light twins?

On Wed, 27 Jul 2005 22:47:34 GMT, Ernest Christley
wrote:

The second quoted problem is a red herring. BSFC. The rotary leans MUCH
better than any piston engine. In actual practice in real airplanes,
fuel burn is indistinguishable.

But the advantages. An engine that will sacrifice itself to get you
home. A $500 rebuild that takes a weekend. Power to weight ratios that
already beat pistons and continue to climb. Did I mention, an engine
that will sacrifice itself to get you home.

All good points. I didn't mention this (at least not recently) but I
had a 13B in my shop at one time that I was going to use for my
airplane.

This was a number of years ago before Tracy began developing his
rotory. I had started with a Buick/Olds 215 cid aluminum V8 but had
sold it because it was too hard to find parts for it.

I was getting increasingly nervous about using the 13B because I knew
I had to fabricate my own intake manifold and exaust system. I had
been an auto mechanic who worked on Mazda's, including the RX7's so I
knew something about them. The intake manifold looked to be almost as
big as the engine, which is why all the folks I'd been talking with
were recommending it be junked and a smaller one fabricated.

Remember, this was in the early 90's, not now.

But the thing that really put me off was the heat of the exhaust
system. It ran something like 500 degrees hotter than piston type
exhaust systems and required a thick wall stainless steel system.
Even with such a system, all that heat seemed a little scary to me.

So I sold that and now have the Ford V6 which is running well at this
point and seems to have all the power I need.

Corky Scott

Rusty,

I've just been thinking about that fellow's contention that a single rotor
needs a redrive as strong as a two-rotor, because the power pulse of a
single is just as strong.

As far as I can see, this cannot be valid. If I'm thinking this through
correctly, each rotor will make three power pulses for each revolution of
the rotor, or one revolution of the e-shaft.

Even if two rotors were running out of phase, there would still be two power
strokes for each revolution of the e-shaft on a two-rotor, versus a single
power pulse per rev on a single. Your redrive would need to handle only half
the power.

Tracy's gearboxes are excellent by all accounts, but why use something so
heavy if it's not necessary? (Even so you overall weight of 220 lbs is
excellent for a 100hp engine).

Also, in terms of packaging, on a high-wing pusher like the Kolb, an upright
belt drive would put your thrust line at wing level where it needs to be,
while the engine could be down low, near the plane's vertical center of
gravity (like on the Challenger, which uses such a tall belt drive with the
Rotax 2-stroke).

I am interested in exploring just such an application with a high-wing
pusher design that I am developing. I've been looking at poly-v belts, which
you see driving the engine accessories on newer autos -- but there are
poly-v belts that will handle upwards of 500hp. You also see them on some
two-stroke UL engines.

The advantage of the poly-v over a cogged (synchronous) belt is that they
naturally dampen torsional spikes, by means of slippage. Another plus is
that the pulleys can be considerably lighter.

Regards,

Gordon.

PS: Regardsing the issue of hot exhaust on rotaries, this makes them ideally
suited to turbocharging.


"Bellsouth News Server" wrote in message
...
Hi Gordon,

I'm starting out with one of Tracy's RD1C drives, which is 2.85:1, and
good for way more power than I'll make wiht the single rotor.
Unfortunately, it's about 45 lbs stock. Speaking with Tracy, there's
probably about 5 lbs of weight that can be removed without losing any
strength, and perhaps more if you're willing to sacrifice strength in the
drive. That wouldn't be a problem for the single rotor, but if you ever
wanted to use it on a two rotor, it would be.

Richard Sohn has a running 12A single rotor now, and he's using a Hirth
G-40 gearbox. At last report, his total engine weight was 170 lbs, which
is pretty great. He's custom made many of the parts on his engine to save
weight, and might produce them if it all works out well. He's currently
on a slow, and careful development and test program, and eventually plans
to put the engine in his Avid, which I believe is flying with a Subaru.
It will be interesting to see how the Hirth box works out, but I'm not
sure how much lighter it really is in the long run. I've asked Richard
for the total weight, but since so much of the adaptation is dependent on
his custom end housings, he hasn't been able to come up with a number. My
guess is something around 30 lbs total for the drive.

I asked about belt drives, and found that someone was making one for the
single rotor that David Atkins is selling. So far, I haven't heard any
reports of how that worked, if it even got finished. One other fellow who
makes belt drives told me that he refused to make such a drive for Atkins,
because it wouldn't be strong enough. His point was that the single rotor
is still full sized, and gives the same strength power pulses as the two
rotor does. Because of this, he felt the drive has to be as strong as the
two rotor drive. This does make sense to me, but I'm sure there has to be
a way to reduce the weight further.

FWIW, my plan was to bolt together off the shelf parts, and see what it
weighs. The Kolb Slingshot that I'll be using initially will handle the
weight, when flown as a single place, and with a BRS chute to balance the
CG. Once I get a worst case weight, then I'll start working on reducing
it.

Cheers,
Rusty (hiding rotary info in the light twin thread)


What gearbox are you using? It seems like overkill to put one of Tracy's
boxes -- or something similar -- on a single rotor.

I would think a belt drive might be engineered that would be considerably
lighter -- expecially if you use the poly-v belts.

Tom,

Thanks for that link. What an amazing aircraft. These self-launching
sailplanes have really become a hotbed of technology. (L/D ratio of 50:1,
laminar flow over 95 percent of chord; wow.)

The fact that a rotary is used instead of the traditional two-strokes speaks
volumes about the rotary's power-to-weight performance.

Regards,

Gordon.




wrote in message
oups.com...
A rotary made by Midwest (originally used in Norton motorcycles) and
now produced by Diamond has been very successfully used to power self
launched sailplanes made by Alexander Schleicher. I fly an ASH-26E
powered by a 50hp single rotor wankel.

More info is at
http://www.as-segelflugzeuge.de/engl...ash26_main.htm

-Tom

PS: Rusty, thanks for the info on the gearbox. That Hirth box or something
similar sounds like a good way to go. 170 lbs is outstanding for a 100hp
engine -- could be even more with peripheral porting.

Best of luck with your Kolb project. I hope you will have some pictures
available.

Thanks Gordon. BTW, Richard Sohn's 12A single rotor is peripheral ported.

PP vs the normal side ports is a hotly contested issue on the rotary list,
and I personally believe it's not worth doing for our 7500 rpm range. I've
been told that a good porting job on 3rd gen housings will get you the same
power as PP at the same rpm. The side ports will lose big if you're going
to run up to 9000 rpm or so, but we don't. There are a number of folks who
are very committed to the PP tests, and are using smaller than "normal" PP
ports, to improve the performance at our rpms, but until some of them are
running, and can be compared to what's already out there, we won't know.

Numbers I've heard for 7500 rpm for a single rotor with side ports are
upwards of 120 HP. Since you have to have a muffler of some type, and since
turbos seem to work pretty well as mufflers, I'm planning to use a small
Garrett turbo as my muffler. It's probaby not much heavier than a muffler,
and associated pipe would be, so it's not that much of a weight penalty. If
you choose to run the boost that you could get from the turbo, it should be
closer to 180 HP. For the Kolb, this would be insane, so I'll have to limit
the rpm, and boost to keep the power down to what the airframe can handle.
Folks have used 100 HP Rotax engines on the SlingShot, so the plan would be
to not exceed that by much, unless some 912S driver needs a lesson :-)

As you may know, Mazda went to NO peripheral ports on the Renesis, which
means they took the exhaust port off the rotor housing as well. Now all
ports are on the side housings, which allows them to have no overlap, but
still have improved power. This also has the benefit of slowing the
exhaust, which helps quiet it some, as well as reducing the temp of the
exhaust. Unfortunately, the temp seems to be picked up by the cooling system
now, so there's a bit of a trade-off there.

Cheers,
Rusty

What is the installed weight of a 12A?



"Russell Duffy" wrote in message
...
PS: Rusty, thanks for the info on the gearbox. That Hirth box or
something similar sounds like a good way to go. 170 lbs is outstanding
for a 100hp engine -- could be even more with peripheral porting.

Best of luck with your Kolb project. I hope you will have some pictures
available.

Thanks Gordon. BTW, Richard Sohn's 12A single rotor is peripheral ported.

PP vs the normal side ports is a hotly contested issue on the rotary list,
and I personally believe it's not worth doing for our 7500 rpm range.
I've been told that a good porting job on 3rd gen housings will get you
the same power as PP at the same rpm. The side ports will lose big if
you're going to run up to 9000 rpm or so, but we don't. There are a
number of folks who are very committed to the PP tests, and are using
smaller than "normal" PP ports, to improve the performance at our rpms,
but until some of them are running, and can be compared to what's already
out there, we won't know.

Numbers I've heard for 7500 rpm for a single rotor with side ports are
upwards of 120 HP. Since you have to have a muffler of some type, and
since turbos seem to work pretty well as mufflers, I'm planning to use a
small Garrett turbo as my muffler. It's probaby not much heavier than a
muffler, and associated pipe would be, so it's not that much of a weight
penalty. If you choose to run the boost that you could get from the
turbo, it should be closer to 180 HP. For the Kolb, this would be insane,
so I'll have to limit the rpm, and boost to keep the power down to what
the airframe can handle. Folks have used 100 HP Rotax engines on the
SlingShot, so the plan would be to not exceed that by much, unless some
912S driver needs a lesson :-)

As you may know, Mazda went to NO peripheral ports on the Renesis, which
means they took the exhaust port off the rotor housing as well. Now all
ports are on the side housings, which allows them to have no overlap, but
still have improved power. This also has the benefit of slowing the
exhaust, which helps quiet it some, as well as reducing the temp of the
exhaust. Unfortunately, the temp seems to be picked up by the cooling
system now, so there's a bit of a trade-off there.

Cheers,
Rusty

Even if two rotors were running out of phase, there would still be two
power strokes for each revolution of the e-shaft on a two-rotor, versus a
single power pulse per rev on a single. Your redrive would need to handle
only half the power.

If I understood him correctly, he was saying that each time the rotor fires,
there is a large power pulse that has to be transferred to the prop. The
belt has to be strong enough to be able to absorb that pulse. Since the
pulse you get from the single rotor is exactly the same amplitude as the
pulse from a two rotor, the belt has to be just as strong. If (big if)
that's the limiting factor of the belt strength, then it wouldn't matter how
many pulses there were. BTW, I'm an electonics guy, so not really qualified
to debate redrives.

Tracy's gearboxes are excellent by all accounts, but why use something so
heavy if it's not necessary? (Even so you overall weight of 220 lbs is
excellent for a 100hp engine).

I looked around, and just couldn't find anything better than Tracy's drive
that was actually available. Amazingly, even some of the belt drives
weighed more than Tracy's drive, so at the moment, it's the best off the
shelf solution. I'm hopeful something else will come along, but it was the
best I could find for now. I also have plans to build another RV-8, or
maybe an RV-7, so the drive can be used for that eventually if I find
something better for the single rotor.

Also, in terms of packaging, on a high-wing pusher like the Kolb, an
upright belt drive would put your thrust line at wing level where it needs
to be, while the engine could be down low, near the plane's vertical
center of gravity (like on the Challenger, which uses such a tall belt
drive with the Rotax 2-stroke).

The Kolb design has the engine on top of the wing, so the belt drive is
actually a problem for the position of the prop. Using Tracy's drive, and a
72" prop, I'm almost exactly where I need to be. It's also nice that the
drive is long enough to let the prop clear the back of the ailerons, while
keeping the engine from having to sit any farther aft for CG reasons.

PS: Regardsing the issue of hot exhaust on rotaries, this makes them
ideally suited to turbocharging.

See other reply :-)

Cheers,
Rusty

"Gig 601XL Builder" wr.giacona@coxDOTnet wrote in message
news:vr6Ge.343$_t.142@okepread01...
What is the installed weight of a 12A?

Richards single rotor (using 12A rotor and rotor housing) is about 170 lbs
at the moment, which is really low because he custom made so many items on
the engine to save weight. Using stock Mazda housings would push the weight
up to about 220 lbs at the most.

A 12A is normally a two rotor engine, which weighs pretty close to the same
as a 13B. We generally use a figure of about 330 lbs for firewall forward
weight of a two rotor.

Cheers,
Rusty

On Thu, 28 Jul 2005 09:36:36 -0400, "Gordon Arnaut"
wrote:

As far as I can see, this cannot be valid. If I'm thinking this through
correctly, each rotor will make three power pulses for each revolution of
the rotor, or one revolution of the e-shaft.

My recollection from my mechanicking days is that the eccentric shaft
rotates at three times the speed of the rotor. Whether this
translates into the number of power pulses you mention gives me a
headache to contemplate.

I know that this is the reason the engine could run for so long at
such seemingly high rpms: the rotors were actually spinning at one
third the rpms the eccentric shaft was going. So at 9,000 rpm
measured at the accentric shaft, the rotors are only turning 3,000.

Corky Scott

As far as I can see, this cannot be valid. If I'm thinking this through
correctly, each rotor will make three power pulses for each revolution of
the rotor, or one revolution of the e-shaft.

My recollection from my mechanicking days is that the eccentric shaft
rotates at three times the speed of the rotor.

Abolutely right Corky. Gordon got it right in the rest of his post, so I
just figured he left out a word above, and it should have read "one PER
revolution of the e-shaft".

Cheers,
Rusty

Rusty,

Yes, I meant exactly what you said: three power pulses per single rev of the
rotor, and one pulse per rev of the e-shaft.

Regards,

Gordon.

PS: I like that you are using a turbo as a muffler -- not much more weight,
similar or even better noise reduction, not to mention the power.




"Russell Duffy" wrote in message
...
As far as I can see, this cannot be valid. If I'm thinking this through
correctly, each rotor will make three power pulses for each revolution of
the rotor, or one revolution of the e-shaft.

My recollection from my mechanicking days is that the eccentric shaft
rotates at three times the speed of the rotor.

Abolutely right Corky. Gordon got it right in the rest of his post, so I
just figured he left out a word above, and it should have read "one PER
revolution of the e-shaft".

Cheers,
Rusty