Original Posted By: AirCampr(at)aol.com
Be careful. I found (when I asked very direct questions) that some of the wood labeled hemlock, fir and hem/fir is really just something from a family of wood types, they can't tell you what it actually is. I don't know about hemlock, but I found that Douglas Fir is very identifiable by color (reddish) and grain. I used a book from the library for identifying wood type.Good luck>Date: Mon, 17 Nov 1997 05:56:35 -0800>From: Brent Reed >Subject: Re: Strength of Various Woods>To: Pietenpol Discussion >Reply-to: Pietenpol Discussion >> Your the man, Mike! Great info! Just so I'm clear, grain run out of less>than 1 in 12 would mean that as it runs lengthwise it is going to one side>of my board less that one inch for every 12. Is that right?>>I found Hemlock at Home Depot. It's graded C or better. If I select>straight grain (as above) knot free 1"x 6" for my ribs am I choosing wisely?>>This group is invaluable! Thanks.>>Brent Reed>Kent WA>-----Original Message----->From: michael list >To: Pietenpol Discussion >Date: Sunday, November 16, 1997 11:06 PM>Subject: Strength of Various Woods>>>>Hello Brent!>>As promised I dug out my copy of ANC-18 Design of Wood Aircraft>>Structures, 2nd ed. 1951, which is 234 pages of wonderful details on>>wooden aircraft construction methods. This manual was put together for>>joint Air Force, Navy and Civil use. I'll provide some basic numbers>>comparing Sitka Spruce, Douglas Fir and Western Hemlock based on a>>typical 15% moisture content from Table 2-6, p. 22.>> Density (lb/cu ft) Spruce 28>> Fir 33>> Hemlock 30>>>> Static Bending Spruce 5,300>> Fiber Stress at Fir 5,900>> proportional limit Hemlock 6,200>> (psi)>>>> Compression parallel Spruce 3,530>> to grain fiber stress Fir 4,220>> at proportional limit Hemlock 4,080>> (psi)>>>> Shear strength Spruce 990>> parallel to grain Fir 950>> (psi) Hemlock 860>>>> Tension strength Spruce 9,400>> parallel to grain Fir 10,900>> (psi) Hemlock 11,000>>>>So what does all this mean? There are other physical properties in>>ANC-18, but I think these are enough to show that the hemlock, properly>>selected for quality and adhering to the standard grain runout of no>>more than 1 inch in 12 (preferrably 1 in 15), is an acceptable>>substitute for spruce in the Air Camper. The Air Camper is a pretty>>conservative design and is not intended for aerobatics, so the hemlock>>should provide you with the robustness Bernie Pietenpol intended. You>>might want to make up some small test samples of your wood to pull and>>bend with your adhesive of choice for your own peace of mind and the FAA>>inspector.>>>>In case you were wondering, I am a design engineer for the Lockheed>>Skunk Works. Just so you knew the data didn't just come off the>>street. Hope this helps.>>Mike List>>>>Dean Dayton - deandayton(at)hotmail.com________________________________________________________________________________