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Topics - propblade

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Hangar Flying / Aeropoxy Questions

« on: July 18, 2013, 05:48:47 PM »

I started using Aeropoxy for my project. I found that using the West System epoxy mini-pump and switching the pump bodies on the two hardener pumps (pulling the whole mechanism out of the cap, then switching caps and re-installing the pump body), then using the one with the larger cap results in a 3:1 ratio by volume. I did some practice layups with this setup, but noticed the cure time to be a lot longer than with, say, West system. Once cured, it still had a tacky feel to it and didn't feel as rigid as a similar layup with West. So, I tried another layup, this time mixing by weight (100:27), with the same results. I read on the company's website that this is likely carbamate, since my shop's RH is over 65%. Their recommendation is to peel-ply everything. I did a practice layup with peel ply and sure enough, it didn't have the tacky feeling. After about a week, all of my practice layups seem to have cured to a rigidity similar to West. Also, the description sheet says it should be a light amber, but when mixed it is as clear as West.

My questions, then, are, is this normal? (longer cure time, carbamating, coloration) Or might I be doing somethng wrong? What is the nominal cure time for Aeropoxy? My shop is at 78F and 60-70% RH.

All that being said, has anyone else run into this issue (carbamate, long cure times) with Aeropoxy? How does it compare to EZ-poxy? Would it be worth it to stick with Aeropoxy and peel-ply everything (other than the extra cost of the peel ply) or switch to another system?

(First 2 paragraphs cc'd to PTM-W) (Attempted to CC, but got an error from the submission form. Will try again later)

Hangar Flying / Starting work on a partially completed LGEZ

« on: July 01, 2013, 09:42:11 AM »

After years of hemming and hawing, reading and researching, I came across a Long project from a friend of a friend; he has built one and is flying it, then started a second with a partner, but the partner backed out. Anyway, I got the project home and did a survey of the project, comparing to the plans and my best judgment on the workmanship. Everything seems in order and decent construction. It appears that the bulkheads and fuselage sides were done using Aeropoxy (guessed because of the red tint), and the floor done with West System (since it appears uncolored). The project is a few years old, so the details from memory are fuzzy. All layups appear to be on the correct schedule.

My only issue that I found is that the F28 bulkhead was not installed prior to cutting the canard shelf. The top longeron and doubler were cut flush with each other. The measurements I took show the cut to be at 6.4" aft of the forward face of F22. A 0.5" thickness F28 would bring the dimension to the correct 5.9". My concern is this, though: the F28 would have to be bonded to the flush faces of the top longeron and doubler; it would not be notched to fit under the top longeron. Would there be any problem with this? I realize that after shaping the top of the fuselage, there is not much of the top longeron left in that notch, and the doubler is where the canard alignment pins fit, so flush bonding F28 as I described should be ok. Or, should I cut back the longeron 10-12", splice in a new section and install F28 per plans? As I see it, F28 is just to contour the nose into the canopy, there is no critical supporting structure relying on F28, correct?

Also, the distance between both longeron ends is about 0.6" wider than what F28 would be. Should I try to draw the longeron ends together while F28 cures in place, or would making F28 wider to fit be acceptable, so long as I translate that increased dimension to the canard for the alignment pins?

(unable to attach pics at this time; will add when able)

Hangar Flying / Using S-glass roving as opposed to flagged UNI for canard cap?

« on: February 08, 2013, 10:21:26 PM »

Any thoughts on substituting S-glass yarn for the flagged UNI spar cap for a Long EZ? Pro's/con's, etc. I read a thread about substituting kevlar as skins and winglet attaching for a VEZ and got a lot of info there, mostly along the lines of, "don't substitute materials, the designer knew what they were doing." My reason for asking comes from reading the construction manual; the wing spar cap is S-glass yarn, while the canard is the flagged UNI. Second reason, I took a Sport-Air workshop, and for the canard/airfoil section we assembled in class, we used S-glass for the spar cap. Granted, this is a big deviation from the Rutan plans, but I found the S-glass easier to lay than the flagging I tried at home. So, again, my question would be yea or nay? Or, perhaps I already answered my own question...