Aircraft Design

[shabowie]

"Both Critical Air and Critical Ground speed seem to get bigger with lower air pressure. I guess it is the Max Speed from Air-resistance."

That makes sense, with denser atmo you have more lift right?

"Max Air Speed is barely affected by the pressure drop. So the Dogfighting performance should be similar (especailly if you consider the enemy also is lower) across atmosphere densities"

You'd think with certain technologies air pressure isn't going to reduce the output of the engine and so max air speed should go up with reduced density.

How do I know? I'm stuck trying to counter my enemy's jets with rocket planes and it seems like no good advantage.

Given BlueTemplar's post below maybe there is a benefit I just don't know because I can't look at the jet side of the coin.

[BlueTemplar]

See also this discussion :
fb.asp?m=4950001

ORIGINAL: Soar_Slitherine

ORIGINAL: zgrssd

I would say at 20% Atmospheric density (200 mBar), you should expect 20% lift.
Given a 0.20g gravity, you would need 20% Lift.
So on the planet you gave, I would expect airplanes to be about as feasible as on earth.

According to this document by Vic, aircraft with non-rocket engines actually lose a lot of efficiency under very low air pressure, even if gravity is decreased by a similar ratio. It's not merely a matter of lift, most aircraft engines require air for combustion as well.

[zgrssd]

"Both Critical Air and Critical Ground speed seem to get bigger with lower air pressure. I guess it is the Max Speed from Air-resistance."

That makes sense, with denser atmo you have more lift right?

With denser Atmosphere you get more lift/speed.
And more Speed/Horsepower.
But, you also loose more power from drag.

In a particulary dense atmosphere, stuff like Thopters become feasible. But you need to make sure not to build anything with too much drag.

"Max Air Speed is barely affected by the pressure drop. So the Dogfighting performance should be similar (especailly if you consider the enemy also is lower) across atmosphere densities"

You'd think with certain technologies air pressure isn't going to reduce the output of the engine and so max air speed should go up with reduced density.

You do not need Air pressure to run the engine. Somehow planes and tanks in a Vacuum still get to burn fuel. There is no need to get oxygen from the air.

What you always will need air for, is push/lift. If you spin a rotor in a vacuum, the biggest force will be the centrifugal force. Wich is pretty useless for getting around.
All engines, all lift is based on forcing Air to go a direction it did not want to go.

Rocket motors can work even in a vacuum as they expell their own reaction mass. But they are pretty inefficient.

How do I know? I'm stuck trying to counter my enemy's jets with rocket planes and it seems like no good advantage.

Given BlueTemplar's post below maybe there is a benefit I just don't know because I can't look at the jet side of the coin.

As I understand it, Propeller planes are capped to the speed of sound. While Jet planes can exceed it.
And the speed of sound is directly tied to Air density/material stiffness.

The denser the material, the faster sound travels
In water, Sound moves 4 times as fast and wide. In Iron 15 times. In Diamond about 35 times.
But in half the pressure, it moves a lot slower.
Even just with the temperature, moisture and pressure variants in earths atmosphere we can get wildly different speeds of sound.

Without knowing a bit more about the planet (particulary Pressure and Gravity), there is little I can do to help.

[shabowie]

ORIGINAL: zgrssd

You do not need Air pressure to run the engine. Somehow planes and tanks in a Vacuum still get to burn fuel. There is no need to get oxygen from the air.

Which for the typical starting tech levels seems a way off, a naturally aspirated or even supercharged engine still needs an oxidizer. Maybe I should just consider this an abstraction like you always have the tech for the envirosuit, even on planets where things have really regressed and there's no real need for the envirosuit to have somehow survived all the tech loss? So conversely, on planets with no atmosphere the default engine system includes like secondary tanks for oxidizer or something and that tech has somehow not been lost.

[zgrssd]

ORIGINAL: shabowie

ORIGINAL: zgrssd

You do not need Air pressure to run the engine. Somehow planes and tanks in a Vacuum still get to burn fuel. There is no need to get oxygen from the air.

Which for the typical starting tech levels seems a way off, a naturally aspirated or even supercharged engine still needs an oxidizer. Maybe I should just consider this an abstraction like you always have the tech for the envirosuit, even on planets where things have really regressed and there's no real need for the envirosuit to have somehow survived all the tech loss? So conversely, on planets with no atmosphere the default engine system includes like secondary tanks for oxidizer or something and that tech has somehow not been lost.

Around Survival and Oxygen there are some oddities.

E-Suits act as the first Armor option, so it is hard to not give it to people. I made a suggestion to fix that a while ago.

We can not not-have Fuel burners, as Electrical Motors come pretty late. I made a suggestion to make the starting tech be more based around exposure and move a electrical motor to the starting tech, but at poorer efficiency.

[Arcalane]

I've found a quick and easy solution to fixed-wing aircraft design that works fairly well so far; just base your specs off existing planes! I'm not sure how engine power compares to horsepower (1:1?), but if you match engine type or total horsepower, hull length, wingspan, and fuel/bomb/cargo capacities, you can get aircraft that should more-or-less perform similarly to existing aircraft (adjusting for atmospheric conditions). You'll have to eyeball the hull lengths since they go 7/10/20/50/80 meters and existing planes won't always fit in neatly, but if you go for the nearest match it ought to be pretty close.

e.g. my current, most-successful campaign, I have the M607 Eclipse, a twin-engine Medium that's intended to perform in the same role as the C-130 Hercules. Whilst the hull is 10 meters shorter, it uses a pair of superheavy turboprops to carry nearly the same cargo mass (18,000kg) a solid 25 hexes in the planet's 498mbar atmosphere/0.36g. By comparison, a C-130 should hit around 12 hexes round-trip range assuming earthlike conditions (1000mbar/1g).

Obviously all bets are off for speculative tech like thopters, and helicopters are still a little fuzzy to me, but it's working OK as a decent starting point.

Also interested in 'crowdsourced' aircraft designs. Anyone got any good templates?

ed- added x-heavy hull length (80m)

[zgrssd]

ORIGINAL: Arcalane

I've found a quick and easy solution to fixed-wing aircraft design that works fairly well so far; just base your specs off existing planes! I'm not sure how engine power compares to horsepower (1:1?), but if you match engine type or total horsepower, hull length, wingspan, and fuel/bomb/cargo capacities, you can get aircraft that should more-or-less perform similarly to existing aircraft (adjusting for atmospheric conditions). You'll have to eyeball the hull lengths since they go 7/10/20/50/?? (I don't have x-heavy yet) and existing planes won't always fit in neatly, but if you go for the nearest match it ought to be pretty close.

e.g. my current, most-successful campaign, I have the M607 Eclipse, a twin-engine Medium that's intended to perform in the same role as the C-130 Hercules. Whilst the hull is 10 meters shorter, it uses a pair of superheavy turboprops to carry nearly the same cargo mass (18,000kg) a solid 25 hexes in the planet's 498mbar atmosphere/0.36g. By comparison, a C-130 should hit around 12 hexes round-trip range assuming earthlike conditions (1000mbar/1g).

Obviously all bets are off for speculative tech like thopters, and helicopters are still a little fuzzy to me, but it's working OK as a decent starting point.

Also interested in 'crowdsourced' aircraft designs. Anyone got any good templates?

I did some math above and I am 90% sure that the Horsepwoer Ratio and Wingload displayed are for a 1G, 1 Bar planet.

The game still seems to use the proper values (adapted for Gavity and Airpressure) for anything that uses the two, but the dispalyed values seem wrong.
I hope Vic gets around to fix those issues for the 1.08.04 beta so we can finally do some proper math.

[zgrssd]

So, we managed to figure out the Fuel Cost Formula for vehicles. It turns out is mostly based on Weight, then number of Engines, with a really miniscule amount from the engine consumption itself.
There have also been some changes to design screen and some formulas, so I can restart with gathering data.

Established Information:
- the displayed Wingload and Horsepower/Weight Ratio seems fixed. However the value that is actually used seems to actually account for Pressure and Gravity adjusted weight
- Engine Efficiency goes down with bigger engines. So I would guess it is a multiplier. Like "Engine Efficiency 15 means, with this engine you make 15km/Fuel unit". The max Distance Note Indicates it is using Engine Power/Engine Efficiency
- Engine Design Roll and thus actuall engine power seems irrelevant for range
- the stated operation Cost is always 10 times the per/hex cost. So it seems unlikely that the Range and Fuel cost are truly related
- the Fuel consumption stated in the text seems wrong. If the plane would consume 0.1 fuel per km, it would need to consume 20 fuel per hex
- the Aerodynamic Rating (wich I would just call drag) is supposedly largely ignored below 50. Wich happens to be rather similar to how Weight under 50 reduces Fuel efficiency in ground vehicles
- I will try to keep using "Tank" for the fuel tank capacity, and "Fuel" for the fuel consumption. "WeightG" will be the weight, multiplied by Gravity

The following examples are from a planet with 0.26g, 443 mBar pressure:
Ultralight Recon
Weight: 1760
WeightG: 457,6
Tank: 800
Engine: 150/15
Range: 7708
Fuel: 4

(Jet)Fighter
Weight: 6180
WeightG: 1606.8
Tank: 3000
Engine: 1400/12
Range: 6294
Fuel: 22

Tac Bomber:
Medium 1E, Jet
Weight: 13380
WeightG: 3478.8
Tank: 5000
Engine: 1400/12
Range: 3612
Fuel: 50

Transport:
Light Copter, Medium Rotor
Weight: 7040
WeightG: 1830
Tank: 3000
Engine: 1000/12
Range: 671
Fuel: 150

Some math:
- "Maximum Distance: Modified for Engine Power/Efficiency and Fuel Cap and Gravity"
Weight/Fuel: 440/280/267.6/49.3
I noticed two oddly Integer Numbers. And two numbers that show the signature of a division by 3, then being rounded.
WeightG/Fuel: 114.4/73.04/69.576/46.93
However on plaents with pretty similar gravity, I get Fuel Consumption that is a order of magnitude away from these figures
And of course the observed comsumption is nowhere near the stated value either

[zgrssd]

I think I need to formulate a theory on Fuel Consumption, just to have something to check.

Theory:
1. The dispalyed Fuel Consumption and operation cost is dead wrong. Something like: Actuall Fuel Consumption, times 10, divided by the actuall Range.
2. The actuall fuel consumption is still simply based on weight before gravity

Let us test that with some Recon Missions:

Recon Plane 1:
Weight: 1760kg
Range: 20 Hex
Actuall Consumption (max Range): 6 Fuel
AC/Hex: 0.3 Fuel
Stated Fuel: 0.4/hex

Fighter Plane 1:
(Heavy Jet)
Weight: 6180kg
Range: 14 Hex
Actuall Consumption (max Range): 33
AC/Hex: 2.357
Stated Fuel: 2.2/hex

Recon Plane 2:
Weight: 1760kg
Range: 10 Hex
Actuall Consumption (max Range): 12
AC/Hex: 1.2 Fuel
Stated Fuel: 0.8/hex

Fighter Plane 2:
(Heavy Jet)
Weight: 6180kg
Range: 14 Hex
Actuall Consumption (max Range): 33
AC/Hex: 2.357
Stated Fuel: 2.2/hex

Results:
This result is unexpected, to say the least! But it looks like a pattern as well:
- Doubling the Range havled the overall Fuel Consumption - or changed the AC/Hex by x4. Their might be a dependance on the same stats or there is a inverted division.
- Similar Ranges at Similar Weight even on totally diffrent planets have the same stated and actuall consumption
- The Fuel Storage seems always 3x the Consumption of a Recon Mission for the Maximum Range. Wich means we now might be able to gather data without needing to nessesarily fly them,
- apparently Recon Planes can varry drastically, even when the Fighters are basically identical
This does give us a simple way to figure out the real Fuel Consumption at least!

[Cladboy2]

Don't suppose anybody figured this one out did they? I'm looking to make an aircraft designer web app and can't figure out what calculations to do to get the range of a plane. This thread has been the closest I've found to discussions on it.
I'd love if Vic gave us the formula. At the moment I'm just trying to recreate a black box with what I assume is is the correct inputs.

[Don_Kiyote]

I'm looking to make an aircraft designer web app

That would be a nice project.

There have been a few other threads about this topic here. According to what I remember of them, there is quite a high degree of fidelity in the model SE uses. That is to say that the formulae being used are chapters of the textbook on fluid dynamics, being applied to speculative planets. And then rendered as model stats.

So I doubt you will receive a full report of how aircraft performance works in SE, but it doesn't hurt to ask.

Perhaps simply trying to build a parallel model in one or another IT environment using your own methods and the same textbooks would be a good idea. The idea of testing aircraft for operation in the atmospheres of alien worlds, xeno-aerodynamics lets call it, is kind of cutting edge right now, having only recently happened for real for the first time last year (2022), on Mars. But doing your own model is a whole new can of worms, sure.

Good luck, and leave me a message if you make any headway

[zgrssd]

Okay, I am willing to give this another shot. It looks like a bunch of new values are now in the design log.

I had a interesting case where a lot of things changed - but only one change that should affect performance - the engine was Upgraded from Ultralight Prop to Ultralight Turbo Prop.

Okay, the good news first: It appears that most Air Design Values seem entirely independent of Design Rolls. Range, Fuel Consumption, Speeds, Dogfighting Value - all seems static. Only Air Attack Values seem dependent on the Attack Roll.

Engine power: went up 150 to 200
Engine Efficiency: went up 15 to 20
Aerodynamic Rating: after engine went up from 30 to 35
Air-Air Penalty Round 2: went up from 20 to 30.
Horsepower: Weight Ratio up from 23% to 27%.
Critical Speed: 670 to 724
Max Speed: 178 to 226
(minimum) Takeoff Speed: 144 to 137
Economic Speed: 158 to 166
Critical Ground Speed: 814 to 914
Max Ground Speed: 157 to 199
Maximum Distance: 2547 to 4516
Max Hex Range: 7 to 11
Turning Score: 8 to 11
Agility Score: 15 to 24
Dogfighting Score: 12 to 15

Remarks:
That jump in range is leaps and bounds. So for Range, even small efficiency gains are massive.

[zgrssd]

Let us try what happens when I try that same recon plane with different wings.

Values from the Prediction are:
Minimum Takeoff Speed
Maximum Ground Speed
Maximum Air Speed
Maximum Range
Maximum Operation Range (Hexes)

Fins:
243
278
318
2089
1044

Tiny:
156
245
280
5088
2544 (12)

Very Small:
137
199
226
4516
2258 (11)

Small:
138
161
182
3040
1520 (8)

Results:
Small Wings make lower Takeoff Speed, but also higher Ground Speed. But notably, with Small Wings the Takeoff Speed started going up again. I figure that Air Resistance plays a factor in Takeoff and Ground Speed. But having a low Wingload seems more important.

Minimum Airspeed just keeps going down with Wing Sizes. I figure it will have a comparable impact on turning and thus doubly on Dogfighting score

Range simply has a Goldilocks Zone for Wingspan. I guess we have to use Trial and Error. Too big or too small are both bad. My guess is that Lower Wingload and higher Air Resistance are having a battle here.

[zgrssd]

Okay, keeping the Very Small Wings, let us try out some different Fuel Tanks!

100 Litre:
105
265
303
427
214 (2)

250 Litre:
113
244
279
1649
824 (5)

500 Litre:
125
216
248
3359
1680 (9)

800 Litre:
137
199
226
4516
2258 (11)

1200 Litre
153
178
202
5735
2868 (14)

1800 Litre:
173
158
179
6876
3438 (16)
can not lift off

Result:
No surprise that increasing the fuel tank size (and thus weight), means that the Takeoff speeds get worse (until they get incapable of lifting off the ground).

But the Range does not follow a sensible pattern:
100->250 Litre is 2.5 times the Fuel
427->1649 km is 3.8 times the Range

250->500 is 2 times the Fuel
1649->3359 is 2.04 times the Range

500->800 is 1.6 times the Fuel
3359->4516 is 1.3 times the Range

800->1200 is 1.5 times the Fuel
4516->5735 is 1.27 times the Range

1200->1800 is 1.5 times the Fuel
5735->6876 is 1.2 times the Range.

So, something is definitely busted there.

[Don_Kiyote]

Okay, keeping the Very Small Wings, let us try out some different Fuel Tanks!
...

But the Range does not follow a sensible pattern:
100->250 Litre is 2.5 times the Fuel
427->1649 km is 3.8 times the Range

250->500 is 2 times the Fuel
1649->3359 is 2.04 times the Range

500->800 is 1.6 times the Fuel
3359->4516 is 1.3 times the Range

800->1200 is 1.5 times the Fuel
4516->5735 is 1.27 times the Range

1200->1800 is 1.5 times the Fuel
5735->6876 is 1.2 times the Range.

Wow, you are really digging in to this.

Those values above look like what I play with too.

Its a relationship of diminishing returns. The way I understood this design step, was that flying with the weight of the additional fuel becomes increasingly costly in terms of the amount of energy lost to transport versus the amount delivered to the engines. The plane first needs to transport that additional fuel to the limit of its range in order to use it to extend its range.

Again iirc, increasing the engine size moves this curve you describe above, the 'diminishing returns on additional fuel' curve, so that optimum wing and fuel tank size are larger. So for instance, at the '800->1200 liter' size jump, you would gain say 1.4x the range instead of 1.27x. But it is the same curve, just at higher value points.

The change in range from a larger engine size I understand as being due in part to a (hopefully) higher air speed, but mainly because the larger engine has more power and so is better able to transport the weight of the additional fuel, because that weight has a lower impact on the power-to-weight ratio.

I think that is how machines behave irl, so it works for me.

[zgrssd]

Okay, keeping the Very Small Wings, let us try out some different Fuel Tanks!
...

But the Range does not follow a sensible pattern:
100->250 Litre is 2.5 times the Fuel
427->1649 km is 3.8 times the Range

250->500 is 2 times the Fuel
1649->3359 is 2.04 times the Range

500->800 is 1.6 times the Fuel
3359->4516 is 1.3 times the Range

800->1200 is 1.5 times the Fuel
4516->5735 is 1.27 times the Range

1200->1800 is 1.5 times the Fuel
5735->6876 is 1.2 times the Range.

Wow, you are really digging in to this.

Those values above look like what I play with too.

Its a relationship of diminishing returns. The way I understood this design step, was that flying with the weight of the additional fuel becomes increasingly costly in terms of the amount of energy lost to transport versus the amount delivered to the engines. The plane first needs to transport that additional fuel to the limit of its range in order to use it to extend its range.

Again iirc, increasing the engine size moves this curve you describe above, the 'diminishing returns on additional fuel' curve, so that optimum wing and fuel tank size are larger. So for instance, at the '800->1200 liter' size jump, you would gain say 1.4x the range instead of 1.27x. But it is the same curve, just at higher value points.

The change in range from a larger engine size I understand as being due in part to a (hopefully) higher air speed, but mainly because the larger engine has more power and so is better able to transport the weight of the additional fuel, because that weight has a lower impact on the power-to-weight ratio.

I think that is how machines behave irl, so it works for me.

So then Engine Efficiency might not be about range after all? Good to know if that is also a HP/weight ratio thing.

Engine efficiency does seem to have a clear relationship to listed Operation Cost, however!
The 15 efficiency Engine needs 1.2 Fuel per hex.
The 20 efficiency Engine needs 0.8 Fuel per hex.
Either figure you can get by 16/Engine Efficiency.

However the fighter with a Engine Efficiency of 12, uses 43 Fuel per hex. Meaning it likely divides down from 512.

Now 16 and 512 are numbers I know well. They are 2^4. And 2^9.

Theory:
Fuel per Hex is a function of [Fuselage specific constant] / Engine Fuel Efficiency

[zgrssd]

Let's try out what happens with bigger Engines!

Ultralight TP (200 HP, 60 W):
137
199
226
4516
2258 (11)

Light TP (400 HP, 100 W):
126
293
336
5321
2660 (12)

Medium TP (800, 190 W):
124
293
336
3482
1741 (9)

Heavy TP (1250, 330 W):
128
293
336
2419
1210 (7)

Result:
Confusingly, minimum Takeoff Speed goes down. That should not be physically possible. And nothing in the Design log indicates it should be possible.
A heavier engine should just be more weight, thus higher Takeoff Speed.
A heavier engine makes it easier to reach said takeoff speed - but that is about it. It should not be reduced.
So I am guessing that is a bug.

Interesting that Max ground speed and Max Air Speed hit a cap pretty quickly. And once they hit said cap, Range only goes down with extra weight. That is a good indicator.
Luckily it is easy to figure out HP/Weight Ratio, as the plane weighs 1700+Engine. Gravity was 0.51g.
1760*0,51 = 897.6.
897.6 / 200 = 22.3%
Listed Ratio: 27%
So, something is not adding up here either.

[Soar_Slitherine]

Okay, the good news first: It appears that most Air Design Values seem entirely independent of Design Rolls. Range, Fuel Consumption, Speeds, Dogfighting Value - all seems static. Only Air Attack Values seem dependent on the Attack Roll.

EDIT: I had a post here about engine design having an effect, but it turns out the results I was seeing were because thopters have their wing area randomized each time the first iteration in a model line is created. Engine Design does in fact seem to have no effect.

[zgrssd]

And now I made a model my with a Bigger engine. And there goes my theory about Operational Fuel!
For some reason the bigger, less efficient engine consumes less Operational Fuel/Hex!

New theory for Operational Fuel:
It is [Some Value]/Range in Hexes. Assuming that, here some Products of Fuel/Hex and Range

UL Prop Engine had:
1.2 Fuel/Hex
7 Hex Range
Product: 8.4

UL TProp Engine had:
0.8 Fuel/Hex
11 Hex Range
Product: 8.8

L TProp has:
0.7 Fuel/Hex
12 Hex Range
Product: 8.4

Fighter with Medium Prop:
4.3 Fuel/Hex
7 Hex Range
Product: 30.1
(Aircraft design actually not valid; Was generated at game start)

Note:
I had to make a new Fighter Design that can actually lift off, just to get usable values as comparison.

[zgrssd]

Okay, now I have a fighter design that can actually lift off. Moreover, it is the equivalent to my Scout Plane in everything but the Fuselage!

Light Turboprop Engine, Very Small (10m) Wings, same MG, same 800 L Fuel Tank
1.6 Fuel/Hex
5 Hex Range
Product: 8

Old Design had a 3000 L Fuel Tank. And a product of 30.
I sense a pattern.

Operational Fuel Theory
Fuel Per Hex is Fuel Tank Size / Range in Hexes, rounded up.