Is it possible that there's a bug that flips ailerons?

[Mister Kerman]

I made my first jet plane last night. I looked at some tutorials and made a very capable jet for survey contracts that I was very very satisfied with the way it looked and it's functionality.

I flew it without any trouble whatsoever to three points fairly far away on Kerbin, then when heading to the fourth for whatever reason the plane became ridiculously uncontrollable regardless of how high or low I flew. I eventually got the altitude survey transmitted and was on my way back to KSC when I figured out that my ailerons were inverted so I couldn't properly control my pitch.

They worked fine on the runway and more than half the flight, I flamed out at one point trying to fly really high in the lower atmosphere (about 18000 m) then after that the plane was completely uncontrollable. Landing was fairly whiteknuckle. I literally can't believe how smooth it went considering my approach and control situation and oddness of the actual touchdown.

I checked in the Hanger and no matter how I rotate the part the aileron seems permenently inverted. I'm going to rebuild it tonight, but it bugs me that they worked properly when I flew it the first time, then went haywire near the end of the flight making getting back to KSC and landing a nightmare.

I run stock KSP and they were definitely working at the start of the flight. Anyone else have this happen to them?

Edited December 26, 2014 by Mister Kerman

[mrmcp1]

If possible could you upload a picture of the plane in question (with the center of mass and lift indicators). Also if you were to launch the plane again will the ailerons work normally at least on the runway if they do I think the problem could lie with a changing center of mass. I think they if they are in front of the center of mass they will work normally but when you have used up some fuel they may be behind the center of mass so will stop working properly.

I may well be wrong and it could be a bug.

[Mister Kerman]

U R smart. That's probably it. I'll post a picture later today. I'm just starting my work day right now so I won't be at my computer for another 13 hours.

EDIT: I'm just thinking about it a little more and putting the plane on the runway didn't fix the problem. My biggest concern is that the build is bugged now because the plane is uncontrollable on takeoff instead of the way it used to be and the only thing I changed was trying to fix the ailerons.

Edited December 24, 2014 by Mister Kerman

[The_Rocketeer]

This is probably caused by the CoM (centre of mass) shifting as you consume fuel.

Control surfaces pitch one way or another depending on where they are in relation to the CoM - if in front, a 'pull up' control input will cause the aileron to hinge downwards to push the nose up, but if it's behind the CoM the same input will hinge upwards to push the tail down. During flight, if you haven't accounted for the change in mass distribution due to burning fuel, the CoM can move past control surfaces near the centre of the plane and cause them to reverse direction. More seriously, if the CoM moves so far back that it's behind the CoL (centre of lift) the plane will become extremely unstable and much harder to fly.

This is easy enough to check. In the SPH, turn on the markers for CoM and CoL, and look where they are with the tanks full. Then use the RMB to open the tweakable menu for the tanks and empty them - see how the CoM moves in relation to the CoL, and also whether it moves past the surfaces you noticed inverting.

Hope this is a help :-)

Edit: Ninja'd again. I need to learn to type faster.

[Kryxal]

Ailerons ... you lost ROLL stability? Odd...

[The_Rocketeer]

Ailerons ... you lost ROLL stability? Odd...

I had assumed this was just an oversight and the guy meant elevons. To most people ailerons are just any control surface on the wings. Not saying that's right, just saying it is.

[QuesoExplosivo]

I had this bug once, too. I had to take the wings off in the SPH and rebuild them.

[Mister Kerman]

Might mean elevons... Horizontally placed/alligned pitch adjusters on my main wings without using any specific terminology.

[Fizwalker]

Might mean elevons... Horizontally placed/alligned pitch adjusters on my main wings without using any specific terminology.

While the discussion is momentarily sidetracked.... Going through the parts list, it seems the game calls the stock control surfaces that attach to wings/tail surfaces elevons. (BTW, I'm not at my computer, so I cannot double check that until I get back to it in a few days....) I also know a little of, at least older, terminology (which has probably changed.....) but here's the list of what I know.

Aileron: Control surface to control roll around the longitudinal axis.

Elevator: Control surface to control pitch (movement around the lateral axis)

Rudder: Control surface to control movement around the vertical axis (Yaw)

Flaps: Devices to increase drag/lift. Usually to lower stall speeds in order to safely land or take off. Located on the trailing edge of the primary lifting wing.

Spoilers: Devices to disrupt air flow over the wings in order to keep the aircraft on the ground after landing.

Leading Edge Slats: Used to increase lift, and lower stall speeds. Adds increased drag and primarily used during take off and landing.

Combat Flaps: Used over brief periods of time to increase lift in order to turn in a tighter circle. Increases drag and reduces speed.

Modern combat aircraft have control surfaces that combine the function of the surfaces described above. (Notable in delta-winged designs) or the entire wing structure is a control surface (the tail plane of the F-16 comes to mind.) I think they have different names, and I am not familiar with what those are. Please note that the names I know are generally those used in civil aircraft and old (WWII era) combat aircraft.

Hope this is useful, and sorry to derail it for a moment.

[The_Rocketeer]

Modern combat aircraft have control surfaces that combine the function of the surfaces described above. (Notable in delta-winged designs) or the entire wing structure is a control surface (the tail plane of the F-16 comes to mind.) I think they have different names, and I am not familiar with what those are. Please note that the names I know are generally those used in civil aircraft and old (WWII era) combat aircraft.

They are called elevons, canards, and ruddervators and they generally combine a pair of the primary controls (pitch/roll/yaw).

Elevons are combined elevators and ailerons, and are usually located on the trailing edge of a delta wing. The Space Shuttle and Concorde used these, as well as some other delta-wing jets.

Canards perform the same function, but are located in front of the main wing, as in the case of the XB-70 Valkyrie or Eurofighter Typhoon.

Ruddervators combine pitch and yaw control, and generally are located on the tail in a V-shape (sometimes called a V-tail).

Stabilators are tail wings that pivot as one piece to control pitch, like the AV-R8 winglet rather than the Delta-Deluxe Winglet. In this respect they are similar to most canards.

Edited December 24, 2014 by The_Rocketeer
typo

[Fizwalker]

They are called elevons, canards, or stabilators and they generally combine a pair of the primary controls (pitch/roll/yaw).

Elevons are combined elevators and ailerons, and are usually located on the trailing edge of a delta wing. The Space Shuttle and Concorde used these, as well as some other delta-wing jets.

Canards perform the same function, but are located in front of the main wing, as in the case of the XB-70 Valkyrie or Eurofighter Typhoon.

Stabiliators combine pitch and yaw control, and generally are located on the tail.

Thanks! So the tail plane on the F-16 would be stabiliators? (Though I thought the -16 used them to just control pitch....?)

[The_Rocketeer]

Sorry I made a typo last time - the correct spelling is stabilators (not stabiliators).

What I said in my last post is actually wrong. I've now edited the post to correct my derp.

In planes with a rigid tailplane, the whole tail assembly is sometimes called a stabiliser, because it helps to keep the nose pointing forward. It's common to refer to the individual rigid wings as horizontal or vertical stabilisers. Stabilator, though, does specifically refer to the pitch controlling surface rather than others. However, there's no reason that ruddervators and stabilators can't actually be the same thing.

Edit: FWIW, yes the tailplane on a F-16 does use stabilators

Edited December 24, 2014 by The_Rocketeer

[Fizwalker]

Sorry I made a typo last time - the correct spelling is stabilators (not stabiliators).

What I said in my last post is actually wrong. I've now edited the post to correct my derp.

In planes with a rigid tailplane, the whole tail assembly is sometimes called a stabiliser, because it helps to keep the nose pointing forward. It's common to refer to the individual rigid wings as horizontal or vertical stabilisers. Stabilator, though, does specifically refer to the pitch controlling surface rather than others. However, there's no reason that ruddervators and stabilators can't actually be the same thing.

Edit: FWIW, yes the tailplane on a F-16 does use stabilators

I know just enough to be dangerous to my poor....Errr... BRAVE and HIGHLY trained Kerbals.... Who, um... Never die because their planes land and spontaneously disassemble themselves in uncontrolled thermal events *Cough* >.>

[The_Rocketeer]

I know just enough to be dangerous to my poor....Errr... BRAVE and HIGHLY trained Kerbals.... Who, um... Never die because their planes land and spontaneously disassemble themselves in uncontrolled thermal events *Cough* >.>

Lol, I too am an enthusiastic amateur more than a real physicist, aircraft designer or top boffin of any description. Still, it's fun to pretend...

[Mister Kerman]

I'm done with work for now. Got to get back to camp then I'll post pictures of my plane. It's my first one, but it feels like the build is bugged now since it was working for a good long time, then became virtually unusable when the wing's (I'm gonna call them: ) "horizontally positioned pitch and roll controlling control surfaces" became inverted for whatever reason mid-flight. Now I can't even edit the build and position the part in a way that the game will let it perform as it did originally.

EDIT Here's the Screen shots of my plane in the hanger.

Keep in mind it flew perfectly for a long time. The "horizontally positioned pitch and roll controlling control surfaces" did work in this configuration the way I wanted them to. Then mid flight inverted themselves somehow.

DOUBLE EDIT: I just rebuilt the same plane from scratch and the "horizontally positioned pitch and roll controlling control surfaces" work perfectly again so I donno. It must have been some sort of bug. I'll update if it happens again!

Edited December 25, 2014 by Mister Kerman

[Mister Kerman]

Allright sorry for the double post. I think my center of mass is moving too far backward when all the fuel is in the rear tanks (Due to my flow design) my plane can't decide what it'd like those "horizontally positioned pitch and roll controlling control surfaces" to do. I'm not sure what to do to fix that. The plane needs fuel but I'm not sure how to balance the fuel in a way that allows the center of mass to not effect the way it flies since this is my first plane. Any suggestions fellas? This is hard!

Maybe get rid of the middle engine and have the center tanks feed the side tanks and use a longer tail with a stabilator?

Edited December 25, 2014 by Mister Kerman

[klesh]

You need the center of lift (blue arrow pointing up) way further back. As you lose the fuel in the tanks (front tank first), the center of mass will move further back. The point at which you plane got jacked up is when the center of mass moved behind the center of lift.

Check out my quickie plane for survey & temp missions. Note how far back my lift is at the launch. Also note that I have only one fuel tank, centrally located. The other two are structural fuselages. This way, when the fuel drains, there is less of it far forward, meaning the center of mass wont change as much. Its a clean, classic design. This thing flys like a dream. Also people, remember to offset those landing gear bays up into the wings.

You could try offsetting those upper wings lower, and tilt them back a bit as well. This will kick your lift angle back, away from the center of mass. You could lose the 3rd engine, 2 is plenty; one is almost enough with a plane that small. My plane will easily get over 1km/sec way up high with just one engine. Fuel lasts forever too, and don't forget about drop tanks to extend your range. I can put some on that thing, and get big distance. They get used first and off they go. An easy start would be to remove half the fuel from the rear fuel tanks, and see what that does for you. If thats not enough, try replacing them with empty structural fuselages and see where that puts the center of mass.

You should also fly it until it freaks out again and note your fuel levels in each tank when it happens. Then you can go back to the hangar and make the fuel levels the same, and observe your center of mass and lift positions at the point at which stability is lost.

Edited December 25, 2014 by klesh

[klesh]

Additionally, look at this sorcery. I went in and dropped the fuel out of my only tank. Note how the center of mass actually moves slightly forward at this point. The longer this plane flies, the less fuel it has, the more stable it becomes. That's something that is a nice feature. Design for a stable, balanced craft both empty and full. Start with the tanks empty, and at the center of mass. When you add fuel, the COM should stay the same.

[Mister Kerman]

I should try simpler designs out first. I got my hopes up because it flew so well after rolling out of the hanger. I still have some experimenting to do before I really get this.

I thought the center of lift was supposed to be above the center of mass?

[The_Rocketeer]

Klesh has it about right.

It doesn't matter very much where the CoL is vertically, but if it's not behind the CoM at any point during a flight, the plane will become very unstable. Did you ever have those toy polystyrene plane/gliders that came in a little envelope when you were small? You slot the wings thru the fuselage and add a plastic weight to the nose - if the weight wasn't on the front (the CoM in front of the CoL) the glider wouldn't stay pointing the right way and just tumbled to the ground.

[Mister Kerman]

K perfect fellas. I'm going to try out some simpler models after work!

EDIT: I found a pretty good tip along the lines of what you guys are were saying in another thread!

Darkfine,

I'm glad it worked out for you.

A few tips for the future:

1) Try to make the plane so that the fuel tank is as close to the CoM as possible.

2) Drain the fuel tank to see where your CoM shifts

2a) If it shifts back, leave the tanks empty while you build.

2b) If it shifts forward, leave the tanks full while you build.

3) Attach and balance all wings such that the CoL is in the middle of CoM.

Finally, refill the tanks if necessary.

That's it. You'll have a nicely- balanced plane every time.

Merry Christmas,

-Slashy

Edited December 25, 2014 by Mister Kerman

[The_Rocketeer]

Yeh GoSlash27 is quite a font of know-how regarding many things kerbal.

[Mister Kerman]

I'm shutting this one down. I think I have a rough idea how to tinker with planes. Thanks for your guys' help.

[klesh]

Nice, glad I could be of some help. Post what you create with your new-found understanding!

[Mister Kerman]

Can do. For now I just copied yours because it's a reliable design and I need to raise some funds for upgrades. It would honestly be quicker and probably more profitable to continue testing parts using rockets but SSTO spaceplanes were always something that interested me that was outside my comfort zone. I'm slowly changing that but I still like rockets, space stations, and landers the best!