13,560 with a 10x8 apc but then I stepped on the elevator and crunched it[:@] Will fly it some other time I guess.

Without having seen the installation.....

If you have the gold muffler drop down to something like an 11x8 or even 11x7 to start with - you are going to have to let the engine turn to get anywhere near making the gold LX muffler work well.

Try the smaller prop. It will not hurt the engine.... its just a big "61" for practicle purposes.

The 12x8 works well on the OS91 combined with the red (longer) muffler.

OK....I'll slap an 11x8 APC on there and see what it does. I suspect an RPM of around 13,000 or so. Will let ya know how it does.

WoW, I think I've read most of this thread and this plane excites me

At this moment my LHS has 1 in stock. Over here the price is £135 (so around $270) so not a cheap option for us poor souls.

Anyway, I only have a 4 stoke Magnum .70 going spare right now and would ask you guys how the plane would be. I'm not after a speed demon right now but would the engine handle this size plane on a rather short runway?

Also, what sort of prop would I be best putting on please?

I really should pick up this model tomorrow, I think it's to nice to pass up on but you guys have to let me know how this engine will handle this plane

I just hope no one else gets in before me

I just recieved my SJ60LX motor today for my Sundowner50. Looks nice Can someone tell me what size tube for the diverter on the back of the muffler and what is the best way to attach it to the muffler. Nevermind, found the answer several posts back.

Some pics of my OS 91 powered SD using std. muffler

ALO 111 did you have to change the mounting holes to fit the 91 FX? Also did you need any weight in the tail to balance?

Yes I moved the holes and added a very small tail weight.
I am crazy about this plane. It tends to land hot but it looks to me that this is more due to the fact that it takes very long to bleed of speed. I have landed rather slow on some occasions and it has not bad tendancies.

That's it in a nutshell.

Like you said, it takes time to bleed off the speed, quite hairy

I flew mine for the first time today, nice calm-ish conditions so was landing with pretty much no wind. I went round about 5 times before I was happy with the approach speed, pukka factor was high!

I brought her in with about 10 ft of runway left (we have a very small field), I had to turn sharply to avoid the Wheat.

This is certainly the most beautiful plane I've ever flown, looks wise she's a picture, it's truly pretty and she flies great as well, can't ask for more really.

I do need to change out my .70 4 stroke though, it really does not do her justice and makes take off on a small field a bit dodgy.

Guys,

While we're all still here can you check this engine out for me.

These guys have a good rep around here and in the UK but I'd like it if some of you guys could just cast your eye over this review of this engine please. I want my Sundowner to do what she was born to do

[link=http://www.justengines.unseen.org/acatalog/JEN_.91_Review.html]JEN .91[/link]

I would probably get it with the pitts muffler to top it off, what ya reckon?

flew mine for the first time sat. very nice plane. put a 75ax w/ a pitts muffler on it. good speed. may buy another one and go the jett 60lx route.

Congrats Russm,

I have an O.S .91 with Bisson Pitts muffler on it and its my new favorite plane. On another note, I was looking through my collection of spare parts, etc, and notice I have an unused OS 91 VR DF and pipe. I am wondering if anyone has thought of using this type of setup for this application. One of our field members uses a ducted fan engine with a pusher prop on antoher plane, and it really hauls. Just a thought.

Hello everyone!

Alright so i just purchased the sd 50 from the LHS, i am having some trouble with it here are my specs

Sundowner 50
TX - DX7
RX - AR7000
Servos - 2-JR126MG for tail controls 2-DS821 for aileron and 1 Hitec for the throttle
Engine and Muffler - OS55 with w/ bison pitts muffler
prop: 13x6
fuel and glow plug: Power Master 15% MG and #8 plug

So here is my problem, i just finished fully assembling the plane and am having trouble breaking in the engine according to the OS intruction booklet
The instruction booklet says to turn the needle out 2.5 turns from close and run the engine at full throttle for about a minute

This is how i start the engine and what my problems is

1) prime engine
2) apply glow plug igniter to glow plug
3) use electric starter to start motor
4) motor starts
5) I unplug the glow plug igniter
6) i try to increase throttle to full, engine dies
7) I made it more rich according to instructions yet the motor still dies

I have notiuced that if i keep the glow plug igniter attatched, the motor idles very well and goes up to full throttle!,
as soon as the plug is out it has trouble maintaining idle or throttling up, I have tried a richer setting but it does not maintain idle very well

Any help or tips are appreciated!

-Alti-

here is your problem........

If this is the OS55AX 2c engine , you want to use a 10x7 or 10x8 prop !!!!!

13x8 is WAY too big. It is a 55, not a 95

Read similar posts on the matter.

That will get you at least on the right track.

sorry about the confusion, I am actually using a 13x6 prop, i checked in the os manual and it says you can use a 13x6 prop on the engine, so i think the prop may not be the issues......please continue posting some solutions or tips! thank you!

I think you should revisit the prop issue again, even though you don't think that Bob is correct. The manual has a range of 12 X 7 to 13 X 7. The 13 X 6 should work, but maybe try a 12 X 7 or 12 X 8 to get an idea of a good needle setting during break-in if you are dead set on going with what the manual recommends.
Also, if the engine is not throttling up after you take the glow driver off, I would venture a guess you are already on the rich side so you don't want to richen it more.

You can try taking the glow driver off and then advance the throttle slowly. Once it gets to a point where it won't get any faster, lean the needle just a little bit. Keep doing this until you can get a good RPM out of it at full throttle, but be careful not to run it too lean. It will take some time, but you should be able to get a good feel for what it is doing.

T.

thanks for the tips tsawyer, i will tray a 12x8 tomorrow and start leaning it out a bit, i wanted to break it in a bit better on rich setting before starting to lean out,
do you think leaning out a bit so early on may cause some damage to the engine?

The general idea is that you need to be able to get the engine up to at least a decent RPM and let it get warm without running too lean so the piston and sleeve will seat well during break-in. Just be careful so as not to get in too big of a hurry to get it broken in. Once you can get it to run well through the whole throttle cycle, then follow the break-in procedure as described in the manual

If you keep the setting on the rich side while you break it in, you should be fine. Is there anyone you can get help from? You will discover that there are some circumstances where the manual becomes more of a general guidline rather than absolute law. Experience, (whether it is your own or someone else's), can become your best resource.

Yes the OS 55 manual says you can run those big props and indeed you can, but you will be way off from where this engine makes its best power. Those prop choices are most likely intended to keep the tip speed down for noise reduction which seem to be of great importance in some countries.
Around 14,000 rpm on the ground seems to be a good target for this engine as bob27s has tirelessly been informing us. The APC 11X6 or 10X8 are good choices, listen to the man.

I have found the 12/8 apc to be the best with the 91 OS what are the other 91,s spinning?

Ran into same issues on my OS55. Finally just left the ign on for two tanks fuel, removed on the third tank and engine has run like a dream ever since. Good Luck

I am using 12x8 APC on my O.S 91 as well. Haven't tach'd it yet. What RPMS are you getting?

Altamash I take the OS 55 is new. If so the low end might be little rich. you may want to check that out

91fx w/ jett muffler, 12x8 apc prop, 15% synth fuel, 13800

freakin fast pretty much summed it up...

The OS manual and prop recommendations are for "ultra-quiet" - not for power.

My experience is the engine struggles a bit with a 13x5 or 13x6 prop (same prop I run on the OS70FS and my old ASP80 FS)

The OS55 engine runs well propped to turn any prop above 11,000 rpm. So yes you can use the larger props. However... it develops its best power as it approaches 15,000 rpm .... so prop selection that delivers around 13,000 to 14,000 peak rpm on the ground will permit the engine to perform at its very best in flight.

It turns out that a 10x7, 10x8, 11x6 and potentially a 11x7 works very well to put the engine into that effective rpm range (regardless of a stock or aftermarket exhaust system). You can probably throw a 12x6 in there for slower flying aircraft too.