Return-Path: Sender: (Marvin Kaye) To: lml Date: Sat, 13 Sep 2003 21:19:22 -0400 Message-ID: X-Original-Return-Path: Received: from imo-r06.mx.aol.com ([152.163.225.102] verified) by logan.com (CommuniGate Pro SMTP 4.1.3) with ESMTP id 2578359 for lml@lancaironline.net; Sat, 13 Sep 2003 15:46:36 -0400 Received: from Sky2high@aol.com by imo-r06.mx.aol.com (mail_out_v36_r1.1.) id q.ba.4661fd9c (4418) for ; Sat, 13 Sep 2003 15:46:32 -0400 (EDT) From: Sky2high@aol.com X-Original-Message-ID: X-Original-Date: Sat, 13 Sep 2003 15:46:31 EDT Subject: Re: [LML] Re: Gross Weight & Balance of IV-P, Other considerations for Lancairs X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1063482391" X-Mailer: 9.0 for Windows sub 1060 -------------------------------1063482391 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit In a message dated 9/13/2003 1:01:58 PM Central Daylight Time, tednoel@cfl.rr.com writes: The maneuvering Speed (Va) can be computed as the (SQRT(G limit)) times Vs so that the new Va is reduced to 132 Kts. **You have applied the 3.2G limit in this calculation. While that may seem appropriate, we know that the tested L-IV wing load limit is significantly higher than that. Therefore, the application of the 3.2G limit may not be necessary. If we take the 4.4G limit, knowing that the airframe is strong enough to support it, then Va should increase to 157kts, not decrease to 132 kts. ** Any of us who recall flying Wichita spam cans will recall the Va placard, which always has Va lower at light weights. Ted, The wing was designed for and then tested to some ultimate breaking point by statically applying weight. Knowing Lancair, this was probably some number like 9 times the design gross weight of the airplane. Unlike the FAA, which only requires the ultimate load to be 1.5 times the gross weight times the G-limit, Lancair likes to be approximately 2 times the gross weight times the G-limit. Thus, the 4.4G limit of the IV. Anyway, that means that if the gross weight is 3550 then the ultimate load is 3550*4.4*2=31240 pounds. The wing will break at this loading. If you increase the gross weight, there is a new G-limit i.e. 31240/2/4550=G-load=3.4G. This is because the breaking load on the wing doesn't change. The formulae are not wrong. The stall speed increases at a higher weight. There is a computation for the maneuvering speed based on the sqrt of the G-load limit - In this case, one is required to go slower. And, at weights less than max gross, the stall speed is less and so is the maneuvering speed. I.E. Va is at a max at max gross weight. Above Va, the lifting capacity of the wing is so great - Hmm, a side discussion: The maximum lift attainable at any airspeed is equal to the weight at stall speed. After some formula simplification, the max load factor attainable is the square of (airspeed over Vs). This means that if you are flying at 3 times the stall speed and the angle of attack is increased to provide max lift, a maximum load factor of 9 (or 9Gs) would result. Gusts or shear can provide just such an angle of attack, thus Va is designed to have the wing stall before such a low probability event ( 50 ft/sec) would occur. Scott Krueger Sky2high@aol.com II-P N92EX IO320 Aurora, IL (KARR) Note: I once carefully flew my II-P at an estimated 1960 pounds - 265 pounds over the 1685 suggested by Lancair or a 16% increase. This was at about 2/3 of the CG range. Until 10 gallons of fuel was burned off (60 pounds), the autopilot altitude hold wandered a bit. I don't want to calculate the various speeds required. -------------------------------1063482391 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable

In a message dated 9/13/2003 1:01:58 PM Central Daylight Time, tednoel@= cfl.rr.com writes:

The maneuvering Speed (Va) can be computed=20= as the (SQRT(G limit)) times Vs so that the new Va is reduced to 132 Kts.

**You have applied the 3.2G limit in this c= alculation. While that may seem appropriate, we know that the tested L-IV wi= ng load limit is significantly higher than that. Therefore, the application=20= of the 3.2G limit may not be necessary. If we take the 4.4G limit, knowing t= hat the airframe is strong enough to support it, then Va should increase to=20= 157kts, not decrease to 132 kts.

** Any of us who recall flying Wichita spam= cans will recall the Va placard, which always has Va lower at light weights= .

Ted,

The wing was designed for and then tested to some ultimate breaking poi= nt by statically applying weight. Knowing Lancair, this was probably so= me number like 9 times the design gross weight of the airplane. Unlike= the FAA, which only requires the ultimate load to be 1.5 times the gross we= ight times the G-limit, Lancair likes to be approximately 2 times the gross=20= weight times the G-limit. Thus, the 4.4G limit of the IV. Anyway, that= means that if the gross weight is 3550 then the ultimate load is 3550*4.4*2= =3D31240 pounds. The wing will break at this loading. If you inc= rease the gross weight, there is a new G-limit i.e. 31240/2/4550=3DG-load= =3D3.4G. This is because the breaking load on the wing doesn't change.= The formulae are not wrong. The stall speed increases at=20= a higher weight. There is a computation for the maneuvering speed base= d on the sqrt of the G-load limit - In this case, one is required to go slow= er. And, at weights less than max gross, the stall speed is less and so= is the maneuvering speed. I.E. Va is at a max at max gross weight.

Above Va, the lifting capacity of the wing is so great - Hmm= , a side discussion:

The maximum lift attainable at any airspeed is equal to the weight at s= tall speed. After some formula simplification, the max load factor att= ainable is the square of (airspeed over Vs). This means that if y= ou are flying at 3 times the stall speed and the angle of attack is increase= d to provide max lift, a maximum load factor of 9 (or 9Gs) would result.&nbs= p; Gusts or shear can provide just such an angle of attack, thus Va is desig= ned to have the wing stall before such a low probability event ( 50 ft/sec)=20= would occur.

Scott Krueger
Sky2high@aol.com
II-P N92EX IO320 Aurora, IL (KARR)

Note: I once carefully flew my II-P at an estimated 1960 pounds -= 265 pounds over the 1685 suggested by Lancair or a 16% increase. This= was at about 2/3 of the CG range. Until 10 gallons of fuel was burned= off (60 pounds), the autopilot altitude hold wandered a bit. I don't=20= want to calculate the various speeds required.

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