Thinking about making the switch to FAR.

[eddiew]

*edit* Whiteknuckle's already won the thread, but I was typing this as he posted so I'll let it stand

Seriously, that's enough wing? Wow...I wouldn't have thought so. How can I tell if I've got enough wing for a given design? Is it one of those green/red number parameter things? Seriously, I still don't know more than "red is bad" with those.

FAR tells you the AoA you need to fly level when you've plugged in an altitude and mach number. If it's crazy large, or zero, then you need more wing area (zero means you can't fly level at any speed). If it's under 10 degrees at 20-25km then you're golden. I'd even allow 20-25 at higher altitudes

And ahh, it's not the same procedural wings mod! B9 procedural wings is not, as it happens, B9 only, and looks pretty good on stock birds. Personal preference as to which you use, but I like the rounder edges and chunkier look of the B9 proc wings myself. Think they fit better with the stock wing appearance, and you can have really hefty control surfaces if you need them.

Also it's fine if the CoM shifts a bit. Obviously it's better if it stays put since the flight characteristics won't change, but sometimes that's just too darn hard to arrange. As long as it's in front of the CoL you can manage - although the plane will be more stable and less flippable with a bit more of a gap. It's well worth allowing the CoM to move during flight in order to get rid of those tanks... they'll be costing you a lot, probably loses the equivalent of 0.1 TWR just from them. Flying with FAR is all about minimising cross section and sleek, streamlined shapes. Try opening your cargo bay on the runway and see how much difference that makes for a working example

Moving the tailfins back to the rear will shift the whole CoL and give you some leeway on the matter. I have a habit of aiming for a "ball's" width between the CoM and CoL; seems to work out ok. This is one of my better flying craft that I'm using as my go-to crew transport within Kerbin's SOI. Little too large and part-heavy to be considered 'sporty', but flies cleanly - and check out the tiny wings vs the size of it

Notably the AoA at 25km and mach 3 here is 24.6 degrees - which is very high, but also fine since it'll generally be at mach 4-5 by this altitude and need much less. It is however stable even at low speed and high AoA, even with tiny wings, meaning it can rush to 25km then hang around here until it's gotten to it's maximum speed.

Dirty secret; there's a pair of shock cones in the forward cargo bay. I'll stop doing it when the game stops letting it work! There's a point here about intakes though: 1 shock and 1 radial or structural per jet engine is plenty. I tried this airframe with four exposed shocks and it struggles to gain speed due to horrible drag. Oftentimes with FAR, less is more

- - - Updated - - -

Another quick question for y'all - it's been mentioned before that Turbojets and RAPIER engines were nerfed for FAR so that they don't produce so much power they tear your planes apart. By how much have those engines been nerfed, does anybody know? Was the Basic Jet also affected?

Don't worry about it, it's been nerfed to adjust for the thinner air with FAR. They're still completely viable, although I'd favour a 50/50 mix of TJs and rapiers when available.

Basic jet is useless for spaceplanes anyway

[Red Iron Crown]

Anything heavy that I could stick up front I did, with the reaction wheel as far forward as possible to give it a lot of leverage.

It might surprise you to learn that reaction wheels impart the same control authority no matter where they are placed on the vessel (it certainly surprised me).

[WhiteKnuckle]

It might surprise you to learn that reaction wheels impart the same control authority no matter where they are placed on the vessel (it certainly surprised me).

Really?

...well then...

Hmmph.

I guess they already violate the laws of physics, so what's a little icing on the cake.

[Crzyrndm]

Your assumption is probably reversed anyway. At best, reality says it doesn't care (this is how KSP models it). At worst, they reduce effective torque the further from CoM (both cases are provided because I still can't prove the worst case scenario, but it seems to be the likely outcome)

Linear forces (ie. engines, RCS) on the other hand increase in effectiveness as they distance themselves from the CoM because they increase the lever arm they have to apply their force.

Edited February 27, 2015 by Crzyrndm

[eddiew]

It might surprise you to learn that reaction wheels impart the same control authority no matter where they are placed on the vessel (it certainly surprised me).

I always thought they should be near the CoM... if you want to spin a stick, you hold it in the middle, not one end But I wouldn't be shocked if KSP's model just applies the total torque power across the vessel as a whole.

[Red Iron Crown]

I always thought they should be near the CoM... if you want to spin a stick, you hold it in the middle, not one end But I wouldn't be shocked if KSP's model just applies the total torque power across the vessel as a whole.

That's a bit of an unintuitive example, by rotating the stick by its center rather than its end you decrease its polar moment of inertia (i.e. resistance to turning). A spacecraft in freefall will always rotate about its CoM, so it's not quite the same thing.

KSP's model applies the torque at the location of the wheel, so placement can matter a bit if the ship isn't very rigid.

[capi3101]

Good morning, gentlemen. So, I thought I'd give a quick update of my efforts from the previous evening. After looking through the thread, I took most of WhiteKnuckle's advice for a redesign of the Death Trap:

There were a few things I didn't do - the big one is the Shock Cone Intake on the nose. That may very well be stock experience talking there; I had a lot of RAPIER-based designs fail in the soup, with the cause traced back to excessive draggy parts (like intakes) up in front. I did fly around last night with the Cd tint on for a bit and noticed it was brightest around the nose.

So if I don't stick an intake up there, maybe I can use a pair of structural intakes instead? Oooh...maybe I could use those to replace those external RCS cylinders (still haven't ditched those just yet).

Control surfaces on the wings - current setup is aileron-aileron-flap/spoiler-flap. I'll take suggestions on how to change this; I didn't realy have any problems with the early part of the flight last night aside from it wobbling up into the air again. I did go ahead and tweaked down the canards to 75% and didn't have any tail strikes, which let me switch back to the Small Gears. Takeoff speed for the design with fully extended flaps is about 85 m/s...which as I recall was a sign of too much wing.

Can anybody walk me through a method of determining takeoff speed using the readouts? That damn thing still confuses me, but I'm learning.

One of the things I had intended to do last night was to take screenies of the stability derivatives at the benchmark levels eddiw3 posted yesterday (M1.0@10k, M2.2@20k, M3.5@25k, M4 for the hell of it) as well as AoA sweeps for those benchmark values and post them up here this morning. Unfortunately, right before I played KSP last night I was in the initial stages of building a VASSAL mod, and a lot of what I was doing involved taking Windows screenshots (Alt-PrintScreen) and when I went to take the screenies my brain farted and started hitting Alt-Printscreen instead of F1. So I don't have any of those like I'd hoped. Which is damn shame. Hopefully I'll get to that this evening.

Long and the short of it - it was green and white across the board with the exception of the N-sub-Beta Lateral/Sideslip Derivative at M3.5/25k. That was the only red I saw. Now, I did note that at subsonic speeds when I swept the AoA that my lift maxed out around 10 AoA at about Mach 0.8; it was around 15 degrees at M0.5 and it started going upwards after Mach 1. I read that as "if you can hold her steady as she goes trans-sonic, you oughta be able to get to space".

Which is where my problems begin again. The design I think has been established as good, so at this point I have to attribute my failure to reach the same degree of success that I had on the first night to poor piloting.

Generally what I've been doing is cranking the nose up to 40 degrees above the horizon once I'm off the ground. Flaps neutralized and gear up, then set FAR flight assist for AoA - generally somewhere in the 10-12 degree range. FAR usually reports minor stalling; the stall tint shows it's happening up on the canards, which unless I'm mistaken is what they're designed to do, so I'm not terribly concerned. (the wings are fine; I've seen some stalling on the inner flap but that's usually right after takeoff, before I've retracted it). Ascent through the lower 10k is pretty smooth but I'm generally not going much above Mach 0.5 once I get to 10k, so I put the nose down to 20 at 10k and start building up speed. KER generally reports the rate of ascent during the entire initial ascent period to be no greater than about 50 m/s. Around Mach 0.8 I start experiencing SAS wobble and it gets reaaaaly bad up around Mach 0.9. I try to correct the wobble by turning off SAS, the plane doesn't hold its heading, and it's off we go - a 12 kilometer drop into the drink. Broke the sound barrier once last night before I went into the spin - so there is that. I haven't yet been able to recover once I'm in the death spin - I've been attempting the PARE procedure, and I generally get as far as A (neutralize the ailerons). I've been trying to get her to level flight again after pressing "X" to kill the throttle, without success. I may be reading the procedure wrong; how can I tell if the ailerons have been neutralized? Is the PARE procedure applicable in KSP? Anyway to tell if I've got a craft that is unrecoverable once it's in the spin (that one has to do with wing loading, right)?

I'm thinking I need to limit myself to a single reaction stabilizer if I go with any degree of stability assist at all; I still haven't changed the setup yet. Anyways.

Source: https://github.com/ferram4/Ferram-Aerospace-Research/blob/master/GameData/FerramAerospaceResearch/FerramAerospaceResearch.cfg#L694

Generic 50% thrust for all engines that use intake air as a propellant

Turbojet: Reduced thrust to 110kN, reduced max effective velocity to 1800m/s (compared to 2400 stock...)

Rapier: Reduced thrust to 100kN in airbreathing mode, reduced max effective velocity to 1700m/s

Basic Jet: Still (?) 150kN, reduced max velocity to approx mach 1

Alright, thanks for that data. I had a thought yesterday for something to try out design-wise once I got the basics of FAR down.

Just to reinforce Crzyrndm's point: the only way to really know how much wing you need is that panel. You can input whatever speeds and altitudes you like; I would suggest first checking takeoff. Increase Mach (and hit calculate) until your AoA is reasonable. If the m/s turns out to be more than 120 or so, you need to add flaps or more wing; 270mph is rather fast to be taking off. Then test up at your cruising altitude and speed, maybe 10km and mach 2? See what the AoA is like there. If it's more than 5 degrees, worry.

I didn't spot what you and Crzyrndm were talking about until this morning when I looked at eddiew's second to last post. I'll have to check it out again when I try again this evening.

Hey y'all, thanks again for your help. I am learning a good deal. With luck, tonight I might make space.

Edited February 27, 2015 by capi3101

[eddiew]

In the FAR 'Data + Stability Derivatives' window, enter 0km altitude, and something sensible like mach 0.35 (default) and see what the AoA is that's required to fly level. If it's more than 10 degrees, by and large you're going to have trouble taking off - although it's entirely possible to have it read 8 degrees and still not be able to lift the nose

A 40 degree pitch is huge - most of my birds go up at 15-20, except the ones with > 1 TWR. Remember the air is thinner with FAR, you can't bounce off it You're wobbling because you went up too fast. Check the stability window for 0.5 at 10km and I bet it's full of red. Take it easy, remember that speed is more valuable than altitude, and be going for at least mach 1 by this point.

I'd say your design looks rather more like a plane now though ^^ Might be worth considering the root-width of the wings; for some reason the forward corners bother me. I feel like they'd be a drag source and need to be nestled cleanly against a nacelle...

Edited February 27, 2015 by eddiew

[WhiteKnuckle]

Yeah you need to climb slower/build up more speed.

By 10k you should be going mach 1, mach 2 by 15k and mach 3 by 20k.

The 25-30k region is always going to be the hard part of getting to orbit, it's all a balancing act of building speed/gaining altitude/staying in control. But I don't think you'll have any trouble getting to 20k with your design as long as you slow your accent a little bit. I think it took me about 3.5 minutes to get from the runway to 20k.

[Renegrade]

Dirty secret; there's a pair of shock cones in the forward cargo bay. I'll stop doing it when the game stops letting it work! There's a point here about intakes though: 1 shock and 1 radial or structural per jet engine is plenty. I tried this airframe with four exposed shocks and it struggles to gain speed due to horrible drag. Oftentimes with FAR, less is more

My probe-bomber uses a single circular intake in it's cargo too for the lulz~

Basic jet is useless for spaceplanes anyway

If you make a more realistic spaceplane (ex, a Skylon-styled thing, which is mostly powered by rockets, and really only has about 1/5th of the delta-v from jets), you actually can launch on basic jets. FAR's basic jet nerfing will reduce the effectiveness over a stock-based one, but flying up to the upper atmosphere on basics still a) gives you an extra 350m/s, which is like launching east again and then some gets your rocket engines above the thick, specific-impulse killing pressure, and c) gives you a higher launchpad so you can transfer to a horizontal burn faster (less gravity and air drag).

Sure it's not as effective as a turbojet craft, but it would fly more like the real thing (well, assuming Skylon ever becomes a real thing).

That's a bit of an unintuitive example, by rotating the stick by its center rather than its end you decrease its polar moment of inertia (i.e. resistance to turning). A spacecraft in freefall will always rotate about its CoM, so it's not quite the same thing.

Note that the discussion in the reaction wheel thread was not able to reach a successful conclusion either way...

It might surprise you to learn that reaction wheels impart the same control authority no matter where they are placed on the vessel (it certainly surprised me).

However, I did some empirical testing in KSP and it supports this statement here ^ (thanks to a weird-looking test craft, a bit of hyperedit magic, and VOID's handy-dandy angular velocity readout)

[Specialist290]

Looks like there's quite a lot of good information in this thread Would any of our experts here be willing to write up a general tutorial on how players can use FAR's stats panels to make good spaceplanes (or planes in general)? I think it be extremely handy for people who are new to the mod and might not know how they can use all the different numbers to their advantage.

EDIT: I've since been made aware that there's already some documentation on the FAR wiki, which I'll link to on the Drawing Board to give it a little more exposure. Still, having the basics explained from a few different approaches and perspectives might help as well, so if any of you feel you could do a good job, feel free to take a crack at writing up a tutorial of your own.

Edited February 28, 2015 by Specialist290

[Crzyrndm]

The best one I've seen is in Wanderfounds craft showcase thread (linky), although it's a bit light on the stability derivatives page (that being said, I don't exactly pay much attention to the numbers page past level flight AoA unless there's red everywhere...)

[eddiew]

Looks like there's quite a lot of good information in this thread Would any of our experts here be willing to write up a general tutorial on how players can use FAR's stats panels to make good spaceplanes (or planes in general)?

Wanderfound has some videos up on his youtube which cover from-scratch building - try the Labrys build for a starting point ^^

I'm no expert, but the short version on how to get a good prototype for a first test is to aim for green numbers at the altitudes and speeds you expect to be doing As a quick-n-dirty I suggest testing planes at:

- 0km @ mach 0.4 (tells you if it can lift off!)

- 10km @ mach 1

- 20km @ mach 2.2

- 25km @ mach 3.5

- 30km @ mach 5 (not really necessary but reassuring if possible)

Other than that, check the hover-over tooltips and see what any reds are telling you:

- yaw instability? add more vertical tailfin

- roll instability? add dihedral (angled up wingtips or tailplane)

- longitudinal instability? need more pitch authority; consider moving canards forward or tail planes back

- 'change in X direction with respect to Z direction' stuff? usually seems to mean you need more, or less, wing

- 'speed required for level flight' of zero? you can't fly level at any speed, add more wing, more canards, bigger control surfaces, etc

But none of these things guarantee your plane will reach space FAR preview doesn't really account for TWR, and I'm not sure it covers drag; it just sort of assumes you can get to the speed you claim you can and then gives you an in-the-moment snapshot. Easy to have a 'stable' design that caps out at a lower speed and altitude than you need. In fact I'm having problems today with a design I posted earlier in this thread - it doesn't want to get to mach 5 anymore and I don't know why. Flies lovely, just won't pick the speed up

Conversely, oftentimes a red number doesn't mean guaranteed failure; it just means wobbly behaviour. More TWR can compensate for a heck of a lot, and more than 1.1 will generally allow you to fly any old pile of junk to orbit, as long as it has fuel enough. A lot of it is just fiddling; once you have an airframe that you like the visuals of, and which gets close to or reaches LKO, it's optimisation time to see how much delta-v you can get it there with.

Edited March 2, 2015 by eddiew

[cantab]

Doesn't a 0 reading under AoA just mean it can't fly level at the speed and altitude specified? Go faster and you can fly.

Also, I suggest testing at more like Mach 0.1-0.3 to study takeoff behaviour. Remember x m/s is about 2x knots and over-fast takeoff and landing speeds are hazardous. They can be lowered to an extent by proper setup of flaps.

[NathanKell]

Mach 0.4 at sea level is 311mph, yes. A bit fast for takeoff, even though it appears to "only" be ~140m/s.

[capi3101]

Thought I'd update y'all on my latest escapades. Friday night I took another crack at flying the Death Trap using a slower ascent profile like y'all suggested - this happened:

Ascent was pretty smooth up to that point; I had some oscillations going on there around Mach 1.5 but they ultimately smoothed themselves out. I assume what happened there was that I was going too slow to be stable; I wasn't quite to Mach 1 at 10k, not quite to Mach 2 at 20 either, but I was close.

Now I need to know how to make that final push into space. I'm assuming it's a matter of keeping the Jet on for as long as can be managed but at lower and lower throttle settings, maintaining a slow ascent and trying to continue accelerating horizontally, lighting the rockets only when it becomes necessary. I panicked on Friday - lit the rockets early and ran out of oxidizer before I had a periapsis off the ground. Mach 6 at 50k. I suspect the design hasn't got enough thrust for its mass - but that's another discussion I can have with y'all. For the record the plane is just over 15 tonnes with one Turbojet (which is the proportion I'd use in stock - in FAR, I suspect it should be 1 Turbojet per 11-12 tonnes, but I need to do some more experimentation there).

Saturday I decided to take a break from the Death Trap and instead turned my attention to rockets in FAR. Now, I've heard all the guidelines there - make the rocket longer than wider, 1.2 TWR is plenty, be gentle with the gravity turn, 3500 delta-V. My main concern is with launching Geschosskopf Sci Landers, such as this one:

Typically I'd launch a craft like that with an asparagus launcher using Temstar's guidelines, so I figured I should at least try to see if they'd still apply for the most part in FAR. I knew the payload would need a fairing in order for it to work properly; I had installed Procedural Fairings, and after some tinkering I finally figured out how to use that mod. I then designed my asparagus in the usual way but set the initial thrust to 1.2 for all stages; the addition of nosecones and fins to the boosters was sufficient to knock the delta-V down into the 3500 range. In the end I had this:

How'd she fare? Got it into orbit on the second try; on the first try I nudged it over too fast and the rocket tumbled out of control. Second time I took it more gently, starting the turn around 5k and not reaching 45 degrees until about 18k. The rest of it went just like a stock launch and once I was up I was surprised to find the mission was not unlike anything I haven't done hundreds of times before - even the aerobraking for landing and chute deployment went off the same way. Does make me wonder - do y'all usually handle rocket launches in FAR with serial staging, onion or asparagus? And are there any other guidelines of which I should be aware other than the ones I already mentioned? Is there an aerobraking calculator extant for FAR? How about a parachute calculator? What are the known delta-V values for launch and landing on other bodies in the Kerbol system in FAR other than Kerbin?

Almost there. If I can get the Death Trap (or perhaps a successor) to orbit, my next goal will be to lift a payload by plane. Have y'all discovered a practical maximum spaceplane mass for FAR designs, just out of curiosity?

[Crzyrndm]

Switch over to rockets wouldn't normally be much past that point (some of my lower TWR and L/D planes ignite at 1300m/s). You might be able to do a little better if you drop down a little to a point where your AoA is a little lower which lets you accelerate (17 degrees produces enourmous amounts of drag, as made obvious by the low L/D ratio), which lets you get higher with lower AoA which means you can go faster (I hope that made sense...). You won't be seeing the periapsis break the ground in FAR though, faster jets are only really 1500-1550m/s.

That p-fairing/rocket combo would get tossed if it was in my VAB. Because it's wide and then reduces down sharply it's going to be a right PITA to launch (needing a silly shallow turn which just throws away comparitively huge amounts of dV). If you can't/don't want to make that payload narrower, place the fairing base lower down under the tank (IIRC, they crossfeed) so that the diameter reduction can be much shallower. Make it taller at the front for the same reason (the shallower the gradient where cross section changes, the more stable your rocket will be.

EDIT

The point of the second paragraph I need to emphasise: Throwing a fairing on something doesn't automatically make it aerodynamic. The fairing has to be more aerodynamic than what it's trying to cover which sometimes means it's best to leave it uncovered.

Edited March 2, 2015 by Crzyrndm

[jedensuscg]

Ive recently been using Mechjebfor ascents. Always had FAR installed and I agree they never worked well together, but my manual ascents were horrible because I get bored doing them over and over.

But I found you can edit the ascent profile settings to make mechjeb work really well. The biggest factor is to limit angle of attack as you go up. I stat around 5 if I am not sure how the rocket will behave, and gradually change it, since Mechjeb does like to do immediate turns. Once past the critical altitude where FAR likes to flip you I disable it.

You also need to change the ascent slope profile a bunch, as shown in this guide https://github.com/NathanKell/RealSolarSystem/wiki/MechJeb-Ascents. It gives you basic directions for both FAR and Real Solar Systems. The one thing that does not work in ascent guidance for me is the limit to terminal velocity checkbox. So instead I use the limit throttle setting checked and make changes here to keep my speed down, as the biggest factor in FAR royally destroying your launch is the combination of high speed and moderate angle of attack changes.

Once I do a few launches I know where I need to set things in advance and it not only really speeds up my launches now, but does them with far less Delta-V expenditure. Rockets that I used to struggle with are a breeze now.

[eddiew]

Doesn't a 0 reading under AoA just mean it can't fly level at the speed and altitude specified? Go faster and you can fly.

Beg pardon, got mixed up - there's an indicator for speed required for level flight. If that is zero, then it's impossible

And most planes that have enough TWR to reach orbit will be doing mach 0.35-0.4 on the runway. FAR isn't far off with it's default ^^

[eddiew]

Now I need to know how to make that final push into space. I'm assuming it's a matter of keeping the Jet on for as long as can be managed but at lower and lower throttle settings, maintaining a slow ascent and trying to continue accelerating horizontally, lighting the rockets only when it becomes necessary. I panicked on Friday - lit the rockets early and ran out of oxidizer before I had a periapsis off the ground. Mach 6 at 50k. I suspect the design hasn't got enough thrust for its mass - but that's another discussion I can have with y'all.

30km at mach 4 should normally be fine for lighting the rockets - although if you're flying level at this, then stay at it and get to mach 5. It's pretty hard to get an air breather over 30km. There's also no harm in keeping the turbo running after the rockets are lit; if it produces so much as a kilonewton of thrust, then it's helping.

Oh, also, I suggest using the VESL tab on your KER; it shows you the % of intake air used, and the current TWR, both of which really matter for the switchover point. An on-rockets TWR of 1.5 or better makes everything easier, since you can haul the nose up much harder. It's possible to circularise with a nuke and 0.4, but it's slow and painful. As yet, I've never managed the stock trick of hitting an AP in vacuum while still running on turbojets.

As yet, I don't know of an upper limit; the principles of FAR don't state any problem with bigger masses, it's all about getting the right aerodynamics. Of course, you're limited by what you can physically fit into an MK3 cargo bay; you can't chain them to indefinite length because they'll just snap. As a compromise, this thing behaves well, but lags due to high part count. In the end I swapped it for a B9 design which halved the parts and doubled the real-time ascent speed.

[WhiteKnuckle]

Almost there. If I can get the Death Trap (or perhaps a successor) to orbit, my next goal will be to lift a payload by plane. Have y'all discovered a practical maximum spaceplane mass for FAR designs, just out of curiosity?

I really don't think there is any hard limit. But IMO the two practical limits you're going to run into are:

-Payload fraction. After a certain point (weight wise) you need so much wing and so many engines to get off the runway that you're going to have a ton of drag in the upper atmosphere, to combat this drag you'll need to burn a ton of fuel. Bringing more fuel means you need more wing and more engine and the problem spirals out of control. This is probably the closest thing to a real upper limit on plane design, but probably not what is actually going to limit you...

-Running out of runway will. This is related to the first issue, essentially to get a super heavy bird off the runway you need a ton of wing and a ton of engines. But adding more wing and engine also increases your weight and drag, so you reach a point of diminishing returns just to get something off the runway. Then you run into issue number 1 when you reach higher altitudes. But even something that is all fuel and no cargo will run into problems getting off the runway first.

Now as far as practical limits go, with stock parts getting an orange tank to orbit is hard but by no means impossible. Over that I personally have started to run into issue #1. Getting two orange tanks to orbit might be possible if you used them as structural members instead of putting them in a cargo bay. Using B9 or other mods I think I could get two orange tanks to orbit as cargo.

[eddiew]

I've definitely seen screenshots of B9 designs with double-orange cargoes

For a while I regarded B9 as kinda cheaty and resisted using it - then I realised it was made for people who want to scale up spaceplanes gracefully. As soon as you surpass a smallish 1.25m cargo, it really is the only sane option. Building an orange lifter with all stock components results in a lot of parts and a lot of lag. Doing it with the larger B9 components means you can stay below 100 parts, and results in a much smoother experience.

[capi3101]

Hey, out of curiosity, what are y'all's thoughts on RAPIERs in FAR? I used to use them heavily in stock but grew to prefer Turbojet/rocket combos. The thing there is that a couple of pages back I asked about the nerfing involved on those engines by FAR, and Crzyrndm told me the maximum effective velocities of jets was about 1800 and RAPIERs was 1700. In my experience that's a substantial slowdown for Turbojets in FAR, but 1700 is just shy of where I'd ordinarily switch a RAPIER over to rocket mode...

[Alshain]

Hey, out of curiosity, what are y'all's thoughts on RAPIERs in FAR? I used to use them heavily in stock but grew to prefer Turbojet/rocket combos. The thing there is that a couple of pages back I asked about the nerfing involved on those engines by FAR, and Crzyrndm told me the maximum effective velocities of jets was about 1800 and RAPIERs was 1700. In my experience that's a substantial slowdown for Turbojets in FAR, but 1700 is just shy of where I'd ordinarily switch a RAPIER over to rocket mode...

I tend to build for looks. I use turbojets when I want that separate engine effect and I use Raipers when I need the convenience or single-engine look.

The difference in effective velocities is not going to change much in the grand scheme. It isn't a big enough change, and unless you have just a massive wingspan or a heck of a lot of engine (TWR 1.5+ on jets), you will want to switch sooner anyway or you will lose control in FAR at those altitudes. The problem with more engines and wings is they are dead weight in space and cause you to spend more fuel doing other things. That second image plane is a pain to dock, but the first one very agile... however I have to switch to rockets much sooner because of it's small wings (remember the air is thinner up high).

Edited March 2, 2015 by Alshain

[eddiew]

Turbojets have about 10-15% more thrust, I think, and are perhaps very slightly more efficient in terms of air use? At least, the primary advice I see for craft that have both rapiers and turbos is to turn off the rapiers when the air gets thin, then fire them up in rocket mode once the turbojets finally conk out. It's either a massive urban myth, or they're very slightly more effective.

My personal habit is to start with rapiers, and add them in pairs. 2 air engines = all rapiers, 4 air engines = 2 of each, 6 air engines = 4 rapiers and 2 turbojets, etc. But it's only an habit, and it tends to work fine with all rapiers.

The real advantage of rapiers is when you do need to kick in the rockets; there they are, without adding weight or drag. Even if you have a nerva on board and want to go long range, being able to use those rapiers for an extra kick out of the atmosphere is very useful. If I have a plane with only 1-2 air breathing engines, they'll be rapiers. Or B9 sabres