Date: Sun, 23 May 2004 11:17:49 -0600
From: Bob White <bob@bob-white.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Beam Motor Mount (semi-long)
Message-Id: <20040523111749.53327773.bob@bob-white.com>
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Bill,

Thanks for the history of your design.  Several months back I chose to
use the MM plate which requires the same type of rear mount that you
need.  I chose it over the Conversion Concepts design because I didn't
want the oil pan seals involved with the mount. I had heard about your
mount, but didn't investigate it since there were willing suppliers for
both of the other mounts. 

I happend to have the MM plate laying on my kitchen table, so I weighed
it.  It's 11 lbs with the Barry mounts.  So my excess weight is 11 lbs
minus the weight of Tracy's flange.  I don't know what the rest of the
tubing weighs, but it's very light.

For the rear mount, I fabricated bracket to hold the rubber bushing tie
rod ends reccomended by Lamar.  The bracket is designed to put the rear
mount in the center of the firewall.  On the firewall, there used to be
a nose gear attached at this point, so it makes for a good hard point. 
The engine bracket is attached to the two tabs that protrude from the
end plate.  (I understand that not all engines have these tabs.)  The
reported weight supported by this rod is ~ 50 lbs. I will measure it,
and inspect it carefully until I'm satisfied that I'm not over stressing
it.

Photo of my rear MM bracket:
http://www.bob-white.com/new_rear_mm_a.jpg

The bracket is built out of 4130 square tubing 2 X 2 X .065 with 2 X
0.25 4130 bar stock welded to the ends.  I cut the end pieces to fit the
engine tabs with my torch.  One side is bolted on with the two 8 mm (I
think) bolts and held with locktite (blind threads on one hole, and on
the other hole, the casting has an angle that would put a lot of stress
on the bolt if I used a lock nut). The other side by three 1/4 in bolts
with lock nuts. The bottom bracket is bolted between two pieces of 1/8"
angle aluminum and held with two 1/4" bolts on each side. This seems
like it should be adequate for the 300 lb loads anticipated in the 6 G
landing.

There are a couple of disadvantages to the MM plate that I didn't
consider.

1) 
It blocks the area on either side of the engine.  This is the ideal
place for the evaporator cores.  On my BD-4, I have a ton of room under
the engine, so I can move the evaporator cores below the MM plate.  I
need to work out just how I'm going to open the cowling for the cooling,
but I'll figure out something.  At one point I had decided to use a safe
and easy cast iron exhaust manifold, but it intefered with the MM plate
also.

2)
The redrive and the motor mount are now connected.  This is a bigger
inconvenience than the motor mount and oil pan seal being connected.  I
can't install or remove the redrive without removing the engine.

Another BD-4 builder working on a rotary installation is using the
Conversion Concepts mount and so far he is very happy with it.


All in all, if I were starting over I would use your design as it's been
modified to pick up the 10 bolts.  It seems the simplest and lightest MM
available to date, it's closer to engine CG reducing the weight on the
rear MM, and it opens up the area at the sides of the enging for the
evaporator cores.

Bob White


On Sun, 23 May 2004 10:11:30 -0500
"William" <wschertz@ispwest.com> wrote:

> 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
> 


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