X-Axis swapped by Default? (Spaceplane)

[Th3F3aR]

Hi there,

i tried to design SSTOs and failed on circularization or even takeoff, somehow i don't manage to get an adequate dV or thrust for my planes.

I started off with normal planes which are quite good working but now i thought about taking the next step for satellite deployment and shove it into a SSTO.

The problem is that the ones i got up most times failed to circularize or the ones not able to take-off, yeah .... crash

I assumed having not enough Thrust to lift but with 4 RAPIER Engines and 2 LV-N I think i got enough power to lift a 15 to 30 Ton plane.

Therefore i checked my Elevons on the Mainwings and saw that on pressing W (up) they went up instead of down, which basically means they are inverted?

Also plonking them at angled wings is a pain and i don't understand how to do this right. My wings are not angled, maybe thats the problem?

My question is this correct or did i mount them wrong? Or is my Liftproblem caused by not enough control surfaces, i usually use wings and elevons with one or 2 main ruders on the end of the plane trying to keep the liftmarker slightly behind the mass.

Might it be the fact that the Liftmarker sometimes is above the mass ?

Thanks for intel.

(Can not post a screenie, at work :/ )

[Laie]

My question is this correct or did i mount them wrong? Or is my Liftproblem caused by not enough control surfaces, i usually use wings and elevons with one or 2 main ruders on the end of the plane trying to keep the liftmarker slightly behind the mass.

Control surfaces are reasonably smart: they will move into the right direction depending on where they are in relation to your center of mass. Elevons near the rear of your plane will need to push the tail down in order to bring the nose up.

I started off with normal planes which are quite good working but now i thought about taking the next step for satellite deployment and shove it into a SSTO.

Your plane should have a TWR > 1 from the get-go (1). That means it must be possible to make a vertical take-off. If that won't work, you don't have enough thrust. (Rolling start is usually better -- vertical take-off is only testing your TWR.) Other than that, standard airplane rules apply. We'll need a screeny before we can talk aerodynamics, though.

A good spaceplane can almost make orbit on Jets alone, apo-/periapsis of 80/20km is common. A short squirt from a tiny rocket motor will suffice to make a stable orbit -- OK, so you're impatient and want to use the rockets earlier, in order to get there in less than twenty minutes. You will still only need perhaps 500m/s worth of rocket power in order to make orbit. There's no point in bringing the heavy LV-Ns unless you want to go (at least) to the Mun and back. If your plane is so lightweight that it can take off on four Rapiers, you *definitely* shouldn't bring more than one nuclear engine.

There's also no point in using Rapiers if you're carrying dedicated rocket motors. I suggest you rebuild your plane with four Turbojets and two 48-7s (2); the turbojets have more power (even more so at speeds >2000m/s), and you can keep them running in parallel to the rockets. With shutting down one pair of jets and throttling down the other, you can milk the jets for some extra thrust up to 40km or higher, even while the rockets are already running.

It's absolutely mandatory that you can take the 30km barrier, though. If your jets allow sustained flight at 30km, that means you're going ~2000m/s, which happens to be almost escape velocity -- enough for a 80/-30km orbit, at any rate. And the higher you get, the less thrust is necessary to maintain that speed. If you can fly at 30km, you can also escape the atmosphere on jets alone.

A plane that "only" makes 1600m/s at 26km can still be brought to orbit with comparatively little rocket power, of course; but you'll need more powerful rockets and the fuel to drive them. If you can do that, you should definitely try to ditch most of the rockets and fuel -- this will save a lot of weight, and with the craft being lighter you may well find that you no longer need them.

(1) TWR > 1 isn't strictly necessary, but as long as you're still struggling to make space at all, I strongly suggest you stay above that threshold.

(2) a single 48-7 would suffice, actually. But from the description of your craft, you need two rocket motors for symmetry.

Edited October 27, 2014 by Laie

[KerikBalm]

Therefore i checked my Elevons on the Mainwings and saw that on pressing W (up) they went up instead of down, which basically means they are inverted?

W is not up, it is the same as pushing forward on a joystick, which pitches down.

[The_Rocketeer]

The problem is that the ones i got up most times failed to circularize or the ones not able to take-off, yeah .... crash

...

Therefore i checked my Elevons on the Mainwings and saw that on pressing W (up) they went up instead of down, which basically means they are inverted?

...

My question is this correct or did i mount them wrong?

...

Might it be the fact that the Liftmarker sometimes is above the mass ?

What you're perceiving as an elevon issue is probably unrelated to your inability to circularise an orbit, but it could have something to do with why you're not getting off the ground. However, if you're wasting a lot of fuel in reaching orbit altitude due to an inefficient design, that could still be related.

y-axis inversion is a question of personal preference. In your typical plane, pressing forwards on the control column (joystick) - your W key - would cause the aircraft to descend. However, in microlights, and some other light aircraft that use a yoke to steer, pressing forward causes the aircraft to climb. Either is a legitimate way to organise your control keys, but most people find one way naturally intuitive and the other simply confusing.

Therefore, in terms of what your elevons do when you press W, it firstly depends on which way around you normally expect or prefer your keys to work, especially if you've changed any keybinds. I have a feeling that you might be able to tweak their steering direction in the VAB/SPH but I rarely do this.

Secondly, it also depends on where the elevons are located in relation to the CoM (assuming a profile view). A surface that tips downwards at the back of the plane - behind the CoM - would cause the tail to rise, and the plane to descend. The same movement at the front of the plane - in front of the CoM - would cause the nose to rise, and the plane would climb. Also, if the control surfaces are close to the CoM, they'll have little or no effect on pitch, but they might perform as airbrakes.

The "liftmarker", or CoL, being above the CoM shouldn't affect the plane's flight characteristics too much as long as it's still in the right kind of place behind the CoM.

A few pictures of your aircraft would definitely help get to the bottom the problem if this doesn't help.

Edited October 27, 2014 by The_Rocketeer

[KerikBalm]

However, in microlights, and some other light aircraft that use a yoke to steer, pressing forward causes the aircraft to climb. Either is a legitimate way to organise your control keys, but most people find one way naturally intuitive and the other simply confusing.

I have *NEVER* heard of a plane where the controls are configured such that pushing forward causes the nose to pitch up, ad I would very much like to see evidence for that.

It simply boggles the mind that someone would make a plane with controls that go agaisnt the instinct of 99.999% of pilots everywhere.

The only case I can think of that is remotely similar to what you describe, are weightshift controlled aircraft, ie a hangglider/Trike, where the control frame is pushed forward relative to the pilot (but really, its pushing the pilot or pilot+ trike backward, shifting weight backwards).

If its anything else, I think the designer should be shot.

[The_Rocketeer]

I have *NEVER* heard of a plane where the controls are configured such that pushing forward causes the nose to pitch up, ad I would very much like to see evidence for that.

It simply boggles the mind that someone would make a plane with controls that go agaisnt the instinct of 99.999% of pilots everywhere.

The only case I can think of that is remotely similar to what you describe, are weightshift controlled aircraft, ie a hangglider/Trike, where the control frame is pushed forward relative to the pilot (but really, its pushing the pilot or pilot+ trike backward, shifting weight backwards).

If its anything else, I think the designer should be shot.

This is what I had in mind. It's essentially as you say, changing the relationship between the aerofoils and the mass, but then it could be argued that that's what all control surfaces do.

I've found that my friends who grew up on a diet of FPS games struggle with W pitching down and S up. As I said, it's a question of preference - as are all keybinds, really!

Edit: Google Image Search "Microlight" and you'll see this is a pretty common control arrangement.

[GoSlash27]

In my experience, control surfaces are pretty dumb. They react to their rotational alignment and whatever control inputs are enabled, but won't reverse themselves or operate proportionally based on where they're placed on the longitudinal axis.

I place any elevators or ailerons behind the COM and canards ahead.

We really need an official test of this...

Best,

-Slashy

[The_Rocketeer]

I place any elevators or ailerons behind the COM and canards ahead.

Ailerons don't need to be in front or behind the CoM, as long as they're spaced wide enough apart. Elevators OR Canards are a must.

See this neat article.

[GoSlash27]

Ailerons don't need to be in front or behind the CoM, as long as they're spaced wide enough apart. Elevators OR Canards are a must.

See this neat article.

Apologies, I mean using a KSP "aileron" part as an elevator/ canard. In my experience, placing it ahead of the CoM will not make it reverse it's direction and start acting like a canard.

Likewise, placing a canard in back will not make it act like an elevator.

Best,

-Slashy

[Laie]

Apologies, I mean using a KSP "aileron" part as an elevator/ canard. In my experience, placing it ahead of the CoM will not make it reverse it's direction and start acting like a canard.

Likewise, placing a canard in back will not make it act like an elevator.

Just fired up KSP and made a testing rig. Took me three minutes. AV-R8 winglet, standard canard, and wing-with-elevon: all three honor their position relative to the CoM. I won't take the time to make and post screenshots, though -- I'm at work after all.

[KerikBalm]

This is what I had in mind.

That is not a yolk, that is fundamentally different. I know of this form of control input quite well.

^that is me.

It's essentially as you say, changing the relationship between the aerofoils and the mass, but then it could be argued that that's what all control surfaces do.

Well, there are control surfaces, and there are controls. FWIW, hanggliders(excepting rigidwings) and trikes have no control surfaces.

With control surfaces, you move the center of lift, with weightshift, you move the center of mass (although in a flex wing hangglider, shifting the weight does noticably warp the wing, soch that roll inputs are much more effective)

Edit: Google Image Search "Microlight" and you'll see this is a pretty common control arrangement.

That is not a flight yolk or a joystick - that is the control frame, two downtubes and a basetube.

I know of no 3axis control aircraft that allows you to push forward and have that pitch up.

Basically, if it controls control surfaces, pushing forward makes it pitch down.

If you are just shifting weight, shifting the weight forward makes it pitch down.

[Wanderfound]

Just fired up KSP and made a testing rig. Took me three minutes. AV-R8 winglet, standard canard, and wing-with-elevon: all three honor their position relative to the CoM. I won't take the time to make and post screenshots, though -- I'm at work after all.

Same here. I routinely use AV-R8's and Standard Canards as tailplane elevators. No problems at all. Ditto for jumbo canards made from wing + control surfaces.

[GoSlash27]

Same here. I routinely use AV-R8's and Standard Canards as tailplane elevators. No problems at all. Ditto for jumbo canards made from wing + control surfaces.

Cool! I stand corrected, then. I'll have to make use of that...

Thanks,

-Slashy

[Dogface]

I had a similar problem. It was that I had multiple control parts. And the wrong one had control. Before you take off, select "control from here" on the part which gives the proper nav-ball orientation.

[The_Rocketeer]

That is not a yolk, that is fundamentally different.

I think you mean yoke. Perhaps more correctly I should have used the term 'control bar'.

Not that I in any way particularly disagree with your post (apart from the spelling ), I'm not sure what the purpose of saying it is. I'm not confused about how a plane is controlled, I'm just trying to help the OP out with his problem, and being as clear as I can about what could be causing it. If he preferred to invert the pitch keybinds (as a number of people I know, albeit a minority, do) that could make a lengthy explanation totally unclear.

Still, kudos to you for knowing your $h*t.

[Higgs]

W is not up, it is the same as pushing forward on a joystick, which pitches down.

The op if i read him right stated that pushing W caused the control surface to pitch up, which is inverted from what irl is.

[The_Rocketeer]

The op if i read him right stated that pushing W caused the control surface to pitch up, which is inverted from what irl is.

Yes if it's an elevator, no if it's a canard.

The difference is related to where the surface is in relation to the CoM. In front = canard, behind = elevator.

What he said was:

i checked my Elevons on the Mainwings and saw that on pressing W (up) they went up instead of down

but without knowing where the CoM is, it's not really possible to say which way they should move.

Edited October 28, 2014 by The_Rocketeer

[Higgs]

The difference is related to where the surface is in relation to the CoM. In front = canard, behind = elevator.

This sounds exceptionally condescending. As an RC pilot i take exception to your phrasing. I am well aware of what control surfaces are. Flaps, ailerons, elevators, rudders, elevons and so on are. I am not sure of your intensions but I am decidedly offended.

reasons:

1. I am a pilot, even if only RC with real stick time on a Cessna 182.

2. I pointed out that the op stated how his control surfaces reacted to HIS inputs and you then make a condescending remark to me.

[GoSlash27]

This sounds exceptionally condescending. As an RC pilot i take exception to your phrasing. I am well aware of what control surfaces are. Flaps, ailerons, elevators, rudders, elevons and so on are. I am not sure of your intensions but I am decidedly offended.

reasons:

1. I am a pilot, even if only RC with real stick time on a Cessna 182.

2. I pointed out that the op stated how his control surfaces reacted to HIS inputs and you then make a condescending remark to me.

Honestly, this is probably just a misunderstanding. Text doesn't convey emotion and it's really easy to confuse the intent behind the words.

When dealing with people who play KSP, I default to "he / she didn't mean anything by it" because this game attracts a certain personality type who strive to be very precise in what they're saying. That precision can come off as condescending, but it's almost never intended to be that way.

Best,

-Slashy

[mdkendall]

...Also plonking them [elevons] at angled wings is a pain and i don't understand how to do this right.

Is the question how to attach control surfaces to wings that are angled, and have the control surfaces be at the correct angle?

The best way I have found to do it is to put the wings on straight, then attach the control surfaces, then pull the wings off (the control surfaces will come with them) and put them back on angled how you want.

[KerikBalm]

I think you mean yoke.

D'oh! I derpted. Technically it is still correct, it is not an egg yolk either

Basically, when it comes down to it, if I rotate the controls one way, I want the aircraft to rotate the same way.

If the control pivot is below where I am holding them, this means that pushing forward should pitch down.

In a hangglider, you hang underneath, and the "pivot" is above you (note that the control frame does not move at all in relation to the aircraft/wing, just your body, in a trike there is your body and some structure - wheels and a mounted engine basically, but I still wouldn't consider that the main aircraft), and thus controls are "reversed" if you think of it as moving the control frame. To roll left, you push the control frame right. Yet... to roll left, you move your body left. Again... its best thought of as moving your body, not the controlframe.

Yes if it's an elevator, no if it's a canard.

The difference is related to where the surface is in relation to the CoM. In front = canard, behind = elevator.

What he said was:

i checked my Elevons on the Mainwings and saw that on pressing W (up) they went up instead of down

but without knowing where the CoM is, it's not really possible to say which way they should move.

True, I simply assumed they were behind the CG. For most designs with a "main wing", the trailing edge of the main wing is behind the CG. Yet there are numerous possible designs where this is not the case - although it depends what you call a "main wing" (is a wing providing only 51% of the lift still a main wing?).

It does depend on his specific craft, and it was probably premature to think that he simply wanted his controls to be inverted.

*edit* ah, reading it again, its again clear to me (as it was when I first responded), that he does want inverted controls.

He stated:

"...and saw that on pressing W (up) they went..."

W is not "up" for standard controls.

It is working as intended.

Edited October 28, 2014 by KerikBalm

[The_Rocketeer]

I am not sure of your intensions but I am decidedly offended.

reasons:

1. I am a pilot, even if only RC with real stick time on a Cessna 182.

2. I pointed out that the op stated how his control surfaces reacted to HIS inputs and you then make a condescending remark to me.

I'm very sorry if you're offended, there was certainly no malicious or scathing intent. I was simply trying to keep a line of clarity between actual input and expected output. The OP may be less experienced than you when it comes to control surfaces. As it happens, I'm not a pilot, tho I have flown RC and spent a lot of time in Flight Sims. I do, however, know a thing or two about the theory of flight - a personal hobby.

Honestly, this is probably just a misunderstanding. Text doesn't convey emotion and it's really easy to confuse the intent behind the words.

When dealing with people who play KSP, I default to "he / she didn't mean anything by it" because this game attracts a certain personality type who strive to be very precise in what they're saying. That precision can come off as condescending, but it's almost never intended to be that way.

Nailed it. +Rep

*edit* ah, reading it again, its again clear to me (as it was when I first responded), that he does want inverted controls.

He stated:

"...and saw that on pressing W (up) they went..."

W is not "up" for standard controls.

It is working as intended.

Yes, this exact phrase is probably what started me off on clearing up expected outputs. If the OP's instinctive expectations are for W to go up, then the obvious solution is to reverse the keybinds rather than learn to write left-handed (if you see what I mean).

[DeathSabre]

Your problem might have to do with not enough lift for your weight.

More often I've found that landing gear are at fault with not being able to lift off.

Your rear landing gear should ideally be in front of your rear Elevons/control surfaces. that way your rear elevons can 'lever' the front up. if they are behind your rear gear they actually wind up pushing your nose down. Assuming you are using stock aerodynamics(not sure about near or far haven't played enough with them), you can think of your Elevons as pushing straight down/up depending on their position relative to center of mass and the direction arrows you are pressing. as stated above they should automatically switch direction based on their relationship to center of mass.

Control surfaces can also help at the front to Pick your nose up.

another trick would be to use part tweaking to empty all your tanks in your SSTO that way you can see where your COM and COL are expected to be when you re-enter after burning all your fuel.

Building an SSTO that can carry any significant weight into Orbit is difficult. if you are running out of fuel you need to look at ways to make it more efficient. e.g.(Carry less RCS feul if you don't need it, tweak your fuel balance so you don't end up with excess Oxidizer or Excess Liquid Fuel, or add more Intakes so you can get higher and faster before engaging your rockets)

Scott Manley has a lot of videos with SSTO's and he explains a lot of the techniques I've discussed here. if you have the time maybe check out some of his video's.

Fly Safe.

[Th3F3aR]

Sorry for the late response and the confusion i made by my W (up) sentence.

The screenies are here

when i push W the elevons go down by the way, that is as i knw it incorrect, and also according to your responses the wrong way

Hope you find the error on my bad design ^^