Choir listens with interest to the ideas of her companions as she struggles to come up with a useful idea herself.  None of her spells or equipment seems useful. She supposes that she could beg the assistance of Akadi, but the Goddess of Air is notoriously inattentive and unreliable.

"Kite," she agrees with Fran, and starts looking for anything that might be useful...curtains or draperies or shrouds or whatever...

It was a rich mansion - you did not even have to search hard for silk curtains and draperies. Light wood for frames could be more difficult but again, rich people love useless decorative things and the owner of this place was no exception - a few display cases for collectibles with some porcelain figurines in it could be easily ... let's call it "disassembled" and used for the purpose.

(Fran, as the only one with the tools and the skills it is up to you to make the deltaplanes. Roll as with Int proficiency (+6 in your case) and advantage if others help to see how many "kites" you can make: 1-4 (impossible but as a measure) - 1 kite, 5-8 - 2 kites, and so on).

The only remaining question was the hang gliding itself - not an easy skill, never trained by any of you. Oh, and in case of Polly - not enough wait to steer the thing, while Brutus might have trouble to do it at all.

Fran was thankful for Choir’s resourcefulness and eagerness to assist with gathering and organizing supplies. Taking advantage of all the space, she’d start by inventorying up the pieces and dividing them up. And before she knew it, all her tools were out and all hands on deck. With help from Choir, Brutus and any of the others, she’d lay out stations for each craft. The artificer would begin tinkering way.

Kites: 19 + 2 Akadi Guidance

(Kites for days! High five Choir)
Edit: (Thoughts, with this roll, would it be possible to rig something up for Brutus and Polly to tandem? We would just need to hook him up for even weight distribution and then have Polly steer? Im imagining like hanging straps or those old baby swings lol )

(I think with this rolls you can craft a Boeing)

Appropriate, considering Fran is getting Guidance from a Cleric of Akadi, Queen of the Air.

Fran felt uplifted in body and spirit, in a way she would have never expected in a place as wretched as this. But here she was, feeling, joyous. Comradery. Without even knowing it, the tinkerer began to whistle as she worked, eventually picking up into a rhythm of an old dwarven smithy shanty. This was the sound of her youth. It was methodical. The redhead was focused, but moved at a steady beat of her own tune as she moved through assembly. She'd even flourish her tools every once and a while as she'd take them out and put them away. It'd have been a while since she felt in her element. And at any point Fran drew a blank, she'd feel a breeze, breathing air of guidance against her back and filling her lungs. It wouldn't take long before she'd start again, continuing her whistling. The battle smith was able to design and craft a tandem kite for Polly and Brutus.

Once completed, Fran would wipe the sweat from her brow as she'd stand upright. She'd return her tools to their respective slots before placing her hands on her hips to look over their work. She felt confident and pleased with what they've achieved. It was all thanks to everyone's help and Choir's guidance. "Whatchya think? Eh? Eh?" The artificer would look around, trying hard not to bob her eyebrows.

Adray looks at the kites.  "I don't know what to think because I don't get what that is supposed to be," Adray responds.

Choir lifts one of the kites, wafting it up and down to feel the flow of air against its fabric.  She tries jumping in the air as high as she can to feel the 'float' on the way down.

"Fabulous, fabulous!" she says excitedly. "Glory to Akadi!  Glory to Fran! Go fly a kite!"

Floating down on these might be a little scary, but it will be almost like flying! Choir hops up and down with eagerness to try the kite.

Ordrag looks at the contraptions with a mixture of admiration and trepidation. They are like a sail, except the mast isn't attached to anything! No steadying keel, no guiding rudder! As a seaman, he had beheld the gulls and terns ride the winds and thermals with ease, but they had such fine control of their wings and tails. These things had no feathers at all. Looking to Choir and Akadi, Ordrag asks: So... how do they work?

Fran couldn’t help but let out a hearty chuckle from Choir’s innocent burst of excitement, especially when she shouted ‘go fly a kite’. She had to wipe a tear from her eye from laughing a little harder than necessary. The artificer would gesture to their Kenku who was running around with the contraption before reaching down to pick one up for herself. She’d pick up the contraption by a bottom bar, lifting the personal kite up to her height. “Aye. It’s much like a sail, except instead of using the sail to catch the wind and push us, we will be gliding along it as it keeps us afloat.” Fran would try to explain it the best she could by tilting the rig a full 90 degrees to have it mimic the look of an upright sail before tilting it back down to run parallel with the ground.

She’d begin explaining the bottom bar which her hands are holding the contraption up with, “This is the control bar.” The redhead will stretch her arms out to extend it ahead of her to mimic being stretched out mid flight. “Tilt down to dive down. Tilt up teh try to catch more wind an’ teh slow yer speed. Tilt right, turn right. Tilt left, turn left.” She’d move along with the instructions she’s giving. Glancing up, Fran will point out the spine of the rig in which a harness is handing from. “Strap yerself to the glider with this harness. Polly and Brutus will pair up for weight distribution for better control. Polly gets the controls of course. Brutus will just hang out.” She will then trot a little forward, “Ye’ll want to have a running start to pick up some speed and jump fer some air to get going. And yer gunna want a running stop, otherwise yeh may just eat your landing.” The artificer will chuckle nervously. She didn’t have any wheels for a smoother landing, but they shouldn’t be coming in so hot on landing that that shouldn’t be a problem. “‘Sides, Polly an’ I can aim to feather fall the landing should there be any concern.” She’d add.

(Imagine an Avernus hang glider! :) )

(Something like this?

(Ordrag wants a green one)

Haha perfect picture 😂 

Polly listens to Frans instruction with fascination. “When I asked you to build something that could help us steer, I never would have imagined you to come up with something like this! It is incredible really.” She’d walk around the kite for a closer look. “Though I won’t be able to cast feather fall until tomorrow. But I think we should stay here for tonight anyway to talk through our plan and rest up before heading out. Btw how far can this thing take us? If I understand this correctly, it won’t take us down in a straight dive right? And what do we do if we get company out their? I’m not too confident that I can cast magic while we’re up there. 

Choir, without hesitation, starts strapping herself in.

"Wings!" she sings, recalling an old hymn from the choir. "Akadi gives us wings! Soaring up through the air! The goddess might meet you there!" Of course, it's unlikely Akadi would hang out in this sulpherous-smelling air long enough to meet anyone.  She preferred to hang out wherever they were burning incense in her honor, especially expensive incense. Still, it WAS still air, and it WAS  near to flying. Maybe Akadi would spare a little peek at their progress.

Just in case, Choir lights a stick of incense.

Kites were big, as colorful as silk drapes and bed sheets allowed them to be, and as scary as any untested device you are about to trust your life can be. All what remained now, is to transport that aircrafts to the nearest jagged posts with the chains of infernal iron. Transportation was (so far) the most difficult part (granted, the previous one was mostly on Fran) - with lightning strikes and demons on the loose. Though, surprisingly, there were not so many devils or demons, and once everyone found the place for a jump - with a good view of the Fort Knucklebone you were aiming at (just 10 miles away, a Lulu calculated), you understood the reason for "demonless" streets: down there you could see the battle taking place, on of the countless many in the Blood War, but right now it needed all demons and devils around generals on both sides could summon.

Armored legions of devils encircled the enormous posts of infernal iron that anchor Elturel to the rocky ground. Squads of demons hurled themselves into the devils’ ranks. Most of those abyssal troops looked (at least from your position - 500ft above) as lowly manes and dretches, who die quickly in vain attempts to drag down devils so that stronger demons behind them can strike killing blows.

You can get  good view of the dark river as well - the legendary dangerous River Styx - that cuts a path across the blasted landscape and flows directly beneath the city. Floating on the river are demonic barges being assailed by squadrons of winged devils under the command of a terrifying pit fiend wearing an eyeless helm and clutching a battle standard.

The battle is certainly one of those things one can watch endlessly - a dazzling terrifying display of pure rage. So far those involved do not care to look up, at the city floating above.

(Just confirming: are we long-resting before departing? Polly doesn't have feather fall until we do, so I'm assuming we do/have)

(Also: based on gliding rules posted before, 500 feet of drop gets us 3000 feet of distance at most. If we are pointing toward Fort Knucklebone, does 3000 feet put us beyond the battles happening below? That's barely half a mile)

Consider it next "morning" (after the long rest): five kites should take time and everyone involved would likely need rest too.

Ordrag waits for someone else to go first. Not because he's afraid - certainly not. He's a rough tough sailor, he's not afraid of anything. Certainly not of a 500-foot drop... into a red river... filled with demons...  He's just waiting for someone to demonstrate how to fly these things. And to watch the battle below for a few moments more. For tactical purposes.

Adray took one and stared out over the edge.  He looked down to the river and then over to the team.  He hesitantly said, "Well... I guess I'll test it out.  If I drop like a stone, don't follow," he said.  He looked forward and swallowed hard.  Trying to remember the instructions given, he grabbed the kite and jumped off the edge.  

Following Adray's lead, Ordrag launches himself off the edge of the city...