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erik(at)erikdahlbeck.com
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 Posted: Sun Oct 04, 2020 1:19 pm Post subject: Stabilator play |
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Hello again,
Me and our local mechanic are still working on getting SE-XRX airworthy.
During the process, I've spent some time reading up on modifications and
service bulletins. After reading about the mod 73 and SB-15 issues I
went to the hangar and found that the port side stabilator sure could be
moved a little bit after the counterweight hit its stop. The starboard
one is solid though.
I put a short video of it on Youtube:
https://youtu.be/_LzkvIJ9T5o
The video shows the stabilator being held so that the couterweight is
against the stop and then moving slightly when more force is applied.
When measured using a metal measuring tape from the floor up to the
trailing edge of the stabilator, the movement is somewhere around 6-8
mm, which is at least less than the 0.5 inch limit set forth by the PFA
FSB006. Still a bit worrying though.
SB-15 (the application of loctite) is supposed to have been done
according to the builder and it also looks like there is loctite along
the edges of the parts that should have it. Please see the attached
photo taken through an inspection port, showing the stabilator drive
train assembly. At least I suspect that the green-ish stuff around the
edge of the TP 12 drive plate cylinder, sticking out of the TP 10
bushing, as well as what (from this angle) is visible on the left side
of the control horn tube, should be the loctite.
Also, what puzzles us is that we cannot actually see anything moving
when looking through the inspection port when the stabilator is moved,
as in the video. We even taped a marker pen onto a stick to let us draw,
well, not a straight line, but at least some marks for visual reference
on the parts (to the right in the image, which was taken before the
drawing). Still, when externally looking down between the fuselage and
the stabilator, onto what should be the TP 12 drive plate cylinder (if
I've understood the design correctly), it looks like that "axis" is
moving along with the stabilator. So we kind of fail to understand where
this movement is happening. Weird...?
Any thought on this would be greatly appreciated.
/ Erik
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peterz(at)zutrasoft.com
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| Posted: Sun Oct 04, 2020 3:45 pm Post subject: Stabilator play |
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Looks like the pins have been replaced by bolts? Likely in a vain attempt to remove play (not the way to do it)?
Pete
C-gnpz
| Quote: | On Oct 4, 2020, at 5:33 PM, Erik Dahlbäck <erik(at)erikdahlbeck.com> wrote:
Hello again,
Me and our local mechanic are still working on getting SE-XRX airworthy.
During the process, I've spent some time reading up on modifications and service bulletins. After reading about the mod 73 and SB-15 issues I went to the hangar and found that the port side stabilator sure could be moved a little bit after the counterweight hit its stop. The starboard one is solid though.
I put a short video of it on Youtube:
https://youtu.be/_LzkvIJ9T5o
The video shows the stabilator being held so that the couterweight is against the stop and then moving slightly when more force is applied.
When measured using a metal measuring tape from the floor up to the trailing edge of the stabilator, the movement is somewhere around 6-8 mm, which is at least less than the 0.5 inch limit set forth by the PFA FSB006. Still a bit worrying though.
SB-15 (the application of loctite) is supposed to have been done according to the builder and it also looks like there is loctite along the edges of the parts that should have it. Please see the attached photo taken through an inspection port, showing the stabilator drive train assembly. At least I suspect that the green-ish stuff around the edge of the TP 12 drive plate cylinder, sticking out of the TP 10 bushing, as well as what (from this angle) is visible on the left side of the control horn tube, should be the loctite.
Also, what puzzles us is that we cannot actually see anything moving when looking through the inspection port when the stabilator is moved, as in the video. We even taped a marker pen onto a stick to let us draw, well, not a straight line, but at least some marks for visual reference on the parts (to the right in the image, which was taken before the drawing). Still, when externally looking down between the fuselage and the stabilator, onto what should be the TP 12 drive plate cylinder (if I've understood the design correctly), it looks like that "axis" is moving along with the stabilator. So we kind of fail to understand where this movement is happening. Weird...?
Any thought on this would be greatly appreciated.
/ Erik
<DSC_1743.jpg>
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budyerly@msn.com
Joined: 05 Oct 2019
Posts: 286
Location: Florida USA
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| Posted: Sun Oct 04, 2020 5:50 pm Post subject: Re: Stabilator play |
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Pete,
Please do not allow any play between the two stabilators.
I personally remove my torque tube and machine replacement zero clearance pins that require freezing in dry ice and insertion when in place. They fit very tight, but require machining, exact measurement, and a generous access hole to work in. But it has held for 14 years.
Because you are most likely in Europe (SE-xxx) simply go on the Europa Club website and have your mechanic look to the method he prefers for stabilator pin replacement. This site is a wealth of information and as an owner operator as well as maintainer, this is an excellent place to start to fix the woes of the aging aircraft, speed construction, and allow you to create a truly custom aircraft you can have confidence in.
I personally like 11969 alternate modification. Even when confronted with the small access hole, it is possible to do. I built a similar fix in the US and found the method was acceptable, but I do prefer to do stab work on the bench rather than in the aircraft. Reason is, much measuring and sizing of the hole should be done to allow the bolt to pin as well as clamp.
Fix it right and have a trouble free aircraft.
Best Regards,
Bud Yerly
Custom Flight Creations, Inc.
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JohnFrance
Joined: 17 Sep 2014
Posts: 78
Location: Grenoble France
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| Posted: Mon Oct 05, 2020 2:40 am Post subject: Re: Stabilator play |
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Hi Erik, I am following the evolution of the play in my tailplane and this is what I have observed.
In my case the play is between TP5 and TP4 almost certainly due to play in the clevis pin on the starboard side.
You can check this by marking the junction between TP5/TP4 with a marker pen.
The edge of TP5 is just visible in your photo exiting the nylon bush TP10. The movement will be very small but should be visible. Check both sides and the same thing for the junction TP4/TP9.
The good news is there are several modifications available to fix this, one being to use Loctite between TP4/5/9 and various clamping methods are available too which are fine.
As Pete pointed out however, the bolts in yours (appear to) clamp directly on the Nylon TP10 and that is not good.
If Loctite has already been used but failed to hold on one of the components you will have to find a way to dis-bond the others to remove TP4 from the aircraft to carry out the mod!
I have a theory on that but not yet put it into practice! If anyone has done that please share your experience?
Here is a text written by the late Nigel Graham on the subject.
Firstly, please find attached, the details of the tailplane clamp arrangement I developed (and you requested) ...... it could be relevant to your problem. I have also attached another mod that I developed to prevent the possibility of a dis-bonded TP5 or TP6 bush (these are built into the tailpanes – refer to the online manual for details)
…. and on that note …
There are two possible reasons for slop in the tailplanes, one is benign and relatively easy to fix and the other is a lot more serious and could kill you if not addressed immediately.
First, an overview of the pitch drive train; the pitch pushrod transfers pitch linear motion into the TP9 arm, this rotates the TP4 (torque tube) via the TP14C pins.
The rotating shaft transmits the motion back out to the TP12 drive plates via the TP14D pins and hence to the tailplanes.
The first thing to check is the cumulative play in the TP14 drive pins.
This is a well-documented issue and was addressed by the factory by increasing the diameter of the pins. This was not a good engineering solution as it only delayed the eventual re-occurrence of the problem.
Pat Tunney’s “clamp block” mode (that you commented on), my clamp mod (attached) and squirting Locktite into the gap were all far better solutions designed to solve the problem of relative movement.
You can test if this is your problem by sliding the tailplanes off the torque tube and placing two long lever bars (gently) against each drive plate (TP12) pin and the torque tube and trying to rotate port and starboard in opposite directions. There should be NO movement. If there is, this is your problem. This is non-critical and can be solved by any of the above mentioned solutions.
If you detect no movement here, then the problem lies in the tailplanes – and this IS serious and the A/C should be grounded immediately until repairs are made.
The problem lies in the way the tailplanes were built. The build instructions called for the two supporting stainless steel bushes to be bonded into the soft blue foam of the TP cores. If you read the attached mod document “070625 – Tail-plane drive pin mod” there is a fuller description of the problem and solution.
Very little supports these bushes laterally, and if they should become dis-bonded, the tailplane can slide laterally until, in extreme cases, it disengages from the two drive pins on the TP12 plate. At this point one tailplane will rotate/flutter with ferocious force and the back of the fuselage will most likely break away – the aircraft will break up in flight.
This happened to G-HOFC in 2007, I passed my information on to the LAA and who subsequently issued mandatory Mod 73 (attached).
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JonathanMilbank
Joined: 14 Apr 2012
Posts: 388
Location: Aberdeen area
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| Posted: Mon Oct 05, 2020 6:37 am Post subject: Re: Stabilator play |
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Disbonding of the bushes from the wooden ribs inside the tail planes can have fatal consequences. Potentially it could allow the tail plane to migrate sideways (outboard) along the torque tube until disengaging from the drive pins and the tail plane would whip up and down destructively.
Some builders make the recess around the pip-pin head too large, so that the distance between the inboard side of the pip-pin head and the side wall of the recess is greater than the length of the drive pins. Therefore if the bush through which the pip-pin passes was to disbond (as one of mine did), nothing could stop the tail plane from drifting sideways.
I favour "belt and braces" back-up solutions to such problems and I also like solutions to be simple. So I bonded a little piece of plywood into each pip-pin recess on the inboard side, to fill the gap between the pip-pin head and the inboard sidewall of each recess.
This was done in addition to other modification instructions to beef up the joints in the tail plane torque tube assembly. I have no free play up and down at the trailing edge of either tail plane.
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