rightflyer

I run a Saito 72 with 13x6 APC on Wildcat 20/20 fuel. What high end RPM should be looking for? I have heard that you should not go above 9500 rpms the ground, true?

w8ye

My Feedback: (16)

Your engine should be close to 10,000 on the ground with that set up. When the engine is set up like this, you are getting good performance from it. But you should not run the engine wide open except to take-off and climb. Any other time, you should be at about 3/4 throttle. Anytime your in a down line, you should throttle way back.

Enjoy,

Jim

Mr T.

My OS-70FS turns that same prop at 10800 peaked and I richen it to 10500 and go fly. I use 15% cool power. I don't understand this less than 10000 rpm story.

Sprink

The whole point of four strokes is they swing bigger props at lower speeds. They are all about TORQUE not REVS. To get the most out of a 70 size four stroke you should be running between 9000 to 10000 rpm. (this excludes the YS 63, which is a special case).

An APC 13x6 is too small, unless you run very rich. Try larger props. I'm currently using an APC 13x8, which gives the best in terms of thrust and speed for the GP Extra 300 I have it in. I run it around 9200 to 9300 rpm.

IMHO the APC 13x7 and Bolly Clubman 13.5x6 are the best props for this engine, but the final selection depends on the plane and your flying style.

If you want to run a prop at such high rpm, buy a 2 stroke and save some pennies.

Mr T.

Why should YS be excluded? Why shouldn't I run it at peak minus 300 rpm? I'm well within manufacturer suggested practical RPM range, even taking unloading in the air.
I'm not running it very far from 10000 either. I just don't understand why should anyone slow down an engine by making it extremely rich so it runs at 9500 instead of 10000 or 10500?

I tried Graupner 13,5x8(very fast) and 14x7(too big), APC14x4W (good thrust, slow spool up) and APC13x6 seemed best overall prop for my sukhoi 31.

futaba1024

From my experience the Saito's I run (56,65 and91) make their best power if allowed to run up to around 10800rpm where as OS's seem to be more happy around the 10000 mark (40s,48s,52s and 91s).
Cheers

Sprink

Mr T, I agree with you, there is no good reason to take more than 300 rpm off the peak, so to keep mine in the 9000 to 10000 range I use a bigger prop, in this case more pitch.

The YS 63 is however designed to run in the 10500 - 11500 rpm range, which is why I excluded it.

Yes, you are right about running within the max operating rpm per the manufacturer, but my point is that you will get more out of the engine running at the rpm I suggest. (and I'm not the only one on RCU to suggest this rpm range either)

Incidentally have you ever run a 2 stoke to 1000 rpm of the manufacturers max? Eg the OS 32 SX has an rpm range of "2000 - 22000". I certainly do not run mine anywhere near that, and I doubt there are many on RCU who run over 15000.

Those limits are the absolute limits, above which you run the real risk of causing immediate damage to the engine. Running near that and you will still increase the chance of longer term damage.

Most engines have a "sweet spot" in terms of rpm where you get the best all round performance from the engine (ie thrust a speed generated by the propeller, not peak HP). IMHO that is between 9000 - 10000 rpm for a 70 size 4stroke.

I did try various props with this engine in this plane:
13x6 (APC): awful, apart from too many revs giving too much noise, the plane did not fly well. Landed after half a flight to change props as it was just too bad.
13.5x6 (bolly clubman): engine far happier, plenty of thrust, not quite enough speed.
13x7 (APC): went very well. Almost settled on this prop, but gave the 13x8 ago anyway.
13x8 (APC): best prop for this plane. Gave best vertical and plenty of authority in the air. Peak rpm about 9400, flying at about 9200.

Never got as far as trying the 14x6 as I knew it would be too slow, but a fellow club member uses one on his OS 70 surpass to good effect on a Flair Fokker DVII.

To get back to rightflyers original question, yes you should aim for around 9500, but you wont get that with an APC 13x6 without running ridiculously rich, especially with 20/20 fuel. I suggest you try bigger props.

Oh and Mr T, I am trying to be helpful here by trying to ensure that everyone gets the most out of their 70 size 4stroke engine and not just spouting off. If you are happy with the 13x6, then so am I.

Hobbsy

My Feedback: (102)

I try to prop all my Saitos in the 9,500 to 9,800 rpm range except for the little .30, I give it about 10,100 with a 10x6 or an 11x5 which won't quite make 10,000.

Spicoli

I like the APC 13X6 on my Saito 72.

bentgear

The first question has to be "What type of plane is it going on?". Very critical piece of info that is being left out. Second is "How much run time on the engine?". Third is "What type of fuel?".

I like a 13 X 6 APC on a profile. Getting over 10,000 on it. Don't remember the exact number, the tach does not fly, the engine and plane does.

On a Venus this would not be enuff prop pitch. Totally different objective out of the prop.

My feeling is you don't know what a Saito 72 will do unless you have over 5 gallons thru it, valves are adjusted correctly, and the needles are set. And it all changes depending on if you want to run 5% or 30% fuel.

If all you want is supper high RPM numbers put a 10 X 6 on it, just don't expect the valve train to last very long.

Ed M.

rightflyer

For a little more background, the Saito 72 is currently on a Ultra Stick 40 and has at least 5 gallons thru. I have been using Wildcat YS 20/20 fuel. The values have been adjusted as well.

I appreciate all the great feedback so far. I will try the 13x7 and 13x8 APCs. I tried a 14x4APC, but didn't like the braking charactistics. The plane would drop like a rock at idle.

bentgear

Rightflyer, if I remember correctly my personal favorite for this combo was a 12.5 X 6 APC. Slightly fatter blades than the 13 X 6.

You just highlighted the main problem when this question comes up, when I was flying mine I might have loved a 14 X 4, just couldn't get one. Low speed, lots of pull, and disk brakes - the perfect combo for this plane, but thats just for my type flying.
Ed M.

sdt22

There must be some torque curves out there that I haven't seen on the saito 72. My 72 breaths fire with the apc 13x6 on the front of it with 30% coolpower. There's no way in hell that I would take the performance of it now and throw a larger prop on it to keep rpms at a ultra-conservative 9000-9500. IMO thats ridiculous, if you wanted that performance why didn't you buy the 56 and save a few bucks. But with that said all is well as long as it serves your purpose fine.

So to help with your question rightflyer I can achieve 11,200 rpms with the above combo, but I run it at10,800. I imagine your combo should put you close to that.

Hobbsy

My Feedback: (102)

To say that a Saito is unpredictable until 5 gallons have run through it is simply untrue, they are quite predictible and reliable after about one half hour of break in, if not, then it isn't set correctly yet.

J.Paul Saure

I get around 10.200 peak with APC 13x6, 15%Nitro

Also used a APC12x8, but didn't tach it. I'd suggest a 13x6 for a funfly/3d or scale plane, and a 12x8 for a pattern plane.

Good luck.

futaba1024

Hobsy.
Absolutely, about 30-40 minutes and they are delightful !
Cheers.

Aero330LX

My Feedback: (-1)

WOW! Lots of differeing answers on this thread. Here's one froma Saito 72 owner. The 13x6 is just perfect for the engine. On some airplanes running anything over 6 pitch will just about gaurantee flutter. Fun fly type planes are not designed to handle speed and they WILL flutter. I run my Saito on 15% Powermaster. It has 15 short flights on it now. It idles reliably, and runs like crazy on the top. I saw that it takes 5 gallons? No way. I don't even have a half of a gallon through this thing yet. It's currently turning 10,500 and it's backed it down some because it's new. I haven't tached it yet at idle but you can count the blades, and it doesn't roll when I let the plane go so that is low enough for me. If the directions are follwed to the letter, and the valves adjusted before the engine is run the first time, and it has an OS plug it will run perfectly. One other thing I noticed is that attitude of the plane doesn't seem to affect my engine at all. This was suprising to me because it normally takes a pumped engine to get that kind of consistency in differeing attitudes. The Saito is also sooooo easy to start...no starters needed for the little 72...just one back flip after priming and it's running. I would expect you would get between 10,5 and 10,8 with your combination. Different fuels run different because of the type and amount of oil they use, and the way they measure the nitro.

RaceCity

Depending on the particular model....

My .70's (OS) run wonderful with the APC 13-7 set somewhat rich to 9500+ on the ground. I've yet to find a better prop for Cubs and AstroHogs with this, and I've been flying the same engine in the same planes for 15 years.

Wonderful combo.

RaceCity

Hey Aero....

Any hand start engine is a GOOD engine IMO.

Never owned a starter...never will.

"If they won't hand start....something's wrong"

'Race

bentgear

Hobbsy, its been my experience that they just keep getting better for the first five gallons before they level off. Very good engine before that, damn good engine after.
Ed M.

tiggerinmk

I've just (a couple of days ago) run my Saito 72 for 40 mins for the break in as stated in the manual.
I used a wood Master Airscrew 13x6 and SIG Champion semi synth 10% fuel. On the last run it was still running rich at around 9500rpm.

I'll probably next run it now after it's installed in the plane when I'll switch the prop for an APC 13x6.

Would there be any problem switching the fuel to coolpower at this point?

Aero330LX

My Feedback: (-1)

Hi tiggerinva ,
Sounds good...How's the oil look that is coming out the crankcase breather? Is it still dark or is it coming out clear or the color of the fuel? If it is coming out the color of the fuel or clear the parts have mated together and you can lean on it some...I stress some. I wouldn't go full lean on it, but instead would see where it peaks and then back off about 300 rpm's and then run a few gallons through her that way. You may have to adjust the low end alot to get a good idle and good throttle response. On the coolpower, I don't see where that would hurt anything...anytime you change fuels on a 4 stroke though, richen the needle valve and then reset so as not to run the engine lean. Just back her out a 1/4 of a turn and reset peak minus 300. If you go up in nitro also be sure to open it back up and reset. These engines are really nice, but 4 strokes (really any engine for that matter) will not take lean runs. Also the APC 13x6 will be a great prop. I plan to try other with a little more diamter a less pitch, but like yours my engine is still new so I want it to turn up some until it's *fully* broke in. The light weight of the Saito 72 coupled to the power it puts out is really a nice package. I love mine and the only deadstick I've had with it is where I ran it out of fuel. When you deadstick you know your having fun. hehe Enjoy!

SilverEagle2

My Feedback: (9)

I am still breaking in my new 72 and have noticed a considerable amount of a black substance running out from somewhere near the top of the case by the lifters. It was coming out of the valve covers untill I reseated those. I am not running lean at all and am getting about 9800 on an APC 14X4. Is this normal. My other 72 does not seem to do this. Is there something that changed in Saitos production? I tightened all the case screws to see if that seals it up, but otherwise, it seems to be running well.


Jason

tiggerinmk

Aero330LX,
I ran it up on a test stand in front of my house and followed the manual on the break in as it's my first Saito and the first 'proper' 4 stroke I've run. I kept a tach on it for almost all of the time so to be honest I didn't even think to look at the breather, I'll try to remember to check it on the next run.

I left the garage door open so now my car is covered in a thin film of castor Never noticed with any other engine I've run, so it sure must've been rich...

I'll be mounting it on its side on a Funtana (everyone seems to be doing this right now, Saito must love this plane ). I'm thinking of reversing the carb so that the needle is on top, are there any problems with this?
I'll probably leave the cowl off for the first few flights so I can keep an eye on things and make changes as it breaks in...

Aero330LX

My Feedback: (-1)

Is is like greyish black oilly greasy muck? If so, yes this is normal. Mine did the same thing. I simply cleaned it up under the valve covers and re-oiled after breakin. It's the metal that is wearing together and polishing. Sometimes you will see this more and sometimes not. Mine did the same thing and it is fine. I would go down a little in prop though until it's got alot more time on it. A 13x6 would be easier on it and will help with cooling until everything wears together real good. There's alot of friction in these things when they're new and they tend to run hotter. I would take off the valve covers and clean the inside with alcohol and scrub the valvetrain with a toobrush and alcohol and re-oil everything. Make sure valves are properly adjusted also. Don't do what I did and mess up a good shirt doing this. If you get that crud on your shirt from scrubbing with the brush it won't come out! LOL