Im writing to you from Australia and am after some
advice/ideas/enlightenment.
I am not yet a pilot; however I hope to soon have a licence. I also hope to,
in the nearer rather than further future, build a kit aircraft and I wish to
power it with a rotary engine. To that end, I have been researching as much
as I can on the internet.


I am a subscriber to your newsletter, I have Traceys manual on rotary
conversion and have gathered heaps of great info on rotary engines.

My dilemma is:
*   Everything anyone writes about seems to be in the
200Hp-300+Hp, and usually based around the 13B, or larger-
(3,4,6 rotors. Good Grief! Now maybe if I could just find and afford a Helio
Courier that needed an engine and a good home)

*    The aircraft I want is a STOL Hornet built by
  Australian Aircraft Kits www.aircraftkits.com.au and is rated
  for 120Hp. It is a 2 + cargo, or a 2 + 2. I have been in
  contact with the company and they seemed happy to accept a
  rotary in the 120Hp-140Hp range and said they would need to
  provide wing extensions to counter the weight of the rotary.

I have purchased a stock 12A (which I understand falls into the 120-140Hp
bracket) from a wrecking yard that seems to be in good condition. If it
measures up, then Im happy to put a master kit through it and build it up as
a power plant.

I know I will loose out on the power to weight ratio that rotaries are
famous for, but so be it. If I could afford a set of Racing Beat alloy
plates Id be ahead of the game.

In your opinion,
*    is it worth my while to continue down this road and
build up this 12A, given the (relatively) low Hp required? Or are there
better options you are aware of? Rotamax????
*    If I do continue, am I better off looking to EFI of
carburetted?
*    What PSRU would you recommend?

I am not an engineer, electrician, or have any sort of trade background. I
am pretty handy with most forms of metal fabrication and welding though and
can usually get around a set of plans or diagrams without too much drama.

Any help you can provide will be greatly appreciated.

Yours in anticipation,

Stewart Woerle.


Stewart Woerle
Nathan River Ranger Station
Limmen National Park
PMB 133
Katherine NT 0852

When aircraft builders are thinking of limiting the HP what they are
assuming is you are going to use an aircraft engine. Well what they are
really thinking about is increased weight with more HP always results in
more weight in a air cooled aircraft engine. More HP will not intrinsically
hurt an aircraft in any way if you don't use it. True it can be hard to
control at sea level during take off due to torque effects but you don't
have to open the throttle all they way if you don't want to.  Where more HP
pays off is at high altitude where the drag is down and the additionally HP
allows you to cruise faster.
I have flown all over your fine, beautiful and large country in a C172 and
what you really need is a faster airplane :) Another advantage is you cannot
have too much HP in a STOL. To get off in a short field what you need is
rapid acceleration to flying speed. Read a large diameter prop with lots of
HP to turn it. In that case what ever engine you choose, 12A or 13B, use a
p-port as it is a cheap additional 50 HP with no increase in weight or fuel
burn if you don't use it a cruise. In fact the weight of the p-port intake
manifold is less than the weight of a side port manifold.

Now that we have that discussed lets talk about engine weight. The 12A is no
lighter than a 13B mostly due to the cast iron water pump. One advantage it
has is cost.
Here in the states they are in many cases free.

Now I am a little worried about your choice of aircraft company as adding
extensions to the wings is not a smart thing to do. You risk wing failure in
turbulences and in normal maneuvers. The current wing is structurally
designed (or it should be) for  the amount of surface area it has and the
gross weight of the airplane.

Now a low cost for the kit may be your main concern but the time it takes to
build an aircraft is not necessarily related to the size. I would pick a low
cost fast build STOL kit aircraft that was designed for the weight of the
13B or 12A engine. A Zenair 800 is a low cost STOL aircraft that will
accommodate the weight of a 13B. You might find an Australian version that
will do the same thing.

Rotamax is out of business.
A  500 CFM 2 barrel Holley carb with leaning kit is the lowest cost way to
go.
Tracy's PSRU works fine.

Paul Lamar

Paul, is there any way I could get the  Zenith 2-rotor
drawing in a .dxf or .dwg format? As my CH-640 shares the same FWF
configuration (with the exception of the top center attach) with the CH-801,
I want to look at where things are, and better visualize where everything
will need to be.
Thanks C. Smith

Yes I think I can do that. One of my NC shops needed some dwgs.
Let me get to that later.

Paul Lamar