Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Fri, 27 Aug 2004 10:30:56 -0400 Message-ID: X-Original-Return-Path: Received: from imo-d23.mx.aol.com ([205.188.139.137] verified) by logan.com (CommuniGate Pro SMTP 4.2) with ESMTP id 380868 for lml@lancaironline.net; Fri, 27 Aug 2004 10:26:47 -0400 Received-SPF: pass receiver=logan.com; client-ip=205.188.139.137; envelope-from=Sky2high@aol.com Received: from Sky2high@aol.com by imo-d23.mx.aol.com (mail_out_v37_r3.4.) id q.7d.56f04897 (25305) for ; Fri, 27 Aug 2004 10:26:06 -0400 (EDT) From: Sky2high@aol.com X-Original-Message-ID: <7d.56f04897.2e609e7e@aol.com> X-Original-Date: Fri, 27 Aug 2004 10:26:06 EDT Subject: Re: [LML] 320 Elevator/Horizontal Stab X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1093616766" X-Mailer: 9.0 for Windows sub 5000 -------------------------------1093616766 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit In a message dated 8/26/2004 8:43:38 PM Central Standard Time, kraus96@optonline.net writes: 1 - Plan to use an elevator trim tab and small RAC servo. What dimensions should I make the trim tab? I know there are easier ways, but I am intrigued by the TruTrack auto pitch trim. 2 - Should the elevator trailing edge have a flat surface - similar to the ailerons? 1/4 inch like the ailerons? 3 - Plans call for the counter balance ends to be 2 inches wide. Is this correct and adequate? Seems that they could be made 1/4 to 1/2 inch wider. 4 - My construction manual states the correct horizontal stabilizer incidence is -1/2 to -1.0 degree. Is this still the proper range? If I could build with 100% accuracy, which would be best -1/2 or -1.0? Ron, 1 & 3: Of course, the addition of a trim tab will require more balance weight. The benefit of making the horns slightly wider is that more of the forward loaded weight will have a longer balance arm thus actually reducing the total weight needed. This is always a benefit in the small tail Lancair since any additional weight in the tail is generally undesirable. Frankly, I don't like "automatic" trim systems or trim tabs. The loss of my autopilot during an IFR flight and the resulting departure from level flight due to out of trim conditions led me to change my procedure. I now turn off the autopilot every 1/2 hour, re-trim and hand fly for 5 minutes to make sure my "scan" is still usable. My situation could have been worse if I didn't feed the header tank equally (automatically) from both wing tanks. BTW, some servo driven trim systems solve the runaway trim problem by using spring-biased linkages that are easily overidden. Examples are Bonanza and Cirrus aircraft. I can't suggest a tab size since I have no trim tabs. 2: I believe the flat aileron trailing edge is to supress "aileron snatch" and/or flutter while maintaining control effectivess - see any small jet aileron. I don't believe there is any "elevator snatch" condition and I think there is a small cruise drag penalty for that sort of trailing edge. IMO, I don't think there is any benefit to a flat elevator trailing edge. 4: Depends on your purpose and other variables. Some racers believe that the negative angle of incidence should be reduced to lower the induced drag at race speeds and loading. Homebuilt parts vary and loadings will also vary. If you can, go for some rides in similar Lancairs and note the displacement of the elevator horn at cruise as this may be a measure of the elevator forces needed to unload the tail (nose down trim). That is, if the negative angle of incidence (NAOI) is too great or the CG is too far rearward, the "horn" may be exposed above the tail as the downward load is reduced on the tail. Ask the builder if he remembers the NAOI. On the other hand, if the NAOI is too small, full flap deployment (causing sigificant nose down pitch) may result in the elevator not having enough authority to overcome those forces. Best angle? ???? Accuracy? ???? I can only relate my experience. Early in the empennage construction (slow build kit), I made the wooden jig with -1/2 degree built in (for use with a bubble level). Being a techno freak, I later obtained a digital level. Even later, during the horizontal stabilizer install, I used the jig with the digital level erroneously set for -1/2 degree. Yep, you guessed it - I ended up with the H-stab at -.9 degrees. However, at cruise I see that the horn is pretty much level with the upper stab surface. At race speeds I never look back, but I do run out of nose-down trim until most of the wing fuel is burned off. Also, I do not have a problem with elevator authority at a full flap landing, single pilot and no fuel in the wings. Note that my empty weight CG is .1" forward of Lancair's recommendation. Scott Krueger AKA Grayhawk Sky2high@aol.com II-P N92EX IO320 Aurora, IL (KARR) Opinions and results may vary! -------------------------------1093616766 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
In a message dated 8/26/2004 8:43:38 PM Central Standard Time,=20 kraus96@optonline.net writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>
1 - Plan to use an elevator tri= m tab=20 and small RAC servo.  What dimensions should I make the trim tab?&nbs= p; I=20 know there are easier ways, but I am intrigued by the TruTrack auto pitch=20 trim.
 
2 -  Should the elevator trailing ed= ge have=20 a flat surface - similar to the ailerons?  1/4 inch like the=20 ailerons?
 
3 - Plans call for the counter balance en= ds to be=20 2 inches wide.  Is this correct and adequate?  Seems that they c= ould=20 be made 1/4 to 1/2 inch wider.
 
4 - My construction manual states the cor= rect=20 horizontal stabilizer incidence is  -1/2 to -1.0 degree.  Is thi= s=20 still the proper range?  If I could build with 100% accuracy, which w= ould=20 be best -1/2 or -1.0?
Ron,
 
1 & 3:  Of course, the addition of a trim tab will require mor= e=20 balance weight.  The benefit of making the horns slightly wider is that= =20 more of the forward loaded weight will have a longer balance arm t= hus=20 actually reducing the total weight needed.  This is always a benefit in= the=20 small tail Lancair since any additional weight in the tail is generally=20 undesirable. 
 
Frankly, I don't like "automatic" trim systems or trim tabs.  The=20= loss=20 of my autopilot during an IFR flight and the resulting departure from l= evel=20 flight due to out of trim conditions led me to change my procedure.  I=20= now=20 turn off the autopilot every 1/2 hour, re-trim and hand fly for 5 minutes to= =20 make sure my "scan" is still usable.  My situation could have been wors= e if=20 I didn't feed the header tank equally (automatically) from both wing=20 tanks.
 
BTW, some servo driven trim systems solve the runaway trim problem by u= sing=20 spring-biased linkages that are easily overidden.  Examples are=20 Bonanza and Cirrus aircraft.
 
I can't suggest a tab size since I have no trim tabs.
 
2: I believe the flat aileron trailing edge is to supress "aileron snat= ch"=20 and/or flutter while maintaining control effectivess - see any small jet=20 aileron.  I don't believe there is any "elevator snatch" condition and=20= I=20 think there is a small cruise drag penalty for that sort of trailing edge.&n= bsp;=20 IMO, I don't think there is any benefit to a flat elevator trailing edge.
 
4: Depends on your purpose and other variables.  Some racers belie= ve=20 that the negative angle of incidence should be reduced to lower the induced=20= drag=20 at race speeds and loading.  Homebuilt parts vary and loadings will als= o=20 vary. 
 
If you can, go for some rides in similar Lancairs and note the displace= ment=20 of the elevator horn at cruise as this may be a measure of the elevator forc= es=20 needed to unload the tail (nose down trim).  That is, if the negative a= ngle=20 of incidence (NAOI) is too great or the CG is too far rearward, the "horn" m= ay=20 be exposed above the tail as the downward load is reduced on the tail. = Ask=20 the builder if he remembers the NAOI.
 
On the other hand, if the NAOI is too small, full flap deployment (caus= ing=20 sigificant nose down pitch) may result in the elevator not having enough=20 authority to overcome those forces.
 
Best angle?  ????  Accuracy?  ????
 
I can only relate my experience.  Early in the empennage construct= ion=20 (slow build kit), I made the wooden jig with -1/2 degree built in (for use w= ith=20 a bubble level).  Being a techno freak, I later obtained a digital= =20 level.  Even later, during the horizontal stabilizer install, I used th= e=20 jig with the digital level erroneously set for -1/2 degree.  Yep, you=20 guessed it - I ended up with the H-stab at -.9 degrees.  However, at cr= uise=20 I see that the horn is pretty much level with the upper stab surface. =20= At=20 race speeds I never look back, but I do run out of nose-down trim until= =20 most of the wing fuel is burned off.  Also, I do not have a problem wit= h=20 elevator authority at a full flap landing, single pilot and no fuel in the=20 wings.  Note that my empty weight CG is .1" forward of Lancair's=20 recommendation.
 
 
Scott Krueger=20 AKA Grayhawk
Sky2high@aol.com
II-P N92EX IO320 Aurora, IL=20 (KARR)

Opinions and results may vary!
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