Return-Path: Sender: (Marvin Kaye) To: lml Date: Wed, 30 Jul 2003 22:18:37 -0400 Message-ID: X-Original-Return-Path: Received: from imo-r02.mx.aol.com ([152.163.225.98] verified) by logan.com (CommuniGate Pro SMTP 4.1) with ESMTP id 2507743 for lml@lancaironline.net; Wed, 30 Jul 2003 22:08:47 -0400 Received: from Epijk@aol.com by imo-r02.mx.aol.com (mail_out_v36_r1.1.) id q.1ea.e0f9cba (4362) for ; Wed, 30 Jul 2003 22:08:42 -0400 (EDT) From: Epijk@aol.com X-Original-Message-ID: <1ea.e0f9cba.2c59d429@aol.com> X-Original-Date: Wed, 30 Jul 2003 22:08:41 EDT Subject: Re: [LML] Re: 68" prop X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_1ea.e0f9cba.2c59d429_boundary" X-Mailer: 7.0 for Windows sub 10689 --part1_1ea.e0f9cba.2c59d429_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit In a message dated 7/30/03 5:59:57 PM Pacific Daylight Time, "Scott percival" writes: .....I believe that Hartzell don't recommend the 68" prop on the 200hp none (sic) counter weighted engine only the 72"? ..... Believe it or not, if Hartzell recommends against the use of a particular prop on a particular engine, there is at least one (and possibly more) sound engineering reason for that position. They do a great deal of highly competent research on various engine/prop combinations. The short blades have a higher resonant frequency and the angle-valve 360 without the 6th and 8th order absorbing counterweights have a grotesque torsional excitation profile. Perhaps you may have noticed that on certificated aircraft with the non-counterweighted 360's, (which use a prop which has been vibration-surveyed and stamped "OK"), there's an RPM band right in the middle of the operating range which is marked in yellow on the tach, with POH notations recommending against operating in that yellow zone. Do you suppose they did that in an effort to use up an oversupply of yellow paint? (If memory serves, Hartzell doesnt like the HC-F2YR-1F/F7068-2 used on the counterweighted 360 either.) ......are there people using the 68" on 200hp none counter weighted engines and do we have a safe history with this usage? ...... What possible difference could the answer to that question make? It's like: Are there people successfully jumping off bridges and not getting killed?? Any combination you decide to bolt together is "safe" until the point at which it sheds a blade segment. If you want to ignore learned and knowledgeable recommendations on the basis of wishful thinking and perpetual motion, that's what experimental aviation enables you to do. But experience has shown that MANY of these recommendations are written in blood. Jack Kane --part1_1ea.e0f9cba.2c59d429_boundary Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable In a message dated 7/30/0= 3 5:59:57 PM Pacific Daylight Time, "Scott percival" <percivalsd@hotmail.com> writes:

.....I believe that Hartzell= don't recommend the 68" prop on the 200hp none (sic) counter weighted engin= e only the 72"? .....

Believe it or not, if Hartzell recommends against the use of a particular pr= op on a particular engine, there is at least one (and possibly more) sound e= ngineering reason for that position. They do a great deal of highly competen= t research on various engine/prop combinations. The short blades have a high= er resonant frequency and the angle-valve 360 without the 6th and 8th order=20= absorbing counterweights have a grotesque torsional excitation profile.

Perhaps you may have noticed that on certificated aircraft with the non-coun= terweighted 360's, (which use a prop which has been vibration-surveyed and s= tamped "OK"), there's an RPM band right in the middle of the operating range= which is marked in yellow on the tach, with POH notations recommending agai= nst operating in that yellow zone. Do you suppose they did that in an effort= to use up an oversupply of yellow paint?

(If memory serves, Hartzell doesnt like the HC-F2YR-1F/F7068-2 used on the c= ounterweighted 360 either.)

......are there people using= the 68" on 200hp none counter weighted engines and do we have a safe histor= y with this usage? ......

What possible difference cou= ld the answer to that question make? It's like: Are there people succe= ssfully jumping off bridges and not getting killed?? Any combination y= ou decide to bolt together is "safe" until the point at which it sheds a bla= de segment.

If you want to ignore learned and knowledgeable recommendations on the basis= of wishful thinking and perpetual motion, that's what experimental aviation= enables you to do. But experience has shown that MANY of these recommendati= ons are written in blood.

Jack Kane --part1_1ea.e0f9cba.2c59d429_boundary--