Posted by dannparks on Monday, October 5, 2015 @ 01:49 AM:
A few days ago after landing, I noticed that a fitting on the right outrigger had broken. It is a rear support post that seems to be unique to the outrigger refit on N2188.
Not sure why it choose that moment to break - the main post is not loose and it wasn't a hard landing or anything. It seems to be a threaded fitting that broke at the threads. It doesn't really have any pressure on it, but it does get a lot of vibration rolling on the grass. Here is a picture of the left side:
Does anyone know the history of this retrofit? And if the part might still be available? A check through ACS didn't find a match.
And I guess the other question would be if these bracing bars are really necessary. The main post goes through the spar and it seems to be plenty strong without the support. And I don't see any other RF4s with this kind of bracing bar -- although the tube holding the nylon rod does seem to stick out below the wing longer than most.
I would prefer to replace the part if I can.
Any information and/or advice appreciated.
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Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1
Posted by Jorgen on Monday, October 5, 2015 @ 02:09 PM:
Hi Dann,
sorry about that but I think that can be fixed, you just have to choose among several options. I'm sure you know the original design was an "U"-shaped hoop with two attachment points and someone chose to modify "N2188" from the original hoop to something in between the hoop and the common single plastic rod- modification. I haven't seen your version before and I'm not sure I understand why the reinforcing arm was thought to be needed. Maybe it was thought to allow a single rod mod without changing the forward fitting to a reinforced one?
The "single rod"- modification are available in a couple of different ("reinforced")versions, the one used on RF 5:s is a fitting attached to the spar, the fitting I have on "SE-XST" is drilled into a wooden block in one of the ribs. I posted drawings of that fitting a while ago, you might recall Bob Grimstead was concerned about the fact that there was no sweep in the rod. I'm not sure that is so much of a problem myself and the reason brings me to why I think you broke your fitting:
When you taxi there is little stress on the outriggers and even if they are pointed a bit forward in a tail low situation I haven't seen any problems because of that. However, if you bang the outrigger into the ground in the landing phase while you're still flying, the stress levels are considerable. I think it's imperative to keep your outriggers short to minimize the risk of hitting the ground while landing, perhaps with a X-wind. Since I shortened my outriggers I have had significantly less outrigger problems. I suggest you shorten yours and to do that and still have a long enough rod left to dissipate the bending forces you might have to modify your modification;) I agree, your fitting protrudes longer under the wing than other fittings I have seen.
May the 4's be with you/ Jörgen
[Edit by Jorgen on Monday, October 5, 2015 @ 02:11 PM]
Posted by SteveBeaver on Monday, October 5, 2015 @ 04:25 PM:
Perhaps something like this would work? "Single-sided, but still stronger than the threaded part.
http://www.mcmaster.com/#hanger-bolts/=z8lpjo
Posted by D. Porter on Monday, October 5, 2015 @ 08:26 PM:
Just curious, how short are your outriggers? Can you give us a measurement to bottom of lowered wing tip?
Thanks for the advice on the broken part. So instead of trying to change the system or find a new part, I just fixed the old one. Cut off the broken stub and welded it to a 1/4-28 aircraft bolt. Fits perfectly.
Fits perfectly. It sticks out a tiny bit further, but won't really change any angles. It is certainly a lot stronger.
It probably broke from a hard hit on rough grass and a weak part (it broke right where the threads start). Nothing on the main tube is loose (the main tube goes through the wing), but it is wood and there is a tiny flex. Vibration over time and a sharp hit was probably too much for it. The nylon rod is angled back and bends easily, so I don't think there is undo force on it. But a sharp jolt could be transmitted to the part. I'll keep an eye on both sides.
