Making my fat aircraft more maneuverable with stock aerodynamics

[drtricky]

I'm building a large, fat, aircraft and I want to know if I can make it more maneuverable (sharper turn radius, faster roll rate, etc.), and how I can make the wings stronger so they can survive higher g forces (can currently handle a max of ~11.5 G's, turn was made at ~250 m/s at I think 1500 m). I want to know what to do besides reducing its size and weight (obviously). My aircraft has modded parts, but the only mod it has is BDArmory. Here are some stats and pictures if they're helpful:

Parts: 154

Mass: 128.7 tonnes

Height: 11.9 m

Width: 36.1 m

Length: 27.2 m

Screenshots:

Spoiler

 

 

Wonder why I call it big eagle? Here's why:

Spoiler

 

 

Edited December 8, 2015 by drtricky

[satnet]

Take a look at Keptin's design thread: http://forum.kerbalspaceprogram.com/index.php?/topic/47818-basic-aircraft-design-explained-simply-with-pictures/.

Now for a some specific advice on your plane. The CoL is above the CoM which is more stable, so you might lower your wings. I'm not sure how much wing aspect matters in stock aero, but you might want to give a lower aspect ratio (stubby instead of wide). Your CoL is nearly on your CoM, which is good for maneuverability though you could probably afford to have the CoL a little further forward if the rest of the changes aren't enough.

As far as making the wings more solid it mostly comes down to reducing the number of wing segments involved if you can. Using larger pieces would help. Reducing the aspect ratio would also help since more of the wing would be attached to the plane fuselage instead of a wing attached to a wing attached to a wing (you get the idea).

P.S. Keptin does NOT pay me to plug his thread, I just find it immensely helpful and worth sharing.

[drtricky]

Question: does adding more struts to one part increase its strength?

And also, is there a general limit on how maneuverable planes can be relative to size? I've noticed that when making hard turns at 3000m at 300 m/s, my airplane seems to stall

Edited December 8, 2015 by drtricky

[Val]

While aspect ratio doesn't affect aerodynamics much it does affect wing strength. Make the wings shorter with a wider cord, will strengthen them if only because there are fewer joints and less leverage on those joints.

Maybe try a sharp arrow or diamond shaped wing?

[arise257]

Don't spam struts, they're draggy. If you use them, connect one end as close to the tip of your wings as possible, and the other to the fuselage. You may need two per wing to keep things stable. From the width and number of segments to your wings, I'd assume you're getting some floppiness. A good way to check for it (without turning) is to crank up the physics warp. If your wings bow up or down, add some struts.

Edited December 8, 2015 by arise257

[drtricky]

So currently, I have one strut on every reachable wing panel. If I were to put all my struts on the furthest reachable wing panels instead, would that strengthen the wings more?

 

Also, the engine pre-coolers currently don't have any kind of aerodynamic shielding in front of them. With the new drag model of 1.0.5, would putting nosecones on those pre-coolers actually make my aircraft more aerodynamic? I had heard prior to 1.0.5 that nosecones made aircraft more draggy due to the way drag is calculated

Edited December 8, 2015 by drtricky

[numerobis]

Basically you've built a plane the size of a Boeing 757 that lets you pull 11.5g, and you're not happy yet. Just pointing that out...

What's breaking? What's bending? What's your real limiting factor? Without knowing that it's hard to provide advice.

My first bet is that the winglets at the end of your wing aren't very effective for roll: those tend to make your wing bend which makes it lose lift, offsetting the intended effect.

My second bet is that you are worried about the wings flexing too much. The solution to that: make them shorter. You can move some of the segments back to be level to your current CoM/CoL, spreading the wing area out over the fuselage.

[Snark]

Joining multiple pieces together is always a design challenge. Each joint added is one more flex point, one more place for stuff to bend and break.  And as arise257 pointed out, struts are draggy.

Any time you have the opportunity to use one big piece instead of many small ones, that's a win.  For example:  What about using the big airliner wings?  They're large, they have lots of lift, they're nicely rigid.

If one pair of them isn't enough, you can get creative.  For example, mount one pair forward and one pair aft.  Or you could stack them biplane-style.  Or do both, which would give you 4 pairs of wings.  I'd be surprised if you can't fly with four pairs of those things.

Also, I gotta say that your screenshots reminded me of this. 

[drtricky]

2 hours ago, numerobis said:

Basically you've built a plane the size of a Boeing 757 that lets you pull 11.5g, and you're not happy yet. Just pointing that out...

The reason why I've added enough struts to allow the wings to survive that many g's is because I'm designing this aircraft to be able to fend off fighters, and the maneuverability from the CoL being that close to the CoM is for dodging missiles (Launching excessive amounts of flares or chaff alone does not seem to work in BD Armory).

Yes, I'm well aware that people usually make small, nimble fighters to fight other small, nimble fighters, but I have dreams, ya know . I probably should have said that earlier to make the purpose of my airplane clear.

2 hours ago, numerobis said:

What's breaking? What's bending? What's your real limiting factor? Without knowing that it's hard to provide advice.

The entire aircraft breaks apart when subject to enough aerodynamic forces during a turn of any kind (dependent on speed and altitude), limiting the maneuverability of my fat plane. Logically, I'd figure the wings are breaking and causing the entire plane to fail because of their width.

The event log, however, always says that the connection between the passenger module and the fuel tank breaks first, despite all the events showing as having occured at the same time, and I'm not sure whether that event is occuring first because it itself is breaking, or it broke because the wings broke.

 

So.....have I perhaps hit the limit on how maneuverable a high speed (300 m/s + at sea level), straight-winged aircraft of that size can be without struts dragging it to death?

Edited December 9, 2015 by drtricky

[drtricky]

1 hour ago, Snark said:

Any time you have the opportunity to use one big piece instead of many small ones, that's a win.  For example:  What about using the big airliner wings?  They're large, they have lots of lift, they're nicely rigid.

I tried that. Two airliner wings placed within one another (slightly offset for visibility in SPH) handled less g's than the current wing set up, which means struts were needed for both pairs of wings, which means I get construction-related headaches, and the plane would look like the failed lovechild of a biplane and an A380.

1 hour ago, Snark said:

Also, I gotta say that your screenshots reminded me of this. 

Spoiler

 

I think another engine or two would suffice

Edited December 9, 2015 by drtricky

[numerobis]

That your fuselage breaks apart makes me think that your immediate problem is that one part of your fuselage stops cold thanks to those big wings, so the inertia of the unsupported parts of the fuselage makes them tear off. If true that would be another argument for spreading the wings around: put wings on every fuselage segment, and shorten the wings you have.

You may also find that your struts move forces around and concentrate them into a joint that then snaps. Struts make your structure rigid, which isn't always a good thing.