A fundamental principle of aeronautical engineering has been overturned • Hacker News Board

Re: A fundamental principle of aeronautical engineering has been overturned

#141

Post by stasomatic » Wed, May 27, 2026, 3:01 PM UTC

xyzzy_plugh wrote: post #127

stasomatic wrote: post #116

Earlier quoted context omitted.

Asking as a complete neophyte - how does this reconcile with modern war planes being inherently unstable as far they flight dynamics go, without their enormous thrust capabilities? I’m just curious, I know nothing about the subject, but it seems that the solution we came up with is thrust, baby.

A key difference is that war planes occasionally want to be able to rapidly change their trajectories. With sufficient thrust you can fly around in a cube.

They can’t “want “. The pilot may want, but can she, under these loads?

Re: A fundamental principle of aeronautical engineering has been overturned

#142

Post by simne » Wed, May 27, 2026, 3:03 PM UTC

stasomatic wrote: post #116

Arodex wrote: post #89

Earlier quoted context omitted.

Water is fairly viscous, and when you try to pull through too fast you completely change regime due to cavitation. In comparison, from my days studying aerodynamics for RC soaring, air has a wider range of "viscosities" (represented by the Reynolds number) depending on the scale of your aeroplane and the speeds you intend to go through the atmosphere. The aerodynamic ideal or what count as useful tricks (winglets, di…

Asking as a complete neophyte - how does this reconcile with modern war planes being inherently unstable as far they flight dynamics go, without their enormous thrust capabilities? I’m just curious, I know nothing about the subject, but it seems that the solution we came up with is thrust, baby.

That's simple - to make quick rotation, you must apply force (torque) and beat inertia - from mathematics could know, the farther from center of mass the more energy will spend to rotate at same speed.

So, to rotate faster, you need larger control surfaces.

From other side, traditionally, self-stabilize spent at least 1% of energy (on small planes normal up to 10%). What all this mean - with 10 000kg of total weight, your control surface will constantly make 1000kg of force to just fly, but when need to turn, will need significantly more than 1000kg, that's all.

Old planes need self-stabilize, because constant corrections was very time consuming, but modern have powerful computers and could provide artificial stabilization - current 1kg computer could provide same stabilization as control surface constantly making 1000kg of force.

Re: A fundamental principle of aeronautical engineering has been overturned

#143

Post by stasomatic » Wed, May 27, 2026, 3:14 PM UTC

bombcar wrote: post #125

stasomatic wrote: post #116

Earlier quoted context omitted.

Asking as a complete neophyte - how does this reconcile with modern war planes being inherently unstable as far they flight dynamics go, without their enormous thrust capabilities? I’m just curious, I know nothing about the subject, but it seems that the solution we came up with is thrust, baby.

Unstable fighters gives them much more maneuverability at the cost of “not returning to straight and level flight” that normal planes have. It’s not directly related to how the wind goes over the wings.

I am curious about humans operating machinery outside of our inherent performance envelopes. Do we have enough runway beyond switching arrow tips from flint to SS?