sandal

A few weeks ago I bought a Pilot-RC Trainer 90 (90", 11 lbs, 20-30cc) for towing and Sunday flying. It came with CA hinges, which I wasn't too happy about, but I installed them and hoped for the best.

I have now logged four hours on it, and one of the aileron hinges is starting to give up. It looks like it has been cut half way through with a knife. The plane is grounded until I can get the hinges sorted.

Robart Hinge Points seem to be a good choice because the existing CA hinges are quite close to the ends of the control surfaces, leaving too little(?) room to cut new slots for flat nylon hinges. I could probably place the new hinges on the other side of the existing hinges, but that would leave at least 3 inches of aileron outside the last hinge, which I doubt is ideal.

Robart recommends the 3/16" hinges for 1/4 scale aeroplanes and the 1/8" ones for .25 to .90, so I should probably use the larger ones. My problem is that the tail surfaces on the Trainer 90 are 5/16" thick, so drilling a hole for a 3/16" hinge is out of the question. There are three CA hinges on each surface now, and I figured if I put one near each end and two in between each of the CA slots, I will have six hinge points on each surface. Would this be strong enough with the 1/8" hinges?

If I decide to use the Dubro HD nylon hinges, how much "untouched" wood will I need on each side of the hinge slot, i.e. how close to the end of the control surface can I put it?

My apologies for asking lots of questions, any feedback and advice is welcome. Thanks in advance.

RBACONS

My Feedback: (3)

There is no reason you can't use the larger Robarts on the ailerons and the smaller Robarts on the tail surfaces. I use the smaller hinges on 1/4 scale cubs for exactly the same reason, the surface is fairly thin. No issues over a decade or more of flying them.

One concern I would have is that leading/trailing edges that are set up for CA hinges generally do not have any balsa block behind them. Normally you would want wood the full length of the Robart hinge to ensure an adequate gluing surface. You can add balsa blocks in but that would involve peeling back the covering.

Three hinges on each of the elevators and rudder should be fine. You can add more if it makes you more comfortable. For the ailerons, since they look like full-span ailerons, five or six is probably a good number.

The Dubros you can put within 1/4 or so of the end of the aileron. However, if you cut all the hinges off, you should be able to cut the old CA hinges out with an exacto knife and some patience and put the Dubros back in the same slots.

sandal

Sounds good. Using 1/8" Robart hinges would probably be the easiest route, and if they are strong enough for a 1/4 Cub, they will probably be fine on my plane as well.

This is what worries me. The tail surfaces have around 1/2" of wood where the hinges are installed. I have no idea what the ailerons and flaps look like until I drill a hole and look inside. Maybe flat hinges will be better after all.

That sounds like an impossible task to me On the other hand, you wouldn't recommend it if it couldn't be done, so I'll give it a try if i decide to use flat hinges.

Thank you for your help!

Gray Beard

My Feedback: (-1)

Just a few photos to give you an idea. First one is the two types I use most the time, hinge pin and the flat, both from DuBro. There isn't a thing wrong with CA hinges if installed correctly. These two control surfaces haven't been sealed yet so you can make out the hinges. The red aileron is on a small 40 size Up-Roar, it has 5 flat hinges in it, the third photo is the elevator on a 90 inch plane with hinge pins. During the build I mark off the hinge area and put in extra wood to make the edges thicker. Each surface has 5 hinges installed, both planes are scratch built so I just have to decide how many hinges I want to use to keep the surface from flexing. Both planes are stunt planes and not trainers.
Trying to cut out an old CA hinge probably isn't going to happen, CA makes the wood as hard as iron. Most people just cut off the control and trim the old hinge flush then cut new slots next to the old ones and install new hinges. How many were used in the first place. The choice of the type of hinge you use is up to you, a trainer doesn't put a lot of stress on hinges. Pins are just really easy to use if you have the drill jig DuBro sells
How many do you really need? I measure the control and divide it by 5 most the time depending on the length and size. I place the first two at the ends then measure and mark where the rest will go. Sometimes I need more and sometimes less.

sandal

Grey Beard,
thank you for your advice and photos!

I have decided to order both DuBro and Robart hinges and try them on some scrap balsa. Then I'll make up my mind about which ones to use on the plane. (I know, I'm hopeless)

Gray Beard

My Feedback: (-1)

You don't need to pick just one either, Nothing new about using the different hinges in conjunction with each other.
I just obtained an old ARF, NIB but it is no longer available. It's a stick and I plan on using CA hinges. To do the wing repairs I had to remove the covering from the wing bottoms and I could have installed a bit of extra wood and used either of the hinges I showed but it is just easier to cut the slots and use the CA hinges.
I fold them in half then brush a thin line of Vaseline on the fold then push a pin in the center. The slots I cut get a hole drilled through the center also so the thin CA will flow better and glue the complete hinge. The hinges are pushed in flush with the pins. I don't use them often but I have never had one fail in any way.

mrdhud

My Feedback: (48)

Need some advice I’m recovering an old plane it has Robart pin hinges installed I have cut sanded and redrilled new hopes for new hinges. The wings ruder and elevator are sheeted foam what would be the best type of glue to use in the foam?
Thanks

Gray Beard

My Feedback: (-1)

Epoxy.