snips..

  I am currently considering options for a Mazda 13b lightweight
  engine installation. these drawings represent one of 2 ways
  to skin the cat. the significant modification I seek
  comment on is the addition of the struts at the top
  of the FW to transmit loads back down to the main spar.
  Please review the included discussion. I look forward to
  your comments, as to wheather this is a good idea, and or if you feel
  any changes to improve it.
  Craig Smith
  CH-640 SN 00078


  Craig,
  This installation looks very messy at best and needs to be
  redesigned in my opinion. However, with the drawings you emailed,
  I can not offer a simple solution for you. The top tube going through
  the firewall will damage the firewall as you will have a large
  up/downward load in that area.
  Mathieu Heintz
  Zenair


  What specifically is "messy" about it Mathieu?

  At 100 FPS second take off/climb speed assume the net thrust from the prop
  is 1000 pounds. To put that in HP perspective that would be 100,000
  foot pounds second. Since one HP is 550 foot pound seconds that is
  181 HP net out of the prop. Since the prop eff. is about 80%
  that translates to 226 engine HP. Since max HP is a constant As speed
  increases the net thrust from the prop decreases until the net thrust
  equals the drag at top speed.

  Given 1000 pounds of net thrust out of the prop the top MM strut takes
half
  or 500 pounds. The two lower rubber bushings take the other half.

  error snips.............

  --------------------------------------------------------------------
  I forgot the down load introduced by the diagonal brace tubes.
  I am so used to thinking of firewalls as being rock solid SS devices
  braced by sheet metal cowling's over the instrument panel area.
  This one appears to be free standing from the longerons up.

  There is a moment around point A of 5000 inch pounds so the download
  on the firewall due to the brace tubes is 5000 / 12.25 or about 400
pounds.

  I don't have a dwg on the fuselage so this is just a guess. I do know
  the 801 had a sheet metal channel section riveted to the front of
  the firewall part number 8F7-3 but I have no dimensions on that either.
  My guess it was  2 inches wide with a one inch flange  so the total
  width was 4 inches. I am also guessing on the fire wall thickness as being
  .032" thick. If the channel was also .032" thick that would provide a
  column
  roughly 4 inches wide .064 thick or .256 square inches. Compressive
  stress would therefore be about 400/.256 or 1600 psi. Well below
  the buckling stress of a column only 10 inches high. If it were
  a 5/8 diameter 2024T3 tube with .035" inch wall it would
  take 2500 pounds to buckle it.

  The buckling formula is shown in the jpg for anybody that would
  like to calculate the load the column will take.
  E is ten million as I recall for aluminum and L is ten inches.
  http://en.wikipedia.org/wiki/Column

  I is a bit complicated to calculate but not impossible.

  I would be helpful if we had some dimensions on this stuff.

  Paul Lamar

  So, what your saying is with the addition of the 801 specific parts to the
  firewall, it might very well be a viable design. I guess we would need the
  help of one of our 801 builders to identify the differences in the parts
and
  reinforcements.
  Paul, are the advantages of the top mount strut brace significant enough
  over the lower brace to the nose gear bracket to warrent the effort?
Sounds
  like a bigger mod than we first thought.
  Why not try bouncing the original method off Mathieu?
  C. Smith

  I would not bother. I have seen his of attitude before. Rather

  than suggest improvements he just bad mouths the entire project.
  He obviously knows nothing about rotary engines. I think it is an
  ideal rear mount as it is the simplest and lightest and half the thrust
  is removed from the lower rubber mounts which are not all that
  good in the radial direction anyway. I got the idea from Steve Beckham
  and Everett Hatch as they used to mount their rotaries that way 15

  years ago. They had to beef up the RV firewalls as well. Since the
  engine is six inches further forward the old 801 bottom mount will not
  work well.

  I have a shear and a brake so when you get the firewall send
  me a picture and I will bend up a reinforcing hat section and send
  it to you.

  Paul Lamar

  Very well, I will take some photographs as soon as I can and forward them
  to you. the firewall pan itself is in my hangar. I can't say I fully
  understand all this, but the point about the longer distance changeing the
  effectiveness of the other system makes some sense. Do you need any more
  structural detail from the prints, or has what I have sent enough for your
  needs?
  I'm sorry about the conflict, too bad there couldn't have been more
  constructive comment. I'm sure that when this aircraft shows up in OSH and
  Sun-N-Fun, we will hear a different song.
  C. Smith

  One high performance take off and they will come with hat in hand :)

  This dwg is good. I think I have enough.

  Is the firewall pan galvanized steel? If so that helps as E is 3 times
  aluminum.


  Paul Lamar


Let me know what dimensions you need, I'll measure them. I've got a handful
of suggestions to help the 801 mount fit a little better too.

I've been installing the connecting arm to the top-center mount point, and
had to fabricate a different mount attach to the center section to provide
clearance between the arm and the top of the renesis front section, among
other things. I'll send photos.

--Kenny A.
http://websites.expercraft.com/kennya/

I think we have it covered by now Kenny.
Thanks anyway.

Paul Lamar

Here are the pictures of the front and back side of the FW pan. It is the
material called out in the prints, galvanized steel, 26ga.
C. Smith

Craig,
I thought it was pre punched or something. OK no problem you have
to drill all the holes anyway so you can add anything you feel like.

Add in a part like the 801 part that looks like this.
Make it out of galvanized 26 gauge sheet steel.
2 inches wide 3/4 inch deep with 1/2 inch wide flanges.
Bolt the whole works together with 4 10-32 screws.

Won't burn in case of an in flight fire. Stiffer than
aluminum. No need for the brace tube in the back but
the top cover over the backside of the instrument panel
should be .032 minimum. If it is .025 increase it
to .032. If it is .032 now increase it to .040.


Kenny, I would still like to see the photos. I was not
referring to those photos. I will revise the 801 mount.

Paul Lamar