X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 27 Aug 2006 10:31:25 -0400 Message-ID: X-Original-Return-Path: Received: from imo-m21.mx.aol.com ([64.12.137.2] verified) by logan.com (CommuniGate Pro SMTP 5.1c.3) with ESMTP id 1350197 for lml@lancaironline.net; Sat, 26 Aug 2006 18:28:52 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.137.2; envelope-from=Sky2high@aol.com Received: from Sky2high@aol.com by imo-m21.mx.aol.com (mail_out_v38_r7.6.) id q.456.4ef09c5 (32913) for ; Sat, 26 Aug 2006 18:28:05 -0400 (EDT) From: Sky2high@aol.com X-Original-Message-ID: <456.4ef09c5.322224f4@aol.com> X-Original-Date: Sat, 26 Aug 2006 18:28:04 EDT Subject: Re: [LML] Fw: Small-Tail LNC2 Stability X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1156631284" X-Mailer: 9.0 Security Edition for Windows sub 5330 X-Spam-Flag: NO -------------------------------1156631284 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit In a message dated 8/26/2006 2:20:23 P.M. Central Standard Time, mjrav@comcast.net writes: To Small-Tail Lancair Flyers, Stability issues relative to the small-tail LNC2 have been debated for years. My small- tail LNC2 exhibits an unstable flying mode that I have not seen discussed. The purpose for submitting this informtation to lml is two fold (1) solicit input from other small-tail LNC2 flyers whether similar instability has been experienced and (2) provide a heads-up to small-tail LNC2 flyers that this potential for instability exists. Instability Description: In the right cross-wind landing configuration (right wing down, left rudder), the nose begins to oscillate up and down. The oscillations increase in magnitude with or without pilot control input. In 3 or 4 cycles the oscillations become uncomfortable during flight tests at altitude and the uncontrolable oscillations are a serious hazard during an actual landing approach. The problem does not exist in a left cross-wind configuration. The problem appears to be caused by a loss of horizontal stabilzer effectiveness as the air flow corkscrews around the fuselage. When the horizontal stabilizer becomes ineffective, the nose drops. When the nose drops, the airflow to the horizontal stabilizer becomes more effective and the nose rises. The oscillations stop when the right wing down and opposite rudder control inputs are neutralized. In the right cross-wind configuration, elevator control inputs have no effected on the oscillations. The pilot can work around this stablilty problem once he knows that it exists by (1) avoiding the right cross wind, (2) using the crab landing technique. If the pilot is not aware of this problem, the natural response is to assume that the oscillations are pilot induced and attempt to dampen them prior to touch down. This pilot response will likely test the ultimate structural integrity of the landing gear. I am sure small-tail LNC2 flyers have attempted many right cross-wind landings and I have not seen problems with oscillations discussed. Perhaps the problem is the result of some quirk in my construction. Although the oscillations are so predictable and so pronounced, it is hard to imagine that my airplane is so different from everyone elses. The following is a description of some characteristics of my small-tail Lancair 360.: * Kit number 383 * 180 hp Lycoming ) 360 A!AD engine, converted to fuel injection * Electronic fuel injection on one set of spark plugs * Hartzel 68 inch, standard Lancair prop * Perfomance -- Cruise speed 207 kts -- Clean stall 68 kts -- full flap stall 62 kts I only recently became aware of the lml web site and it appears like an appropriate place to pass on this type problem. I have not addressed this matter with Lancair. They always seem defensive rather than proactive in dealing with flight problems and after I drove my right landing gear through the right wing on my first right cross-wind landing attempt five years ago, the FAA had me take remedial landing lessons with a certified flight instructor. That did not seem to fix the problem. So this is my way of getting the word out to folks who may really care. George, That is very interesting. The next time I am at altitude, I will try the cross control you reference and see what results. Generally speaking, rudder only inputs cause yaw with little or no roll component in my airplane. Frankly, I prefer right crosswind landings to those with a left crosswind component - it is so much easier to handle the weathervane effect. I do start the process with a crab and then switch to right wing low left rudder (although I am trimmed for right rudder at slow speed and flaps). Unless it is a violent crosswind, I do land with full flaps. You do not mention the flap configuration when you experience the "bob". Another thing that would be interesting to know is where the CG is located. I have done everything in my power to keep the CG in the forward 1/2 of the range although further aft CG in manageable, but uncomfortable. Did you build the craft? Of course you did. What is the horizontal stab incidence? Do you have trim tabs? Where do you set the trim on landing? Are you going to be at the Lancair Fly-inn? If so, why not( you are nearby in Spokane, WA)? Kit 423 (I think). 1?? hp Lyc "B" engine injected with 9:1 CR EI everywhere Hartzell heavy-weight 70" boat screw. Perf- Cruise at 200 KTAS @ 7-9000 MSL - Stall yes maybe Full flap stall ? Scott Krueger AKA Grayhawk Lancair N92EX IO320 SB 89/96 Aurora, IL (KARR) Everything in moderation. PS <<>> Hmmmmmm, what unique quirk were you thinking about?. -------------------------------1156631284 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
In a message dated 8/26/2006 2:20:23 P.M. Central Standard Time,=20 mjrav@comcast.net writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>
To Small-Tail Lancair Flyers,
Stability issues relative to the small-tail LNC2 have been debated fo= r=20 years.  My small- tail LNC2 exhibits an unstable flying mode that I h= ave=20 not seen discussed.  The purpose for submitting this informtation to=20= lml=20 is two fold (1) solicit input from other small-tail LNC2 flyers whether=20 similar instability has been experienced and (2) provide a heads-up to=20 small-tail LNC2 flyers that this potential for instability exists.
 
Instability Description:  In the right cross-wind landing=20 configuration (right wing down, left rudder), the nose begins to oscillate= up=20 and down.  The oscillations increase in magnitude with or without pil= ot=20 control input.  In 3 or 4 cycles the oscillations become =20 uncomfortable during flight tests at altitude and the uncontrolable=20 oscillations are a serious hazard during an actual landing approach. = The=20 problem does not exist in a left cross-wind configuration.
 
The problem appears to be caused by a loss of horizontal stabilzer=20 effectiveness as the air flow corkscrews around the fuselage.  When t= he=20 horizontal stabilizer becomes ineffective, the nose drops.  When the=20= nose=20 drops, the airflow to the horizontal stabilizer becomes more effective and= the=20 nose rises.  The oscillations stop when the right wing down and oppos= ite=20 rudder control inputs are neutralized.   In the right cross-wind= =20 configuration, elevator control inputs have no effected on the=20 oscillations.   
 
The pilot can work around this stablilty problem once he knows that i= t=20 exists by (1) avoiding the right cross wind, (2) using the crab landing=20 technique. If the pilot is not aware of this problem, the natural response= is=20 to assume that the oscillations are pilot induced and attempt to dampen th= em=20 prior to touch down.  This pilot response will likely test the ultima= te=20 structural integrity of the landing gear.
 
I am sure small-tail LNC2 flyers have attempted many right=20 cross-wind landings and I have not seen problems with oscillations=20 discussed.  Perhaps the problem is the result of some quirk in my=20 construction.  Although the oscillations are so predictable and so=20 pronounced, it is hard to imagine that my airplane is so different from=20 everyone elses.  The following is a description of some=20 characteristics of my small-tail Lancair 360.:
*  Kit number 383
*  180 hp Lycoming ) 360 A!AD engine, converted to fuel=20 injection
*  Electronic fuel injection on one set of spark plugs
*  Hartzel 68 inch, standard Lancair prop
*  Perfomance
    -- Cruise speed 207 kts
    -- Clean stall 68 kts
    --  full flap stall 62 kts
    
I only recently became aware of the lml web site and it appears like=20= an=20 appropriate place to pass on this type problem.  I have not= =20 addressed this matter with Lancair.  They always seem=20 defensive rather than proactive  in dealing with=20 flight problems and after I drove my right landing gear through=20 the right wing on my first right cross-wind landing attempt five year= s=20 ago, the FAA had me take remedial landing lessons with a certified flight=20 instructor.  That did not seem to fix the problem. So this=20= is=20 my way of getting the word out to folks who may really=20 care.   
 
George,
 
That is very interesting.  The next time I am at altitude, I will=20= try=20 the cross control you reference and see what results.  Generally speaki= ng,=20 rudder only inputs cause yaw with little or no roll component in m= y=20 airplane. 
 
Frankly, I prefer right crosswind landings to those with a left crosswi= nd=20 component - it is so much easier to handle the weathervane effect.  I d= o=20 start the process with a crab and then switch to right wing low left rudder=20 (although I am trimmed for right rudder at slow speed and flaps).  Unle= ss=20 it is a violent crosswind, I do land with full flaps.  You do not menti= on=20 the flap configuration when you experience the "bob". 
 
Another thing that would be interesting to know is where the CG is=20 located.  I have done everything in my power to keep the CG in the forw= ard=20 1/2 of the range although further aft CG in manageable, but uncomfortable.
 
Did you build the craft?  Of course you did.
What is the horizontal stab incidence?
Do you have trim tabs?  Where do you set the trim on landing?
Are you going to be at the Lancair Fly-inn?  If so, why not( you=20 are nearby in Spokane, WA)?
 
 
Kit 423 (I think).
1?? hp Lyc "B" engine injected with 9:1 CR
EI everywhere
Hartzell heavy-weight 70" boat screw.
Perf-
Cruise at 200 KTAS @ 7-9000 MSL
- Stall yes maybe
Full flap stall ?
 
 
Scott Krueger=20 AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL=20 (KARR)

Everything in moderation.
 
PS <<<Perhaps the problem is the result of some quirk in my=20 construction.>>>  Hmmmmmm, what unique quirk were you thinking= =20 about?.
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