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kensmith(at)springnet1.co
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 Posted: Wed Feb 20, 2008 8:13 am Post subject: Zenith-List Digest: 29 Msgs - 02/19/08 |
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Subject: Re: Zenith-List: Sabrina Re: Pitching the H-Stab.
Two changes to the aircraft by changing the pitch to the H-Stab has not yet been addressed.
#1 - People in the agriculture spraying business sometimes increase the up pitch to the H-Stab
because they have a out of aft CG when fully loaded. The tail assembly on an aircraft helps the
loading and CG of the aircraft's stability in the flying mode. When you increase the angle of attack
on the H-Stab you increase the loading on the tail section of the aircraft which in turn decreases
some of the loading on the main wing spar section. Reduce the main wing loading and you will
reduce the stall speed of the aircraft.
#2 - If you reduce the angle of attack of the H-Stab, just the opposite will occur. You have
reduced the loading to the tail section and in turn increased the loading on the main wing spar
section. You have then made the aircraft a less stable as well as you have increased the
STALL SPEED of your aircraft.
Ken Smith
Time: 12:29:31 AM PST US
[quote] | Quote: | From: Bryan Martin <bryanmmartin(at)comcast.net> (bryanmmartin(at)comcast.net)
Subject: Re: Sabrina Re: pitching the H-stab
The stabilizer has little to do with the cruise flight attitude of the
fuselage, it mainly has to do with the trim condition of the airplane.
If you can trim out the elevator forces in cruise without excessive
trim tab deflection, re-pitching the stabilizer won't help you. I re-
pitched my stabilizer because I couldn't trim out the stick forces,
not because the attitude of the airplane was wrong. I had to hold back
pressure on the stick all the time to keep the plane from diving.
The cruise flight attitude of the fuselage is controlled mainly by the
angle of incidence of the main wing. Increasing the angle of incidence
of the main wing will bring the nose of the fuselage down, but then
you will also have to pitch the stabilizer up to get it back into trim.
On Feb 19, 2008, at 1:26 AM, NYTerminat(at)aol.com (NYTerminat(at)aol.com) wrote:
| Quote: | Hi all,
With all the talk of pitching the horizontal stabilizer lately I
have a quick question. I am doing my conditional inspection on my
701 and decided to replace the front horizontal stabilizer brackets
to the .063 material. There were no cracks in my old ones but I
figured I might as well bite the bullet now while the weather is
keeping me from flying anyway. I have always felt that I was flying
in a nose high attitude while at cruise and that I do not see the
higher MPH that others see. I purchased a digital level and have
discovered that my horizontal stabilizer was about a half of a
degree low in the front (approx 3 mm). I plan on raising it one
degree so that I will be a half of a degree higher in the front
based on the A-E line. I am wondering if this is a good idea as I
believe this will get me flying in a better attitude at cruise and
pick up some speed. Any thoughts?
Bob Spudis
N701Zx/ CH-701/ 912S/ 140hrs
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bryanmmartin
Joined: 10 Jan 2006
Posts: 1018
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| Posted: Wed Feb 20, 2008 11:37 am Post subject: Zenith-List Digest: 29 Msgs - 02/19/08 |
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I situation #1, in addition to the lower stall speed, the airplane has
less pitch stability. If you add too much angle of attack to the
stabilizer you may end up with a situation where the stabilizer,
generating positive lift, can stall before the main wing. This would
result in a pitch up which you may not be able to recover from.
In situation #2, increasing the stall speed of the airplane does not
make it less stable. Actually, decreasing the angle of attack of the
stabilizer (pitching it down) INCREASES the pitch stability of the
airplane. The stabilizer will be flying at a lower angle of attack
than the main wing and the main wing will stall first, resulting in a
pitch down towards stall recovery. The stabilizer will most likely be
flying at a negative angle of attack and producing a down force on the
tail. In this case, even if it stalls first, the result will be a
pitch down towards stall recovery. The higher stall speed just means
you will need a longer runway and faster approach speeds.
Unfortunately, it also it makes an emergency landing more dangerous.
On Feb 20, 2008, at 11:10 AM, kensmith(at)springnet1.com wrote:
| Quote: |
Subject: Re: Sabrina Re: Pitching the H-Stab.
Two changes to the aircraft by changing the pitch to the H-Stab has
not yet been addressed.
#1 - People in the agriculture spraying business sometimes increase
the up pitch to the H-Stab
because they have a out of aft CG when fully loaded. The tail
assembly on an aircraft helps the
loading and CG of the aircraft's stability in the flying mode. When
you increase the angle of attack
on the H-Stab you increase the loading on the tail section of the
aircraft which in turn decreases
some of the loading on the main wing spar section. Reduce the main
wing loading and you will
reduce the stall speed of the aircraft.
#2 - If you reduce the angle of attack of the H-Stab, just the
opposite will occur. You have
reduced the loading to the tail section and in turn increased the
loading on the main wing spar
section. You have then made the aircraft a less stable as well as
you have increased the
STALL SPEED of your aircraft.
Ken Smith
|
--
Bryan Martin
N61BM, CH 601 XL,
RAM Subaru, Stratus redrive.
do not archive.
| | - The Matronics Zenith-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Zenith-List |
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_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive. |
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