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Subject: Re: [FlyRotary] Re: carbs vs efi
Date: Tue, 24 Jul 2007 19:07:55 -0400
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Hey George!
The note is fine except for one thing. The rotary "sucks" or more to=20
the point vacuums just like a piston of similar size chambers. If it=20
didn't it would never start!
Bill Jepson


-----Original Message-----
From: George Lendich <lendich@optusnet.com.au>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Tue, 24 Jul 2007 3:10 pm
Subject: [FlyRotary] Re: carbs vs efi


Jerry,

Sounds good!

The Street port single will give about 116hp at 7,500, but you need=20
1.18=A0 x2=A0sq" minimum ( 2.36 sq") =3D 44 Dia inlet.

=A0

David McCandles has found some old info, which I will forward under=20
separate cover, which confirms these numbers although I haven't read it=20
through myself as yet.

=A0

The RX8 uses smaller runners but more of them, the inlet area is=20
massive in total, the smaller runner maintains the velocity. However=20
because the Rotary doesn't suck like a piston engine ( sucking creates=20
velocity) the advantages of velocity over=A0area needed,=A0are limited.

=A0

The 12A and 13B are the same size P-port 43mm, the timing/position are=20
the same.

We have to start to accept that they know the advantages of sizing and=20
position.

George

George,? I just got back from Oshkosh which would have been a wasted=20
trip except that I got to fly a CH 701 amphib off the water.? This was=20
a first for ?yours truly. ? ?What a lot of fun.? The airplane handles=20
perfectly and is the right one for me. ? ?It is limited by the designer=20
to 100 hp and 200 lbs for the engine installation. So I am in the in=20
enviable situation of not wanting to get too much out of my p port. The=20
plane was powered by a 100 hp Rotax.? ?It did very well.? ?


Re your analysis comparing side ports with p ports, I wonder if such an=20
analysis is even possible as they are quite different.? Anyway, I doubt=20
that a standard port can deliver 100 hp or a street port 130 hp. per=20
rotor, certainly not when limited to 7500 rpm.? Of course I am only=20
guessing.? No real knowledge or experience.??


The only carb I saw at Oshkosh was the aero carb.? It is sized by HP=20
and they recommend the 38mm for? 125 to 160 hp.? This is too large for=20
my purposes.? I am considering going down to 35mm? (90 to 125 hp) ?=20
?The problem is that I already have 38mm p ports.? Also, of interest is=20
that they do not recommend ram air. That simplifies the plumbing and=20
the cowl. ? ?The demo engine had rather long, small dia runners and an=20
air filter attached to the carb.? That is the "system." ((on an 80 hp=20
v.w.))? ?If I can get the drive figured out, ?I will build it with RB's=20
aluminum side plates and Atkins eccentric. ?BTW the 701 is a high wing.=20
?The system will be strictly gravity. ? ?? ?Jerry


On Jul 21, 2007, at 10:14 PM, George Lendich wrote:


Jerry,

I'm trying to compare the carb inlet area to port or P-port areas.

Standard Port area 32 deg ATDC to 50 degree ABDC =3D 1.18 sq " each side=20
(x2 =3D 2.36sq")- using the front and back housings only.

?

A street port will be 1.5sq" x 2 =3D 3sq"

.

A 44mm P-port =3D 2.35sq"

A?42mm p-port =3D 2.14sq"

A 40mm P-port =3D 1.94sq"

A 38mm P-port =3D 1.75sq"

So you see a side port on a single has more port area than a small=20
P-port.

Perhaps the velocity will make up for less area.

The street port is bigger again at 3 sq" - this equates to 50mm port.

?

The standard port gives about 100 hp, the street port about 130hp each=20
rotor.

I wouldn't want to choke down the port areas with too? restrictive=20
inlet carby?area. I can't see how a 38mm will cut the mustard when your=20
own calculations suggest 1.6 P-port =3D 42mm sq".

?

In reality I'm only looking for 130HPat most, if I can get that.

?

I can run a 41mm ID SS tube p-port with a 42mm Carby ( and hope=20
velocity makes up the difference) Or I can run with two 1.5 street=20
ported side ports 3 sq" with two smaller carbs, perhaps 2x32mm.

?

BTW street ported 13B has been dynoed to 264hp can't remember the RPM -=20
it might have been higher than what we run.

More confused than ever!

?

Does anyone know the IO/IC and size and HP?of the factory P-port.

?

Lynn, does the timing given, calculated by the rotor uncovering and=20
covering the port, or the side seal uncovering/covering the port=20
opening?

I was thinking the RX8 rotor will be slightly different (bigger) with=20
the harased edges.

George ( down under)

?

?

?

?

----- Original Message -----


From: Jerry Hey

To: Rotary motors in aircraft

Sent: Sunday, July 22, 2007 9:17 AM

Subject: [FlyRotary] Re: carbs vs efi


George,? maybe I have the wrong idea, but I don't understand why you=20
need such a large bore carb for the single rotor.? No way you are going=20
to produce more than 150 hp.? I think 38mm would be enough.? This is=20
what Aero Carb recommends for the 0-320.? Jerry


On Jul 21, 2007, at 5:56 PM, George Lendich wrote:


Jerry,

Looks like Pat was wrong about Revmaster having a 44mm, the biggest=20
they go to is 42mm ( at the present time)?and that costs $380. If I=20
remember the 32mm costs $320.

Jerry I would be interested in feed back on what you thought about the=20
Aero Carb, especially how it's constructed - their all a little=20
different.

I do like the Ellison but it's too bloody expensive.

George ( down under)


George,? the web site says $326.00.? You might want to compare the aero=20
carb which is similar.??http://www.aeroconversions.com
I will be looking at both at Oshkosh on Tuesday and Wednesday next=20
week.? Jerry


Jerry


On Jul 20, 2007, at 10:06 PM, George Lendich wrote:


?


I have been surprised at the recent flurry of carb postings.? I assumed=20
that everyone was doing EFI.? having experienced total electrical=20
failure in march on a trip to the Bahamas I was thinking a lot about=20
that Neanderthal carb bolted under my O320 and the magnetos, all=20
unaware of what was going on in the radio, GPS,?and nav lights=20
departments.??? the reality is that you don't want a reserve battery to=20
get you to the ground safely, you want to get to the Bahamas and back=20
and THEN look into what's wrong.

my questions are "how much power/performance is lost with a carb, and=20
which carbs can do manual mixture?".? is it stupid to ask if the=20
Lycoming carb could run a 13B?? someone mentioned Harley carbs?having=20
a?good history of rough service.? what about marvel/schebler?? is this=20
question heresy? :-)? isn't efi a bit of overkill for an engine that=20
basically runs at 100% power, 75% power and idle?? scanning thru the=20
archives I see a lot of postings regarding mixture, mapping, abrupt=20
failures and such.? does this complexity buy us 5%, 20%?? the question=20
of turbo-charging seems to?beg similar line of questioning.??? kevin

?

Kevin,

It's probably my fault, with a number of chaps helping me out with=20
information.

My Buddy Bill Jepson will tell you nothing beats EFI and when it's=20
running well, he's absolutely right!

Not only that it is the best for? fuel efficiency, leaning reading fuel=20
flow etc. etc.

However I'm developing a single rotor and looking at all sorts of=20
issues including cost effectiveness of less elaborate installations.=20
I'm also not keen on high pressure

fuel under the cowl.

Most importantly I'm not?an electronics person and seeing the problems=20
experienced by others has me more than a little nervous, in regard to=20
EFI.

Of course I know very little about carbies, so their helping me with=20
this as well.

The Revmaster might be the choice for me, but I'm awaiting the sticker=20
shock!

George ( down under)


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