Message #51

Date: Nov 16 1999 21:21:29 EST
From: Ron Wanttaja <>
Subject: Re: Wood Substitutions

> Mike Lund wrote:
> FlyBaby
> Hi Guys
> Just a quick note to let ya know there is a new lurker here.
> I have been aware of the flybaby for a number of years, but untill
> today I had never seen the plans or the plane up close (all my wooden
> airplane experience is with Pietenpols).
> Then, I came upon a treasure at about 9:30 this morning... a 1971
> issue of the complete EAA plans for the fly baby. I have had my nose
> burried in the book and on every flybaby site I could find all day.
> NEAT little plane, and after a Sky Scout and an Aircamper the
> construction would be a snap. AND I happen to have an EA-82 handy
> without an airframe behind it ;-) hmmmm grey cells are turning ;-)
> Have there been any major changes to the design since '71 (safety
> wise) ?

Major change has been the addition of a steel strap reinforcing the rear
spar carry-through.  There was a change page issued for the plans with a
batch of corrections on them; the change page is dated April 1970 so
your plans set probably includes the change page (page 9-1 in my copy). 
The information on the spar carry-through mod is summarized on my Fly
Baby web page.

> Also, being in Southern Ontario, aircraft spruce is hard to get, and
> worth more than gold when you get it...has anybody used a different
> wood for the plane (with appropriate sizings of course)?

FAA Advisory Circular AC 43.13-1B has a chart denoting what woods can be
substituted.  Jim Pratt has made this document available for downloading

To summarize the table:

Douglas Fir:  Stronger than spruce, a bit difficult to work with hand

Noble Fir:  Slightly exceeds spruce, but 8% deficient in shear. 
Slightly less hard than spruce.  Can be used as a direct substitute,
except where shear is critical

Western Hemlock:  Slightly stronger than spruce, less uniform in
texture, but can be used as a direct substitute.

White Pine:  85% as strong as spruce, low in hardness and
shock-absorbing capability.

White Cedar:  Stronger than spruce, but gluing difficult.

Yellow Poplar:  Slightly less strong than spruce

Weight comparison:

Spruce:  28 lbs/ft^3
Red Pine:  33 lbs/ft^3
Douglas fir:  33 lbs/ft^3
Western Hemlock: 30 lbs/ft^3
White Cedar:  29  lbs/ft^3
Red Fir:  28 lbs/ft^3

Note that the most obvious replacements for spruce, hemlock and fir, are
quite a bit heavier (10% and 18%, respectively).

However, keep in mind that there are definite standards for quality that
should be followed even if something other than spruce is used.   AC
43-13 includes some of these standards.   Dave Munday referred to the
EAA Wood publication; the title is "EAA Building Techniques:  Wood."  It
includes a chapter on evaluating wood.  It's available from a fine
Experimental Aircraft Association near you.... :-)

Ron Wanttaja