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Old Feb 11, 2013, 10:51 AM
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Robarts Noob

I picked up a used Deuces Wild last week which has Robart retracts (spring/air) installed -- my first experience with the Robarts system.

The PO advised me he'd had some initial problems with the nose wheel collapsing on touchdown, and found that the pull/pull strings were too tight, which prevented the nose wheel from locking down when deployed. He introduced some slack in the lines and that supposedly resolved the problem -- at least, that's what he said. Not true, as it turned out.

Took the plane up for first time with 110# air in the tank, and quickly found I needed to add some expo to the ailerons, so landed after only a couple quick laps to make the adjustment. Normal good landing, no stress....and the nose collapsed. Dialed in the expo, pulled the wheel into position, & took off again. Flew the LiPos out, came onto final & dropped flaps - slowed to a near walking pace. Set 'er down ever-so-lightly on the mains, & just before the plane stopped, it touched down on the nose so gently a down pillow couldn't have softened it any more.....and the darn thing collapsed again!

With the soft landing there's no real damage, except one thing that's amazing is how much grass clippings pile up in there -- you'd have thought I'd landed a hi-volume hay baler or something!

I didn't get any kind of manual for the retracts - and frankly don't know squat about them other'n what they're supposed to do. Don't even know the model/size/series that're in there, if it matters. Is there a way of finding out (thru markings, etc) which Robarts I have? And have I (hopefully) provided enough info for someone/anyone to make some suggestions as to what I need to do to fix this mess?

Deeply appreciate any advice or assistance!
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Old Feb 12, 2013, 10:50 AM
An itch?. Scratch build.
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Never used them, but I don't mind searches.

Here's a comment I found -

Q. 'problem is the brand new Robart retracts do not lock down with any authority.'

A. 'The spring doesn't lock them down, the scissors going overcenter locks them down. Make sure that you are getting enough travel out of the cylinder.'

So it look like you need to check the lock down mechanism.
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Old Feb 15, 2013, 08:18 AM
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I would check for mechanical binding. Loosen the entire retract a bit and see if the action seems a bit faster. If the mounting pads are not perfectly parallel or the slot it fits into is not true there can be stress placed on the retract body once tightened down.
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Old Feb 15, 2013, 08:40 AM
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Thanks guys. Cougar, it's already so loose it 'raised an eyebrow' when I was pre-buy checking the plane. That's when the FO told me about loosening the initially 'banjo-tight strings' (the pull-pulls) to allow full deployment. I'll be taking a closer look when I can get to it but I'm going in sorta blind & not knowing the 'finer points' trying to get a better idea of what to look for if beyond the glaringly obvious, and hoping someone more expert might recognize the symptoms & know the solution.
Still all ears!
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Old Feb 15, 2013, 08:48 AM
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I was not referring to the steering controls, but the actual mechanical mounting for the retract unit itself. As stated, if there is any stress placed on the retract body itself that can have a major influence on freedom of action and the higher air pressure will not help there as spring force alone is what drives the gear down and locked. If also mounted to drop forward into the airstream/propwash and with the added resistance from a gear door and you could be fighting a losing battle.
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Old Feb 15, 2013, 09:06 AM
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Quote:
Originally Posted by Cougar429 View Post
I was not referring to the steering controls, but the actual mechanical mounting for the retract unit itself. ...
Oops. Should have noted, loosening the mechanical mounting was how he took the tension off the strings. When I mentioned raising the eyebrow? He picked up the fuse & turned it over while taking it out of his trailer & I noticed the wheel/strut 'flop' a bit. I grabbed the tire & wiggled it around & there was quite a bit so asked why. That's when he went into the 'intentionally loosened' spiel.
Thing is, he told me that solved the gear collapsing-on-landing problem. No way I couldn've known at that moment, having not flown it, but it didn't.

No gear doors, BTW....just an opening in fuse/nose bottom. Perhaps before this is over I'll post some pix....but can't get to it right now. Again, appreciate you guys' assistance - big time!
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Old Feb 15, 2013, 11:23 AM
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OH, forgot to ask. How can I find which particular set of Robarts I've got here?
(In case I need to contact them for tech support, parts lists/drawings, &c?)
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Old Feb 15, 2013, 12:46 PM
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The Robart part number is as follows EFL4565

Here's the link to their page:

http://www.robart.com/products/e-fli...-wild-tri-gear

Unfortunately, from their description and the EFL prefix I assume they are custom built for this plane and only available through Horizon Hobby. I would contact them first:

Product Support 877-504-0233

Only addition I can make would be to post a request here on RCG asking if anyone else has experienced problems with this gear. From my own past I've seen or read of distributors playing ignorant despite many reported product faults.
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Old Feb 16, 2013, 06:08 AM
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Thanks for that info, Cougar -- I'll check it out later. Especially about the 'Deuces' set; first I knew of it. Too, I'm planning to call the FO later this morning & ask if he remembers what he put in it, any paperwork available &c.
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Old Feb 17, 2013, 10:19 AM
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take a picture of the nose gear unit installed in the plane and post it for us, sometimes things just pop out at those who have experience
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Old Feb 17, 2013, 09:01 PM
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Good thought. I'll make arrangements & do that asap.
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Old Feb 24, 2013, 06:14 AM
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Haven't had a chance to take pix yet, but got the plane into the shop & out of curiosity tried something. It had been sitting, gear deployed & without re-pressuring the air tank, ever since the re-maiden & I figured the air pressure might've leaked down a mite. I first pushed back on the nose wheel trying to force it to 'give' or collapse, no success, so hit it with the heel of my hand fairly smartly, then harder, and a 3rd time about as hard as I could hit it without hurting myself. It doesn't budge!

Not knowing the internal structure or all mechanisms nor the forces involved (beyond the obvious), should that 'slam test' have been sufficient to break it down if it wasn't firmly locked in the down position? Or even if it was?
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Old Feb 24, 2013, 07:14 AM
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That should of been enough to pop it out of its down lock.
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Old Feb 24, 2013, 08:30 AM
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That's what I thought. I'm totally mystified!
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Old Feb 24, 2013, 09:11 AM
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From what I can see of this system it is about as simple as it gets: Air Up/Spring Down.

Only recommendation I have at this point is to check or mark all 3 gear travelers in what I'm assuming is now their full DOWN AND LOCKED position, pressurize the system again, retract the gear and then release to watch if they all return all the way to that same position in their grooves. I'm guessing your nose or all are not due to either a restriction in the air line(s) or valve. Any of the following could have an effect on one or all the gears:

A dab of lube, a piece of the tubing or other contaminant creating a restriction in the line, (I've seen tubing slice from a sharp fitting to form a flap, in effect making your own "check valve"). Also, check closely for signs of compression or kinking/folding in the tubing. This could still be present or occurred much earlier. One of the crude methods to slow down air gear action was to slip a wheel collar onto the tube and use the set screw as a sort of regulator, restricting flow till the speed was to their liking. Even if later removed the tubing could remain permanently deformed. The same could be the case in a fold or kink in the tubing.

You could have something in the valve assembly, either in the form of foreign contaminant or a miss drilled port. You could even have a mechanical fault, (something internal with the design or manufacture) where the valve does not travel fully into the extend position to allow for system venting to atmosphere. This could be something as simple as linkage or servo travel setting.

Check all your gear, including the mains. They likely are side loaded so not as prone to collapse under ground ops or landing loads. If only the nose is an issue, swap the air line with one of the main gears and try again.

The fact your system is in full lock now sure points to this being an air source problem.

One thing extra to check is this: Leave the gear in the EXTEND position throughout this test. As before, mark the traveler positions of all 3 gear with the system discharged, then have a boo once the system is up to operating pressure. If any of them have shifted then you likely have an internal leak in the valve allowing some pressure to feed into one or more lines. This is a low probability as any leak of this nature would eventually have the gear retract on its own.
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Last edited by Cougar429; Feb 24, 2013 at 09:23 AM.
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