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Aug 25, 2011, 12:07 AM
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Mini-HowTo

T-blade Installation


Lately I have been asked by a number of people how I install a T-blade in a DLG wing. There are two different methods I use which depend on the wing construction: molded or bagged. The bagged method is similar in principle to molded method and varies only slightly. I will focus on the method I use for molded wings and will perhaps in time post something regarding the bagged wing method when I have time and a bagged wing on hand.

T-blades have gained quite a bit of popularity over the last year, at least with me. I love them! So I may be a bit biased. They seem to help me get faster and more consistent turn-arounds and I find them much more comfortable than traditional blades. They can also be mounted farther out on a wing compared to a traditional blade installation, which reduces the chance of contact between the webbing on the hand and the wingtip. For example, the Steig has a very aggressive wing sweep at the tip and in order to mount a traditional blade in the recommended location, the webbing of my hand hits the tip of the wing. The tongue of the blade also stiffens up the thin tips of our planes. The V3 and T2 both benefit from the installation of a T-blade. Lastly, there is a theoretical advantage to mounting the launch blade as far out on the wing as possible. In practice, however, I have not noticed any increase in launch height. So dont rely on that argument too heavily.

Currently, I know of two producers here on this forum, Craig Robinson (RCG handle: C Robinson) and Gavin Trussell (RCG handle: Gavin Trussell), that make T-blades for sale. Both are great guys and make a great product! I would have no reason to choose one over the other on the basis of quality and reliability. They have slightly different geometry of the curve of the blade. In this how-to I am using Craig Robinsonís heavy duty (HD) T-blade.

Before you go jump on the T-blade wagon, there are two drawbacks that should be considered: they are much more work-intensive to install and they have a higher failure rate compared to conventional blades due to the design and fabrication process. I address both of these drawbacks and suggest methods for reinforcing the blade and installing them with good results.

While I am the author of this thread, I by no means am an expert. There are many smarter and more experienced builders here that I hope will make contributions and expound on the methods I use and post their own tips and tricks. Additionally, you donít need to be in the aforementioned cohort to make comments or add your tips or methods. I am hoping this will become a thread where all types of methods and techniques are shared.

Enough introduction. Lets begin.
Paul
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Aug 25, 2011, 12:11 AM
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Step 1: Blade reinforcement


The first step is to shape the blade the blade for comfort by rounding off the square edges. I use my dremel tool with a sanding wheel to knock off the edges. I then take 100grit sandpaper to smooth down the blade further. I finish off with 220grit. There is no need to go further with sandpaper since you will be covering the naked carbon with reinforcements. Make sure to sand the entire blade and take off the “shine” so that you create a better surface for adherence.

After shaping, it is time to reinforce the blade. The main failure mechanism is delamination of the carbon fabric layers due to a shear force. On launch, if one finger releases before the other, torque is placed on the blade and the layers see a large shear force. It is therefore necessary to counter this by wrapping the blade. This method is akin to wrapping a spar in order to combat shear forces.

I use 1510-denier Kevlar tow to wrap my blades. I know others using Spiderwire with excellent results. I opt for the tow because it lays down flatter and doesn’t build up the thickness of the blade as much. I can also get a smoother finish on the blade, which is important for my comfort.

I begin by cutting off ~2’ length of tow. I tack glue one end of the tow with thin CA to the tongue of the blade and begin to wrap from the base of the blade to the tip. Keep the tow as tight as possible. Try not to twist the tow as you wrap; the tow will inherently twist as you wrap. If you stop every wrap to untwist the remaining tow, you will get a nice flat application of the tow. Once you reach the tip of the blade, tack glue the end of the tow with thin CA and cut off the unused, remaining tow. Also tack glue the tow where is touches the base of the blade and cut off the length of tow from the base (where you just tack glued the tow) to the tongue. Now wrap the other branch of the blade as well using the same method.

After the blade is completely wrapped, soak the tow with thin CA and rub it into the wrappings. I rub the glue in with my fingers but to protect them I place a piece of packing tape on my index finger and thumb. After the thin CA is thoroughly rubbed in, hit it with some kicker. Then use medium/gap-filling CA to fill in the voids of the wrapping and to create a coating around the blade. Hit it with kicker and then repeat with another coating of medium CA and kicker. The rationale behind two coatings of medium CA is you want to build a layer of glue over the wrappings so that when you sand the glue down, you do not sand through the Kevlar wrappings. The first time I tried this method I only used one layer of thin CA and found myself sanding through the tow at the edges of the blade. This is the LAST place you want to weaken the wrappings. If you destroy the threads that traverse across the fabric layers, you defeat the purpose of wrapping the blade.

Kicking the glue between coatings is important since is makes the CA gum up and helps build up thickness faster.

Once you finished with the application of CA, sand the CA coating smooth. I use 100grit and proceed to 400grit, and if I am feeling motivated I go all the way to 1500grit.

This process of wrapping the blade does not add much weight. In this thread, I am using blade that weighs 2.6gr before shaping and reinforcing. After shaping and reinforcing, it weighed 2.5gr. That’s right, it weighed less. I account for this because when shaping, I remove more in carbon and resin than I put back with Kevlar and CA.
Last edited by RCPC; Aug 25, 2011 at 12:39 PM. Reason: used 1510-denier instead of 195
Aug 25, 2011, 12:17 AM
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Step 2: Routing the wing


So the blade is shaped and reinforced. Now for the hard part. If you like to compete, it is important that the projected span of the wing not be greater than 1.5m. In order to conform to the span limit, the blade might need to be ďsunkĒ into the wing.

The first step is to put masking tape over the wing tip and mark where you will place the blade. Make sure the blade is placed at such a depth that it does not break the span limit. Another reason for slightly sinking the blade in the wing is that the wing is thicker. With our thin tips these days, it is very easy to destroy the wing skin will routing out the channel in which the blade is fixed; since the tongue of the blade will be fixed to both the top and bottom wing skins, we want them to stay intact. Additionally, the thickness of the tongue may be more than the wing tip, so again this would require the blade be sunk slightly.

I like the place my blades as far aft as reasonable. Ideally, I like to nest them up against the drag spar. I then glue the tongue to not only the top and bottom skins, but also the drag spar. This makes for an even more secure installation. The only requirement is that the thickness of the drag spar be equal or greater than the thickness of the blade.

Once the cutout is marked on the masking tape, I use a cutoff wheel to remove it. This is where the right tool matters. Instead of using the standard dremel cutoff wheel, I found a third-party bit that has a very thin wheel. The thinner wheel produces a thinner cut so we donít lose much material. We will be gluing this bit of the wing back later, so the smaller the gap, the better.

After the wing is notched, the routing begins. Again, this is where the proper tool will pay dividends with a clean and easy install. I use another dremel cutoff wheel that is small in diameter and nearly the same thickness as the bladeís tongue. I love this tool! Take the wheel and notch the wing as in the picture below. This initial notch is very helpful in setting the direction of the routing bit used later. Without the notch, keeping the routing bit centered is difficult. When the routing bit is off center, you chew up the wing skin, which should be avoided. The strength of the blade-to-wing bond comes from fixing the tongue of the blade to BOTH the top and bottom skin of the wing. So if you chew up the skin, you lose strength.

Next, find the skinniest routing bit you can. The one shown in the picture below is my favorite. Again, it is a third-party bit I got at the last AMA Expo in Ontario, CA. It is tapered so it is easy to plunge and the abrasive area is just as thick as the tongue of the blade. Plunge the routing bit carefully and route out the wing. Try to take out only as much material as necessary to fit the tongue in the wing without the skin bulging. If you take out too much, it will only need to be filled with heavy epoxy.

Some tips for routing the channel for the tongue:
1) Plunge two channels down the sides of the initial notch to create a boundary for the routing. This will ensure you donít remove more material than you need.
2) Put your fingers on the top and bottom skin where you are routing. This will help you feel if you are about to break through the wing skin. If the skin begins to get hot, stop routing and let the wing and bit cool. This might also be indicative that the routing bit is getting gummed up. Clean it by blowing on it.
3) Remove the tape before you being routing. In the pictures below, I didnít do that and subsequently broke through the wing skin without knowing. I am always learning
4) Donít use a bit that is significantly thicker than the blade or the wing. You will destroy the skin and create a channel that is too big for the tongue. The right tool is VERY important here. Again, the right tool will yield great results, and the wrong tool will make you curse me for ever trying to convince you this is easy. It is easy, but only with the right tools.
5) Use a backlight under the wing to see how deep you are and where the bit is. This is sometimes not possible, but in this tutorial I am using a wing in which this technique is possible. This technique can also be used to see where the tongue of the blade is and where the epoxy is going.
6) Check the fit of the tongue often. Make sure that when the blade is installed, the wing skin does not bulge out.
7) Be patient! This is the most critical part of the entire installation. If you are going to take your time on ONE thing, let this be it.

Now that the channel has been routed, hold the wing vertical with the modified tip pointing at the ground. Tap on the wing so all the debris and material that was pushed into the wing falls out. If this material is locked into the wing, it will always rattle. I hate things rattling in my wing.
Last edited by RCPC; Aug 25, 2011 at 12:23 AM.
Aug 25, 2011, 12:30 AM
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Step 3: Fixing the blade


It is now time to fix the blade into the wing. First begin by blowing down the channel in the wing to remove all the shavings and dust from the channel. You want a dust-free surface for the epoxy to bite. Notch the tongue of the blade slightly with a cutoff wheel and scuff it with 60grit sandpaper. Clean it with some IPA. Place some masking tape on the wing tip to mask off the wing around the cutout. This will limit the amount of cleaning needed if you get some epoxy on the wing or it oozes out when installing the blade, which it slightly should.

The glue I use is West Systems G-Flex. It is a 45min epoxy and has good shock resistance. I mix up about 3-4gr of epoxy (which is more than enough) and add milled glass, cabosil, and microballons. I usually add a small amount of carbon black for color to match the blade and wing. This is optional. Next, I empty the resin into a syringe with a 1.5Ē long 18AWG needle. I then apply the resin into the channel with the needle. You can use a small wooden stick or wire to get the resin into the channel, but that is a little more tedious. After the inside of the channel is coated, I coat the tongue of the blade with resin as well and then insert the blade. Clean up any epoxy that oozes out.

Get the proper placement of the blade then tack glue the blade to the wing with black/rubberized CA at the edges. I do this so that the blade canít move when I clamp it later.

After the blade is properly set and I clean up any epoxy overflow, place mylar over the tip (top and bottom) and weight it down between two pieces of stiff foam. I use some EPP. I then apply about 10-15lbs and let it sit until the epoxy cures.

Just a note, if you do break through the wing skin when routing the channel, you can laminate a layer of fabric over the tip where the tongue is at the same time you fix the blade in the wing. I did this to two wings and used 2.5oz/yd carbon fabric with good results.
Aug 25, 2011, 12:31 AM
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Step 4: Finishing up


Itís all downhill from here. All that is left to do is glue back the small bit of wing that you notched out before routing the channel. This is purely a cosmetic step. I usually fix it with black/rubber CA to match the color and fill the gap, and hit it with kicker. I sand the overflow with a small rat-tail file. Thatís it! You are all done!

If done properly, you will add no more than 3.5gr total. The blade will weigh about 2.5gr and you should certainly need less than 1gr to fix the blade. You should not be able to feel the difference in tip weight in flight if you do it right. At least I canít.

Hope this helps elucidate this process and spurs some discussion. I am always eager to refine my methods so if you have any suggestions, please post them here!
Paul
Aug 25, 2011, 12:54 AM
Mike M.
like.2.fly's Avatar
Very clean and nice Paul! Thanks for your efforts to write up, photo, and post the procedure. Wish I could have seen this info a month or so ago. I've done two of these, and it wasn't fun. Hopefully next time will be much easier...
Aug 25, 2011, 03:45 AM
Launch low. Fly high ;)
Hanger Rash's Avatar
Thanks Paul. Lots of really good information here. I have a T-blade I am about to install and will certainly follow your method.
Aug 25, 2011, 04:10 AM
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Quote:
Originally Posted by like.2.fly
Very clean and nice Paul! Thanks for your efforts to write up, photo, and post the procedure. Wish I could have seen this info a month or so ago. I've done two of these, and it wasn't fun. Hopefully next time will be much easier...
Thanks, Mike. If I am able to help one person, then it's worth it. Sorry for the poor proof-reading. I just read through the posts and feel sorry that my high school allowed me to gradumatate after writing it all, I had no energy to proof-read....and now...well, I have had too much scotch

I can't emphasize enough that the right tools make this so much easier. I used to spend over an hour just routing a channel for the blade using a smorgasbord of drill bits, rat-tail files, dental picks, voodoo, and even lucid dreaming. Now it takes about ten minutes with some practice and the right tools. The majority of the time should be spent shaping the blade for comfort since that's where there is the biggest impact.

I was an R&D engineer in my previous life and prided myself on my resourcefulness. I thought with the proper techniques and ingenuity, the choice of tools was inconsequential. Unfortunately, in this case I am not creative enough and have fallen back on tool choice. Hopefully others will give some input on creative solutions. I am eager to hear from you and others regarding your experiences.
Paul
Aug 25, 2011, 06:46 AM
Limbo with 30,000V...
J_Arner's Avatar
Great write up and install Paul! One question on the black CA, is it the type they sell for mounting R/C car tires, or is it the high dollar Loctite 410?
Aug 25, 2011, 07:01 AM
Kyle Clayton
Wave Glider's Avatar
Black rubberized CA is generally the stuff used for the rc car tires, to my knowledge. It works good for a lot of things on DLG's
Latest blog entry: Helios and XXLite DLG
Aug 25, 2011, 07:14 AM
Thermal Hunter
jnoel's Avatar
Nicely done Paul...

What supplier would have the 195-denier Kevlar tow ?

- Jim
Aug 25, 2011, 09:33 AM
Where is the lift?
cptsnoopy's Avatar
Thanks Paul, great writeup!

Charlie
Aug 25, 2011, 09:35 AM
Launch low. Fly high ;)
Hanger Rash's Avatar
Quote:
Originally Posted by RCPC
I just read through the posts and feel sorry that my high school allowed me to gradumatate
Paul
Paul - I shouldn't have graduated either. I had no problem in English class. I didn't learn much, but I had no problem.

When I was in high school in Hawaii one year the first day of English class I was sitting in the back with all the blalas (tough guys; but I wasn’t one of them. I was a surfer). No joke, the teacher said, ‘ If all you kolohe go come my class, I goin teach you good kine eng lish. So I raised my hand and said, “ Is kolohe eng lish?” “Oh”, he said, “What’s anada word for Kolohe?” I said, “rascal.” “OK”, he said, If all you rascal go come my class, I goen teach you good kine eng lish."

I like pigeon English. I think it is eloquent.
Aug 25, 2011, 10:02 AM
Chuck 'Em and Chase 'Em
Fly2High's Avatar
Can carbon tow, glass fiber or cotton thread be used to wrap the blade?

very nice tutorial. Came just in time.....

Frank
Aug 25, 2011, 12:25 PM
Limbo with 30,000V...
J_Arner's Avatar
Quote:
Originally Posted by Fly2High
Can carbon tow, glass fiber or cotton thread be used to wrap the blade?

very nice tutorial. Came just in time.....

Frank
I've used Spiderwire and Dandy-line (spectra line). I'm not sure glass fiber or carbon would work, since you want something that isn't going to crack under the stresses we put on these blades. Cotton may work but I like the assurance of the braided spectra lines.


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