X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 28 Jan 2010 12:47:36 -0500 Message-ID: X-Original-Return-Path: Received: from mta31.charter.net ([216.33.127.82] verified) by logan.com (CommuniGate Pro SMTP 5.3.2) with ESMTP id 4102016 for lml@lancaironline.net; Thu, 28 Jan 2010 10:23:28 -0500 Received-SPF: pass receiver=logan.com; client-ip=216.33.127.82; envelope-from=troneill@charter.net Received: from imp10 ([10.20.200.15]) by mta31.charter.net (InterMail vM.7.09.02.04 201-2219-117-106-20090629) with ESMTP id <20100128152252.PQLZ1847.mta31.charter.net@imp10> for ; Thu, 28 Jan 2010 10:22:52 -0500 Received: from [192.168.1.100] ([75.132.241.174]) by imp10 with smtp.charter.net id b3Nr1d00K3mUFT7053NsRy; Thu, 28 Jan 2010 10:22:52 -0500 X-Authority-Analysis: v=1.0 c=1 a=84ZvpW_iPN0A:10 a=ndVRne3UAAAA:8 a=PVQL3CdWvwdJm_i_aTcA:9 a=LUX62Amr-QPV-Nn2z2oA:7 a=lsHJm4E35_LTDg_VZZlFVMC7kDgA:4 a=to7rdFyn7ZTuCBxK3VwA:9 a=p6ZnSyE_o6tBkWhbytEA:7 a=Ty4gwOJWzevwlw5ZKXiDvKd9aQwA:4 From: Terrence O'Neill Mime-Version: 1.0 (Apple Message framework v1077) Content-Type: multipart/alternative; boundary=Apple-Mail-23-769646749 Subject: Re: [LML] Re: Airspeed sensing switch /Auto gear extension / Engine out gear down Issue! X-Original-Date: Thu, 28 Jan 2010 09:22:51 -0600 In-Reply-To: X-Original-To: "Lancair Mailing List" References: X-Original-Message-Id: <0501F0CD-4222-4488-8CE0-EAB02529FCA8@charter.net> X-Mailer: Apple Mail (2.1077) --Apple-Mail-23-769646749 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Chris, Yes. I over-simplified. The descent rate.... As we descend, power off, gear and flaps down, prop in high pitch, at = the Best L/D AOA mark, we see the glide path angle. If it is steep, we = reduce the AOA by nosing down a little, which increases the V a little, = increasing the reserve lift. If it is shallow we can get closer to the = Final AOA mark, nosing up and slowing just a little. Now we have the = optimum lift coefficient available for flare. =20 If there's wind, we lower the AOA to compensate for the airspeed loss as = we get close to the ground. We use our depth perception to decide just when to start the flare at = the right distance from the ground. Flare increases the AOA, using the = Cl we've reserved below the lift curve peak... but by then I'm too busy = to look at the AOA. Pilotage -- I need to refresh my reworkable depth perception to be able = to start the flare at just the right distance above the ground. By = practicing. It's a habit. It's fun. How's that sound? One way I use to understand using an AOA is to look at some lift vs = angle curves for various airfoils, as in Abbott & Doenhoff, or on the = internet. for one's Lancair's airfoil. (the NLF-0215?). The lift = increases to a maximum and hen reduces about 10-15% before the stall = where it drops to about half. =20 As you said, increasing the lift alsoincreases the drag, using energy, = slowing the plane. The actual degrees aren't important because of fuselage part-span, = part-span flaps, and tip losses. I just find the stall break and mark = the AOA, and then find the best rate of climb AOA and mark that... which = should be close to best glide. (I haven't checked power off, flaps, = gear glide yet in the Lancair. Just have about 50 hours on it, Still = working on LOP and a com antenna problem.) Terrence On Jan 27, 2010, at 5:52 PM, Chris Zavatson wrote: > Terrence, > AOA will compensate for weight very nicely. It doesn't know, however, = what descent rate is being flown and how much energy is needed to arrest = that sink. The energy needed goes up as a squared function of the = vertical speed. In the 360, I span descent rates from 500 to 2,000 fpm = on final (ILS to short approaches). The energy thus varies by a factor = ~16. It is the higher end of the scale where one can get into trouble. =20= > The sink rate introduces a time element that the AOA indicator can't = factor in. Here is a thought experiment to illustrate the point. In = the flare you bump your AOA from your mark to just under stall. This = will generate a new, higher quantity of lift that will immediately begin = to decay as the new added drag slows the plane. Now, the higher your = descent rate was, the longer that new, higher, but tapering lift must = act on the plane to stop the sink (F=3Dma). The question becomes: Do = you have enough time before you run out of speed? If you do, then you = stop the sink and all is good. If not, you smack the runway at a high = AOA but still descending. > =20 > Chris Zavatson > N91CZ > 360std > www.N91CZ.com >=20 > F --Apple-Mail-23-769646749 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=us-ascii Chris,
Yes. I over-simplified.  The = descent rate....
As we descend, power off, gear and flaps = down, prop in high pitch, at the Best L/D AOA mark, we see the glide = path angle.  If it is steep, we reduce the AOA by nosing down a = little, which increases the V a little, increasing the reserve lift. =  If it is shallow we can get closer to the Final AOA mark, nosing = up and slowing just a little.  Now we have the optimum  lift = coefficient available for flare.  
If there's wind, we = lower the AOA to compensate for the airspeed loss as we get close to the = ground.
 We use our depth perception to decide just when = to start the flare at the right distance from the ground.  Flare = increases the AOA, using the Cl we've reserved below the lift curve = peak... but by then I'm too busy to look at the AOA.
Pilotage = -- I need to refresh my reworkable depth perception to be able to start = the flare at just the right distance above the ground.  By = practicing.  It's a habit.  It's fun.
How's that = sound?

One way I use  to understand using = an AOA is to look at some lift vs angle curves for various airfoils, as = in Abbott & Doenhoff, or on the internet.  for one's Lancair's = airfoil.   (the NLF-0215?).  The lift increases to a maximum = and hen reduces about 10-15% before the stall where it drops to about = half.  
As you said, increasing the lift alsoincreases = the drag, using energy, slowing the plane.
The actual degrees = aren't important because of fuselage part-span, part-span flaps, and tip = losses.  I just find the stall break and mark the AOA, and then = find the best rate of climb AOA and mark that... which should be close = to best glide.  (I haven't checked power off, flaps, gear glide yet = in the Lancair.  Just have about 50 hours on it, Still working on = LOP and a com antenna = problem.)

Terrence

On = Jan 27, 2010, at 5:52 PM, Chris Zavatson wrote:

Terrence,
AOA will = compensate for weight very nicely.  It doesn't know, however, what = descent rate is being flown and how much energy is needed to arrest that = sink.  The energy needed goes up as a squared function of the = vertical speed.  In the 360, I span descent rates from 500 to 2,000 = fpm on final (ILS to short approaches).  The energy thus = varies by a factor ~16.  It is the higher end of the scale = where one can get into trouble.  
The sink rate introduces a time element that the AOA = indicator can't factor in.  Here is a thought experiment to = illustrate the point.  In the flare you bump your AOA from = your mark to just under stall.  This will generate a new, = higher quantity of lift that will immediately begin to decay as the new = added drag slows the plane.  Now, the higher your descent = rate was, the longer that new, higher, but tapering lift must act on the = plane to stop the sink (F=3Dma).  The question becomes:  = Do you have enough time before you run out of speed?  If you do, = then you stop the sink and all is good.  If not, you smack the = runway at a high AOA but still descending.
Chris Zavatson
N91CZ