raw110

The plane looks great bud. But could u take a pic of the muffler area...i am pickin a sd up on thurs and was thinkin bout the 91. i believe u just convinced me!!!

altamash_rah

Well I have done about 11 total flights now with my new SD50, so far things have gone pretty well, had a slight hitch today though. Here are my specs just in case you dont want to scroll back and read

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: 10x8
fuel and glow plug: Power Master 15% MG and #8 plug

So i averaged about 10-15 minutes each flight for the last 11 flights or so. I am running the highspeed needle about 2.25 turns out from close.

Today i had flown the plane 3 times with 3 succesful takeoffs and landings. On the fourth flight however, i decided to slow down and cruise for a little bit so i dropped the throttle to a bit lower then 3/4 throttle and flew around, all of a sudden the engine started to lose rpm and shut down, I dead sticked the plane safely in to some weeds , the only damage from the landing was that one of the pipes from the bison pitts muffle snapped off, but other then that the plane is perfectly fine!.

I am not sure as to what happened, my guess would be that the engine is still new and only has about 4-5 tanks gone through it, with each tank of gas i do two takeoffs and two landings and flying the plane at a lower throttle may have loaded up the engine with too much fuel causing the igniter plug to stop causing combustion. im hoping that this was a minor fluke and that if i continue to do the next few tanks at WOT that the engine will have sufficient break in for me to cruise around at slower speeds

here are my questions

1) I know i am running the engine a bit rich, but i am trying to be safe and break it in well, on the high speed needle, how many turns out from close do you guys usually run an os 55 ? I had a friend with a Tachometer that that verified my WOT to be in a good range
2) should i continue flying at WOT for a few more tanks before trying to cruise around at slower speeds??

any suggestions or theories as to why this happened will help tremendously, thanks in advance!

-Alti-

bob27s

My Feedback: (19)

The engine issue you noted has little to do with WOT flight time. The engine takes very little time to break in.

Have you taken the time to adjust the midrange and idle mixture?

The engine does not require a great deal of break-in time. However the bench setup is important. Sounds like you skipped the test-stand time, and likely skipped the time to set up the mixtures properly. There is no real substitute for that.

Spend some time with another modellers and get the engine dialed in. The engine comes from the factory set well for use with the stock muffler. Usually requires just the smallest of adjustments on the idle mixture.

When you swap to an aftermarket muffler, the backpressure, tank pressure and fuel delivery will be different. That requires taking the time to make appropriate adjustments.

You must take the time to adjust things properly on the ground before flying it any further.

altamash_rah

Thanks for the response bob27s, I will not be able to see anyone at the field till the coming weekend, till then, can you provide some tips on how to tune the mid range and idle ?

For the high end, i opened the throttle to full and closed the needle till the rpm started to drop, then i opened the needle about 1/4 - 1/2 turn till the rpm went back up. The engine still produced good smoke which let me know that it was not too lean. A fellow hobbyist also tached my high end and it was in a good range.

Do i tune the mid range and idle the same way?

I have seen some decent guides on rc universe on how to tune, but it did not seem too accurate, can you point me to a good article or how to?

Appreciate the help!

jamesrxx951

i also had tuning problems with my pitts muffler a few people in my club told me to install a fuel pump and that should cure the problem because the pitts mufflers don't seam to create enough backpressure. i switched over to the stock muffler on my os 91 for now. i don't know if this is correct because it is untested yet but thats just what i was told. hope this helps.

rsmith0525

I purchased a sundowner 50 w/.55AX, what prop should I use for racing. I'm not getting the speed I was looking for. I wanted to exhaust my options with the OS55 prior to getting another engine. I tried 12 x 6, 12 x 8 and 11 x 7 and I'm not satisfied.

altamash_rah

well im not sure wht kinds of speeds you are looking for but i am satisfied with the speed of of my SD50 using a 10x8

altamash_rah

install a fuel pump???

how do you install a fuel pump on the plane???

can you give a link to a picture of what you are talking about?

thanks

Brew07

Some guys are using a 10x8 they say it works good. Going to try thay with the 55ax as soon as I get the SD fixed and up in the air again. Had a dead stick thought I could do a turn to get on the runway ran out of air speed and lets say gravity took over. [:@]

rsmith0525

Thanks, I'll try using a 10 x 8.

Some guys are using a 10x8 they say it works good. Going to try thay with the 55ax as soon as I get the SD fixed and up in the air again. Had a dead stick thought I could do a turn to get on the runway ran out of air speed and lets say gravity took over.

bob27s

My Feedback: (19)

I could attempt to describe how to set the low end mixture...... but that is one of those things that is most defineatly best learned from your club members or flight instructor.

Start the engine,
take it to full throttle for 30-45 seconds to warm it up and clear it out.

Pull the engine to idle (around 3000 rpm).
Allow it to stay there 5-10 seconds.
Advance the throttle rapidly.
If the engine stumbles and loads up, turn in the low speed mixture about 1/4 turn.

Try again.

You are looking for a smooth transition from idle to full throttle.

If it quits immediately as you throttle up, it is lean, and you adjusted in too far.
Back out 1/8 of a turn and try again.

Once it transitions well, allow the engine to idle for 30 seconds.
Advance the throttle quickly.
It should not faulter. If it does, only tiny adjustments from that point.
Chances are it will be perfect.

Oh.. forget the fuel pump . Its a bandaide for a problem. Fix the problem.

altamash_rah

Thanks for the quick how to! One question....

Do i need to made the adjustment while the engine is on or off? or does it not matter

russm

for your own safety, shut it off.

patzane

like Russ said off but very small adjustments

altamash_rah

I will make the LSN adjustements some time this week, I wanted to get everyones opinion on another possible issue when i posted in the "OS engines support" forum,

The moderator suggested that it may not be an issue with my needle adjustments but rather an issue of the Bison Pitts Muffler not creating enough back pressure....

at mid-low throttle there is not enough pressure being created so the fuel has a hard time reaching the CARB.

If back pressure issue is a potential problem will adjusting the LSN make any difference in engine stability at less then full throttle positions?

bob27s

My Feedback: (19)

Set the high end mixture first, then adjust the low end. They tend to be independant. If a problem arrises, it will be at the transition throttle from the two needles. OS has an excellent carb design.

That is accurate regarding backpressure. It is an important factor many people over-look when switching mufflers to an aftermarket product. Some of the aftermarket products do not address the pressure balance needed by many engines.

Some have run the 55 with aftermarket mufflers. So it can be done.

You may find that the engine runs fine with your muffler following some basic adjustments. Make small adjustments. If it does not find the performance within 1/2 a turn either way from the factory setting, suspect the muffler.

An easy test there, if you have two exhaust outlets, temporarily place a plugged-rubber tube over one exhaust outlet, and run the engine. That will increase back pressure. You may find that the engine runs a great deal more consistantly.

Learning to adjust an engine is just as important as learning how to take off and land. And it can not be done on a simulator. Requries hands-on instruction by your flight instructor or other helpful club member. Every engine you will own will run differently in each different aircraft and with each different prop. Understanding how to adjust both the high speed and low speed mixtures is a critical modelling skill.

camdyson

If this has been discussed already, apologies. Read whole thread briefly and saw no reference to it:

I have an OS FS 91 Surpass II looking for a home, and would like to put in in a Sundowner 50. Has anyone tried this particular engine/plane combo? I don't care about it being a record-beater, just want a fast sport plane. Nose-heavy sounds like the obvious issue - is there room to bring the tank back and fit a perry pump? (I'd love to lose the muffler and have a straight-out header, so a perry would be nice anyway)

Thanks for any advice. They're on back-order in Aus. so I can't make a rash decision![8D]

Cam

ALO 111

Flew my OS 91 powered SD again this weekend and once again must say this is such a great plane it does not really matter what motor you fit just enjoy it and fly it like you stole it
I was wondering have any of you increased the control throws over the suggested. I was not happy with the roll rate so I increased the control surface travels quite a bit and its made it a lot more exciting>

altamash_rah

the control surfaces are so small i dont think i wanna take the chance to increase them beyond recommended, but if your going to fly it like you stole it.....then by all means, increase the throws and report the results to us!!!!

patzane

Alo I did increase throw on alirons and rudder. I did try on elevator 15 mistakes high and it snapped before I said "WOW". I would recommend the suggested throw on elevator as this baby will high speed snap. If you doing a low flyby when this happen, you will not have time to recover.

ALO 111

Thanx for the info, will leave the elevator as is. Are you still spinning a 12/8 ?

patzane

Had 4 great flight on the SD today with at 20 mph gust. It was a blast going with wind.

Alo I am using 12x8 prop

FA82Showtime

what would a o.s 46ax with a macs tunned pipe do on this plane

russm

fly it and not much else

ALO 111

GO BIG OR GO HOME