| Hi colleges,
Exactly the same happens with my elevator as Christian's picture. No problems for me, the elevator does not loose authority, perhaps could be a bit fast if the incidence of the horizontal had been fixed a little less negative. Lyc 320, 2450 RPM, 21 to 22 MP, 185 kt TAS, big tail, wing extensions.
Some movies at YouTube, choose PP-XSN.
Silvio Novelli
Lancair 320 PP-XSN +55 (14) 9.9614-3129
On 24 Sep 2013,w 39, at 7:19 AM, Christian Meier wrote: Chris,
today I made a picture during Cruise with Autopilot at 7500ft with following configuration: 770 kg 40l in header, 20l in each wing (80l total), 75kg and 83kg for pilot and co. Flap was on 7° reflex CG 26,20" My design CG is 22,8 - 30,3 from firewall back, horizontal was installed - 0.6°
So it looks like if I would add more reflex than 7°, I would need more down elevator. So the gain with the higher reflex would be lost with the down elevator....
Christian
<IMG_4920.jpeg>Scott, Thanks. Examining the 360 (MkII) performance and characteristics in greater detail as been very interesting. The small tail has a very low aspect ratio and may indeed be subject to higher drag if the stabilizer incidence requires significant elevator input to trim. The MkII tail adds about 2 sqft, but more significantly has a much greater aspect ratio. My stab was well aligned for the sweep of flap settings as the elevator deflection was about 0.5 degrees TE down. In fact, all of the points were inside of 0.1 degrees of elevator movement. The concept of aft CG being more efficient is by reducing trim drag. It is used quite successfully in aircraft that
adjust the entire stabilizer for trim. A fixed stab angle that is too far from neutral in the aft CG or in the 'super-reflexed' cruise condition could negate any benefit. In my case the plot of flap setting vs. airspeed showed that I had not yet reached a peak. Extrapolating the curve gives me another 2 kts at 12 degrees reflex. Extrapolating is a bit dangerous with any polynomial curve, but on the other hand this one has an exceptionally well behaved 2nd order trend. -7 degrees certainly provides a large portion of the benefit. It would be very interesting to run through the same series of tests with a small tail at the same static margins for a side by side comparison. Chris Chris
Zavatson N91CZ 360std
Chris,
Great research.
In my small tailed 320, increased flap reflex experimentation did not
result in increased top end speed. The nose up pitch was increased,
requiring increased nose down trim - probably resulting in greater
empennage drag negating any reduction in drag from the
greater reflex. Of course, we would have to discuss the angle of
incidence of the small tail and its relationship to the elevator correcting for
nose down pitching ( my incidence was at -.9 degrees).
By moving weights forward and aft in the same flight, forward CG
was better for maximizing speed - unlike some aircraft that see max speed
when the CG is at the neutral point, probably a consequence of more standard
wing/tail design that saw drag from wing/horizontal +/- lift factors more
balanced and minimized.
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