Martin,
I'm working on a single rotor development for my aircraft using 12A
housings
with early 13B rotor housing and a RX8 rotor with apex seals cut to 3mm.

I don't have the problem of balancing the rocking couple, so the balance
of
the single rotor should be close to static balance.

Advice to me with balancing is to consider full rotor oil weight as well
as
all seals except the apex seal and add this to the rotor weight. Not to
include the apex seal and springs as their carried by the rotor housing.

Can you comment on this in regard to balancing the single rotor, I would
like to get it right the first time, if at all possible, as the single
has
the big torque reversals, so is not as smooth as the 2 rotor.
George (down under)


George,

I have been working on single rotor engines for more than ten years -
including their balancing. So I am fully aware of their potential
problems with torsional vibrations. At MWE/Diamond for instance it was a
set rule not to run the engines below 2,500 rpm, preferably 3,000 rpm
plus. We had more than a couple of dyno couplings literally explode
within seconds when engines were run at low speeds and high loads!

The assumption to add the inner rotor volume of oil was one of the
points discussed more than once. All plain bearing engines I had built
at WankelSuperTec had been balanced outside the company based on the
aforementioned assumption. They ran quite smooth taking into account
their high compression ratio and the very crude mapping those early
days.

The MWE/Diamond rotors are fresh air cooled by a blower fan though. So
apparently there is no oil in the rotors. But we had the permanent
discussion of whether to include the weight of the apex seals and their
springs when being balanced. The designers and calculators said:
NO, the apex seals are not part of the rotating assembly as they "rest"
on the rotor housing.
BUT test comparisons carried out at Norton in the 1980s showed that
engines, balanced WITH the additional weight of the apex seals and
springs, ran smoother still than those without! Theory behind it was
that the inertia of those seals and springs is still imposed on the
outer structure of the engine, hence the frame as well.

If I remember correctly the total weight of a set of apex seals and
springs of a Diamond single rotor engine is in the order of 30gramms. A
Mazda set weighs a lot more still.

To sum it up in one sentence: If I was to balance a Mazda Single Rotor
engine I would add the weight of all seals and springs and the weight of
the oil as well. Hope you get it right that way!

One question with regards to your set-up: Why will you be using an RX8
rotor in an RX7 rotor housing? What benefit are you expecting form that
mix?

Regards and good luck,

Martin.

George,

With all of your work with single rotor units, do you believe that it is
feasible?

Don Bedwell

May I add some practical results on single rotor work?

I have a single rotor running, based on 12A dimensions, meaning, the rotor
and housing are from a 12A.
It is peripheral port, with carburetor and long intake runner. The power at
this time is 92hp at 6000 RPM, calculated from fuel consumption and mixture,
assuming a BSFC of .5 .
It idles nice at 2000 RPM. If I would want it to idle slower, it would need
a heavier fly wheel.. The engine was balanced at MazdaTrix.
There is no torque vibration problem at the speed range I have run it so
far. The gear ratio is 3.3:1 .
The weight of the engine FF is comparable to the Rotax 912.
There are a lot of pictures from the evolution of that engine on Paul's web
site. Attache is my poor-mans test stand.

Richard Sohn
N2071U

Thank you Richard. Very interesting.

DON  BEDWELL