View Full Version : A lesson learned
03-23-2004, 06:41 PM
Just started my Dominator plans built and almost just finished the Keel and Mast.
I just found out almost by accident the 6061 T6 2"*2" Aluminum Tubing that I purchased was really 6063 T52. There was no markings on the metal and something stuck in my mind that I better make sure of this. I called the supplier and asked the manager to verify and provide a spec sheet for my files. Low and behold, wrong stuff.
My Aircraft Spruce catalog lists this as a harder and more brittle Architectural type alloy for Windows, Doors and trim items. Not the thing for construction of a Gyroplane!
Needless to say I have learned a very important lesson here early on. Identify and verify your materials!
It's a good idea to ask for a certificate of origin (C of A) for critical parts. Aircraft Spruce charges $25 for a certificate, and Wicks $5.
BTW - just making sure you are buying 2 1x2" tubings for your double mast...
03-24-2004, 06:16 AM
I had called RFD / Dominator to ask the question about using 2 - 1*2s for the Mast. Ernie had stepped out but I talked to Dick DeGraw about it. He recommended that I use the 1- 2*2 Mast for the following reason.
During the flight phase the Rotor system undergoes changing drag created by the turning rotor. When the rotor is parallel to the line of flight, less drag. When perpendicular to the line of flight, the most drag. This changing drag cycle happens 4 times per one Rotor revolution.This drag cycle creates 4 vibrations that is then transmitted to the mast.
The 2-1*2 mast will be a stiffer mast and will transmit the vibrations to the rest of the airframe. By staying with a one piece 2*2 mast it will flex and the vibrations will stay more localized to the rotor.
Strenghwise the one piece mast is more that adequate and as an example Dick referred to Steve McGowans two place trainer. He is utilizing the 2*2 one piece mast system and hasn't had any problems.
I am sure the 2x2 mast is strong enough, at least on paper. The problem is that you have no redundancy. People started using double masts after a few accidents in which the mast broke. The fact that the mast is flexing back and forth at 2 per rev (about 10 times per second) is a good enough reason for me to want redundancy.
Although the 2x2 is strong enough on the paper, manufacturing flaws, hidden scratches, etc, can weaken it. Personally, I would go with a double mast and, to reduce your 2 per rev shake you can install RFD's flexible rotor head, or whatever they call it.
03-24-2004, 08:40 AM
Benson originally used a 2 inch round tube. I use a single 2x2 tube with a round tube inside for redundancy.
Using 2~ 1x2s came about from Air Command when some ships crashed and snapped the mast off. The actual problem was improperly placed and drilled holes.
03-24-2004, 12:19 PM
The two 1x2 mast long, long predates Air Command. I recall it being announced as a "new" product by Bensen in the late 60's. The stated reason for its use at the time had nothing to do with in-flight strength. Rather, the idea was that it was less likely to snap off in a rollover, and thus was a more reliable roll bar. Bensen went on to point out that he had recently beefed up the U-block of his gimbal head so that IT was unlikely to shear in a blade strike. Without such a weak link, the mast was MORE likely to shear. People have died from broken necks upon rollover after a hard blade strike in which the mast broke at the seat back.
Using a clamp-on mount instead of drilled holes at the seat back adds more strength to the mast than doubling the tubes. However, I like the idea of having two separate load paths. Extrusions are not the very finest form of aluminum. They can have flaws.
On a small gyro, the double 1x2 mast provides enough flexibility to minimize the problem Dick DeGraw mentioned. Ernie's "slider" head is a more elegant and complete solution, however.
03-24-2004, 12:30 PM
Thanks Doug. I stand corrected. :)
03-24-2004, 06:17 PM
Thanks for all the input Guys.
I will be going with the (2) piece 1*2 stronger Mast.
Imperfect tubing and Redundant Load path makes alot of sense.
03-24-2004, 06:45 PM
Bill, did Spruce send you the wrong material or did you just use the Spruce catalog to get a description of 6063 t52 aluminum? If not Spruce, who sold you the wrong stuff?
03-25-2004, 05:54 AM
The screw up was the fault of my local supplier (DBQ).
Its still kind of unnerving that I specifically asked about 6061 T6 several times before the pickup and then was sold the 6063 T52. I also found out later they never have stocked 6061 T6. :o
I just used the Spruce Catalog as a reference tool.
03-25-2004, 08:48 AM
Bill and all: 2x2 and 1x2 tubing are not normally stocked by the aluminum industry in 6061-T6. If you order these sizes from a commercial aluminum company, you're almost certain to get 6063-T5. It's the standard for these shapes. It's used to frame up supermarket doors and the like. I've found that, even if you specify 6061-T6 on the phone, you're likely to get 6063-T5.
During the years of the AEROTEC gyro-supply business, I found that I had to order custom runs of these sizes to get a reliable supply of 6061-T6. This meant ordering at least a half-ton at a time. The larger aircraft catalog suppliers -- Wicks, Aircraft Spruce and Dillsburg -- will usually send you the correct alloy, with manufacturer's markings. Sometimes, the material is pretty badly scratched, however. You can try to get them to commit to sending you clean stock.
03-26-2004, 08:25 AM
Just had that on the phone with wicks, the operator swore they had 6061 but even the online catalog is keyed to indicate 6063. So I knew she was just telling me what I wanted to hear.
03-26-2004, 09:00 AM
The Wicks online catalog says 6061-T6 for 1 x 2 rect tubing:
or for 2 x 2 sq tubing:
03-26-2004, 09:03 AM
Isn't there some kind of acid test you can do to determine the alloy??
The tube should have 6061-T6 stamped all over it. If it doesn't, send it back or ask for a certificate. Certificate of origin states the name of the part and where it came from. In the US all aviation/aerospace hardware must, by law, be traceable back to a manufacturer and batch number.
03-26-2004, 05:56 PM
The problem with the 1x2 paired tubes is the inflexibility, as Doug and others have said.
two reeds are vibrating at the same frequency, they are both accumulating the same amount of fatigue. This isn't redundancy. You need two different load
paths with different cross-sections and different fatique properties.
2x2 has plenty of redundancy...it has four sides and if properly capped at the top all four sides carry the load.
Clamp to it instead of drilling and it will not fail.
For redundancy, I use chromoly tube inside the aluminum and end up with a stronger and lighter mast than with 2 1x2's.
03-26-2004, 06:59 PM
How would you construct this Mast?
What size OD and wall thickness of Chromoly tubing would you put in a 2*2 Mast?
How would you cap the ends?
How would you drill to connect the Rotor and the Keel Plates?
03-26-2004, 11:05 PM
Down under we use 2" X 2 1/2" 6061-T6 for our masts and keels.
03-27-2004, 08:27 AM
I like your thought Paul more is better..
03-29-2004, 03:18 PM
More isn't always better. An aircraft must be light and STRONG ENOUGH. Excessive strength means excessive weight. Really clever design gets the maximum strength for a given weight out of each piece of material. OTOH, material is used wastefully and inefficiently when we do things like drilling holes that take away half the (undrilled) material's strength.
Usually, the labor goes up as the part becomes more clever, of course.
04-04-2004, 08:15 PM
You were right, local suppliers don't commonly have 6061 T6 and cann't get it.
I again specifically ordered 6061 T6 tubing from a second supplier, (RFD)
and they assured me they could get it. Guess what showed up? 6063.
Looks like I'm wasting my time on local sources, I better go to Spruce or Wicks.
04-05-2004, 08:02 PM
6061 T6 1x2 and 2x2 extruded can be had from Dillsburg Supply in Dillsburg, PA. They are not on the web but look them up in the yellowbook. They are excellent folks to work with and have most any aviation metals you could possibly need.
04-07-2004, 03:03 AM
What would be better 6061t6 or I think it's 2024? for strut attach fittings. I'm going to have new ones machined for the wing struts on my plane making them a little longer to put some dihedral in it.
04-07-2004, 03:26 AM
What are wings? Are you in the right place?
04-07-2004, 03:30 AM
Yeah Yeah I know. Used to have a gyro. Sold it built a plane. Sorry I did. Will be building a new one. But in the mean time.....
04-21-2004, 05:35 PM
When we last left our intrepid Dominator builder, he had just returned the 6063 Aluminum tubing from (RFD) and was looking for good source for 6061 T6.
Wickes Aircraft was chosen and a order was called in for their best material. Received the 6061 T6 in about a week and was stamped as such, but the tubing was quite nicked and scratched. A phone call was made and they offered to take it back or offered a 10% reduction in price. It was sent it back.
Dillsburg Metal was next called and the gentlemen informed our budding Gyronaut that his 6061 T6 was fresh from the factory and in impeccable condition. An order was placed and two weeks passed. The tubing was delivered and inspected and was indeed great looking stuff. But no where is it stamped 6061 T6. So whats our frazzled flyboy to do?
04-21-2004, 08:15 PM
Bill, The 6061 material Dillsburg sells is 6061. I bought my material from Charles years ago that came to me without markings. I called about this & he told me he has to buy a large run of 6061 tubing from the mill at one time like Doug stated earlier. He will send you certification on the material if you call & ask him. I have never had any problems with anything from Dillsburg Aeroplane Works!
04-22-2004, 02:22 PM
Thanks for your reply, I will call Dillsburg and request the certification.
Whew! For a while there I sure was keeping the shippers in business.
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