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Anyone experienced trim runaway?

 
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Richard Lamprey



Joined: 15 Jul 2011
Posts: 93
Location: Kenya

PostPosted: Sun Apr 07, 2019 11:24 pm    Post subject: Anyone experienced trim runaway? Reply with quote

Having taken the Ethiopian Airlines flight from Addis to Nairobi recently, the recent B737 tragedy made me think about aircraft systems turning rogue… If there’s an electric trim runaway on the Europa (either nose up, nose down), is there enough pitch movement in the column at normal C of G to contain it? Has anyone had such experience? I seem to remember someone talking about it some years ago, but can’t find it in the thread.
Richard
Europa Classic 912UL, 5Y-LRY


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JonathanMilbank



Joined: 14 Apr 2012
Posts: 272
Location: Aberdeen area

PostPosted: Mon Apr 08, 2019 12:30 am    Post subject: Re: Anyone experienced trim runaway? Reply with quote

The possibility of pitch trim runaway crossed my mind in 1996, while I was planning where to place everything on my panel. So when it came to deciding which circuit breakers would get priority in the central panel section above the tunnel, the pitch trim was given the first left spot in the upper row. This made it nearest my hand and easiest to see, directly above the pitch trim indicator.

I've not yet done the experiment in various flight stages, of deliberately running the trim towards full nose up or down to find out how that feels. Perhaps I should.


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brian.davies44(at)gmail.c
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PostPosted: Mon Apr 08, 2019 12:53 am    Post subject: Anyone experienced trim runaway? Reply with quote

The LAA acceptance initial test flight requires an examination of the effect of an electric trim runaway in both directions and at various aircraft speeds in order to confirm that the aircraft remains controllable after leaving the trim in a simulated runaway for 4 seconds before taking any action, which would be to trip the CB to isolate the system. I have not tried to simulate a runaway that takes the trim to the full extent of its travel.
Regards

Brian

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ptag.dev(at)talktalk.net
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PostPosted: Mon Apr 08, 2019 1:16 am    Post subject: Anyone experienced trim runaway? Reply with quote

Hi! Richard /all.
I had at least two situations which were in comparison and the indications of the recent enquiries caught my attention.
The nature of my problems were such that a fault appeared in the trim unit such that at indeterminate positions the trim wouldn't reverse. It took quite some courage to allow the trip to extend to its full travel to get a reverse to occur and the control stick forces were phenomenal at the extreme travel position and very scary .
The last time it occurred my brother was with me and we shared the control stick loads until the full normal control was recovered.
I ordered a replacement trim deck and the suppliers were alleging that my wiring of the panel along with duplication of the trim control at the panel and the control stick were the cause.
I noticed that the replacement unit they sent was a) a different shape b) was described as MARK II Serial number?
On discussion with them they acknowledged that they has found a fault with the original unit so that on reaching "full trim position" the fault was eliminated ....until the next time so that further testing wouldn't allow the fault to be identified!
I replaced the unit and have had no further issues except I don't use the trim control on the panel anymore and only use the flap control on the panel and not on the stick.
Hope this helps with your thoughts ?Perhaps the LAA should have been involved in the outcome so I have copied Malcolm McBride into this message.
Regards
Bob Harrison G-PTAG.

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m.j.gregory(at)talk21.com
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PostPosted: Mon Apr 08, 2019 3:05 am    Post subject: Anyone experienced trim runaway? Reply with quote

Richard,

Further to Brian's advice, the Europa electrical system design included a separate circuit with a switch and fuse or CB to feed the trim. Ivan Shaw insisted that the pilot should still be able to operate the trim even if the master switch was off, e.g. because of smoke in the cockpit, so that it would be possible to conduct a forced landing without the distraction of an out-of-trim force.

Of course, where you site the switch so that you could turn the trim off quickly in the event of a runaway is a matter of cockpit layout.

Although heavy, I believe the forces on the Europa control column as a result of a full trim runaway are not so large that the average pilot could not cope, but there may well be airspeed or flight situations where such a runaway would cause difficulties.

When there were in-service problems with trim runaway on the Hawker Hunter, which had an all moving tail that could definitely provide forces beyond the control of the pilot, the ability of a stray positive to cause an commanded trim movement was virtually eliminated by "back-contact earthing". This involved grounding the contacts of the trim control when movement was not required. This is probably not justified for a Europa, where it is less likely that a stray positive would cause a runaway that was uncontrollable.

It is important to understand the actual circuit installed on your aircraft, which may of course differ from the basic Europa diagram. Some people have switches on one or both control columns, possibly operating a relay. The greater the complexity, the more chance there is of a contact getting stuck on or failing to operate.

I am sure others will respond with advice as to their experience of exercising the trim at a safe height, airspeed and location (e.g. over the home airfield) and saying whether this was reassuring or worrying.

Best regards,

Mike
Dr Mike Gregory
Europa Club safety officer
01480 451655
07885 355765

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clivesutton



Joined: 23 Jan 2013
Posts: 143
Location: KENILWORTH

PostPosted: Mon Apr 08, 2019 11:19 pm    Post subject: Re: Anyone experienced trim runaway? Reply with quote

I've not experienced runaway but i did experience a failed switch during the initial permit flight testing - with Andy Draper on board. I think it stopped responding to trim switch inputs just after the full trim up tests that Brian mentions. Anyway, although the a/c was almost at MTOW 1370lbs, it was quite controllable by using a fair amount of forward stick force and reducing the speed to just above Vfe to make the 10min flight back to base from the test area. At no time did i feel unsafe. Mine is wired though the master SW - perhaps this SW should be wired direct to the battery/be live all the time - for the dead-stick situation that Mike G mentions?

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BobD



Joined: 05 Jan 2016
Posts: 67
Location: Sheffield UK

PostPosted: Tue Apr 09, 2019 12:34 am    Post subject: Re: Anyone experienced trim runaway? Reply with quote

When I was planning my Panel, I removed and replaced the trim switch a couple of times, and this involved removing and replacing the self adhesive surround to get at the screws. After one such removal, and on testing on the ground, I experienced trim runaway due to the sensitive switch catching slightly on the snug fit surround. I replaced the surround with home made labels, just on the top and bottom of the switch to remove the potential problem.

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Europa XS TG || 912 ULS || G-NHRJ || Dynon Skyview || PilotAware || SmartAss3
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Remi Guerner



Joined: 14 Dec 2010
Posts: 254

PostPosted: Tue Apr 09, 2019 1:22 am    Post subject: Re: Anyone experienced trim runaway? Reply with quote

I was concerned about a trim runaway and made some testing about ten years ago. From my notes, this is what I found:
1. At cruising speed, trimming full nose up and trying to stay level requires an extreme force and it was nearly impossible to avoid climbing. After reducing power and speed to 70kts, the push force becomes manageable but is still high. I thing a landing in this configuration would be possible but difficult (I did not try!). Turning helps reducing the push force
2. At cruising speed, trimming full nose down and trying to stay level requires a good pull force but it is manageable. At lower speed the push force becomes quite small and landing would be easy.

Of course those findings are for my own aircraft and could be slightly different for others. The results would also be affected by weight and balance.
I also have both roll and yaw electric trims but a runaway of those trims is a non issue as the generated stick forces are very small.

Remi Guerner


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kingsnjan(at)westnet.com.
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PostPosted: Tue Apr 09, 2019 1:52 am    Post subject: Anyone experienced trim runaway? Reply with quote

A few years ago, just after take-off from an airport a long way from
home, I experienced a trim runaway as I was trimming forward.   I can
assure you it quickly got my attention as the control force was
uncomfortably heavy.  After toggling the trim switch quickly in both
directions, normal trim function thankfully resumed.

The aircraft has trim switches on both sticks and has a relay in the
circuit.  It was the relay that stuck and after replacing it with the
later heavier duty relay supplied by Ray Allen, no further problems were
experienced.

This incident dictated I put a trim on/off switch next to the trim
indicator on the panel.

Cheers
Kingsley in Oz


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ptag.dev(at)talktalk.net
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PostPosted: Tue Apr 09, 2019 3:34 am    Post subject: Anyone experienced trim runaway? Reply with quote

Hi! Kingsley.

Fine to add a switch if it isolated the trim circuit except the original Europa electrical circuit stipulation was for it to be wired direct to power supply and by pass the isolating switch for the remaining circuit.
My experience involved the Ray Allen relay decks and it was them who discovered the fault in the original relay deck, so resulting in the update to the Mark II type
The loads developed on the control with maximum trim position is phenomenal and would be impossible to land the aircraft with one control stick . the resulting loads on the controls linkages are frightening .
Regards
Bob Harrison G-PTAG
Original Message-----
From: owner-europa-list-server(at)matronics.com [mailto:owner-europa-list-server(at)matronics.com] On Behalf Of Kingsley Hurst
Sent: 09 April 2019 10:52
To: europa-list(at)matronics.com
Subject: Re: Anyone experienced trim runaway?



A few years ago, just after take-off from an airport a long way from
home, I experienced a trim runaway as I was trimming forward. I can
assure you it quickly got my attention as the control force was
uncomfortably heavy. After toggling the trim switch quickly in both
directions, normal trim function thankfully resumed.

The aircraft has trim switches on both sticks and has a relay in the
circuit. It was the relay that stuck and after replacing it with the
later heavier duty relay supplied by Ray Allen, no further problems were
experienced.

This incident dictated I put a trim on/off switch next to the trim
indicator on the panel.

Cheers
Kingsley in Oz


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brian.davies(at)clara.co.
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PostPosted: Tue Apr 09, 2019 4:58 am    Post subject: Anyone experienced trim runaway? Reply with quote

Bob,

Although Europa recommend the Trim power supply comes directly off the battery their circuit diagram clearly shows an isolating switch in the circuit. Personally I would regard this as a mandatory requirement to cover the trim runaway situation. It can be provided by a pull to break circuit breaker, again as stated in the build manual.

Regards

Brian

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wdaniell.longport(at)gmai
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PostPosted: Tue Apr 09, 2019 6:29 am    Post subject: Anyone experienced trim runaway? Reply with quote

The dynon AP panel that I have (I am still trying to figure out how to use the advanced AP functions) is connected to the trim because it has an auto trim function.   The AP panel cuts off the trim power after about 3-4 seconds of continuous use.  You have to press the switch again if you want to continue moving the trim tab.  
William Daniell

LONGPORT
+57 310 295 0744
On Tue, Apr 9, 2019 at 9:01 AM Brian Davies <brian.davies(at)clara.co.uk (brian.davies(at)clara.co.uk)> wrote:

[quote]--> Europa-List message posted by: "Brian Davies" <brian.davies(at)clara.co.uk (brian.davies(at)clara.co.uk)>

Bob,

Although Europa recommend the Trim power supply comes directly off the battery their circuit diagram clearly shows an isolating switch in the circuit. Personally I would regard this as a mandatory requirement to cover the trim runaway situation. It can be provided by a pull to break circuit breaker, again as stated in the build manual.

Regards

Brian

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Richard Lamprey



Joined: 15 Jul 2011
Posts: 93
Location: Kenya

PostPosted: Wed Apr 10, 2019 4:19 am    Post subject: Re: Anyone experienced trim runaway? Reply with quote

Thanks everyone for the answers. Trim runaway seems to be rather alarming. It seems that a quick CB cut off is needed close to hand. I followed the original Classic panel/ circuit diagram and put the CB in the inset step at the bottom of the panel, but it looks rather like all the others so a more visible placard might be useful..
Thanks again
Best
Richard
Classic Monowheel 5Y-LRY, Kenya


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rowlandcarson(at)gmail.co
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PostPosted: Wed Apr 10, 2019 5:07 am    Post subject: Anyone experienced trim runaway? Reply with quote

On 2019-04-10, at 13:19, Richard Lamprey <lamprey.richard(at)gmail.com (lamprey.richard(at)gmail.com)> wrote:
Quote:
Trim runaway seems to be rather alarming. It seems that a quick CB cut off is needed close to hand


Richard - I agree! Here’s the bottom corner of my “radio” panel showing the guarded isolator switch close to the trim switch & display.

in friendship

Rowland

| Rowland Carson ... that's Rowland with a 'w' ...| <rowlandcarson(at)gmail.com (rowlandcarson(at)gmail.com)> http://www.rowlandcarson.org.uk| Skype, Twitter: rowland_carson Facebook: Rowland Carson
[img]cid:54C13A8D-5004-4BE2-AFFE-01BE7EF34323(at)home[/img]


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danny shepherd



Joined: 27 Jan 2006
Posts: 116
Location: north Wales, United Kingdom

PostPosted: Wed Apr 10, 2019 8:03 am    Post subject: Anyone experienced trim runaway? Reply with quote

Paint the CB orange, that's what I did after my test pilot in 2009 trimmed the servo the wrong way. He just managed to do a very hard landing Sad.

Danny G.c.e.r.i SX TRI
On 10/04/2019 13:19, Richard Lamprey wrote:

Quote:
Quote:
--> Europa-List message posted by: "Richard Lamprey" <lamprey.richard(at)gmail.com> (lamprey.richard(at)gmail.com)

Thanks everyone for the answers. Trim runaway seems to be rather alarming. It seems that a quick CB cut off is needed close to hand. I followed the original Classic panel/ circuit diagram and put the CB in the inset step at the bottom of the panel, but it looks rather like all the others so a more visible placard might be useful..
Thanks again
Best
Richard
Classic Monowheel 5Y-LRY, Kenya


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jglazener



Joined: 14 Apr 2010
Posts: 65
Location: Schoonhoven, Netherlands

PostPosted: Mon Apr 15, 2019 4:07 am    Post subject: Re: Anyone experienced trim runaway? Reply with quote

As you may be aware there was a fatal crash involving PH-BGV last december. Investigations are still ongoing, but it is known that the tailwheel dug into the grass on take-off, leading to a stall. Some form of runaway trim is certainly a suspect.

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