REFLECTOR: barn door speed brake

[Paula & John Schoorl]

Terry:
Too add a little more info to Craig's reply about our XL-5FG with speed
brake:
Our max extension angle is about 75 degrees.  Chap 14 recommends not to
exceed 60 degrees.  How we ended up that way was we converted to the cutdown
keel halfway through the build and had to adjust our actuator position to
make it work.  It resulted in more extension angle than we originally had.
It also resulted in the actuator being installed in a nearly vertical
position which makes for a not very good load path from door through
actuator to keel.  On my to do list is to do the math and figure what loads
our actuator is seeing in our configuration versus the book installation.

Our test pilot likes to fly his final approach with the speed brake extended
so he can keep more power in and have better engine response.  I tried the
same technique but was not very comfortable with it and my landings showed
that.  I went back to flying without it like I was primarly taught at the
factory and my landings improved greatly.  Once I am more comfortable in the
airplane I will probably go back and experiment with the speed brake some
more, especially to shorten landing distance.

As a side note to the discussion about rapid descents with gear or brakes
extended:  The factory airplane wires the speed brake so it is either fully
extended of fully retracted.  I assume this air load on the door and into
the actuator and keel is what drives the 110kts speed brake limitation.
Craig and I wired our speed brake so the brake only extends while you hold
the switch down so we can extend to any angle we want by how long we hold
the switch (we have a position indicator on the panel).  Flip the switch up
and the brake retracts completely for a go-around, in case your wondering.
While I'm figuring out loads on the brake, I also intend to look at whether
I can get away with a shallower speed brake angle at a higher speed than 110
and get the benefit of the drag for a higher rate of descent.  Thats an
engineering problem for down the road if I don't convince myself its a bad
idea before then.

Hope that wasn't too much information....
John Schoorl
XL-5FG
Palmdale, CA

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Terry Miles
Sent: Wednesday, October 11, 2006 1:31 PM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: barn door speed brake


Thanks you guys.  ...and thanks Jorge.  The only one I could half way
measure looked to be between 55 to 60.
Terry

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Craig and/or Denise Woolston
Sent: Wednesday, October 11, 2006 8:32 AM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: barn door speed brake


I'd say our extension angle is around 60 degrees.  I honestly can't
remember right now if the manual said to limit it or not.  The test
pilot landed with it down every time, but I haven't used it yet.

Craig
XL-5FG Flying in Palmdale, CA


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