Hi Jon,
I stand corrected. I should of included the disclaimer of the author, I also didn't include the text that included who asked the man the questions and what the question entailed. That is why I included the link for the source of that quote.
Hydrodynamic properties and aerodynamic properties have a fair bit of cross over in my opinion, so I don't always look to invent some thing totally new, but look around me to see has been done in other areas. Even if they are from very different areas. Many things can be used very successfully for other applications. Just like Rain-X wasn't designed to keep tiny bubbles of submerged submersible viewports and other clear surfaces. The main point I was trying to get across was that flaps, once a plane has touched down are part of the braking system, and that some planes use additional flaps just for braking. The Deep Flight Subs show that aircraft type configuration work under water for flying/gliding underwater. Since water is far more dense then air those surfaces don't usually need to be as large, and the far reduces cruising speeds of the Deep Flight subs also changes things.
The term "stopping flaps" I used until I decided I liked the term braking flaps better. But even in that first post I used the term speed brakes as was used in the below article. This is how I put it. "You could install some sort of stopping flaps (speed brakes) on both sides of your sub that are curved to fit the shape of your hull. Much like a US Navy test sub USS Albacore." Would you prefer I use the term hinged panels instead?
For my gliding subs I was talking about adding braking flaps on the wings like they are on a airplane, but with an additional flap moving upwards to keep the sub on the same heading.
"The Dorsal rudder was reinstalled and enlarged and the boat
was outfitted with speed brakes. These brakes - another concept borrowed
from aviation - technology, consisted of 10 hinged panels ringing the
after part of the ship. When needed, they were hydraulically opened into
the waterflow, bringing the boat to a rapid stop.
http://www.hazegray.org/navhist/albacore.htm
I worked up my concept for my double rudder/braking flaps with out seeing that it had already been done in part on planes. Seeing it had been done successfully on a number of production planes, made me for confident that I might me onto some thing.
Your resident possibility thinker ;)'
Regards,
Szybowski
From: jonw@psubs.org
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] planes control surfaces
Date: Fri, 29 Aug 2008 23:52:05 -0400
Brent,
You
forgot to add the disclaimer of the author..."Now I'm not an expert on
airliners, but I am happy to expose my ignorance (best way to learn!) and so
here, for those interested, is my answer:"
I wouldn't
say he's ignorant, but he certainly does not understand the purpose of
flaps. While it is all very interesting of course regarding airplanes,
none of it applies to submersibles even in the context of "speed brakes".
Your original message with the subject title "Stopping Flaps" was a misnomer
since nobody is really talking about installing "flaps" as they appear on
airplanes. Whether anyone successfully installs "speed brakes" on a small
sub is another matter, but it is a more accurate term for what has been under
discussion and will help prevent a debate on airplane flaps which has no
relevance on this list.
Thanks,
Jon
"The purpose of flaps is to enable the
aircraft to fly more slowly without
stalling. Deploying flaps increases
both lift and drag. Use of flaps when landing thus enables a steeper approach
path, better visibility over the nose and a slower touch-down speed. The
slower the touch-down speed (perhaps 120~160kts for an airliner, or around
60~70kts for the smaller aircraft I fly), then the less braking and runway
length are required to complete the landing roll before safely exiting the
runway at taxi speed. Generally speaking, full-flap will be used for landing
as this provides maximum benefit in terms of reduced landing speed and extra
drag during the landing roll. (Flaps are also commonly used for take-off in
order to decrease the speed at which the wing starts to provide lift - but
only partial flap is used for take-off to avoid having too much drag whilst
trying to accelerate to take-off speed). A simple definition of aircraft flaps
is here: http://en.wikipedia.org/wiki/Flap_(aircraft)
The purpose of
spoilers is to decrease lift, while the purpose of air-brakes is to increase
drag without altering lift. Sometimes the two effects are combined. One of the
most difficult things to do in an aircraft is to "go down and slow down" at
the same time - spoilers and air-brakes help with this. In flight, air-brakes
are used in the approach phase to slow the aircraft down (it is common for
example to have speed restrictions in busy terminal control areas e.g. below
250kts when 30 miles out say, or max holding speed of 180kts below 10,000 feet
perhaps). The second use of air-brakes/spoilers is provide additional drag and
dump any residual lift during the landing roll, as you have noticed. See
simple definition here:
http://en.wikipedia.org/wiki/Air_brake_(aircraft).
When landing an
airliner, they need to combine the effects of flap (primarily to reduce
touch-down speed, secondarily to add some drag) with the effects of
spoilers/air-brakes (primarily to add drag, secondarily to dump lift once
safely on the ground) as well as reverse thrust, and wheel braking. The
shorter the runway / heavier the aircraft / faster the touchdown then the more
of these forces will be required at once.
Confusion here seems to stem
from the idea that flaps add lift, but during the landing roll we don't want
any more lift: the answer to this is that once the aircraft has touched down,
it is quickly decelerated (by combined effects of drag, reverse thrust and
wheel brakes) to less than the the stall-speed of the fully-flapped wing;
therefore the wing (by definition) is no longer producing enough lift to be
able to fly. Airline pilots have to calculate in advance a target touch-down
speed to be just above the stall speed as they reach the landing threshold -
for a given aircraft, this speed will vary considerably depending on the
weight (load, fuel, etc), runway length, surface type (e.g. grass has less
friction than tarmac) and external conditions (headwind, crosswind, gusts,
windshear, runway condition e.g. wet/dry etc).
Landing small aircraft
is far simpler of course, but we still have to make take-off and landing
performance calculations - see GASCO (General Aviation Safety Council) article
here on this:
http://www.gasco.org.uk/upload/docs/2005_1_Flight%20Safety16-18.pdf.
Regarding
landing without flaps: this is something that we practice because we have to
be prepared for situations where e.g. the flaps malfunction for some reason.
When landing without flaps, you have to make a flatter approach, you have less
forward visibility over the nose therefore, and you touchdown say 10kts faster
- which significantly increases the landing run (i.e. runway length required);
which is as you would expect given the explanatiom above
perhaps!"
http://hardyboysblog.blogspot.com/2005/07/why-do-we-use-flaps-when-landing.html
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