RV-9A plexi glass canopy frame update with vans

[ron sterba]

RV9a canopy story of 7-7-2011 thread I stated my feelings about the canopy frame. Its a twist and pull and turn type of job.
This past weekend I attended the Arlington Washington 4 day fly-in. I always enjoy volunteering there. Its so rewarding and you get to check out a-lot of fine aircraft.
As I said, I would bring up the subject to VANS Aircraft President Scott Risan. I asked Scott if I could use his name here and he allowed it. Nice Guy!
Well what I brought to his attention was old school bending of the 4130 square steel side bow canopy frames. Many builders have struggled with bending the same curve of the fuselage to the side frame bow. I explained to Scott that us old guys can hardly find the strength and technique to do that bending. I did meet one gentleman whom shall remain nameless threw his first canopy frame away because of over bending and bought a second one. Scott said that many builds of the fuselage are different. I can agree with that and that bending to fit was a good solution for the canopy frame. A more precise fitting canopy would be better I said.
I also got more that I expected by getting into a conversation with a builder in the Seattle area about our builds. The Seattle gent explained about the 4130 steel alloy being made up of crystals ( the small particles that make up the steel alloy) . There are layers of the alloy crystals and when exposed to heat will change shape and the compatibility with the other alloy crystals in that piece of metal. Change is controlled by heat in the manufacturing process as well as the cool down when welding is performed on the metals and is of the up-most importance. He recommended a oil bath cool down and not a water or air cool down.
I'am talking about the RV9A in my case. Well its not a fighter jet but all in all its unique airplane. My main point in talking to Scott was about perfecting the bend in the canopy frame square side bow to the exact curvature as the Quick build kit fuselage prior to the welding of the canopy frame. In the educational dialog with Scott was consideration for VANS providing the vendor with a more accurate jig with consideration to cooling after welding to bring the frame to close tolerances. Bending round tubing is more predictable than trying to bend a square tube because the collapsing side of the square tube that has more resistance. Trying to bend square tubing AFTER its been welded can change the internal make-up of the weld at the molten layers in the alloy.

I asked Scott to look into a more accurate bend and have a little more respect for the slider folks. Now I do want to say that Scott did have his own problems with his canopy and it was inventive idea that corrected his build. I felt that Scott would rekindle curriculum on the canopy frame plans.

NOW change the subject. You got to see VANS factory RV-12 inside the cockpit. WOW!

Ron in Oregon

[David Paule]

Ron, I'm not an expert in metal heat treatment, but I think that the air cooling gives a normalized part for 4130, while the oil bath cooling gives something closer to an annealed part. The normalized case is considerably stronger than annealed. Here's an extract from MIL-HDBK-5H, page 2-11 (this is the reference book for aerospace stress analysts and designers for the mechanical properties of metals):

"In general, the annealed condition is achieved by heating to a suitable temperature and holding for a specified period of time. Annealing generally softens the material, producing the lowest mechanical properties. The normalized condition is achieved by holding to a slightly higher temperature than annealing, but for a shorter period of time. The purpose of normalizing varies depending on the desired properties; it can be used to increase or decrease mechanical properties. The quenched and tempered condition.... ....is used to produce the highest mechanical properties while providing relatively high toughness."

At any rate, the as-welded and air-cooled strength has long been known and counted on for the structure of welded 4130 parts for aircraft.

Dave