Wa great thread!
I guess the inference then is that the Europa's laminar wing also has a
"bucket"? Which would explain the "step" some have experienced?
I wonder if anyone has asked this question of Mr. Dykins? It shure would be
neat to know the weight/speed numbers for the "bucket" of the XS wing.
On another note, could anyone tell me how sensitive the XS wing is to rain?
i.e. does rain destroy the laminar flow enough to cause problems?
Has anyone flown through any heavy weather lately? :-)
Cheers & thanks,
Pete
-----Original Message-----
From: Fred Fillinger
Subject: Re: Speed Kit
Very interesting, Hans. Wing aerodynamics could play a role also, as
in a laminar flow wing there is a "bucket" of low drag at low lift
coefficients, ideally at design cruise speed. The laminar bucket on
Mike Arnold's record-holding AR-5 is so pronounced that the pilot can
feel her going in, or dropping out, such as in a steep bank
(reportedly like "hitting a wall of feathers"). However, it
accelerates into the bucket on its own, without need to dive into it.
But on Rutan's Voyager as described in Rutan & Yaeger's book, there's
frequent discussion of the "bucket," and the struggle it was early in
the flight, due to weight of fuel, to stay in that region. I can't
recall from the book now, but I suspect they tried diving into a lot.
Their fuel computations demanded they stay in the bucket. They did
not have fuel quantity gauges -- tank design would have rendered them
useless -- and fuel remaining was a serious worry throughout the
round-the-world flight.
Regards,
Fred F.
Hans Jrgen Danielsen wrote:
>
> To Fred and all you other speed-freeks...
>
> On all the aircraft I have flown, there is a net gain in speed when
you fly
> it "on the step". The results are more pronounced with "cleaner"
aircraft.
> In the old days when we flew DC-6, C-46 and so forth - although not
> standard operating procedure - we used to climb slightly higher
(100-200ft.)
> than cleared FL, maintaining climb power throughout until cruise
speeds
> where achieved, then slowly descending to correct altitude while
reducing to
> cruise power. A net gain of 5-6 kts where achieved. (NB: This was
before
> Mode C times - not at all tolerable today!!)
>
> On the B 737 -200 we used to maintain climb thrust to a slightly
higher
> speed than chart values - after which cruise EPR was set. Speed gain:
Mach
> 0.005 to M 0.01 with fuel flow about the same as best economy
(M.0.72). The
> interesting thing is that fuel used was thus lower throughout while
cruising
> a wee bit faster than best economy. Sheer magic!
>
> On the -400 and -500, - aircraft with approximately similar drag
curves,
> the Flight Management Computer found out just the same: Best economy
speed
> turned out to be M 0.73/M 0.74 - instead of the more "draggy" 0.72.
(Of
> course the picture is quite complicated with all the various inputs
to the
> computer, of which Cost Index plays a major part).
>
> The lessons learned from this is that of Body Angle while in the
cruise. The
> faster you go - the less is your angle of attack. Which again spells
less
> down pull on the stabilizer (less drag from stabilizer "lift") and
less
> wetted area from aircraft structure. As others have pointed out, a
more
> rearward placement of C of G also plays a major part in obtaining the
> flattest - or optimum - angle. For the pure reason of easing off the
load on
> the Stabilizer. All this is of value to the Europa with its all flying
tail.
> Its really a little Boeing!!
>
> With Christmas greetings to you all!
> Hans.
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