I have an OS .91 Surpass II in my Skybolt ARF which is working well but i want just that little bit extra power.

Which engine would you choose between the Saito 125 and OS 1.20AX with Bisson Pitts Muffler?

I know the Saito would be an almost drop-in fit and probably wouldn't need any cowl cutting.

But the 1.20AX is substantially cheaper here and i also figure i can save on fuel costs by running on 5% Nitro.

Would either motor with an APC 15x8 be an improvement over the .91 turning the 14x7 at 9,200?

Would the stock 1.20AX muffler with the angle adapter fit within the cowl like a Pitts?

I replaced an OS91 S-II with a Saito 100 (same bolt pattern) in a TF Corsair and there was a very noticeable difference in power. I didn't think the Saito would be that much stronger but it was. The 125 should be even better. Try both the Saito 125 and OS 120 AX and let us know your results.
Fred

Hi Fred,

The Saito 100 was also considered but here in Australia at the moment the 125 is actually on sale and slighly cheaper.

Here is my Skybolt with a 1.20 AX. I had a pitts muffler when this picture was taken, but I now have the stock muffler. Just use the adapter offered by OS to turn the stock muffler 90 degrees like a pitts muffler. The stock muffler without the noise baffle runs better that the pitts muffler. This is a great combination. I have hundreds of flights on this plane and it definitely has unlimited vertical.

I went with the Saito 125 and flew it yesterday.

I'm pleased to report that it gave me the performance i was looking for. I'm still running the engine rich but it was turning an APC 15x8 at 8,800rpm.

The model now has unlimited vertical and I found i was cruising at around half throttle and increasing throttle for the climbs whereas before i was at full throttle most of the time and would run out of puff in the vertical manouvers.
It tracks much better through the air and my aerobatics were improved. I was able to knife edge the entire length of the runway.

I don't know whether that's because of the greater thrust, higher propspeed or the extra 2oz of weight in the nose.

I'm pleased with it.

I am really thinking of getting this engine (Saito 125) for my skybolt, here are some questions:

Also I assume the engine mounts do not need to be modified?

How much extra do you have to cut the cowling?

Is the throttle linkage OK or does it require some tweaking?

Any prop issues?

Did you strengthen the firewall? If not has your stock ARF firewall held up without issue.

Any pictures would be appreciated

(BTW posted these ? on the big thread, but thought I might get more info from this thread...

According to the sales blurb and the specs in the manuals, the Saito 100 and 125 share exactly the same mounting dimentions as the OS .91.

It fits the Supplied (.60-1.20) Great Planes mount just fine.

In reality i found that the Saito 125 was about 5mm longer from the mounting holes to the prop nut so i ended up drilling new holes in my mounts 10mm behind the holes i was using with the OS .91. If you haven't drilled your mount yet, then that won't be a problem.

I also found the cowl is a better fit now that the engine is back 5mm from the suggested length.

When both engines are complete with muffler the Saito is 50gm (1.8Oz) heavier but that is not an issue because the Skybolt is tail heavy and needs some noseweight anyway.

The throttle linkage is no problem. You will have to rotate the carb 180 degrees and drill a new hole in the firewall to line up with the throttle arm. You have to do that with any engine install on the Skybolt.

No prop issues but 15" is the largest safe diameter with the standard landing gear so a 15x8 is the best choice. Also, the Saito has an 8x1.25mm metric crankshaft so you'll need a new spinner nut.

I haven't touched the firewall. It was never a problem with the .91 but i will be keeping a close eye on it to make sure the 125 is not ripping it out.

The saito needs quite a bit more cowl cutting than the OS. Both for the Cylinder head and the Muffler. My Saito 125 head is bigger than expected and i've just read that they've upgraded the cylinder to a larger size with more cooling fins.

Perfect thanks custom PC.

[quote] No prop issues but 15" is the largest safe diameter with the standard landing gear so a 15x8 is the best choice. Also, the Saito has an 8x1.25mm metric crankshaft so you'll need a new spinner nut.

Ordered the 125 today, what size spinner nut did you use (short, long etc...). thanx for the help..

Mark in Texas

I use a TruTurn 2.5" spinner with the 120 slots and that suits just about any prop you'll use on the skybolt.

The spinner supplied with the skybolt is decent but the slots were too small for 4-stroke sized props and i hate grinding spinner so elected for an aftermarket spinner.

I used the adapter finder on TruTurn's website to find the right spinner nut. Off memory it's part # TT-0828-A but you should check first.

http://www.truturn.com

My Skybolt has just under 9" from the shaft to the ground.

It's gear isn't the stiffest you'll find on most 8-10lb models. If you land with the prop turning, you need to consider gear flex. Over the years, my gear has relaxed a number of times and needed straightening.

I fly off of grass mostly. That's probably a 13x6 prop in the picture. (Picture taken back in 2006.) It's got how much clearance?

All the props I fly on that airplane show grass stains.

That's an OS61FX on the airplane. Gives really good vertical.

I'm going to have to remember that so I can use it as an excuse!

e.g.

"No I did NOT land hard and flex my gear out, instead they elected to 'relax' today".

Heh...

Can anyone give me a link to a alum spinner that will work with the 125? Got this baby about ready to fy....Thanks

Mark

http://www.truturn.com

You need the 2.5" standard spinner with 120 slots.

http://www.truturn.com/cgi-bin/store...exact_match=on

And this adapter

http://www.truturn.com/cgi-bin/store...8a&ppinc=adapt

Thanks for the link. Ordered it today.


Was thinking of running a 3 blade with the 125, anyone try that?

Take a look at the numbers and props shown here:

http://www.rcgroups.com/forums/showthread.php?t=495580

and in here:

http://www.rcgroups.com/forums/showthread.php?t=478975