Old Foxboy

Put a thermometer on it. Sometimes, you get contracts to "transmit scientific data from space over XY". Having a thermometer and an antenna enables you to do this easily. (Don't forget a small solar panel to recharge the energy!)

With the current gimbal implementation, it can help to steer and to stay on course, but it can also induce flipping, because every gimbal movement of the engine makes it's thrust deviate from the ideal centre of mass / centre of thrust line. I would recommend limiting the gimbal and working with aerodynamic controls instead if possible. When correcting the course, the ungimbaled engine still thrusts through the centre of mass and doesn't induce a snowballing effect for flipping. However, you could even do a little trick if you have multiple tanks in a row. Then you can disable the fuel feed for the upper fuel tanks, moving the centre of mass up during ascent. This reduces flipping dangers, too. However, you must manually (or by action group) reenable the fuel feed once the lower tanks are empty.

Hello, i am searching for a decent autopilot mod. Getting fed up of flying standard Jet engine contracts half way around Kerbin. Something that not only adjusts AOA (like Mechjeb), but can actually hold a certain altitude and can track a navigation waypoint (like those you must fly to in contracts). It would be great if this was working by only adjusting trim so if you disengage it, the trim would remain stable. Anyone?

I would strongly recommend using the new Mechjeb to have at least an idea where the journey might be going. As for the validity of aerobraking: Given the fact you want to have a heat shield, maybe airbrakes and parachutes on a craft only if you are going to land on a planet with atmosphere, i would only do an aerobrake maneuver in those situations. And then you would only need it to bleed off some speed if a direct reentry would toast you in an instant. There's no sense equipping a craft with all this stuff if you are going to Gilly. It's wasted weight, which means wasted fuel from the first second after liftoff, and you can save all this fuel for a nice, controlled, safe, delta-V maneuver in high Eve orbit without the need to aerobrake. But hey, it's stylish, isn't it? That's why people want to do it.

For your motivation. look at 17:30 or 21:25 The pro's can do it, too. What many don't seem to know: Gimbaling cannot only help against, but can cause flipping, too, since the centre of thrust moves out of line with the centre of mass. (This has caused many of the failures in the video seconds after ignition) It's better to control the rocket with control surfaces as much as possible. Add more fins.

"Warranty is void if you press spacebar"

I think it's good to develop a habit of remembering alt/velocity/pitch at certain points during the ascend. For instance, i try to start my gravity turn when passing 2000 metres, before aerodynamic forces get too strong to make significant corrections. However, if i am flying a fast accelerating rocket, i will pitch down faster. When flying a very sluggish "big barndoor" with loads of drag, i stay almost vertical a little longer and hesitate to let the nose come down too fast. It's almost always a matter of experience. Once you have a feeling for it, you will *know* during ascend when and how to adjust your ascend profile.

Nope. Only the upper stages usually will be smaller, but that doesn't mean they have to be lighter compared to the relative size of the 1st stage. However, you only need a top heavy rocket until you are out of the dense lower atmosphere. So, have big enough fins on the bottom of the 1st stage, and don't deviate too much from the flight vector when punching through maxQ.

Hello, the answer is simply: Changing atmosphere properties during time of day and latitude. Hotter and thinner air makes your engine lose power and vice versa. For example, flying at the poles at night will help increase thrust.

Well, i roughly did it with 3 rapiers on a shorter MK 2 craft with a cabin. Maybe if i build one more tank, optimize the relation between oxidizer and liquid fuel and eliminate piloting errors, i can lift a real payload or add a docking port. But yeah, exchanging one rapier with a turbo will save a lot of fuel for the initial climb.

Quote: "Reaction Engines is still years away from a completed engine and the construction of SKYLON is years after that, though the company remains optimistic and is currently seeking additional funds to continue development."

If this is true, the Jet engines are hopelessly overpowered.

Your guess ist right. Kerbin simulates a near-Earth atmosphere while being 10 times smaller than Earth and having an atmosphere of half the height, but the first 30km of altitude feel like flying at earth, so after 30km the atmosphere thins out dramatically fast.

I guess your plane is constructed a) too heavy with too much drag and c) too few engines. With the rapier, you should be able to kick through Mach 1 below 5km and go continuously up, accelerating while climbing. Don't try to achieve the jet stage ceiling, but rather try to achieve vmax at an altitude where you still have enough air + power for the engines. Then pull (gently) up, zoom into a steep climb and kick in the rocket stage when air is running out. This is the most efficient way of operating the Rapiers: 1st: Get them to optimum performance speed at a reasonable height as soon as possible to avoid wasting fuel down low&slow. 2nd: Fly into the danger zone of speed + heat. 3rd: Pull gently into a zoom and kick in the rockets.

Take the Rapier out, and the basic Jet resembles a high bypass turbofan and the turbo RAMjet resembles a P&W J58 pretty well. However, the atmosphere of Kerbin is weird. It is similar to Earth up to 15.000 or so, and then it falls off much quicker. However, the gravity is the same, but the diameter is WAAAY less. There are many comparisons to be found in the internet. If Kerbin's atmosphere was up to scale, you would run out of air with the basic Jet engine at 1500 metres. However, the Kerbin atmosphere is about 1/2 that of earth, which means your Jet engine should run out of power at about 7000 metres (which it doesn't). This means: The atmosphere scaling compared to earth is not linear, but it resembles earth's atmosphere up to about 20.000 metres, and then it starts to fall off dramatically. A real Blackbird SR 71 (with the Kerbal turbo RAMjet equivalent) or the Mig-25 would fly Mach 3.2 at 20.000 to 25.000 metres on earth and would be able to make a ballistic zoom flight to about 35 km. That's pretty much what we get in KSP. But everything beyond 25.000km on Kerbin is scaled down to make things easier. What's different: The thrust at sea level is dramatically higher from what i feel. I have no numbers to prove it, though. But being able to zoom up from liftoff, reaching Mach 1.0 in a 70° steep climb and reaching almost Mach 3 before the engine runs out of air feels not right to me. But hey, that's a game.

The Wheesley can go up to about 13.000m if you construct a craft that has a low stall speed (add more wings, make it look like a glider). And no, that's not impressive. It's more like what you would expect from a normal turbofan. As for the Mk3 crafts: The Wheesley is too small for them. You'll simply need more of them. Try modeling a 707 instead of a 737. The older 707 had 4 engine nacelles. A nice addition for MK3 parts would be a bigger Wheesley engine, like a modern turbofan which is used on the 767 or 777 As for the so-called "Turbojet": I don't know what the KSP developers had in mind. If it simply was a low bypass turbofan (like in most military aircraft today), it would get you to mach 2 at best. Or a RAMjet? (Which will practically produce 0 thrust at 0 speed). I guess it's something like the Pratt&Whitney J58 (like the ones in the SR-71 Blackbird), which have a normal turbojet stage combined with a RAMjet that leads compressed air at higher speeds directly into the afterburner stage http://de.wikipedia.org/wiki/Pratt_%26_Whitney_J58#/media/File:SR71_J58_Engine_Airflow_Patterns.svg However: such an engine would require a suitable intake, so using a KSP "turbojet" should force you to build a shock cone intake or equivalent. Given the variety of rocket motors in KSP, i'd love to see at least 2 more aircraft engines: One on the lower end (maybe a prop on lvl 1?), and one SCRAMjet engine that would not b able to provide thrust below mach 1, but would boost the plane beyond mach 3 up to orbital speeds (as long as you are still flying through any atmosphere). The Rapier's are science fiction anyway, so why don't combine them with a stronger SCRAMjet stage?

Nah, it's okay. Nothing i couldn't see with Mechjeb, too. I would love to have it as another reference in the Navball (Orbit/Surface/Target/IAS). TAS would be nice, but it matches Surface, since there's no wind. Groundspeed would be great, too, but that's nothing you need very often, and you get it with Surface speed if you fly level, which is mostly the case when you need it to navigate around, anyway. But if you are into creating mods, i'd LOVE to see one mod i didn't discover yet: A graphical display of the flight envelope, like that: http://www.newbyte.co.il/products.html or like that: http://www.christiancurry.com/primary-flight-display/ http://niquette.com/books/chapsky/glossfly.htm (look for "envelope, flight") With such a display one could easily figure the correct speed/altitude to keep any craft in it's optimum performance window. I bet the difficulty would be to create a pop up window that shows the correct information for each craft.

Let me come back to my main problem, to make clear why there is so much confusion when talking about speeds and jet engines. A jet engine's thrust is very nicely defined in this Article: http://en.wikipedia.org/wiki/Jet_engine#Thrust Though true airspeed (the speed with which a craft moves through the air) ist part of the equation, a major portion is the mass rate of air flowing through the engine, which is directly related to the dynamic pressure or, so to say, roughly what the IAS gauge on an airplane will measure. This means: Given a constant true airspeed (=surface speed in KSP),when climbing, the available mass rate of air flowing through the engine is being reduced the higher you fly, resulting in less thrust. Period. That's one of the reasons why i'd love to see a IAS gauge in KSP for planes. You get a lot more information that's important for piloting: Correct stall speeds, engine effectiveness etc. For now, i help myself with Mechjeb and a custom display which shows me dynamic pressure.

"relative terms". Now practically, for the basic jet engine, it goes down, because you simply aren't able to get the same IAS airflow into the turbine - that's what i was trying to say. The turbojets on the other hand can maintain enough thrust to keep the game going a little longer - up to the structural or heat limit, or up to the point where you simply run out of intake air I believe the real problem hasn't shown up yet because you "only" need ~Mach 6+ to get to a reasonable apoapsis on Kerbin. On Earth, you'll need ~Mach 20+ So, a good addition to the spaceplane series would be an actual hypersonic SCRAM jet engine that can boost the plane to orbital speeds above what Kerbin needs.

I used Orbiter for years. The Orbiter Deltaglider is anything but real. It has unrealistic ISP. Bad example.

What do you expect? There's no jet that can leave the atmosphere in real life. The maximum you'll get is a Mach 3+ speed boost to pull up for a parabolic flight profile and go suborbital at best. To get into orbit, you'll always need rockets. However, i'd like to see an addition of experimental hypersonic flight engines that allow greater heights and speeds to achieve a near orbital flight profile.

If there's no wind, TAS is equivalent to the speed above ground, not equivalent to IAS. IAS is the indicated airspeed, as "seen" by the pivot tube. Though there are many factors that influence IAS which cannot be taken into account in a game like KSP, IAS would be directly related to the dynamic pressure. So, using Mechjeb or something like that, you can see how this pressure differs dramatically with altitude while flying the same speed above ground (="surface" speed). It's as great as 2% per 1000ft, so at 33000 ft (10.000 m equivalent), you'll get 66% difference in speed readouts (oooops!!). For flying, it's very important to have an IAS (or CAS) airspeed readout, so you know if you are near stall speed or near a critical speed limit. So, to simulate spaceplanes better which pass through very thin atmosphere, an IAS gauge would be imperative! As for the thrust: Believe me: It decreases with altitude for a simple reason: missing speed (and that's IAS, not TAS, that's why i put up this topic) - - - Updated - - - To do this, the basic Kerbal Jet would need an afterburner. You can go beyond mach 1 in a dive, but it's not enough to break the drag barrier and accelerate further.

Well, i wouldn't say this. The problem is that it has too much excess power at sea level, but behaves correctly at higher altitudes. But i'd love to see the IAS / TAS. Now seriously: While it is true a modern subsonic Jet engine (like on small subsonic Fighter Aircraft or a civil Jet) have nearly the same top speeds and ceilings as a Kerbal Jet, the structural limits are not correctly simulated in KSP by what i "feel". Maybe some aircraft nerds can tell us more.

Sure you can? You can "pull" more TAS, but you can't raise your Airspeed beyond the drag limit. That's why craft go faster higher up in the atmosphere. The "Surface" speed is TAS, since no matter how high you go, the respective Orbital Speed in level flight (same heading) is always the same. You can check it: fly 100 m/s at sea level. ~275 m/s Orbital speed when heading east from KSC. And it's the same at 5000 metres or at 10.000. However, you won't be able to maintain 100m/s in most craft at 20.000 because the Airspeed is WAAAY lower. Now here's the real issue in KSP: With a standard jet engine, you get nearly exactly the same TAS at sea level as you are getting at 5000 metres. But that's not real. Blimey, it's not even real for propeller driven airplanes of WWII. Even with a propeller airplane you will reach higher TAS than at sea level. With any commercial jet aircraft in the world, you will easily reach higher TAS up to 10.000 metres. While this is earth atmosphere, Kerbin resembles it at a certain scale. There are different limits to a flight profile of speed / altitude. 1. On the low end, it's the lift of the wings. Go too slow, and you are out of the game. This low end curve will start at stall speed at sea level and increase in TAS (not IAS!) the higher you go. You IAS stall speed stays the same, but the higher you go, the higher the TAS gets. 2. The second limit is the airframe integrity limit. If you pass beyond a certain dynamic pressure, it's game over. KSP models this in a neglectable way. The only thing you have to care about are high G-forces or heating. However, it's a major factor in aviation. Go beyond the red line, and you won't walk away from this landing. Now dynamic pressure is nothing other than an IAS issue. The higher you go the less dynamic pressure you will get at a given TAS, which means you can speed like a bullet and pull high AOA at high altitudes without breaking your craft. 3. So what is the limiting factor then? It's the third limit, which is the thrust vs. drag ratio. To go fast, you want to go up high. But somewhere there's the equilibrium between your engine's thrust and the remaining drag. That's your service ceiling. Now in KSP, the jet engine's thrust/drag ratio seems to have the same value at all altitudes from sea level almost to it's ceiling. While it is perfectly clear you can't break the sound barrier at sea level because IAS = TAS at sea level, the IAS at 10.000 metres is way lower, and the drag is not much of a deal. But the jet engine in KSP loses his power too quickly. It behaves more like a prop engine. My suggestion to make it feel more like a real jet would be to reduce it's overall power, but to make the power loss up to 10.000 less dramatic, so you could slowly accelerate to a maximum of 300 at sea level, and fly about 400-450 at 10.000 (TAS). Maybe you would even be able to make parabolic flights then up to those "report above xxxxx m at yyyyy" contracts.

Hello and welcome to some Physics discussion. As you all know, Thrust decreases with Altitude, and Drag should decrease, too. However, Kerbal Space Program obviously doesn't make any differences between True Airspeed and Indicated Airspeed (TAS / IAS). So, no matter how high you fly, you'll always hit the drag wall at the same speed (for basic jet engines, this is about the speed of sound or 330 m/s). However, since in lower density atmosphere, 330m/s Airspeed means you are actually flying faster than 330 m/s above the ground. Now i don't have figured out yet if the Navball indicator really displays IAS when you set it to surface mode or if it indicates TAS. "Surface" means it should indicate TAS. Anyone?