Am I just a bad pilot? (Noob spaceplane help)

[goldenpsp]

Hey gang. I'm still pretty new to KSP. Although I have gotten quite good at getting on and off the Mun and Minmus, docking etc.

I totally suck at planes however. I'm not sure if it is my build or piloting skill.

I have had a little success with some early planes that just flew within Kerbin's atmo.

But I came across this post and I was intrigued by the simple "rescue SSTO" design. So I tried to replicate it based of the picture and video. I am pretty sure I got it right, albeit unsure if I have the balance setup correctly. I can fly it into orbit using a similar amount of fuel and so forth.

What gets me every time is this. I can take off, orbit, de-orbit, and come into sight of the runway fine.

Then, while going maybe around 180 m/s I will run into the following.

"I'm coming in a little high" ever so slightly nose down, BAM spin out

"I'm a little to the left/right" ever so slightly bank and BAM spin out.

Its getting highly annoying to be able to go up, orbit and come back only to splatter in the last few minutes.

I thought maybe the burning of the fuel was messing up the COM, but I have tested just by taking off, circling around and trying to land again.

Any hint/tips etc would be greatly appreciated. Also let me know if any particular pics/files would help.

Edited July 31, 2014 by goldenpsp

[Hodo]

I couldnt tell you about stock, but you are coming in at half the speed of sound, which is REALLY fast.

But it sounds like your CoM has shifted due to fuel burn.

[tg626]

Off the top of my head you're too close to stall speed.

And when landing its pitch to control attitude, throttle to control decent rate. Its counter intuitive, but that's how it works.

[Wanderfound]

Give us some screenshots (preferably with the resources tab open) of it all going wrong? Are you using FAR or NEAR or stock aero?

Pics (from directly above and directly from the side) of your spaceplane in the SPH with CoM/CoL/CoT indicators would also be helpful, especially if you do one set with tanks full and one set with tanks empty.

The spaceplane in that video does look like it might tend to the unstable side, though; it's hard to get your balance right with such a short fuselage. If you'd like, I'll design you an SSTO spaceplane that's relatively easy to fly. A properly built ship shouldn't spin unless you deliberately provoke it to.

[Wanderfound]

Off the top of my head you're too close to stall speed.

If it's stalling at 180m/s, there's something seriously wrong with the design. Typical landing speeds are closer to 100m/s.

[goldenpsp]

It may be close to stall speed.

And to be fair in the video he does a nice spin out at about the same place I do.

I do get the concept TG626, I fly alot in both simulation and R/C. In this case I couldn't really slow down any further so I was trying different things, namely to dive down a little to gain speed at the same time. bottom line is it flies fine if i don't touch anything

Wander, I appreciate the offer. While I am new and mildly annoyed at the moment, I'd still rather muddle through and learn through trial and error.

[Wanderfound]

Wander, I appreciate the offer. While I am new and mildly annoyed at the moment, I'd still rather muddle through and learn through trial and error.

I admire your dedication.

Here's a pretty screenshot for design inspiration:

[Taki117]

The big thing with landing in KSP is to be sure to flare. (you being a familiar pilot means I don't have to go over this maneuver) Flying Stock KSP Is like flying in soup, since you are used to simulators might I suggest Getting FAR to help with the aerodynamics. Also, while copying a design is a good place to start, it is not the best way to learn. So I point you to this wonderful aircraft building guide. (With pictures)

[O-Doc]

Most likely what's happened is that you've burnt all your fuel and now your center of mass is behind your center of lift. Or, they're on top of each other. There's an interesting bug/feature I've noticed with the aerodynamics that change dramatically in the lowest 100m of altitude that makes some of my craft flip when making very aggressive turns at high speed. I've tested this extensively and it is now something I avoid close to the ground. The best solution is to get a good line on the runway and turn caps lock on so your ""keyboard" turns are not pushing your stick to the max. Also, 180m/s for landing is way too fast. You will be giving yourself every opportunity to disassemble your landing gear at those kind of speeds. It's best to throttle down or cut entirely your engines and flare before landing. My rule of thumb is under 70m/s surface speed and under 5m/s vertical speed.

[LethalDose]

I totally suck at planes however. I'm not sure if it is my build or piloting skill.

Honestly, it's probably both.

And that's okay.

Pretty much everyone is bad at building and flying aircraft in KSP when they start. Because of this, I'd recommend not starting your foray into the wonderful world of KSP aircraft with SSTOs. You're much better off building some small (REALLY small, like < 30 part) aircraft, and then practice landing them from different altitudes and speeds. This'll teach you design basics and get you comfortable with flight and landing. If you're good enough to land the little guys reliably, you should be able to land the SSTOs too.

Also let me know if any particular pics/files would help.

They help. Also (as noted above), we really need to know if you're using FAR/NEAR/Stock aero.

Onto the original problem: You say you're "spinning". Is that spinning around like a top (yaw) or is it spinning around the long axis of the plane (roll). I'm going to assume it's not a problem with "pitch" because you would probably describe that as a "flip" not a "spin", but I could be wrong. Also, 180 m/s sounds like a pretty high stall speed (but I play with FAR, it may be different is stock). All of these have different solutions.

If the problem is yawing, aka a "flat spin", then I think the solution is probably "moar rudder". Larger rudders, multiple rudders, and moving the rudder as far behind the CoM as possible.

If the problem is rolling, the issue is probably stability. High wings and dihedral wings can help with that problem by allowing your CoM to rest below your CoL. These are addressed in the aircraft tutorial, which was also linked by Taki117 above. It's awesome.

For either, you can try adding SAS to improve control. It's... really a band-aid, and if one advance SAS unit isn't enough, more probably won't help (it's either a fundamental design issue or bad piloting). But it's still something you can try.

Another thing that may help is limiting the control surface inputs. Set your rudder to only respond to yaw, ailerons to only respond to roll, and elevators/canards to only respond to pitch. This is just tends to be good advice, regardless of the situation, but in your case, you may be getting some unwanted control surface action which is causing your spin.

EDIT: Thinking about how you're describing the problem, I gotta wonder if you're using a "low-wing" design, like the space shuttle. Just a thought...

Edited July 31, 2014 by LethalDose

[goldenpsp]

Lethal,

Stock KSP.

The plane is a replica from the post i linked in the OP.

In this video of the same plane

At about 3:55 he spins out. Its pretty much identical to what I have encountered. In fact it happens about the same distance from the runway as well.

Keep in mind this isn't while actually landing. I'm usually still about 8000m up, going around 180-200m/s and still a good ways from the KSC. Like just after coming over the mountains if you were approaching from the west.

I have built several non-space planes just to tool around and have had far better success. I'm guessing this plane design is fairly squirrelly to begin with.

[Wanderfound]

Yeah; thats a dodgy plane. Nothing should be flipping at those speeds and altitudes.

Try to make something that looks a bit more like a real-world plane. They look like they do for a reason.

[Tarmenius]

... it flies fine if i don't touch anything.

One look at the aircraft plus this comment, and it seems to me that the canards are the culprit here. On such a light craft with low fuel, they will easily wreak havoc with a plane's stability. I'd bet a lot of Funds that replacing the Winglets with Tailfins will resolve the control issues, assuming that the CoM and CoL are then properly arranged.

[Shisouka]

It may also help to install TAC Fuel Balancer (it works in 0.24.2) and setup planes to auto-balance fuels so your plane's CoM doesnt shift.

[BudgetHedgehog]

It omay also help to install TAC Fuel Balancer (it works in 0.24.2) and setup planes to auto-balance fuels so your plane's CoM doesnt shift.

TACFB makes all tanks drain equally. This may or may not move the CoM depending on the planes design. However, PWB Fuel Balancer is the mod that holds the CoM in place, get that instead (or as well as).

[Wanderfound]

Or, alternatively: design your plane properly. Arrange your tanks and fuel lines right and the CoM will stay fairly stable no matter what stage of the flight you're at.

[O-Doc]

Plane and simple, that craft has more control surface lift in front of the CoM than behind it. That will almost always spin out on re-entry. Those wings need to be moved back and the small winglets need to be replaced with full size control surfaces or a group of three winglets on each wing. Once your control surfaces move your CoL moves according the lift generated from each control surface. When designing a plane you should make sure the CoL and CoM relationship is good before adding control surfaces.

[goldenpsp]

Everyone.

Thanks for your input. I did some additional playing around with the plane last night. But it was too late to respond until I got some sleep. Overall I agree with most that it is just an unstable design.

1. I'm gonna go more with "It's the plane" than "It's the pilot". I have built some other test planes that flew much better.

2. The short fuselage makes it very difficult to get it properly balanced. Even then you end up with a situation where your COM and COL are pretty close to each other.

3. The control surfaces up front make it overly controllable. For example in other designs I can pull off a hard turn, aka banking hard (70+deg) then pull up the nose. With this setup trying that procedure at any speed causes an uncontrollable tuimble. I replaced the front surfaces with smaller non-moving winglets it was more controllable.

Overall the whole thing was a good exercise. While I have enjoyed and prefer to try and figure out designs on my own, trying to copy someone's helped a bit vs starting from scratch. By utilzing the design and technique from the video I gained tons of understanding about getting a spaceplane into orbit (not just point up like a rocket) Rather than completely trying to figure out what it takes to get a plane out of the atmosphere I started with something that can. From there I am now working on something easier for me to fly as well.

[LethalDose]

For what it's worth, I think the biggest issue was the planes very short long axis (axis along which the plane flies). Early on, I tried building some "flying wing" SSTOs, somewhat similar to what you have here. I think the goals were similar: Lots of lift, low mass, and a wide aft section for easy engine placement. Overall, I found they had horrid pitch authority because control surfaces simply couldn't be distant from the CoM. WHile they look cool, the benefits of the design don't outweigh the problems.

I watched the video, but the video is so fast I can't tell what happened just prior to the flip, or even in which axis/es rotation occurred. Given it's shape, I assume it was a pitch-tumble, but the player is obviously familiar enough with the craft to recover from it.