RONW

I am curious to know if anybody has had any failures with 'live hinging' such as found on CARF and Skymaster models?
Also I would like to know how exactly how the hinge is constructed. Is the hinge fabric laid up when molding the wing and the hinge line cut later on or is the fabric glued in after the skin is cut along the hinge line?
The reason I ask is I recently had a hinge failure (one elevator half of my L39) after a rough landing. The model was not damaged but one elevator half had parted and hanging loose.
There are lots of models with this hinging, I also have a Eurosport many years old with no sign of wear along the hinge lines, so I assume that this hinging is very good and the failure I experienced was maybe due to a manufacturing error. I lost the L39 later on when it rolled inverted in a turn and then nose dived. At the time I thought probably a tip stall as it was completely unresponsive to any input in the 2 or 3 seconds I had left but examining the wreckage I noticed all the wing hinges had parted but the elevator hinges including the repaired half were still intact. It was a violent arrival and the cause will never be known for sure............Ron

DrScoles

My Feedback: (18)

The live hinges on both rudders of my BVM bobcat tore about half way up. But that was because I was using the bobcat like an ATV on some of my landings.... ;-) Easy enough fix with kevlar tape, its had many 200mph+ flights since then.

roger.alli

Hi Ron,

Here is how BVM do it at, 3.45min.
https://www.youtube.com/watch?v=qHi8PtEbvsI
Actually the video doesn't show too much detail of what is laid underneath the hinge "cut".. There is a strip of Mylar laid in during moulding. this strip of mylar becomes the hinge .The trick ,and skill of the builder/factory worker, is to cut through the glass/balsa layers, without cutting the Mylar..

Thud_Driver

My Feedback: (1)

I have an older SM L-39 where I had the left flap rip off during the turn to downwind with gear down and flaps at full. Did recover and had a less than stellar landing. Currently flying with about a 3/4" tear in one of the aileron hinges which I've covered with tape and still holding 50 flights later. I cut the other flap off and hinged both with Robart hinge points.

tp777fo

My Feedback: (28)

The problem is caused by putting flaps down at too high of an airspeed. I am guilty of this too and have been trying to do better. I now go throttle idle, count 3-4 potatoes, 1/2 flaps, a couple of more potatoes and full flaps. I then increase throttle to my normal landing position which is about 1/2 throttle. I trim my jets to fly hands off at 1/2 throttle, gear & flaps down and have a normal glide glide path. Makes landings much more consistient

melvin

My Feedback: (3)

Hi I had an Ultralightining shed a part on flight 15 but could not figure out what it was. The jet was totally destroyed.Bought and built a new UL and on flight 16 on that one i noticed right before taking off that my right aileron wouldn't go down. Shut the jet down and checked out the aileron and found that it was starting to peel away. From that point on i now run a very small bead of BVM epoxy along the foam sandwich that runs parallel to the hinge line. I do this on all the surfaces now and haven't had a problem since. It's a little tedious but it is well worth the effort in my opinion. I also repaired a flap on a King Cat that had delamanted about half it's length so it's not just Comp/Arf jets that it can happen to.
Mel

Springbok Flyer

Does anyone know if SM also use a mylar strip during the manufacture of their live hinges, like BVM does?

Jan

rhklenke

My Feedback: (24)

I thought that the live hinge material is kevlar cloth, not mylar...

Bob

roger.alli

Sorry Bob, I may have been spreading misinformation.. I do know mylar is commonly used for this application, but I am not sure what BVM use.. Kevlar would certainly make sense..

Roger

FenderBean

Good lord I hope not since my current project has this, I looked at the area and I dont really see any kevlar

turbinebuilder

My Feedback: (5)

Hey fellas i build my own planes and i do the live hinge,the hinge is made of a heavy peel ply,the same that carf models uses.Most composite planes that i have had my eyes on use this.
Can't confirm they all do it though.

FalconWings

My Feedback: (57)

My BARF left aileron hinge line started cracking after about 75 flights. The aileron eventually delaminated in the air, but the airplane didn't even feel it. I kept flying, only noticing a small reduction in roll rate sensitivity.

I sent pics to BVM asking for repair procedures (if any) and they sent me some balsa triangular pieces to make a new aileron using normal hinges. The response was so below what I was expecting that I just had to laugh. "I" decided the repair was not acceptable and just purchased a new wing and carried on.

On a Skymaster F-16, had an aileron hingeline tear out, and I fixed with fiber reinforced clear tape, then painted over it. That fixed it permanently, though paint eventually peeled off right at the seam, leaving a visible line (but still barely noticeable).

As a matter of fact......this is one of my best kept "secrets". I seal hinge lines on gear doors using the same fiber reinforced tape painted over it. I trim the tape to look like an actual hinge cover panel. On my JSF, you almost have to!

mick15

Me too, I had a hinge delaminate on a Kingcat, both ailerons delaminate on a Ultra Bandit and an aileron hinge split on an A10. I repaired the Ultra with G10 hinges with the long pin type pivot.

I modified the ailerons on my Airworld Hawk before I flew it, they are more scale anyway. Lastly I'm awaiting delivery of the new FB Hunter, that has pin(rod) hinged ailerons and "live" hinged elevators so, you know what will happen to them!

m

ww2birds

My Feedback: (14)

In addition to the interesting discussion on mechanical properties, there are some aerodynamic issues to note here.

The main issue is that with the live hinge, ALL the mass is behind the hinge line which makes the surface more prone to flutter at a given airspeed than other hinging methods where the pivot point is behind the leading edge, and gives the opportunity to mass balance by, for example, filling the LE area with lead shot.

I've lost a jet to flutter with live-hinged elevators, only to learn that the manufacturer knew all about it and was advising those who asked to use an arm extending ahead of the hinge line with some lead weights attached to mass balance the surfaces. The community now knows about this aircraft and most folks I have talked to are cutting the live hinge and doing conventional hinging with the pivot point behind the LE of the elevators.

I've seen something like this on full scale planes, but the usual explanation there is to compensate for the forces required to deflect the surface. Here is a link:

http://www.airport-data.com/aircraft...000201906.html

I do not know if it is just a force issue or if the spades also have a mass balance function on full scale aircraft.

Dave

mick15

No the spades have no balance effect they are an aerodynamic servo to lighten the required stick force.

m

dbsonic

My Feedback: (3)

kevlar can be used but it's mainly polyester cloth on most live hinges I've seen. Which is the same material you can use for finishing in composite layups done without the mold. My sense is that the this type of hinge does well under loading in the "tensile" direction but not so much in a shearing direction(90 degrees to the surface). I think that is when the delam occurs so likely to happen with hard landings or in cases when a linkage fails and the surface is free. I've definitely seen a number of delamination cases with this type of hinge but fixable.

RCFlyerDan

My Feedback: (54)

Hum? I guess I have been lucky with my CARF planes. I have had the CARF 44% Giles 202, the CARF 2.6M Extra, the CARF 3.2 Extra, the CARF Flash, and CARF Viper, some with hundreds of flights. I guess I should knock on wood that I haven't seen an issue...........yet.

rhklenke

My Feedback: (24)

Yea, I wasn't sure if it was Kevlar or some other fabric - I thought I heard somewhere that Kevlar was used for this application.

The main point thought is that at least in the ones I'm familiar with, its a threaded fabric as opposed to a continuous material like mylar. This means that once it begins to tear, its difficult to stop it. I've seen a delamination failure on a buddy's Flash, but the live hinge failures I've experienced myself have been tears of the hinge material right along the hinge line. Those are hard to stop and repair, but I've had some luck with backing up the torn part (plus a little past that) with Kevlar cloth on the inside of the hinge, or on smaller, slower jets that don't stress the hinge as much, a strip of mylar hinge material that you can get from Radio South...

Bob

dbsonic

My Feedback: (3)

I agree, that once it starts, it will likely continue. I've seen attempts to hit with CA(meaning applied directly to the flexing portion) and that only makes the hinge more brittle. In one case I cut the ailerons off and did hinge points as a more deterministic fix. In this case, both ailerons were affected and one aileron came off shockingly easy and likely about to fail completely. The other was still very strongly hinged.

CA can work if the flex portion is still in good shape and it is just a delamination from the surface.

Springbok Flyer

Reading all this; I have to ask what you guys do when painting over these hinges. A case in point would be when you use a white kit and custom paint it yourself - the hinges become rather stiff and getting them to move freely can be a challenge.

Cheers,

Jan

joeflyer

My Feedback: (48)

Agreed. I noticed the elevon hinges starting to tear on my Skymaster Gripen. After trying several things I finally put a bead of clear silicone about an inch long on the underside of the hinge area at each end. This seemed to prevent it from getting any worse. Then when I put my F4 together I added silicone beads as a preventive measure. However, I need a bunch more flights before I can say that it's a permanent fix.

RONW

Hi Roger. I cannot remember if I discussed this issue with you at Tokoroa but thanks for the link as it confirmed how the hinging is finished at the factory. As the commentary says the builder must be careful not to cut too deep and this confirms what I thought after inspecting the wreck. All the hinges had cleanly parted along the line without any other signs such as any delamination or pulling out. The material is some type of woven fabric..
With so many models flying successfully with these type of hinges makes me believe the material is ok as long as it is not cut or scored during manufacture.................Ron

George

My Feedback: (57)

Here's a nice little trick Krill does on the Avanti flap which uses a 'live' hinge. It's simple but very effective!

I'm trying to post from my phone but the pics show upside down, but if click on the pic, it expands right-side up, so not sure how it is displaying on a PC. I'll edit the post when I'm at a PC if it's not correct.

dbsonic

My Feedback: (3)

That's a nice quality touch. At the ends will help prevent a tear starting.

CRye

My Feedback: (15)

Hello to all,
(Jan, I am awaiting factory parts to complete my Skymaster 1/5 F86 any build tips would be appreciated.)

I bought an Aurora, huge, and after I received I noticed how stiff the hinges were. I wish I had put a pull scale on them but had to be may pounds of force and could not achieve anywhere near recommended max deflection. It had been repainted and turns out to be very thick paint and many other problems. What would have been a square skin cut over the hinge was reduced to just a tiny depression line in the paint.

I drew a deep breath and used the point of a dull pocket knife and began to scrape out paint. By the time the cut out skin began to show some definition the hinges began to move far more normally. Since flaps and one elevator already have hinge point repair I was willing to risk cutting through. Happily it did not and ailerons and rudder saved.
.
Anyway if paint or repaint I strongly recommend finding a way to protect hinge skin cutout.
Charles

Very shocking how strong the paint in the hinge cutout was and even stopped the movement away from the paint side. I thought that would have just split the paint open but probably urethane paint