While they were fooling around with different ideas, Birb hopped through the shop door. "We got cloth!"

A crate had arrived already, with a big bale of the fabric Selen had been using. With it came a refined version of the metal framework she'd used to hold fire gems and provide a hot air supply. It was a tube sealed at one end.

A letter with it said, "Put a wind gem at the bottom, set to continuously create or shove air outward, so that it flows up and gets heated by several fire gems. Might make a good fur dryer too!"

There were jokes and gossip that Vonn wanted to read, but he stood there staring at the gemstone rig and the one paragraph.

"What?" asked Tazo.

"Did I ever mention the concept of a jet engine?"

He explained. This "fur dryer" was something like a ramjet, a potentially bladeless engine that sucked in air at one end and used burning fuel to heat it and fling it out the other side at high speed. Normally it relied on extreme speeds, not the waddle of his barely functional first machine. But if the air supply was coming from a gem -- which was roughly what he already knew how to do from building wind guns -- he should be able to get propulsion force at any speed.

Tazo took only a moment to figure out the basic idea. "Action and reaction. But without fuel?"

"Right. The question is how much force we'd get. I suspect not enough, but this is an easy thing to try."

"Come to think of it, Ralator mentioned using fire and wind together to fling flames around. What if we used earth magic to generate rocks and fling those?"

"Could be a sort of infinite-ammo version of the wind gun. But remember, hot air expands, so hitting the generated air with intense heat will help it push back against the engine. Yeesh, Selen may've solved our problems by accident. What else did she put in that box?"

Tazo rummaged. "A bottle of dye marked for Mom, two brass bracelets, and some kind of painting." She held out a photograph of Selen.

A photograph! It showed the Aves leaning against one of her hot air balloons, looking cool. Fuzzy black and white and a bit blurry where she'd fidgeted during a minutes-long exposure time, but she'd proved the concept. "We need ten more of her."

#

They built an extremely primitive jet engine while Birb worked on the balloon. This new device was basically an iron tube made by Ashfall, with a wind crystal in its sealed end and a fire gem in the middle. The pairing created a stream of hot air that Vonn carefully (and then playfully) determined was basically a blow dryer. "Yeah, too weak." Still, he set it down on a smooth table and leashed it with a spring, to see how far it could pull away and hence how much force it exerted.

He tuned several more crystals and wedged them into the device. "Uh, maybe we should test this outside. Near the water."

They had to drag their improvised test stand outside to the snow-dusted ground. The device pulled harder at its spring, now, and Vonn recorded the number. Then he gingerly tried to apply Crystal Integration, boosting the output, but felt a numbing buzz in his fingers as he failed to invoke the power. Wasn't a complex enough machine. He said so. "I like the force output now, though it's not enough to lift an airplane."

Birb had gotten distracted by this new experiment. "Why not use more than one? Or combine it with the propeller?" Her eyes widened. "Or, get a greater shard?"

To this point, Vonn had only worked with the thumb-sized nuggets of magicite that a good adventurer could pick up easily, a few per dungeon run. Greater shards were roughly bowling ball sized, with about ten times the weight but with more than ten times the output. They were the real prizes for advanced enchantment, to say nothing of grand shards. Vonn had gotten to hold a greater piece, twice, but the things were automatically nobles' property, with a finders' fee to the delver.

Tazo said, "I see a dangerous grin there."

Vonn was imagining a metal barrel with a terrifying ongoing blast of hot air driving a plane. Or a steel furnace. "Ha! It's worth asking the Baron, but only after demonstrating a lesser shard doing something useful. Let's start by getting this flying boat up, and testing the basic jet as a possible substitute to the propeller. If it's not good enough we might still have one or two as supplemental thrusters."

[Skill gain: Clockwork 2 (Learning)]

#

When the Baron's Engineer was ready to go home, Vonn sent him off in style by assigning him a motorboat to deliver. First of many, probably. It was stenciled Rising World Company, Shieldpoint.

Spikes' delver squad had been visiting Murk Passage over there on the east side, but came right back when they saw the thing. "Can you build us one of those?"

"Sure! I'm not confident about the reliability yet, though."

"Maybe we'd better wait."

"That's fine. We'll have another one soon that you can try. But first..." He called out to the hangar, "How are we coming, Birb?"

"Time to fire it up!"

There wasn't much to see yet. This boat was a light one with hard-points, in this case iron rings, at six spots. The bird girl had attached ropes there and was slowly inflating the balloon inside the hangar, until Vonn pointed out the obvious problem and he helped her scoot everything safely outside.

"Come back in an hour," she told the onlookers.

Vonn checked everything over. They had installed an engine near the middle, and ran a shaft aftward to their propeller. So the overall balance was decent and Birb had had the idea to put the heavy engine slightly starboard to counter any roll from the prop's torque. A light wooden box somewhat protected any passengers from the contained storm of heat and cold. A few sandbags served as ballast.