Hi Paul, what info do you need, to construct a cad model of a rotary
engine mount for a tango XR? In broad terms the firewall dimensions
are 42" wide x 26 3/8" at the widest points, the thrust line is
approximately 11" below the top of the firewall. More accurate thrust
line measurement to follow soon but11" is pretty close

Also I have been chatting to Milo with the RV8 FWF for sale, there's
obviously a lot of changes to make that fit, what we thought of doing
was superimposing the rv8 mount over the tango XR mount to get an idea
of what sticks out the cowling and would have to be moved, would you be
able to help with this?

Alex

The firewall dimensions. You can take a perpendicular picture of the
firewall looking back at it and then tell me the max width. From that
I can scale the dimensions that I need.

Also i need the point on the firewall that represents the thrust line.
A
piece of tape will mark that point. This way I can do a cowl drawing to
make sure everything fits. If you have a cowl we can use that. I need
 the
lenght and the size of the spinner. If no cowl I suggest using an 18"
spinner as the rotary engine is roughly round and that gives more room
 in
the cowl.

Paul Lamar

Hi Paul sorry for the delay I just got back to my project today, a
perpendicular picture of the firewall as well as cowling photos are
attached. The accurate dimensions are:

Firewall:

The thrustline is 10 7/8" down (from the top centre of the firewall) and
marked by an X, also marked as the line on the top edge of the tape.

Maximum firewall width is 42 7/16"
Maximum firewall height top to bottom along the vertical line is 26
5/16"

Firewall width running through thrust line marked by X on firewall is 42
3/8"

I still need to incorporate a 1.25 degree offset from the X point, (as
is
required by the plans for the lycoming install) or can this be done with
computer modeling? I would prefer to offset the rear of the engine from
  the
X mark to achieve the required 1.25 degree offset, because the cowling i
have already has the offset built into it.

Cowling:

Length 36 3/4" (as measured along the top)
Spinner diameter 14"
Spinner 1 length 14.5" (same spinner as in the photo)
(Optional spinner 2) length 19"

Additional cowl info, lower cowl circular inlet is 2.5" inner diameter,
both forward air intakes are 2.5" wide and approximately 6.75" long

I'm planning on using Tracy's 2:85 reduction so thrust line offset would
  be
to the right as viewed from the cockpit and I was hoping to incorporate
 an
exhaust augmenter setup to help with cooling,

I forgot to mention, my pre drilled engine mount holes on the firewall
 are
both 37 15/16" apart from each other in width, and vertically 19 13/16"
apart, all measured from centre to centre. These holes are already
hardpointed to take the mount,


Alex Molteno


Good work Alex. I'll see what I can come up with.
Unless you want to put something under the fuse there will not be enough
room for a proper  exhaust augmenter. If the cooling diffusers are done
right there will be no need.

Paul Lamar

  Hi Paul
  I  hadn't firmed up my ideas entirely regarding the lower cowl setup. I
  thought i might need to hang a spintech muffler underneath the cowl if i
  need to quiet the beast downwhich would negate using an augmenter.

  i also wanted to go with a sub cowl design like Ed Vettermans (or better
  yet the one that was posted a couple of days ago on the newsletter) to
  clean up the cooling drag for any air exiting the bottom cowl. i know
 there
  is a bit of reverse flow going on there because where oil pools up on
  another completed tango next to mine, it doesn't streak and run backward
 in
  flight like usual, so I need to do something there anyway to clean it up.
  The current firewall design makes cowling air turn through an abrupt
  90degree bend on the bottom of the firewall, and after the bend no
attempt
  is made at accelerating the cooling air back to free stream flow

  What I liked most about the augmenter idea was that with the pumping
gains
  from the exhaust I could ditch the thermostat, cooling air flow through
  heat exchangers would be automatically regulated (more or less) by the
  amount of power I've set. Having such a wide range of hp my aircraft will
  be flying at, also helps keep the inlets from having to be oversize or
  undersize in order to be able to keep within limits.

  Alex

  It is not a good idea (I think) to use any commercail muffler. I am
afraid
  you will need to weld something up. There is a possiblty that the guts
 will
  melt and plug the exhaust. Especially if you are using a 13B as opposed
to
  an RX8 engine.

  Ejectors have to be rather long to work well.

  Paul Lamar

 Paul, noted on any of the automotive off the shelf mufflers. It seems
 tuning an ejector is a hassle too as a fixed size design only works for
one
 speed and air density, and its performance drops off on either side of
that
 optimum combination. I've read it can create more drag than it makes
thrust
 at higher speeds, if its tuned to provide adequate ground cooling which is
 what i wanted it for.

 I will try and optimize the cooling diffusers as much as possible, and
 might look at shaping the subcowl as an "inverted turbulent flow wing" to
 try and generate more of a low pressure area just aft of the firewall that
 can suck out expended cooling air with some propwash over it,

 Alex

 The trick is to use a long, small diameter coaxial muffler under the fuse
 like Brian
 is building. That minimizes the frontal area increase and the aero drag
 yet providing
 good silencing. The optimum hole sizes are yet to be determined.

 Paul Lamar

I look forward to hearing from Bryan how well it works - Alex

In any event it is visually inspect-able and easily repaired.

Paul Lamar


Hi Paul,

I assume you have the C of G for a generic rotary install (not sure if this
changes much with individual installations such as heat exchanger
placement, etc) I have the old style horizontal stab which is 10 lbs
heavier than stabs on newer tango's nowadays, plus I think I could be
lighter with Milo's rotary FWF than a standard lycoming for this aircraft,
and I moved the rear bulkhead backward 3,5" aft for space to put a child
seat. Additionally, all tangos so far have a 45-60lb aero composites prop
or hartzell. This is all trending towards an aft cof g, so I want to try
and put the rotary as far forward as I can (as well as mount 2 batteries on
the cool side of the firewall instead of behind the rear bulkhead.

On the standard lycoming install as measured off a plane next to mine in
the hangar is 33" from the firewall to the front plate of the flywheel for
the lycoming, I can go to 36.5" on the rotary then I only need a small prop
spacer to clear the spinner against the cowl rather than a prop extension.
I could, at a stretch, sand down the back of the spinner but this will also
reduce spinner diameter and it won't be a flush fit.

Is it possible to move the rotary further forward?

With this in mind, regarding the engine mount, is it possible to move the
front of the rotary to 36.5" from the firewall. The standard

I have forward and aft fuel tanks on the wing. If the C of G turns out to
be slightly fwd then I can keep fuel in the aft tanks to compensate, but
rather fwd than aft I think.

33" from the firewall to the front plate of the flywheel
36.5" max 39 3/4

2 7/8 inches

Alex

The standard is 37 inches + or - 2 inches from prop flange to firewall. If the cowl is done it is best to use the stock cowl as it is a lot of work to make a new cowl.

I'll do a 3D shortly.

Paul Lamar