>
> 1). What do you think of dry vs wet oil sump? All comments and
> suggestions
> welcome
>
> 2). As it is impractical, if not impossible, to make a fully
> aerobatic
> rotary engine on the basis of a Mazda block, what level of
> "limited"
> aerobatics capabilities is acceptable/wished for? I am
>especially
> concerned
> with vertical or near vertical manoeuvres... tricky
situations >for
> rotaries...
>
> Thanks in advance for the feedback.
>
> Francois Badoux
>
>Francois,
>1) Dry sump gives you much greater flexibility. I plan to use
dry sump
>on my 20B from the start. With respect to inverted operation, a
>pickup with a dedicated scavenge segment can be placed at the top
of the
>engine to scavenge inverted. You have probably thought of this
but I
>must offer the thought.
>
>2) Your concern with vertical maneuvers is drain back
problems? This
>could be the tougher of the problems to surmount. But since so few
of us
>are Sean Tucker it is probably the least often used acrobatic
mode for
>most of us. (straight and level is fine with me for the most part)
>For crankcase pickup most of the auto applications use pickups
at the
>front and rear of the pan anyway. (for acceleration and
braking) Your
>concerns about filling the rotors is a much more serious item.
With dry
>sump you do have the option of placing more scavenge pickups in
critical
>areas. I have seen V8 engines with 6 or 7 scavenge segments; in
addition
>to the oil pan they have pickups at the back of the valve covers
and the
>back of the intake valley. Tests in the past by Chevrolet
showed the
>more oil you could remove that wasn't in the bearings (drain
back oil)
>the more HP you could generate. There is a point of diminishing
returns
>on this of course. We need to concern ourselves with weight of the
added
>plumbing too. Dry sump does give you these options though, wet
sump
>doesn't.
>Bill Jepson
Francois, my automotive experience which is a drag racing back
ground,
proved the wet vs dry sump showed no hp difference if designed
for the
application ie 1 G gravity and 1 or 2 G's lateral acceleration.
The wet
sump
can be designed for this! All you want to do is get the oil away
from the
rotating assembly and then both systems are equal.
The big advantage, was the engine with the dry sump could be
lowered
in the
chassis for better aerodynamics and reduced weight transfer!This may
be a
big factor in a high speed aircraft too!
Not being totally familiar with the rotary I would think a sump or
pick up
point could be located on the engine so as to scavenge oil from the
rotating
assembly in a 1 or more G negative system. In the piston engines
most
people
use an accumulator to provide pressure when oil is not available
from the
sumps via the inverted systems ie in vertical maneuvers or in slow
inverted
maneuvers where the inverted system has not made the switch over!
Just a few thoughts on your subject!
Regards
Ron
I just got this weigh scale from Robin for a Christmas present. I
have been
looking for a scale like this for years. Robin found it in a farm
supply super market here in SZP. Thanks again Robin.
Getting to the point this rear main bearing holder weighs
a bunch and only has one oil drain back hole. It is conceivable
that a
bunch
more drain back holes could be drilled reducing the weight of
this heavy
part and enhancing the drain back at the same time.
Paul Lamar ...No rotor no motor.
Good point Paul,
A point for Ron to consider, you may be able to get your drag race
engine to endure 2G acceleration with a wet sump, but when was
the last
time you made a pass inverted?
Bill Jepson
I never did the inverted test with my car drag car Bill, thank goodness,
but I fly my Glasair inverted some and it has a wet sump, with a
Christiansen Inverted system and it works fine. A lot simpler and much
less to go wrong than in a dry sump plus considerably less costly!
However,you will loose a little HP when you roll over and all that oil
falls down past your crank, but you'll probably never feel the
difference or at least I haven't. All the heavy aerobatic guys Tucker
included, I think, have wet sumps and inverted systems, if they are
using the Lycoming or continental engines and probably use an
accumulator to keep pressure on the oil system when the positive to
negative switch is made. With no accumulator and a loss in pressure for
too long, in a Lycoming 540, will lead to the prop going into low
pitch as these propellers are hydraulically actuated to high pitch,
with out pressure they relax via spring pressure to low pitch.
They usually don't have counter weights to force them to high pitch as
in the 4 cylinder Lycoming. At high speed the result of the prop going
to fine pitch would be more than entertaining. Also the accumulator
feeds oil to the engine for the 4 or 5 seconds of low or zero oil
pressure during the transition to going inverted.
I am not completely familiar with the rotary, but if a pick up could be
installed on the top and rear of the engine it would satisfy the
inverted and vertical requirements, I would think. Maybe the dry
sump is
the way to go for some people, but you will still need to scavenge oil
from the top and rear(as installed in the plane) of the engine.
I hope, I am not talking out of school here. I hope to get my hands
on a
rotary engine soon and learn a bit more about them.
Ron
Speaking of capturing oil while inverted this is the rear
chamber between the rotor and the rear main bearing.
As you can see there is only that one small hole to drain
this area. I suspect there would be some HP loss as well
as foam and heat added to the oil.
You can see the drain hole looking through the rotor in about the ten
O-clock position. Normally the drain hole is located on the bottom
of the chamber.
The shot through the rotor also shows the rotor oil drain passages.
These passages are also how the oil gets into the rotor to cool it.
Looks like there are lots of chances for the oil to drain out of the
rotor no matter the orientation of the aircraft.
Paul Lamar ...No rotor no motor.
Paul is the rear main bearing at the rear of the engine when installed
in a tractor position( front of the airplane)? I am not clear on this.
Ron
Front in a tractor. The engine is ass backward in a tractor airplane
compared to a car.
BTW The oil is squirted into the rotor under 100 psi
oil pressure. If the rotor fills up it is forced out by centrifugal and orbiting
forces at 6000 RPM or above. Also by the same oil pressure gaining a lot
of foam and heat in the process of course. The magnitude of these forces
on the oil far exceeds the one G vertical penetration forces due
to the attitude of the airplane. You get a lot of G's doing aerobatics
radial but not much longitudinally if you get my drift.
Paul Lamar ...No rotor no motor.
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