Running-in and Tuning SZ-H (p/p) in Stratus

[Aviation addict]

Guys,

I've just completed my Stratus build and have to say what pleasure it was to do. The kit fitted together very precisely and the manual was just fantastic.

My other heli is a Raptor 50, and so what I'd appreciate advice on now is how you would advise I go about 'running-in' and 'tuning' the OS91 SZ-H engine. I do have a manual and will be following it, but wondered if you guys had any practical tips gained through experience which may help me with my first 3 needle engine.
-------------------
My concerns are as follows;

I'm using Magnum (20%) which is smokey - so does not give very much help if the engine is running lean.

I can't touch the engine back plate (like I can on the Hyper 50) for the 'back plate temperature check' as the pump is in the way. [Don't have a lazer temp probe].

I know when my Raptor 50 is running rich or lean by its climbout performance - but I don't know what to expect from the Stratus.

-----------------
Running in

With regards 'running-in'. I have a friend who put a new OS50 in his Raptor recently and was doing 3D with a headspeed of probably 1900 tank No 1. ! I'd personally rather put a couple of Gallons through a new engine before putting it through its paces. How many tanks or indeed gallons would you guys recommend before beginning to tweak the needles towards max performance?

[mevigavant]

i ran my SZ at idle for 1/2 tank, I then flew it rich(stock settings) for the rest of the tank. I let it cool down, refueled and ran it again at the head speed that I intend to fly at(1900) in my case. I don't put a load on the engine or run it lean. I flew like this for several more tanks, but each time I would lean the needles a bit(never going too lean or putting to much load). After about 1 gallon I tuned it for max performance to my HIGHEST head speed. I run my revmax at 100% in idle up 2(1900) so i tune the engine to this head speed. what ever you do DON"T run it lean at anytime of the break-in process or anytime after that.

[Aviation addict]

Running it rich for 1 gallon sounds like a good idea. That's about 40 mins flight time I'd guess.
What indications are you using to ensure it's not running on the 'lean' side in Medium and High speed needle zones of effectiveness?

[mevigavant]

Since you have a pump, put your finger above the pump on the case itself.

[Aviation addict]

Thanks, will do that.

[Aviation addict]

Have just found the post in the 'Main Forum Heli Talk' section called 'OS91SZ-H Problems' where on page 2 the best SZ needle settings are discussed i.e. close off the Mid needle and slowly close in the High. Once the engine has had a Gallon through it I think this is the way I'll head. Seems like the best guys in the business have found this method the most effective way of tuning the SZ...

[WayneBrown]

Start with main at 1 1/2, mid closed and lean the main from there after a few tanks...

[mevigavant]

mid closed and lean the main from there after a few tanks

won't that cook the engine? I had a local pilot due that once to my c-spec because that's what he read on Curtis's site and when I landed the engine was to hot to touch. Is the sz different somehow? Will this be true if you run an OMI moded carb?

[Aviation addict]

Start with main at 1 1/2, mid closed and lean the main from there after a few tanks...

Thanks Wayne. Will do exactly as you say after passing a few tanks through it at the stock settings. It sounds a bit radical, but seems to be the way to go with the SZ...

[WayneBrown]

worst case scenario. You set the main at 1 1/2, close the mid. start and spool up. If it doesn't like it, you'll KNOW before it gets off the ground, or very very shortly after..hit hold, land and readjust..

[Aviation addict]

If it did sound ok in the hover at 1 1/2 turns where should I go from there to hone in on the perfect setting? Do you go fly around then hit hold, auto down and see how warm she is or are you leaning until she sounds a little crackly then opening up a few clicks? How do you lean her off and know when you've got it right ?

I don't want to lean her off too much and damage the engine but equally I don't want to be running her too rich and miss out on a large percentage of power.

[WayneBrown]

This particular engine will want to be rich to make the power. Most are running average 1 turn on the main, 1 1/2 should be pretty rich, even with the mid closed.

[DavidH]

One thing to bring up. There is a few factors that go into tuning the engine.

Fuel is a factor, amount of nitro and oil content and type of oil will make a difference in how the engine is tuned.

Weather : Air density, temperature, will affect tuning.

Glow Plug: different heat ranges of glow plugs will affect tuning

Exhaust : Different mufflers will affect tuning.

All of this comes into play. So needle settings for one person may not be exactly the same for another.
The 1 1/2 turns that Wayne mentioned should be safe. The needle jet openings on the SZ carbs are fairly larger than most carbs. So 1 1/2 turns open on the main is about the same as 2 1/2 turns on some other carbs.


David

[Aviation addict]

The 1 1/2 turns that Wayne mentioned should be safe. The needle jet openings on the SZ carbs are fairly larger than most carbs. So 1 1/2 turns open on the main is about the same as 2 1/2 turns on some other carbs.


Thanks Gents. I appreciate what you're saying about Fuel/Weather/Glow Plugs/Exhaust David and that no two people's settings are identical, but its good to hear that the 1 1/2 turn open on the High should be a safe place to start from. I don't even want to come close to cooking it. Didn't know 1 1/2 on the SZ was around the same as 2 1/2 on other engines. Good to know.

[DavidH]

Didn't know 1 1/2 on the SZ was around the same as 2 1/2 on other engines.

Just an example.
The 60 K carb that comes on the CSpec. At 3 turns open on the main needle. It is flowing all the fuel it can flow. That is why OMI modifies the 60 K carb when they install the Cline. So it can flow more fuel thru the needle passages. After modification by OMI. The motor runs fine with the needles anywhere from 3/4 to 1 1/4 turn open on the main from what I have seen.

The openings on the carb that come on the SZ are already larger from the factory than the needle openings on the previous OS 91 engines. Plus the bore of the carb is 10.6 mm. Where the 60 K carb on the Cspec is basically 10 mm in stock form.

David

[mevigavant]

Good to know. I'll give it a try once i change out the bearings in my SZ.

[Aviation addict]

If it did sound ok in the hover at 1 1/2 turns where should I go from there to hone in on the perfect setting? Do you go fly around then hit hold, auto down and see how warm she is or are you leaning until she sounds a little crackly then opening up a few clicks? How do you lean her off and know when you've got it right ?


I started running the engine at the stock settings then slowly closed off the Medium speed needle to fully closed over the first 5 tanks. She is currently still at 2 1/2 clicks open on the High (after 9 tanks) where she seems quite happy. I was going to start leaning her down towards 1 1/2 turns open (and below) next time out but I still have the same question as above i.e. - as I'm not used to 90 performance and my fuel is very smokey anyway (Magnum 20%), what factors would you guys suggest I go on to know when I've tuned the engine well?

I don't need to squeeze every last bit of performance out of the engine with the flying I'm doing so a slightly 'rich' setting would be fine for me. In the past (with my OS50 Hyper) I've just gone on temperature on the (base/back of the) crankcase and whether it boggs during stationary rolls. Should I just do the same with this engine, or do you have any other methods?

[Dr.Ben]

Though I hate to direct anyone there, go over to RR and search for a post that Jerry Sudimick made a while back on exactly how to needle a SZ. Follow those notes exactly, and you'll be fine.

Ben Minor

[saary]

guys do you use vent with check valve or muffler pressure as per the manual? :badair:

[DavidH]

Vent the line straight to atmosphere below the tank. No check valve, no muffler pressure. This is for the SZ Hyper.

David