Blended-wing Airliner

Bertie, I'm not too good at explaining this. It isn't the angle of
banking that matters but how fast you roll the airplane on its axis to
to get to the back angle that matters. We've gone thru the arguement
that one can rotate an airplane around its roll axis 360 degrees and
not have someone on that axis feel anything but 1 G into the seat.
This is different -- someone else ran the numbers to show what happens
to the local G sense as a function of how fast the airplane
accelerated into the roll -- we'd have called that alpha with two dots
above it back in the long hand calculus days. Accelerate into the bank
angle too quickly and if I was sitting far from the roll axis you'd
lift the wine from my glass. You would, I promise, need a locked
cockpit door if you did that.

I'd be at whining over spilt wine.

OK, put the stun gun away, or aim it over there at the other widebody
and frequent poster here.



On Oct 19, 2:58 pm, Bertie the Bunyip wrote:
Tina wrote groups.com:

Bertie, the issue isn't the degree of bank, but rather how fast you
roll the airplane into the bank, that would make a px well off center
feel the gs Dave mentioned. For example, if you had Mx sitting on a
wing tip and you wanted to drop the wing out from under him, you'd
bank into that wing quickly. If you banked slowly he'd not feel
himself grow lighter, but if you did it sharply you near the center
line wouldn't feel much but you could yank that tip down at better
than 1 G even when going to a bank limit of 20 degrees. That was the
issue Dave addressed.

The question was, when you start to bank into a turn, how quickly do
you establish the bank angle? I'm guessing you go from wings level to
20 degrees in a slow count of 3 or 4 -- not too much acceleration --
but would appreciate a guesstimate from some who does it for a living.

Well, even in a conventional airplane you try to do it as smoothly as
you can Actually, you try to do that in any kind of flying no matter how
outwardly frantic it may appear! But I can't see it being significant to
pax comfort unless they were out at the wingtips. In any case the
aircraft would almost certainly be fly by wire anyway so the
opportunities we'd have to raise your red wine out of your glass!

Given a cabin width of fifty feet and a rate of rotation of, say, ten
degrees a second, you'd be moving, you'd move about four or five feet in
a second. You'd hardly feel it at all if the rate was introduced
smoothly.
In fact, you'd be closer to the CG than you would be if you sat in the
nose or tail of any other modern jet whilst it was making a pitch
change.

Bertie

Tina wrote in
oups.com:

Bertie, I'm not too good at explaining this. It isn't the angle of
banking that matters but how fast you roll the airplane on its axis to
to get to the back angle that matters.


Yes, I understood that and that was what I was adressing. If you were 25
feet from the roll axis ant the rol rate of 10 deg per second was
introduced smooothly, you'd rotate a bit under five feet in that second,
less than you would if the airplane was rotated on it's pitch axis at
even a third that rate if you were parked in the front or rear of the
airplane.




We've gone thru the arguement
that one can rotate an airplane around its roll axis 360 degrees and
not have someone on that axis feel anything but 1 G into the seat.
This is different -- someone else ran the numbers to show what happens
to the local G sense as a function of how fast the airplane
accelerated into the roll -- we'd have called that alpha with two dots
above it back in the long hand calculus days. Accelerate into the bank
angle too quickly and if I was sitting far from the roll axis you'd
lift the wine from my glass. You would, I promise, need a locked
cockpit door if you did that.

I'd be at whining over spilt wine.

OK, put the stun gun away, or aim it over there at the other widebody
and frequent poster here.


Well, I have only Anthony's frequent postings to weight loss froups as
evidnce of his widebodiedness, but..


Bertie

A back of the envelope scribble says a smooth sinusoidal quatercycle
from 0 to 20 degrees bank if done in something like a half a second
would make a px sitting about 20 feet from the centerline experience a
third of a g max. I think a half second is doable -- but very
unlikely.

Sounds like mountains and molehills, or, more likely, I really don't
remember how to scribble meaningful stuff on the back of an envelope.

Tina wrote in news:1192833924.408887.249380
@t8g2000prg.googlegroups.com:

A back of the envelope scribble says a smooth sinusoidal quatercycle
from 0 to 20 degrees bank if done in something like a half a second
would make a px sitting about 20 feet from the centerline experience a
third of a g max. I think a half second is doable -- but very
unlikely.

Sounds like mountains and molehills, or, more likely, I really don't
remember how to scribble meaningful stuff on the back of an envelope.



Well, as someone else posted, t'd more likely through turbulence, but the
thing would be FBW anyway, so it wouldn't be an issue.
I can definitely see something like this appearing in the future. In flight
anything that is not a wing is a waste, and as the Horten's proved, they
can be made to work, and work well.


But let's ask the expert,

Anthony?

Bertie

... a px sitting about 20 feet from the centerline
[would] experience a third of a g max.

A third of a g is what the forward acceleration of a jetliner is.

Imagine that vertically, up and down and down and up, as the plane banks
into and out of a turn.

What do building elevators do?

Jose
--
You can choose whom to befriend, but you cannot choose whom to love.
for Email, make the obvious change in the address.

I chose a third of a G on a pretty arbitrary basis -- but you'd agree
that amount is much more noticable in the local vertical direction --
a direct sense of increased weight or more importantly the sense of
growing lighter -- than into the back of the seat as a PX experiences
during takeoff.

My goal was to get a sense of how realistic the issue of Gs induced by
rate of change of bank was, and have concluded (a rebuttable
conclusion) it's not a problem for realistic airplane operations. Your
comments tend to support that.




tarOn Oct 19, 11:32 pm, Jose wrote:
... a px sitting about 20 feet from the centerline
[would] experience a third of a g max.

A third of a g is what the forward acceleration of a jetliner is.

Imagine that vertically, up and down and down and up, as the plane banks
into and out of a turn.

What do building elevators do?

Jose
--
You can choose whom to befriend, but you cannot choose whom to love.
for Email, make the obvious change in the address.

and have concluded (a rebuttable
conclusion) it's not a problem for realistic airplane operations. Your
comments tend to support that.

Actually, my comments are not intended to support this. I think people
would have a problem going up and down and down and up at a third of a
g. It would feel like a roller coaster ride.

Jose
--
You can choose whom to befriend, but you cannot choose whom to love.
for Email, make the obvious change in the address.

Jose wrote in news:mmfSi.60532$YL5.26439
@newssvr29.news.prodigy.net:

and have concluded (a rebuttable
conclusion) it's not a problem for realistic airplane operations. Your
comments tend to support that.

Actually, my comments are not intended to support this. I think people
would have a problem going up and down and down and up at a third of a
g. It would feel like a roller coaster ride.


Wouldn't be as much as that in practice and you get g from the airplane
rotating around it's pitch axis when you sit in a cigar tube anyway!


Bertie

"Tina" wrote ...
Bertie, I'm not too good at explaining this. It isn't the angle of
banking that matters but how fast you roll the airplane on its axis to
to get to the back angle that matters. We've gone thru the arguement
that one can rotate an airplane around its roll axis 360 degrees and
not have someone on that axis feel anything but 1 G into the seat.
This is different -- someone else ran the numbers to show what happens
to the local G sense as a function of how fast the airplane
accelerated into the roll -- we'd have called that alpha with two dots
above it back in the long hand calculus days. Accelerate into the bank
angle too quickly and if I was sitting far from the roll axis you'd
lift the wine from my glass. You would, I promise, need a locked
cockpit door if you did that.

I'd be at whining over spilt wine.


Just my two cents. I'd agree that any pilot would fly smoothly and avoid
jerking the controls. The issue is, as far as I can see, more about
turbulence-induced roll motion such as in windshear and wake turbulence. In
those situations there might occur large roll accelerations, both when the
gust hits and when the pilot has to correct quickly with large control
deflections.
I found a B767 pilot report which stated:

" We entered an arbitrary working area into the Honeywell Pegasus FMC and
set up for some flight maneuvers. The first was a check of roll rate in
bank-to-bank rolls from 30 degrees to 30 degrees at ½ wheel deflection.
Flying the clean airplane at 350 knots, bank-to-bank took 4 seconds, for a
roll rate of 15 degrees per second. Here is where a sharp control input
initiated an aeroelastic response from the airframe. A later check of this
same maneuver with flaps 30 at Vref=136 gave a bank-to-bank time of 6
seconds, or a roll rate of 10 degrees per second. This excellent response at
slow speed in the landing configuration is another indication of the
exceptional handling qualities of this airplane."

So in the first case the average roll rate was 15 degrees / sec. I guess
someone with fresher math / physics knowledge can estimate the instantaneous
start/stop g-forces from those numbers. To me this looks like your wine
might stay in the glass, but Mx at the wingtip may have a hard time hanging
on.

"Snowbird" wrote in
i.fi:


"Tina" wrote ...
To me this looks
like your wine might stay in the glass, but Mx at the wingtip may have
a hard time hanging on.




That would be a good thing.

Bertie