B095

MAKE: Dragonfly - Rotor - Blade - 8-H-12 Aluminum

Conversation with Robert Pegg of PAM Group Sept. 8, 1998

There is a 2# tip weight for 8-H-12 blade.

The balance is at 27% on 8-H-12 blades.

Vortech nose weight takes balance to only 30-31%. Some brass [or something heavier and smaller – my idea] should be inserted in front of tip weight. [my idea – make the "grit", which will be added to the leading edge for wear protection, xxxx uranium.

He had not heard of anyone using the 8-H-12 for a helicopter except temporarily by Ben Showers. Ben Showers added weight to the pitch horn. He saw no reason why not except that the 8-H-12 is lighter than the 0012 and thus will have less structural strength. He said that he thought the 8-H-12 disk loading should be limited to 2# per sq.ft.

Conversation with Marty Hollmann of Aircraft Designs Inc. Nov. 10, 1998

He said that the 8-H-12 is an excellent blade, particularly at low blade loading. He said to add 1# at each tip to reduce the coning and improve autorotation. (my comment – Maybee for the 4.75" chord blade the weight should be a little less?)

Notes Related to Bonding of Leading Edge Spar into Airfoil:

Posts from PRA:

Date: March 01, 2000 12:59 AM

Author: CA BEATY (cabeaty@worldnet.att.net)

Subject: Blade Glue

The original 269 blades had a phenolic wedge at the trailing edge and were bonded with a one part, purple epoxy film cured at 250 degrees F. It is still available from Hysol but they have a minimum order of several hundred dollars. The original blades also had rivets every 3 inches or so.

Later model blades, 300C series had an aluminum sheet metal Vee at the trailing edge and no rivets.

The only 2-part, room temperature curing epoxy with any chance of producing a fair bond is Hysol EA-9430, available from Aircraft Spruce. A structural bond to aluminum requires cleaning in caustic soda followed by a chromic acid etch. Swabbing down with lacquer thinner is an exercise in futility.

Date: March 03, 2000 10:47 AM

Author: CA BEATY (cabeaty@worldnet.att.net)

Subject: Bonding

I don't understand the physics of an epoxy-aluminum bond , Herm. I do know that with proper surface preparation, when the bonded pieces are pulled apart, the failure is adhesive rather than adhesion; that is, the epoxy splits apart, leaving a layer attached to both surfaces; at least with the heat curing films and Hysol 9430.

Surface prep consists of cleaning in caustic soda followed by treatment in chromic acid or phosphoric acid anodizing. Cleaning with a solvent never seems to help.

Date: March 02, 2000 08:30 PM

Author: Ronald Herron (rotopup@aol.com)

Subject: Blade glue

Chuck, My blades have the phenolic faying surface and regular driven rivets. I realize that the epoxy (JB Weld) is merely "leaching" to the metal surface but it sure seems to hold well. I've used that stuff on eveything imaginable. I filled in nicks the size of half dollars on a wooden prop one time to get it in a "limp home" mode. It worked so good that we continued to use the prop for nearly a year before we were able to get Sensenich to build us a new one.

Date: March 03, 2000 07:15 AM

Author: Herman-J. Wimmer (Hermie-Joe@msn.com)

Subject: Purple goo

Are you saying that the special goo, such as was used by Grumman American, actually forms a molecular bond to the aluminum? I always thought (but never knew for sure) that it was all done by "tooth adhesion".

Date: March 03, 2000 10:47 AM

Author: CA BEATY (cabeaty@worldnet.att.net)

Subject: Bonding

Surface prep consists of cleaning in caustic soda followed by treatment in chromic acid or phosphoric acid anodizing. Cleaning with a solvent never seems to help.

Date: March 03, 2000 12:18 PM

Author: Larry Goodhind (larry@ihtmedia.com)

Subject: surface prep for skins

Horizontal tail: Would it be good for me to use a brush on application of commercial metal prep 79 (phosphoric) followed by alodine 1201 (chromic) on the inside surface of the horizontal tail skins before I glue it over the ribs and span tube?

Would hot-wired 1/2" styrofoam ribs on 2" centers be an adequate replacement for the epoxy/cardboard ones? It looks like the span tube carries the load and it would be easier for me to cut out the 0012 sections cleanly (no big belt sander or bandsaw) ... do you know if 9430 eats styrofoam?

Date: March 03, 2000 03:23 PM

Author: CA BEATY (cabeaty@worldnet.att.net)

Subject: Bonding

Metal Prep plus Alodyne should work fine Larry, if you take enough time to make sure the surface is converted, perhaps 20 minutes.

Hysol 9430 won't eat styrofoam but the styrofoam eats a lot of epoxy by soaking it in all the pores.

For ribs, corrugated box board is several orders of magnitude stronger than styrofoam. An aluminum sheet metal template, a utility knife and a package of blades should, with a bit of sweat, produce all the ribs you need. Drill several nail holes through the template and nail template plus rib blank to your cutting board. Dip the rib blanks in diluted epoxy and allow to cure before cutting out. That way, you have a fresh surface for bonding to the skins.

Date: March 03, 2000 12:25 PM

Author: Herman-J. Wimmer (Hermie-Joe@msn.com)

Subject: Solvent clean

Right! Solvent cleaning doesn't work because a fine layer of aluminum oxide is formed on the surface within hours of cleaning. Nothing adheres well to the oxide. The caustic soda removes the oxide. The etch replaces the quickly forming oxide layer with something that (paint is what I'm thinking of) the material will adhere to and not continue to oxidize after the coating is applied. The continuing oxidation (I think the word is filiform corrosion) is what pops paint back off again. The oxide is also harder, tougher and melts at higher temps than the aluminum. I thought that you were saying that something other than mechanical bonding was going on with the super $100.00 a quart

Date: March 05, 2000 08:35 PM

Author: Daniel Holmes (dholmes1@columbus.rr.com)

Subject: More glue

I do composite repair work on DC-8 bi-pass ducts, and for most of our repairs, we use EA 934 from Hysol. It is a 2 part epoxy which is grey in color and has the consistency of JB Weld. Granted, a Bi-duct isn't a rotor blade, but I think it's a little better suited for "cold bond" ( no heat blankets or an autoclave)repairs than the purple stuff. Neither product should damage styrofoam, but I would use Last-a-foam insted. It's higher quality stuff and has more compressive strength. Good luck! Dan

Date: March 05, 2000 10:18 PM

Author: Doug Schwochert (abheli@mia.net)

Subject: adheasives

I have done a little testing. I have had the best results using Araldite 2013 epoxy I sanded the surfaces with a rotary scotch brite pad on a die grinder then washed it with a phosporic acid and a 30 min. soak in a chromatic etch. both of these chemicals are available from automotive paint stores they are used to prep aluminum for painting.I did 3 tests one on plain alclad aluminum with no prep at all peeled right off with little effort. The next was the sanded surface this one peeled off but not as easy . the 3rd was the sanded and etched I was able to pull the 2 pieces apart but this time it was the epoxy that failed the epoxy stayed adheared to both halves of the aluminum. I tried several different types of epoxies with about the same results. the surface prep is the most important step in bonding aluminum.

Doug Schwochert

Date: March 05, 2000 11:21 PM

Author: Robert W. Rominger (rwrominger@yahoo.com)

Subject: adhesives: glue expansion rate vs aluminum

Sounds like you got a strong bond, but how does the epoxy joint hold up with the relatively large expansion/contraction rates of aluminum as it heats and cools?

Date: March 05, 2000 11:49 PM

Author: CA BEATY (cabeaty@worldnet.att.net)

Subject: Glue

All the epoxies intended for structural bonding of aluminum, Bob are modified by the addition of something to give flexibility and improve peel strength. Some are modified by the addition of Nylon; others by the addition of nitrile rubber. The optimum thickness at the bond line is normally something on the order of .005" so the glue will follow the aluminum. There is a problem when bonding dissimilar substrates having differential expansions.

Date: 16-Nov-00 08:09
Author: Mike Schallmann (rotors@uswest.net)
Subject: I am simply amazed ...

...at some of the misinformation floating around about Vortech Blades! Ive been flying these blades for about three years and I have a friend who has been flying them for a lot longer than that. These are very good blades -they are well made and easily assembled and balanced. The average homebuilder can assemble all of the blade components in less than one hour per blade with ordinary hand tools.. careful measuring and a drill press would make joining these to you hub bar easier. An OVEN is NOT necessary to assemble these blades.

The Blades come in 13 ft long sections so you will have to cut them to length . Cut the blade extrusions -- NOT the noseweight extrusions at this time.. once this is done clean up the end and remove ALL burrs. Lay the blade on a raised flat surface or sawhorses. Prepare the noseweight extrusion by carefully examining it and drawfiling any nicks or dings that occurred during shipping or handling --you dont want any "high spots" that will grab and gall during final assembly. Clean the inside of the blade nosecavity with a solvent as well as the outside of the noseweight extrusion --this removes all contaminants and provides a good bonding surface.. Align the noseweight extrusion with the cavity in the blade. Using a good grade of epoxy coat the first foot of the nose extrusion and gently slide it into the cavity ---aligning it carefully, continue to coat the extrusion as you slide it into the cavity. The extrusion will slide easily into the cavity as the epoxy acts as a lubricant. Once the noseweight is inside of the cavity and flush with one end --LEAVE IT ALONE and let it cure. Complete the second blade. This whole procedure takes less than two hours (including cleanup). Let the blades cure overnight . Using a hacksaw and file cut off and clean up the protruding portion of the noseweight extrusion.You now have a complete set blade blanks that are(almost) ready to mate to your hub bar. Additional bonding of the noseweight extrusion by mechanical mean is recommended. If you are using a McCutchen Hub Bar the addition of two 5/16 bolts passing through the hub bar/blade/nose weight complete the task. If you are using another style of hub bar make sure that you add two additional bolts to further lock the noseweight in place. Balancing the blades is relatively easy as the extrusions have consistent wall thickness and the weight between the blades is nearly identical. The first set of blades that I had required the addition of several washers added to one blade. The second set of blades required absolutely no balancing adjustments. They came out perfect -- all you have to do now is install the end caps and you are FINISHED!!

Note: The Vortech blades are aluminum 6063-T6

Date: 16-Nov-00 16:05
Author: Ken Rehler (rehler@stic.net)

A very important quality (not listed) is "metal fatigue". 6063 will fatigue quickly! 6061-T6 will not.

I used 6063 one a few items (wheel pants bracket, muffler bracket, beace for auxillary fuel tanks) several years ago and every one of them failed due to vibration. After being replaced with 6061-T6 (same size parts) no problems occured.

Last Revised: May 4, 2003