Bruce's Cozy Mark IV

This blog documents my ongoing project to build my own aircraft, a Cozy Mark IV.

This past Saturday I got together with Joe Hull over at his shop to break the confidence piece. This was by no means a stringent scientific test, I just wanted to see roughly how much weight the confidence piece would bear before failing.

Here are some photos and raw video footage (please ignore my excited commentary):

Here is a video with the brightness corrected some and with no sound-track:
Confidence Piece Break Video

The test rig consited of:

• 2 x 2000 lb. calibrated scales
• 1 hydraulic floor jack
• 1 long 2x4 board
• 1 exposed ceiling joist in Joe's workshop

I tried 2 different setups. First I tried using some foam blocks to help distribute the load to the scales, but that made the whole setup wobbly.

Then I just placed the piece on 2x4 blocks. I was concerned that this would cause the piece to fail at the outer edges, but that didn't happen.

I bridged the piece across the 2 of Joe's calibrated scales, so you have to add the numbers each scale is showing for the total load on the piece.

A long 2x4 transmits the jack's force into the shop ceiling which isn't likely to budge.

Joe steadied the whole rig while I slowly pumped the jack to gradually increase the force on the piece.

I had already stood on the piece and so I knew it could support close to 200 lbs.

I was very shocked when we reached 500 pounds and the piece showed only a mild deflection.

I started video taping with my digital camera's record feature which produces not-so-good footage, but it's acceptible for this simple test.

The piece failed at about 600 lbs. Which, when you stop to think about it is remarkable given that the piece itself only weights about 4 ounces (130 grams).

The failure was actually not that abrupt: the piece deflected quite a bit and made some 'creaking' noises, I suppose as some of the glass fibers stretched.

The failure point was at the location where the jack's square based traversed the piece. This caused stress points on each side of the jack as the piece defelected from the force.

I'd be willing to bet the piece could have withstood a much higher load had we distributed the weight more evenly across the piece.

The failure caused a small area of delamination and a tear.

Next steps are to learn how to repair this piece, then test it again.

I'd also like to find a way to compute the theoretical maximum that the piece should support given an ideal epoxy and cure to give my testing a little more scientific meaning.

WileEZ on one of the forums (http://canardaviationforum.dmt.net/showthread.php?t=4037) snapped these photos.

Larry Aberg was kind enough to let me sit in Cozy. Thanks Larry!

(Click photo for more)

2007 Northwest EAA Fly Arlington, WA

The confidence piece has been curing in Joe's workshop for 2 days now. This evening we:

• Outlined the dimensions for the cut on the back of the piece
• Used a Fein saw to cut out the piece
• We compared the piece to Joe's confidence piece he made 4+ years ago
• We weighed the piece

Comments

I had never seen a Fein Multimaster saw before. It's basically a vibrating saw. The blade for cutting fiberglass layups is fine-toothed, but not razor sharp. You can hold the running saw against your hand and it won't cut you.

It's a good idea to score the part first before trying to cut through. There is a some amount heat generated when cutting due to friction and I was concerned about effects on the epoxy. It might be interesting to point an infrared thermometer at a piece being cut.

Joe says that for parts like the bulk head, it is actually easier to glass a large sheet of foam, and then do cutting as opposed to trying to cut the raw foam. I asked why the plans didn't spell it out that way? i.e. Does it somehow weaken the part to do that (i.e. the heat?). He said no, it's his opinion it's just something they never went back and added to the plans to make them more convenient.

We spent a fair amount of time coming up with a plan to test the confidence piece to failure. I'm keenly interested in seeing how strong it is. We're going to use a hydraulic jack and a 2000lb. scale to test it to failure. I may try to video-tape that since I can't find a lot of that kind of research on the net.

Other Topics

We also spent a lot of time talking about cooling, since that is something on Joe's mind right now. He's in the middle of replacing his rotary engine with a Lycoming. Most aircraft engines like these have exhaust ports on the bottom, and the Cozy design has cooling air coming up from below from the large NACA scoop on the bottom of the fuselage. Apparently there have been concerns about cooling the engines with this "bottom-up" configuration.

The problem is exacerbated by the speed-brake being directly in front of the cooling air intake scoop, so if you have to do a go-around, and forget to raise your speed-brake, your engine is gonna be warming up rapidly.

Joe spoke of someone who has a dual-NACA scoop design on the upper engine cover that does top-down cooling the way the engine designers intended.

I decided to investigate this some more. Here is what Nat Puffer had to say on a forum:

"I learned early on in my engineering career that if you are trying to solve a problem, you should define what the problem is before you start thinking of solutions.
If the problem is engine overheating, you can have that with either updraft cooling or downdraft cooling. So you need to look a little farther. Before giving up on updraft cooling, you should first of all consider the advantages. The flush NACA scoop is a low-drag scoop. Translated, that means faster speed. Secondly, when climbing you need better cooling than in cruise, because you are at a slower speed. With the NACA scoop on the bottom, it is in a higher pressure area, so you are getting more efficient air intake. A scoop on the top would be in low pressure air and less efficient. Thirdly, when taxiing or idling at the end of the runway waiting for clearance, updraft cooling is more efficient because convective airflow is aiding, rather than impeding cooling. And lastly, when parked with the engine off, natural convection will cool the engine and reduce its cooking.
I have investigated cooling problems in both Long EZs and Cozys. In all cases the problem has not been updraft cooling, but rather a very poor baffling job. For example, some builders think that there should be 1/4 inch of clearance around the exhaust pipes. That thoroughly destroys the pressure gradient, so there is little pressure drop to force air through the cylinder fins. Also, some builders never caulk between the baffling and the engine.
We have an 0-360 Lycoming (180 hp) and in high-speed cruise at altitude my hottest 2 cylinders do not exceed 350 deg F, measured with probes at the bottom, and my coolest 2 cylinders rarely get over 300 deg. F. My hottest cylinder (#1) has a probe at the bottom and a thermocouple under the top plug. The thermocouple runs about 40 deg. hotter than the probe. But since a thermocouple under a plug alongside a probe always runs 40 degrees hotter, this means that there is very little temperature difference, if any, across the cylinder, which is remarkable.
I have a 13 row oil cooler using cowling air (no extra scoop) exiting under the strake, and my oil temperature runs 170 - 180 deg F at altitude in the summer time.
My installations are per plans, or per newsletter, in the case of the oil cooler. I haven't used any magic. You should get the same results if you do the job properly, and there will be no incentive to go to downdraft cooling, which has fewer benefits. On the other hand, if you do a poor job at downdraft cooling, it will be worse." -Nat Puffer (Source : http://www.canardzone.com/forum/archive/index.php?t-75.html)

Spending time with Joe is proving to very valuable. Do find another builder if you plan to tackle this project. By my estimates, Joe has already saved me from 50 beginner mistakes. Thanks Joe!

Photos (click for the whole album):

First layup - Part 2

Today I visited with Joe Hull, fellow Cozy builder, programmer, and just all-around nice guy. Joe completed a Cozy flew it about 80 hours or so on a rotary engine before deciding to change to a Lycoming engine. He's in the middle of the engine replacement and is still taking time out to help me learn the ropes. Thanks Joe!

I was invaluable to spend time with Joe today because I learned so many tips and tricks like:

• Don't waste time trying to clean brushes, just buy cheap ones and toss 'em after a lay-up
• Use a digital scale, not a pump: how will you know if the pump has malfunctioned?
• DO build a glass-cutting table
• DO use masking tape where you make cuts on UND glass so it doesn't fray out so badly
• Only mix epoxy in small quantities
• DO NOT use too much epoxy, it actually weakens the structure

I was pleasantly surprised at the simplicity of the process compared to aluminum construction (I started the tail of an RV-7 several years back). It's more akin to being a taylor than a machinist, and it's quite peaceful. The materials are very forgiving and mistakes (which you will make) are easily spotted and corrected.I think I'm going to enjoy building my Cozy.

Here is a slide show of my visit with Joe today where I created a 'confidence' piece. It is a simple lay-up that you build, stress to failure, then repair. I think this is Chapter 3 in the plans which haven't arrived yet, so Joe is letting me look at his plans. You can get the photos here.

Photos (click for the whole album):

Learning Composite Construction Techniques

This is my tale of how I came to be a Cozy builder:

I first took the controls of an aircraft when I was about 5. It was my grandfather's twin Commanche, N7761Y. I grew to love flying and flew with my grandfather off and on throughout my childhood.

In my late-20's I bought a beat-up old Cessna 172 that was barely airworthy and spent a small fortune updating and repairing it. THEN I started officially working on my private license which I completed in near-record time (2 months or so).

I flew that old Cessna about 300 hours all over the Eastern US including New York city, the Florida keys, the Appalachian mountains, and even to Texas one time. It never really let me down except for a stuck valve over Clemson SC one night, but I had no trouble landing safely.

But I eventually grew tire of how slow it was. My average cruise speed was 110 to 120 mph and it seemed I always had a 20 mph headwind.

Late one night coming back from the Florida keys I stopped for fuel in Savannah, GA. While paying, I overheard some Leer-jet pilots down from New York were complaining of 90 knot head wind at 20,000 feet. I wondered if I might climb up high enough to get some that as a tail-wind back to NC.

Sure enough, at about 12,000 feet I was getting about a 60 mph tailwind.

My ground speed was close to 180 mph and I was simply amazed at how fast I was getting back home. It was that experience that really made me want a faster plane.

But faster planes are expensive...and that's what led me to consider building my own plane.

And that's what led me to Florida, to the Sun-N-Fun fly-in, and that's how I came to meet Nat Puffer.

I was looking for a fast economical plane that I could carry a small family in. And the Cozy fit the bill...if I don't count my hours to build it.

After that trip I got involved with the local EAA chapter where almost every builder was flying an RV. A fellow member convinced me that I'd be better off building an RV. Flying his RV-6 was so fun I went out and bought all the tools and the empennage parts of an RV-7. Into which I never put the first rivet...

It wasn't the RV's fault. I just wasn't at a place in my life to realistically put any time into the project. So I sold it and just kept flying my 172. At least I had a plane.

Then I had to sell my plane for various financial reasons. That was about 4 years ago.

I kept current by joining a flying club, but that had it's own set of issues namely: beat up old planes, 'sharing', and club dues. There had been enough accidents in that particular club that the dues and prices kept creeping up.

Then I took a job on the west coast and moved to the Seattle area. I found that where I work there are tons of pilots and several builders. I went to a local EAA meeting and I was strongly bit by the builder bug again.

I visited the Northwest EAA fly-in and sat in a Cozy again (thanks Larry from Oregon) and my wife sat in it too. She liked it a little better than the Long EZ (thanks Mike from Seattle).

I ordered the plans yesterday and I wrote this letter to Nat Puffer last night:

Nat,

I met you at Sun-N-Fun back in 1999 (or 2000, or 2001).

You let me sit in your Cozy and answered a lot of my questions.

Shortly after Sun-N-Fun an RV-6 builder convinced me to build a metal airplane and I started on an RV-7....I never put in the first rivet before losing interest and selling the tools and kit.

Then a few life-changing things happened, a divorce, financial down-turn, my software company tanked, and I had to sell my C-172, then I re-married, had 2 children, and got a great job at Microsoft in the Seattle area.

To make a long story short:
I've been talking on and off to Joe Hull here who's built a Cozy.
I went to Arlington today and sat in a finished Cozy with my wife.
And tonight, I ordered the plans from Aircraft Spruce.

I'm not sure if you read these emails or what your involvement is now in aviation, but I just wanted to reach out and let you know that 7 years ago you were kind and patient with me and I'm gonna build the aircraft you designed.

Thank you for you great contribution to aviation, your wisdom, your patience, and your concern for safety.

I know not how long it'll take me to build a Cozy, but when I'm done, every time I fly it, I'll remember you.

-Bruce Shankle
http://www.bruceshankle.com/