Fifth Engine for the White Knight II?

I was just thinking it might be wise to put a fifth small turbofan,
something like a Williams International, above the pylon, just in case.

I'm assuming this thing can just about glide anywhere, but I'm wondering
how well this thing flies with multiple engine outs. Since they will
presumably have paying passengers in this thing, a small pusher fan
might be in order. Those main engines seem pretty powerful for that.

Anybody have any idea how something like this might handle with a single
engine, and almost empty on fuel?

On Jan 24, 10:27 am, kT wrote:
I was just thinking it might be wise to put a fifth small turbofan,
something like a Williams International, above the pylon, just in case.

I'm assuming this thing can just about glide anywhere, but I'm wondering
how well this thing flies with multiple engine outs. Since they will
presumably have paying passengers in this thing, a small pusher fan
might be in order. Those main engines seem pretty powerful for that.

Anybody have any idea how something like this might handle with a single
engine, and almost empty on fuel?

The rendering I saw showed four engines on White Knight II. The
chances of losing all four engines is really low (note I did not say
impossible or incalculably low).

Two engines out on the old Boeing 707 (and presumably the current
similar KC-135) was said to be very interesting when both engines were
on the same side. I wonder if anyone could lend insight into how the
747, Airbus 340, or Airbus 380 handle with two out on the same side.
There are tales of a 707's and DC-8's landing with only one engine.
But there are also stories of how airline crews were killed on
training flights (without passengers) practicing for some of these
scenarios back in the pre-simulator days.

You have to weigh the cost of the additional weight and complexity
versus the value a 5th engine would bring if needed. I suspect
numerically, it might not work out.

Take care . . .

John

John wrote:
On Jan 24, 10:27 am, kT wrote:
I was just thinking it might be wise to put a fifth small turbofan,
something like a Williams International, above the pylon, just in case.

I'm assuming this thing can just about glide anywhere, but I'm wondering
how well this thing flies with multiple engine outs. Since they will
presumably have paying passengers in this thing, a small pusher fan
might be in order. Those main engines seem pretty powerful for that.

Anybody have any idea how something like this might handle with a single
engine, and almost empty on fuel?

The rendering I saw showed four engines on White Knight II. The
chances of losing all four engines is really low (note I did not say
impossible or incalculably low).

Two engines out on the old Boeing 707 (and presumably the current
similar KC-135) was said to be very interesting when both engines were
on the same side. I wonder if anyone could lend insight into how the
747, Airbus 340, or Airbus 380 handle with two out on the same side.
There are tales of a 707's and DC-8's landing with only one engine.
But there are also stories of how airline crews were killed on
training flights (without passengers) practicing for some of these
scenarios back in the pre-simulator days.

You have to weigh the cost of the additional weight and complexity
versus the value a 5th engine would bring if needed. I suspect
numerically, it might not work out.

This vehicle in no way compares to a conventional airliner.

I can see no way this thing can fly with asymmetric thrust, but I'd be
happy to be proven wrong on that. I'm pretty sure that's why they went
with four engines in this manner, besides the obvious thrust levels.

Like I said, I'm sure this thing can glide back no problem, but they'd
have to dump a lot of fuel into the environment to do it. It would be
interesting to see what kind of abort profiles they are anticipating.

kT wrote:
I was just thinking it might be wise to put a fifth small turbofan,
something like a Williams International, above the pylon, just in case.

I'm assuming this thing can just about glide anywhere, but I'm wondering
how well this thing flies with multiple engine outs. Since they will
presumably have paying passengers in this thing, a small pusher fan
might be in order. Those main engines seem pretty powerful for that.

Anybody have any idea how something like this might handle with a single
engine, and almost empty on fuel?

Seems to me that if you lose two on one side, you're going to be
wondering where the required area of rudder is. Maybe you just pull the
thrust on the other two as well, and glide down (hoping, or planning,
that there's somewhere to glide to from rotation onwards).

I'd also be worrying about the whole thing coming apart from the
transients arising from an abrupt loss of an engine. That structure just
doesn't look very stiff.

Sylvia.

On Fri, 25 Jan 2008 20:07:22 +1100, in a place far, far away, Sylvia
Else made the phosphor on my monitor glow
in such a way as to indicate that:

kT wrote:
I was just thinking it might be wise to put a fifth small turbofan,
something like a Williams International, above the pylon, just in case.

I'm assuming this thing can just about glide anywhere, but I'm wondering
how well this thing flies with multiple engine outs. Since they will
presumably have paying passengers in this thing, a small pusher fan
might be in order. Those main engines seem pretty powerful for that.

Anybody have any idea how something like this might handle with a single
engine, and almost empty on fuel?

Seems to me that if you lose two on one side, you're going to be
wondering where the required area of rudder is. Maybe you just pull the
thrust on the other two as well, and glide down (hoping, or planning,
that there's somewhere to glide to from rotation onwards).

I'd also be worrying about the whole thing coming apart from the
transients arising from an abrupt loss of an engine. That structure just
doesn't look very stiff.

I'm sure that it's a lot stiffer than it looks. It's composite, and
Scaled has been building airplanes like this for a long time.

Sylvia Else wrote:


I'd also be worrying about the whole thing coming apart from the
transients arising from an abrupt loss of an engine. That structure
just doesn't look very stiff.

If Rutan did the design, it won't be stiff- it well flex under stress,
rather than break.
But this is very much a fair-weather aircraft; you wouldn't want to fly
it into a thunderstorm by any means.
The widely separated engines hit me as odd also. I would have thought
they would have mounted them above the center section rather than under
the outer wings. Still, it's not wise to second-guess Rutan when it
comes to aerodynamics. ;-)

Pat

Pat Flannery wrote:


Sylvia Else wrote:


I'd also be worrying about the whole thing coming apart from the
transients arising from an abrupt loss of an engine. That structure
just doesn't look very stiff.

If Rutan did the design, it won't be stiff- it well flex under stress,
rather than break.
But this is very much a fair-weather aircraft; you wouldn't want to fly
it into a thunderstorm by any means.

Since when would anyone purposely fly into a thunderstorm?

Flown much, Pat?

The widely separated engines hit me as odd also. I would have thought
they would have mounted them above the center section rather than under
the outer wings. Still, it's not wise to second-guess Rutan when it
comes to aerodynamics. ;-)

Which is precisely why I am questioning it.

On Fri, 25 Jan 2008 20:07:22 +1100, Sylvia Else wrote:

Seems to me that if you lose two on one side, you're going to be
wondering where the required area of rudder is. Maybe you just pull the
thrust on the other two as well, and glide down (hoping, or planning,
that there's somewhere to glide to from rotation onwards).

It'll always be flying back to the same airport, sorry, spaceport,
so "alternates" is hardly an issue.

--
One way ticket from Mornington Crescent to Tannhauser Gate please.

Fevric J Glandules wrote:
On Fri, 25 Jan 2008 20:07:22 +1100, Sylvia Else wrote:

Seems to me that if you lose two on one side, you're going to be
wondering where the required area of rudder is. Maybe you just pull the
thrust on the other two as well, and glide down (hoping, or planning,
that there's somewhere to glide to from rotation onwards).

It'll always be flying back to the same airport, sorry, spaceport,
so "alternates" is hardly an issue.


From a descent height, yes. But what about during the initial climb?
You don't want to make the greenhorn mistake of attempting the
"impossible turn".

Sylvia.

On Jan 25, 12:27 am, kT wrote:

Anybody have any idea how something like this might handle with a single
engine, and almost empty on fuel?

Probably better than a typical rocket. That is where the comparison
should be, not with airliners.