Help on building cargo plane wings?

[captain_fiddlesticks_]

I need some help on building stable and large wings. I am building a C-130 type cargo plane using stock and KAX. Does anyone have good, stable, and strong wing designs for large aircrafts? Thanks.

Edited January 1, 2015 by captain_fiddlesticks_

[Specialist290]

Welcome to the forums!

Before we go any further, mind uploading a few screenshots and / or .craft files of some of your previous attempts? It might be possible that you're on the right track already and just need a few fixes in order to get it functional.

[Wanderfound]

As Specialist says, screenshots. Preferably in the SPH from square on side and above, with CoL and CoM markers turned on.

We'll also need to know if you're flying FAR, NEAR or stock aero, and whether or not you use the Procedural Wings mod.

The wings need to be built to suit the aircraft; we can't give good advice unless we can see what we're dealing with.

[captain_fiddlesticks_]

Okay, I'm working on it. P.S. I am ONLY using Kerbal Aircraft Expansion mod and stock parts.

[captain_fiddlesticks_]

The texture on the MK3 cargo bay is glitched out, only cosmetic; runs fine.

[Specialist290]

Your best course of action is to upload the screenshots to an image-hosting site like Imgur, then use the [ IMG ] tags to link to them here. There should be an option to copy-paste the BBCode script when you're viewing the picture, to help minimize the tag-finagling.

[captain_fiddlesticks_]

Okay, here are the Screenshots of teh plane.

[MiniMatt]

You've got some issues with the image URL there, but a bit of tinkering reveals these:

and

First thoughts are that it looks like you're certainly on the right track. Perhaps dial in a bit of attack angle on the main wings - ie. a slight ~10 degree angle - move the wing angle from present --- shape toward a \ shape (but nothing like that sharp). This will aid in take off and allow the wings to generate optimum lift whilst your nose is pointed to the horizon.

You've an awful lot of yaw authority on there, and I'm not entirely sure the canards on the wing tips are helping in that regard - though I may well be wrong here. Possibly experiment removing those main wing canards and instead giving an upward inflection to the delta wing tips, a little like the wing tips on a 737-NG. This should help encourage the plane to keep it's tummy pointed toward the ground and it's top toward the sky.

Suspect you can also daisy chain the fuel lines under the wings from the body, to one engine pod to the next, to keep things looking neat too.

EDIT: Occurs to me that we haven't actually asked the problem you're having. If it's one of stability in flight then the suggestions above might begin to put things right, but like I say you're definitely on the right track. If it's a case of bouncy wings, well that does indeed get a little problematic, easiest solution is one you've already started - moar struts. If it's a case of insufficient lift then your options are bigger wings, or less mass. On the mass front, there's at least one part in your plane which by default comes loaded with oxidiser - the Mk3 to 2.5m slanted adaptor part toward the back of the plane - assuming you're not taking this thing to space and all your engines are air breathers then you have no need for that oxidiser and removing it prior to launch will reduce your mass quite noticeably.

Edited December 24, 2014 by MiniMatt

[captain_fiddlesticks_]

While I was waiting I was bored and redesigned it! I will post pics shortly.

[Wanderfound]

Pretty much anything will fly in stock aero. So long as you have sufficient wing area and keep your CoL sitting on the back of CoM, the issue is mostly cosmetic.

The wing strakes are very handy for fine-tuning wing profiles; they're designed to clip without z-fighting. Have a look at the leading edges of this one for an example:

[captain_fiddlesticks_]

So, the problems are, the plane is VERY hard to control, it is just heavy enough to tip over and lean on it's tail, and even with 4 powerful engines, it only skips. Here:

and

[Vicomt]

First two things I noticed, you need to move your landing gear backwards, they need to be slightly (but not far) behind CoM, that'll sort out the "sitting down" on the strip. Then you need to sort out the CoT, it really needs to aim through the CoM (probably also behind it), or you'll get thrust induced pitch going on

On a general design note, I know you're doing a replica, but your version feels slightly short, but that might just be my aesthetics kicking in

[captain_fiddlesticks_]

I can see. This wasn't supposed to be an exact replica. I was using the C-130 as a "reference".

[MiniMatt]

Well the centre of mass being behind the rearmost wheels will be why it wants to tip back on the runway - maybe mount the rear wheels splayed out on small hardpoints attached to the main body, further back.

The suggestions I wrote in the earlier post may go some way to alleviate airborne control issues. In your new design I'd suggest the centre of lift is edging a little too far back from the centre of mass, but should still be controlable - until that is fuel starts depleting - with the bulk of the fuel being apparently held in the rear (and do double check for oxidiser in there, as previously mentioned) the centre of mass is only going to move further forward as reserves deplete.

What is the power output of the engines you're using & what is the mass of the plane on the runway? Mk3 cargo planes can get *very* heavy, I've got one design I'm struggling to sufficiently power with 8 stock turbojets.

[captain_fiddlesticks_]

I will look.

[captain_fiddlesticks_]

It has 4 propellers, which output 120 thrust each. It weighs 24 tons.

Edited December 24, 2014 by captain_fiddlesticks_
just a typo

[captain_fiddlesticks_]

you there guys?

[Anquietas314]

you there guys?

Well, I'm here. Are you sure that plane is only 24 tonnes? The one plane I did successfully build with (stock) mk3 parts was a similar size, but far heavier (>100 tonnes). Most of that was from the fuel tanks.

EDIT: I decided to build a mock-up of the plane myself based on the visible parts. Before adding wings, gears, cargo, etc it weighs in at 28.4 tonnes, which means unless you drained almost all of the fuel from the tanks for some reason, it should be (a lot) heavier than 24t.

Edited December 25, 2014 by armagheddonsgw

[Wanderfound]

First, you have insufficient power for the weight. Second, you have massively excessive amounts of roll authority and insufficient amounts of pitch and yaw authority. More rudder, more tailplane. Lose the wingtip vertical fins; they won't do anything in that position. Control surfaces need to be distant from CoM in the axis they control.

[cosmos33]

Your col is too far back. Needs to be behind com but if it touches it its more like it... Make your col toutches the com but put it behind the com by a tiny bit. You Will need to move your tail forward most likely. Because your col is far behind (not to mention your wheels that needs to go back a bit ) this thing wont get off the ground the nose is too heavy.

Edited December 26, 2014 by cosmos33

[captain_fiddlesticks_]

Well, I'm here. Are you sure that plane is only 24 tonnes? The one plane I did successfully build with (stock) mk3 parts was a similar size, but far heavier (>100 tonnes). Most of that was from the fuel tanks.

EDIT: I decided to build a mock-up of the plane myself based on the visible parts. Before adding wings, gears, cargo, etc it weighs in at 28.4 tonnes, which means unless you drained almost all of the fuel from the tanks for some reason, it should be (a lot) heavier than 24t.

Yeah, I did drain all the fuel in those back 2 adapters.