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You're flying with up-elevator but the trim spring
is pushing forward ? ?
That does not compute . . .
Wolfgang
----- Original Message -----
Sent: Thursday, October 10, 2013 8:37
AM
Subject: RE: [LML] 320/360 performance
and stability
Hi
Chris,
Since
I have upgraded from 320 to 360 my airplane is now on the forward side of its
CG range. It's nice now when I throw a few things in the back.
Since this discussion all came up I looked at my elevator in flight and it is
clearly is flying in an up elevator condition even though the trim spring is
trying to push the stick forward to keep level flight. That is why I was
thinking that a little reduced down thrust may not have the tail fighting so
much to keep everything in balance for level flight. Don’t have room to
do much but wondering it that would help put the elevator in more of a neutral
position.
Craig
Schulze
N73S
From: Chris Zavatson
[mailto:chris_zavatson@yahoo.com]
Sent: Tuesday, October 08, 2013
4:55 AM
To: lml@lancaironline.net
Subject: Re: [LML]
320/360 performance and stability
"I was
thinking about reducing engine downthrust. Any thoughts on this
Chris?"
Less downthrust is
destabilizing.
If you are going
to change downthrust, I would love to record your neutral point before
and after. It is rare to get stability data on a propeller changes like
this.
Here is paper that
discusses the stability changes to the Hawkeye E-2C simply by increasing prop
disc solidity. Four blade to eight blade prop.
From: Craig Schulze
[mailto:craig@skybolt.net]
Sent: Thursday, October 03, 2013 1:04
PM
To:
'dudewanarace@yahoo.com'
Subject: RE: 320/360 performance and
stability
What type of odd
experiences are you having with yours? I have been noticing that the
faster I go the more pitch sensitive it is. I have the small tail too
and my elevator position is about the same as yours in cruise. I was
thinking about reducing engine downthrust. Any thoughts on this
Chris?
What were the results
of flattening the bottom of the flaps? Any speed
gain?
From: dudewanarace@yahoo.com
[mailto:dudewanarace@yahoo.com]
Sent:
Wednesday, October 02, 2013 4:50 AM
To: lml@lancaironline.net
Subject: 320/360 performance and
stability
I have been watching
this conversation with interest. I have some odd experiences with
stability in my small tail 360 that was improperly built (not by me).
Geez, that is going to hurt resale.. haha
Anyway, I have been
waiting to comment as it will just fog the data that has been presented given
my totally odd arrangement and lack of any real data. All of my 'data'
is seat of the pants, thus not worth mentioning. But, figured I could
expand on an envelope probably few have visited just for interesting
reading.
This is my elevator
angle with the airplane in a forward C.G. condition (header fuel only, single
pilot), flaps in reflex and, well, going as fast as an RV-7 will go in
formation. :)
http://www.n54sg.com/images/tuft_test_08.jpg
So, this problem poses
a few issues.
First, this is
obviously drag, probably a measurable amount thus for me the driving force
behind correcting it one day. Second is the available elevator travel.
If you read the manual, I have the correct amount of up / down elevator
travel. But, if the photo is my starting point, it means I have much
less up, and way too much down available to use. The important part
being the elevator up while in the flare. Given a forward C.G. and a
huge amount of flaps, this can be an issue. (ask me how I
know...)
Next I would like to
mention that not all small tails trim the same. Some use a spring system
to bias the entire elevator. Others use trim tabs. I have a tab
that due to its placement and odd elevator deflection has a limited functional
envelope. Another driving force to change incidence.
Now the often obvious
question people ask is why haven't I fixed it yet. Well, because the job
of fixing it is going to totally suck, and I wanted it to be the last thing I
do as my other aerodynamic changes may affect the angle of incidence.
This brings me to the next subject, what I have
changed.
So I have this airplane
going faster than most and figured why stop now.. I made a rather drastic
change that some call the beluga belly. It has been done to a few
Legacys that race with varied applications of the same idea. Those
familiar with the 320/360 fuselage will notice it in this
picture:
http://www.n54sg.com/images/tuft_test_04.jpg
I'm working on a write
up for my website detailing the project and its purpose and will have that
posted sometime soon. But, I will report that this did change the
downwash on my horiztonal and did change my required angle of incidence.
Hence, I'm glad I waited to change that. It actually requires less up
elevator than it did before so less negative incidence. The general
theory is I have corrected some flow around the fuselage thus making the
entire horizontal a bit more effective. Some modified Legacys
experienced something similar. I only wish it would have corrected it
more! I now know more about this mod and maybe would have applied it
differently. Just not sure I'm willing to do the work again for unknown
gains.
The other aerodynamic
change I made (that relates to the original stability post) is I removed the
cusp from the bottom surface of my flaps as suggested in a book about GA
airfoils by Harry Riblett. Below is a simplified version of his drawing.
(Not accurate, just for explanation purposes) The solid black is
the modification.
http://www.n54sg.com/images/Flap_Drawing.jpg
So, what I have done to
the camber of the wing is a bit odd I suppose, but it was odd to start with.
Keep in mind, the 320 / 360 ailerons already have this modification.
I didn't get the 10 kts I thought I would. (Aren't all mods worth
10 kts? haha) But, it is a different airfoil. Stall was no
different, but the pitch force did increase with flaps extended. Not a
bad thing in my opinion. Overall it is hard to explain, it is a
different wing, just can't pinpoint how.
In the end I think I
have made the airplane aerodynamically better, but I have moved the problem.
It seems with just a little bit cleaner airplane I ran in to the limit
of the propeller. Previously more rpm always netted more speed.
Now the top 250ish rpm doesn't do much at all. Total bummer!
Having to learn a lot more about propellers than I ever thought I would
now...
Results of my airplane
at Reno this year:
Qualifying: 268.272
mph
Sport Medallion: 1st 261.906 mph (only 2600
rpm!)
Heat 1C: 3rd 268.300
mph
Heat 2C: 2nd 265.030
mph
Heat 3C: 2nd 266.717
mph
Bronze Race: 2nd 266..944
mph
I have some really cool
video from my helmet/dash cameras, just trying to get it all edited.
Hear is a teaser of some VERY close racing with Dave Morss in his
Legacy: http://youtu.be/iegd6ylVHI4
Best to watch in full
screen in HD. Keep in mind, objects in a wide angle lens are closer than
they appear! haha
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