BobsV35B(at)aol.com
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 Posted: Sat Jun 26, 2010 9:58 pm Post subject: Way Off Topic! Was: Re: Push Button "Speed Brakes"? |
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Good Morning 'Lectric Bob,
I note this comment in your excellent dissertation concerning the difference between speed brakes and spoilers: "The space shuttle has a bifurcated rudder that can be simultaneously extended both to the right and left of the vertical fin for the purpose of throwing out some aerodynamic drag."
You might recall that Ted Wells used the same device on the original Model 17 Beechcraft.
Those folks had things pretty well figured out!
Happy Skies,
Old Bob
Do Not Archive
In a message dated 6/26/2010 11:49:16 P.M. Central Daylight Time, nuckolls.bob(at)aeroelectric.com writes:
| Quote: | --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
At 08:24 PM 6/26/2010, you wrote:
| Quote: | I think it has to have a voltage applied at pin 7 continuously to
keep the speed brakes up. It's designed so that if the unit loses
power they fail to the retracted position.
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This is an excellent topic for discussions of failure
mode effects analysis =AND= understand the simple-ideas
behind the system design goals.
A really important side note concerning the Precise Flight
product is that it's not a "speed brake" in the aerodynamic
sense of the phrase . . .
A speed brake is a means by which aerodynamic DRAG is
added to the mix of thrust-lift-mass-drag combination
that dictates airframe behavior/performance. Drag can
be and most often is added to the performance mix by
throwing large surface areas out into the slipstream.
I've participated in programs that crafted special
actuators to extend large panels out of aft
locations on the airplane where design goals called for
an increase in the airframe's total drag component
while having little or no effect on lift.
Large air transport aircraft will lift rather large
areas of aluminum from the top surface of the wing.
In cruising flight, only the outboard panels will
occasionally lift during roll control maneuvers. In
this mode, the panels are SPOILERS that reduce lift
on one wing at a time. Loss of lift augments rolling
moment offered by the ailerons.
However, during landing roll-out, one often sees
every square foot of aluminum through out into
the breeze with the obvious intent of making the
whole machine a very draggy aerodynamic shape where
flying efficiency is not important while slowing
down is most important.
The space shuttle has a bifurcated rudder that can
be simultaneously extend both to the right and left
of the vertical fin for the purpose of throwing out
some aerodynamic drag.
The Precise Flight product is the brainchild of on
Bill Thompson who was chief of flight test at Cessna
single engine division while I was a tech writer.
Bill was directly responsible for introducing me to
Ken Razak, former dean of engineering at Wichita
State who became my second most revered mentor,
business partner and friend with more than 40 years
of collaboration on interesting things. But that's
another story.
Bill's product first evolved on the Cessna 210
and was later approved for installation on a host
of TC aircraft. I was introduced to the device
in Kerrville, TX by a Mooney test pilot and later
on another Mooney by George Masey.
It was then that I was given to understand that
the Precise flight product is NOT A SPEED BRAKE.
It's a SPOILER. Design goals for this device call
for reducing lift on the wing while having very
little effect on total drag. The artfully installed
blades can be extended during a stabilized approach
to offer a profound effect on rate of descent
while having little effect on pitch angle or
indicated airspeed.
There are similar devices on the top of the wing
in a Beechjet that offer augmentation of tiny
ailerons for roll control in fight -OR- an increased
rate of descent when fully extended on both sides.
These also are NOT SPEED BRAKES. They might be extended
during a roll out for the purpose of killing lift
to increase weight on wheels and improve braking
by the tires . . . but their effect as aerodynamic
speed brakes is nil.
The reason why this distinction is important has
to do with proper and useful deployment of SPOILERS.
I'm working an accident case where a pilot reports
having extended his Precise Flight "speed brakes"
a few seconds before an off-airport landing. He
was under the mistaken understanding that they
would help slow things down before an un-planned
contact with the ground. In fact, the impact forces
were probably GREATER than if he had not extended
the SPOILERS at all. The net effect of extending the
Precise Flight paddles on top of the wing was to
INCREASE rate of descent to the ground.
So after understanding what these things are designed
to do for you, I'll suggest that its a really good
thing to make sure that under no circumstances
can they can extend when you don't want them to
and that they can always be retracted when they're
not needed . . . or their extension would increase
risks of bent airplanes or broken people.
When considering departures from the manufacture's
instructions, make sure that you're not crafting
a situation that increases risk of unintended
extension or loss of pilot control for that
extension. The system should probably include an
easily accessed power switch. Removal of power
from the system insures positive retraction
irrespective of what other switch becomes
stuck.
Itty-bitty switches on stick-grips are not renowned
for their robustness. Take care that your quest
for convenience does not increase risks for
un-intended consequences.
Bob . . ========================= Use utilities Day ================================================ - MATRONICS WEB FORUMS ================================================ - List Contribution Web Site sp; ===================================================
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