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Lutz Pritsehow
Unregistered

Posted Saturday, July 3, 2010 @ 11:03 AM  

Hi to all

Well after the long and cold winter, I was able to get my spraypainter to redo the fuselage, and various bits and pieces, and have finally started with the reassembly of my RF3. As usual, hardly started and already stuck.....literally. I reassembled and installed the undercarriage, only to find that it was scraping on the right side, and needs to be moved left a little. I have had tips ranging from "take a mm off the fork or the wood" up to "scarf a wooden block to insert behind the main block of the u/c (tricky getting the right angle). If I did move the u/c, how would I know it was straight? Any sage advice?

Secondly the undercarriage lever has a certain ammount of play. The problem is the two screws in the u/c which stop the tube, attached to the gear lever, from moving. When I bought the a/c and dismantled the u/c, these screws were secured with wire. Due to this, it was not possible to turn them in as far as they could go (see link with photo's). If I removed the wire, I could turn the screws in further, which would stop the play in the lever. So my question is, is it ok to have some play or do I need to turn in the screws to the point where there is no play, and secure with loctite? Or just get longer screws, that will go in further and still allow a wire lock?

http://picasaweb.google.com/118415219216085898523/RF3Restoration#

I would appreciate any advice that the RF3/4 owners might have.

Keep the rubber side down!
Lutz

Donald
Unregistered

Posted Sunday, July 4, 2010 @ 04:41 AM  

Hi Lutz,

First of all I would say "take nothing off the fork". That item is probably very nearly irreplaceable so I don't think you want to mess with it in any way. Also, if the fork was not scraping on the side before you began the work it should reassemble without scraping on the side, so what has changed?

From recollection of the time I dismantled mine 8 years ago the things which might affect the lateral location or the alignment of the undercarriage are:
1) the lateral position of the upper fork within the base mount, the part that bolts to the fuselage frame.
2) the closeness of the bolt holes through the fuselage frame and the wing spar.
3) the flatness of the joint between the base mount and the fuselage frame.

From your photographs the undercarriage looks to be assembled OK but as a factor to eliminate you could verify that the upper fork is centrally located in the base mount. It probably is for there is not much free space in there.

Have the bolt holes through the fuselage frame and the wing spar become enlarged? Or are the bolts you have used too small in diameter? In short, is it possible to displace the base mount laterally on the fuselage frame?

Since you have had the fuselage repainted, and the gear itself, my guess is that the culprit here is the flatness of the joint. Do you perhaps now have thicker paint on the left side of that fuselage frame than on the right? Or is there a bead of the blue paint on the mating face of the gear base mount? Either of these, or possibly both, could disturb the alignment of the undercarriage enough to make it touch the wheel well side. There's not a lot of clearance. If the back face of the base mount is painted I'd be inclined to clean it off and use a jointing compound when reassembling. Have you tried tightening the screws on the left a little more than those on the right? Take care with that idea for you don't want to crush the wooden structure but it might let you see if a little misalignment is at work here.

As to your second question, I'm afraid my memory fails me here but as a general principle I'd say the screws should be tight in but that you should still use lock wire rather than locktite, but your remark does bring back a memory that these screws are recessed somewhat and that lockwiring was not easy.

Are you certain the play is where the tube goes through the fork? The other place where you might get play in the system is at the base of the handle itself which, from recollection, is pinned through its collar to the tube by a tapered pin.

Nice to discuss an RF3 for a change. Let us know how you get on.

Donald

[Edit by Donald on Sunday, July 4, 2010 @ 05:14 AM]

Lutz Pritsehow
Unregistered

Posted Sunday, July 4, 2010 @ 09:24 AM  

Hi Donald

Well thanks for all that advice. Certainly some things I am going to be looking into.......I will let you know how I get on and whether any of the problems you pointed out were the cause of the mis-alignment. I'm only off by maybe 1-1,5 mm.

The second problem is definitely a problem with the two screws. I did turn them in all the way when the u/c was out, and then there was no play in the lever. I have also just spoken to a fellow RF3 owner here in my neigbourhood, and he confirms that there should be no play in the lever. So I will either turn them in all the way and secure them with loctite, or get longer screws, have a hole drilled in the head and secure with wire.

If there is anything else that comes to mind, please feel free to post it. I am a firm believer in learning from others mistakes, without landing in the ditch myself first.

I will post some more pictures on the picasa page when I have them.

--------------------

Markku
Unregistered

Posted Wednesday, July 7, 2010 @ 01:55 PM  

Hi Lutz
The gear is the same in RF-3 and 4, I can send you an assembly drawing if you give your e-mail adress. The screws which connects the upper fork to spring loaded shaft are specially made and it might be that you have in your plane something different.
For the side tolerance, have you taken off the shaft bushings, it might be that the flange thickness is not the same in both ones and if they have changed, it migh cause the problem.
Lutz Pritsehow
Unregistered

Posted Monday, July 19, 2010 @ 06:03 AM  

So I've just spent an interesting day in the hanger getting the gear sorted out.

First off the good news. The gear is in straight and retracts without any problems. There is very little room on either side though, but at least no more scraping the sides.
I suspect that when I bought the plane, and started taking things apart, I should have paid more attention to the undercarriage. It might have been that there was a shimmy under the the main block that I overlooked in my haste. In any event, after some testing I found that adding a piece of ply (1mm) on the right side behind where the main block attaches to the spar, it swung the gear over to the left just enough for it to fit into the wheel well. So no work on the fork required.
I suspect that that Donald hit the nail on head with:
"Since you have had the fuselage repainted, and the gear itself, my guess is that the culprit here is the flatness of the joint. Do you perhaps now have thicker paint on the left side of that fuselage frame than on the right? Or is there a bead of the blue paint on the mating face of the gear base mount? Either of these, or possibly both, could disturb the alignment of the undercarriage enough to make it touch the wheel well side".

The second issue with the play in the lever. I turned in one of the screws all the way, as far as it would go (see picasa link in previous post for a picture) and subsequently there was no more play. The gear lever is locked solid and so my plan is to get a longer screw, drill a hole in the top to run the safety wire though, and then problem solved.

So thanks to Donald and Markku for their suggestions and help. I will keep you updated on my progress as and when something happens.

Cheers Lutz

--------------------

Donald
Unregistered

Posted Monday, July 19, 2010 @ 08:32 AM  

Hi Lutz.

It's amazing what trouble a little paint can cause, if that's really the culprit. I just recently finished working on an engineering project which called for some tight fit ups and we had the same problem. Even thought the mating faces had been masked for painting beads of paint found their way over the edges and had to be cleaned off to get the thing together.

Had a look at your photograph of the screw and the one on the right looks sunk in much deeper than mine. From memory I'd say that mine have about 1/3 to 1/2 of the socket head above the face of the fork, just enough to get the lock wire through. Of course, mine might be wrong and your's right, or my aging memory might be failing me. I've only ever seen one example, the one on my aircraft.

Donald

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