How Safe?

In a typical 35mph automobile crash, the human body is subjected to over 200Gs, but only for fractions of a second. people are pretty tough for squishy fluid bags.

That number sounds pretty high- I seem to remember from flight school that at 60-80 g (even gx) can be fatal (can tear your aorta), and more than around 100g will cause fragmentation and dismemberment.

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jesse said:
John Stapp during his testing survived 46.2Gs. 0-632 mph in 5 seconds followed by 632 to 0 mph in less than a second.
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Sure glad they took photos of his rocket sled rides! The coyote could have learned a thing or three....

StappSled.jpg
 
Tristar said:
An even more difficult question is how much can the body take before something such as your spinal chord breaks?
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Depends on the force vectors alignment with the body and the duration of the acceleration/deceleration. Depending on the vector our structures can take anywhere from 3gs or less to a couple hundred gs. It sometimes amazes me the accidents that some people walk away from, and some people die in.
 
i love my wood glider. as long as it stays dry i plan to fly it. its strong and flexible. i love the feeling of the way a wood wing flies. a little more cushion and flex than a stiff aluminimum wing. hard to describe but you'll know it when you feel it.

plus, the parts grow on trees!
 
bullwinkle said:
In a typical 35mph automobile crash, the human body is subjected to over 200Gs, but only for fractions of a second. people are pretty tough for squishy fluid bags.
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Got an authoritative source for that info? 200 g (a force of 36,000 lbs for me) seems awfully high, even for a very brief time. And how could that be applied for such a short time in a way that would actually couple the applied force to the body?
 
Several years ago I asked the very same origional question to a guy that was rebuilding a fabric plane. He took a 6" square piece of fabric and streached it out. Gave me a 16 penny nail and told me to shove it thru..I couldn't. Incredible.
 
gismo said:
That gauge seems to imply that there's such a thing as too much fun. How can this be?
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I have been informed on several occasions by the constabulary that I was having too much fun. So it must be true.

New Pitts aircraft are constructed with wood spars and ribs for all the reasons already mentioned. I'm good for +6/-5, and then some. I've often wondered though how they qualify the particular wood that's used for a spar. Is it like my trip to Home Depot were I'm looking for the straight ones with no knots? Or is there something more scientific involved like x-rays?
 
PittsDriver said:
I have been informed on several occasions by the constabulary that I was having too much fun. So it must be true.

New Pitts aircraft are constructed with wood spars and ribs for all the reasons already mentioned. I'm good for +6/-5, and then some. I've often wondered though how they qualify the particular wood that's used for a spar. Is it like my trip to Home Depot were I'm looking for the straight ones with no knots? Or is there something more scientific involved like x-rays?
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It starts just like that, and then we check the moisture of the wood, and if the mill of the wood to the grain is appropriate for the application. A spar is just like a baseball bat in that if the stressor loads on an end grain it will flex and spring with great resilience, while a lessor load applied perpendicular to the grain will cause the wood to fracture and fail. Diagonal grains hold both benefit and weakness, so you have to know where to use them to advantage and where to avoid them. In an aircraft wing spar, I would avoid them to the extent possible. Unless you're getting old growth stuff, you'll have to put up with a certain amount most likely. Another thing is the grain density and straightness of the grain (again, advantage to old growth which is getting rare as hens teeth and valued like platinum). If you can have perfectly straight grains both lengthwise and vertically, densely spaced with ends only on top and bottom and on the ends, none on the faces, nice evenly spaced grain end milled like that, out of Sitka Spruce preferably (though I have built sailing spars out of other woods, and an sailboat mast sees way more load than an aircraft spar of the same length) is the best piece of lumber you can start with. From there, you can increase the strength and dimensions of strength by cutting and re laminating the wood back together in an engineered form.
 
PittsDriver said:
I have been informed on several occasions by the constabulary that I was having too much fun. So it must be true.

New Pitts aircraft are constructed with wood spars and ribs for all the reasons already mentioned. I'm good for +6/-5, and then some. I've often wondered though how they qualify the particular wood that's used for a spar. Is it like my trip to Home Depot were I'm looking for the straight ones with no knots? Or is there something more scientific involved like x-rays?
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More than you wanted to know

http://members.eaa.org/home/homebui...pecification MIL-S-6073_ Aircraft Spruce.pdf

Inspection, procedures for shipping / drying / etc.

No X-ray or stuff like that - the latest spec's date back to the 1940's.
 
Capt. Geoffrey Thorpe said:
More than you wanted to know

http://members.eaa.org/home/homebui...pecification MIL-S-6073_ Aircraft Spruce.pdf

Inspection, procedures for shipping / drying / etc.

No X-ray or stuff like that - the latest spec's date back to the 1940's.
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One thing I'd like to make clear that they didn't really stress is that you don't want kiln dried for a spar, you want air dried. Kiln drying changes the properties of the wood and takes away some of that "spring" and makes the wood harder to form, especially carved bits for trusses and such. More subject to chatter marks on machined faces. Note the say "If Kiln Dried" and the spec it is referring to greatly limits the temp of the kiln. Best thing is to build the rough hewn, oversized lumber a solar drying box and leave it in there until you get core samples of less than 10% humidity as when you take it out, unless you are in a desert, it will reabsorb a percent from the atmosphere. Now the lumber is ready to mill. The problem is, with the rate we use lumber today (actually, from WWII onwards), nearly all of it is kiln dried unless you order it from the initial rough mill for air dry, or go to a spar guy who has contracts and buys raw, air drying and selling to a very specialty market. These guys keep getting harder to find. (I'd look for the diver loggers though since they have old growth pressure cured lumber and often mill to order). If you look in the engineering specs, you'll see the size difference required between kiln and air dried woods.
 
Sorry to bring this up again, but one question about wood aircraft has been nagging at me. What if you are on a long tour of the country, like say oshkosh, and you take detours other places where there aren't hangar's to protect the plane for a long period of time, what do you do in this situation? And if there ARE hangars can you leave a plane in one for a day or two or are most hangars long-term rentals?
 
HawkEye007 said:
Sorry to bring this up again, but one question about wood aircraft has been nagging at me. What if you are on a long tour of the country, like say oshkosh, and you take detours other places where there aren't hangar's to protect the plane for a long period of time, what do you do in this situation? And if there ARE hangars can you leave a plane in one for a day or two or are most hangars long-term rentals?
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Depends. You can often find a vacant hangar. But, back in the olden days when Cubs and Taylorcrafts and... were everywhere, they sat out all the time. Didn't help the life of the fabric, but that's the way it was.

Remember, trees stay out in the rain all the time. They seem to do OK.
 
HawkEye007 said:
The trees in a plane are no longer re-generating new wood though.
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Ok, that was supposed to be a joke.

But I bet this one has spent many of the last 60 years tied down outside: http://barnstormers.com/classified_234049_Taylorcraft+BC12+1941.html and it still appears to be flying...

The wooden boat I sail on has been outside (and in the water) for all of the last 63 years and is nearly all original wood. (And we were third in our class in the Port Huron to Mackinac Island race this year)

A little weather isn't an instant death sentence for wood. But being in a hangar is better for any airplane - wood, metal or plastic.
 
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HawkEye007 said:
Sorry to bring this up again, but one question about wood aircraft has been nagging at me. What if you are on a long tour of the country, like say oshkosh, and you take detours other places where there aren't hangar's to protect the plane for a long period of time, what do you do in this situation? And if there ARE hangars can you leave a plane in one for a day or two or are most hangars long-term rentals?
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Sitting outside occasionally will not hurt them. Give it a good wax job. If you are concerned they do make aircraft covers.
 
HawkEye007 said:
Sorry to bring this up again, but one question about wood aircraft has been nagging at me. What if you are on a long tour of the country, like say oshkosh, and you take detours other places where there aren't hangar's to protect the plane for a long period of time, what do you do in this situation? And if there ARE hangars can you leave a plane in one for a day or two or are most hangars long-term rentals?
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There are a number of Decathalons and Citabrias at KPAO which are parked outside year round, and have been for years. I've flown Citabrias in both good weather and in rain (no snow in these parts) -- it just never has been a concern -- the fabric is waterproof.

Chris
 
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