Broken vertajet. Something strange is going on.

[Jakalth]

Well, I've been playing with large vtols and found an odd occurance that I can't quite explain... It started off as a 6 engine lifter that I wanted to see how fast I could get it going horizontal and still be able to take off vertically without wings. It turned into one of the strangest things I've encountered that is neither a kraken event or a bug. Something I can't quite explain is going on with the physics here, it works, but I don't quite know how. I would like to figure it out, and I'm sure a few other people would find this oddity useful if it could be predicted. Self stabilizing airship/carriers for example?

What I have here, is a stock auto pilot. One that is induced by a combination of aerodynamic strangeness and thrust.

It starts with this craft on the runway: [URL="http://www./download/3939kj09c6rxs24/vertajet_broken_2.zip"]vertajet broken 2[/URL].
[IMG]http://i1346.photobucket.com/albums/p685/Jakalth/Kerbal%20Space%20Program/brokenvtol1_zpssgd8trba.jpg[/IMG]

The name says it all. It's broken somehow. When the craft is set to take off from the runway, it starts building up speed and the tail takes off first. This puts the craft into a nose down orientation. As it builds more speed, the front also lifts off. With the nose lifted, it starts to level off again and continues to pick up speed. After it has accelerated a bit more, the nose continues to lift, putting it into a nose up orientation. With the nose up like this, it starts to slow down, but climb much quicker. It keeps climbing, slowly nosing down until at around 8,000m it's flying level, and accelerating again. From here on out it hold its self mostly level, with the nose going into a slightly nose down orientation, but pretty much holding direction. The odd part is, it does all this without me ever touching the controls. It does it all on it's own. The maneuvers are all slow and smooth as well, making it even more odd.

What I would like to figure out, is what combination of aerodynamic forces and thrust positioning is allowing the craft to act like it has an auto pilot guiding it too altitude. I started the craft as a simple vtol, then added the extra tail surfaces and angled the engines to give it more forwards thrust. It took me several tries to stop it from simply flipping over on it's back and crashing. now I don't know what combination of things has given this craft the auto pilot like trait to fly to altitude and self level with no player input...

To test this out on your own, follow these simple steps:
1: make sure the brakes are off
2: set the throttle too full
3: turn on SAS
4: stage the engines on
5: This is the most important step!!! [U]Do not touch the controls at all.[/U] Let the craft fly its self to altitude and just watch it do its thing.
6: think for a bit and see if you can decipher what is causing it to act like this. I'm drawing a blank and I've had all day to ponder over it.

This craft has me all confused... But finding out what triggers this to happen would be useful for anyone planning on making a flying base/airship/carrier.

[Guest Space Cowboy]

Look at it from the angle of "what is changing". There is an F key that displays life vectors in realtime. Can't remember which one but I would start by watxhing them and seeing how much lift the fore and aft surfaces are generating, during the various regimes of liftoff.

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Oh SAS is on. You have some serious stabilizers on the aft section those are fighting all the time to keep it level if thats the attitude you engage SAS at, so anytime the vehicle pitches, aerodynamics are overcoming them.

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Oh SAS is on. You have some serious stabilizers on the aft section those are fighting all the time to keep it level if thats the attitude you engage SAS at, so anytime the vehicle pitches, aerodynamics are overcoming them. If you got rid of the wings or places them more equally, I bet there would be less pitching.

[YargJay9991]

That is strange. And could be really useful as well. Have you seen this on other craft? What about different engine configurations? Try adjusting a few things but only one at a time, and see what happens. :)

Here's my scientific look at it. Well, it's basic science anyway.

Looking at your picture, I noticed the horizontal wings are angled such that the leading edge of each wing is tilting up wards. If you look at how control surfaces behave when pitched up for example (when elevators are at both the front and back), the rearward elevator's trailing edge points up (producing less lift) and the frontward elevator's trailing edge points down (producing more lift). The imbalance of lift causes the plane to pitch up.

How does this help you? What I think, is that the horizontal control surfaces on your plane (the wings :P) are both trying to lift their end of the plane. The front is trying to pitch the plane up and the back one is trying to pitch the aircraft down. My theory is that the lift/speed ratio varies through different speeds and altitudes for each type of wing, where maybe at one speed the front wing is producing more lift than required to fly level than the back one is, causing the aircraft to pitch up. Then at a different speed the rear wing is producing more lift, which causes the aircraft to pitch down again. This pitching motion is dampened by the SAS which, at higher speeds, is able to utilize the elevators more effectively meaning it can hold the level altitude.

I know this is a bit of a read, and I don't think I've ever written anything so scientific in my life! (I feel pretty cool now.:cool:) But this analysis is only based on my very basic knowledge of aerodynamics and my clever assumption skills, so someone correct me if I'm completely off track...

I have an idea for a test, so I'll possibly get back to you soon.

[quote name='Space Cowboy']Look at it from the angle of "what is changing". There is an F key that displays life vectors in realtime. Can't remember which one but I would start by watxhing them and seeing how much lift the fore and aft surfaces are generating, during the various regimes of liftoff.

Oh SAS is on. You have some serious stabilizers on the aft section those are fighting all the time to keep it level if thats the attitude you engage SAS at, so anytime the vehicle pitches, aerodynamics are overcoming them. If you got rid of the wings or places them more equally, I bet there would be less pitching.[/QUOTE]


The F key your talking about is F12. And I assume you mean lift vectors as opposed to life vectors? :P

I'm not sure he wants it to not pitch, I think he just wants to know what is happening so it could be used as an aerodynamic autopilot.

Happy Flying
YargJay9991