Why do the swept wings in ksp cause tailspins, and is there any way to calculate it?

[JokingHinge]

Okay, so I have an obsession with WW2 fighters and the ones that use swept wings tend to fail due to tailspins. Has anyone figured out the cause?

(Still, even copy and pasting the code into a spoiler won't work because I don't know how to use them)

Research progress:

Here is a laythe ssto from a livestream that had this problem

Note that at high speeds it went into a tailspin, this happens even with lawn dart type crafts.

Before anyone asks I am a veteran at building planes with FAR, do not ask me about center of lift and mass.

Again, the lift rating increases how much the wing affects the craft, the wingspan gives it a high tailspin rating, and higher speed activates the tailspin. I also think that this is a airhogger specific problem(Drag induced tailspin?). And just to avoid confusion, there are no flameouts in this example. Also the ksp devs made this intentional, as you can see in the description of the swept wing.

It appears depending on how high your angle of attack is, the wings also make a tailspin.

I have done no testing on how putting wing on top or below the craft affects this problem, feel free to take notes on what this does.

Okay, I can't reproduce this with any other wing, I will try as hard as possible to reproduce with other wings.

Okay, somebody make a chart, I just figured out how to calculate this. Look at my notes and do whatever it takes to research this thing.

Sorry if I may seem like a jerk with all this updating.

So, the swept wings have the least weight, it makes since for the developers to balance them by adding the mysterious tailspin value.

The way to calculate it is solved, now we need to find out the cause.

Edited August 5, 2014 by JokingHinge

[allmhuran]

Swept wings are definitely my favourite wings. Do you have a picture as an example of one of your designs?

My suspicion is that you have the swept wings too far forward, with not enough lift at the rear, giving you a centre of lift that is too close to the centre of mass or even ahead of it, which will be very unstable.

[JokingHinge]

Sadly, all of my examples were part of an old ksp folder that went into the trash, but I know all about center of thrust, lift, and mass.

[allmhuran]

Bummer. I've never had any problems with swept wings and most of my planes rely on them completely since I find the deltas take up too much fuselage space, and swept wings are actually better overall anyway. I can't think of anything specific to them that might be causing the issue.

[JokingHinge]

Well, I am preparing a craft to reproduce to problem, it will be put up soon.

Edit: How do you upload crafts again?

Edited August 1, 2014 by JokingHinge

[FleshJeb]

I recall reading somewhere that swept wings have the center of lift at the root instead of the middle of the wing like all the others. Might this contribute to instability?

[allmhuran]

You can upload the craft file to google docs or something, or a picture uploaded to imgur is probably sufficient.

[Wanderfound]

Well, I am preparing a craft to reproduce to problem, it will be put up soon.

Edit: How do you upload crafts again?

Dropbox etc.

Pics in the VAB from top and side with CoM/CoT/CoL indicators on would be more useful for a first look, though.

[JokingHinge]

I think that the cause may be too high lift, too wide of a wingspan, and too high of a speed. All of my examples are airhoggers that go the maximum speed in the atmosphere.

If I am correct you can calculate wingspan, speed, and lift to build the perfect wing.

(Still, even copy and pasting the code into a spoiler won't work because I don't know how to use them)

Edited August 2, 2014 by JokingHinge
Massive OCD rampage

[Nurph]

Just paste an imgur link in your post, don't need anything fancy.

Also the ultimate KSP aircraft guide if you haven't seen it yet: http://forum.kerbalspaceprogram.com/threads/52080-Basic-Aircraft-Design-Explained-Simply-With-Pictures

[Tortoise]

Well first, are you using FAR for realistic aerodynamics?

[The Fleet Master]

I've had multiple successful Swept Wing design. Here's a few examples.

Always keep the CoL behind the CoM, For maneuverable aircraft the closer the CoL is to the CoM the better but don't go ahead of the center line.

[JokingHinge]

Ugh, I don't need any help with center of lift and mass, and this is stock.

[JokingHinge]

Here is a laythe ssto from a livestream that had this problem

Note that at high speeds it went into a tailspin, this happens even with lawn dart type crafts.

Again, the lift rating increases how much the wing affects the craft, the wingspan gives it a high tailspin rating, and higher speed activates the tailspin. I also think that this is a airhogger specific problem(Drag induced tailspin?). And just to avoid confusion, there are no flameouts in this example.

Edited August 2, 2014 by JokingHinge

[Nurph]

Can't tell at all what's happening in your picture, it's just a plane-shaped fire. Can you give us a picture in the SPH at a better resolution with all the markers on?

One thing is that the CoM could have moved behind the center of drag, causing the plane to want to fly backwards. Intakes have more drag than normal parts when open.

[JokingHinge]

Sure, Here

(This is a different plane, but it shows what I mean.)

Edited August 2, 2014 by JokingHinge

[Nurph]

Yup, you have a metric butt ton of drag ahead of the CoM. You're trying to fly a lawn dart backwards, basically. Short and stubby planes tend to be less stable and you don't have a rudder either.

[SpenSpaceCorp]

This may or may not be the problem, but this is what I think MAY be happening: although the engine(s) are not flaming out, one engine does tend to lose thrust right before this point, as one engine "takes" all the air from the intakes leaving less air for the other, causing asymmetrical thrust, which may be sending you

into a tailspin. To check if this is the problem, right click the engines to check the thrust of each. (right click one engine then alt right click another to bring up both engine stats at the same time).

Hope that helps!

[Claw]

So, the swept wings have the least weight, it makes since for the developers to balance them by adding the mysterious tailspin value.

The way to calculate it is solved, now we need to find out the cause.

I don't think the developers would have specifically added tail spin tendencies just to offset the lift/weight ratio.

I can't see in your picture very well, but my what I think I see is two fold.

- Like you said, it looks like you have a lot of intakes which may be contributing. See if you can move some of them aft to offset the drag tendency. If you recall, drag in stock aero dominates the lifting surfaces at high speed.

- It doesn't look like you have much in the way of tail surface. Wide wing craft in KSP can sort of fishtail around. At high speed, the combination of drag and this tendency might be causing the problem.

- Also, you say there's no flameout, but also watch out for one of the engines to throttle back some. It might not flame out completely, but you can get situations where one engine will throttle back lower than the others.

(Still, even copy and pasting the code into a spoiler won't work because I don't know how to use them)

If you want to use spoilers, it looks like this:

[noparse]

Do all your spoiler text and pictures in here.

[/noparse]

And it'll look like this:

Do all your spoiler text and pictures in here.

Cheers,

~Claw

[JokingHinge]

True, never thought about that, but the swept wings say "A prototype swept back wing. Made of light weight composite materials. Guaranteed to generate lift, not guaranteed to ensure crew safety." Perhaps they mean a ton of drag relative to lift? Also the intakes do not contribute, I did a high pitch at low altitude test.

I am going to test the one engined with only one intake to prove my point.

Edit: Test seems to have the same results as the the airhogger

Edit: Test two seems to have different results, pointing to the intakes causing the problem

Edited August 2, 2014 by JokingHinge

[JokingHinge]

I give up, I think it was just a error with the intakes, even though they said they were at max capacity, drag tests show otherwise.

I guess everyone else was right, and I was trying way too hard to prove my point.

[Wanderfound]

True, never thought about that, but the swept wings say "A prototype swept back wing. Made of light weight composite materials. Guaranteed to generate lift, not guaranteed to ensure crew safety." Perhaps they mean a ton of drag relative to lift? Also the intakes do not contribute, I did a high pitch at low altitude test.

The descriptions are written for comedy, not accuracy. Ignore them unless you need a giggle.

[MarvinKitFox]

Okay, so I have an obsession with WW2 fighters and the ones that use swept wings tend to fail due to tailspins. Has anyone figured out the cause?

The cause is clear.

Your aeroplanes suffer from a severe case of PEBKAC, aggravated by an ego-id imbalance resulting in supercilious behavior.