Glider Wings on a 747?

On 10/22/2012 5:25 PM, Craig Funston wrote:
On Monday, October 22, 2012 3:12:22 PM UTC-7, Bob Kuykendall wrote:
On Oct 22, 12:15 pm, Bob Whelan wrote:

This being RAS, take a look back at Dick Schreder's original HP-15...a
failed attempt to utilize extremely high aspect ratio to maximize
performance. It likely ran afoul of structural and aerodynamic
considerations, mostly the latter, I'd guess. The small chord almost
certainly meant its airfoil (even if laminarly executed) was operating
outside the theoretical laminar bucket at slow (thermalling) speeds due
to Reynolds number effects, even without considering profile accuracy.
What's the most effective way to hurt average XC speed?

Bob, I don't think that there were any particular structural issues with
the HP-15. As I understand it, Dick built it while he was in a phase of
experimenting with honeycomb cores. So it had thick skins for bending
stiffness and milled honeycomb core to give it shape--but no wing ribs or
discrete spar caps. The carrythrough consisted of a set of knuckles
bolted or riveted to the skin that joined to their counterparts on the
opposite wing.

As I recall, you are spot-on regarding its performance characteristics.
It went like stink in a straight line, but had huge sink rates when
slowed down and compelled to circle.

Thanks, Bob K.

Dick was years ahead of his time on the HP-15. I did a quick comparison to
the Duckhawk. Wing Area: HP-15 75 sq.ft. Duckhawk 80 sq.ft.

Aspect Ratio: HP-15 33 Duckhawk 30
Empty Wt. HP-15 330 lb. Duckhawk 390 lb.
Gross Wt. HP-15 600 lb. Duckhawk 960 lb.

I suspect the airfoil was a significant part of the problem for the HP-15.
I don't have any information on the percentage thickness of the profile,
but given the materials it's likely to have been thicker than the
Duckhawk. Dick did some amazing things during a time without sophisticated
CFD and carbon fiber.

Cheers, Craig

Bob

I goofed including the "structural" comment...but at least I tried to "mostly"
lay the blame on the "aerodynamic" part! And thanks for the structural
methodology fill-in...all completely unknown to me, prior. (Sounds like an
amazingly simple wing, in structural terms, too. As I'm sure you well know,
it's relatively easy to design/engineer complex things...more difficult to
keep things simple.)

I agree with Craig's assessment of Dick Schreder's doing "some amazing
things...". IMO he was one of those "once in a generation" geniuses, blessed
with an amazing mind, far-ranging mechanical competence/expertise, and obvious
piloting skills, not to mention excellent business skills. Truly a renaissance
man, in our field!

As a former owner of an HP-14, I never had any qualms about its structural
integrity, and the ship remains airworthy today (though not regularly flown in
the past few years). More generally, I know of only 3 HP's that fell prey to
structurally-based problems: the one-off HP-7; the original HP-12; and an
Australian-registered HP-14. In my mind, none of the accidents can be
attributed to any fundamental structural design issue. In short, I think
Schreder's design body of work as measured by the record of the large fleet of
homebuilts he helped create have a heckuvan impressive structural safety
record. Just wanna be clear on this point...

Bob - apologies for contributing to thread creep - W.

On Oct 22, 2:15*pm, Bob Whelan wrote:

If range exclusively was what was being optimized, then the short form answer
to your first question is, "Yes."

Thank you very much for this quite coherent explanation. Others have
mentioned to me the same basic point that a glider has a much simple
"mission" to execute than a 747 and thus the 747's wing has to fulfill
many competing roles and needs leading to design compromises (as in
any engineering endeavor).

No it is not winter yet - but this discussion walks and talks like a
good article for Soaring!

Thanks again. John

Great responses Papa3 & BobW. For those wanting to quantify glide ratios, the Airbus A330-300 quotes a glide ratio of 18:1 with a double engine failure. This includes the added drag from the RAT, an emergency windmill that extends to provide hydraulic and electrical power in such a situation. Not bad for a 238,000kg machine

Casey

On Friday, November 23, 2012 10:00:08 AM UTC+1, wrote:
Great responses Papa3 & BobW. For those wanting to quantify glide ratios, the Airbus A330-300 quotes a glide ratio of 18:1 with a double engine failure. This includes the added drag from the RAT, an emergency windmill that extends to provide hydraulic and electrical power in such a situation. Not bad for a 238,000kg machine Casey

Yeah but what is the sink rate? And at what speed?

Kirk
66

On Tuesday, October 23, 2012 6:03:13 AM UTC+13, jfitch wrote:
On Monday, October 22, 2012 6:11:38 AM UTC-7, JohnDeRosa wrote:

I was asked last night "Why don't commercial airliners (747, A380,



etc) have 'super wings' like gliders?" I mumbled something semi-



coherent but didn't really know the correct answer.







So, would high aspect ratio and highly efficient glider-like wings



enhance fuel economy for all airplanes? What are the engineering



tradeoffs for wing design between a hulking airliner and a slim/trim



glider?







Sign me "I ain't no AeroE".







Thanks, John



Nearly all powered aircraft cruise at speeds way above stall. That means the lift coefficients in cruise are low, therefore the induced drag (proportional to Cl ^2) is low, therefore aspect ratio is less important.

Not really true of jet airliners. They fly so high that although they're going fast they're at a pretty big angle of attack and not all that far from the stall.

On 11/23/2012 9:59 PM, Bruce Hoult wrote:

Nearly all powered aircraft cruise at speeds way above stall. That means the lift coefficients in cruise are low, therefore the induced drag (proportional to Cl ^2) is low, therefore aspect ratio is less important.

Not really true of jet airliners. They fly so high that although they're going fast they're at a pretty big angle of attack and not all that far from the stall.


Google "coffin corner". Here's Wikipedia's entry
http://en.wikipedia.org/wiki/Coffin_corner_(aviation)

Tony "6N"

I understand the reason why glider type high aspect ratio doesn't work on
jet
liners is really more simple than suggested by some replies here.

Basically no one has yet figured out how to get laminar flow at above 0.7
Mach. A number of paper study airliners have been investigated with very
high aspect ratio wings and high degrees of laminar flow but they are
cruising
at 0.5 Mach. Despite the significant reduction in fuel burn most of the
airline
operators have rejected them because they are just too slow.

There's a lot of R&D work going on looking at high Mach laminar flow right

now.

Fraser

A330:
Actually the angle of attack at cruise on an A330 is in the 2.5 degree range, so not that big of an AOA. But still close to stall. Because of the supercritical airfoil and compressibility effects, the stall angle of attack is quite dependent on the Mach number. Somewhere around 6° at M.82 (stall warning at 4°) and a higher AOA when slower (stall warning at 10° at .3M), becoming more constant at Mach numbers below .3.

For descent, we plan about a 3:1 (3 miles per thousand feet; 18:1 in glider terms) for idle descents, and that's at M.81/300 knots then 250 kts below 10,000. L/D speed being at landing weight usually around 210 kts, depending on weight.
Airbus quotes the same glide ratio (3:1) for dual engine flameout glide at best L/D (known as green dot speed due to the symbol used on the airspeed indicator for it). The exact speed varies with weight and altitude.

The 330's wing is a thing of beauty, with a 198' span, which is wider than the -200 is long (191') (which is actually quite similar to the 777's dimensions). However, it often flies higher than its widebody counterparts (767, 777) at the same mission stage (often by a significant margin). It's usually capable of FL410 at the last part of any ocean crossing.

In terms of "coffin corner", typical cruise numbers at FL 410, M.82 IAS:241kts Vmo/Mmo:257kts/M.84, minimum recommended speed (Vls)210kts., Which is really not that tight of a window. The Mach buffet is actually difficult to achieve due to the airfoil(according to Airbus test pilots), and the Mach buffet speed would be well beyond the given Mmo speed. Usually it's propulsion limited (the ability to be able to climb 300 ft/min) rather than aerodynamically limited (low and high speed limits converging).
The A330 is optimized for about M.82. which is slower than the 747, 777, & 787, but faster than the 767, 757, 737.


On Friday, November 23, 2012 6:59:52 PM UTC-8, Bruce Hoult wrote:
On Tuesday, October 23, 2012 6:03:13 AM UTC+13, jfitch wrote:

On Monday, October 22, 2012 6:11:38 AM UTC-7, JohnDeRosa wrote:



I was asked last night "Why don't commercial airliners (747, A380,







etc) have 'super wings' like gliders?" I mumbled something semi-







coherent but didn't really know the correct answer.















So, would high aspect ratio and highly efficient glider-like wings







enhance fuel economy for all airplanes? What are the engineering







tradeoffs for wing design between a hulking airliner and a slim/trim







glider?















Sign me "I ain't no AeroE".















Thanks, John







Nearly all powered aircraft cruise at speeds way above stall. That means the lift coefficients in cruise are low, therefore the induced drag (proportional to Cl ^2) is low, therefore aspect ratio is less important.



Not really true of jet airliners. They fly so high that although they're going fast they're at a pretty big angle of attack and not all that far from the stall.

I have no idea! I do know that that the winglets on a 737 are the same as
those on an ASW27b and where designed by Afandi Darlington who is a UK
glider pilot.

I have no idea! I do know that that the winglets on a 737 are the same as
those on an ASW27b and where designed by Afandi Darlington who is a UK
glider pilot.