[briandw]

In a conventional aircraft you sit on the roll axis. In a blended wing body design you can have off-axis motion that can increase motion sickness. Rather than rolling with the longitudinal axis of the aircraft, you move up and down when the aircraft banks. Not necessarily a deal breaker, but an additional difference to deal with.

[JumpCrisscross]

> In a blended wing body design you can have off-axis motion that can increase motion sickness

This sounds fixable in avionics and training. (Shallow, gradual banks.)

Note, too, that a larger lifting body needs to bank less to execute the same turn as a craft with more loading.

[amluto]

> Note, too, that a larger lifting body needs to bank less to execute the same turn as a craft with more loading.

This is not really helpful for passenger comfort. For a turn to be comfortable, you want the turn to be such that the effective force the passengers feel has no sideways (relative to the passengers) component, and the required roll angle is only a function of the velocity and turning radius. The aircraft design is irrelevant.

The Wikipedia article is mediocre: https://en.wikipedia.org/wiki/Coordinated_flight

[JumpCrisscross]

Coördination stops lateral passenger movement. It does nothing for up and down. (Coördination is also about more than comfort. It keeps the flow attached to the wing. If your passengers are slipping, so is your wing.) In a roll, with a tubular fuselage, everyone—pilot and passengers—feel about the same vertical Gs. OP’s point is in a flying wing, the folks on the tips will lift up or drop down relative to the pilot and thus experience extra Gs.

My response is (a) this can be controlled in avionics and training, i.e. don’t do that, and (b) now that I think about it, vertical Gs aren’t as sickening as lateral ones.

Specify a maximum roll rate in training and normal-law software and this problem is solved

[amluto]

> Specify a maximum roll rate in training and normal-law software and this problem is solved

I’m wondering whether there are major airfields with traffic patterns that require roll rates that would exceed whatever maximum is desired for comfort. My intuition is that the situation would be tolerable at most airfields but that normal-law limits that are too restrictive could be dangerous.

[JumpCrisscross]

> major airfields with traffic patterns that require roll rates

One, this is where the more lifting body turning faster with less roll kicks in. Two, I suspect those airfields would also be the last ones to add terminals that can dock with a non-standard plane.

[amluto]

> this is where the more lifting body turning faster with less roll kicks in

Can you explain what you mean? If an aircraft follows a given trajectory (center of mass position as a function of time x(t) where x is a 3D position), then it has an acceleration a(t) that is just the second derivative of x(t) and has nothing to do with the shape of the airframe.

Now account for gravity and kinematics: the force per unit mass that must be applied to the airframe is F/m = a + g • ẑ (ẑ is the upward unit vector).

The exact same result applies to a person inside the aircraft. If you want comfortable flight you need F/m to have no sideways component from the perspective of the passenger (and in the absence of gimballed seats the passenger is facing the same way as the airframe).

So far none of this has anything to do with the shape of the lifting body. And I’m wondering why you think more lifting body makes much difference. There are only two real flight parameters knobs you can turn to achieve this condition. You can roll, and you can sideslip. And, unless my intuition about the geometry is quite wrong, you would need a very extreme sideslip angle (pointing the nose quite close to the center of curvature) to have much effect on the required roll angle. So the roll angle needed is mostly a function of the angle of the acceleration vector plus gravity relative to the velocity and not much of a function of how the airframe is able to generate lift.

For another way to think of it, imagine a fancy rocket performing the exact same maneuver with no lift or drag whatsoever. Either the rocket could point itself toward the center of curvature (adjusted for gravity as above) and use its main engines to generate the required acceleration (extreme sideslip), or it could point roughly the same direction as its velocity vector and use a sideways-firing rocket to generate the required acceleration. If the latter, then, for passenger comfort, the roll angle needs to be such that the sideways rocket is in the front/back/up/down plane with respect to the passengers, which determines the required roll angle.

And I don’t see how any of this has anything to do with the same of a lifting body or the actual capabilities of the maneuvering thrusters of a hypothetical rocket. On a given flight path, you have a constrained set of valid roll, pitch, and yaw angles.

[decimalenough]

> Coördination

A few years ago, I would your use of diaeresis an admirable quirk. But now, especially given the em-dashes, I'm wondering if you're an LLM overtrained on the New Yorker.

[ben_w]

I've been following JumpCrisscross's comments for years, either he's real or he's gone to the trouble of fine-tuning the LLM to sound like himself.

(Myself, I've been doing em-dashes since about 2012, I think I found out by accident that you got them on MacOS from option-shift-minus after finding out by accident you could get en-dash from option-minus)

[hahahaa]

I learnt on mentour pilot (or maybe captains speaking?) that the airbus most of the time optimizes for comfort by having a constant g force as you ascend or descend or something like that. Unless you are high aoa. So there are systems that so this sort of passenger comfort thing for sure.

[VectorLock]

Sounds fixable by making the outer seats cheaper.

[xnx]

True, but I have to guess it would feel like a real rollercoaster when making small quick adjustments while landing.

[unsnap_biceps]

I don't understand your point. Does the wider passenger compartment leads to more extreme transitions at the edges? Is there something else at play I'm not thinking of?

[mlyle]

Picture being on the end of the wing and how much you move up or down when the plane rolls.

An airliner entering a 30 degree roll over 3 seconds would have passengers pop up or down 25 feet, with at least +0.3 and -0.3G of acceleration. It would come with a "going over the top of the roller coaster" feeling. This is in addition to the roll / rotation.

Yaw is interesting for similar reasons.

[numpad0]

sin(bank_angle) x cabin_width/2 = max_vertical_displacement_at_angle

[deadbabe]

Just gimbal the seats.

[fugaziboutit]

New commercial seating design: Oops, All Pinch Points!

[beau_g]

Bean bag chair seats solve every problem.

[fastball]

Gimbal the floor?

[NegativeLatency]

Doesn’t fix translation?

[cr125rider]

Simply noclip the passengers!

[samplifier]

Might as well iddqd and idkfa at that point. Or grantme all. Pick your flavor.

[mmh0000]

That only works if the engines move the planet around the airplane.

[ffsm8]

Great, so there is the solution!