What is it with multi-engine planes!?

[mushroomman]

I don't know what it is! I just can't do it! I swear I've gotten them to work in the past (using FAR or NEAR), but I seem to have lost that ability. I can get single engine planes to work just fine, I would even say they're amazing. But I just can't do multi engine! They just do that horrible swerve dance on the runway and proceed to explode at the cost of many innocent lives. What am I doing wrong?

Could it be that the COL is too far back? The more I think about it the more that makes sense...

Edited October 26, 2014 by mushroomman

[Hodo]

I have to ask, what plugin is that for those cockpits and engines?

But it looks like your CoL is shifted to far to the rear of the craft.

[mushroomman]

I have to ask, what plugin is that for those cockpits and engines?

But it looks like your CoL is shifted to far to the rear of the craft.

The first plane uses stock, SXT, and Retro Future. The second one is just stock and Retro Future.

I'll have to give bringing the CoL further ahead, maybe that'll fix it.

[Hodo]

You will want the CoL right behind the CoM, not that far back though... ideally a few feet. I like to place mine right at the back of the CoM marker.

[NFUN]

Make sure your wheels are on no angle at all. Recently that has been causing swerve dances, as you put it.

[Mitchz95]

Your COM and COL are way too far apart, for starters. I remember suffering the same runway problem, but I'm afraid I don't remember how I solved it.

[Wanderfound]

If you're wiping out on the runway, it has nothing to do with CoL being too far back. Yes, you want them closer than they are, but the effect of your current setup is going to be uncontrollable nosedives at altitude, not takeoff mishaps.

First suspect: double check to make sure that steering is unlocked on the steering gear (usually the front one) and locked on all the others. Check both sides: symmetry is not reliable for this.

Second suspect: your gear may not be quite straight. A tiny misalignment can cause all sorts of horrible effects after it's amplified by the suspension travel. Have you tried just swapping the gear for stock gear bays and placing them with 90° angle snap?

[Kryxal]

Also note that those planes can't possibly lift off with the CoM so far forward of the rear wheel(s) unless you have a significant AoA with a level plane. On pulling up, the first plane is going to put a LOT of force on that single wheel, and I'm not sure what the other will do.

[MarvinKitFox]

I don't know what it is! ... that horrible swerve dance on the runway

That is all the info needed.

You are overloading a wheel, causing it to run out of alignment.

In this case, likely caused by the torque of trying to fly with a badly misaligned CoM/CoL

Your first plane, at 31 tons, would also put an unbearable strain on the single wheel when rotating for liftoff, or landing.

[Redshift OTF]

Your rear wheels need to be closer to the CoM or the plane can't angle up on the runway. As it is you are trying to put so much pressure on the rear wheels to pitch up that they start to buckle and you go all over the place. Why would this only affect multi engine planes? Maybe because when you use more than one engine you are usually putting them on the wings which brings the CoM forward and exasperates the problem. Imo.

[Hodo]

If you're wiping out on the runway, it has nothing to do with CoL being too far back. Yes, you want them closer than they are, but the effect of your current setup is going to be uncontrollable nosedives at altitude, not takeoff mishaps.

First suspect: double check to make sure that steering is unlocked on the steering gear (usually the front one) and locked on all the others. Check both sides: symmetry is not reliable for this.

Second suspect: your gear may not be quite straight. A tiny misalignment can cause all sorts of horrible effects after it's amplified by the suspension travel. Have you tried just swapping the gear for stock gear bays and placing them with 90° angle snap?

The crashing while still on the ground is definatly a landing gear alignment issue. I noticed the wings on the first craft are at a slight upward angle, this means the landing gear mounted on the engines are out of alignment, the camber on them are most likely canted outward.

But with that said, the last aircraft will not fly well at all, due to the CoL being so far to the rear of the craft. I would see about getting some of the mass to move towards the rear of the craft, if you want to maintain that design shape, otherwise you would have to move the wings forward to a more "traditional" design.

As for the landing gear being to close to the back of the plane on the first one, its a tail dragger people. As long as the main gear are longer than the tail gear it will have a positive AoA for take off. And it isnt such a big deal as long as it can get its tail off the ground before it reaches take off speed.

[mushroomman]

Allright! So I gave it a test, and yes. It was because the CoL was too far back. Thanks for the help! I guess I just overcompensate with larger planes.