Ventus C rigging

I have a 1987 Ventus C that I purchased in 1995. Love
the plane but it wants to roll to the right at high
speeds (90kts or greater). Actually I guess it always
wants to roll to the right but I start to notice how
much left aileron pressure I have to apply to counter
the roll at the higher speeds, especially above 100kts,
for any period of time (long final glide). It makes
my arm tired. At speeds below 80kts I don't notice
it. I have tried various riggings with the flaps/ailerons
but other than slight improvements I don't seem to
be making any progress and have just 'lived with it'
over the years. I'm afraid that the problem might
be 'built-in' to the airframe with one wing having
a different angle of incidence than the other. I sent
an email to Schempp-Hirth about this and never got
a reply. Anyone have any ideas?

Jimmy Hamilton
Reno, NV
JLH

It's unlikely to be built in unless there has been
damage and a poor repair.

Are you using 17.6 extensions, these have a spring
to set a 'neutral position' is it still present on
both wings and is the neutral position the same.

Have you set up the flaps for equal displacement, eg,
does the same deflection happen from both full left
and right stick, normal check here in UK for CofA.

If you set the flaps to equal positions is the stick
still in the centre.

Its quite a complicated setup and could well have gone
adrift over the years or you might be seeing damage
or impending problems. If you have actually started
to notice it then it must be fairly dramatic by now.
Do a control movements check to see if anything is
out and work back from there.

John

PS reading between the lines, I presume that it is
only evident at neg flap positions, 86 being the change
over to -1. If so ten you need to check control movements
at all flap settings

It's unlikely to be built in unless there has been
damage and a poor repair.

Are you using 17.6 extensions, these have a spring
to set a 'neutral position' is it still present on
both wings and is the neutral position the same.

Have you set up the flaps for equal displacement, eg,
does the same deflection happen from both full left
and right stick, normal check here in UK for CofA.

If you set the flaps to equal positions is the stick
still in the centre.

Its quite a complicated setup and could well have gone
adrift over the years or you might be seeing damage
or impending problems. If you have actually started
to notice it then it must be fairly dramatic by now.
Do a control movements check to see if anything is
out and work back from there.

John

PS reading between the lines, I presume that it is
only evident at neg flap positions, 86 being the change
over to -1. If so ten you need to check control movements
at all flap settings

You may want to make three accurate templates pattern
A stable material like 1/2" thick Birch ply or 5/8 Flooring
plywood will be OK.
Make one template for the 2 ft station away from the root
one at the first taper break and the third near the tip.
use the top surface of the template as a reference
to measure your angle deviation.
your measuring device should be accurate to within 1/4 degree
over 2 ft. make sure to position the templates in the same
relative position on the other wing when measuring it.
Always point the measuring device in the same relative direction.

You need to print out the airfoil with the correct chord dimension
for each station. The Ventus has a different tip airfoil, you must
find out what airfoil it is.
You can see a sample picture on my web page under personal
http://www.wingdolly.reach.net/personal.html
All this assumes you checked your aileron and flap settings.
Even if the aileron is set right, if the flap is off by 11/2 degree you will
have that effect.
Regard
Udo

James:

I had the same problem with my old ASW-20 a couple of years ago and it
nearly drove me crazy until I found the cause. In my case, a short
section of my mylar flap gap tape had come slightly unglued,
effectively giving a slight aileron effect that was really noticeable
at high speeds. It was almost impossible to see and even when I found
the unglued tape I was skeptical that it could be the cause as it
looked so insignificant. However, when I resealed it, the problem went
away completely.

This may not be your problem, but I'd check first as it's an easy fix.

regards

Mike


James Hamilton wrote:
I have a 1987 Ventus C that I purchased in 1995. Love
the plane but it wants to roll to the right at high
speeds (90kts or greater). Actually I guess it always
wants to roll to the right but I start to notice how
much left aileron pressure I have to apply to counter
the roll at the higher speeds, especially above 100kts,
for any period of time (long final glide). It makes
my arm tired. At speeds below 80kts I don't notice
it. I have tried various riggings with the flaps/ailerons
but other than slight improvements I don't seem to
be making any progress and have just 'lived with it'
over the years. I'm afraid that the problem might
be 'built-in' to the airframe with one wing having
a different angle of incidence than the other. I sent
an email to Schempp-Hirth about this and never got
a reply. Anyone have any ideas?

Jimmy Hamilton
Reno, NV
JLH

I would check the tape first, too. It's difficult to believe the impact
a small piece of loose tape can have...or the difficulty of finding it.
Many years ago at the U.S. 15M Nationals (why do these things always
happen at contests?), my LS-3 began to pitch down abruptly when
thermaling. Just enough to get my attention. It didn't appear to stall,
but the nose dropped enough to make me wonder.

After a while, I noticed this only happened when I was carrying water
ballast. Day after day, as I talked to experts, I'd take off with
water, find myself feeling uncomfortable in gaggles, and finally dump
ballast to fly the task. The problem didn't always show up
immediately--sometimes it was 15 to 30 minutes before this started--but
it was always there eventually.

Finally I discovered that a 4" wide section of cloth tape on the top
side of the elevator hinge joint was not stuck down firmly. Apparently,
at flying speeds the front 1/4" of the tape would eventually work loose
and flip up intermittantly. On the ground it looked normal (and the
vast majority of it was). The only reason I found it was running my
fingernail along the front edge of the tape. The sticky part had dust
on it, indicating it had been in the airflow for a while.

The fix was easy: I simply applied the usual white plastic wing gap
tape to the front edge of the cloth tape to hold it down until I could
replace it, with immediate results.

Chip Bearden
ASW 24 "JB"

I have corrected this problem on unflapped gliders before. On one glider in
particular one aileron had a bit more undercamber than the other due some
damage. The temporary fix was to add a small trim tab on the trailing edge
of the aileron. It worked! The aileron was subsequently fixed due to another
repair.
It always came down to a twist, bend or some damage of the aileron. The
reasoning is; If the aileron rigging was wrong and with the stick central
and the left was down further than the right. Then when flying if the stick
was held central then a roll would result. If it was flown hands off then
the ailerons would balance at a nuetral posiotn and it would fly level.
Hence if the pilot is having to apply side stick loads whilst in flight it
can not be due to incorrect lenght of pushrods and rigging and must be due
to twists or some such. This of course does not hold if there are
centralising springs or dampers that are set up. However if the stick loads
increase with speed as described then it is centainly not due to springs or
dampers.
Of course flaps being set differently on each side would give rise to the
same sort of characteristics as a twist or bend.

Also I would have to agree to check the mylar seals and such like they do
have dramatice effects if they are loose.



"James Hamilton" wrote in message
...
I have a 1987 Ventus C that I purchased in 1995. Love
the plane but it wants to roll to the right at high
speeds (90kts or greater). Actually I guess it always
wants to roll to the right but I start to notice how
much left aileron pressure I have to apply to counter
the roll at the higher speeds, especially above 100kts,
for any period of time (long final glide). It makes
my arm tired. At speeds below 80kts I don't notice
it. I have tried various riggings with the flaps/ailerons
but other than slight improvements I don't seem to
be making any progress and have just 'lived with it'
over the years. I'm afraid that the problem might
be 'built-in' to the airframe with one wing having
a different angle of incidence than the other. I sent
an email to Schempp-Hirth about this and never got
a reply. Anyone have any ideas?

Jimmy Hamilton
Reno, NV
JLH

John Orton wrote:
I have corrected this problem on unflapped gliders before. On one glider in
particular one aileron had a bit more undercamber than the other due some
damage. The temporary fix was to add a small trim tab on the trailing edge
of the aileron. It worked! The aileron was subsequently fixed due to another
repair.
It always came down to a twist, bend or some damage of the aileron. The
reasoning is; If the aileron rigging was wrong and with the stick central
and the left was down further than the right. Then when flying if the stick
was held central then a roll would result. If it was flown hands off then
the ailerons would balance at a nuetral posiotn and it would fly level.
Hence if the pilot is having to apply side stick loads whilst in flight it
can not be due to incorrect lenght of pushrods and rigging and must be due
to twists or some such. This of course does not hold if there are
centralising springs or dampers that are set up. However if the stick loads
increase with speed as described then it is centainly not due to springs or
dampers.
Of course flaps being set differently on each side would give rise to the
same sort of characteristics as a twist or bend.

Also I would have to agree to check the mylar seals and such like they do
have dramatice effects if they are loose.



"James Hamilton" wrote in message
...

I have a 1987 Ventus C that I purchased in 1995. Love
the plane but it wants to roll to the right at high
speeds (90kts or greater). Actually I guess it always
wants to roll to the right but I start to notice how
much left aileron pressure I have to apply to counter
the roll at the higher speeds, especially above 100kts,
for any period of time (long final glide). It makes
my arm tired. At speeds below 80kts I don't notice
it. I have tried various riggings with the flaps/ailerons
but other than slight improvements I don't seem to
be making any progress and have just 'lived with it'
over the years. I'm afraid that the problem might
be 'built-in' to the airframe with one wing having
a different angle of incidence than the other. I sent
an email to Schempp-Hirth about this and never got
a reply. Anyone have any ideas?

Jimmy Hamilton
Reno, NV
JLH






As John commented any aerofoil discrepancy will result in progressively
different forces. If there is any damage history on the wings or reprofiling
history, this would be a place to look.

Assuming this is not the case - Just a thought, but have you looked at the wings
when you are applying the force. The Schempp-Hirth airbrake caps are spring
loaded, over time the springs weaken and you may have assymetric protrusion.

Similarly they lock down from the outside in - if the over centre is not
symmetrical you could have the same effect. Not sure how this is set on the
Ventus, on the Cirrus it is by rotating tie rod ends in the fuselage, so it
would be easy to have different tension left to right.

At high speed these would introduce significant forces with the slightest
differences.

At 06:12 07 July 2006, Bumper wrote:

'John Orton' wrote in message
...
I have corrected this problem on unflapped gliders
before. On one glider in
particular one aileron had a bit more undercamber than
the other due some
damage. The temporary fix was to add a small trim tab
on the trailing edge
of the aileron. It worked!


It's easy to experiment by adding a wedge shaped strip
to the underside of
the aileron trailing edge, affixing it with double
sided tape. This will act
like a downward bent trim tab.

bumper

.... as well as altering the mass balance, risking
flutter and invalidating the C of A and, therefore,
insurance ... in most countries but not in the USA,
of course, where aerodynamics work differently under
the 'experimental' category.