peterz(at)zutrasoft.com
Guest
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 Posted: Thu Dec 20, 2007 5:13 am Post subject: Update from the Gemini 100 Folks. |
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Sounds like they are covering the bases fairly well.
Cheers,
Pete
A239 (still a pile of parts)
PS- apologies for the formatting..... it was a simple cut and past from the .pdf I received.
Gemini 100 Current Status
There has been
some slippage in
PPD' original
schedule, mainly
due to long lead
time items such
as castings, forgings and more specifically
crankshafts which will not be arriving in Hastings
until the first part of January. This pushes the
running of the engine on the test cell out to the
first week of February.
Shortly afterwards we will complete some
propeller analysis, installation work and flight
test. Once this is accomplished we will start
production and anticipate deliveries to the
experimental market in July 2008. In parallel we
will be working towards ASTM approval and
anticipate achieving it in December 2008.
We appreciate the patience that each of our
customers have shown since our announcement
at Air Venture in July, 2007. We have received
nothing but support and congratulations from the
industry.
Gemini 125 Current Status
We have received a tremendous amount of
interest in the Turbocharged Gemini 125 with
most of the questions centered on availability.
We anticipate delivering the Gemini 125 to the
market in December 2008.
The major difference between the Gemini 125
and the Gemini 100 is of course the
Turbocharger and attaching hardware.
Engineering is also contemplating a piston
change which of course prohibits any field
conversions, which is one of the common
questions we are asked. PPD will offer a special
exchange price for those customers originally
purchasing a Gemini 100 and then upgrading to
a Gemini 125 once available.
Overall dimensions of the Gemini 125 will be the
same as the Gemini 100 for the width 22.68 in.
and the height 15.75 in. The length will be 1.18
in. longer than the Gemini 100 coming in at
22.83 in.
Pricing Status
PPD has established the introductory retail price
for the Gemini engines at:
Gemini 100 $18,000.00
Gemini 125 $23,500.00
These are introductory prices and are
subject to change. Please contact PPD for
updated pricing and delivery schedules.
Order Status
Currently PPD' production through August has
been sold out. If you would like to place an order
a refundable $2500 deposit (which will be held in
escrow) is required to place your engine into our
production plan. PPD will notify you when the
engine is ready to be built at which time you will
have the choice of affirming your order and the
$2500 is no longer refundable. You will be
notified again when the engine is ready to ship
and full payment of the balance will be required.
Gemini Power Notes
Volume 1, Issue 1 December, 2007
Powerplant Developments, Ltd.
The Old Stables, Hoadlands, London Rd.
Handcross, West Sussex
RH17 6HB, UK
Telephone: +44 (0) 1444 401325
Fax: +44 (0) 1444 400745
U.S. Cell: 214-404-3981
Frequently asked Questions
One of the frequent questions we are asked
deals with vibration being commonly associated
with Diesel aircraft engines and what PPD has
done differently.
A vibration problem lies with the fight between
the acceleration forces (acting on the pistons
and rods) and the main inertia mass (the
propeller) via the spring in the system
(crankshaft, propshaft, gear flexure, etc). This
can also have an undesirable effect on the
auxiliary drives (although the auxiliaries usually
have their own damping if found necessary, but
they in turn can sometimes help slightly by
providing a low level of damping).
The method we have chosen on the Gemini
engine to dampen the 3rd and 6th order vibratory
forces common to a three cylinder engine, is to
have pendulum dampers fitted to the crank in a
similar way to those fitted in conventional aircraft
piston engines. The pre-production engines we
are running on in the test cell will also to be fitted
with a torque limiter (clutch) for added protection
and evaluation. This effectively dumps any
excessive forces and is really the only way to
guarantee that no twisting forces can be above
the design level, the dampened energy being
converted into heat that is taken away by the oil.
If after final torsional analysis on the running
Gemini engine we find the damper cannot be
fully tuned to keep vibration to an acceptable
level for the range of propellers to be used
because of their various inertia values, we will fit
a clutch as standard.
The acceleration loads on the propeller should
be well within its specified limits because the
Gemini engine being a two stroke with relatively
small cylinders produces quite a low peak torque
from firing loads when compared to rival aircraftengines.
Think of a conventional IO-360's 90
cu.in. cylinders pounding away with only two
firing strokes per prop revolution compared to
the Gemini's 32 cu.in. cylinders firing at 4.8
times per prop revolution. The propeller will feel
like it is being driven by a turbine in comparison.
This in turn leads to the problem that other
Diesel aircraft engine manufacturers have had to
overcome. The four-stroke, large capacity of one
of these engines (76 cu.in. per cylinder) has the
same firing pulses as the conventional gasoline
four cylinders, however, their problems are
greatly compounded by the exceptionally high
rotational accelerations due to its higher
compression ratio increasing the rate of deacceleration
on compression and then
acceleration over TDC, this is exacerbated by
the longer stroke needed for a diesel, this in turn
can produce severe 2nd & 4th harmonic orders.
The peak torque loads acting on the crankshaft
are also so much higher on these four stroke
diesels. The Brake Mean Effective Pressure
(BMEP) of the competitive 4-stroke diesel
engines currently in the market place is between
226 and 272 psi at max power; compare this
with the Gemini's 101 psi BMEP.
It is also worth mentioning that while almost all
aircraft and automotive engines take their
camshaft and auxiliary drives from the whippy,
free end of the crankshaft, the Gemini engine
has its oil pump, injector pump and
supercharger drives from the smoother drive
end. The drives are actually taken from close to
the smoothest point in the drive system - the
nodal point. [quote][b]
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