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Oct 05, 2011, 01:03 AM
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Curved + T Throwing Blade by C Robinson


I just received a handful of curved throwing blades by Craig Robinson. His lovely tooling is shown here.

I've seen a few curved blades out here in the southwest, usually accompanied with an admonition from their owners to wrap the blades in Kevlar tow or thread.

This latest batch by Craig came with a set of instructions that directed one to shape the blade, and a personal reply from Craig, suggesting that I will not need to wrap any of the latest batch.

Comparing the original photo in the above link with what I received, these curved T blades seem a bit beefier.

From the photos you can see a blade as delivered, and another blade with both my rough and final sanding. Hopefully I am following the directions literally and within Craig's intent.

1) I rounded the leading edges but tapered to no rounding at the root.

2) I was reluctant to thin these much, but I decided to thin a bit aggressively at the trailing edge. As the following profile photos show, the thinning abates to nothing near the root, and some of the mid-chord is left unthinned.

I'm seeking an airfoil shape, as much as possible. Unless Craig pops up here and gives me a verbal spanking for abusing his beautiful work , I'll install it in an existing wing.
Last edited by ASK; Oct 05, 2011 at 09:55 AM.
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Oct 05, 2011, 01:04 AM
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Sanding, prep


First I rounded the leading edge of the blade on a belt sander, very gently and carefully. Then I thinned from about 50% of chord back to the trailing edge.

To sand the inside of the curves I used a round 9/16" dowel with coarse sandpaper attached with 3M77.

Then did a little detail work with a coarse sanding stick (paint stick covered with 3M77-bonded sandpaper).

I wet sanded the altered surfaces with progessive grits of paper, starting with 100 and ending with 2000.
Last edited by ASK; Oct 05, 2011 at 10:41 AM.
Oct 05, 2011, 01:04 AM
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Installation


The blade installation epoxy is curing as of this post, mixed with colloidal silica.
I left the tongue at the default length. It could probably be cut down 1/4 to 1/2 of the original length, particularly if it is pinned. There is so much surface area on this, I doubt I'll bother pinning it. Pinning would be just drilling two 1/16" / 1.5mm diameter holes, and bonding pultruded rod through the skins and control horn. Cut it close, sand to skin surface afterwards.

After the primary cure, I think there will be some modest fill and fairing to do, particularly on the tip gap area where I returned part of the original wing tip.

I'm thinking I can do a brand new installation better than this "remove and replace", and I can probably do it with half the epoxy weight.
Last edited by ASK; Oct 05, 2011 at 12:42 PM.
Oct 05, 2011, 07:24 AM
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I came onto one of these, and did exactly as you have done. It has proven to be stiff and so far no issues. I am sure mine is of the earlier variety, but I have not yet wrapped it.

I have one in a Blaster 3 wing. My other Blaster 3 is still functioning on the originally installed blade (which I got from you!). I put the new, curved blade in when the wing surface failed around the blade.

See you this weekend, we can compare.

Yours, Greg
Oct 05, 2011, 09:09 AM
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It's backwards for me..... My blades have less curve and I put the concave side towards myself. I tend to hook my plane with blades that grab my fingers that well.

Paul
Oct 05, 2011, 09:16 AM
Oleg Golovidov
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Aradhana, thanks for the pics.

I am curious about the installed weight. If you or anybody else weighed your wing before and after installing a T-blade, I would love to hear the actual weights.

My personal experience (rather limited I must say, only 2-3 installations) was such that I ended up using a lot of epoxy to embed the tongue into the wing. I did not weigh the wings myself before and after but I am afraid it can easily add a few extra grams to the wing tip (as compared to a regular blade install).
Oct 05, 2011, 09:27 AM
usaf3kteam
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Quote:
Originally Posted by olgol
Aradhana, thanks for the pics.

I am curious about the installed weight. If you or anybody else weighed your wing before and after installing a T-blade, I would love to hear the actual weights.

My personal experience (rather limited I must say, only 2-3 installations) was such that I ended up using a lot of epoxy to embed the tongue into the wing. I did not weigh the wings myself before and after but I am afraid it can easily add a few extra grams to the wing tip (as compared to a regular blade install).
Oleg it is with string 2 grams heaver than stock peg and has been no problem for me in the Stobel wings. I do however thin tapper at the end that goes into the wing and never try to install flush to the tip. I install them where the stock tip would normally be installed. The wing tip on most DLGs is much to thin to get the tip flush. When installing where stock peg goes that is thick enough to make great fit for t peg. Will show you at your contest.
Oct 05, 2011, 09:49 AM
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I had made a handful that actually had two tongues so they went on the outside of the wing and bonded to skin and or spar.

Paul
Oct 05, 2011, 10:10 AM
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Originally Posted by olgol
Aradhana, thanks for the pics.

I am curious about the installed weight. If you or anybody else weighed your wing before and after installing a T-blade, I would love to hear the actual weights.

My personal experience (rather limited I must say, only 2-3 installations) was such that I ended up using a lot of epoxy to embed the tongue into the wing. I did not weigh the wings myself before and after but I am afraid it can easily add a few extra grams to the wing tip (as compared to a regular blade install).
The blade itself is 3.4 grams raw. I didn't weight it after sanding, but I didn't take much, this time. Maybe it could be brought down to 2.5-2.8 grams? Maybe lower still?

Working backwards from the installation, it looks like 2.2 to 2.5 grams of epoxy on the install. A lot! And I didn't dare use a lightening thickener or filler, only colloidal silica to increase hardness & viscosity.

If I like the throw from these blades, I will reduce weight by shortening the tongue, and whatever else I dare remove by additional sanding.
Last edited by ASK; Oct 06, 2011 at 12:11 AM.
Oct 05, 2011, 10:17 AM
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Originally Posted by The_Builder
I had made a handful that actually had two tongues so they went on the outside of the wing and bonded to skin and or spar.

Paul
At contests this season I've seen this type of blade on Blasters come off clean (not break off) a couple times. This design has a short tongue length, so perhaps they could be pinned?
Oct 05, 2011, 10:25 AM
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Craig's straight T blade looks considerably lighter. No fancy curve, but again they seem to be beautiful parts. I bet Kevin Caldwell's straight T blades are nice, if he's still offering them. Who else is out there that I'm not aware of?

In terms of understanding the benefits, I'm disregarding the weight for now. The feel of these blades, the way they capture my fingers, is intriguing.

I want to know what it's like to throw with it! ??

More Weight Comparison
Our own straight blade through the wing in our solid core LightHawk III, LightSpeed III, Blade, or Razor, adds 1.2-1.3 grams total. I have two more glider types in the queue, and I expect the same result.

In the same case, if one digs out foam to make a 1/2" round hard point around the slice, it goes up to maybe 2 grams total. The rest of the reinforcement is built into the wing, in several layers of Kevlar and carbon--no patches.

George,
After installing one of these, are you re-balancing your wings laterally?
Last edited by ASK; Oct 05, 2011 at 10:36 AM.
Oct 05, 2011, 10:33 AM
usaf3kteam
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Quote:
Originally Posted by ASK
The blade itself is 3.4 grams raw. I didn't weight it after sanding, but I didn't take much, this time. Maybe it could be brought down to 2.5-2.8 grams?

Working backwards from the installation, it looks like 2.2 to 2.5 grams of epoxy on the install. A lot! And I didn't dare use a lightening thickener or filler, only colloidal silica (increases hardness & viscosity).

If I like the throw from these blades, I will reduce weight by shortening the tongue, and whatever else I dare remove by additional sanding.

George, after installing one of these, are you balancing your wings laterally?
No I do not balance the wing and the plane flies fine. I have been flying his blades for a year and I like them. However the Concept I fly with stock peg and the wing is strong enough I don't need T peg. When I was flying the Stobels the wing tips would brake off and that is why I used the T blade as recommended by Paul Anderson and no more broken tips. However the Concept wing is balanced with stock peg in it. Craig makes a great product and I like it.
Oct 05, 2011, 10:34 AM
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Oct 05, 2011, 12:37 PM
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Finishing


So here is the mounted blade, with new thickened epoxy smoothing and fairing the installation.

A hefty amount of the bonding epoxy splooged out into the hinge gap, so I carefully removed and sanded that while doing the rest of the prep for fairing it out.

After curing and sanding for final smoothing, I'll fly it in the next few days, and probably fly with it Sunday in an eight round contest.

I want to improve my tip catch turnarounds. I'll report next week if I think having a curved blade is helping that. Otherwise, I've been pretty happy with straight blades.
Oct 05, 2011, 05:53 PM
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Looks great


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