Official FAR Craft Repository

[Wanderfound]

 

 

 

Craft file at https://www.dropbox.com/s/gvn716m7k3rjo9p/Kerbodyne%20Solo.craft?dl=0

[kcs123]

4 mach @ 16km ?  Such a waste of energy due to drag and overheating.

[Wanderfound]

4 hours ago, kcs123 said:

4 mach @ 16km ?  Such a waste of energy due to drag and overheating.

You can get to Mach 4 for less fuel if you do it higher up, but doing it down low lets you get to Mach 4 with a simultaneous 300m/s zoom climb:

 

This lets you float through the low-thrust 25-30km zone at zero AoA, because the low-altitude zoom climb has already raised the apoapsis over 30km.

The zero AoA helps by minimising drag at a time when your jets lack the power to resist drag losses, allowing you to retain as much speed as possible until lighting the oxidising rockets at 30km. Add a nuke and you may even gain a little speed:

 

I'm getting my speed up lower than usual so that I can do a high-drag maneuver that costs speed (initiating the zoom climb) in a place where the air is still juicy enough for me to regain that lost speed before the jets lose power.

The value of that flight profile increases with the wing loading of the ship (because high-loading ships require extreme AoA in thin air). This is a very high wing-loading ship; something built like a U2 would be better off with a high, floaty profile.

A Silbervogel float & bounce approach (climb to 25km, dive to 15km, climb again) might be a little more fuel efficient, but would take longer. Given that it's hitting orbit with several thousand m/s of ΔV in the tanks, I'm not overly concerned.

[kcs123]

My ascent profile is quite different, but I build crafts in different way. I tend to build SpacePlanes with TWR between 0.30 and 0.80, depending on payload.
I'm not always successfull, as my piloting skills sucks, but I found that optimal AoA is around 10 degree.

At 10 AoA degree, on high speeds @ mach 2 or higher, L/D ratio is near peak level while drag is reasonably low. That way you gain most from wing lift without speed/energy loss due to drag. Also at low speeds at 10 AoA you have high L/D ratio and benefit most from wings without much of speed loss.

So, I go at subsonic speeds, up to 10km, slowly accelerating on the way up. My aim is to hit 1 mach near 10km. After that, I tend to keep climbing rate and acceleration in a way to hit 3 mach near 20km. From that point, accelerate and klimb slowly to squeeze out as much as possible from engine air breathing mode. I no longer wait to switch to rocket mode when engines run out of air, usually engine thrust drops as you gain speed, so I tend to switch to rocket mode once engines does not have power to accelerate further.

Need some practice, but when done properly, there is almost no diving/climbing flight area when you loose lift if you climb too much with relatively low speed.
It also helps to set controls in a way that plane is not capable to have more than 10 AoA that is needed. That way you will not get much drag trough SAS controls that tends to keep craft leveled regardless of high drag on too high AoA. In upper atmosphere, between 30 and 70 km, it is still possible to have higher AoA than 10 AoA, but air there is thin enough, so it have much less influence to speed loss due to drag.

Trough ascent path, I try to keep eye on dynamic pressure, to keep it between 10 and 20 kPa, providing good lift from wings without putting in danger to rip them off due to too high dynamic pressure. When I'm capable to not make much piloting mistakes, I can put craft in orbit with "suffering" forces at only 1.5g. That way wings does not have to be strong, having much less mass, giving more dV once in space.

[blowfish]

One other thing to consider is that with higher dynamic pressure, which means that you have a shorter ascent, which mitigates the effect of higher drag.  I generally try to keep dynamic pressure between 40 and 50 kPa, but I also use AJE and I think this effect is more important there.

[kcs123]

12 minutes ago, blowfish said:

One other thing to consider is that with higher dynamic pressure, which means that you have a shorter ascent, which mitigates the effect of higher drag.  I generally try to keep dynamic pressure between 40 and 50 kPa, but I also use AJE and I think this effect is more important there.

 

Well, yes, that also depend on craft design. I often create crafts for stable low speed landings, so dynamic pressure between 10 and 20 kPa might not be enough for level flight at 10 AoA on crafts with shorter wingspan.

For shorter wingspan you might aim for higher pressure, but there is also tradeoff for stronger(heavier) wings and more careful piloting to avoid riping off wings.

[Hodo]

10 hours ago, kcs123 said:

4 mach @ 16km ?  Such a waste of energy due to drag and overheating.

Wanderfound has a tenancy to build WAY over powered craft for the task at hand.  In my opinion his craft are more brute force than style or elegance.  It isn't a bad thing it is his style though.   I went through that phase and didnt like it.  Started building more practical craft that had more function and style without having to be all power.

Like this drone I have been using for simple missions.

It can take off and land vertically, make it to my space station, collect science, send up small payloads, and return.   All without risking a kerbal.

 

A decent picture of my space station, provided by a person here on these forums... I had to use it it was just to pretty.

 

But I have simple.

Older picture, but design has not changed.   It is a successful fighter aircraft, and used for some missions that require a bit of "oomph".

[kcs123]

That's one realy good looking space station. A lot of patience and effort put to build it, that's for sure

[Wanderfound]

We've got three profiles described, here, which you might label as bounce, float and zoom:

* Bounce involves a steep-as-possible ballistic zoom climb to 25km, then keeping AoA minimised while the ballistic arc peaks and turns into a descent. Hold a small constant AoA (5 degrees or so) during the descent and wait for the increasing speed and thickening air to reduce the AoA required for level flight below that value. Once level flight is regained, the final ascent can be either float- or zoom-style; high-lift low-loading ships are better off with float, low-lift high-loading ships with zoom.

The advantage of this approach is that it allows fairly rapid acceleration, even with very low TWR designs. The disadvantage is that the bounce is hard on the airframe, and can be difficult to escape from if you misjudge it and go too deep.

 

* Float involves a steepish climb into the low drag zone above 20km, but with the climb rounded off at the top so as to keep the plane in aerodynamic lift (instead of a ballistic zoom climb). Then, keep the AoA high enough to maintain level flight above 20km while you climb as gradually as possible. You're then faced with the choice of lighting the rocketry at 25km, or keeping on jet thrust to 30km but losing a bit of speed as you do so.

The advantage of this approach is that it minimises stress on the airframe and places the bulk of the ship's acceleration in the high altitude zone where drag losses are minimised. The disadvantage is that it's slow and requires a bit of piloting finesse to get right. It's particularly problematic for high-loading ships (either heavy Mk3 cargo ships or small speedsters with minimal wings), as they may struggle to maintain level flight in thin air without excessive AoA-induced drag.

 

* Zoom involves a fairly shallow initial climb, levelling off below 20km in order to take advantage of the maximum-thrust zone for the jets. The idea is to build as much speed as your heat limits can tolerate, before pulling into a steep zoom climb that pushes the apoapsis over 30km. Once that is achieved, the nose is dropped back to prograde and kept there until 30km is passed and the rockets are lit.

The advantage of this approach is that it minimises drag through the low-thrust 20-30km zone and maintains a large amount of horizontal speed while also maximising vertical speed at the 30km jet/rocket boundary. The downside is that it's very hard on the airframe from both a heat and aerodynamic stress POV, requiring tougher wings than otherwise. It's also less fuel efficient for the jets, as the high power output at lower altitude also means higher fuel consumption, and a lot of the fuel is wasted countering drag. However, this relatively wasteful use of the high-efficiency jet engines is balanced by the benefit it provides during the low-efficiency oxidising rocket burn (the momentum of the zoom allows for later ignition and lower AoA during the rocket burn).

 

Exactly which one is best is going to depend on the ship and the mission; low-TWR sailplanes like the U-2 prefer a float approach, micro-winged high TWR interceptors like an F-104 are more suited to the zoom style of ascent.

 

 

Which approach is best for a "typical" Kerbal SSTO spaceplane is an open question. Anyone want to take a "representative" spaceplane (perhaps something with a small Mk2 cargo bay, designed for satellite runs to LKO?) up for three ascents and see which approach leaves the most in the tanks once you hit orbit?

Edited January 2, 2016 by Wanderfound

[Wanderfound]

Half the thrust, still zoomy:

 

 

 

Craft file at https://www.dropbox.com/s/m6nisqcrxsfsql4/Kerbodyne%20Solo%20R.craft?dl=0

[cantab]

Heh. I find myself having to light the rockets at around 20-22 km. If I get the aircraft flying too high too slow it becomes a real handful to keep under control. I think my ascent is most similar to the "float" type, maybe that's not great and I can do better. Thing is I'm often a bit deficient on pitch authority because good flight characteristics at low speeds tends to mean a nose-heavy aircraft at supersonic speeds as the lift shifts back and that makes entering a zoom climb problematic.

[Wanderfound]

40 minutes ago, cantab said:

Heh. I find myself having to light the rockets at around 20-22 km. If I get the aircraft flying too high too slow it becomes a real handful to keep under control. I think my ascent is most similar to the "float" type, maybe that's not great and I can do better. Thing is I'm often a bit deficient on pitch authority because good flight characteristics at low speeds tends to mean a nose-heavy aircraft at supersonic speeds as the lift shifts back and that makes entering a zoom climb problematic.

If you use Dynamic Deflection, try this: reverse the order of the default settings on your elevators (i.e. reduce deflection at low dynamic pressure, increase it at high). It'll keep you from overcontrolling at low speed while still retaining supersonic authority.

Or, if you don't use DD, crank up the max deflection but also add some AoA. That gives you strong control at low AoA (as is needed when supersonic) but throttles back the deflection if you're headed for a high-alpha stall. The only problem with this is that if you overdo it, the ship may refuse to hold a high-AoA posture when you want it to (e.g. during reentry) and may develop a tendency to pitch oscillate at full stick (i.e. surging between high and low AoA instead of climbing steadily when you hold down the S key). Just reduce the AoA settings if that happens, though.

If SAS wobble is the problem, look at stiffening your airframe (struts can do wonders when you use the translate tool to hide them inside wings) and/or tweaking your PID tuner settings.

[Hodo]

9 hours ago, Wanderfound said:

Half the thrust, still zoomy:

 

 

 

Craft file at https://www.dropbox.com/s/m6nisqcrxsfsql4/Kerbodyne%20Solo%20R.craft?dl=0

Two things I have to say.

 

First; While that is half the thrust it is still a VERY small aircraft with a MASSIVE engine, the RAPIER puts out almost a 1:1 TWR on a craft that size if not greater at max velocity.   That craft weighs in just under 14 tons and at take off you have a 115kn thrust rating.   Which is way high for most aircraft.  Then once you reach mach 3 you have a 3:1 TWR!   That is insane.  

 

Second;

I have to ask why such large landing gear on such a small frame?  You should only need about 13-17deg clearance to get that aircraft off the ground.   Well placed regular gear should give you that.  That craft is no bigger than my old F-119C/A Akula.  Which is also an SSTO in the F-119C variant.

[Wanderfound]

The chunky landing gear is a user friendliness measure.

Small landing gear will work just fine...so long as the pilot is careful to avoid tailstrike. But when I post designs like that, I tend to get responses complaining about tailstrike. Therefore: idiot-proof landing gear, standard on all Kerbodyne designs.

[Hodo]

17 minutes ago, Wanderfound said:

The chunky landing gear is a user friendliness measure.

Small landing gear will work just fine...so long as the pilot is careful to avoid tailstrike. But when I post designs like that, I tend to get responses complaining about tailstrike. Therefore: idiot-proof landing gear, standard on all Kerbodyne designs.

I prefer the term.... "Kerbal" proof.

[Kagame]

So proud of this thing. Wave-drag profile is less than 1 square meter when loaded with air-to-air ordinance. Supercruises like nothin'.

[Hodo]

38 minutes ago, Kagame said:

So proud of this thing. Wave-drag profile is less than 1 square meter when loaded with air-to-air ordinance. Supercruises like nothin'.

 

One problem.... AIM-9X Sparrow... no, AIM-9X Sidewinder.

 

AIM-7 Sparrow.

[Toonu]

Hello, I have problem not with mod, but with my planes, I decided to build a flying wing, I read few things about how they keep stability and so on. But, when I tried do it one of my first prototypes crashed in style of takeoff nose totally up->velocity too low->nose down and crash. In my later prototypes it take off good, but when I tried turn it was so unstable and stall was there. So on last try I put rudders on back and it fly very fast and maneuvre good if it's piloted with precise. After some time I decided make a real flying wing, it take off good, but is higly unstable. Usually it star go sideslip at higher velocites, I usually make it flight straight by control flaps, wings, spoilers, etc....but after some time (and on higher velocity) it just go into sideslip that can't be stoped and few seconds and meters bellow, crash into ocean. Any ideas how make real flying wing with FAR?

 

 

 

Spoiler

First craft, flying bad until adding rudders on back....

 

Second higly unstable craft even withou many(8 spoilers...4on top and 4 on bottom of wing) 

 

 

 

Edited January 4, 2016 by Toonu

[blowfish]

@ToonuYou need split rudders at the ends of the wings to maintain yaw control.  I think FAR supports this now (but I forget what the option on control surfaces is called) .  Even then, you'll have to fly carefully - stock SAS really wasn't designed for this sort of stabilization.

[Toonu]

Oh, thanks for quick reply! I thought theese planes have only one flaps(like your split rudders, but just with the top one...)

I ll try it!  Thanks

 

EDIT: It s more stable, but still needs more stabilization, but thanks anyway!

Edited January 4, 2016 by Toonu

[blowfish]

29 minutes ago, Toonu said:

Oh, thanks for quick reply! I thought theese planes have only one flaps(like your split rudders, but just with the top one...)

I ll try it!  Thanks

Well, it could sorta work with just one, but then you'd get a pitch moment too, which you generally don't want.

[Toonu]

Thanks it helped a lot, stabilized it...but it still needs more stabilizing, have you any idea? It keep stable to Mach 1, but over 1 Mach it just get unstable(but it s ok, I needen't so fast plane...just if u know how improve it..) It turn nice around and everythings seems much better, but it keeps all the flight pitching down, very pitching down, I must fly with nose at 15 degrees up to keep horizontal flight.

 

Anyway, I know ferram and other said milion times NO to milion questions about x64 versions of KSP, but still...In development is KSP 1.1 version where developers said it ll be muc more stable on win 64 bit, because some updates like unity, etc. So when It should be more stable, is there any chance to don't refuse 64bit version by Ferram?

[Motokid600]

I'm more then confident that should 1.1 give us a stable 64bit client the... Embargo lets call it will drop on all mods that don't support it. However Squad has been very quiet about there progress with x64. Which worries me that the stability issues are still present in Unity5. I don't know, well see. You know the saying that if it's too good to be true it's usually not? Well... Lets hope that's not the case.

[tetryds]

@Toonu @blowfish and @Motokid600, your posts have been moved here.

Please discuss designs on this topic rather than on the mod one, thanks.

[SimGuLiM]

F-15

The plane is a bit nose heavy, suggestion are appreciated

Edited January 4, 2016 by SimGuLiM