I just got back from a week at First Light Aviation Group in Livermore, California with Rick Lindstrom & Rich Vetterli. I went down to help them with the Upgrades on their Corvair powered CH601's. We had a great time and made excellent progress on both airplanes.
Rick Lindstrom will bring his airplane up to our booth at the Arlington Fly-in this year July 7th- 11th, so feel free to stop by and see his bird and talk to us about the upgrades.
For those of you who may be looking for help with the 601 upgrades, please feel free to contact me:
I will be posting pictures & helpful hints that might be of use to those in the process of upgrading or gearing up to upgrade their Ch-601xl's.
Please be advised that this is free advice and therefore comes with a money back guarantee and is worth exactly what you paid for it. :)
Some of this information might not be applicable to your specific situation, so disregard anything that doesn't apply.
Final caveat: My opinion is by no means the last word in aircraft repair!
I hope this helps.
First, we should Drill out some rivets!
Most of us have had to drill out an Avex rivet now and then during our build and most of us are fairly proficient at this.
But I have found some neat tricks that make this much easier and minimize enlarging the hole. One cool trick is to punch the steel mandrel down a bit with an automatic center punch. This lowers the mandrel so it doesn't deflect the drill bit. It doesn't take much and drilling the head off is a snap. Once the head is removed the pieces will separate and either the tail will fall out or it will need to be pulled off later. I use a pair of snips that I have ground flush and this works fairly well.
I heard of another trick just today that is certainly worth trying, and that is to modify your automatic center punch in to a drift punch by grinding the tip into a long straight punch rather than its original tapered shape. Then with a couple of whacks the mandrel is completely punched out. This will make drilling out the Avex even easier and will produce a clean hole much more reliably. WIsh I could give credit to whoever thought of this first (it's not my idea) but it came to me anonymously from a friend who saw it on the internet. :) But I thought it was worth mentioning.
Once the wing skins are removed we get to tackle what most people sweat the most over: Removing SOLID RIVETS.
This isn't really all that difficult and I have found a few tricks that make it quite simple. I first thought of this all on my own, only to find that I wasn't the fist to think of it and then found out later that not only has it been done this way before but this is the way it has been done probably longer than I have been alive! (If I only had a dime for every time this has happened to me.....Well, so much for the process patent! :) The real keys to this process are patience & precision.
First, I center punch the head of the rivet, and they already have a dimple in the center so this is easy. Next, I drill out the body of the rivet with a #20 drill bit leaving the shop head (bucktail) intact. (don't drill all the way through it!)
The head of the rivet will stay on for now. Next comes the (not so) top secret weapon
This is simply an air hammer punch that has been ground down into a drift punch that is slightly smaller than the # 20 drill bit. Now with a C Clamp holding the pieces together or a bucking bar to support the part use the air hammer drift punch and drive out the rivet. First the head will pop off and this stays on our punch as a cushion to help protect the part from the punch bottoming out. The rivet should easily come out, if not literally shoot across the shop. Be careful and gentle so as not to damage the parts, if the rivet doesn't come right out, just drill a little deeper. Drilling through the center of the rivet's body relieves the stress in it and allows it to come out easily. I have done this successfully from the manufactured head and from the shop head so either way works well.
So, see? That wasn't all that bad now was it?
Next, I would like to address a few things I have read here and on other lists.
1. Heat treating your rivets at home:
This is a very bad idea & totally unnecessary, and this is why:
Modifying the heat treatment of any fastener in any way changes its mechanical properties and therefore renders it useless for it's intended purpose. Heat treating is a complicated process that requires extremely accurate temperature control and your home oven is not even close.
In addition to accurately controlling the heating process, the quenching or cooling process must be a controlled environment also. Heat treatment also requires very accurate equipment to VERIFY the results. Unless you have followed the exact process on 100s of rivets and have paid a metallurgist to test your results to verify you have accomplished a specific goal consistently as well as(and more importantly) the results after setting the rivet, you have no way of being sure you have a safe assembly.
I have successfully set rivets from Zenith, Aircraft spruce as well as other vendors, without any noticeable difference. Practice makes perfect, and a true craftsman never blames his tools (or fasteners). Replacement rivets are cheap, there is no need to risk inaccurate heat treating. If you are having trouble seek the help of someone who has been successful at it. (like a professional).
The rivets we are using are AD rivets and are made from 2117 aluminum alloy.
They are marked with a dimple in the center of the manufactured head.
This alloy does not get harder over time when stored at room temperature!
If you put them in your oven and heat them up, you have changed their mechanical properties and they are useless!
Remember: THIS IS YOUR WING SPAR.
And I quote: FAA AC 43.13-2B Acceptable Methods, Techniques & Practice
"The 2117 rivets may be driven in the condition received'...
2.How to set a rivet:
There are several ways to set solid rivets successfully. Some ways are easier than others and every process has a learning curve. The rivet has no preference! Bucking rivets:
this process is not black magic. It will take some practice if you have never done it before or if you haven't done it in a while. Bucking rivets is a tactile thing, you can feel and hear when the rivet is finished. But until you develop the "feel" for it you will have to do it incrementally and measure the rivet's progress. This is easily done with a tool called a shop head rivet gauge.
The shop head gauge has two ends to it; one end is the optimum set height and the other is the optimum set diameter. When the rivet is set properly the shop head will either fit snugly in the hole or will not go in. But it must also be taller than or equal to the height gauge end. Each rivet diameter size has its own gauge.
Another important consideration is to make sure the rivet protrudes far enough beyond the grip length. If it doesn't, you will never get a properly set rivet. I have scribed a line into the anodized finish on each of my rivet gauges to
show me how far the rivet should protrude, and it's easy to check this dimension before setting. (Having this measurement scribed onto the Height gauge means I have one less tool to lose this way.) Once you are sure you have enough rivet protruding, the shop head gauge will tell you when you have set it to the optimal dimension. Luckily the fine people at Zenith have provided us with the proper size and length rivets which makes this job a lot easier.
The idea is to set the rivet with as few hits as possible, because overworking the rivet will over harden it. And as the rivet's diameter increases, the force required to set it increases, so you will need a gun that will at least set a 3/16" diameter rivet.
There has been a lot of discussion about this as well as the necessary weight of the bucking bar. I have successfully bucked 3/16" diameter rivets with a 3X gun and a standard bucking bar, however. I prefer a 4X gun and my favorite bucking bar is a piece of polished mild steel measuring 1" x 2 'x 3", which weighs in at 2.5 lbs. My second favorite bucking bar is actually the remnant from my welding certification test. The heavier the bucking bar the faster your arm gets tired, and the lighter the bucking bar the faster your hand gets numb from the vibrations. so find what's comfortable for you.
NOTE: Long term exposure to low frequency vibration caused by riveting may be harmful to your hands and arms. I suggest you take frequent breaks when riveting to reduce this exposure.
(No bucking around) This is by far my favorite way to set solid rivets; it's quiet, precise, fast, consistent and way more fun.
Pneumatic Squeezers come in 2 types; the "C Squeezer" and the "alligator squeezer". These tools are very expensive but are well worth the money if you are doing a lot of this work. The squeezers I have both produce 6000 lbs of force, so a 3/16" rivet doesn't have a chance! The cool thing about the squeezer is that once you have it set you can squeeze your rivets perfectly every time and very quickly. I use the shop head tool to set up the squeezer by squeezing a rivet and then measuring it. If it isn't squeezed far enough you just add a spacer under the set and try again. Once you get it adjusted the rest is gravy.
The disadvantage is (like most production tools) you have to set it up specifically for the length of the finished rivet. So, when you change from doing your spar rivets to doing your center section rivets you have to readjust the squeezer. However, this doesn't take that long and is well worth the time because of the consistent results you can achieve. There are also hand squeezers on the market that will squeeze a 3/16" diameter rivet. You will need to order a special 5" yolk to get around the spar extrusion.
Squeezing the rivets is how Zenith originally set the rivets in your spars and center section, because this method is much faster and more accurate. Remember they are in a production setting and must be able to set the rivets exactly the same every time to achieve their quality standards.
Does this mean you have to squeeze your rivets? No, but it is a lot easier, faster, and more accurate than bucking.
I hope this has been helpful.
Thank you for reading,
Magnificent Machine LLC
5686 Minder RD # 101
Poulsbo, WA 98370