Timthetoolman1

My Feedback: (6)

I agree, I have a 125, 120 and a 91 mounted inverted and I can't recall ever having a dead stick.

w8ye

My Feedback: (16)

You do have to get accustomed to an inverted engine or at least be aware of the potential problems of flooding

mike early

I think I might be a new Boca convert....

Timthetoolman1

My Feedback: (6)

W8YE, I think I know what you mean, it might be better for cooling to mount it horizontal in a Cub because of the scale openning locations. I've mounted it inverted in similar planes but ducted the factory air vents down to the engine with fiberglass and vented it out the back. As long as you have good flow over the fins and a large enough openning in the back to cool it tuning shouldn't be a problem. Most of the guys I see with problems on a 4 stroke with inverted mounting also have cooling issues.
Follow the 1:3 (air intake to air exhaust openning respectively) and you'll be fine.

Tim

NM2K

My Feedback: (14)

I would lean more toward RC Bearings. Lower prices and the same quality.


Ed Cregger

jdkxtreme

I am going to mount it horizontal after all the reading..I just wished I had not cut the hole in the bottom of the cowl already..

mike early

same quality, sometimes. But with the lower cost comes lower quality control tolerances....maybe.
The bearing was brand new, from RC-Bearings. I've bought sets from both companies. Only one has exploded in the first 5 minutes.

NM2K

My Feedback: (14)

So, you can draw a conclusion from one sample? Baloney.

Paul doesn't make the bearings. He only sells them. Just like Boca.

Whatcha gonna do when Boca's bearing does the same thing?

I know Paul. I've been dealing with him for a decade or so. Let him stand behind his product. He doesn't need this kind of bad press.


Ed Cregger

Timthetoolman1

My Feedback: (6)

With a stadard prop on both engines
Saito .91 = 12 lbs of thrust
OS .61FX = 7.7 lbs of thrust
Does that sound right?
The guys flying SPA are saying the 4 strokes are not working for them, but they are also using OS 4 stokes. The planes are weighing between 6-8 lbs.

jdkxtreme

I have the twist 40 out side tied down running more fuel thru it..I have almost a gallon thru the saito 82..What should be a good idle?

w8ye

My Feedback: (16)

That sounds a little high for a Saito 91?
There are a couple reasons the SPA guys use a OS 91 Surpass rather than the Saito 91. The OS 91 Surpass II seems to have a little more power than the Saito 91. (And it weighs more too)

But what the SPA guys will tell you is that you can set the needles on the OS 91 Surpass II early in the day and when your turn to fly comes, you start the engine, take-off and fly the pattern. They claim you cannot do that with the Saito 91 without a run-up and a needle check?

w8ye

My Feedback: (16)

If you are running a APC 14-4W you should be able to get a 2200 rpm idle

NM2K

My Feedback: (14)

Put the same prop diameter and pitch on the .61 two-stroke that you are running on the Saito .91. You may have to switch glow plugs toward the cold side in the two-stroke to prevent preignition, but you should see a bit more rpm from the .61 than the .91 if both are burning 15% nitro fuel. Any more than that and you might have to shim the head of the two-stroke to prevent preignition with the large prop.

Folks have been running OS four-strokes in SPA for years with great success. But, they are burning 30% nitro heli fuel and they have to shorten the nose/lengthen the rear fuselage in order to get the models to balance. Frankly, I can't see how they would have enough control authority with the stock size control surfaces. They are also running large diameter/low pitch propellers to slow down the top speed and to enhance vertical performance. The large prop diameter also helps keep the speed down in vertical ascents.

I have talked to a few of the SPA folks and they claim that the Saito .91 doesn't hold up as well as the OS FS-91 SII with all of the heavy practice flying that they must do to remain competitive. Yeah, it surprised me too.

The best way to compare the two engines that you have mentioned is to go through a bunch of props and find out exactly which size favors each particular engine. You will find that the two-stroke needs to turn up a bit in order to generate the same or more thrust than the .91 four-stroke. What really hurts the two-strokes in SPA is the inability to legally run a long, stretched out tuned pipe, which would also help quiet the two-strokes considerably. This is one area in which I disagree with the practicality of the SPA rules, but whatcha gonna do? It's their contest.


Ed Cregger

w8ye

My Feedback: (16)

When I was at the field and saw that all the pattern planes had OS 91 Surpass I & II four strokes, I asked Bruce Underwood, the Pres. of SPA who I happened to be helping to set up his sun shelter. He more or less told me what I posted above. At the time I couldn't believe what I was hearing but all those SPA guys couldn't be wrong.

I have three Saito 91's and a Couple of OS 91 Surpass II's and used to have a OS 91 Surpass I.

I would rather use the Saitos any day. They weigh less and don't have the screwed up speed changes and surging apparently caused by carb icing in the OS engines. The OS Surpass II will pull a bigger prop than a Saito though. The Saito 100 compares more favorably powerwise with the OS 91 Surpass II and weighs about the same also.

Timthetoolman1

My Feedback: (6)

Thanks for the info, that is a shock. I always hear them talking about OS 4-S but none of them run as well as my Saito; however, I've set the valve clearance on some OS and they run a lot better. It seems like the Saitos are more durable but that's just my experience...weird the SPA guys don't agree.
Thanks again,
Tim

w8ye

My Feedback: (16)

From a aerodynamic Stability point of view, when you lengthen the tail moment arm, you increase the effectiveness of the same size control surfaces. I suppose the sensitiveness of the controls would be diminished? Maneuverability would be less but the smoothness would be increased?

NM2K

My Feedback: (14)

That makes perfect sense, Jim. I was thinking that they had diminished authority because of the much lower airspeed when using the low pitch/high diameter props. Maybe they get some of that back with the longer tail moment.


Ed Cregger

mike early

I've bought quite a few bearings from Paul. I crash (auger) and replace the ceramic bearings just to be safe. And I crash quite a bit.

johnS555

My Feedback: (27)

About the ceramic bearings, in my misguided life talking to the boys that make the noise etc. 99.9 cases of ceramic bearings going bad is in the installation, they are prone to crack if they are not installed correctly, cocked or hammered on, a lot moreso than metal ones.........John

mike early

There's a difference between smooth and loose vs tight and ratchety. Cockeyed is tight and ratchety. Chipped ball is ratchety of a different nature. Smooth and free is correct. Loose is a new one that I will know next time. These were installed correctly Thanks.

blw

My Feedback: (3)

On probably the same day, I heard another guy ask Bruce why they all ran OS 91s. His answer was that they could get 300 more RPM out of them on 30% nitro. Not that I bought that for an answer. I've read one engine review by a SPA reviewer in their newsletter, and I remember that I disagreed with a lot of what he had to say about both the OS and reviewed engine.

PearHead

Greetings Gentlemen,
I was hoping your vast experiences could tell me if what I noticed this weekend with my 1.25 was normal.
After one of my flights, I grabbed my aluminum spinner and noticed it was very warm to the touch. I haven’t ever really done that before, so I don’t know if I should have expected that. The valve covers were too hot to touch comfortably. I didn’t notice anything strange during the flights (though this is a new engine, so I don’t have a feel for ‘normal’ yet). The engine is cowled with a 1:2 entry/exit ratio for the airflow (The opening oposite the cylinder is covered with a screen to restrict airflow).
So, am I just paranoid? Is there some other way to ensure the engine is not getting too hot?
Thanks!
Pearhead

w8ye

My Feedback: (16)

Run without the cowl and compare

The plane will fly pretty much the same without the cowl

you must do your "feeling" immediately at shutdown or the engine will heat soak all the way through.

Rudolph Hart

Yes don't run it,just kidding mate

Hey mike 109 just running in my 30 and will post a pic.Sounds and purrs like a kitten,will be a good match for the rainbow[img]

Hobbsy

My Feedback: (102)

Hey OF, you'll love that lil engine, I bought a second one when it was announced that Horizon was going to quit handling them. The first one was just like yours and the second is a GK. I sent the first one to Bill Ribison in Fla. to be part of his Saito notes, he sent it back with a black cylinder. Now that he has passed on it one of my most prized posessions. I run Graupner a 10.5x5 or a 10x6 depending on the length of grass where I'm flying that day. Sweet engines.