L/D of Virgin Atlantic GlobalFlyer

[Mika Koski]

The subject says it all. Has anybody found information about L/D of
GlobalFlyer? My guess is that Steve knows it, because he is also known
as glider pilot.

Regards,

Mika Koski

[[email protected]]

There was an article in Popular Mechanics I found on the web that
claims that the GlobalFlyer has

"a lift-to-drag ratio of 37-to-1--topping even the Voyager's 27-to-1"

(http://www.popularmechanics.com/science/aviation/1262012.html?page=3&c=y).
There was another interesting piece of information on the GlobalFlyer
website in an article
(http://www.globalflyer.com/ScienceAviation/AviationNuts/TestPilotsView2.jsp)
by Jon Krakow, the GlobalFlyer's chief engineer:

"One of the characteristics of the aircraft is that it glides well. It
glides so well that with the gear up and at light weights with the
engine at idle, it cannot descend. Switching to ground idle helps
reduce the idle thrust, but to descend at a normal 3-degree glide
angle, the gear must be extended and the drag chutes deployed."

Scaled Composite's website (Burt Rutan's shop - the designer/builder of
the GlobalFlyer, the Voyager and the SpacShipOne) can be found here:

http://www.scaled.com

Looks like on a final glide the GlobalFlyer would beat more familiar
gliders such as a Grob 103 or an ASK 21... And you got a beefy
self-launcher in case you blow it...

Markus

[Bruce Hoult]

In article . com>,
wrote:

> There was an article in Popular Mechanics I found on the web that
> claims that the GlobalFlyer has
>
> "a lift-to-drag ratio of 37-to-1--topping even the Voyager's 27-to-1"

And yet they said yesterday that if he ran out of fuel he could glide
200 miles from 50,000 ft. Which is 24:1, assuming nautical miles.
Which makes one suspect that the 37:1 is with the engine idling, not
dead.



> "One of the characteristics of the aircraft is that it glides well. It
> glides so well that with the gear up and at light weights with the
> engine at idle, it cannot descend. Switching to ground idle helps
> reduce the idle thrust, but to descend at a normal 3-degree glide
> angle, the gear must be extended and the drag chutes deployed."

Which doesn't contradict the above.


> Looks like on a final glide the GlobalFlyer would beat more familiar
> gliders such as a Grob 103 or an ASK 21...

ASK21 certainly. But that's right around the same as our Grob Twin
Astirs. Assuming he still has fuel to keep the engine idling...


> And you got a beefy self-launcher in case you blow it...

They say it can climb with the chutes (called "shoots" in one article on
their site yesterday!) deployed. Good thing as they don't jettison.

--
Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------

[Marc Ramsey]

Bruce Hoult wrote:
> And yet they said yesterday that if he ran out of fuel he could glide
> 200 miles from 50,000 ft. Which is 24:1, assuming nautical miles.
> Which makes one suspect that the 37:1 is with the engine idling, not
> dead.

If someone was going to tow you out to sea in your Standard Cirrus,
would you determine how far you can glide back based on the
manufacturers advertised 37:1 glide ratio, or perhaps something a bit
more reasonable like, say, 24:1?

Marc

[Andreas Maurer]

On Sun, 12 Feb 2006 19:44:42 GMT, Marc Ramsey >
wrote:


>If someone was going to tow you out to sea in your Standard Cirrus,
>would you determine how far you can glide back based on the
>manufacturers advertised 37:1 glide ratio, or perhaps something a bit
>more reasonable like, say, 24:1?

Any current airliner features an L/D better than 20:1 with engines
off. Looking at the GlobalFlyers aspect ratio and design, I get the
impression that it's probably even better than 37:1.




Bye
Andreas

[Bruce Hoult]

In article >,
Marc Ramsey > wrote:

> Bruce Hoult wrote:
> > And yet they said yesterday that if he ran out of fuel he could glide
> > 200 miles from 50,000 ft. Which is 24:1, assuming nautical miles.
> > Which makes one suspect that the 37:1 is with the engine idling, not
> > dead.
>
> If someone was going to tow you out to sea in your Standard Cirrus,
> would you determine how far you can glide back based on the
> manufacturers advertised 37:1 glide ratio, or perhaps something a bit
> more reasonable like, say, 24:1?

From 50,000 ft? If I was going for a world record and had a parachute,
people standing by to pick me up, and a wealthy backer? I would expect
that the probability of sink the whole way would be vanishingly low and
that working on 32:1 or 33:1 would be pretty safe but that there would
be a pretty good chance of using what atmospheric variation was
available to manage a good bit better than the glider's raw glide angle.

--
Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------

[Jack]

Andreas Maurer wrote:

> Any current airliner features an L/D better than 20:1 with engines
> off.

Cite?


Jack

[Martin Gregorie]

Bruce Hoult wrote:
> In article >,
> Marc Ramsey > wrote:
>
>> Bruce Hoult wrote:
>>> And yet they said yesterday that if he ran out of fuel he could glide
>>> 200 miles from 50,000 ft. Which is 24:1, assuming nautical miles.
>>> Which makes one suspect that the 37:1 is with the engine idling, not
>>> dead.
>> If someone was going to tow you out to sea in your Standard Cirrus,
>> would you determine how far you can glide back based on the
>> manufacturers advertised 37:1 glide ratio, or perhaps something a bit
>> more reasonable like, say, 24:1?
>
> From 50,000 ft? If I was going for a world record and had a parachute,
> people standing by to pick me up, and a wealthy backer? I would expect
> that the probability of sink the whole way would be vanishingly low and
> that working on 32:1 or 33:1 would be pretty safe but that there would
> be a pretty good chance of using what atmospheric variation was
> available to manage a good bit better than the glider's raw glide angle.
>
It was pretty late in the day when he landed at Bournemouth and would
have been later still at Manston. Good glider or not, I wouldn't count
more than still air, with maybe a bit of added sink, at that time of day.

BTW I agree it would be interesting to see how it performed as a glider.
Let's see now:
- restricted vis - I wouldn't want to share airspace with it
- it might run a cloud street, but could it turn tight enough to
core a thermal?
- with a design cruise of 250kts, it may be too fast to use
anything but wave or ridge lift.
- Anybody fancy running the Appalachians in it? A two hour 750
should be on in theory.

--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot

[Andreas Maurer]

On Mon, 13 Feb 2006 07:10:06 GMT, Jack > wrote:

>Andreas Maurer wrote:
>
>> Any current airliner features an L/D better than 20:1 with engines
>> off.
>
>Cite?


For a gerneral overview, look here at a phantastic NASA report:
http://www.hq.nasa.gov/office/pao/History/SP-468/ch12-2.htm


--- Start quote ---

Abut the B-47 (of 1948!) it says:
The thin, high-aspect-ratio swept wing of the B-47 coupled with its
long high-fineness-ratio fuselage contributed to the high aerodynamic
efficiency of the aircraft. The maximum lift-drag ratio of about 20 is
the highest of any aircraft yet considered in this book, and the
zero-lift drag coefficient was a low 0.0148

707:
The aerodynamic efficiency of the 707-320B may be judged by the value
of the maximum lift-drag ratio, which is estimated to be in the range
from 19 to 19.5.


747:
The aerodynamic configuration of the 747 is very similar to that of
the 707. The 747 wing has slightly more sweepback than that of the 707
and is of about the same aspect ratio. An improved airfoil design is
also incorporated in the wing of the 747. The maximum lift-drag ratio
of the aircraft, (L/D)max, is estimated to be about 18, as compared
with a value somewhat over 19 for the 707, The lower value of
(L/D)max, results from a higher value of ratio of wetted area to wing
area on the 747 than on the 707.

DC-10/Tristar:
The aerodynamic design of both of the three-engine jet transports is
conventional. The wings of both aircraft have about 35° of sweepback
with aspect ratios in the range of 7.0 to 7.5 and feature transonic
airfoils of advanced design. The wings have double-slotted trailing
edge flaps and leading-edge slats. Lateral control is provided by a
combination of ailerons and spoilers. The spoilers are also used to
control lift and drag when deployed symmetrically. Longitudinal
control of the L-1011 is provided by a variable incidence stabilizer
to which the elevator is mechanically linked. The DC-10 employs
separately actuated elevators and stabilizers. Neither aircraft
employs longitudinal trim tabs. The maximum lift-drag ratio of the two
aircraft is estimated to lie in the range between 17.0 and 17.5.

--- End quote ---



With a little searching it should be simple to fnd the numbers of
current airliners which feature significantly higher aspect ratio,
resulting in an increase of L/D over the older airliners mentioned
here.
I haven't seen any official numbers yet, but for the Airbus 340 max
L/Ds between 16 and 24 can be found on a quick search on the net - I
tend to believe that it's provavly a little over 20 due to the high
aspect ratio of the 340.







Bye
Andreas

[Shawn]

Bruce Hoult wrote:
> In article >,
> Marc Ramsey > wrote:
>
>
>>Bruce Hoult wrote:
>>
>>>And yet they said yesterday that if he ran out of fuel he could glide
>>>200 miles from 50,000 ft. Which is 24:1, assuming nautical miles.
>>>Which makes one suspect that the 37:1 is with the engine idling, not
>>>dead.
>>
>>If someone was going to tow you out to sea in your Standard Cirrus,
>>would you determine how far you can glide back based on the
>>manufacturers advertised 37:1 glide ratio, or perhaps something a bit
>>more reasonable like, say, 24:1?
>
>
> From 50,000 ft? If I was going for a world record and had a parachute,
> people standing by to pick me up, and a wealthy backer? I would expect
> that the probability of sink the whole way would be vanishingly low and
> that working on 32:1 or 33:1 would be pretty safe but that there would
> be a pretty good chance of using what atmospheric variation was
> available to manage a good bit better than the glider's raw glide angle.

Maybe they were factoring in a headwind.

[Stefan]

> For a gerneral overview, look here at a phantastic NASA report:

Just found on an other site (http://www.luftpiraten.de/glos_g32.html):

Wright Flyer 8.3
Cessna 172 10

Now that's what I call progress!

Stefan

[Bruce Hoult]

In article >,
Martin Gregorie > wrote:

> BTW I agree it would be interesting to see how it performed as a glider.
> Let's see now:
> - restricted vis - I wouldn't want to share airspace with it
> - it might run a cloud street, but could it turn tight enough to
> core a thermal?
> - with a design cruise of 250kts, it may be too fast to use
> anything but wave or ridge lift.
> - Anybody fancy running the Appalachians in it? A two hour 750
> should be on in theory.

The 250 kts is TAS, at altitude. IAS VNE is 170 knots, similar to
modern gliders.

We also know that empty it has about the same wing loading as typical
gliders, and so presumably about the same stall speed and turning
circle. Note that fully fuelled, at which it has six times the wing
loading it has empty, best powered climb is at 100 knots dirty, 130
knots clean. The corresponding speeds with empty tanks will be 2.4 -
2.5 times lower, or 40 knots and 53 knots. So min sink empty probably
lies somewhere around this range.

--
Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------

[bagmaker]

did he run bug wipers??

[Martin Gregorie]

Bruce Hoult wrote:
> In article >,
> Martin Gregorie > wrote:
>
>> BTW I agree it would be interesting to see how it performed as a glider.
>> Let's see now:
>> - restricted vis - I wouldn't want to share airspace with it
>> - it might run a cloud street, but could it turn tight enough to
>> core a thermal?
>> - with a design cruise of 250kts, it may be too fast to use
>> anything but wave or ridge lift.
>> - Anybody fancy running the Appalachians in it? A two hour 750
>> should be on in theory.
>
> The 250 kts is TAS, at altitude. IAS VNE is 170 knots, similar to
> modern gliders.
>
OK, not as fast as I thought, then, but could still be fun in wave or on
a ridge.

> We also know that empty it has about the same wing loading as typical
> gliders, and so presumably about the same stall speed and turning
> circle.
<
I'd agree about the speed, but doesn't turning circle also depend in
control surface size and deflection range?

> Note that fully fuelled, at which it has six times the wing
> loading it has empty, best powered climb is at 100 knots dirty, 130
> knots clean.
>
Not good to winch with full ballast, then.

--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot

[Jono Richards]

On the global flyers website, it says that it was sensitive
to turbulance, at it might cause structual failure
(certainly whilst full of fuel anyway!) so maybe a
bumpy ridge or rotor may not be that fun...!

It certainly looks better than ETA though.

[Gerhard Wesp]

Martin Gregorie > wrote:
> I'd agree about the speed, but doesn't turning circle also depend in
> control surface size and deflection range?

No. More control will just enable you to get into and out of a turn faster,
but it has no influence on the turn radius itself.

-Gerhard
--
Gerhard Wesp
Zuerich, Switzerland
+41 (0)76 505 1149 (mobile)
+41 (0)44 668 1878 (office)

[Martin Gregorie]

Gerhard Wesp wrote:
> Martin Gregorie > wrote:
>> I'd agree about the speed, but doesn't turning circle also depend in
>> control surface size and deflection range?
>
> No. More control will just enable you to get into and out of a turn faster,
> but it has no influence on the turn radius itself.
>
I'd agree for ailerons and rudder, but I think that in a steeply banked
turn elevator deflection can limit the turn radius. Of course that's
only the case if there's not enough deflection to cause a stall at the
turning bank angle.

I'd further suggest that if there's not enough aileron and rudder
deflection for fairly crisp manoevering it all becomes academic if the
plane can't turn sharply enough to get into the thermal in the first place.


--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot