. Between these three, thrust and weight are both equal. If they were to differ in performance, it'd have to come from either lift or drag.
Simply by eyeing the three designs, it's highly improbable that all three have identical wing area(and thus the same amount of lift), or the same drag. Despite this, all three of these turn exactly the same on the board, need the same amount of runway to take off if not using VSTOL equipment, gain altitude at exactly the same rate, and have the same top speed(IIRC it's a strict and rigid 5x safe thrust value.). This implies that they have nearly identical lift and drag. The sole difference between the three is that the Simurgh has the "easy-to-pilot" design quirk and so the pilot is slightly less likely to screw up and crash in the process.
Obviously, to accomodate differences of individual models of aerocraft in an atmosphere would require a huge and complex revamp in the rules, and perhaps a change in how you design an aerospace fighter itself.(Don't even get me started on how it'd effect LAMs) It probably wouldn't even be practical without some software to compute anything and everything related to it. But as long as they perform the same, even in atmosphere, and their biggest difference between aerocraft in an atmosphere remains it's guns and armor, they'll continue to be viewed as bland and remain in the shadow of the 'Mech.
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Cray
10/27/14 06:55 PM
67.8.171.23
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Retry, when trying to compare BT's fighters to real world fighter performance, you need to consider the vast difference in performance. A lightly-loaded F-15 on afterburners has 3 thrust points if you're being generous about its acceleration. A sluggish BT heavy fighter has 4 safe thrust points and can run on 6 thrust points of "afterburner" for hours, not minutes. Every BT aerospace fighter has RCS thrusters that can get it off the ground like a Harrier, giving a thrust reserve for maneuvering unlike almost any fighter except, well, a VIFFing Harrier, and that's without tapping its main engine's thrust vectoring.
In that sort of thrust-dominated flight regime, you can easily hit drag-related and pilot-related limits before exhausting the capabilities of the fighter.
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Retry writes:
The same doesn't hold true elsewhere. An aerocraft moving near a large mass will be affected by at least two forces. In addition to thrust, the aerocraft will have to deal with the force of gravity that the nearby planetary body exerts on it. If an atmosphere exists around said planetary body, they will have to deal with two additional forces related to movement through air:Lift and Drag. Aerodynamics in general would begin to greatly matter in atmospheric operations.
Aerodynamics imposes a constant drag on flight movement; see Low and High Altitude Movement rules in Total Warfare. In addition, it sets a maximum safe speed in High Altitude Movement. Further, there are aerodynamic advantages of conventional fighters over aerospace fighters / small craft / DropShips.
Finally, it is important to note that thrust also defines maneuverability in an atmosphere - you do have a stat that embraces every aerodynamic and thrust factor in the aircraft. (Barring the use of Strategic Operation's poor / good aerodynamic advantages, anyway.)
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Less clean aircraft with more drag will have a lower top speed than an otherwise similar airframe.
This is all well and good if you're talking about a 20th/21st Century fighter, which rarely exceed a thrust-to-weight ratio of 1:1 and guzzle fuel in comparison to BT fighters.
However, even the most sluggish BT aerospace and conventional fighters - which have thrust ratings of 4/6 - can out-accelerate the US space shuttle and US carrier catapult launches, to say nothing of out-accelerating any F-15, F-22, or whatever "high" thrust-to-weight ratio real world fighter you care to name. High thrust light BT fighters with thrust ratings of, say, 12/18 can blackout their pilots with linear thrust (9Gs), never mind hard turns.
Having this much thrust brings you to an aerodynamic regime dominated by the maxim: with enough thrust, even a brick can fly. And fly well.
When your brick has enough thrust to launch vertically at 3Gs (6 thrust points), there's not going to be a lot of difference in peak speeds between the brick and a sleeker design. Both are going to start incinerating at the same speed, and both have more than enough thrust to reach that speed. (Again, see High Altitude Movement rules for peak speeds and the effects of exceeding them.)
To drop back to real world aircraft, look at the SR-71: it cruised at mach 3.2 using only 35% of its thrust, but couldn't go much faster without exceeding maximum engine inlet temperatures and nose temperatures. Most of its thrust was used to accelerate to mach 3.2, not to cruise. Pound for pound, kilo for kilo, BT fighters have vastly more thrust than the SR-71. Can they use it all for speed? No, so that leaves a lot of other applications.
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Wing loading (Weight of the aircraft divided by the area of the lift-producing wings) becomes a factor in stall speeds, climb rate, overall turning performance(although vectoring thrust can cancel this out to an extent).
Thrust vectoring can help BT fighters take off vertically, so I'm sure it can do wonders for maneuverability when aerodynamic surfaces are lacking. That probably explains their low atmospheric stall speeds of about 100mph.
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Amazingly(from a physics perspective anyways), every single aerospace fighter in the Battletech universe behaves identically in an atmosphere.
If you avoid optional rules, yes, and the fighters have identical thrust (as in your example). But go figure: they operate in thrust-dominated regimes where the limiting factor is the pilot's durability.
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and have the same top speed(IIRC it's a strict and rigid 5x safe thrust value.)
No, that is not the top speed. It differs between Low Altitude and High Altitude movement (see Total Warfare), but is never 5x safe thrust.
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This implies that they have nearly identical lift and drag.
You cannot leave out thrust in aircraft so powerful their secondary RCS thrusters can get them off the ground. Aerodynamics become less relevant when your aircraft has excess thrust able to match the performance of more aerodynamic fighters with brute thrust. The thrust available to BT aerospace and conventional fighters is simply enormous, far beyond any real world fighter.
Mike Miller, Materials Engineer
Disclaimer: Anything stated in this post is unofficial and non-canon unless directly quoted from a published book. Random internet musings of a BattleTech writer are not canon.
Edited by Cray (10/27/14 07:00 PM)
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His_Most_Royal_Highass_Donkey
10/27/14 09:42 PM
172.56.6.7
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Cray did they change the rule that said to launch a fighter vertically you had to spend 10% of the fighters weight on VTAL equipment on fighters?
Why argue if the glass is half full or half empty, when you know someone is going to knock it over and spill it anyways.
I was a Major *pain* before
But I got a promotion.
I am now a General *pain*
Yay for promotions!!!
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Cray
10/27/14 10:51 PM
67.8.171.23
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Quote:
His_Most_Royal_Highass_Donkey writes:
Cray did they change the rule that said to launch a fighter vertically you had to spend 10% of the fighters weight on VTAL equipment on fighters?
No, yes, sort of. Aerospace fighters were changed, conventional fighters were not.
AT2-Revised (pub. 2004, as I recall) introduced the idea of aerospace fighters having integral vertical takeoff because, oops, it was realized aerospace fighters' wings don't work well in a vacuum. It was sort of awkward for aerospace fighters to crash land every time they tried to operate from a moon or airless planet even though they were supposed to operate from such bases. 
However, aerospace fighters made their vertical takeoffs and landings at a penalty.
Meanwhile, conventional fighters did NOT change. They did not automatically gain vertical takeoffs and had to pay 10% of their weight if they wanted the ability. But they took off easily and safely because of their larger, more sophisticated systems.
As I recall, aerospace fighters could purchase the 10% equipment for the same pilot skill roll benefits as conventional fighters, but no one bothers.
Mike Miller, Materials Engineer
Disclaimer: Anything stated in this post is unofficial and non-canon unless directly quoted from a published book. Random internet musings of a BattleTech writer are not canon.
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Retry
10/27/14 11:24 PM
76.7.225.145
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Quote:
Retry, when trying to compare BT's fighters to real world fighter performance, you need to consider the vast difference in performance. A lightly-loaded F-15 on afterburners has 3 thrust points if you're being generous about its acceleration. A sluggish BT heavy fighter has 4 safe thrust points and can run on 6 thrust points of "afterburner" for hours, not minutes. Every BT aerospace fighter has RCS thrusters that can get it off the ground like a Harrier, giving a thrust reserve for maneuvering unlike almost any fighter except, well, a VIFFing Harrier, and that's without tapping its main engine's thrust vectoring.
In that sort of thrust-dominated flight regime, you can easily hit drag-related and pilot-related limits before exhausting the capabilities of the fighter.
Actually, my intent was to compare BT aerocraft with each other, specifically in an atmosphere.
I understand there's pilot related limits. Unless it's a drone, then there are no pilot related limits. There's also structural limits, which is also oddly rather seemingly identical with all the Battletech aerospace fighters.
Drag-limitations? Can you explain this further? I was under the impression that an aircraft's top speed, if not limited by structural limitations, was a limitation related to the drag and thrust of an aircraft.
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This is all well and good if you're talking about a 20th/21st Century fighter, which rarely exceed a thrust-to-weight ratio of 1:1 and guzzle fuel in comparison to BT fighters.
However, even the most sluggish BT aerospace and conventional fighters - which have thrust ratings of 4/6 - can out-accelerate the US space shuttle and US carrier catapult launches, to say nothing of out-accelerating any F-15, F-22, or whatever "high" thrust-to-weight ratio real world fighter you care to name. High thrust light BT fighters with thrust ratings of, say, 12/18 can blackout their pilots with linear thrust (9Gs), never mind hard turns.
Having this much thrust brings you to an aerodynamic regime dominated by the maxim: with enough thrust, even a brick can fly. And fly well.
When your brick has enough thrust to launch vertically at 3Gs (6 thrust points), there's not going to be a lot of difference in peak speeds between the brick and a sleeker design. Both are going to start incinerating at the same speed, and both have more than enough thrust to reach that speed. (Again, see High Altitude Movement rules for peak speeds and the effects of exceeding them.)
To drop back to real world aircraft, look at the SR-71: it cruised at mach 3.2 using only 35% of its thrust, but couldn't go much faster without exceeding maximum engine inlet temperatures and nose temperatures. Most of its thrust was used to accelerate to mach 3.2, not to cruise. Pound for pound, kilo for kilo, BT fighters have vastly more thrust than the SR-71. Can they use it all for speed? No, so that leaves a lot of other applications.
I don't think you really answered what you quoted.
If you ignore structural limitations, something that could be handwaved in the Battletech universe(or be made into a design consideration), you're left with pilot durability and the drag v thrust relationship to effect max speed.
Correct me if I'm wrong, but the pilot's ability to handle G's would only affect the rate at which it can accelerate to the top speed early on. As speed increases, the effect of drag would increase. As the effect of drag increases, you can apply more thrust and still have the pilot feeling the same amount of Gs(For example, if you start from a standstill accelerating at a rate of 5Gs, the pilot feels the effects of 5Gs. If you are flying at such a speed where the net effect at a point of time of drag is a deceleration of 10Gs, and you apply enough thrust that you accelerate at 15Gs, your net acceleration will be 5Gs, as the 10Gs of deceleration cancel out some of the 15Gs of acceleration. The plane would have a net acceleration of 5Gs, and that's also the amount of acceleration the pilot feels.) So in theory, if you gradually increase thrust as velocity increases, discounting structural limitations of an aircraft in an atmosphere, you can reach a speed where maximum thrust and the effect of drag equalize.
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If you avoid optional rules, yes, and the fighters have identical thrust (as in your example). But go figure: they operate in thrust-dominated regimes where the limiting factor is the pilot's durability.
I'm aware that thrust is a large factor. That's why I picked three aircraft with the exact same thrust and weight. Since the these factors are equal in these aircraft, if they were to differ it'd be in lift and drag. Even if you were to replace the cockpit with drone equipment in exchange by removing some of the weaponry, which would remove the pilot durability element, the aircraft still handle identically in an atmosphere, which suggests that drag and lift is the same, or any differences are somehow compensated by some factors such as thrust vectoring.
Quote:
You cannot leave out thrust in aircraft so powerful their secondary RCS thrusters can get them off the ground. Aerodynamics become less relevant when your aircraft has excess thrust able to match the performance of more aerodynamic fighters with brute thrust. The thrust available to BT aerospace and conventional fighters is simply enormous, far beyond any real world fighter.
Naturally, thrust can make up for the lack of aerodynamics somewhat. The point is that with two aircraft with the same amount of thrust and weight, or three in the examples I gave, aerodynamics remains very relevant. Despite this, they fly about the same, so apparently the effects of the aerodynamics between the two/three is about the same, which is rather silly.
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ghostrider
11/14/14 07:36 AM
67.49.78.45
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Only things I have seen with fighter quirks was the thrush/sholagar fighters with their round bodies having issues in the atmosphere, but that was fluff stuff.
I agree that a lot of fighters should have a bonus or penalty flying in the atmosphere, due to aerodynamics. Space shouldn't make that much difference, but weight should.
An object in motion tends to stay in motion. For ease of play they don't force you to use more fuel trying to change the direction of the 100 ton craft over the 20 ton craft.
They do force issues with speed when changing direction. Which makes sense.
I don't know if they fixed it, but I do not remember them allowing a craft to flip over and fly backwards. Which is something that would benefit space superiority fighter tremendously.
We know that in a design, having the proper placing of maneuvering thrusters would make for a superior turning craft, or at least without changing thrust vectors. Those same thrusters used in the air could very well destroy the craft as it pushes it out of the flight characteristics for a stable flight.
It also does not say anything about variable wings, which some of the faster fighters entering the atmosphere would rip off at the speeds they travel.
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