Attached is a calculation of the shear pin strength and the basis to LAA ag
reeing to a stronger (steel) pin. Correspondence justifying the steel is no
t to hand , although I have the LAA letter referencing and accepting it.
>From this you can see that a pin several times stronger than brass would be
possible whilst still complying with JAR-VLA. You can also see that only 5
to 10lbs of (additional) stick force is required to shear the brass pin; y
ou'd hardly notice this in the heat of a moment, as has been the case!
Duncan McF.
> On 04 January 2023 at 22:29 Dpc <dpc@knightonweb.com> wrote:
>
>
> Rowland
>
> Thanks for that info. I=99ll see if I can source them or will e
nd up making them by turning a suitable machine screw as Duncan seems to ha
ve done.
>
> Yes, there are two other tapped holes in the hub that could be used i
nstead if I can=99t get the broken stud out, but I=99ll still g
ive extraction a go if I can find a tool small enough. Slightly odd design
to have a threaded shear pin which breaks off flush. Might have made more s
ense to have a smooth bore hole and a smooth pin where you put a nut on its
far end. That way, when it sheared, it would be relatively easy to push it
out and replace.
>
> Great build journal, by the way! I was amused to see I make a
=98guest appearance=99 in row 11! That takes me back!
>
> David
>
>
>
> > > On 4 Jan 2023, at 17:33, Rowland Carson <rowlandcarson@gmail.
com> wrote:
> >
> >
> > >
> > > David - I found out the hard way about that shear scr
ew - see my build journal at <http://www.rowlandcarson.org.uk/aviation/euro
pa_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
=99s not essential to remove the broken end.
> >
> > in friendship
> >
> > Rowland
> >
> >
> > > > > On 2023-01-04, at 16:47, David Cripps <dp
c@knightonweb.com mailto: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 retainin
g clip refitting over it.
> > >
> > > I can see that the shaft of the brass pin has broken belo
w the surface of the hub so unfortunately there is nothing to grab onto. Ho
wever, I also notice that there are two other similar screw holes in the hu
b 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 replaceme
nt 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 extr
actors but they=99re much too big.
> > >
> > > Also, do you know where I can obtain replacement pins? Yo
u 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 she
ar 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 to
rque 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 cross
head 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 D
avid 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 thin
k this is the small brass screw located just above the main central cross-h
ead screw that holds the control arm onto the servo in the photo I=99
ve attached here? I looked at mine more closely and saw that the head of th
at 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
=99re 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 cr
oss-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 the
re (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 hu
b without the pin there? Question also now is how to get the threaded bit o
ut and the pin replaced?!
> > > >
> > > >
> > > >
> > > > Best regards
> > > >
> > > >
> > > >
> > > > David
> > > >
> > > >
> > > >
> > > > I'd not seen before the clip on the servo arm; ther
e 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 b
y Loctite!).
> > > >
> > > > The control column stops should take priority, as t
he servo stops are probably too light to limit enthusiastic control movemen
ts 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/con
tent/dam/bendixking/en/documents/document-lists/downloads-and-manuals/TruTr
ak-RV10-Roll-Installation-Guide.pdf
> > > >
> > > > The shear pin is merely a 6-32 screw with a short p
art 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 Eur
opa 'tunnel' and connects to a horn bolted to the rear end of the roll torq
ue tube. This area used to get hot under certain situations via heat from t
he stainless firewall and no tunnel ventilation. Subsequently a 'fire blank
et' (two thin layers of woven Kevlar with thin fibreglass loft insulation s
andwiched between, rather like Orkotek) placed on the back of the firewall
enabled cooler temperatures. I've not heard of the standard under-seat serv
o 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 fee
dback.
> > > > >
> > > > >
> > > > >
> > > > > It seems that the Skymap III should work OK f
or us, despite its 0.5Hz data refresh rate. A bit of =98hunting
=99 shouldn=99t really be a problem. We hadn=99t planned to hav
e it fly a full route and navigate itself around turning points. I had thou
ght we=99d be manually changing the selected track at each turning po
int, and then lock the tracking to the new direction required. However, the
Skymap III does have a =98Turn Anticipation=99 feature if we s
hould 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 t
urns?
> > > > >
> > > > >
> > > > >
> > > > > Good to know about the shear pin in the arm a
s a last resort! Do you have any drawing of the necked stainless pin that y
ou got the LAA to agree to?
> > > > >
> > > > >
> > > > >
> > > > > The servo that I have came out of an old Euro
pa 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 scr
ew 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 a
nother 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 s
hould look like or be made of? Should they be set so that the servo arm tou
ches them at the same time as the control column reaches its full deflectio
n (if not, then which stop should =98take priority=99 and be hi
t first)? Does anyone have a photo of what the stops look like in their set
up? I imagine them being mounted on the bolts that attach the servo motor t
o 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 addin
g a little cooling fan to the seat locker to keep the air circulating aroun
d the servo?
> > > > >
> > > > >
> > > > >
> > > > > Many thanks for all the input!
> > > > >
> > > > > David
> > > > >
> > > > > i). The Trutrak will work on a Europa at 0.5H
z update frequency (i.e. every 2 seconds). Sometimes the AP will hunt gentl
y (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). I
f too many options of output data are requested in the GPS NMEA output setu
p then there won't be enough time to output all that data within a faster u
pdate period; the GPS set will normally tell you if this is going to be the
case.
> > > > >
> > > > > iii). The servo does not care about torque fe
edback. The servo will provide a force (torque) only up to the maximum valu
e that has been preselected.
> > > > >
> > > > > iv). The Europa needs quite a high torque set
ting (10 or 12 from memory, which can on hot days plus a high 'activity' se
tting result in servo overheating and shutdown if you have a trigear with '
heated'/unventilated fuselage tunnel and depending where the servo is mount
ed).
> > > > >
> > > > > The pilot stick force required to overcome ma
ximum 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 instru
ment mounting screw) in the servo arm that can be easily sheared (even with
out 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 pr
ovide a little more strength and haven't sheared it since.
> > > > >
> > > > > I also think that when the servo gets very ho
t (as above) it's internal voltage regulator starts to shut down (as many a
re designed to do). Again, there is no way of knowing when this happens unt
il 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 wou
ld be better adjusted so that the stops never have to resist the pilot's st
ick inputs.
> > > > >
> > > > > Otherwise, the Trutrak system and its dynamic
s work extremely well and can do a much better job than the pilot, especial
ly in turbulent conditions.
> > > > >
> > > > > Have you found a setting on your Skymap that
allows adjustment of the pre-emptive steering sensitivity (or "turn anticip
ation")?
> > > > >
> > > > >
> > > > >
> > > > > Duncan McF.
> > > > >
> > > > > > > > > > >
> > > > > > On 03 January 2023 at 13:10 David Cripp
s <dpc@knightonweb.com mailto:dpc@knightonweb.com > wrote:
> > > > > >
> > > > > >
> > > > > > So, I've slowly been making some progre
ss on this, having mocked up the whole system out of the aircraft. I have n
ow been able to test it in the workshop and yesterday in a car (it needed t
o 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 t
rack on the Trutrak, so that's progress! However, I note from the Skymap ma
nual 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 yo
ur 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 to
o 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 o
r less static, and moved in the correct direction when there was a small de
viation between what was set on the Trutrak and what we were tracking. Howe
ver, because our roads are not straight, there were frequently occasions wh
en the actual track from the Skymap was miles away from that set on the Tru
trak. In that situation the servo went a bit crazy and rotated its arm by m
any 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 th
at it had expected, that it just moves the servo even further in order to t
ry to get aircraft to do something?
> > > > > >
> > > > > > iii) Clearly my mock-up does not provid
e any sort of 'force feedback' to the servo control arm (ie the arm is comp
letely free to rotate as it likes). In an aircraft, would this be taken car
e of by aerodynamic feedback via the aileron torque tube? What happens to t
he servo when it reaches the full movement that the aileron would allow (th
e 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 fo
r a very violent manoeuvre! I see that there are settings that can be adjus
ted in the Trutrak set-up menus that control activity level and also contro
l 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 impossib
le to override the servo arm when the A/P is engaged (though I appreciate t
hat with no control column attached the leverage I can apply to the servo a
rm with my fingers is very low. I also appreciate that normally if one want
ed 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 t
hat the servo can never try to move the pushrod beyond the point where full
aileron is applied?
> > > > > >
> > > > > > Apologies for all the questions but I w
ant 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" <o
wner-europa-list-server@matronics.com mailto:owner-europa-list-server@matro
nics.com <mailto:owner-europa-list-server@matronics.com mailto:owner-europ
a-list-server@matronics.com > on behalf of alanb@dpy01.co.uk mailto:alanb@d
py01.co.uk <mailto:alanb@dpy01.co.uk mailto:alanb@dpy01.co.uk >> wrote:
> > > > > >
> > > > > >
Burrill <alanb@dpy01.co.uk mailto:alanb@dpy01.co.uk <mailto:alanb@dpy01.c
o.uk mailto:alanb@dpy01.co.uk >>
> > > > > >
> > > > > >
> > > > > > Ok I=99ve had a. Ha ce to fly min
e 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 w
hen you switch it on.
> > > > > >
> > > > > >
> > > > > > The are no heading digits on the displa
y 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 eithe
r 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 ha
ve the -|=94|- on the display.
> > > > > >
> > > > > >
> > > > > > Useful if you have a GPS failure but wo
uldn=99t want that as normal mode of operation so my suggestion is yo
u need a GPS feed with the right NEMA message set to get the most out of th
e AP and the ability for it to follow a track you have programmed in is a b
onus.
> > > > > >
> > > > > >
> > > > > > One word of caution, I have come across
some GPS that don=99t put out any messages, even the position messag
e for driving a Transponder ADS-B output, unless there is a track in the GP
S. That was how some of the older version worked, GARMIN 430 and possible t
he early AVMAP were guilty of that.
> > > > > >
> > > > > >
> > > > > > Hope that helps.
> > > > > >
> > > > > >
> > > > > > Alan
> > > > > >
> > > > > >
> > > > > > Sent from my iPad
> > > > > >
> > > > > > > > > > > > >
> > > > > > > On 10 Nov 2022, at 10:52, D McFad
yean <ami-mcfadyean@talktalk.net mailto:ami-mcfadyean@talktalk.net <mailto
:ami-mcfadyean@talktalk.net mailto:ami-mcfadyean@talktalk.net >> wrote:
> > > > > > >
> > > > > > > --> Europa-List message posted by
: D McFadyean <ami-mcfadyean@talktalk.net mailto:ami-mcfadyean@talktalk.net
<mailto:ami-mcfadyean@talktalk.net mailto:ami-mcfadyean@talktalk.net >>
> > > > > > >
> > > > > > > Digitrak only needs basic positio
nal information from the GPS on a regular basis. It will use this informati
on to fly the track that has been set on the Digitrak.
> > > > > > > If a route is programmed in to th
e GPS, it will fly that too (with different commands being set at the Digit
rak control head to enable this), so long as the GPS is also putting out th
e crosstrack error signal; not all of them do.
> > > > > > >
> > > > > > > Duncan McF.
> > > > > > >
> > > > > > > > > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > http://s.com/Navigator?Europa-List
> > > > > >
> > > > > > >
> > > > > > ion>
> > > > > >
> > > > > > > > > > >
> > > > > > > > >
> > > > > > >
> > > > >
> > | Rowland Carson ... that's Rowland with a 'w' ...
> > | <rowlandcarson@gmail.com mailto:rowlandcarson@gmail.com >
http://www.rowlandcarson.org.uk
> > | Skype, Twitter: rowland_carson Facebook: Rowland Carson
> >
> >
> > >
|