[WIP] R.E.L Skylon C2. Alpha Released. FAR config broken. (08 Dec 2014)

[White Owl]

... for take off it should rotate around the rear gear, resulting in a fairly large angle of attack ...so I think getting the center of mass almost directly over the rear gear to be fairly important.

All airplanes takeoff from a runway like this. Of course the Skylon must.

... I also suspect that on takeoff and through the early stages of flight the center of lift would sit in front of the center of mass...

Oh no! You can try this in KSP very easily. Just build an airplane with lift in front of mass, takeoff, and watch the airshow stunts! CoM must be forward of CoL, always. This ain't a jet fighter, and KSP control surfaces aren't smart enough to emulate true fly by wire trickery, so our airplane has to be stable.

Is it intended to make a powered landing or glide in?

It's a glider.

[Akira_R]

All airplanes takeoff from a runway like this. Of course the Skylon must.

Well not all planes, there are designs that have a high enough coefficient of lift at take off speeds that they simply pick themselves up lol

Oh no! You can try this in KSP very easily. Just build an airplane with lift in front of mass, takeoff, and watch the airshow stunts! CoM must be forward of CoL, always. This ain't a jet fighter, and KSP control surfaces aren't smart enough to emulate true fly by wire trickery, so our airplane has to be stable.

Yes I have done this and yes it is a pain in the ass to control, however given the thrust angle of the engines they should help balance each other, and I doubt this thing will be performing any kind of maneuvers, essentially just get the damn thing pointed and GO, i was simply stating what it looks like to me given the amount of wing out front and the fact CoM needs to be over the gears, also why I stated in the end of my post that some of this would not be possible in KSP

It's a glider.

Well this solves trying to keep it from flipping out under power with little fuel in the system, still doesn't look like it would glide very well lol

[Neutrinovore]

It's interesting reading all of these discussions about the aerodynamics of this vehicle. First, I'll point out that I have absolutely zero education whatsoever in the fields of aeronautics, astronautics, or any other disciplines having to do with aircraft or spacecraft design, other than playing KSP for quite a while, as well as just having a general interest in 'cool looking planes and spaceships' ever since I was a little kid. So, with that being said, and given my level of 'expertise' on this subject, here's my considered opinion:

I do not believe that this vehicle is physically capable of aerodynamic flight.

That's in the real world, mind you. I'm sure you guys will be able to finagle KSP's and Unity's parameters, and take advantage of their many flaws and loopholes regarding physics modeling, to get this thing flying in the game. But if you think about how real aircraft are designed today, and the MANY designs that have been tried because they 'worked on paper' but never came close to working in real life, this concept is just too far out for me to think that it might be plausible.

I'm not talking about the engines, btw. I don't doubt that their design can and will be developed to the point that they'll be capable of generating enough delta-v to get a vehicle weighing about what the Skylon does into LEO, using about as much fuel as the concept is projected to carry. No, my problem is with the wings. They're just too small to me, that's all. Yes, I get that the body itself will be capable of generating some lift... SOME lift. Not enough, though, and those stubby little wings won't be nearly enough to make up the difference, IMO. Also, what wing surfaces there are won't be able to exert nearly enough control authority to allow the ship to rotate for takeoff, or really to have any significant control in any axis to allow controlled flight at all, ESPECIALLY at takeoff when fully loaded with fuel.

Eh, anyway, this doesn't mean that I don't think that a future version of this design can and will fly, but I'm sure that the final flight-worthy craft will have MUCH larger wings, and while it may be able to take off like an airplane, I still think it may require some sort of supplementary booster system to get it off the ground and up to a reasonable altitude before dropping that 'stage' and heading to orbit on its own engines and fuel supply.

Anyway, these are just my opinions, and they're worth every penny you paid to read them.

One more 'however', however. Even if I don't think this could fly in real life in its current form, I am very much looking forward to flying this in-game, so I certainly encourage continued work, it's really looking fantastic! Keep up the great work, Captain!

[CaptainKipard]

I've made some of the changes suggested and progress has been made.

Re: Gliding.

I have to make some compromises for the sake of gameplay. Most people will not be able to glide a spaceplane to the runway. I'll need to make the approach powered.

Re: Fuel flow

The official animations seem to show fuel and oxygen being pumped equally from all tanks.

Re: Mass/Thrust/Lift balancing

White Owl if you want to be more involved you might as well wait until I configure the parts for the new resources at which point I'll give you the mod in the state that it's in for experiments.

I managed to find a very detailed breakdown of masses of the real Skylon components, which should help get things going in the right direction.

Re: Wings

Their size is mitigated by a high angle of attack during ascent, like in the explanation I posted on the second page.

Also IIRC, high speeds increase effectiveness of wings and control surfaces, and Skylon is meant to reach Mach 5.5 in air-breathing mode alone.

Honestly let's forgo speculating on this. People much wiser and more intelligent then you and me have designed this.

Edited November 14, 2014 by Cpt. Kipard

[Akira_R]

It doesn't look super air worthy does it, I think it could theoretically fly, given what was said that it's take off speed is 0.5 mach and with a nice high angle of attack the body and the wings I think would be producing enough lift to get into the air, however they would also be producing a significant amount of drag. This is where the engines come in, given any kind of normal engine this thing wouldn't be able to push through the drag at the AoA it would need to produce sufficient lift, but with those engines I could see it being able to.

As far as control surfaces those front canards would have a significant amount of torque at least for pitch, and the thing would be horrendously unstable, but that is where the magic of modern computer systems and fly by wire comes in and makes it so this thing could be wrestled into orbit given a sophisticated enough flight control system. It wouldn't be able to pull off any kind of controlled areal maneuvers, I suspect it would very much be a get the thing pointed upwards and just GO kind of flight, any kind of turning would be very very slow.

[blowfish]

Runway length might partially explain the takeoff issues - IIRC the KSC runway is only 2.5km long.

[Haze-Zero]

One of the things I tend to do in testing my space-plane designs in KSP, is to use hack gravity and get the plane in the air and off the runway, usually using RCS to lift it straight up about 50-100 meters or so. I also have typically turned on SAS by this time as well. I then turn on my engines and get the thing going to a speed I suspect would allow it to sustain some lift once I turn off hack gravity. Turn off hack gravity and see how my space-plane performs in the air in flight.

If it does well, then that tells me that my issues with getting the thing off the ground concern the landing-gear and such.

If it does not do well in flight, I now atleast know, usually by looking at the yaw-pitch-roll indicators that 'my nose wants to pitch down for whatever reason', or that my space-plane is too heavy and I need more lift or to lighten the load.

Perhaps you can use this trick to see what your Skylon is doing

ALSO, regarding the B9-fix. I did some poking around on google and the forums here. The B9-fix tightened up the values that were being used by B9 landing gear. The B9 landing gear used Firespitter.dll for its landing gear. Unless you are also using the firespitter.dll landing gear code, my suggestion I made earlier would be pointless.

If you are using Firespitter for your landing gear, then you can make the tweaks I mentioned earlier, which someone else in the forum covered already.

All this talk about the Skylon's flight profile and its aerodynamics makes me REALLY wish that someone would develop a mod that showed (stock) CoL, CoM, and CoT in flight, outside of the VAB/SPH. I have wished for it before, but I feel that here, such a mod would prove to be very insightful.

Edited November 14, 2014 by Haze-Zero
spelling

[montyben101]

I don't mind a powered landing but PLEASE don't add an extra engine to the plane just for this. An unpowered glide is quite easy as long as you get the right reenty.

[CaptainKipard]

I don't need to, I'll just make sure there's some fuel left over.

[Virtualgenius]

So looking forward to flying this

[CaptainKipard]

Me too. I've completely stopped playing KSP a long time ago, and I really don't want to start again, until I can use this

============

I'm trying to configure hydrogen and oxygen consumption for the engines, and all I can think of is molar ratios. Should it be 1 unit of hydrogen to 16 units of oxygen?

[MightyDarkStar]

I'll be taking early preorders Captain. *Salute*!

[CaptainKipard]

- Is it a bird?

- Is it Superman?

- It looks nothing like a person! Honestly, who would confuse those two?

- No, it's a Skylon!

Some rough balancing work has been successful. Thanks to the fact that I worked off of official blueprints, the COM, COL and Thrust vector are all pretty much exactly where they should be. A small gimballing range on the engines can take care of any small discrepancies. I'm still trying to figure out how to make the engines use the correct amount of fuel and oxygen, so if anyone has any experience with this then let me know. Once that is done I can finally start experimenting with taking the thing into orbit with various amounts of fuel and oxygen and payloads.

Actually this turned out to be a lot simpler than I thought. This ladies and gents is why you should always plan ahead and use blueprints

Still on the to-do list (in order):

• Configure both engine resource consumption
  
• Configure both engine heat generation
  
• Configure precooler to be functional
  
• Configure intake animations
  
• Set up the cargo bay for payloads
  
• Send the thing to those modders who want to test it privately.
  
• Configure the parts for FAR and DRE
  
• Test again with FAR and DRE (hopefully with help from other modders)
  
• Finish the texture
  
• Release.
  
• Create the Skylon Personnel and Logistics Module as the first addon for this mod
  

[White Owl]

WOO!

Not sure how to get the most accurate fuel/intake air/LOX ratios for both engine modes, though.

But I'm real happy it flies.

[MightyDarkStar]

Looks like my pre-order is paying off!!

[Guest]

Since you've got the blueprints, will you be adding a full-scale version for RSS?

[CaptainKipard]

I'm torn on this idea. I'd love to get into RSS myself at some point (then I'd have to do it), but it seems like too much of a hassle, and if I'm right it's a little limiting in terms of what mods you can use.

Until I start playing with RSS though I don't really fancy making that effort. I'm sorry, someone else will have to do it buuuut if they do I'll gladly include the config in the release.

It's just scaling isn't it?

Edited November 16, 2014 by Cpt. Kipard

[Reddragon]

I'm torn on this idea. I'd love to get into RSS myself at some point (then I'd have to do it), but it seems like too much of a hassle, and if I'm right it's a little limiting in terms of what mods you can use.

Until I start playing with RSS though I don't really fancy making that effort. I'm sorry, someone else will have to do it buuuut if they do I'll gladly include the config in the release.

It's just scaling isn't it?

I think it's mostly just balancing for the proper in-game delta V results. At least for rockets, it pretty much is. Maybe resizing parts to be more compatible with RO.

[White Owl]

Concerning engine resource balancing, I recall one of the old SABRE mod engines... maybe as long ago as two years, I think? Anyway, instead of directly using intake air with the fuel, that one was configured to convert intake air into oxidizer. And that's actually closer to how the real SABRE works, if we consider oxidizer to be liquid oxygen.

That change would simplify the problem in one way, since you'd need only one ratio of H2 to O2, whether in atmosphere or vacuum. But also adds the complication of adding the intake air conversion. I suppose it would simplify changing engine modes too; as soon as you climb high enough that intake air can't keep up with the demand for LOX, then it would automatically start consuming LOX from the internal tanks, so just close the intakes and go to max throttle for the climb.

[CaptainKipard]

There's a small problem with proportions that I've described here. The numbers for stock vs real resources just don't match up, and stock jet engines seem to get an awful lot oxygen out of the atmosphere.

edit

I might have to make this mod only compatible with Real Fuels.

Edited November 16, 2014 by Cpt. Kipard

[Guest]

It's just scaling isn't it?

Well... it depends. You'd also have to adjust fuel loads and mass. In particular, since you've got the blueprints, you could likely find just how much LH2, LOX and other fuels are loaded into Skylon, and where they are placed. Also, mass of every segment would have to match real life one. You're doing FAR and DRE configs anyway, so they're not a problem (you'd just have to rescale FAR values). I also recommend you take a look at the Advanced Jet Engine mod. With that, you'd have pretty much everything. Maybe add a RemoteTech2 antenna and MechJeb, as they're also applied by RO. Realism Overhaul also rescales electric charge reserves, but it's just a minor change.

[Val]

All the parts are now in the game. The next task is configuring eeeeeverything. Here are some current troubles I'm having. They are all related. I'm configuring it for stock aerodynamics first.

1. I managed to get the plane flying once, however as soon as I added a proportional amount of fuel and oxidiser (based on the values and dimensions of the largest tank in the game) The joints again started to wobble and/or slouch a bit, and the plane would not take off. The wobbling gear also makes the aircraft swerve a bit during acceleration.

2. The deflectionLiftCoeff values are all based on Spaceplane+ values, scaled up according to surface area. Not enough to lift the plane.

3. The engine thrust values are already buffed by 1.5 (from their real-world values), and I'm only reaching about 140m/s by the end of the runway in rocket mode. The actual Skylon takeoff speed is 0.5 Mach (171.5 m/s) in air-breathing mode.

4. The engines in air-breathing mode are being starved of IntakeAir after only a second or two of functioning.

This is truly an awesome looking project. Great work Cpt. Kipard.

I only recently discovered the Skylon while reading about SSTO on wikipedia and decided to try recreate it in KSP. I have no modding skills what-so-ever, so I used mod parts from various packs. Mainly B9, KW Rocketry, RetroFuture and Hangar. It's been a lot of trial and mostly error. My version isn't quite as close to scale as yours, though. Made my fuselage using 3.75m parts (couldn't find a 5m cargo bay to my liking), but probably longer. It's length is roughly equal to 8 of the B9 HL 8m Cargo bays.

The reason for this post is, that I recognize some of the flight problems you describe, with take-off speeds and mystery forces inducing yaw and roll, during ascent and re-entry. I still have these problems, but I managed to fly anyway. And I wanted to share these pictures as a fellow Skylon enthusiast.

http://imgur.com/a/qwhvi

[CaptainKipard]

I've seen several Skylons in The Spacecraft Exchange. Do a search for them out if you haven't already.

The reason for this post is, that I recognize some of the flight problems you describe, with take-off speeds and mystery forces inducing yaw and roll, during ascent and re-entry.

I'm pretty sure your problems are different from mine. Mine were caused by badly oriented meshes in the first place. Because you're working with existing parts then the only thing that could cause what you're describing is either an unbalanced design, or careless flying. You can try RCS Build Aid, to help you balance your craft. Also I can't be sure but it's possible that because yours is so long and made up of many cargo bays, that it's causing wobbling which in turn moves your wings and control surfaces in unwanted ways.

[Val]

I've seen several Skylons in The Spacecraft Exchange. Do a search for them out if you haven't already.

Thanks, I've seen them, but they were not of the scale I wanted.

I'm pretty sure your problems are different from mine. Mine were caused by badly oriented meshes in the first place. Because you're working with existing parts then the only thing that could cause what you're describing is either an unbalanced design, or careless flying. You can try RCS Build Aid, to help you balance your craft. Also I can't be sure but it's possible that because yours is so long and made up of many cargo bays, that it's causing wobbling which in turn moves your wings and control surfaces in unwanted ways.

Yeah, sorry, my bad. I didn't actually mean to imply that they were caused by the same things. Just thought it curious that I'd had seen the same symptoms, even if it was caused by something different.

And you're probably right about the size causing the yaw and pitch problems. I've had to use a lot of struts to keep it from buckling and breaking in flight. Probably didn't do a good enough job.

That's all from me. Sorry, for the derail.

[CaptainKipard]

I got the plane to a useable-ish state, and I thought that because all the remaining to-do items wont impact development much or at all, I would release it to some closed alpha testing.

This isn't for fun, remember. It is meant to get feedback on tweaking all the settings in Unity and configs and trying various cargo loads and flight profiles. I don't remember who expressed an interest so report in again if you don't mind.

You'll need the Community Resource Pack and just the Interstellar.dll from KSP Interstellar and just the KineTechAnimation.dll from B9. These first tests are for stock mainly, so no DRE, FAR or anything else that would have an effect on the craft.

Edited November 21, 2014 by Cpt. Kipard