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grahamsingleton(at)btinte
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 Posted: Sun Jun 12, 2011 4:54 am Post subject: Landing gear Failure, ATTN Bud Yerly |
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Hi Graham
First I think we need to absolute clarify what you mean by O/C. My interpretation is Over Center. In other words if you load the main tire, it will load the swingarm which will load LG08, and if Over Center, LG08 will try and move forward, in other words towards the prop. It will be jamming into the undercarriage mounting frame, the more you load it, the harder it will push into the undercarriage mounting frame.
Yes, that's what I was trying to say.
In Jeffs case I think he was under center and the loading caused the lever to bend. There is a good chance he has an ill fabricated undercarriage mounting frame that did not allow over center, but caused an under center situation.
I think you are probably right that Jeff's frame was inaccurate and the LG08 could have been under centre.
So, do you mean O/C is Over center,
Yes
Thus you want 1/16" in my term Over center where when you push up on swingarm LG08 is loaded and pushes forward. You want LG12 held by the down indent where LG08 is held forward against the undercarriage mounting frame stop where there is little to no slop that would allow LG08 to go under center (in others allow LG08 to swing aft towards the tail).
And LG12 will try and swing aft too. The nearer to dead centre the LG08 is the less load on the stops on the frame and the less load on the LG12 too. Also the less effect G loading will have on the position of the LG08.
When LG08 and the shock absorber assembly pivots are all in line there is no force trying to move them, they are in pure compression.
Bud, do you have an opinion on this? I hope I'm not confusing the issue?
Graham
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budyerly(at)msn.com
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| Posted: Sun Jun 12, 2011 12:18 pm Post subject: Landing gear Failure, ATTN Bud Yerly |
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DIV { MARGIN: 0px } <?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> [img]cid:007101cc293d$687f7870(at)adminPC[/img][img]cid:007201cc293d$68843360(at)adminPC[/img] Photo E-mail [url=http://photos.msn.com/Viewing/Album.aspx?PST=8nK2AN1B!1LEiKSdooxx9v4CFFiF2tnPzfqiCRx5lZJ3t2ol6z9!Q9u31z2Gf34UKChg6aSaSkGODYJ1SdylXQ%24%24]Play slideshow[/url] | [url=http://photos.msn.com/viewing/Photos.aspx?pi_Type=SlideshowTask&Task=Download&stppData=&pi_ImagesOnly=1&Folder=nBuRgwTGIGjZPMtNhxCyPhYLUBR*bYP2J4rmv14KfYE%24&User=23IQaj7Z2BRqNO1wUECSpX*P0Ju9hSGI&pi_NoLogin=1]Download images [/url] Graham and others,
I see my first email did not get sent complete with photo's and discussion.
Also, I did not include on the net the answer to Jeff.
First, I will reprint my answer to Jeff on his probable cause.
Second, I will include the design and installation considerations on the mono hopefully addressing the over center on down design:
Answer to Jeff:
Jeff,
Nobody hurt, hopefully the engine has a clutch in the gearbox, so it shouldn't be harmed, the prop can be replaced.
The rest is cosmetic.
Now for the gear.
It is clear from the photo's that the gear handle was in the down and locked position.
It is also clear that the swing arm came aft with the gear handle in the lock position and since there is not an over center lock for aft movement (the only stop for the gear is for the LG 08 to contact the gear frame stops with the gear handle locked down), then the arm was fatigued until failure. Yes, it can fail (normally from twisting) just from sitting with the gear down on the ground and the swing arm now unsupported by the vertical LG 08. Here is a more complete discussion:
If during the build of the mono, the landing gear retraction arm LG 08 was not positioned hard against the frame stops the gear will collapse. When the LG 08 is against the stop, the entire retraction arm is slightly (and it is only slightly) forward of vertical with the shock block hinge points of LG 04 and LG 05 and against the gear frame stops when the handle is in the handle slot in the locked position. If the gear frame stops are not the right length, keeping the gear aft of vertical, movement can occur with disastrous results. However, if the stops leave the LG 08s too far forward, it has been surmised that the gear in a bounce can actually spring the other way (aft) when the airplane bounces up (extension) and then will collapse (especially if the handle is loose, or the slot for the lock is sloppy fore and aft or bushings are worn out in the system) if the gear goes over center (aft) on the the return impact. Note that in Chapter 28M page 2 the handle position in the locked position is set by fixing the LG 08s (even before attaching the rest of the gear) pushed up hard against the gear frame stop and then setting the handle into position in the lock spot. Many hours were spent by the builders and the factory to warn that the gear arms LG08 must be located against the stops to preclude the gear from collapsing and from inadvertent retraction during rough field operations.
It is interesting but necessary that the gear handle is set in the section where we set the flaps to the full down position, and the manual does amplify the results of the discussion but does not include warnings in the next chapter when setting the gear and checking the alignment of the gear LG 08 and the bock pivots below. I thought we made sure in Annex E that the LG 08s were checked prior to initial flight testing. I may need to readdress that.
I see by the damage that the gear collapsed by folding aft after the gear handle finally gave up as is was the only thing that held the gear from collapsing.
I have one mono in the shop, and will see if I can provide pictures. I fear that somewhere in the build or perhaps a defect in manufacture of your gear frame may have put the gear arms slightly aft of vertical or with the LG 08s not quite touching the stops. In the mono's I have inspected, I see more often the three bolts on the gear retraction handle are worn or miss-drilled allowing the gear to move. I have seen only one gear collapse and that was due to an off field landing. The plane was not built particularly well and the problems were very easy to fix. The collapse was because even with the gear handle retract lever in the lock position, you could move the gear LG08 arms fore and aft due to a poorly installed gear handle. The gear frame was bent in the collapse so a new gear frame was installed, and the gear reinstalled uneventfully.
Now for the analysis of the installation and techniques with photo's not included in my first email:
Chapter 21M gives clear instruction on the LG 09 and bushing installation. The stops are called appropriately the over center stops.
These stops allow a slightly over center position of the gear LG08 and shock block assembly. Again, this is only just over center.
Chapter 28M clearly indicates that for setting the flap in the down position that LG 08 must be positioned hard against the stops built into the landing gear frame. From the initial set of the flap, the builder is instructed in how to install the gear handle. Note that the lower gear swing arm is not set on the aircraft at this time.
Chapter 29M explains the install of the rest of the gear frame. No other comments to my knowledge are made about the gear geometry.
Annex E (Mono) indicates that the LG 08 arms are to be affixed against their stops prior to clearance for flight.
The gear handle is not the mechanism to hold the gear in the down position. In fact, the gear handle has the following jobs to do in its design: - The handle is the lock for the over center condition of the gear when extended (arms LG08 and rubber block lower shocks bent slightly forward as LG 08 contacts the frame stops). As the instruction manual indicates the LG 12 safety lock prevents inadvertent gear retraction. Please note that technically, you can, while sitting on the ground, retract the LG 12 safety lock and pull the gear handle out of the slot and as long as you don't put ANY forward pressure on the handle, the gear should not retract. I haven't tried this.
- The handle is the retraction mechanism, but is assisted by the bungees in the actual retraction of the gear.
- The handle is the up lock mechanism only! The bungee geometry really helps hold the gear up, but the handle does the job. So that diagonal gear handle brace is necessary for both up and down, because those three bolts that attach the gear handle to the LG08 are going to wear those holes out eventually.
[url=http://photos.msn.com/Viewing/Album.aspx?PST=8nK2AN1B!1LEiKSdooxx9v4CFFiF2tnPzfqiCRx5lZJ3t2ol6z9!Q9u31z2Gf34UKChg6aSaSkGODYJ1SdylXQ%24%24][img]cid:007301cc293d$6886a460(at)adminPC[/img][/url]
Note that the wire line shows the center pivot at the pin through the lower LG08 arm is just forward of vertical. Typically just about 1mm when everything is bench fitted.
[url=http://photos.msn.com/Viewing/Album.aspx?PST=8nK2AN1B!1LEiKSdooxx9v4CFFiF2tnPzfqiCRx5lZJ3t2ol6z9!Q9u31z2Gf34UKChg6aSaSkE!zuM!0*scuA%24%24][img]cid:007401cc293d$6886a460(at)adminPC[/img][/url]
I rigged this arm without bearings in the LG09 to show what a stop that was too long would look like. Note that if the main swing arm was put under pressure the gear would collapse.
In the the past some discussions were made that the gear leg stops on the frame were too long (as shown in the photo above) and the gear mechanism was not vertical. In this case the stops needed to be ground down.
As with all installations, some fit and check operations should be done. I know of a couple of gear frames that were incorrect in pre 2004 sales, but Roger worked out these issues and the welding subcontractor has a superb jig to keep this from happening, but mistakes can happen.
Problems I have seen: - If the gear frame is inserted into the aircraft as per the manual before thinking about the gear and trial fitting the gear parts first to check geometry, then very inconvenient checks must be made with your head in the wheel well to ensure the gear geometry is correct. It is not hard to do, but requires some dexterity.
- It is a main quality control point to make sure the gear stops are installed and spaced correctly at the factory. However, I trust no component completely and inspect components myself when setting the flap, gear handle and gear lock mechanism. I trial fit the retract mechanism after installation of the LG 08 / 09 in chapter 21 and prior to gluing it in. It allows me to ensure the under aircraft work is minimized.
- Next I make sure that during gear installation (Chapter 29M) the gear handle and swing arm geometry assures that the LG 08 and shock arm assembly is just forward of vertical on both arms a slight amount (1mm at the joint). To do this I insert a #20 wire or similar through the LG 08/09 and pull it down to the center of the main swing arm 1/4 inch pin LG 04. Simply look up and check the MS 20392-5 pin is slightly forward of vertical. Finally, check that the gear handle is secure in holding the LG08 affixed to the stop, and you are good to go.
- Finally, since the LG 08s are fixed together by us amatuers, one arm may be lazy about hitting the stop, especially if the flap is dragging or the rubber block shock mount is loose or worn or was installed twisted slightly (really hard since it is a welded structure but it probably could). So be really anal about this installation getting the arms straight and the pins installed well.
Most of us are relieved and gratified when we put the gear handle down, a distinct snap to the down position is made during retraction/extension tests. The bungee amplifies the sound of the slight over center and normally you cannot even get a feeler gauge between the LG08 and stop when extended. Further, in a well built gear system, the gear handle drops itself into the lock slot and the safety catch drops in on its own. That is the test of the gear down lock, when the gear handle is taken from the up lock position, and it drops itself and slams firmly into the lock position.
Finally, if the gear over center locks are filed so they are grossly over center, this is a major problem. If too far forward, the gear handle geometry is going to be off. The gear handle will work against the bungee to spring the gear from its over center then up and the motion of the gear handle travel will be longer than normal. It also will allow the rubber block and shock when compressed and released to act as a spring and pull so hard on the LG 08 that if the gear handle has any sloppiness in it, then it is possible, if the frequency of the gear shock/block and the landing surface were just right, the LG08 may be snapped from its contact with the uplock back to vertical, or worse yet, rebound to slightly over center aft to the unlock side and become unlocked. This condition is seen as an unintentional gear retraction with bent handle as in Jeff's excellent pictures.
I believe someone has built a latch that firmly holds the LG 08s to the stops, but this is quite a bit of more Rube Goldberg work. The existing gear has gone hundreds of hours and landings without failure when installed correctly and without any manufacturing defects.
Don't ask me about outriggers, I follow the instructions in the book, and I have never installed the new bushing mods in my shop, in fact Jim Butcher showed me on his plane. It takes me a couple tries to get one right. And it is a comedy routine to watch me try to reassemble one after disassembly after paint if the lock blocks were not marked with the orientation. My hat is off to you guys that get it right the first time.
Hope this does not add to the confusion.
Regards,
Bud
[quote] ---
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rparigoris
Joined: 24 Nov 2009
Posts: 796
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| Posted: Sun Jun 12, 2011 12:51 pm Post subject: Re: Landing gear Failure, ATTN Bud Yerly |
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Hi Bud
Thx. for pictures and explanations.
Just to make sure everyone knows that under center is a bad thing, your second picture clearly shows that the LG08 is under center which is exactly what you don't want. The first picture looks OK.
Instead of using a string, I turned a pin that fits into the large shaft of LG08 and has a portion turned the same diameter as the other two pins. Now in situation can check with a straight edge
Ron Parigoris
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grahamsingleton(at)btinte
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| Posted: Sun Jun 12, 2011 2:26 pm Post subject: Landing gear Failure, ATTN Bud Yerly |
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Thanks Bud 
Graham
From: Bud Yerly <budyerly(at)msn.com>
To: europa-list(at)matronics.com
Sent: Sunday, 12 June, 2011 21:14:56
Subject: Re: Re: Landing gear Failure, ATTN Bud Yerly
DIV { MARGIN:0px;} [img]cid:1.4204664819(at)web87112.mail.ird.yahoo.com[/img][img]cid:2.4204664819(at)web87112.mail.ird.yahoo.com[/img] Photo E-mail
Play slideshow | [url=http://photos.msn.com/viewing/Photos.aspx?pi_Type=SlideshowTask&Task=Download&stppData=&pi_ImagesOnly=1&Folder=nBuRgwTGIGjZPMtNhxCyPhYLUBR*bYP2J4rmv14KfYE%24&User=23IQaj7Z2BRqNO1wUECSpX*P0Ju9hSGI&pi_NoLogin=1]Download images [/url] Graham and others,
I see my first email did not get sent complete with photo's and discussion.
Also, I did not include on the net the answer to Jeff.
First, I will reprint my answer to Jeff on his probable cause.
Second, I will include the design and installation considerations on the mono hopefully addressing the over center on down design:
| | - The Matronics Europa-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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budyerly(at)msn.com
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| Posted: Sun Jun 12, 2011 3:35 pm Post subject: Landing gear Failure, ATTN Bud Yerly |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Yes, picture two, on the good bad scale, is bad.
I have used a straight edge also. The custom pins are a bit over the top, but useful as sometimes the cradle structure gets in the way of seeing just how close it is to over center aft where a collapse can happen....
By the way Ron, I still haven't gotten to fly my bird after the Sun n Fun damage, but a couple years ago you commented on running the 914 at altitude in turbo and the way the turbo waste gate automatic programing worked. It took a bit of time for me to comprehend what you were saying and I started troubleshooting.
We have a slight adjustment to the turbo cable. It seems you had hit the nail on the head about the turbo control unit. Now that I have a new controller for the turbo and I can monitor the engine on the laptop computer, I hope to cure or at least minimize the problem with "the worlds slowest Europa with 914" problem I have been chasing. I hope to cure the problem of my manifold pressure climbing as I increase altitude which limits my speed. More to follow, but your question of the pressure/temp controls on the 914 kept me thinking on it.
At the time of engine installation, I set my turbo control cable exactly as the manual calls for as I have on all the birds in my shop, but on my aircraft, it sucks. The Rotax method to set the turbo cable position actually puts my engine well over 40 inches of boost at takeoff (if I let it, but the waste gate controller of course pulls the gate closed to prevent that) and when I throttle back out of turbo to the 100% stop (max continuous) my manifold pressure is well above 34 inches requiring me to throttle back below 100%. Even with the throttle pulled back to maintain 34-35 inches, the airbox pressure is running a bit high and the airbox will actually blow off the carbs on climbout. The cable on my aircraft has been adjusted to allow the turbo waste gate to only open just far enough to give me 34 inches at 100% and behold, I just make the 38 inches at full tubo (that is the limit on my engine). Of course full power is available at sea level and 100% throttle for climb so no risks are anticipated in testing. It was only about 2 threads on the turbo cable adjustment point to achieve this. So now I have to flight test and go through some trial and error to get the climb/max continuous setup to allow me to not have to fly at 60% throttle at cruise. I have found in the past, my fuel mileage is great, but my cruise power sucks.
More to follow and thanks for your comments which hopefully will solve my problem.
Regards,
Bud
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