X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 22 Dec 2008 11:30:53 -0500 Message-ID: X-Original-Return-Path: Received: from smtp1.av-mx.com ([137.118.16.57] verified) by logan.com (CommuniGate Pro SMTP 5.2.11) with ESMTP id 3391229 for lml@lancaironline.net; Sun, 21 Dec 2008 19:41:05 -0500 Received-SPF: pass receiver=logan.com; client-ip=137.118.16.57; envelope-from=pinetownd@volcano.net Received: from DennisDell (65-166-100-164.dsl.volcano.net [65.166.100.164]) (Authenticated sender: pinetownd@volcano.net) by smtp1.av-mx.com (Postfix) with ESMTP id 6E8AB290532 for ; Sun, 21 Dec 2008 19:40:27 -0500 (EST) X-Original-Message-ID: From: "Dennis Johnson" X-Original-To: "Lancair Mailing List" Subject: Legacy W&B X-Original-Date: Sun, 21 Dec 2008 16:40:22 -0800 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_003B_01C9638A.D17E45C0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5512 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 This is a multi-part message in MIME format. ------=_NextPart_000_003B_01C9638A.D17E45C0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Hi Alan, I made all my Legacy's CG calculations from the firewall joggle. I = wrote in my POH that the firewall joggle is assigned the arbitrary value = of fuselage station (FS) 65.0, regardless of the actual distance from = the propeller spinner. I used 65.0" instead of the 64.625" number in = the factory POH because since both the 65.0" and 64.625" are arbitrary = numbers, I started with a round number. (Besides, perhaps due to my = finance background, I don't like to use numbers that imply more = precision than is actually there. (Sure, I know that 64.625" is the = round number of 64-5/8", but who uses fractions to compute CG?)) I could have just as easily assigned the value of 0" to the firewall = joggle, but then I would have to deal with negative numbers forward of = the firewall joggle and positive numbers aft. That would just make this = more difficult than it needs to be.=20 Once I defined the firewall joggle as FS 65.0, I measured the distance = between the center of the nose wheel and FS 65.0 and the distance = between the center of the main gear and FS 65.0. I measured the = distance between the leading edge of the wing at butt line (BL) 27 and = FS 65.0". From there, the rest is straight mathematics from the factory = POH. Using this method, I don't think it makes any difference where a builder = sets the reference point. So long as they use actual measurements of = the distance between the reference point and the wheels and leading edge = of the wing at BL 27, the mathematics will be identical. =20 I backed into the CG of the baggage area by weighing the airplane with = and without weight in the baggage area and then computing the actual CG. = In my case, the baggage CG is 144.5" (with a firewall reference point = of 65.0"). That was with the weight loaded into the approximate center = of the baggage area. This part isn't related to your question, but so long as we're talking = about CG, I compute my Legacy's CG with and without fuel. My empty = Legacy has a forward CG and burning fuel moves the CG forward. I can = theoretically take off with the CG within limits and then be too far = forward on landing. My zero fuel CG calculation checks to make sure = I'll still be in limits on landing in the worst case situation that I = land with empty tanks. To eliminate the need to compute the baggage effect on CG for every = flight, I made up the following table that shows the minimum and maximum = allowable baggage weight for various combinations of pilot weights. = Note that this is based on forward CG considerations; many of these = combinations would result in exceeding max gross weight of 2,400 pounds = with full fuel. However, if the amount of fuel is managed to stay = within the max allowable gross weight, the following baggage weights are = acceptable. Here's the page from my POH: =20 Acceptable Baggage Loading, in Pounds Combined Wt of Pilots, Any Fuel Baggage, with Oxygen Bottle Baggage, without Oxygen Bottle =20 150 30-160 38-160 =20 175 20-160 28-160 =20 200 12-160 20-160 =20 225 2-160 10-160 =20 250 0-160 0-160 =20 275 0-150 0-160 =20 300 0-130 0-140 =20 325 0-100 0-110 =20 350 0-75 0-85 =20 375 0-55 0-65 =20 400 0-30 0-40 =20 Note: The baggage weights are the minimum and maximum weights for the = combined weight of the pilot and copilot. For example, a pilot weighing = 175 pounds would have to carry at least 20 pounds of baggage in addition = to the oxygen bottle, or 28 pounds if not carrying the oxygen bottle. = The weight of the baggage should be roughly centered (forward-aft) in = the baggage area. Moving the bags aft is better than moving them = forward. Although heavier baggage is acceptable, the maximum = recommended is 100 pounds. The weight of the pilots includes gear they = carry and wear and center console glove box contents. The maximum = weight of instrument panel glove box contents is three pounds.=20 =20 The key factor in this table is the forward CG upon landing, assuming = the worst case situation of zero usable fuel. If additional fuel is = assured on landing, each gallon of fuel eliminates the need for 1.5 = pounds of baggage. For example, a 175 pound pilot would have no minimum = baggage requirement if the usable fuel upon landing was assured to be at = least 20 gallons.=20 =20 *The empty weight of the airplane includes all avionics, radios, = instruments, two gallons of unusable fuel in each wing, eight quarts of = oil in the engine, a headset, and a two-pound toolkit behind the seat. =20 =20 Happy landings, Dennis Legacy, 220 hours ------=_NextPart_000_003B_01C9638A.D17E45C0 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable
Hi Alan,
 
I made all my Legacy's CG calculations from the firewall = joggle. =20 I wrote in my POH that the firewall joggle is assigned the = arbitrary value=20 of fuselage station (FS) 65.0, regardless of the actual distance from = the=20 propeller spinner.  I used 65.0" instead of the 64.625" number in = the=20 factory POH because since both the 65.0" and 64.625" are arbitrary = numbers, I=20 started with a round number.  (Besides, perhaps due to my finance=20 background, I don't like to use numbers that imply more precision than = is=20 actually there.  (Sure, I know that 64.625" is the round number of = 64-5/8",=20 but who uses fractions to compute CG?))
 
I could have just as easily assigned the value of 0" to the = firewall=20 joggle, but then I would have to deal with negative numbers forward = of the=20 firewall joggle and positive numbers aft.  That would just make = this more=20 difficult than it needs to be. 
 
Once I defined the firewall joggle as FS 65.0, I measured the = distance=20 between the center of the nose wheel and FS 65.0 and the distance = between the=20 center of the main gear and FS 65.0.  I measured the distance = between=20 the leading edge of the wing at butt line (BL) 27 and FS = 65.0".  From=20 there, the rest is straight mathematics from the factory POH.
 
Using this method, I don't think it makes any difference where a = builder=20 sets the reference point.  So long as they use = actual=20 measurements of the distance between the reference point and the wheels = and=20 leading edge of the wing at BL 27, the mathematics will be=20 identical.   
 
I backed into the CG of the baggage area by weighing the = airplane=20 with and without weight in the baggage area and then computing the = actual=20 CG.  In my case, the baggage CG is 144.5" (with a firewall=20 reference point of 65.0").  That was with the weight loaded = into the=20 approximate center of the baggage area.
 
This part isn't related to your question, but so long as we're = talking=20 about CG, I compute my Legacy's CG with and without fuel.  My empty = Legacy=20 has a forward CG and burning fuel moves the CG forward.  I can = theoretically take off with the CG within limits and then be too far = forward on=20 landing.  My zero fuel CG calculation checks to make sure I'll = still=20 be in limits on landing in the worst case situation that I land with = empty=20 tanks.
 
To eliminate the need to compute the baggage effect on CG for every = flight,=20 I made up the following table that shows the minimum and = maximum=20 allowable baggage weight for various combinations of pilot = weights.  Note=20 that this is based on forward CG considerations; many of = these combinations=20 would result in exceeding max gross weight of 2,400 pounds with = full=20 fuel.  However, if the amount of fuel is managed to stay within the = max=20 allowable gross weight, the following baggage weights are = acceptable. =20 Here's the page from my POH:   
 
 

Acceptable Baggage Loading, in Pounds

Combined Wt of Pilots, Any=20 Fuel

Baggage, with Oxygen = Bottle

Baggage, without Oxygen=20 Bottle

150

30-160

38-160

175

20-160

28-160

200

12-160

20-160

225

2-160

10-160

250

0-160

0-160

275

0-150

0-160

300

0-130

0-140

325

0-100

0-110

350

0-75

0-85

375

0-55

0-65

400

0-30

0-40

Note:  The = baggage=20 weights are the minimum and maximum weights for the combined weight of = the pilot=20 and copilot.  For example, = a pilot=20 weighing 175 pounds would have to carry at least 20 pounds of baggage in = addition to the oxygen bottle, or 28 pounds if not carrying the oxygen=20 bottle.  The weight of the = baggage=20 should be roughly centered (forward-aft) in the baggage area.  Moving the bags aft is better = than=20 moving them forward.  = Although=20 heavier baggage is acceptable, the maximum recommended is 100 = pounds.   The weight of the pilots = includes=20 gear they carry and wear and center console glove box contents.  The maximum weight of = instrument panel=20 glove box contents is three pounds.

 

The key factor in this table is the forward CG upon = landing,=20 assuming the worst case situation of zero usable fuel.  If additional fuel is assured = on=20 landing, each gallon of fuel eliminates the need for 1.5 pounds of = baggage.  For example, a 175 pound pilot = would=20 have no minimum baggage requirement if the usable fuel upon landing was = assured=20 to be at least 20 gallons.

 

*The empty weight of the airplane includes all avionics, = radios,=20 instruments, two gallons of unusable fuel in each wing, eight quarts of = oil in=20 the engine, a headset, and a two-pound toolkit behind the seat. 

 

Happy landings,
Dennis
Legacy, 220 hours
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