The range of an airplane

[Guest doughbred]

I\'ll give you this, I play KSP on my freshman physics teacher\'s laptop every recess and lunch. We just had version 15.0, and I built a space plane which has a fuselage consisting of 5 of the smallest fuel tanks (used by C7 aerospace). The delta wing takes up roughly half of the length, I have canards, and I use the engine with the spike on the rear.

I have the mass of a concorde, except most of the plane is fuel. An me 163, which is nearly a quarter of my mass can travel 25 miles. It takes 2 minutes and 45 seconds to go up to 10,000 meters. Now the issue is that my plane can reach that altitude; but when considering size, it is obscenely mass inefficient. My rocket runs out of fuel at 12,000 meters. The me 163 has fuel to go to a bomber formation and do two strafing runs. Me? I have to glide back to the surface, and a plane many times bigger, and has an air breathing engine.

All I know is that kerbin is like a tenth of the size of Earth. But then, I\'d expect an airplane a to be much smaller. Something to scale. maybe even less do to less gravity. Unless Kerbin has a higher iron content than than earth.

But of all things, I do not know. Can someone explain to me, if Kerbin and it\'s inhabitants, everything is the size and mass of there earth counterparts, are the airplanes less efficient, or more. And, if it is more efficient, or as efficient, can someone explain to me how he managed to make an airplane with one small fuel tank, go up to 12,000 meters, stay straight for a few, and go back to the surface. AND if it does not have to be 12,000 meters, why?

Though I always thought it was efficient. Prior to this, I made a simple rocket with the smallest available fuel tank and rocket, hit max throttle, and the atmosphere bar only wen\'t up close to the end of the \'light blue\', I don\'t know the exact altitude.

[Temstar]

10,000m above ground on Earth is nothing like 10,000m above ground on Kerbin. Earth\'s exosphere is at least 100,000km above the surface, on Kerbin you\'re out of the exosphere once you\'re above 70km. 10,000m above Earth puts you in the troposphere where most planes fly. 10,000m above Kerbin is probably either upper stratosphere or the mesosphere where jet engines are not even suppose to work.

You can see that because the basic jet engine only works till about 6,000m. That turbojet is actually an incredible piece of engineering being able to produce thrust till 20,000m. To put that into perspective that 20,000m on Kerbin is like 100km+ on Earth in terms of atmosphere density. SpaceShipOne had to use rocket engine to just get that high at the apoapsis yet here you have an air breathing engine that can still produce thrust at what would be considered beginning of space on Earth.

On top of this those jets have physics defying thrust to weight ratio. Air breathing engine is always going to have lower thrust to weight ratio compared to rockets because they need a heavy and complex air intake which rocket engine avoids completely. Air is what 1000+ times less dense than liquid/solid oxidizer so the plumbing involved in getting outside air into the combustion chamber is enormous compared to what\'s required to pump liquid oxygen into the combustion chamber. In KSP that turbojet has better thrust to weight ratio than every other engine except those RCS thrusters. That\'s why it\'s so simple to build SSTO in KSP compared to real life.

[rkman]

As far as i know the engine with the spike has very high fuel consumption and is not an air breather. For normal airplane operation use one of the other airplane engines.

My primary airplane is large (5 large fuel tanks and then some), cruises at ~450m/s @ ~15k and has about 1/2 fuel left after making the trip from main KSC to the other KSC.

[trbinsc]

Also, the mass of kerbin is the same as earth, even though it is 11 times smaller.

[maltesh]

Also, the mass of kerbin is the same as earth, even though it is 11 times smaller.

The surface gravity of Kerbin is the same as Earth.

The mass of Kerbin (5.29 * 10^22 kg) is less than 1% of the mass of Earth (5.97* 10^24 kg.)

[Tosh]

As far as i know the engine with the spike has very high fuel consumption and is not an air breather. For normal airplane operation use one of the other airplane engines.

On the other hand, Me-163 is also a rocket plane using not the most efficient fuel (H₂O₂, IIRC)...

My primary airplane is large (5 large fuel tanks and then some), cruises at ~450m/s @ ~15k and has about 1/2 fuel left after making the trip from main KSC to the other KSC.

With 3 mk1 tanks (450 units of fuel) and one turboJet engine, my small plane flew 650+ Km reaching up to 17+ Km altitude and up to 620+ m/s speed. Fuel efficiency is roughly the same as of your one (1125 units of fuel, distance covered 2 * 700 Km)

[rkman]

On the other hand, Me-163 is also a rocket plane using not the most efficient fuel (H₂O₂, IIRC)...With 3 mk1 tanks (450 units of fuel) and one turboJet engine, my small plane flew 650+ Km reaching up to 17+ Km altitude and up to 620+ m/s speed. Fuel efficiency is roughly the same as of your one (1125 units of fuel, distance covered 2 * 700 Km)

I forgot to mention: my plane has 2 turbojet engines (and a ram air intake, probably useless but it looks cool), and it does about 550m/s at ~17k (when about half the fuel is used).

Picture: it kind of fell apart after holding the wheel brakes for a few seconds, but you get the idea

[samstarman5]

As far as i know the engine with the spike has very high fuel consumption

Can say that again. I never saw the fuel gauge go down so fast before, even with the mod parts. I\'d say that engine is best as a booster with its own tank and not for main thrust.

[vexx32]

The aerospike? For me, it has a slightly lower fuel consumption and higher thrust to normal rocket engines. I use it where possible on rockets... not planes

[Guest doughbred]

Well, I guess Kerbin has allot of nuclear fuel and iron.

[GenJeFT]

My first long distance play for the 'around the world' challenge in the challenge part of the forum traveled 1,110,519m (or 1,110.5 km) using 1650kg of fuel and 2 engines. Every 1kg of fuel that was burned the aircraft traveled 673m.

My next plane which got a bit further had 4 engines, traveled 1,177,964m (or 1,178 ish km) and carried 2,850kg of fuel traveled 413.32m per kg of fuel burned.

Per engine for plane 1 worked out to 336.5 meters.

Per engine for plane 2 works out to 103.33 meters.

Cruise alt was around 9,500m since the challenge had a alt restriction of 10,000m. The first plane was not flown as well as the 2nd plane and I could probably do better.

This is using the Turbojet engine.

Making your aircraft larger and adding more fuel/engines to it really brings diminishing returns.