The Yardstick
 2006.05.26
 


The Yardstick
The yardstick is balanced on a beam in the hangar. Strings from each end attach to a water bottle suspended below.

Another yardstick balanced on the beam has a second layer added to the middle, wrapped with a layer of gray tape. I feel that the use of duct tape adds to the credibility of this experiment.

As water is added to the bottles, I hold my breath and imagine the drumroll intensifying and the tension mounting. The first yardstick breaks at 2.25 liters. The second, doubled yardstick breaks at 2.5 liters.

So, any main spars fabricated from yardsticks should probably be destroyed.

If you’re wondering what a yardstick has to do with anything, a previous note alludes to the theme of lightness and simplicity and staying with the plans. It includes a reference to an early builder that added a number of layers to the VariEze main spar, but not the wings. This created stress points in the design’s normally uniformly flexible wings and spar components.

Evidently, someone questioned the example of the doubled yardstick in the spar note. They were right. The example is interesting, but not an exact parallel. Playing with the yardsticks indicated to me that the one with the doubled center section wrapped in duct tape was actually more like the design of the VariEze spar and wings.

On a recent road trip I had the luxury of enough time to consider the previous spar note. A lot has happened since that note was written, not to mention the CP comments which spurred the thoughts. Here are a few thoughts that settled out.

That adding layers to a component could actually have a result far different than the builder intended, was an EZ entry-level concept that got my attention. There are a myriad of examples of this paradox in other fields of endeavor, maybe even giving rise to a saying about ‘good intentions’?

Like many of you, in weaker moments I have awakened from a fanciful half-sleep and come to my senses in the midst of envisioning a more rounded fuselage with sleeker intersections and a more aesthetically pleasing and certainly faster and lighter assemblage that would more closely approach glassic nirvana. Dream on.

In these very enjoyable episodes, which I hope my wife never gets wind of, when I sneak a sideways glance over at the parts waiting in the wings, I still don’t gravitate toward the current promoters of substitute materials and techniques. Rather, I find comfort in the old tried and true, remembering CP pictures of wings and canards bolted to hangar beams and loaded with sandbags or crowds of grinning builders. Maybe that’s how I should have tested the yardsticks!

As I revisit the early CPs, along with the initial rush of plans corrections and productive builder suggestions and improvements, there is a push for builders to stay with the simplistic theme.
Here are a couple of quotes. I think that Burt and/or Mike Melville were the writers here.

CP 17 page 8.
Question: I am considering adding a few extra plies of glass in a few areas to beef them up for extra strength is this OK?
CP answer-- NO! …The extra weight in most places will actually weaken your airplane in that its maximum G capability will be less and failure on hard landings will be more likely. The best thing you can do for optimum safety is to do perfect workmanship with the exact ply arrangement in the plans. Also, stiffer structure can change flutter modes.

CP 18 page 3
“Most of the airplanes over 650 lbs are either loaded with equipment or are built with excess material than that shown on the plans. Remember, excess equipment or structure actually weakens the airplane. You can pull less G and will fail more easily on landing. The strongest airplane all around, is one built with all materials like the plans, with good workmanship, and kept as light as possible.”
“These airplanes (over 650 lbs) are either single place airplanes, or are at best marginal with two people.”

Another very early comment recognized one newly finished VariEze’s weight at 575 lbs, and suggests that as a legitimate target. Not long after, another comment suggests that if the plane is over 620 lbs that it should be chopped up and started over. How far from that initial expectation the average EZ is today.

Where the rubber hits the road
I remember one of the first times when this Eze structure stuff came up in practice.

The weight game rubber hit the road during a return leg from the Kerrville fly-in with Jim Ivey in his C-85 powered VariEze. I was well along building and had read each CP, including the seven or eight pre-Eze editions. By this time in the early 90s everyone was impressed with the EZ structure. At altitude as we approached Spinks I grinned and pushed the nose over to have a little fun on the way down and see some impressive numbers during the descent that we could casually mention and claim later.

As we approached the bottoms of the clouds at about 5000 feet, it started to get hotter, and bumpy. Jim suggested that we pull the power back and slow down to maneuvering speed.

In Hangar 30 while putting the plane to bed we talked about maneuvering speed. His aeronautical engineer perspective was that during the descent we had been in the squeeze between the maneuvering speed and gross weight. During the early part of the descent we were above both.

At this juncture of the conversation you often hear folks swerve away from the design limits, and over to how the VariEze is overbuilt and has strength beyond what mere mortals can comprehend. And of course, the follow-on designs are even more superior (a little sarcasm here).

But Jim didn’t take that direction. We surmised what would happen if someone chose to charge on down below the cloud deck holding in some power at say, 220 mph. That would be fun!

His eyes rolled back in his head and he ticked through a quick equation including mumbles of speed in excess of maneuvering speed and weight in excess of the operating handbook figure of 1050 lbs, a transient jolt of four Gs...

He quit ticking and was silent and I asked him what happened. He said the spar would have failed. Not enough yardsticks I guess. Or duct tape.

I just recently re-read Burt’s comment that he had used 1050 lbs over a million times (sorry) - hundreds of times in the VariEze design calculations.
Yet you can easily find threads with expert comments basically saying go ahead and add or change materials – what could go wrong?

My VariEze is pretty typical of those struggling with “balance” between the effort to keep things light and simple, but with just the right dash of operational practicality carefully blended in. How easy it is to rationalize away our ability to experience Burt’s lightweight VariEze dream.

In sweet contrast, it’s always great to get a surprise email from Joe Person telling me again how light his VariEze is. Certainly a mixed gift, encouraging and discouraging at the same time. I particularly appreciate his educated professional approach between materials and weight. Lead on, Joe. Congratulations on your plane.

This September will be ten years in the air for N95BJ. I guess that anniversary is what is spurring thoughts to pull in the early days and blend in how things are playing out.

I sit here now radiating and still cooling down from today’s sunset run. Me and twelve gallons. Eight gallons used to be optimal with the 0-235, but I’m still checking out the 0-290 and here, more (fuel) weight is good.
Today is the second run in the last thirty days that the plane has flown six days in succession. After the normal oil temp drill, this sunset flight sailed through some red copperish wingovers and then went up for some really slow flight. Im not really too keen on the slow flight, but the ride confirmed again, for me, Burt did good.

Bill James, Fort Worth VariEze

Contact Contact Bill
  EZ Home