OS 91FX matched to Mac header and 15cc pipe (aircraft/standard)

[John Gausby]

I am assuming that the landing gear is the stock tri-gear set up. The stock
EU1 A gear was set for an 11 to 12 inch (Max) prop. The OS 91 2S is
designed to haul a larger diameter prop.

Thinking back.....The EU1 was pretty fast with a Rossi .61 screaming at
16,000 rpms and the midrange was lousy with a pipe set for max power. So it
was either full bore or idle flying most of the time. 

I guess the big question is ....How much prop can go on the engine before
you run out of reasonable ground clearance? You may have to lengthen the
L.G. for the OS 91 FX

I think if you pipe that engine with a 12 or 13 " prop that you will have a
guided missle. Even with that large wing. I recommend to test fly with a
muffler. Then pipe it if you really feel that you need more power.

Without a pipe , you should have a decent midrange so the plane is not
always a bullet IMHO. I havn't owned  the .91 FX so i'm not an expert on
that particular engine. It should have plenty of power in the stock setup
for the EU1. You will need to experiment some with props depending again on
the diameter that is usuable.

Maybe this helped a little Don.......................John G.


> [Original Message]
> From: <DPeckNSRCA at aol.com>
> To: <discussion at nsrca.org>
> Date: 10/17/2003 1:12:24 PM
> Subject: OS 91FX matched to Mac header and 15cc pipe (aircraft/standard)
>
> Hi Guys,    
>     Our club sec. is refurbishing his dad's EU-1 and has anew OS .91 FX 2 
> stroke.  Drew wants to know what header/pipe length settings to use.  My
limited 
> Rossi, Picco .60 drawings used measurements from exhaust port to pipe
high 
> point.  Props then became the flying and "pipe tuning length" factor, to
get the 
> engine "on the pipe."  
>     The MAC Co. is not giving any info. as they "haven't any data."  I
told 
> Drew maybe he bought the wrong brand.  Seriously, my man Drew is our
club's VP 
> for 2004 and may very well be our tenth local entry in our Huntsville, AL
RCRC 
> 2004 Sept. Pattern Meet.  I don't want to mislead him with poor info. 
All my 
> attention has been .91YS 4S using 13.5x10 or 14x10 APC.  I am asking for
the 
> following advise:
>
> 1. Prop size (with muffler) to test fly EU-1 (big 60 size wing CI,
1,200+?)
> 2. Recommended starting prop size with header/pipe
> 3. Suggest minimum and maximum pipe length, measuring exaust port to high 
> point of pipe.
> 4. Any RPM specs. you may have on idle and top end of OS .91 2S motor.
> 5. Comments wanted on use of .91 2S using back pressure from pipe/header
to 
> pressurize tank.  I have Rossi old pipes with Mac pressure fittings for
back 
> pressure.  If you do recommend tank back pressure, where do you drill
your 
> pressure fitting? At approximately what point on pipe, or header,
(distance for 
> exaust port)?  Some guys ran pressure fitting just in front of the pipe
high 
> point.  That sure made a long line, however, ducted fan 91's live with
the 
> pressure!  Seems like our lower RPM's of today are not worth the pipe
pressure 
> fitting trouble. 
>
> Thanks for your reading time.
>
> The 2nd best "billfold builder" in the Rocket City,
> Don Peck
> NSRCA 585
>
>     
> =====================================
> # To be removed from this list, send a message to 
> # discussion-request at nsrca.org
> # and put leave discussion on the first line of the body.
> #



=====================================
# To be removed from this list, send a message to 
# discussion-request at nsrca.org
# and put leave discussion on the first line of the body.
#