David - I found out the hard way about that shear screw - see my build
journal at
<http://www.rowlandcarson.org.uk/aviation/europa_435/200904.php> on 21st
& 30th of the month.
As you will see, I got my replacement shear screws direct from TruTrak.
I don=99t seem to have a picture of it, but I seem to recall that
there are several tapped holes that can be used for the screw so it=99
s not essential to remove the broken end.
in friendship
Rowland
> On 2023-01-04, at 16:47, David Cripps <dpc@knightonweb.com> wrote:
>
> Thanks, Duncan.
>
> I have removed the arm now (and the crosshead screw does indeed have a
nylon washer under it). I note the LAA requirement that this screw needs
Loctiting when it is put back in, as well as the screw retaining clip
refitting over it.
>
> I can see that the shaft of the brass pin has broken below the surface
of the hub so unfortunately there is nothing to grab onto. However, I
also notice that there are two other similar screw holes in the hub
which could be used instead, by rotating the hub through 120deg. Perhaps
this is a deliberate design to give a chance of doing an in-field
replacement of a sheared pin in order to get it working again, enabling
the removal of the old pin stub to be done at a later time.
>
> Any ideas how to remove that stub? I have some screw extractors but
they=99re much too big.
>
> Also, do you know where I can obtain replacement pins? You probably
made your own when you switched to the stainless screws? If I do the
same with a brass or stainless 6-32 screw is there a defined amount of
=98necking=99 required so that it shears at an appropriate
shear force?
>
> David
>
>
>
> With a failed pin, there would now be no shear connection between the
servo hub and the arm other than friction. So, given enough torque it
will slip, and it must have slipped at some point otherwise the pin
wouldn't be sheared. The earlier servos had a nylon washer under the
crosshead screw to help it slip!
>
> I guess if you take off the arm, the remains of the shear pin may be
projecting from the hub sufficiently to get a grip on it.
>
>
>
> Duncan mcF.
>
> On 04 January 2023 at 12:21 David Cripps <dpc@knightonweb.com
<mailto:dpc@knightonweb.com>> wrote:
>
> Thanks very much for this extra info, Duncan.
>
>
>
> If you can find that spare stop that would be great. I had seen a
picture similar to the one you sent of the stops in another aircraft
application.
>
>
>
> Following your comments about the shear pin, I think this is the small
brass screw located just above the main central cross-head screw that
holds the control arm onto the servo in the photo I=99ve attached
here? I looked at mine more closely and saw that the head of that brass
screw appeared to be slightly loose and with some tapping I could get
the screw head to drop out of the arm. If that is the shear pin you=99
re referring to then it appears mine is already sheared! However, the
arm doesn=99t show any tendency to rotate on the hub? I guess the
cross-head screw is holding it onto the hub pretty firmly, but I can see
that the arm could potentially rotate against the hub without the pin
being there (since there is no positive locking mechanism against
rotation), but the cross-head screw would need to be looser than it
currently is for rotation of the arm to be possible. Should the arm be
free to rotate against the hub without the pin there? Question also now
is how to get the threaded bit out and the pin replaced?!
>
>
>
> Best regards
>
>
>
> David
>
>
>
> I'd not seen before the clip on the servo arm; there was an earlier
Factory 'fix' of Loctited replacement screws. Later servos have a stud
and pinned locknut instead (I guess the stud is held in only by
Loctite!).
>
> The control column stops should take priority, as the servo stops are
probably too light to limit enthusiastic control movements by the pilot,
but should at least contain a runaway servo or some other breakage in
the servo. I might have some spare stops (if I can find them). The stops
are half-visible and annotated 'F' in the photo at:
TruTrak-RV10-Roll-Installation-Guide.pdf (bendixking.com)
<https://www.bendixking.com/content/dam/bendixking/en/documents/document-l
ists/downloads-and-manuals/TruTrak-RV10-Roll-Installation-Guide.pdf>
> The shear pin is merely a 6-32 screw with a short part of its length
(where this crosses the interface between the mating arm and hub) necked
and polished to the roots of the screw thread.
>
> My own servo is mounted towards the back of the Europa 'tunnel' and
connects to a horn bolted to the rear end of the roll torque tube. This
area used to get hot under certain situations via heat from the
stainless firewall and no tunnel ventilation. Subsequently a 'fire
blanket' (two thin layers of woven Kevlar with thin fibreglass loft
insulation sandwiched between, rather like Orkotek) placed on the back
of the firewall enabled cooler temperatures. I've not heard of the
standard under-seat servo location getting too hot.
>
>
>
> Duncan McF.
>
> On 03 January 2023 at 22:30 David Cripps <dpc@knightonweb.com
<mailto:dpc@knightonweb.com>> wrote:
>
> Thank you for the comprehensive reply, Duncan, and also for the
replies from Alan and Peter. I really appreciate the feedback.
>
>
>
> It seems that the Skymap III should work OK for us, despite its 0.5Hz
data refresh rate. A bit of =98hunting=99 shouldn=99t
really be a problem. We hadn=99t planned to have it fly a full
route and navigate itself around turning points. I had thought we=99
d be manually changing the selected track at each turning point, and
then lock the tracking to the new direction required. However, the
Skymap III does have a =98Turn Anticipation=99 feature if we
should in the future want it to follow a route, and not overshoot a
waypoint. Do most people use it to follow a full track, and make all the
waypoint turns?
>
>
>
> Good to know about the shear pin in the arm as a last resort! Do you
have any drawing of the necked stainless pin that you got the LAA to
agree to?
>
>
>
> The servo that I have came out of an old Europa and didn=99t
seem to have any physical stops on the servo arm. It did, however, have
the extra alloy =98clip=99 to secure the screw that attaches
the arm to the servo. I=99ve seen that that clip was an LAA
requirement too (see photo). For the physical stops, I did see on
another forum something that looked like it would do the job on this
servo (may even have been a Trutrak part). Does the LAA specify what
these stops should look like or be made of? Should they be set so that
the servo arm touches them at the same time as the control column
reaches its full deflection (if not, then which stop should =98take
priority=99 and be hit first)? Does anyone have a photo of what
the stops look like in their setup? I imagine them being mounted on the
bolts that attach the servo motor to its mounting frame.
>
>
>
> My servo would be mounted under the pax seat per Mod 75, so there is
not really any ventilation there. Is it worth adding a little cooling
fan to the seat locker to keep the air circulating around the servo?
>
>
>
> Many thanks for all the input!
>
> David
>
> i). The Trutrak will work on a Europa at 0.5Hz update frequency (i.e.
every 2 seconds). Sometimes the AP will hunt gently (yesterday was a
case in point, but there were sites yesterday that were GPS-jamming as
well, so that might have been a cause' or possibly I have a too low
torque setting than optimal in order to limit servo overheating). If too
many options of output data are requested in the GPS NMEA output setup
then there won't be enough time to output all that data within a faster
update period; the GPS set will normally tell you if this is going to be
the case.
>
> iii). The servo does not care about torque feedback. The servo will
provide a force (torque) only up to the maximum value that has been
preselected.
>
> iv). The Europa needs quite a high torque setting (10 or 12 from
memory, which can on hot days plus a high 'activity' setting result in
servo overheating and shutdown if you have a trigear with
'heated'/unventilated fuselage tunnel and depending where the servo is
mounted).
>
> The pilot stick force required to overcome maximum torque will be
applied without even thinking about it and in any case there is a necked
brass shear pin (comprising a modified 6-32 brass instrument mounting
screw) in the servo arm that can be easily sheared (even without knowing
it, and then you wonder why the AP is not tracking!). I agreed with LAA
to replace this with a (necked) stainless steel pin in order to provide
a little more strength and haven't sheared it since.
>
> I also think that when the servo gets very hot (as above) it's
internal voltage regulator starts to shut down (as many are designed to
do). Again, there is no way of knowing when this happens until
realisation that the AP is not tracking!
>
> v). The LAA will insist upon the stops on the servo, although these
stops are not particularly robust and the set up would be better
adjusted so that the stops never have to resist the pilot's stick
inputs.
>
> Otherwise, the Trutrak system and its dynamics work extremely well and
can do a much better job than the pilot, especially in turbulent
conditions.
>
> Have you found a setting on your Skymap that allows adjustment of the
pre-emptive steering sensitivity (or "turn anticipation")?
>
>
>
> Duncan McF.
>
> On 03 January 2023 at 13:10 David Cripps <dpc@knightonweb.com
<mailto:dpc@knightonweb.com>> wrote:
>
>
> So, I've slowly been making some progress on this, having mocked up
the whole system out of the aircraft. I have now been able to test it in
the workshop and yesterday in a car (it needed to be moving to get a
track signal). See attached photo. However, I now have a couple more
questions/observations!
>
> i) It seems that the Skymap III that I used in these tests works in
terms of making the servo move and display a track on the Trutrak, so
that's progress! However, I note from the Skymap manual that it only
gives its GPS info every 2 seconds, rather than the once every second
that the Trutrak recommends to avoid 'wandering'. Peter, in your post
you mentioned that you were using a Skymap III - have you ever had a
problem with this (assuming your A/P is the Trutrak Digitrak too)? Alan,
is the Garmin 196 that you've mentioned as suitable, able to be set to
give data at the 'once per second' rates, as from the manual it seems it
may too default to once every 2 seconds?
>
> ii) I noticed when testing in the car, that when the track that was
displayed in the Trutrak was close to what we were actually tracking (as
read from the Skymap), that the servo was more or less static, and moved
in the correct direction when there was a small deviation between what
was set on the Trutrak and what we were tracking. However, because our
roads are not straight, there were frequently occasions when the actual
track from the Skymap was miles away from that set on the Trutrak. In
that situation the servo went a bit crazy and rotated its arm by many
more degrees than it could ever do in the plane. Is this to be expected
in this rather 'offline' mode? I can imagine that when the Trutrak
senses that its control input is not creating the sort of aircraft track
change that it had expected, that it just moves the servo even further
in order to try to get aircraft to do something?
>
> iii) Clearly my mock-up does not provide any sort of 'force feedback'
to the servo control arm (ie the arm is completely free to rotate as it
likes). In an aircraft, would this be taken care of by aerodynamic
feedback via the aileron torque tube? What happens to the servo when it
reaches the full movement that the aileron would allow (the point when
the control column hits its roll stops)?
>
> iv) I can imagine that I wouldn't want the servo ever applying full
aileron to create a turn as that would make for a very violent
manoeuvre! I see that there are settings that can be adjusted in the
Trutrak set-up menus that control activity level and also control
maximum torque. What values have people set in theirs? I note that when
I have set the recommended value of 12 for the torque, it is almost
impossible to override the servo arm when the A/P is engaged (though I
appreciate that with no control column attached the leverage I can apply
to the servo arm with my fingers is very low. I also appreciate that
normally if one wanted to override the A/P you would disengage it
first).
>
> v) Lastly (for now!) has anyone fitted physical 'stops' to the servo
body that the servo arm would hit to ensure that the servo can never try
to move the pushrod beyond the point where full aileron is applied?
>
> Apologies for all the questions but I want to make sure it is really
working correctly before I contort myself to fit it into the aircraft
itself!
>
> Best regards
>
> David
>
> On 19/11/2022, 16:26, "Alan Burrill"
<owner-europa-list-server@matronics.com
<mailto:owner-europa-list-server@matronics.com>
<mailto:owner-europa-list-server@matronics.com
<mailto:owner-europa-list-server@matronics.com>> on behalf of
alanb@dpy01.co.uk <mailto:alanb@dpy01.co.uk> <mailto:alanb@dpy01.co.uk
<mailto:alanb@dpy01.co.uk>>> wrote:
>
>
<mailto:alanb@dpy01.co.uk> <mailto:alanb@dpy01.co.uk
<mailto:alanb@dpy01.co.uk>>>
>
>
> Ok I=99ve had a. Ha ce to fly mine with the GPS feed off.
>
>
> As Duncan says below the display drops to show -|=94|- but
maintains the track last set or you are holding when you switch it on.
>
>
> The are no heading digits on the display so you will need use your
compass/DI to show that.
>
>
> If you press the left or right =A4=B5=EF=B8=8F buttons then you can
alter the track the AP is following either left or right and a number
appears which if you press the button you can increase or decrease after
the AP locks on the numbers disappear and you have the -|=94|- on
the display.
>
>
> Useful if you have a GPS failure but wouldn=99t want that as
normal mode of operation so my suggestion is you need a GPS feed with
the right NEMA message set to get the most out of the AP and the ability
for it to follow a track you have programmed in is a bonus.
>
>
> One word of caution, I have come across some GPS that don=99t
put out any messages, even the position message for driving a
Transponder ADS-B output, unless there is a track in the GPS. That was
how some of the older version worked, GARMIN 430 and possible the early
AVMAP were guilty of that.
>
>
> Hope that helps.
>
>
> Alan
>
>
> Sent from my iPad
>
> On 10 Nov 2022, at 10:52, D McFadyean <ami-mcfadyean@talktalk.net
<mailto:ami-mcfadyean@talktalk.net> <mailto:ami-mcfadyean@talktalk.net
<mailto:ami-mcfadyean@talktalk.net>>> wrote:
>
<ami-mcfadyean@talktalk.net <mailto:ami-mcfadyean@talktalk.net>
<mailto:ami-mcfadyean@talktalk.net <mailto:ami-mcfadyean@talktalk.net>>>
>
> Digitrak only needs basic positional information from the GPS on a
regular basis. It will use this information to fly the track that has
been set on the Digitrak.
> If a route is programmed in to the GPS, it will fly that too (with
different commands being set at the Digitrak control head to enable
this), so long as the GPS is also putting out the crosstrack error
signal; not all of them do.
>
> Duncan McF.
>
>
>
>
>
> s.com/Navigator?Europa-List <http://s.com/Navigator?Europa-List>>
> ion>
>
| Rowland Carson ... that's Rowland with a 'w' ...
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|