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Building Tips and technical articles. => Building techniques => Topic started by: Mike Scholtes on January 24, 2014, 08:52:07 PM
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I don't see the stunt community using the grey plastic knuckle-type hinges from Robart or similar; the flat "pin" hinges are universal and are all I have used on stunters myself, for that matter. I have used the Robart hinges on large RC models that get way more stress than our 55mph stunters, with no problems. The Robart hinges are easy to install, needing only a drilled hole, and line up nicely without worry about whether the hinges are all in the same line and bind-free. Anyone here have experience using these hinges in CLPA, or know why they would be disadvised?
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I have them on my new Pawnee semi-scale, but haven't flown the beast yet. I like the ease of installation and will likely use them again.
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The Robart jobbies work but are awfully draggy by comparison to pinned hinges.
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I have used them on serious performing stunt ships for years and will continue to do so. They can be loose such that they will flex on their own weight. (I will never use a stiff hinge of any kind and the Robart hinges fit my needs in many ways.)
Keith
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Keith;
How do you choose the size? Do you make the stab/elevator a certain thickness so that you can use a particular size? Use the same number of hinges per surface as you would a flat hinge? I've never tried them before, but I'll try anything once, twice if I like it!
Type at you later,
Dan McEntee
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I have used them on serious performing stunt ships for years and will continue to do so. They can be loose such that they will flex on their own weight. (I will never use a stiff hinge of any kind and the Robart hinges fit my needs in many ways.)
Keith
I'll take your word for it Keith but the few I've that ever checked out definitely had a noticeable drag to them. It was some time ago now but they were fresh from a new package at the time. I suppose batches or even individual hinges can vary.
I always use pinned hinges but still sort through them to find and use the free-est(?) ones.
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I've used virtually every hinge on the market in my decades of C/L and R/C. I stopped experimenting with hinges many years ago and settled on the Robart's. That's all I use on both C/L and R/C. I've never had a problem with them and they are so much easier to install. For C/L I use the size that requires a 1/8 inch hole for installation. I think it's the medium size, but I'm not sure. I install them with Canopy glue which is water soluble and allows you to keep the hinge clean during the installation. Also the canopy glue is designed for use with plastic products and remains flexible enough to keep the flight control from cracking around the hinge. I use the same number per surface as you would any other hinge. I use two spaced close together at the tip of the flap and elevator to carry the extra aerodynamic stresses. You can cut the length if needed for tight clearances. Never had one fail or come loose.
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I've used them a number of time. They work well.
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I've used them on 1/2A profile scale projects. They work very well.
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I've used them plenty of times in R/C. I plan on starting up again on this F1F project which will be CL.
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Surely drilling an 1/8" hole in a 1/4" trailing edge compromises its integrity somewhat.
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Chris, you're right, but how much load do you think a stab or control surface will see across that hinge opening? I recently hinged my profile model with robarts, (I couldn't buy the big Du-bro hinges) and I don't think I compromised the structure very much at all.
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You don't drill a hole and leave it empty. You put a plug in it. The plug is the hinge. Plastic hinge, epoxy, it's probably stronger.
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You don't drill a hole and leave it empty. You put a plug in it. The plug is the hinge. Plastic hinge, epoxy, it's probably stronger.
Hey Charles,
where ever there is an abrupt change in material strength you will get a stress riser.
Just try and drill a piece of wood, then plug it with something that is obviously stronger, say steel and then bend it to break point.
Where does it snap? At the perimeter of the plug or where the stress has collected and concentrated.
Similarly with a beam and a post hinge that consists of balsa, then epoxy, then plastic, then epoxy and then back to balsa - somewhere within that group there will be enough of an abrupt change to cause a rise in stress.
Whereas a tab hinge provides very little in the way of a section change and will leave the parent materials properties much closer to its original state.
That's my beef here.
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Hey Charles,
where ever there is an abrupt change in material strength you will get a stress riser.
Just try and drill a piece of wood, then plug it with something that is obviously stronger, say steel and then bend it to break point.
Where does it snap? At the perimeter of the plug or where the stress has collected and concentrated.
Similarly with a beam and a post hinge that consists of balsa, then epoxy, then plastic, then epoxy and then back to balsa - somewhere within that group there will be enough of an abrupt change to cause a rise in stress.
Whereas a tab hinge provides very little in the way of a section change and will leave the parent materials properties much closer to its original state.
That's my beef here.
Chris,
Thanks for that heads up, I believe you may be correct.
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Surely drilling an 1/8" hole in a 1/4" trailing edge compromises its integrity somewhat.
Chris,
Good point, but you have to put a doubler block on the inside of the trailing edge where the hinge is installed. There is not nearly enough strength in the trailing edge. Also, the doubler block is needed to capture the glue. Otherwise you just push the glue through the tailing edge into the rib bay.
Paul
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Hi Paul,
I don't disagree with you mate, it's just that I am trying to give a valid point as to why pin hinges are not more widely used.
On first glance they would seem to rob most of the structure that is put in place - and of course you can always add material to make up for a deficit.
Cheers.
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Here's an example of what I was talking about above. I see your point Chris, and you are correct. Maybe these photos will help those unfamiliar with the installation. I glue the hinge receiver block to the trailing edge, rib, and both pieces of the trailing edge sheeting. Four glue surfaces and pretty secure. Hope this helps.
Paul
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Paul,
WOW! Nice looking model.
Nice wing design, and those flap tips, nice radius. Hummmm.
What is the model?
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Paul, do you taper fit the doubler blocks to match the TE planking?
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Dick,
Yes. I taper the blocks to fit the TE sheeting for about 3/4 inch. Beyond that, the size becomes pretty excessive. The 3/4 inch has served me well and I've never had one come loose. I think the important point is to glue them securely to the rib. That allows the stress to be directed to the rib which is much more solid than the TE sheeting.
Charles,
The plane is a Continental, scratch built from Tom Dixon plans. The styling is beautiful, but challenging. I've had to plan well ahead during the build to assemble the pieces in a logical order. A fun airplane to build. Planning an O.S. 46 LA for power. Biggest challenge so far has been the cowling. Looks simple on the plans, but a bit of a pain to make it fit the O.S.
Paul
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Paul,
Chris may have a good point with those Robart hinges, about removing material.
I looked at a Gee Bee Y I guilt many years ago and noticed I used the Robart on the ailerons but not on the stab and elevator.
Been a long time since I biult it, but I'm guessing I opted not to because these surfaces were much thinner. I used the nylon type hinge.
Chris's point is probably well made.
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Hinge pins are hard to align, flat hinges are more forgiving.
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Hinge pins are hard to align, flat hinges are more forgiving.
Robart makes a jig to eliminate error.
http://www3.towerhobbies.com/cgi-bin/WTI0001P?I=LXET65&P=8
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I am using these on my new twister. I mocked up the flaps and elevator, they seemed quite stiff. Any tricks for getting these to loosen up.
Jim
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I would think a jig along the lines of a "dowelling jig" would work better than the Robarts. With a dowelling jig you line up both pieces on top of each other, then drill both holes before moving to the next. I think using some hardwood and the appropriate drill bit bushing, one could make alignment nearly painless.
Steve
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I would think a jig along the lines of a "dowelling jig" would work better than the Robarts. With a dowelling jig you line up both pieces on top of each other, then drill both holes before moving to the next. I think using some hardwood and the appropriate drill bit bushing, one could make alignment nearly painless.
Steve
The holes go in the edges, perpendicular to the components. How can you lay them on top of each other?
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I would think a jig along the lines of a "dowelling jig" would work better than the Robarts. With a dowelling jig you line up both pieces on top of each other, then drill both holes before moving to the next. I think using some hardwood and the appropriate drill bit bushing, one could make alignment nearly painless.
Steve
Have you tried the Robart fixture?. My experience is that it works just fine. It centers the holes on the LE of the elevators and flaps, and it centers the holes (a separate operation for each hole) on the horizontal tail TE and wing TE. And it yields near perpendicular if not perpendicular holes to be drilled. It is not an operation that requires micrometer precision. Carefully performed, alignment is almost automatic and virtually "painless". And accurate centering the holes on the leading and trailing edges is almost automatic. Only if the operation is careless will the holes not be centered.
Keith
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I am using these on my new twister. I mocked up the flaps and elevator, they seemed quite stiff. Any tricks for getting these to loosen up.
Jim
Yes, you can get the Robart hinges un-assembled in a pkg. of 50. Product#321 & 322. This means they come with out the pin. Use a full span length of music wire for a continuous hinge pin for each flap and elevator. You can use a wire one size smaller than the hole size for just a couple thou of play for minimum friction. Also you will still find some pairs when put together will have a little friction. With the 2 parts unassembled you can fine tune the fit of the fingers if necessary with Xacto knife or sandpaper. Added benefit is control surfaces are removable, which makes it much easier for the finishing process.
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Yes, you can get the Robart hinges un-assembled in a pkg. of 50. Product#321 & 322. This means they come with out the pin. Use a full span length of music wire for a continuous hinge pin for each flap and elevator. You can use a wire one size smaller than the hole size for just a couple thou of play for minimum friction. Also you will still find some pairs when put together will have a little friction. With the 2 parts unassembled you can fine tune the fit of the fingers if necessary with Xacto knife or sandpaper. Added benefit is control surfaces are removable, which makes it much easier for the finishing process.
Neat trick!
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A dowelling jig is used to piece together multiple panels(table tops, bookcases). It is designed for edge use. I haven't used Robart hinges(yet) but I would think there could be an alignment problem as far as measuring from TE position to flap.
Steve
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Yes, you can get the Robart hinges un-assembled in a pkg. of 50. Product#321 & 322. This means they come with out the pin. Use a full span length of music wire for a continuous hinge pin for each flap and elevator. You can use a wire one size smaller than the hole size for just a couple thou of play for minimum friction. Also you will still find some pairs when put together will have a little friction. With the 2 parts unassembled you can fine tune the fit of the fingers if necessary with Xacto knife or sandpaper. Added benefit is control surfaces are removable, which makes it much easier for the finishing process.
I think this is the way I will go. Punch out the pins on true hinges I have and replace with music wire.
Thank you
Jim
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I haven't used Robart hinges(yet) but I would think there could be an alignment problem as far as measuring from TE position to flap.
Steve
Unless you have installed these hinges, it does little good to state that you "think there could be an alignment problem". Particularly when others state that there is little or no problem.
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I have used the Dubro hinge guide that looks like the Robart tool. I am not saying there is anything wrong with the hinges or tool, just that it would be possible to have an alignment issue. No different than the Ca hinges or flat hinges. The old adage " measure twice, cut(drill) once" comes to mind. When building what furniture I have built(for family& friends) the dowelling jig came in very handy. Nothing like scrapping expensive hardwoods to ruin your day.
Steve
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I have used the Dubro hinge guide that looks like the Robart tool. I am not saying there is anything wrong with the hinges or tool, just that it would be possible to have an alignment issue. No different than the Ca hinges or flat hinges. The old adage " measure twice, cut(drill) once" comes to mind. When building what furniture I have built(for family& friends) the dowelling jig came in very handy. Nothing like scrapping expensive hardwoods to ruin your day.
Steve
I have to disagree. I have used both the Dubro and Robart tools with great success. Used properly they assure good alignment, and it is very easy to do so. That's the design of the tool, it automatically centers the slot/hole on the workpiece just like your doweling jig does on your furniture projects. I am also a woodworker and have several different doweling jigs for the same reason.
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Allen
Its not the centering on the work piece that I concerns me as the problem, its whether I have the two holes drilled in the proper place. I'm thinking on my next plane I will make a predrilled jig that I can use on both the TE and flap. I should be able to predrill all the hinge holes and not worry about that part of the alignment. I would still have to make sure I'm centered on the work piece(TE & flap).
Steve
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Allen
I should be able to predrill all the hinge holes and not worry about that part of the alignment.
Steve
Have you ever installed the Robart Hinge Points? You are criticizing the function of keeping the things aligned. It is a fairly simple operation. The Hinge Points are very forgiving of minor alignment issues. As has been tried before to explain to you, they do not require micrometer positioning. You are being critical of a very nice method to install hinges on our models. Your criticism of your imagined issues does little good for those who are trying to learn new and very satisfactory methods.
Keith
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Butt the control surface up against the trailing edge. Make a pencil line on both surfaces where you want the hinges. Transfer that line vertically down the abutting surfaces. Use the Robart jig and center it on the vertical lines. Drill the holes. They will line up. There are videos that explain this.
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Lay out hinge locations on trailing edge of wing/stab. Masking tape the mating control surface to wing/stab with its leading edge adjacent to the trailing edge with the marks you layed out for the hinges. Use a small square to transfer all the locations to the control surface.
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Are the 3/32 1/2A hinges strong enough for 35 size airplanes with 1/8 stabilizers? Or should a person upgrade the tail feathers to 3/16 and use the larger hinges? I do realize that 3/16 surfaces are stronger and more warp resistant but many of the older designs used 1/8 and there are times I like to stay period correct.
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Are the 3/32 1/2A hinges strong enough for 35 size airplanes with 1/8 stabilizers? Or should a person upgrade the tail feathers to 3/16 and use the larger hinges? I do realize that 3/16 surfaces are stronger and more warp resistant but many of the older designs used 1/8 and there are times I like to stay period correct.
For the smaller airplanes that use only 1/8" tail surfaces, the 1/2A hinge point type things will hold up to the flight loads. There might be a problem with them if the ground hits the airplane very hard.
But for .25 sized airplanes and up, use the heavier hinges, even if it means using , gad, 3/16" thick tail surfaces.
Keith
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Thanks, Keith.