I'm looking for a good technique for applying Blenderm surgical tape to seal hingelines. I've found that this tape works great but is difficult to apply and trim. The adhesive is gooey making it difficult to trim off the excess and instantly grabs onto whatever it touches making it difficult to position before burnishing it. What's the trick?

Thanks,
Verne Koester

I don't know for sure, but the solution might involve waxed paper. I have used it with other kinds of tape when precise positioning was involved.

Hey Verne,

I've had pretty good luck sealing hinges with Blenderm.  No real "tricks" persay, but if there is one, it's DON'T STRETCH it.  I'm careful to attach about 1/8" to the wing for the entire length and then working from the center of the aileron, with it fully deflected, attach it to the aileron. 

The real problem comes AFTER that, in that it when you deflect the surface the other direction, the tape attaches to the inside of the hinge gap and doesn't release well.  I've solved that but putting talc into the gap area after attaching the tape so that the talc will cover all the open tacky surfaces of the tape and prevent it from sticking.  Never had a problem after that.

Rereading this it's a pretty cryptic description of my process.  Give me a shout if you need more.

-M

What's your technique for trimming the excess? I've found the an exacto or razor gums up with adhesive pretty quick.

Verne

Verne,

I actually used some of the application fluid that is sold for apply vinyl graphics. It works similar to the "windex" method of applying graphics on wings and such, except that the fluid actually helps activate the glue, you just have to let it sit for about 10 minutes after you squeegee everything out.

Arch

Thanks, I thought about trying that. I have some Rapid-Tac for applying vinyl and that would help eliminate the tape trying to grab everything it touches. The final bond isn't affected?

Verne

I'm not sure what you mean by "excess".  I don't trim the width of the tape. I use 1" wide blenderm and just run it the length of the gap, so the only trimming is cutting it to length which isn't a problem.

Verne,

I used it on my Wind 50e with no problems. The final bond seems to be very strong.

Arch

Out near the tip, I don't have an inch of surface area for the tape to stick to resulting in overhang that I want to trim off.

In my case, I'm only going to use Blenderm on the rudder which has more than an inch of surface area at the bottom and probably only 1/2 to 3/4" of surface area at the top, so that's where I'll have overhang to trim off.

I use monocote to seal the ailerons and elevators which I find much easier to work with and just as effective. My reason for using Blenderm on the rudder is because the painted surface on the fuse doesn't like the heat of an iron.

Verne

Blenderm has so much "grab" that I'm pretty sure the wax paper would be torn and shredded trying to take it back off. I've tried using the non-stick backing that comes with vinyl graphics and that worked okay except that it was hard to avoid the stretch that Mark talks about. Once it stretches and sticks to something, you've got a guaranteed wrinkle.

Verne

Lots of sharp straight edge razor blades then.  And yes, they "gum" quickly.

I stopped using clear monokote on the ailerons and elevators when I had the film "blow out" of the hinge gap during practice up at Weak Signals.  Rather than fold IN to the gap when it closed, it folded OUT in flight...adding significant trim in the process. One minute I'd need 7 clicks of  right, the next 7 click back left.  Thought I had a bad servo until I landed and luckily saw that the hinge piece of monokote was sticking out.  Changed it to blenderm at the field and never looked back.

I had the same problem on my first Integral. I think the pressures seen by the hinge sealing material have a lot to do with the airfoil because I never had the problem before in 25 or 30 years of flying. After three or four flying sessions of the problem re-appearing, I cured it by sealing both sides of the aileron (top and bottom). As I recall, I used Blenderm on the top side and already had monocote on the bottom. On the two Integrals I've built since then, I just sealed all the control surfaces on both sides (monocote for aileron and elevator, Blenderm for rudder). It's been maintenance free. I've just never had a good handle on applying Blenderm.

On the razor blades, do you use a shearing cut where you pull the excess up against the blade, or do you slice it off by running the blade along the edge of the surface? Sorry if I seem to be nit-picking this. I've already tried a bunch of things and haven't been real happy with any technique I've come up with so far.

Verne

Pulling the tape against the blade won't work.  The tape is too stretchy, regardless of how sharp the blade is.  I typically do a little of both.  I do NOT cut against the surface, but rather I'm lightly pulling the tape against the blade and sliding the blade at the same time.  I new blade will cut very cleanly.  I have also taken a metal straight edge and laid it on the surface, placed the tape down and cut it on the surface of the straight edge. 

Got it, that makes sense. I'll be sealing hinges tonight. I'm going to try Archie's idea with the Radid-Tac which probably means I'll be letting it sit until tomorrow before I trim off the excess.

Thanks,
Verne

Blenderm is pretty amazing stuff. I've used it exclusively as hinge material on all surfaces of my foamy aircraft. Cuts down on weight and it doesn't loosen up. Love it.

Jesse

Have you tried putting masking tape down on the painted surface, to cut the blenderm against? I'm thinking mask tape so 1/16 inch is under blenderm then cut belenderm on top of mask tape, them peel mask from under the blenderm. I'm guessing you are trimming the blenderm by guiding your blade against the rudder edge and collecting gglue.

ok...why are we taping hingelines?  Please remember I only have 1 contest under my belt and 1 flying season ever.  Thanks in advance for explaining it to me!

Corch,

Sealing the hingeline prevents air from flowing through the gap.  This is especially important when you're pushing or pulling as the increased angle of attack can force a lot of air pressure there.  If the gaps on both sides are unequal( and they likely are) you can get some induced roll when you push or pull that you can't really trim out.  

Granted...in this day of paper CA hinges, the gaps are very very small and this really may be a relic of a day gone by (older pinned hinges tended to create a larger gap and this was more critical), but for those of us that have been doing this a long time, it's habit.  <br type="_moz"/>

Okay, got er done. I ended up using most of Mark's first suggestion on my rudder. I pulled the tape out the full length of the hingeline without cutting it off the roll (gave me a temporary handle). The real trick was to get that first 1/8" down straight without stretching it as Mark suggested. Once that was done, I cut the tape from the roll. I ended up putting it on the rudder half of the hingeline first so that the excess would be on the rudder post at the trailing edge of the vertical stab, or fin if you prefer. More on that later. Then I took a 3" wide bindo spreader and burnished the tape from the edge of the 1/8" strip already secured to the hingeline. I started in the middle of the rudder and went up toward the top first and then down toward the bottom second, making sure to overlap the portion I just finished burnishing so I wouldn't trap any air. As I expected, portions of the tape had grabbed the rudder post along the way. I just took my time and got those spots lifted back off the post so that the leading edge of the tape was free. For this edge, I used the bondo spreader to secure the first 1/8" to the rudder post at the hingeline with the rudder fully deflected. Once that was done, I just started in the middle and burnished it just opposite of the way I did the rudder, burnishing from the hinge line toward the intersection of the fuse and rudder post. The technique of overlapping was done as before to prevent trapped air (bubbles). Everything looked great and now I just had the overhang to contend with.

The reason I wanted the overhang to be at the rudder post of the vertical stab is because it's finished with 3/4 ounce glass cloth which gave me a nice, relatively hard surface to cut against. I used an X-acto with a standard #11 blade and basically scored the overhang just inside of where it was sticking out. I grabbed the edge and it peeled off nice and clean. Done! Then I repeated the process on the other side of the rudder.

Thanks for all the tips everyone. I hope this wordy description helps out someone else that has struggled with this in the past. I still like Archie's idea of using vinyl application fluid, though I didn't use it here. Had I done my ailerons with Blenderm, I probably would have gone that way.

Verne

When I'm trimming the overlapping blenderm from the hinge gap, I use a really sharp pair of canopy scissors. I first make a small cut at the end of the over lap and then lay the scissor blades, which are slightly open, flush with the surface. Then while holding the cut end of the blenderm, I just run them along the edge until all the overlaping blenderm is cut flush with the surface. Works every time.

J

Thanks Mark.

I bend whatever material I am using adhesive side out over a steel ruler. Helps to give some control over the initial contact.
The best thing to cut blenderm is scissors.