I welcome feedback on motor mounts, and would like to clarify some
possible misconceptions.

First of all, my butt will be on the line when I fly my plane,
therefore I truly want things to work, so if there are shortcomings in
something I am doing, I would want to hear about it, and then make my
own judgement as to whether the concern has been adequately addressed.

I subscribe to "both" lists, and try to take the best of what each
offers and reject what my engineering judgement tells me is suspect. The evolution of the mount as best I can remember it is as follows.  Paul Lamar is also building a KIS Cruiser, same as I am, and he
designed a motor mount that used two tripods coming forward from the
firewall to a pad for Barry mounts.  He then designed a massive (in my
mind) aluminum plate that replaced the back plate of Tracy's redrive
to span from one tripod to the other.  I liked the tripod idea, but
had many reservations about the redesigned back plate, including the
fact that it did not allow for the use of the two evaporator cores
that I planned on using for cooling.

Therefore, I adopted the tripod idea and searched for an alternative
way of making the connection to the engine.

I made many mockups using wood, balsa wood, and glue to test the
geometry.  I had several criteria that I wanted to meet. 1. Keep the
weight down, but have adequate strength. 2. Be compatible with
Evaporator cores for water heat rejection. 3. Provide for excellent
oil cooling, with a duct feeding into the oil cooler with a short
path.  I followed Ed Andersons oil cooling trials, and wanted the oil
cooler right up front like Ed found worked. 4. Be able to use Tracy's
redrive with NO modifications, i.e. keep the starter location where it
is at 6 o'clock.

With those criteria in mind, I settled on a cross beam arrangement to
span across the tripods. There were several impediments to doing this
that I had to design around. 1.    I wanted to capture 6 holes in the
oil pan, but due to the curvature of the stock oil pan, that cannot be
done without making a new oil pan.  So I designed and had fabricated a
new oil pan out of Aluminum.  It allows the beam to capture SIX of the
oil pan bolts (not just one Tracy). 2.    I needed adequate strenght
-- Paul Lamar (other list) states that you should design for a 6-G
loading to simulate a hard landing.  Is that over-kill or not enough? I don't know, but it seemed reasonable to me, therefore I used a
design load to be supported by the beam of 1800 #. 3    I needed to
fabricate the beam with a minimum of tools, I don't have easy access
to metal bending brakes or mill, therefore I wanted to use stock
materials.  I made up a spread sheet in Excel, entered for formulas
for stress as a function of geometry from Roark, and explored
different geometries and materials for the cross bar.  I explored
round tubes, I-beams, rectangular tubes, etc. calculating the stress
and the weight of each option. 4.    Since I wanted the oil cooler to
fit just below the cross-beam, I was limited in depth of the beam, in
order to still fit in my cowling.   Having too deep a beam (good for
stress) would put the oil cooler too low, and the cowling would not be
wide enough.  I finally settled on a 2"x1" rectangular tube made from
0.065" 4130 steel, that I could order from Wicks or Aircraft spruce.

For the ends, I need a thickness of 1/2" to fit in the Barry mounts,
so I made some 1/2" Aluminum ends out of 2024 Aluminum plate. I could
cut and shape this material with my tools. These are held in with 4
AN-4 bolts, with metal spacers to fill the difference between the
aluminum ends and the other wall of the tubing.

Since I have bolts going through the beam into the oil pan (6), I had
to be concerned with crushing or bending the beam when tightening the
bolts. To alleviate that problem, I had small tubing welded in the
holes to bridge from the top to bottom of the beam, so I can torque
down the oil pan bolts, and the tubing takes the compressive load.

That pretty much describes my design and criteria.  I posted the
pictures (I thought to both lists), and got some feedback from Lamar's
list.

Someone expressed a concern that the outer two of the six oil pan
bolts would be taking too much of the gyroscopic load and that this
represented a failure mode.  They recommended having an extension on
each side of the oil pan that would tie the beam into a couple of the
side oil pan bolts. This would make the mount be attached with 10
bolts when accomplished.  I have not done that yet, but plan to when I
next go to my welder.

As this has gestated for over a year, Jerry Hey became interested in
possibly making these. He has access to a bending brake, and an
alternative method of obtaining the same stiffness is to use a 'hat
section'. He has incorporated the concept of the side wings that
capture some of the side oil pan bolts, and will fully load the beam
before declaring it a product. I personally like the closed
rectangular tubing, but life is full of compromises.

The beam motor mount requires a third mount point, at the rear of the
engine. The beam is most certainly NOT at the exact center of gravity
of the engine/redrive/propellor assembly, but I believe that it is
CLOSE to the CG.  It goes under the front cast iron of the engine, not
off the redrive plate with is 3" further forward (tractor airplane). The contention is that a single mount point for the rear end of the
engine can be used -- this was done with the Questair Venture from
what I understand.  I am still evaluating the best way of making this
mount, a PRELIMINARY method that I am evaluating is to tie into the
big 12mm bolt hole on the rear casting and run to a hard point on the
firewall.  I can make a hardpoint anywhere I want on a fiberglass
airplane. Have I SETTLED on this rear mount -- NO, not yet, I need to
make a number of calculations, and would like to have feedback from
others.

I would like feedback on this design, with your concerns and comments,
bearing in mind that the beam is attached with 6 bolts, soon to be 10,
and that the rear motor mount is still under construction and
evaluation.

Bill Schertz
KIS Cruiser # 4045
  ----- Original Message -----   From: Tracy Crook   To: Rotary motors in aircraft   Sent: Saturday, May 22, 2004 1:27 PM
  Subject: [FlyRotary] Re: Shertz Beam





    I have examined the "Shertz Beam" Motor mount on "the other" Mail
    List.

    Searched and did not find a comment on this list.

    Other than it is recomended by "The Other" list, is there anything
    wrong with it?

    I am looking for solid/semi solid engineering critique.  I really
    dont want to talk about "feelings" or "preferance".

    Thans for your time.



    I prefer the straight stuff too so to get right to the core of it:

    1.  Shertz Beam -  Which incantation do you mean?  There is no
    single definition.  I have seen at least 6 versions.  In it's
    original incantation, a SINGLE 6mm bolt in tension absorbed ALL of
    the torsion forces (prop torque and vibration loads).  This was
    unacceptable.  I have seen a few attempts to fix this, some good
    some not.

    2.  The beam is NOT at the CG, contrary to claims otherwise.     There are significant loads on the rear mount which is not even a
    part of the Shertz beam design.  It has been proposed that the
    rear of the engine be hung from a central point off the engine
    front housing from an assembly made from 2 rod ends.  The other
    end is supposedly attached to a hard point near the center of the
    firewall.  On most aircraft, there IS NO HARD POINT at this
    location.  In addition, on an aerobatic plane where negative loads
    can occur, the "hanging rod" in compression is 'less than ideal'.     3.  This mount more or less assumes that the rad is going to be
    mounted under the engine.  This rad location and the Shertz beam
    makes more sense on a composite canard design but on a tractor,
    the mount ends up taking up space in the wrong places.  The most
    popular and successful cooling scheme so far use two heat
    exchangers in a location that interfears with this mount.   It
    would also not work with what I plan to do on my -8 with a single
    rad.

    Tracy Crook