X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 01 Aug 2008 20:45:23 -0400 Message-ID: X-Original-Return-Path: Received: from web62503.mail.re1.yahoo.com ([69.147.75.95] verified) by logan.com (CommuniGate Pro SMTP 5.2.5) with SMTP id 3051605 for lml@lancaironline.net; Fri, 01 Aug 2008 14:13:42 -0400 Received: (qmail 76596 invoked by uid 60001); 1 Aug 2008 18:13:24 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Received:X-Mailer:Date:From:Subject:To:MIME-Version:Content-Type:Message-ID; b=oIMADccn3w+luMLhyC5p/KadN/Dgfku36Ux/CrZdhn12YaSqaH3yz0c9lP5Gp1Cj5KnjJGDT8okIWTVPEVet1t+uprJ+s9t/g1l9/gRkGmV4KyMz0jr5ihHJ9n7fP7NOU7+eJ0zXq1yUgEW2JSuruwHIb6w3IKHeOwsN9B4dFlk=; Received: from [70.118.224.199] by web62503.mail.re1.yahoo.com via HTTP; Fri, 01 Aug 2008 11:13:23 PDT X-Mailer: YahooMailRC/1042.48 YahooMailWebService/0.7.218 X-Original-Date: Fri, 1 Aug 2008 11:13:23 -0700 (PDT) From: Charlie Kohler Subject: Stalls X-Original-To: LancairList MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-1140626678-1217614403=:76510" X-Original-Message-ID: <152458.76510.qm@web62503.mail.re1.yahoo.com> --0-1140626678-1217614403=:76510 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Time to=A0refresh our stall awareness. ALL Lancairs should have stall strip= s.=0AThis is a paper written by Mark Kirchner, IVP owner, concerning stall = strips.=A0 I have them on my IVP.=A0 It stalls straight ahead with a defini= te buffet and very docile.=A0 I only do these at 10,000agl with a factory p= ilot on board.=A0 There is no wing drop.=A0 I don=92t do power on stalls, a= ccelerated stalls or spins.=0AMARK KIRCHNER NOTES ON STALL AND SPIN PREVENT= ION=0AWashington Lancair Builder's Meeting, February 2001=0AObjectives:=0AI= f stall characteristic provides a "wing-drop", recovery might require subst= antial altitude. Therefore, eliminate "wing-drop" characteristic.=0AIf the = aircraft wing loading is high (L-IVP is 32- 34 #/sq.ft.), even an incipient= stall entry might require more altitude for recovery than is available dur= ing final approach. Therefore, provide adequate means to insure speed margi= n during final approach --- and inherent aircraft buffet warning if speed m= argin is violated and stall condition is approached.=0AIf, during the banke= d turn to final approach, distractions due to weather, traffic, or whatever= , result in the pilot pulling excess "g=92s" during the turn, then the stal= l angle of attack can be reached while still maintaining the target approac= h speed. Of course, a combination of factors -- such as drifting below targ= et approach speed due to the same distractions - can amplify this risk. The= refore, a means to provide a warning of the approach to a stall angle-of-at= tack -- independent of the maintenance of accepted speed margins - is desir= ed. Again, the added warning of wing-buffet is desired.=0ATechnical Approac= h:=0AAdding wing "stall strips" to the inboard leading edge of the wing wor= ks on both the "wing-drop" problem and the objective of developing wing-buf= fet warning.=0AInstalling the Frantz-type AOA-instrument, along with judici= ous calibration, works on the objective of providing adequate stall angle-o= f-attack margins and normal approach speed margins.=0AWING STALL-STRIPS=0AW= ing stall strips have been discussed at least three times in the Lancair Ne= twork News.=0AIn Issue 33, Martin Hollman's original recommendation was des= cribed. It consisted of 16" strips, starting 24" out from the side-of-body.= In Issue 36, Bob Young described a construction technique for adding these= to the wing leading edge --- and at the same time, pointed out that Martin= Hollman had revised his recommendation to 18" long strips.=0AIn Issue 37, = Peter Yates (from Australia) pointed out that the Australian regulatory off= ices would not certify his aircraft (even though a homebuilt) without meeti= ng certain minimum stall qualities. Yates' aircraft, being the first of typ= e in Australia, would set the standard for future L-IV certifications in th= at country. Yates ran a very interesting and extensive set of flight experi= ments using different lengths of stall strips. His objective was to make th= e minimum mod that would be accepted by the governmental agency. Also, sinc= e he noticed significantly higher touch-down flare stick forces with the st= all strips, he wanted to keep the change to a minimum for that reason. (Not= e: I fail to notice significant flare stick-force differences with strips.)= Another important factor influencing the Yates design is the right-wing-dr= op characteristic that is typical in the L-IV stall. Yates figured that it = was more important to balance the stall by working on the left wing (by stalling it earlier) than to have identical stall strips= on both wings. His final design had a stall strip only on the left wing, 8= " long, starting 18" out from the side-of-body. His tests showed that the a= ircraft had a balanced wings-level stall, with reasonable buffet warning, a= nd low landing flare stick-forces. The strips were triangular in cross-sect= ion with about a 9/16" base attached to the wing and 3/8" sides leading to = the leading edge apex. The center-line of the strips met the leading edge o= f the wing about 0.2" below the leading edge vertical tangency plane inters= ection. (This is the vertical orientation originally suggested by Martin Ho= llman). The idea, of course, is that the apex of the stall strip be placed = as closely as possible to the airfoil cruise stagnation point (so there is = no cruise drag created), but still allowing stall initiation at high angles= of attack.=0ATaking all of the above into account, I decided upon the foll= owing design for N776CM.=0A=A0Same vertical positioning as described above.= =0AStrips on both wings; 10" long starting 18=94 out from the side-of-body.= =0A(THIS IS WHAT I HAVE AND ADVOCATE---- Charlie K.)=0AI decided to go for = both wings to help promote balanced stall regardless of power effects or un= symmetrical flight effects. I decided on 10" lengths because I wanted to mi= nimize the size, but felt a couple of inches longer than Yates' successful = design would be conservative. Also, I hadn't seemed to have the problem of = landing flare stick forces that bothered Yates.=0AI found both the buffet s= peed margin and the strength of the buffet to vary with power setting and f= lap setting. A range of approximately 3 knots to 6 knots buffet speed margi= n was experienced. The initial stall break is balanced without wing drop, a= lthough I have never held the airplane into the stall beyond the initial br= eak to test the characteristics beyond. I do not recommend that the airplan= e be tested beyond initial stall break.=0AThe increase in stall speed due t= o the stall strips was small and difficult to measure -- so I would guess 1= to 2 knots is close to right. The same is true with respect to the effect = upon cruise speed at a given power. It was difficult to measure any change = in cruise; this implies that the vertical location of the stall strip at th= e leading edge was close to optimum.=0AFinally, I would advise that any tes= ting ( even simple approach-to-stall testing) be conducted at 10,000 feet A= GL or higher.=0AFRANTZ AOA (Angle-of-Attack) INSTRUMENT=0AThere are two maj= or benefits for using an AOA instrument to provide stall margin compared to= simply using airspeed. First, at one "g" flight, the stall airspeed varies= with the square-root of aircraft weight; therefore, if a constant (average= ) target landing-approach airspeed is used, it is only an approximation for= very heavy or very light weights. Secondly, at a given airspeed (which may= be chosen to provide adequate stall margin at one "g"), the margin diminis= hes rapidly in a turn -- without any indication to the pilot as to the exte= nt.=0AThe AOA instrument allows one to index the desired margins with respe= ct to wing angle-of-attack, and the margins stay the same regardless of wei= ght. And, for a given airspeed, the "g-effect" is automatically included in= the display (and aural warnings). One can select different margins for dif= ferent flap settings. For example, my landing margins are used only for ful= l flaps. For partial flaps, I have larger margins because I feel I do not n= eed "tight" margins if I am not on final landing approach. I have experimen= ted quite a bit with different calibrations (margins) for my instrument. He= re is what I have the instrument set up for at the present time. The exampl= e numbers are for a typical landing weight of 2900 Ibs. (2250 Ib. W.E. + 2 = men + 45-50 gal. fuel). For other landing weights the airspeeds would vary = as the square root of the weight (for the same AOA reading).=0AAt 12" Man. = Press. Full flaps:=0A2900 lbs. weight, gear down.=0ATarget Vapp.=A0=A0=A01g= Aural Warning=A0=A0=A0=A0=A0=A0=A01g Light Buffet =A0=A0=A0=A0=A0=A0=A01g = Stall Break=0A99 knots=A0=A0=A0=A0=A0=A0=A0 84 knots=A0=A0=A0=A0=A0=A0=A0 = =A0=A0=A0=A0=A0=A0=A0 70 knots=A0=A0=A0=A0=A0=A0=A0 =A0=A0=A0=A0=A0=A0=A0 6= 5 knots=0A(1.52 Vs)=A0=A0=A0=A0=A0=A0 (1.29Vs)=A0=A0=A0=A0=A0=A0=A0 =A0=A0= =A0=A0=A0=A0=A0 (1.07 Vs)=A0=A0=A0=A0=A0=A0 =A0=A0=A0=A0=A0=A0=A0 (1.0 Vs)= =0ASeveral comments:=0AThose who have experience flying heavy transports ma= y know that their published approach speeds are 1.3Vs (compared to my 1.52V= s, above). However, the factors that govern the requirements for margins te= nd to favor equivalent incremental speed margins rather than equivalent spe= ed ratio margins. Thus, the lower speed aircraft needs a higher speed ratio= margin than the higher speed aircraft.=0AThe 99 knot approach speed (for t= he average landing weight shown) is essentially the same as the 100 knot ap= proach speed advocated in training at Redmond.=0AFor a light landing weight= of 2600 lbs, the Vapp would be 94 knots; for a heavy landing weight of 320= 0 lbs, the Vapp. would be 104 knots.=0A=A0=A0=A0=A0=A0=A0=A0 At the target = approach speed, the Aural Warning would sound at 1.38 g.=0AThe AOA instrume= nt has one other feature that should be noted. It has an Aural Warning at a= n absolute speed (not angle-of-attack) for "Gear Down". This can be set at = any speed. I have mine set at 110 knots. I fly a target speed of 120 knots = on instrument landing patterns (15 in. 2500 RPM, Half-flaps gear-up). If I = drift down to 110 knots, I get a gear-down aural warning --- which, since I= am slow, means I have probably crept up in altitude from my target pattern= altitude.=0AMy theory on why the aircraft has a right-wing-drop at initial= stall break: The propwash provides an incremental upwash on the left wing = and downwash on the right wing. However, this is concentrated primarily on = the inboard part of each wing. In order to balance this, a small amount of = down-aileron on the right (and up-aileron on the left) is flown. Although a= down-aileron wing section (like a flapped wing) stalls at a higher total l= ift, it does so at a lower wing section angle of attack than does an up-ail= eron wing section. Thus the right wing stalls first, providing the wing dro= p.=0A=0A=0ACarl Cadwell=0A=A0=0AI second this.=0ACharlie K.=0A=A0=0ACharlie= K.=0ASee=A0me on the Web at=A0 www.Lancair-IV.com --0-1140626678-1217614403=:76510 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable
=0A
Time to refresh our stall awareness. ALL Lanca= irs should have stall strips.
=0A
 
=0A
=0A

This is a paper written by Mark Kirchner,= IVP owner, concerning stall strips.  I have them on my IVP.  It = stalls straight ahead with a definite buffet and very docile.  I only = do these at 10,000agl with a factory pilot on board.  There is no wing= drop.  I don=92t do power on stalls, accelerated stalls or spins.

=0A

MARK KIRCHNER NOTES ON= STALL AND SPIN PR= EVENTION

=0A

Washington Lancair Builder's Meeting, February 2001

=0A

Objectives:

=0A

If stall characteristic provides a "wing-dro= p", recovery might require substantial altitude. Therefore, eliminate "wing= -drop" characteristic.

=0A

If the aircraft wing loading is high (L-IVP is 32- 34 #/sq.ft.), even = an incipient stall entry might require more altitude for recovery than is a= vailable during final approach. Therefore, provide adequate means to insure= speed margin during final approach --- and inherent aircraft buffet warnin= g if speed margin is violated and stall condition is approached.

= =0A

If, during the banked turn to= final approach, distractions due to weather, traffic, or whatever, result = in the pilot pulling excess "g=92s" during the turn, then the stall angle o= f attack can be reached while still maintaining the target approach speed. = Of course, a combination of factors -- such as drifting below target approa= ch speed due to the same distractions - can amplify this risk. Therefore, a= means to provide a warning of the approach to a stall angle-of-attack -- i= ndependent of the maintenance of accepted speed margins - is desired. Again= , the added warning of wing-buffet is desired.

=0A

Technical Approach:

=0A

Adding wing "stall strips" to the inboa= rd leading edge of the wing works on both the "wing-drop" problem and the o= bjective of developing wing-buffet warning.

=0A

Installing the Frantz-type AOA-instrument, along w= ith judicious calibration, works on the objective of providing adequate sta= ll angle-of-attack margins and normal approach speed margins.

=0A=

WING STALL-STRIPS<= /P>=0A

Wing stall strips have bee= n discussed at least three times in the Lancair Network News.

=0A=

In Issue 33, Martin Hollman's or= iginal recommendation was described. It consisted of 16" strips, starting 2= 4" out from the side-of-body. In Issue 36, Bob Young described a constructi= on technique for adding these to the wing leading edge --- and at the same = time, pointed out that Martin Hollman had revised his recommendation to 18"= long strips.

=0A

In Is= sue 37, Peter Yates (from Australia) pointed out that the Au= stralian regulatory offices would not certify his aircraft (even though a h= omebuilt) without meeting certain minimum stall qualities. Yates' aircraft,= being the first of type in Australia, would set the standard = for future L-IV certifications in that country. Yates ran a very interestin= g and extensive set of flight experiments using different lengths of stall = strips. His objective was to make the minimum mod that would be accepted by= the governmental agency. Also, since he noticed significantly higher touch= -down flare stick forces with the stall strips, he wanted to keep the chang= e to a minimum for that reason. (Note: I fail to notice significant flare s= tick-force differences with strips.) Another important factor influencing the Yates design is the righ= t-wing-drop characteristic that is typical in the L-IV stall. Yates figured= that it was more important to balance the stall by working on the left win= g (by stalling it earlier) than to have identical stall strips on both wing= s. His final design had a stall strip only on the left wing, 8" long, start= ing 18" out from the side-of-body. His tests showed that the aircraft had a= balanced wings-level stall, with reasonable buffet warning, and low landin= g flare stick-forces. The strips were triangular in cross-section with abou= t a 9/16" base attached to the wing and 3/8" sides leading to the leading e= dge apex. The center-line of the strips met the leading edge of the wing ab= out 0.2" below the leading edge vertical tangency plane intersection. (This= is the vertical orientation originally suggested by Martin Hollman). The i= dea, of course, is that the apex of the stall strip be placed as closely as possible to the airfoil cruise stagnation point (so there is no= cruise drag created), but still allowing stall initiation at high angles o= f attack.

=0A

Taking al= l of the above into account, I decided upon the following design for N776CM= .

=0A

 Same vertical positioning as described above.

=0A=

Strips on both wings; 10" long s= tarting 18=94 out from the side-of-body.

=0A

(THIS IS WHAT I HAVE AND ADVOCATE---- Charlie K.)

=0A

I decided to go for bo= th wings to help promote balanced stall regardless of power effects or unsy= mmetrical flight effects. I decided on 10" lengths because I wanted to mini= mize the size, but felt a couple of inches longer than Yates' successful de= sign would be conservative. Also, I hadn't seemed to have the problem of la= nding flare stick forces that bothered Yates.

=0A

I found both the buffet speed margin and the str= ength of the buffet to vary with power setting and flap setting. A range of= approximately 3 knots to 6 knots buffet speed margin was experienced. The = initial stall break is balanced without wing drop, although I have never he= ld the airplane into the stall beyond the initial break to test the charact= eristics beyond. I do not recommend that the airplane be tested beyond init= ial stall break.

=0A

Th= e increase in stall speed due to the stall strips was small and difficult t= o measure -- so I would guess 1 to 2 knots is close to right. The same is t= rue with respect to the effect upon cruise speed at a given power. It was d= ifficult to measure any change in cruise; this implies that the vertical lo= cation of the stall strip at the leading edge was close to optimum.<= /P>=0A

Finally, I would advise th= at any testing ( even simple approach-to-stall testing) be conducted at 10,= 000 feet AGL or higher.

=0A

FRANTZ AOA (Angle-of= -Attack) INSTRUMENT

=0A

There are two major benefits for using an AOA instrument to provide st= all margin compared to simply using airspeed. First, at one "g" flight, the= stall airspeed varies with the square-root of aircraft weight; therefore, = if a constant (average) target landing-approach airspeed is used, it is onl= y an approximation for very heavy or very light weights. Secondly, at a giv= en airspeed (which may be chosen to provide adequate stall margin at one "g= "), the margin diminishes rapidly in a turn -- without any indication to th= e pilot as to the extent.

=0A

The AOA instrument allows one to index the desired margins with resp= ect to wing angle-of-attack, and the margins stay the same regardless of we= ight. And, for a given airspeed, the "g-effect" is automatically included i= n the display (and aural warnings). One can select different margins for di= fferent flap settings. For example, my landing margins are used only for fu= ll flaps. For partial flaps, I have larger margins because I feel I do not = need "tight" margins if I am not on final landing approach. I have experime= nted quite a bit with different calibrations (margins) for my instrument. H= ere is what I have the instrument set up for at the present time. The examp= le numbers are for a typical landing weight of 2900 Ibs. (2250 Ib. W.E. + 2= men + 45-50 gal. fuel). For other landing weights the airspeeds would vary= as the square root of the weight (for the same AOA reading).

=0A=

At 12" Man. Press. Full flaps:=

=0A

2900 lbs. weight, gear do= wn.

=0A

Target= Vapp.    1g Aural Warning    = ;    1g Light Buffet      &n= bsp;  1g Stall Break

=0A

99 knots        84 = knots            &nb= sp;   70 knots         &n= bsp;      65 knots

=0A

(1.52 Vs)       (1.2= 9Vs)            &nbs= p;   (1.07 Vs)         &n= bsp;     (1.0 Vs)

=0A

Several comments:

=0A

Those who have experience flying heavy transports = may know that their published approach speeds are 1.3Vs (compared to my 1.5= 2Vs, above). However, the factors that govern the requirements for margins = tend to favor equivalent incremental speed margins rather than equivalent s= peed ratio margins. Thus, the lower speed aircraft needs a higher speed rat= io margin than the higher speed aircraft.

=0A

The 99 knot approach speed (for the average landing = weight shown) is essentially the same as the 100 knot approach speed advoca= ted in training at Redmond.

=0A

For a light landing weight of 2600 lbs, the Vapp would be 94 knots; for a= heavy landing weight of 3200 lbs, the Vapp. would be 104 knots.

= =0A

     = ;   At the target approach speed, the Aural Warning would sound a= t 1.38 g.

=0A

The AOA i= nstrument has one other feature that should be noted. It has an Aural Warni= ng at an absolute speed (not angle-of-attack) for "Gear Down". This can be = set at any speed. I have mine set at 110 knots. I fly a target speed of 120= knots on instrument landing patterns (15 in. 2500 RPM, Half-flaps gear-up)= . If I drift down to 110 knots, I get a gear-down aural warning --- which, = since I am slow, means I have probably crept up in altitude from my target = pattern altitude.

=0A

M= y theory on why the aircraft has a right-wing-drop at initial stall break: = The propwash provides an incremental upwash on the left wing and downwash o= n the right wing. However, this is concentrated primarily on the inboard pa= rt of each wing. In order to balance this, a small amount of down-aileron o= n the right (and up-aileron on the left) is flown. Although a down-aileron = wing section (like a flapped wing) stalls at a higher total lift, it does s= o at a lower wing section angle of attack than does an up-aileron wing sect= ion. Thus the right wing stalls first, providing the wing drop.

= =0A



=0A

Carl Cadwell

=0A 

=0A

I second this.

=0A

Charlie K.

=0A
 
= =0A
 
=0A
 
=0A
 
=0A
Charlie= K.
=0A
See me on the Web at  www.Lancair-IV.com
=0A
--0-1140626678-1217614403=:76510--