Wolfgang=2C et al=2C

<=3B<=3BAny more to the rear and you get negative stability at cru= ise and a larger tail doesn't help much with that anyway.>=3B>=3B

=3B

A =3Blarger tail moves the MAC rearward allowing the CG to move fa= rther aft while maintaining the same level of stability.

There has been =3Ba lot of discussion about Cm. =3B We need to= be careful to distinguish between the Cm for the wing=2C tail and total ai= rcraft. =3B It is the later that is critical to stability and this is w= here the larger tail influences the situation. =3B The large tail moves= the MAC to the rear approx. 1.5 inches. =3B For the same CG=2C the mor= e rearward MAC produces a greater restoring force if the plane is disturbed= from level flight. =3B The practical benefit for us is that it allows&= nbsp=3Ba lot more baggage to be thrown the rear of the plane before sufferi= ng =3Bstability problems. =3B You pointed out the other benefit of = increased control authority at slow speed with full flaps.

=3B

Chris Zavatson

N91CZ

360std

www.N91CZ.com

From: Wolfgang <=3BWol= fgang@MiCom.net>=3B
To:= lml@lancaironline.net
Sent:= Tue=2C July 13=2C 2010 2:51:23 AM
Subject: [LML] Small tail=2C MK II tail=2C CG rang= e

The quest continues.

=3B

I'm checking further into the data on these questions and am coming to= question the need for a larger tail. I'm not sure a larger tail by itself = will solve the problem. After doing some static and in flight measurements= =2C it looks like the tail authority is not a big problem=2C if a problem a= t all.

=3B

Static measurements of N31161 have shown "vanilla" parameters. 2.5=BA = incidence between the wing root at full reflex and the tail and a 1.3=BA wa= shout. Put the flaps at 0=BA and you get an additional AoA of 1.8=BA at the= root for a total incidence of 4.3=BA . . . . not radical at all.

=3B

What is interesting is the POH (Dec. 1994 pg. VI-3) gives the CG range= as 24.5" to 30.3" aft of the rear face of the fire wall and the MAC at 15%= to 20%

=3B

. . . well . . . no . . . that range is more like a MAC range of 15% t= o 30% - - - a good range made touchy only by the small size of the air fram= e.

=3B

After going over the plan view kit drawings=2C I come up with a CG ran= ge of 23-1/4" to 29-1/4" for a MAC range of 15% to 30%

That range is about 1-1/4" forward of the book and fits better with fi= rst hand flight experience.

=3B

Any more to the rear and you get negative stability at cruise and a la= rger tail doesn't help much with that anyway.

Negative stability makes pitch control a real chore. As Scott K. has i= ndicated=2C going to 0=BA flaps helps under that loading condition.

=3B

Too far forward and landing becomes "interesting". A larger tail can h= elp there . . . or don't use as much flaps.

=3B

I think understanding these conditions can help everyone.

=3B

. . . The quest continues . . . Comments welcome.

=3B

Wolfgang

=3B

From:	"Wolfgang" <=3BWolfgang@MiCom.net>=3B
Sender:	<=3Bmarv@lancaironline.net>=3B
Subject:	Small tail=2C MK II tail=2C CG range
Date:	Sat=2C 10 Jul 2010 21:01:11 -0400
To:	lml@lancaironline.net

The LNC2 uses the NLF(1)-0215F airfoil. A lot can be found by doing a = Google search on that number.

More detail can be found by =3Bgoing to Google for "NASA Technical= Paper 1865".

=3B

I have not taken the time to reverse engineer the CG range of the LNC2= but let me offer some observations.

=3B

The airfoil used has long been touted as "the greatest thing since sli= ced bread" for General Aviation and it definitely has some advantages. But = it's not new. Compare this airfoil to the P-51 airfoil and you will see som= e close similarities. The LNC2 being composite construction instead of alum= inum lets the airfoil show more of it's theoretical advantages.

=3B

It's a laminar shape with a good drag bucket. That bucket can be made = to move to the lower Cl (lift coefficient) ranges with reflex allowing noti= ceably lower drag at higher cruise speeds. Along with reflex=2C the Cm (mom= ent coefficient) goes positive=2C the center of lift of the wing travels fo= rward giving a nose up force requiring down trim. This is in addition to th= e usual nose up force that goes with most all airfoils =3Bat high speed= before considering flaps.

=3B

With down flap=2C the drag bucket will move to higher Cl's making slow= er flight more efficient. And=2C of course=2C the Cm goes negative giving a= nose down force requiring up trim.

=3B

. . . and appropriate variations in-between . . .

=3B

So=2C the rear CG limit is determined by high speed flight and availab= le control authority=2C

and the forward CG is determined by low speed / landing flight and ava= ilable control authority.

=3B

What is becoming clear here is that the center of lift does quite a bi= t of traveling fore and aft which is exaggerated by allowing negative or "c= ruise" flaps. Since you can't shift the CG during flight=2C you need a larg= e amount of pitch authority from the tail to cover that range of lift trave= l.

=3B

You have two choices in the LNC2=2C live with the limitations or insta= ll a larger tail to give that extra pitch authority.

. . . A larger tail area can also help with =3Babnormal attitude&n= bsp=3Brecovery.

=3B

Wolfgang

The New Busy think 9 to 5 is a cute idea. Combine mul= tiple calendars with Hotmail. Get busy. = --_10861046-4e57-4989-9cf0-e20d11530822_--