RE: Pietenpol-List: What wood to use?

[matronics]

Original Posted By: Kent Hallsten
Ervin Luke wrote: As a builder more familiar with metal than wood, I am interestedto know which type of wood is best for each application, or area of theairplane. I notice some builders are using cedar, spruce, fir, etc., invarious areas of their project, and I am wondering what it is about eachtype of wood that makes it better for one area, than another type ofwood. Is their a source where I can find this information? Or wouldanyone care to give a brief synopsis? Thank you.Ervin Lukeerviator(at)juno.comRV-6potential Piet builderHi Ervin"What wood to use?" is sure to spark a long-string discussion, as will a fewother topics such as "what glue to use?". However, at the risk of startingsuch a discussion I will try to help you out.There are a number of good structural woods for the basic structure.Probably the best from the standpoint of strength-to-weight ratio isaircraft grade Sitka Spruce, but it is also the costliest. Douglas Fir isconsiderably cheaper, and it is actually stronger than spruce, by 23%, butit is also heavier, by 26%, so overall it has a lower strength to weightratio than spruce. If all the pieces in the structure are assumed to be ofspruce, then they could be scaled down somewhat if built in fir to save someweight. However, it would be a major pain to do so. The total weight ofspruce in the wooden structure is probably not over 100 lbs in a Pietenpol,so a 26% increase in weight is probably less than 25 lbs. The cost savingsis significant.Other alternatives to spruce include Western Hemlock, which is 11% strongerthan spruce but 5% heavier, and western red cedar, which is 19% lighter thanspruce, but is only 74% as strong as spruce. I would be careful about usingcedar for major structure like spars and longerons.Probably of more importance than the species of wood chosen is the actualgrain structure of the wood you will use. For this reason I chose to useaircraft grade spruce, although it is pretty expensive. Still, I doubt I'vegot over $2,000 in spruce in my project. The wood is one of the lessexpensive components of the finished airplane, compared to engines, coveringmaterials, etc. Still, if you have plenty of time and a careful eye, youcan select wood suitable for use in an aircraft.At one point in my project, I decided I would use Douglas Fir rather thanorder more spruce, because the local Home Depot had some good looking fir,and both Aircraft Spruce and Wicks Aircraft were on backorder. I selected afew pieces and brought them home. As soon as I started working them Idecided to go back to spruce. I find the heavy turpentine aroma of douglasfir objectionable, as well as its tendency to split and splinter. If youonce work sitka spruce, you will never want to use another wood.But your question was what woods to use where? The plans spell out theplaces where you need woods other than the main structual woods. Plywoodcan be either birch or mahogany (or luaun or anything else you want, butbirch and mahogany represent the bulk of the aircraft plywoods). Birch isharder and stronger, Mahogany is softer and lighter - take your pick.The only other wood called out on the Pietenpol plans to my memory is whiteash. This is important. You will notice that Ash is called out whereverthere are vibration loads, such as the engine mounts, or shock loads, suchas the landing gear attach points. Ash has a couple of very interestingproperties - it has a remarkable ability to absorb shock (which is why it isused for baseball bats), and it does not splinter (which is why gymnasticparallel bars are made of Ash). Ash is readily available at most lumberyards, although Home Depot doesn't carry it, and it is not terriblyexpensive. I would not substitute another species for the ash called out inthe plans.Use your best judgement, and change species as you see fit as long as it isnot major structure. As I said, most of my structure is aircraft gradesitka spruce, but I use douglas fir for the ribs over the fuel tank in thecentersection due to their increased stiffness over spruce. I used ashwhere it was called out, and anywhere that I have screws that need to anchorinto wood for removable fairings and access panels, I have used BlackWalnut - primarily because it is hard and holds screws well and I have a lotof it in my shop. If I had to buy it I certainly would not use walnut - tooexpensive. Most of my plywood is mahogany, particualrly aft of the CG whereany additional weight can cause problems, but even there I used birch whereI needed durability - for example the doublers in the tail where the bracingwires attach, or where the tail attaches to the fuselage. Just use commonsense.Sorry for the long-winded answerJack PhillipsPietenpol NX899JP getting closer all the timeRaleigh. NC________________________________________________________________________________

[matronics]

Original Posted By: "Kip & Beth Gardner"
Kip,Engine mount bearers use the ash. Many of the old engines of the daymounted just like the model A does in the piet. The good old OX-5 in theJenny is a prime example. The bearers in the piet are supported by tubes infront and a wood "engine support" in the back (per the flying and glidermanual figure 1C). The "engine support" is spruce by default but making itof ash is not necessary but wouldn't hurt either.Chris Bobka----- Original Message -----

[matronics]

Original Posted By: owner-pietenpol-list-server(at)matronics.com
You're right, Kip. The air-cooled engines mount directly to the longerons,like on any other airplane. The ash was specified for the long bearers thatthe Model A sits directly on.Jack -----Original Message-----

[matronics]

Original Posted By: del magsam