Monokote hinges.... are they OK for a 2M sailplane?

I understand that they would not be a good idea on a faster, more precise type aircraft, but the kit I am building now is described as 'slow and easy'..

The reason I ask, is that I am to the point where the instructions are having me cutting slots for CA hinges, which I am finding to be a royal pain in the heiney. Was looking around on the web for alternatives and found a how-to article on hingeing with monokote, I would like to try this instead of the CA hinges, but dont want my control surfaces falling off in flight hehe.

gtmattz, I'm not familiar with a 2M sailplane. However, I use MonoKote hinges on my 1/8 scale - and very fast - Corsair as well as on my aerobatic Super Skybolt with no problems whatsoever. A felllow club member who flies pattern uses them exclusively on all of his high performance planes.

Installed correctly, MonoKote hinges will cover the void between the control surface and the wing and/or tail surfaces, providing better flight characteristics and a more crisp response to pilot inputs.

Unlike hidden hinges, MonoKote hinges are visible so you are able to inspect them. If you find a hinge weakening, replacing it with a fresh MonoKote hinge takes but a few minutes. I personally see this as the greatest advantage over any hidden hinge or any hinge that is permanently installed - and any hinge will eventually fail.


Mike

Thanks for the fast response. The plane I am building is a Dynaflite Daydream if you wanted to look at it. The point you made about easier inspection is one thing that I was thinking about that puts the monokote hinge at an advantage. And the fact that they should be really simple to replace when they do wear out. Looking at CA hinges, I'm not sure how one would be able to replace them in the case where the hinge cracked in the middle, which according to some of my research, happens more than I would like.

This is the guide I am going to follow when I hinge my control surfaces. If you see anything in there that is wrong, or that you would do different, please let me know.

[link=http://www.airfieldmodels.com/information_source/how_to_articles_for_model_builders/construction/film_hinges/]Monokote Hinges[/link]



Matt.

gt, MonoKote hinges will work well for your application. But don't count out CA Hinges. When installed correctly CA Hinges work great. I have several that are more than 10 years old that still work as good as the day they were installed.

For tips on proper installation, read this:

[link=http://www.rcuniverse.com/magazine/article_display.cfm?article_id=55]Installing CA Hinges[/link]

I've seen this design before. My hinges are a bit different though.

I make a series of hinges about 1" wide, applied side by side for the length of the control surface. That way, if one hinge did for some reason fail, all the other hinges would still be good. If the single hinge in the plans you posted lets go, then you'll lose your control surface.

I made up these sketches real quick. If they aren't clear, shoot me an email at [email protected] and I'll explain it a little better.


Mike

I've been using Mirwins method for years with both the films like Monocote and the fabrics like Solartex on many very large (1/4 scale size) as well as the smaller ones. I've never had a hinge failure even with the big Pheaton with the Quadra 72 on it (at least 500 flights if not a 1000) and the hinges are as good as when new. You can not beat it for functionality nor reliability. The nice thing is that you can leave the trailing edge of the wing squared off, the leading edge of the aileron squared off and have perfect function, no gap and no cost (use the scraps from the other coverings).

I like this method. Seems a bit more secure than the one in the article I posted. I was a little unclear at first, but I went back and looked at all your sketches there and I understand what you are doing. Looks like a little more work than the other method, but It appears that it will still seal the hinge joint, and make a more reliable hinge. Thanks for the tip.

Unfortunately, I have already shaped my control surfaces as-per the instructions on the plan, I am assuming this method will still work however, and on future models will leave the surfaces squared off.


After looking at it a little more, one thing I am a tiny bit concerned with, is the fact that all the hinge joints are 'against the grain' of the airflow over the surface, I understand you guys have had no problems with this, but have you heard of anyones hinges getting 'blown off'? Or am I to assume that if ironed down properly, the strips will hold tight with no problem?

They won't blow off any more often than any of the monokote covering on the entire a/c blows off. There are lots of covering seams on a model that're against the airflow. And you can inspect how they're doing and if you see any coming up, just iron it back down.

BTW, don't worry about having already shaped the surfaces' leading edges. The unshaped gaps actually aren't the best mechanical setup for hinging except on very thin surfaces. What happens is that the axis for your surface winds up with two different locations. Instead of having one "joint" it winds up with two. When your surface is moved up for example, the surface hinges at the top. When it is moved down, it hinges at the bottom. Now, where is your control horn positioned? It winds up seeing one pivot point when it goes one direction, and a different pivot point when going the other. What happens isn't a big deal, but that system shows the servo different leverages and sometimes different lever-arm lengths depending on how wide the surface joint is and where the control horn is placed. Not a big deal, but not a good deal either. And it will give you some differential deflections, again according to how wide the top of the surface is from the connection to the horn and how wide the bottom surface is from that same connection. More of a big deal depending again on how wide that "now flat" joint is from top to bottom.

Here is a quick sketch to illustrate the problem with square hinge joints.

When the pushrod pulls the horn a given amount, the surface deflects (in the sketch) 22 degrees down.

When that same pushrod pushes the horn the same amount, the surface rotates off a different point and in this case the surface only deflects 10 degrees.

The difference in deflection is a function of how far apart the top and bottom of the joint is and how far from the hinge line the pushrod connects from that hinge line. So if the surfaces aren't very thick, there won't be a big deal. But if you're hinging an aileron on a decent sized model, you will see significant differential.

Gtmattz,

". . . already shaped my control surfaces as-per the instructions on the plan, I am assuming this method will still work however, and on future models will leave the surfaces squared off.. .. " ABSOLUTELY. I do ARFs that come with the edges already shaped all the time.

". . . concerned with. . . hinge joints are 'against the grain' of the airflow . . . . " I failed to mention that I always round the corners. Square corners seem to come loose where rounded ones tend to stay put. One other thing I should have mentioned: I use Top Flite's Trim Solvent in lieu of ioning the hinge on. Trim Solvent is far mor permanent.

Here's a tip: Use clear covering material and you won't have to worry about the hinge matching the color of the airframe.

Mike

I hinged the peices this weekend using this method, I have to say I'm very happy with the results.

Great!

Here are a couple photos of the finished product. Have only a few minor details to take care of then when the weather gets a little better im going to take her out and toss her around to get her trimmed out.