[rebel-builders] Stall Speed Response
Posted: Sun Feb 19, 2012 8:34 pm
I did not do a lot of testing with different flap settings to give you
accurate comparisons before and after. I had bought the VGs to put on a
different airplane, but thought I would try them on the Rebel first with 2
sided tape. The results really surprised me (in a good way), so I decided to
keep them.
When I removed them, I went up and did a test loaded to 1650 (amphibs) and
noted a 47 mph stall at neutral flaps. I then installed them permanently and
did another test at the same weight and it now stalled at 38 mph with the
VGs. That is the only good comparison test that I did. And as I said, this
is ASI, not GPS verified at those speeds. You get a pretty steep nose up
angle with the VGs, so not sure what that does to my ASI readings.
Also, I tested it to the full stall break. As others have said, you get a
lot of sink before that, which can be mistaken for a stall. But mine would
do a clean break, if I held it long enough.
Hard to say what exactly 18 degrees flaps is on mine. What you see on the
ground is not what you get in the air, that's for sure, with all the flex.
My full flaps in the air is probably closer to 10 degrees. But I will say,
full flaps do make a big difference in float take-offs, so I use that all
the time. For landings, I always use half flaps, to ensure good aileron
authority in crosswinds.
Cruise and top speeds were not affected by the VGs. If they were, was not
enough for me to measure.
I use the Landshorter.com VGs at 10% chord spaced 3 inches apart.
Walter
-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Gary
Gustafson
Sent: Tuesday, December 14, 2010 5:29 PM
To: rebel-builders@dcsol.com
Subject: [rebel-builders] Stall Speed Response
I will reply to the following helpful emails with 3 answers
1. Walt - That is a very good reduction in stall speed which leads me to two
other questions.
First what is your indicated stall speed with VG's now at 18 degree
flaps. Second, How
did the VG's affect your top speed? I am sure others would like to know
these figures.
2. Drew - Yes I calibrated against a GPS and the static ports (have two -
one on each side)
is on the tail cone 1/3 of the way back from the cabin. I believe that
should be okay. My
pitot hangs down 6 inches just outside of the strut which also should be
okay. However,
I did talk to GRT (the manufacturer of my EFIS) and find that I may have
calibrated the
airspeed table wrong. I recorded stalls and airspeeds while in the air
and then entered the
data into a table in the GRT EFIS. It turns out that I should have had
the GPS in the GRT
EFIS average in the wind and with the wind speeds and have it populate
the table while
flying so that it can adjust for pressure altitude. Also the stall
points should be calibrated
from the corrected airspeed data already contained in the unit. GRT
tells me that I could
have compounded errors by not doing the calibrations in the air. So I
thank you for
questioning my airspeed and causing me to reread the instructions more
carefully.
3. Hank - I have been impressed with what I have read about LRI's and am
tempted to get
one. However, my GRT EFIS also has an AOA indicator that is supposed to
not be
affected by weight and weight distribution. I was getting disappointed
in the new feature
added as id did not seem to work right (which I now think is my error -
one of many). So
I will hold off until I recalibrate my GRT EFIS and see how it works (It
is supposed to be
within 1 degree if calibrated right). However, I would like to see your
pictures of your
installed LRI if it is not too much trouble. Send to email off-line.
Thanks
I also appreciate all responses to my questions as it is a learning
experience for me and I
hope others.
Gary Gustafson
----------------------------------------------
1. From Walter Klatt
My VG's lowered the stall by about 8 or 9 mph, according to my ASI, not
verified by GPS.
-----------------------------------------------
2. From Drew Dalgleish
Seems high Gary. Have you checked your airspeed against a GPS? Is it
possible that your static port is in a low pressure area? My airspeed
indicator always reads higher than my GPS unless I have a screaming
tailwind. I'm using the MAM pitot/static tube and it doesn't leak.
----------------------------------------------------------
3. From Hank Balch
I have a LRI on my Rebel and love it. On takeoff I watch the LRI and when
the needle moves into the yellow I know I have the speed for takeoff and
rotate. I also use it on landing. This is a real valuable instrument and I
rely on it more than my airspeed indicator during critical phases of
flight. I can send you some pictures of my installation if you are
interested.
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accurate comparisons before and after. I had bought the VGs to put on a
different airplane, but thought I would try them on the Rebel first with 2
sided tape. The results really surprised me (in a good way), so I decided to
keep them.
When I removed them, I went up and did a test loaded to 1650 (amphibs) and
noted a 47 mph stall at neutral flaps. I then installed them permanently and
did another test at the same weight and it now stalled at 38 mph with the
VGs. That is the only good comparison test that I did. And as I said, this
is ASI, not GPS verified at those speeds. You get a pretty steep nose up
angle with the VGs, so not sure what that does to my ASI readings.
Also, I tested it to the full stall break. As others have said, you get a
lot of sink before that, which can be mistaken for a stall. But mine would
do a clean break, if I held it long enough.
Hard to say what exactly 18 degrees flaps is on mine. What you see on the
ground is not what you get in the air, that's for sure, with all the flex.
My full flaps in the air is probably closer to 10 degrees. But I will say,
full flaps do make a big difference in float take-offs, so I use that all
the time. For landings, I always use half flaps, to ensure good aileron
authority in crosswinds.
Cruise and top speeds were not affected by the VGs. If they were, was not
enough for me to measure.
I use the Landshorter.com VGs at 10% chord spaced 3 inches apart.
Walter
-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Gary
Gustafson
Sent: Tuesday, December 14, 2010 5:29 PM
To: rebel-builders@dcsol.com
Subject: [rebel-builders] Stall Speed Response
I will reply to the following helpful emails with 3 answers
1. Walt - That is a very good reduction in stall speed which leads me to two
other questions.
First what is your indicated stall speed with VG's now at 18 degree
flaps. Second, How
did the VG's affect your top speed? I am sure others would like to know
these figures.
2. Drew - Yes I calibrated against a GPS and the static ports (have two -
one on each side)
is on the tail cone 1/3 of the way back from the cabin. I believe that
should be okay. My
pitot hangs down 6 inches just outside of the strut which also should be
okay. However,
I did talk to GRT (the manufacturer of my EFIS) and find that I may have
calibrated the
airspeed table wrong. I recorded stalls and airspeeds while in the air
and then entered the
data into a table in the GRT EFIS. It turns out that I should have had
the GPS in the GRT
EFIS average in the wind and with the wind speeds and have it populate
the table while
flying so that it can adjust for pressure altitude. Also the stall
points should be calibrated
from the corrected airspeed data already contained in the unit. GRT
tells me that I could
have compounded errors by not doing the calibrations in the air. So I
thank you for
questioning my airspeed and causing me to reread the instructions more
carefully.
3. Hank - I have been impressed with what I have read about LRI's and am
tempted to get
one. However, my GRT EFIS also has an AOA indicator that is supposed to
not be
affected by weight and weight distribution. I was getting disappointed
in the new feature
added as id did not seem to work right (which I now think is my error -
one of many). So
I will hold off until I recalibrate my GRT EFIS and see how it works (It
is supposed to be
within 1 degree if calibrated right). However, I would like to see your
pictures of your
installed LRI if it is not too much trouble. Send to email off-line.
Thanks
I also appreciate all responses to my questions as it is a learning
experience for me and I
hope others.
Gary Gustafson
----------------------------------------------
1. From Walter Klatt
My VG's lowered the stall by about 8 or 9 mph, according to my ASI, not
verified by GPS.
-----------------------------------------------
2. From Drew Dalgleish
Seems high Gary. Have you checked your airspeed against a GPS? Is it
possible that your static port is in a low pressure area? My airspeed
indicator always reads higher than my GPS unless I have a screaming
tailwind. I'm using the MAM pitot/static tube and it doesn't leak.
----------------------------------------------------------
3. From Hank Balch
I have a LRI on my Rebel and love it. On takeoff I watch the LRI and when
the needle moves into the yellow I know I have the speed for takeoff and
rotate. I also use it on landing. This is a real valuable instrument and I
rely on it more than my airspeed indicator during critical phases of
flight. I can send you some pictures of my installation if you are
interested.
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