X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 16 Aug 2007 21:19:17 -0400 Message-ID: X-Original-Return-Path: Received: from smtp144.iad.emailsrvr.com ([207.97.245.144] verified) by logan.com (CommuniGate Pro SMTP 5.1.11) with ESMTP id 2266291 for lml@lancaironline.net; Thu, 16 Aug 2007 10:03:11 -0400 Received-SPF: none receiver=logan.com; client-ip=207.97.245.144; envelope-from=marknlisa@hometel.com Received: by relay4.r5.iad.mlsrvr.com (Authenticated sender: marknlisa-AT-hometel.com) with ESMTP id 4742DC0D5 for ; Thu, 16 Aug 2007 10:02:32 -0400 (EDT) From: "Mark Sletten" X-Original-To: References: Subject: RE: Apologies to the farmer's daughter X-Original-Date: Thu, 16 Aug 2007 09:02:32 -0500 X-Original-Message-ID: <003c01c7e00e$17ecb020$6401a8c0@Main> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_003D_01C7DFE4.2F16A820" X-Mailer: Microsoft Office Outlook 11 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3138 Thread-Index: AcfgBd4216AFQmRwQl+BHPWWsS4IhQABZaAA In-Reply-To: This is a multi-part message in MIME format. ------=_NextPart_000_003D_01C7DFE4.2F16A820 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit I believe the analogy describing the impact by referring to falling or jumping from a particular height doesn't account for the attitude of a BRS-equipped aircraft on impact with the ground following chute deployment. Since the aircraft descends in a nose-low attitude, the nose hits first (assuming level ground) absorbing a great deal of the impact energy -- the rest of the airframe would rotate downwards behind the nose until coming to rest (upright hopefully). Assuming the main gear hits after the nose, this would dissipate even more energy as it (the landing gear) is designed to absorb landing energies. In short, landing under a BRS would be more like two smaller impacts instead of a single large one. During jump training in the USAF we learned to do the same thing with our bodies; the Air Force calls it a Parachute Landing Fall - I don't know what the other services call it. Essentially you land into the wind - feet first - then roll forward while rotating your body so as to dissipate the impact energy. Instead of keeping your feet and legs rigid so as to absorb the full impact - as the Cirrus would if it pancaked flat onto the ground - you roll sideways allowing your knees, hips and shoulders to take their share of the beating. If done properly, one can easily jump from 8 feet without (permanent) injury. Mark _____ From: rtitsworth [mailto:rtitsworth@mindspring.com] Sent: Wednesday, August 15, 2007 5:47 PM To: lml@lancaironline.net Subject: RE: [LML] Apologies to the farmer's daughter Rob, etal, FYI: 25fps ~= 17 mph. About like running (full sprint) into solid wall. Perhaps survivable, by OUCH. More math. Gravitational acceleration is approx 32ft/sec^2 (drag-less freefall at the Earth's surface) Doing some algebra to solve for the time to reach 25 fps results in: (25/32)^.5 = 0.88 seconds Doing some integral calculus (not shown) results in a distance traveled of approx 7.5 feet Thus, 25 f/s is about the impact speed from falling off the top step of an 8' step ladder Be careful when cleaning your gutters out there :-) Or another analogy (in case you haven;t fallen off the top of a 8' step ladder lately), terminal velocity from the top of a 34" bar stool would be approximately 12.5 fps (note: 1/2 speed = 1/4 of the impact energy). Rick ------=_NextPart_000_003D_01C7DFE4.2F16A820 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

 

 

I believe the analogy describing the impact by referring to = falling or jumping from a particular height doesn’t account for the attitude = of a BRS-equipped aircraft on impact with the ground following chute = deployment. Since the aircraft descends in a nose-low attitude, the nose hits first (assuming level ground) absorbing a great deal of the impact energy -- = the rest of the airframe would rotate downwards behind the nose until coming to = rest (upright hopefully). Assuming the main gear hits after the nose, this = would dissipate even more energy as it (the landing gear) is designed to = absorb landing energies.

 

In short, landing under a BRS would be more like two smaller = impacts instead of a single large one.

 

During jump training in the USAF we learned to do the same thing = with our bodies; the Air Force calls it a Parachute Landing Fall – I = don’t know what the other services call it. Essentially you land into the wind = – feet first – then roll forward while rotating your body so as to = dissipate the impact energy. Instead of keeping your feet and legs rigid so as to = absorb the full impact – as the Cirrus would if it pancaked flat onto the = ground – you roll sideways allowing your knees, hips and shoulders to = take their share of the beating. If done properly, one can easily jump from 8 feet = without (permanent) injury.

 

Mark

 

From: = rtitsworth [mailto:rtitsworth@mindspring.com]
Sent: Wednesday, August = 15, 2007 5:47 PM
To: = lml@lancaironline.net
Subject: RE: [LML] = Apologies to the farmer's daughter

 

Rob, = etal,

 

FYI:  25fps ~=3D 17 mph.  About like running (full sprint) into solid = wall.  Perhaps survivable, by OUCH.

 

More = math…

Gravitational acceleration is = approx 32ft/sec^2 (drag-less freefall at the Earth’s = surface)

Doing some algebra to solve for the = time to reach 25 fps results in:  (25/32)^.5 =3D 0.88 seconds

Doing some integral calculus (not = shown) results in a distance traveled of approx 7.5 = feet

Thus, 25 f/s is about the impact = speed from falling off the top step of an 8’ step = ladder

Be careful when cleaning your = gutters out there J

 

Or another analogy (in case you = haven;t fallen off the top of a 8’ step ladder lately), terminal velocity = from the top of a 34” bar stool would be approximately 12.5 fps = (note: 1/2 speed =3D 1/4 of the impact = energy).

 

Rick

 

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